U.S. patent application number 10/374669 was filed with the patent office on 2005-03-10 for gray scale all-glass photomasks.
This patent application is currently assigned to Canyon Materials, Inc.. Invention is credited to Wu, Che-Kuang.
Application Number | 20050053844 10/374669 |
Document ID | / |
Family ID | 46278036 |
Filed Date | 2005-03-10 |
United States Patent
Application |
20050053844 |
Kind Code |
A1 |
Wu, Che-Kuang |
March 10, 2005 |
Gray scale all-glass photomasks
Abstract
A narrowly defined range of zinc silicate glass compositions is
found to produce High Energy Beam Sensitive-glass (HEBS-glass) that
possesses the essential properties of a true gray level mask which
is necessary for the fabrication of general three dimensional
microstructures with one optical exposure in a conventional
photolithographic process. The essential properties are (1) A mask
pattern or image is grainiless even when observed under optical
microscope at 1000.times. or at higher magnifications. (2) The
HEBS-glass is insensitive and/or inert to photons in the spectral
ranges employed in photolithographic processes, and is also
insensitive and/or inert to visible spectral range of light so that
a HEBS-glass mask blank and a HEBS-glass mask are permanently
stable under room lighting conditions. (3) The HEBS-glass is
sufficiently sensitive to electron beam exposure, so that the cost
of making a mask using an e-beam writer is affordable for at least
certain applications. (4) The e-beam induced optical density is a
unique function of, and is a very reproducible function of electron
dosages for one or more combinations of the parameters of an e-beam
writer. The parameters of e-beam writers include beam acceleration
voltage, beam current, beam spot size, addressing grid size and
number of retraces. A method of fabricating three-dimensional
microstructures using HEBS-glass gray scale photomask for three
dimensional profiling of photoresist and reproducing the
photoresist replica in the substrate with the existing
microfabrication methods normally used for the production of
microelectronics is described.
Inventors: |
Wu, Che-Kuang; (San Diego,
CA) |
Correspondence
Address: |
Chuck Wu
Canyon Materials, Inc.
6665 Nancy Ridge Drive
San Diego
CA
92121
US
|
Assignee: |
Canyon Materials, Inc.
|
Family ID: |
46278036 |
Appl. No.: |
10/374669 |
Filed: |
February 25, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10374669 |
Feb 25, 2003 |
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10160573 |
May 30, 2002 |
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6524756 |
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10160573 |
May 30, 2002 |
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09934218 |
Aug 21, 2001 |
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09934218 |
Aug 21, 2001 |
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09507039 |
Feb 18, 2000 |
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6562523 |
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09507039 |
Feb 18, 2000 |
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08961459 |
Oct 30, 1997 |
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60030258 |
Oct 31, 1996 |
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Current U.S.
Class: |
430/5 ; 430/296;
430/321; 430/325; 430/942 |
Current CPC
Class: |
G03F 9/00 20130101; C03C
3/093 20130101; C03C 15/00 20130101; G03F 1/50 20130101; G03F 1/54
20130101; C03C 23/004 20130101; C03C 3/11 20130101; G03F 1/60
20130101 |
Class at
Publication: |
430/005 ;
430/296; 430/321; 430/325; 430/942 |
International
Class: |
G03F 009/00; G03C
005/00 |
Claims
What is claimed is:
1. A device and/or method substantially as shown and described.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
10/160,573, filed May 30, 2002, which is a continuation of U.S.
patent application Ser. No. 09/934,218 filed Aug. 21, 2001, which
is a continuation-in-part of U.S. application Ser. No. 09/507,039
filed Feb. 18, 2000, which is a continuation-in-part of U.S.
application Ser. No. 08/961,459, filed Oct. 30, 1997, which claims
priority from U.S. provisional application Ser. No. 60/030,258,
filed Oct. 31, 1996.
BACKGROUND OF THE INVENTION
[0002] "High efficiency diffractive coupling lenses by
three-dimensional profiling with electron lithography and reactive
ion etching," by A. Stemmer et al, J. Vat. Sci. Technol. B 12 (6),
November/December 1994, teaches three dimensional profiling of a
photoresist and transferring the three-dimensional microstructures
of photoresist into the substrate using reactive ion etching.
Three-dimensional profiling of photoresist with electron beam
direct write on photoresist however is not cost effective for
production quantities.
[0003] "Fabrication of diffractive optical elements using a single
optical exposure with a gray level mask," Walter Daschner, et al,
J. Vat. Sci. Technol. B 13 (6), November/December 1995 teaches
generating a gray level mask with eight discrete gray levels by
means of cycles of evaporation of Iconel and a following lift-off
step. This gray level mask allowed to expose a multi-level DOE in a
single optical exposure step for three-dimensional profiling of
photoresist. CAIBE was used to transfer the analog resist structure
into the substrate. The tight thickness control necessary in the
Iconel evaporation steps makes this method of fabricating the gray
level mask economically undesirable.
[0004] "Gray scale microfabrication for integrated optical
devices," George Gal et al., U.S. Pat. No. 5,480,764, issued Jan.
2, 1996, teaches the fabrication of three-dimensional
microstructures including photonic waveguide surface, lens surface,
and inclined planar surface for use as a beam splitter in a
photonic device, using a half tone gray scale photomask for
three-dimensional profiling of photoresist and reproducing the
photoresist replica in the substrate with differential ion milling.
However, a half tone gray scale mask is not desirable due to
limited resolution.
[0005] Other gray level mask fabrication methods have been
demonstrated and show potential for mass fabrication. See for
example: H. Andersson, M. Ekberg, S. Hard, S. Jacobson, M. Larsson,
and T. Nilsson, Appl. Opt. 29, 4259, 1990; and Y. Oppliger, P.
Sixt, J. M Mayor, P. Regnault, and G. Voirin, Microelectron. Eng.
23, 449, 1994. After the mask fabrication only a single-exposure
step is necessary to generate a multilevel resist profile. These
approaches, however, have limited resolution since silver
halide-based photographic emulsion is used and the grayscale mask
is a halftone mask, that is not a true gray scale mask.
[0006] The fabrication of microoptical elements such as refractive
microlens arrays, diffractive optical elements, prism couples, and
three-dimensional microstructures in general can be realized with
the existing micro-fabrication methods normally used for the
production of microelectronics. The well-established
microfabrication technologies include photolithographic process and
reactive ion etching. Photolithographic processes are employed to
print a mask pattern in a photomask onto photoresist film, which is
typically coated on a silicon wafer or a glass wafer. Commercially
available photolithographic printers for microfabrication include
contact and proximity printers, 1.times. projection printer,
1.times. steppers and 5.times. as well as 10.times. reduction
steppers. Reactive ion etching is employed to transfer and/or
replicate patterns in photoresist into the underlying substrate
material. Commercially available systems include plasma etchers,
inductive coupled plasma (ICP) and chemically assisted ion beam
etchers (CAIBE).
[0007] For the fabrication of integrated circuits (IC) in
microelectronics industry, a set of binary masks is used in the
photolithographic process. The binary masks typically have IC
patterns defined in a chrome film which is coated on a silicate
glass plate, typically a fused silica glass plate. However, for the
fabrication of microoptical elements, a gray scale photomask is
needed to define the three dimensional microstructures.
[0008] A gray scale photomask carries patterns with areas of
different transmittance. When the pattern is printed on
photoresist, areas of different transmittance in the gray scale
mask create areas of different thickness in photoresist after
development. Therefore, a gray scale pattern in a gray scale
photomask can be used to create predetermined 3D microstructures in
photoresist film, which are then transferred and/or replicated into
the underlying substrate material in a reactive ion etcher.
[0009] Instead of using a gray scale photomask a varied exposure in
a photoresist can also be generated by directly exposing the
photoresist with an e-beam writer or a laser beam writer. The
developed 3D resist structure can then be transferred into
underlying substrate material to produce microoptical elements.
However, in this case no mask is created. Each element must be
written one at a time, with no benefit from economies of scale.
Namely, it is not cost effective for making microoptical elements
in production quantities using this direct write method.
[0010] There have been several methods of making gray scale
photomasks in the past, but each of them have a major shortcoming
as described below.
[0011] U.S. Pat. Nos. 5,480,764 and 5,482,800 of Gal et al and an
article by W. W. Anderson et al "Fabrication of Micro-optical
Devices" conference on Binary Optics 1993, pp. 255-269, teach half
tone gray scale masks. According to this technique, the mask is
created by constructing a plurality of precisely located and sized
openings, the frequency and size of these openings produce the
desired gray scale effect provided the mask pattern is blurred in
the photolithographic process to print on photoresist. The smallest
features of this mask are binary, either open or closed, i.e. on or
off. A group of a large number of on and off spots is needed to
create a gray scale resolution element. The gray scale resolution
element appears for example as 80% transmittance or as 20%
transmittance depending on the ratio of the number of the on-spots
and off spots. Therefore, the resolution of a half-tone gray scale
pattern is much reduced from that of a binary pattern in a chrome
mask.
[0012] Photographic emulsion has been used to provide gray scale
masks. A gray area consists of a number of silver grains and
openings. The silver grains are totally opaque and the openings are
totally transparent. Therefore, the photographic gray scale mask is
also a half-tone mask. The gray scale resolution element of a
photographic film is in general larger in size than that of the
halftone gray scale chrome mask. This is because the silver gains
in a developed photographic emulsion film are in general larger
than an opening or a chrome spot that can be made in a chrome
mask.
[0013] One improvement in the production of gray scale masks for
use in fabricating microoptical elements has been realized with the
provision of a gray scale mask wherein different thicknesses of a
light absorbing material, such as Inconel are coated on a glass
plate to form the gray scale mask (see U.S. Pat. No. 6,071,652 of
Feldman, et al, Jun. 6, 2000). This gray scale mask could have the
high resolution required for fabricating microoptical elements.
However, one disadvantage of this technique is the cost of the mask
generation, wherein multiple direct write steps on photoresist are
required to provide the lift off process of the light absorbing
material for each discrete thickness desired. The tight thickness
control necessary in the material evaporation steps makes this
technique economically undesirable.
[0014] The gray scale photomasks described above cannot be utilized
for the fabrication of high quality micro-optical elements in
production quantities, because of their failure to satisfy either
one or both of the following requirements: 1.) a sub-micrometer
gray scale resolution element, 2.) acceptable cost in the mask
generation.
[0015] High Energy Beam Sensitive (HEBS) glasses were described in
U.S. Pat. No. 4,567,104, No. 4,670,366, No. 4,894,303, No.
5,078,771, and No. 5,285,517 (Wu patents herein after) by Che-Kuang
Wu who is also known as Chuck Wu, the latter name is used in some
of his publications in technical journals. The size of a gray scale
resolution element in an HEBS-glass gray scale mask is limited only
by the e-beam darkened spot size recorded in the high energy beam
sensitive glass plate. It is typically 0.1 micrometer to 0.4
micrometer depending on the acceleration voltage of the electron
beam and on the electron dosage. It is obvious that an HEBS-glass
gray scale mask satisfies the high resolution requirement. However,
the HEBS-glass plates of Wu patents did not satisfy the second
requirement listed in the paragraph immediately above. The reason
for not being able to satisfy the requirement of acceptable cost in
the mask generation is elaborated below:
[0016] 1. To render HEBS-glass of Wu patents opaque, the required
e-beam dosage is typically about 1,000 microcoulomb/cm.sup.2. This
should be compared with the sensitivity of the electron beam resist
used in IC industry to fabricate the binary chrome photomask. The
required e-beam dosage for the electron beam resist employed by the
mask shops in IC industry ranges from 0.1 to 1
microcoulomb/cm.sup.2. HEBS-glass of the Wu patents has an e-beam
sensitivity that is a factor of 1,000 to 10,000 times less than
that of electron beam resist used in IC industry. 1,000 to 10,000
times less in sensitivity is herein after referred to as the
sensitivity factor. Relative to photographic emulsion, HEBS-glass
is also very insensitive. This is expected because there is not a
development step for the HEBS-glass to enhance the contrast of the
e-beam exposure induced optical density. The amplification in the
optical density of a photographic film by a chemical development
step is a factor of 107. Namely there is a contrast enhancement of
ten million times from the latent image to the chemically developed
image in a photographic emulsion film.
[0017] E-beam writers are very expensive, the write time of a mask
has to be in the order of minute or hours, not days, otherwise
there would be little economic value. E-beam exposure systems that
are commercially available include flood electron beam exposure
systems, raster scan e-beam pattern generators, variable shape beam
vector scan e-beam pattern generators and Gaussian spot vector scan
e-beam pattern generators. The price of the systems together with
the write time for generating a mask determines the cost of making
an HEBS-glass mask.
[0018] Flood e-beam exposure system, for example, EVC Electron Cure
systems manufactured by Electron Vision Corp. are priced at about
$250,000 each. Raster scan e-beam pattern generators, for example,
MEBES systems manufactured by ETEC are priced at more than ten
million dollars each. Variable shaped beam vector scan e-beam
pattern generators, for example ZBA 23H manufactured by Leica
Microsystems, Inc. are priced at about $6 million each. Gaussian
spot vector scan e-beam pattern generators such as Vector Beam
manufactured by Leica Microsystems, Inc. are priced at more than $6
million each.
[0019] Flood e-beam exposure system is ideally suited for
HEBS-glass composition research for comparing the e-beam
sensitivity among many glass compositions via uniformly exposing
the entire area of many HEBS-glass plate samples in one exposure to
an identical electron dosage.
[0020] However, flood e-beam exposure system, which is much less
expensive, is not an option for making a photomask for the
following reason. EVC Electron Cure systems has no capability of
delivering an e-beam dosage having a predetermined functional
variation in x and y coordinates. An Electron Cure 30 flood e-beam
exposure system provides an 8 inch diameter beam to uniformly
expose an area of up to 8 inch diameter. HEBS-glass of Wu patents
are typically darkened to 1 unit of optical density value under the
flood gun exposure for about 10 minutes. If one aperture down the
beam size of the EVC Electron Cure system to 0.1 micron spot to
write a gray scale pattern in HEBS-glass, it would take 10.sup.10
minutes or in other words, 6.9 million days, to expose a pattern
size of 1 cm.times.1 cm area. Moreover, there exists no fixture in
EVC Electron Cure system for precision movements of an aperture in
the X-Y plane to create a mask patter. U.S. Pat. No. 5,468,595 of
William R Livesay teaches a method of controlling the solubility of
photoresist layer in the depth dimension, i.e. Z-axis, through
flood exposure on photoresist a uniform electron dosage in X-Y
plane. This is accomplished by the electron beam having a
controlled acceleration voltage. This method is not applicable and
is undesirable for making a HEBS-glass gray scale photomask for the
following reason. The gray scale patterns in a photomask have to be
in one plane (X-Y plane) without variation in the thickness
dimension so that all patterns in the mask can be in focus
simultaneously during the photolithographic printing process.
[0021] During the months of March and April of 1987, Motorola, one
of the world's largest manufacturers of integrated circuits (i.e.
IC chips), evaluated the HEBS-glass plates of Wu patents for use as
a binary mask for IC photomask applications and concluded that
HEBS-glass plates of Wu patents require too much e-beam write time
creating a high cost of mask generation. This deterred their use of
HEBS-glass photomask. Motorola's evaluation report of 6-25-87
stated "Numerous hours of e-beam write time are required to produce
one photomask. This condition is totally unacceptable on Motorola's
present and future mask making plans." This began the search for
new applications for HEBS-glass of Wu patents. The possibility of
making a gray scale photomask using HEBS-glass of Wu patents was
pursued. In 1988, gray scale test patterns were written with a
MEBES e-beam writer using the number of retraces as a variable
parameter to vary the electron dosage. CMI purchased an EVC
Electron Cure 30 flood e-beam exposure system and a Hitachi
Spectrophotometer Model u2000 for the purpose of HEBS-glass
composition research, in search of a much improved e-beam
sensitivity. Glass batches of a large number of different glass
compositions were melted in alumina crucibles. Ground and polished
glass plates from the glass melts were ion-exchanged in acidic
aqueous solution containing silver nitrate to produce HEBS-glass
plates. Groups of 5 to 10 HEBS-glass plates, typically in sizes up
to about 0.5".times.1" each were exposed together in the 8"
diameter electron beam of the Electron Cure 30 with an electron
dosage of 400 microcoulomb/cm2. Spectral absorption curves of the
darkened HEBS-glass plates were measured with Hitachi
Spectrophotometer Model u2000 in order to compare the e-beam
sensitivity among the compositions of glass melts for further
iterations of glass melts in the optimization of the HEBS-glass
compositions.
[0022] 2. The industrial standard mask making tool is a MEBES
e-beam writer. In the IC industry, only binary photomasks are
required, and all commercial photomask shops in the U.S. use MEBES
systems to write the binary photomasks for the fabrication of IC
chips. The MEBES system is a raster scan system. An electron beam
is raster scanned in a serial manner to each and every address of
for example 10.sup.10 addresses in a 1 cm.times.1 cm area when a
0.1 micron addressing grid size is chosen. Patterns are generated
by blanking or un-blanking the beam at each address. The raster
scan is done at a fixed constant rate for each MEBES system; for
example at 160 MHz rate, the e-beam dwell time at each address is
6.25 nanosecond. To produce a gray scale pattern in a HEBS-glass
plate, it is necessary that the electron dosage at each address is
predetermined by the design of the gray scale pattern. Since the
MEBES system have a constant dwell time of 6.25 nanoseconds for
each of all addressing grid points and the e-beam dwell time cannot
be varied from one address to the next address, a gray scale
pattern in a HEBS-glass plate can only be generated with multiple
retraces. This exposure scheme is impractical for making HEBS-glass
gray scale photomasks.
[0023] A gray scale pattern of continuously varying optical density
on a HEBS-glass plate requires a large number of gray scale levels.
Gray scale patterns having more than 1,000 gray levels can be
produced in a HEBS-glass plate when a practical exposure scheme
becomes available. Using a raster scan e-beam writer, the write
time of writing one gray scale level in a HEBS-glass plate would be
the same as that of writing a binary chrome mask if the e-beam
sensitivity of a HEBS-glass plate is identical to that of an
electron beam resist. However, the write time of generating a gray
scale photomask in a HEBS-glass plate is the write time of a binary
chrome mask multiplied by the sensitivity factor of 1,000 to 10,000
and then multiplied by the number of gray scale levels. For a
HEBS-glass gray scale photomask having 1,000 gray scale levels,
1,000 retraces is required and the write time would be at least
1,000,000 times that of writing a binary chrome mask. In other
words, the throughput of making a HEBS-glass mask with 1,000 gray
levels is 1,000,000 times lower relative to making a binary chrome
mask. The write time of a binary chrome mask is typically more than
1 hour at a cost of about $1,000 per hour of e-beam write time. The
cost of e-beam write time, e.g. 1,000,000 hours to write 1 plate
clearly prohibits the use of a HEBS-glass plate of Wu patents to
make a gray scale photomask.
[0024] Besides the prohibitive cost, the technical feasibility of
making a HEBS-glass gray scale mask is doubtful due to the
properties of HEBS-glass described immediately below:
[0025] 1. The heat effect of HEBS-glass is described in the section
"Heat Effect of the Write Beam" in this application, and is also
described in an article co-authored by Wu and E. B. Kley et al
"Adapting existing e-beam writers to write HEBS-glass gray scale
masks" in Proceedings of SPIE Vol. 3633 (January 1999). The heat
effect increases the sensitivity of HEBS-glass, but the heat effect
is a strong function of exposure beam sizes and shapes. As a
consequence, for a constant e-beam exposure dosage, the e-beam
induced optical density in HEBS-glass is not a constant value and
is a function of exposure beam size and shape. This property of
HEBS-glass restricts the utilization of the advantages of the
exposure scheme inherent in a variable shape beam system for
increasing the throughput of writing a mask pattern.
[0026] 2. The e-beam darkening mechanism of HEBS-glass includes an
intermittence effect in addition to the heat effect. The e-beam
darkening mechanism is not known with certainty and is postulated
as follows. In the presence of a high energy electron beam
(e-beam), some of Cl- ion and Ag+ ion in the silver halide
alkalihalide complex crystal or complex microphases in the integral
ion exchanged surface glass layer of a HEBS-glass plate react with
energetic electrons to produce Cl atom and Ag atom. Cl atom and Ag
atom are not stable species and a reverse reaction takes place
simultaneously. A third reaction process also occurs simultaneously
wherein portions of Cl atom and Ag atom become stable species of
Cl.sub.2 and Silver specks Ag.sub.0 with the help of lattice
vibrations as described in the section "Heat Effect of the Write
beam" in the above application.
[0027] If the e-beam exposure is done with intermittence such as an
exposure with multiple retraces, the e-beam induced optical density
in a HEBS-glass plate resulting from a constant total exposure
dosage of multiple retraces is not a constant value, but is a
function of the intermittence time duration. This is because the
intermittence time duration contributes additional time duration
for the formation of the stable species of Cl.sub.2 and silver
specks and retards the reverse reaction of Cl atom and Ag atom back
to Cl- ion and Ag+ ion, due to the reduced concentration of Cl atom
and Ag atom. Due to the intermittence effect, exposure schemes with
multiple retraces is complicated by the additional variable
parameter, the intermittence time duration. The intermittence
effect is described in the article co-authored by Wu and E. B. Kley
et al "Adapting Existing E-beam Writer to Write HEBS-glass Gray
Scale Masks" in Proceedings of SPIE vol. 3633, January 1999.
[0028] In the IC industry, direct write on photoresist to generate
binary IC patterns is benefited from the choice of a variable
shaped beam system to increase the throughput of pattern
generation. However, for the fabrication of HEBS-glass photomasks,
an exposure scheme utilizing a variable shaped beam does not
produce a constant value of e-beam induced optical density in
HEBS-glass for a constant e-beam exposure dosage, particularly when
a high e-beam current density is used. Therefore, the fabrication
of HEBS-glass gray scale photomasks using an exposure scheme with a
variable shaped beam requires multiple retraces and a low current
density, and thus the throughput of writing the HEBS-glass mask is
further reduced.
[0029] MEBES e-beam writers, the only e-beam writers commercially
available for mask writing service, do not provide a practical
exposure scheme for making HEBS-glass gray scale masks. A raster
scan e-beam system can write at a very high data rate, which is
ideally suited for writing a binary mask. For a gray scale mask
requiring many gray scale levels such as 1,000 gray scale levels,
1,000 retraces is needed to write 1 mask using a raster scan e-beam
writer. A vector scan e-beam writer with a capability of changing
dwell time at each address on the fly may not require multiple
retraces to write a HEBS-glass gray scale mask. Therefore, C. Wu
set forth to look for e-beam writing tools that are designed for
R&D purposes in the universities. CMI (Canyon Materials, Inc.)
product information No. 94-88 "HEBS-glass Photomask Blanks" was
prepared by C. Wu in December 1994, for the purpose of encouraging
researchers and e-beam operators in the university to test write
HEBS-glass places.
[0030] On Apr. 13, 1995, C. Wu visited Mr. Robert Stein, who was an
e-beam operator at UCSD (University of California, San Diego), and
showed Mr. Stein e-beam written plates of HEBS-glass. The
HEBS-glass plates were written with a MEBES e-beam writer. Test
patterns with variation of optical density were written with
different numbers of retraces.
[0031] After explaining to Mr. Stein the e-beam direct write
phenomenon, Mr. Stein agreed to test write on a HEBS-glass plate
using an EBMF 10.5 e-beam writer.
[0032] By May 24, 1995, Mr. Stein finished writing a HEBS-glass
plate with EBMF 10.5 e-beam writer using various beam currents at
30 kv and at 20 kv. An addressing grid size of 0.1 micron was
employed. Sixteen gray levels were generated with each setting of
beam current and kv combinations using 16 clock rates.
[0033] C. Wu had Mr. Walter Daschner examine the gray scale pattern
in the HEBS-glass plate written by Mr. Stein, and met with Mr.
Daschner, a graduate student under Professor S. H. Lee, on Jun. 12,
1995 at 10 AM at UCSD for the first time. During the meeting C. Wu
presented to Mr. Daschner a copy of CMI Product Information No.
94-88 "HEBS-glass Photomask Blanks," one plate of a HEBS-glass
photomask blank, and a copy of U.S. Pat. No. 5,078,771 "Method of
Making High Energy Beam Sensitive Glass."
[0034] This meeting led to joint research and the following
publications that C. Wu co-authored with others:
[0035] A. "General aspheric refractive micro-optics fabricated by
optical lithography using a high energy beam sensitive glass
gray-level mask" by Walter Daschner, Pin Long, Robert Stein, Chuck
Wu, and S. H. Lee, in J. Vac. Sci. Technol. B 14(6),
November/December 1996.
[0036] B. "Cost-effective mass fabrication of multilevel
diffractive optical elements by use of a single optical exposure
with a gray-scale mask on high energy beam-sensitive glass" by
Walter Daschner, Pin Long, Robert Stein, Chuck Wu, and S. H. Lee,
in Applied Optics, Vol. 36, No. 20, Jul. 10, 1997.
[0037] CMI Product Information No. 94-88 was cited as reference No.
11, and as reference No. 7 in the above listed publication A of
November/December 1996 and B of Jul. 10, 1997, respectively.
[0038] Based on the results of written HEBS-glass plates by Mr.
Stein, C. Wu, being the Chairman of Canyon Materials, Inc., caused
Canyon Materials, Inc. to purchase a EBMF 10.5 e-beam writer from
Leica Microsystems, Inc. for the purpose of developing an e-beam
exposure scheme and optimizing e-beam write parameters for making
gray scale photomasks using HEBS-glass plates, and for
commercializing HEBS-glass gray scale photomasks. Before the EBMF
10.5 e-beam writer became available in-house, CMI purchased write
time of EBMF 10.5 e-beam writer from UCSD for the above stated
purposes.
[0039] C. Wu also conducted other efforts to write HEBS-lass plates
using other e-beam writers and efforts to write LDW glass plates
using laser beam pattern generators through joint efforts with
other research institutions and universities in the US as well as
abroad.
[0040] These other efforts result in, for example, the following 3
publications that C. Wu co-authored:
[0041] C. "Adapting existing e-beam writers to write HEBS-glass
gray scale masks" by E.-Bernhard Kley, Matthias Cumme,
Lars-Christian Wittig, and Chuck Wu, in Proceedings of SPIE Vol
3633, January 1999.
[0042] D. "Applications of gray scale LDW-glass masks for
fabrication of high-efficiency DOEs" by V. P. Korolkov, A. I.
Malyshev, V. G. Nikitin, A. G. Poleshchuck, A. A. Kharissov, V. V.
Cherkashin, and C. Wu, in Proceedings of SPIE Vol. 3633, Jan.
1999.
[0043] E. "Fabrication of gray scale masks and diffractive optical
elements with LDW-glass" by Victor Korolkov, Anatoly Malyshev,
Alexander Poleshchuk, Vadim Cherkashin, Hans Tiziani, Christof
Prub, Thomas Schoder, Johann Westhauser, and C. Wu, in Proceedings
of SPIE Vol. 4440, July 2001.
[0044] It is not at all obvious and is a total surprise that the
high throughput of e-beam writing HEBS-glass gray scale photomasks
such as mask No. 81, 82, 83, and 84 were produced. The surprise is
that the 1,000,000 times too low throughput of making a HEBS-glass
mask has been overcome by the combined efforts of the glass
compositions of this application and an e-beam exposure scheme
optimized for the properties of the HEBS-glass of this application.
Mask No. 81, 82, 83, and 84 were written with an EBMF 10.5 e-beam
writer using the write parameters necessary for producing the
combined effects. These write parameters of the exposure scheme are
described in the section "Description of the Invention" of this
application. EBMF 10.5 is a Gaussian spot vector scan e-beam writer
manufactured by Leica Microsystems, Inc. This e-beam writer is a
research tool and is not available in commercial mask shops for IC
photomask fabrication. The write parameters necessary for producing
the combined effects of this application has never been and can
never be applied to expose electron beam resists for which the
e-beam writers were designed. This is because the e-beam power that
generates the heat effect for the enhanced e-beam sensitivity in
HEBS-glass, would burn or decompose the electron beam resist. The
e-beam power is the input-power density defined as (beam
current).times.(beam acceleration voltage)/(beam spot size) in the
section "Heat Effect of the Write E-Beam" of this application.
[0045] HEBS-glass gray scale mask No. 81 having 1,000 gray scale
levels was written in 1 hour, 14 minutes, and 16 seconds. This gray
scale mask is fabricated for making 50 copies of 100 micron.times.6
mm prism couples in each contact print on wafer. Each prism couple
has a right angle triangular cross section of 2 micron height and
is 6 mm long. The gray scale pattern for each prism has 1,000 gray
levels. There is no other product, apparatus, or method that could
produce such a gray scale mask at the cost of a HEBS-glass
mask.
[0046] HEBS-glass gray scale mask No. 82 having 100 gray scale
levels was written in 57 minutes 35 seconds. This gray scale mask
is fabricated for making blazed gratings having a 20 micron pitch
in fused silica glass wafer using a contact printing process. The
20 micron pitch grating is 10 mm long, and has 500 periods. The
grating is 1 cm.times.1 cm in size.
[0047] HEBS-glass gray scale mask No. 83 having 23,040 lens
patterns, each of 100 gray scale levels was written in 13 hours 12
minutes and 1 second. A large portion of the e-beam write time is
consumed by data loading since circular patterns with a large
number of gray levels require a very large data file. This gray
scale mask is fabricated for making 1.times.40 arrays of refractive
microlenses for fiber optical interconnect. Each lenslet has 200
micron diameter and 100 gray levels. There are 576 dies in the mask
pattern, each die being a 1.times.40 lens array.
[0048] HEBS-glass gray scale mask No. 84 having 62,500 lens
patterns, each of 57 gray scale levels, was written in 3 hours and
36 minutes. This gray scale mask is fabricated for making a
250.times.250 array of refractive microlenses. Each lenslet is a 40
micron.times.40 micron square lens having 57 gray levels in the
HEBS-glass mask. The array has 100% fill factor for use in detector
enhancement. To create an array of square lenses (100% fill
factor), a circular lens whose diameter is the diagonal of the
square, i.e. 56.56 micron in this case, with the appropriate number
of gray levels is created, trimmed into a square, and stepped and
repeated to create the lens array. Each gray level of the mask is a
layer in the data file.
[0049] Based on the postulated model of e-beam darkening mechanism
in HEBS-glass described herein, high throughput of e-beam
patterning HEBS-glass gray scale photomasks is made possible as
follows:
[0050] 1. In the section of this application "Heat Effect of Write
Beam" the e-beam darkening mechanism is elaborated. The formation
of a silver speck consisting of 2, 3, or more atoms requires the
deformation of silver halide lattice to silver lattice. Cycles of
lattice vibration of sufficient amplitudes are necessary to cause
the formation of the silver specks. Since larger amplitudes of
lattice vibrational modes exist at higher temperatures, silver
specks are formed more quickly at a higher temperature. HEBS-glass
compositions No. 1 to No. 20 represent the HEBS-glass compositions
of this invention having produced silver halide alkalihalide
complex crystals, in the integral ion exchanged surface glass layer
of the HEBS-glass plates, that are optimized to maximize the e-beam
sensitivity enhancement of the heat effect. The relative
concentrations as well as the total concentration of alkali oxides,
i.e. Li.sub.2O, Na.sub.2O and K.sub.2O are among the more important
parameters of the base glass composition that determine the heat
enhanced e-beam sensitivity of the silver halide alkalihalide
complex crystals. Other variable parameters of the HEBS-glass
compositions of this application are represented in Exhibit A of
the application.
[0051] 2. The acceleration voltage of an electron beam among all
the commercially available e-beam writers ranges from 1 kV to 100
kV. In other words, the kinetic energy of electrons in the e-beam
writer ranges from 1 keV to 100 keV. When a high energy electron
enters into any solid material, i.e. HEBS-glass in this
application, it creates secondary electrons and third generation
electrons due to electron-electron collision. For example, a 100
keV electron penetrating HEBS-glass could in principle produce up
to 100,000 energetic electrons, each having a kinetic energy of 1
ev on the average. The secondary and third generation electrons are
the energetic electrons that cause the chemical reaction of Cl- ion
and Ag+ ion to form Cl atoms and Ag atom. A higher kV electron beam
creates a larger number of energetic electrons. However, the bulk
of the energetic electrons exists deeper into the thickness
dimension from the HEBS-glass surface as the acceleration voltage
of e-be increases. By adjusting the thickness dimension, i.e.
x.sub.1 and x.sub.2 (see FIG. 1 of the Application) of the ion
exchanged surface glass layer of a HEBS-glass plate, the bulk of
the energetic electrons can be captured within the e-beam
sensitized glass layer. However, to produce a gray scale photomask
with a high resolution capability in a photolithographic process, a
smaller value of (x.sub.2-x.sub.1), such as less than 3 micron is
necessary. Therefore, for each of the glass compositions No. 1 to
No. 20 of Exhibit A of the Application, x.sub.1 and x.sub.2 values
were optimized for a maximum sensitivity to 20 kV electron beam to
produce HEBS-glass plate No. 1 to No. 20. Although HEBS-glass plate
No. 1 to No. 20 were optimized for the penetration depth of a 20 kV
electron beam, a 30 kV electron beam in general produces a higher
OD (Optical Density) value with the same electron dosage. This is
due in part to a stronger heat effect described above.
[0052] High throughput of e-beam patterning HEBS glass gray scale
masks is made possible by maximizing the heat enhanced e-beam
sensitivity of the HEBS-glass compositions of this application and
writing gray scale patterns in HEBS-glass plates with an exposure
scheme that produced the combined effects described herein. The
exposure scheme employed for the high throughput writing of
HEBS-glass plates is not available from the e-beam writers such as
MEBES that are typically utilized by IC photomask shops.
[0053] U.S. Pat. Nos. 4,567,104; 4,670,366; 4,894,303; and 078,771
and 5,285,517, all of inventions of Che-Kuang Wu, described High
Energy Beam Sensitive glass (HEBS-glass) articles exhibiting
insensitivity and/or inertness to actinic radiation, the HEBS-glass
articles which are darkened and/or colored within a thin surface
layer of about 0.1-3 micron upon exposure to a high energy beam,
electron beam, and ion beams in particular, without a subsequent
development step, and which need no fixing to stabilize the colored
image, since both the recorded image and the glass article are
insensitive to radiation in the spectral range of uv and longer
wavelengths. These patents are concerned with Ag+ ion-exchanged
glass articles having base glass within alkali metal silicate
composition fields containing at least one of the oxides of
transition metals which have one to four d-electrons in an atomic
state. The base glass composition can be varied widely, spontaneous
reduction upon ion-exchange reaction as well as photo-reduction of
Ag+ ions are inhibited and/or eliminated due to the presence of
said transition metal oxides in the glass article. The HEBS-glass
is suitable for use as recording and archival storage medium and as
phototools. The recorded images and/or masking patterns are
up-dateable, can be any single color seen in the visible spectrum,
and is erasable by heat at temperatures above 200.degree. C. Heat
erasure mode of recording the high energy beam darkened glass
article using a high intensity light beam, focused laser beam in
particular, was also described.
[0054] Diffractive optics technology is maturing see for example,
the publication by 15 C. W. Chen and J. S. Anderson, "Imaging by
diffraction: grating design and hardware results," in Diffractive
and Miniaturized Optics, S. H. Lee, ed., Vol. CR49 of SPIE Critical
Reviews Series (Society of Photo-Optical Instrumentation Engineers,
Bellingham, Wash., 1993) pp. 77-97. Diffractive Optical Elements
(DOE's) of various designs have been found useful for improving the
design and performance of optical systems. Instead of using the
binary method, such as described in "Binary Optics Technology: The
Theory and Design of Multi-level Phase Diffractive Optical
Elements" by G. J. Swanson of MIT, documented in MIT Tech. Rep.
854. (MIT, Cambridge, Mass., 1989), a cost-effective way of
fabricating large numbers of DOE's in the shortest possible
turnaround time has become increasingly important. Gray scale mask
fabrication methods offer these features by drastically reducing
the amount of processing steps involved to generate a multilevel
and monolithic DOE. Currently multiplexing schemes exist to
fabricate a quasi-gray-scale mask by changing the number of area
openings in a binary mask (similar to the halftone method) or by
photographic emulsions. These approaches were described by Y.
Opplinger et al. in Microelectron Eng. 23, 449-454 (1994) and by H.
Anderson et al. in Appln. Opt. 29, 4259-4267 (1990). Other methods
of fabrication of gray-scale masks involve the cumberstone task of
multiple binary exposures and following evaporation steps such as
described by W. Daschner, et al. in J. Vac. Sci. Technol. B 13,
2729-2731 (1995). The High Energy Beam Sensitive (HEBS) glass of
the present invention offers the advantage of a one-step
fabrication of true gray-scale masks.
[0055] The continuing development of exceedingly small or so-called
micro-devices such as micro-optic elements and micro-machines is of
great importance to optoelectronic interconnection technologies and
the development of communications and control systems. Diffractive
optical elements such as spherical, cylindrical, Fresnel lenses,
aspherics and other micro-devices having rather precise three
dimensional profiles or contours present certain problems with
respect to volume production of these elements of an acceptable
quality, in particular. The fabrication of large arrays of such
elements covering large areas is very costly with regard to known
methods of production.
[0056] One technique for mass production of diffractive optical
elements involves fabricating a master element which itself is made
by etching processes similar to those used in the fabrication of
micro-electronic circuits and similar devices wherein a
multi-masking process using binary masks is conducted. The
fabrication of a master or individual elements using a multi-binary
mask method can result in significant dimensional errors in the
master and the fabricated element due to residual alignment errors
between consecutive masking steps. Although diamond turning, for
example, can be employed in producing a mater element, the
multi-binary mask technique is limited with symmetric elements, for
example. Still further, diffractive optical elements can be
produced by injection molding, embossing or casting. However, the
materials used in these techniques have limited optical and
environmental properties, and are, for example, operable to be
transmissive to radiation only in the spectral range visible to the
human eye.
[0057] Some of the disadvantages of prior systems including those
mentioned above have been overcome with the development of
so-called gray scale masks which avoid multiple processing steps by
providing a single mask which contains all of the information
necessary for generating multi-phase levels, i.e., the
three-dimensional contours required in a diffractive optical
element and the like. Photographic emulsions have been used to
provide gray scale masks which can be generated using a laser
writer or an optical imaging system, for example. However, the high
resolution required of diffractive optical elements and other
micro-elements is limited with this technique due to the limited
resolution of the laser writer and the graininess of the image on
the emulsion based mask. Moreover, photographic emulsions are not
particularly durable and do not allow cleaning of the mask with
water or mechanical scrubbing.
[0058] Other gray scale masking techniques, including the so-called
half tone binary mask, are also limited due to the small holes in
the mask which will also diffract light passing through the mask,
further limiting the resolution of the desired diffractive optical
element, for example.
[0059] One improvement in the production of gray scale masks for
use in fabricating diffractive optical elements and other
micro-elements has been realized with the provision of a gray scale
mask wherein different thicknesses of a light-absorbing material,
such as Inconel, coated on a glass plate mask element, for example,
can provide for the fabrication of a gray level mask with high
resolution and compatibility with substantially all wavelength
ranges used in optical lithography. However, one disadvantage of
this technique is the cost of the mask generation method wherein
multiple direct write steps are required to provide the lift off
process of the light-absorbing material for each discrete thickness
desired. The tight thickness control necessary in the material
evaporation step makes this technique somewhat economically
infeasible for many applications.
[0060] The use of a gray scale mask fabrication method for
producing large quantities or large arrays of diffractive optical
elements and similar micro-elements requiring high resolution of
three dimensional contours has several advantages. Gray scale masks
require only a single exposure of a photoresist when fabricating
the elements on a substrate using an etching process. Gray scale
masks thus avoid the alignment errors resulting from processes
requiring the use of multiple binary masks. Moreover, if a suitable
gray scale mask material is provided, thermal expansion and
contraction of the mask can also be avoided.
[0061] Accordingly, there has been a continuing need to develop an
improved fabrication method for relatively large quantities of and
large arrays of micro-elements, such as diffractive optical
elements or other elements covering large areas, such as computer
generated holograms. It is to these ends that the present invention
has been developed.
SUMMARY OF THE INVENTION
[0062] Since there is no graininess, HEBS-glass is capable of
resolution to molecular dimensions. HEBS-glass turns dark
instantaneously upon exposure to an electron beam, the more
electron dosage the more it darkens. Therefore, HEBS-glass is
ideally suited for making gray level masks. HEBS-glass gray level
masks can be written with an e-beam writer using a 0.1 .mu.m
addressing grid size. Every 0.1 .mu.m spot in the 5".times.5"
HEBS-glass plate acquires a predetermined transmittance value
ranging from 100 percent down to less than 0.1 percent upon e-beam
patterning with a predetermined dosage for each address. A gray
level mask made of HEBS-glass does not relay on a halftone method.
Therefore, it is a true gray level mask.
[0063] It is the objective of the present invention to design
HEBS-glass compositions so that the HEBS-glass gray level mask of
the present invention facilitates new designs and low cost
manufacturing processes for high-performance diffractive optics;
asymmetric, irregularly shaped microlens arrays; and general three
dimensional surfaces.
[0064] Application of the HEBS-glass of the present invention
include micro-optical devices, microelectrical devices,
micro-opto-electromechani- cal devices, integrated optical devices,
two-dimensional fanout grating, optical interconnect, fiber
pigtailing, diffractive optical elements, refractive microlens
arrays, microprism arrays, micromirror arrays and Bragg
grating.
[0065] The essential properties of a HEBS-glass gray level mask
which is necessary for the fabrication of general three dimensional
microstructures are:
[0066] 1. A mask pattern or image is grainiless even when observed
under optical microscope at 1000.times. or at higher
magnifications.
[0067] 2. The HEBS-glass is insensitive and/or inert to photons in
the spectral ranges employed in photolithographic processes, and is
also insensitive and/or inert to visible spectral range of light so
that a HEBS-glass mask blank and a HEBS-glass mask are permanently
stable under room lighting conditions.
[0068] 3. The HEBS-glass is sufficiently sensitive to electron beam
exposures, so that the cost of making a mask using an e-beam writer
is affordable for many applications.
[0069] 4. The e-beam induced optical density is a unique function
of, and is a very reproducible function of electron dosages for one
or more combinations of the parameters of an e-beam writer. The
parameters of e-beam writers include beam acceleration voltage,
beam current, beam spot size and addressing grid size.
[0070] The essential properties No. 1 and No. 2 are properties of
HEBS-glasses described in the US patents listed above. However,
HEBS-glass compositions having a better e-beam sensitivity is in
general more sensitive to photon energy as well.
[0071] It is the objective of the present invention to optimize
HEBS-glass composition so that the HEBS-glass of the present
invention is sufficiently sensitive to electron beam and that the
cost of writing a gray level mask is affordable for many
applications, and yet HEBS-glass of the present invention is
totally inert to actinic radiation of 436 nin and longer
wavelengths and has no sensitivity to actinic radiation at 365 nm
for practical purposes, eg. no significant darkening for 1,000,000
exposures in I-line steppers.
[0072] It has been determined that with a given value of e-beam
exposure dosage the e-beam induced optical density in HEBS-glass is
a function of beam acceleration voltage, of beam spot size, of beam
current and of addressing grid size. Therefore, it is another
objective of the present invention to design e-beam write schemes
such as that the essential properties No. 3 and No. 4 of a
HEBS-glass gray level mask are both fulfilled.
[0073] The present invention is directed to a gray scale mask
comprising a transparent High Energy Beam Sensitive-glass
(HEBS-glass) having at least one gray scale zone with a plurality
of gray scale levels, each gray scale level having a different
optical density, the High Energy Beam Sensitive-glass in bodies of
0.090 inch cross section will exhibit the following properties:
[0074] (a) transmittance of more than 88% at 436 nm; and
[0075] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size of from 0.1 to 0.4 micrometer, and a value of beam current
selected from 25 to 250 na, an electron beam darkening sensitivity
in the linear portion of the sensitivity curve, of at least 2.454
unit of optical density value in the spectral range of 365 nm to
630 nm per electron dosage unit of milli coulomb/cm.sup.2, said
HEBS-glass having a base glass composition consisting essentially
on the mole % oxide basis 11.4 to 17.5% of one or more alkali metal
oxide, 2.4 to 10.2% of photosensitivity inhibitors and RS
suppressing agents with at least 2.4% TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0076] In one embodiment, at least one gray scale zone has a
continuous gray scale comprising a plurality of grade scale
levels.
[0077] The present invention is also directed to a method of making
a gray scale mask comprising writing on a plurality of areas on at
least a portion of a High Energy Beam Sensitive-glass (HEBS-glass)
with an electron beam having an acceleration voltage of 20 is to 30
kilovolts, a beam current of 25 to 175 nanoamps, and addressing a
grid size of 0.1 to 0.4 micron; the writing carried out at an
electron dosage that falls on the net optical density vs. electron
dosage sensitivity curve of the High Energy Beam Sensitive-glass,
the initial slope of the sensitivity curve being from 2.454 to
12.507 per electron dosage unit of milli-coulombs/cm.sup.2; the
exposure duration of the writing on each area are different than
the exposure duration of the immediate adjacent areas; the High
Energy Beam Sensitive-glass in bodies of 0.090 inch cross section
will exhibit the following properties:
[0078] (a) a transmittance of more than 88% at 436 nm; and
[0079] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size of from 0.1 to 0.4 micrometer, and a value of beam current
selected from 25 to 250 na, an electron beam darkening sensitivity
in the linear portion of the sensitivity curve, of at least 2.454
unit of optical density value in the spectral range of 365 nm to
630 nm per electron dosage unit of milli coulomb/cm.sup.2; said
HEBS-glass having a base glass composition consisting essentially
on the mole % oxide basis 11.4 to 17.5% of one or more alkali metal
oxide, 2.4 to 10.2% of photosensitivity inhibitors and RS
suppressing agents with at least 2.4% TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0080] The present invention is also directed to a method of making
a three dimensional microstructure with three dimensional surfaces
in a photoresist comprising exposing a photoresist to a gray scale
pattern in a gray scale mask using an optical lithography tool and
developing the exposed photoresist to form three dimensional
microstructures in the photoresist;
[0081] the gray scale mask comprising a transparent High Energy
Beam Sensitive-glass (HEBS-glass) having at least one gray scale
zone with a plurality of gray scale levels, each gray scale level
having a different optical density, the High Energy Beam
Sensitive-glass in bodies of 0.090 inch cross section will exhibit
the following properties:
[0082] (a) a transmittance of more than 88% at 436 m; and
[0083] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size of from 0.1 to 0.4 micrometer, and a value of beam current
selected from 25 to 250 na, an electron beam darkening sensitivity
in the linear portion of the sensitivity curve, of at least 2.454
unit of optical density value in the spectral range of 365 nm to
630 nm per electron dosage unit of milli coulomb/cm.sup.2; said
HEBS-glass having a base glass composition consisting essentially
on the mole % oxide basis 11.4 to 17.5% of one or more alkali metal
oxide, 2.4 to 10.2% of photosensitivity inhibitors and RS
suppressing agents with at least 2.4% being TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0084] The present invention is also directed to an analog
photoresist with a three dimensional microstructure produced by
exposing a photoresist to a gray scale pattern in a gray scale mask
using an optical lithography tool and developing the exposed
photoresist to form the three dimensional microstructure in the
photoresist; the gray scale mask comprising:
[0085] A gray scale mask comprising a transparent High Energy Beam
Sensitive-glass (HEBS-glass) having at least one gray scale zone
with a plurality of gray scale levels, each gray scale level having
a different optical density, the High Energy Beam Sensitive-glass
in bodies of 0.090 inch cross section will exhibit the following
properties:
[0086] (a) a transmittance of more than 88% at 436=nm; and
[0087] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size of from 0.1 to 0.4 micrometer, and a value of beam current
selected from 25 to 250 na, an electron beam darkening sensitivity
in the linear portion of the sensitivity curve, of at least 2.454
unit of optical density value in the spectral range of 365 nm to
630 nm per electron dosage unit of milli coulomb/cm.sup.2, said
HEBS-glass having a base glass composition consisting essentially
on the mole % oxide basis 11.4 to 17.5% of one or more alkali metal
oxide, 2.4 to 10.2% of photosensitivity inhibitors and RS
suppressing agents with at least 2.4% being TiO.sub.2 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.5% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0088] The present invention is also directed to a method of
producing three dimensional microstructures in substrate material
comprising exposing a substrate through a developed analog
photoresist with a three dimensional microstructure with an ion
beam in an ion beam etching system to transfer the three
dimensional microstructure of the developed analog photoresist on
to the surface of the substrate in a single step exposure; the
analog photoresist with three dimensional microstructure being the
product of the process comprising exposing a photoresist to a gray
scale pattern in a gray scale mask using an optical lithography
tool and developing the exposed photoresist to form three
dimensional microstructures in the photoresist; the gray scale mask
comprising a transparent High Energy Beam Sensitive-glass
(HEBS-glass) having at least one gray scale zone with a plurality
of gray scale levels, each gray scale level having a different
optical density, the High Energy Beam Sensitive-glass in bodies of
0.090 inch cross section will exhibit the following properties:
[0089] (a) a transmittance of more than 88% at 436 nm; and
[0090] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size of from 0.1 to 0.4 micrometer, and a value of beam current
selected from 25 to 250 na, an electron beam darkening sensitivity
in the linear portion of the sensitivity curve, of at least 2.454
unit of optical density value in the spectral range of 365 nm to
630 nm per electron dosage unit of milli coulomb/cm.sup.2, said
HEBS-glass having a base glass composition consisting essentially
on the mole % oxide basis 11.4 to 17.5% of one or more alkali metal
oxide, 2.4 to 10.2% of photosensitivity inhibitors and RS
suppressing agents with at least 2.4% being TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0091] The present invention is directed to a component having a
three dimensional microstructure selected from the group consisting
of tapered structures for microelectronics, micro-optical devices,
integrated optical components, micro-electro-mechanical devices,
micro-opto-electro-mechanical devices, microelectrical devices,
diffractive optical elements (DOE), refractive microlens arrays,
micromirror arrays, and diffractive microlens arrays; the component
comprising a substrate having a three dimensional microstructure
produced by exposing a substrate through a developed analog
photoresist with a three dimensional microstructure with an ion
beam in an ion beam etching system to transfer the three
dimensional microstructure of the developed analog photoresist on
to the surface of the substrate in a single step exposure; the
analog photoresist with three dimensional microstructure being the
product of the process comprising exposing a photoresist to a gray
scale pattern in a gray scale mask using an optical lithography
tool and developing the exposed photoresist to form three
dimensional microstructures in the photoresist; the gray scale mask
comprising a transparent High Energy Beam Sensitive-glass
(HEBS-glass) having at least one gray scale zone with a plurality
of gray scale levels, each gray scale level having a different
optical density, the High Energy Beam Sensitive-glass in bodies of
0.090 inch cross section will exhibit the following properties:
[0092] (a) a transmittance of more than 88% at 436 nm; and
[0093] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size of from 0.1 to 0.4 micrometer, and a value of beam current
selected from 25 to 250 na, an electron beam darkening sensitivity
in the linear portion of the sensitivity curve, of at least 2.454
unit of optical density value in the spectral range of 365 nm to
630 nm per electron dosage unit of milli coulomb/cm.sup.2, said
HEBS-glass having a base glass composition consisting essentially
on the mole % oxide basis 11.4 to 17.5% of one or more alkali metal
oxide, 2.4 to 10.2% of photosensitivity inhibitors and RS
suppressing agents with at least 2.4% being TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0094] The present invention is also directed to a component having
a three dimensional microstructure selected from the group
consisting of electrical connections between two metallic layers
separated by tapered structures of thick polyimide, bifocal
intraocular lenses, widely asymmetric DOE, random phase plate DOEs,
miniature compact disc heads, antireflective surface, complex
imaging optics, grating couples, polarization-sensitive beam
splitters, spectral filters, wavelength division multiplexers,
micro optical elements for head-up and helmet mounted display,
micro optical elements for focal plane is optical concentration and
optical efficiency enhancement, micro optical elements for color
separation, beam shaping, and for miniature optical scanners,
microlens arrays, diffraction gratings, diffractive lenses, laser
diode array collimators and correctors, micro optical elements for
aberration correction, hybrid optics, microprism arrays,
micromirror arrays, random phase plates and Bragg gratings, two
dimensional fanout gratings, optical interconnects, signal
switches, fiber pig tailing, DOEs for coupling laser light into a
fiber, micro-electro-mechanical sensors and actuators, micro
valves, inertial micro sensors, micro machined RF switches, GPS
component miniaturization devices, laser scanners, optical
shutters, dynamic micro mirrors, optical choppers and optical
switches; the component comprising a substrate having a three
dimensional microstructure produced by exposing a substrate through
a developed analog photoresist with a three dimensional
microstructure with an ion beam in an ion beam etching system to
transfer the three dimensional microstructure of the developed
analog photoresist on to the surface of the substrate in a single
step exposure; the analog photoresist with three dimensional
microstructure being the product of the process comprising exposing
a photoresist to a gray scale pattern in a gray scale mask using an
optical lithography tool and developing the exposed photoresist to
form three dimensional microstructures in the photoresist; the gray
scale mask comprising a transparent High Energy Beam
Sensitive-glass (HEBS-glass) having at least one gray scale zone
with a plurality of gray scale levels, each gray scale level having
a different optical density, the High Energy Beam Sensitive-glass
in bodies of 0.090 inch cross section will exhibit the following
properties:
[0095] (a) a transmittance of more than 88% at 436 nm; and
[0096] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size of from 0.1 to 0.4 micrometer, and a value of beam current
selected from 25 to 250 na, an electron beam darkening sensitivity
in the linear portion of the sensitivity curve, of at least 2.454
unit of optical density value in the spectral range of 365 nm to
630 nm per electron dosage unit of milli coulomb/cm.sup.2; said
HEBS-glass having a base glass composition consisting essentially
on the mole % oxide basis 11.4 to 17.5% of one or more alkali metal
oxide, 2.4 to 10.2% of photosensitivity 15 inhibitors and RS
suppressing agents with at least 2.4% being TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0097] The present invention is directed to a method of producing a
component having a three dimensional microstructure selected from
the group consisting of tapered structures for microelectronics,
micro optical devices, integrated optical components,
micro-electro-mechanical devices, micro-opto-electro-mechanical
devices, diffractive optical elements, refractive microlens arrays,
diffractive microlens, and micromirror arrays, the method
comprising exposing a substrate through a developed analog
photoresist with a three dimensional microstructure with an ion
beam in an ion beam etching system to transfer the three
dimensional microstructure of the developed analog photoresist on
to the surface of the substrate in a single step exposure; the
analog photoresist with three dimensional microstructure being the
product of the process of exposing a photoresist to a gray scale
pattern in a gray scale mask using an optical lithography tool and
developing the exposed photoresist to form three dimensional
microstructures in the photoresist; the gray scale mask comprising
a transparent High Energy Beam Sensitive-glass (HEBS-glass) having
at least one gray scale zone with a plurality of gray scale levels,
each gray scale level having a different optical density, the High
Energy Beam Sensitive-glass in bodies of 0.090 inch cross section
will exhibit the following properties:
[0098] (a) a transmittance of more than 88% at 436 nm; and
[0099] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size of from 0.1 to 0.4 micrometer, and a value of beam current
selected from 25 to 250 na, an electron beam darkening sensitivity
in the linear portion of the sensitivity curve, of at least 2.454
unit of optical density value in the spectral range of 365 nm to
630 nm per electron dosage unit of milli coulomb/cm.sup.2; said
HEBS-glass having a base glass composition consisting essentially
on the mole % oxide basis 11.4 to 17.5% of one or more alkali metal
oxide, 2.4 to 10.2% of photosensitivity inhibitors and RS
suppressing agents with at least 2.4% being TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0100] The present invention is also directed to a method of
producing a component having a three dimensional microstructure
selected from the group consisting of electrical connections
between two metallic layers separated by tapered structures of
thick polyimide, bifocal intraocular lenses, widely asymmetric DOE,
miniature compact disc heads, antireflective surface, complex
imaging optics, grating couples, polarization-sensitive beam
splitters, spectral filters, wavelength division multiplexers,
micro optical elements for head-up and helmet mounted display,
micro optical elements for focal plane optical concentration and
optical efficiency enhancement, micro optical elements for color
separations, beam shaping, and for miniature optical scanners,
microlens arrays, diffraction gratings, diffractive lenses, laser
diode array collimators and correctors, micro optical elements for
aberration correction, hybrid optics, microprism arrays,
micromirror arrays, random phase plates and Bragg gratings, two
dimensional fanout gratings, optical interconnects, signal
switches, fiber pig tailing, DOEs for coupling laser light into a
fiber, micro-electro-mechanical sensors and actuators, micro
valves, inertial micro sensors, micro machined RF switches, GPS
component miniaturization devices, laser scanners, optical
shutters, dynamic micro mirrors, optical shoppers and optical
switches; the microlens, and micromirror arrays, the method
comprising exposing a substrate through a developed analog
photoresist with a three dimensional microstructure with an ion
beam in an ion beam etching system to transfer the three
dimensional microstructure of the developed analog photoresist on
to the surface of the substrate in a single step exposure; the
analog photoresist with three dimensional microstructure being the
product of the process of exposing a photoresist to a gray scale
pattern in a gray scale mask using an optical lithography tool and
developing the exposed photoresist to from three dimensional
microstructures in the photoresist; the gray scale mask comprising
a transparent High Energy Beam Sensitive-glass (HEBS-glass) having
at least one gray scale zone with a plurality of gray scale levels,
each gray scale level having a different optical density, the High
Energy Beam Sensitive-glass in bodies of 0.090 inch cross section
will exhibit the following properties:
[0101] (a) a transmittance of more than 88% at 436 nm; and
[0102] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size of from 0.1 to 0.4 micrometer, and a value of beam current
selected from 25 to 250 na, an electron beam darkening sensitivity
in the linear portion of the sensitivity curve, of at least 2.454
unit of optical density value in the spectral range of 365 nm to
630 nm per electron dosage unit of milli coulomb/cm.sup.2; said
HEBS-glass having a base glass composition consisting essentially
on the mole % oxide basis 11.4 to 17.5% of one or more alkali metal
oxide, 2.4 to 10.2% of photosensitivity inhibitors and RS
suppressing agents with at least 2.4% being TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0103] The present invention is also directed to a Laser Direct
Write-glass (LDW-glass) which is a High Energy Beam Sensitive-glass
(HEBS-glass) having at least a portion uniformly darkened to a
uniform optical density, said LDW-glass prior to being darkened
with an electron beam is a transparent HEBS-glass which in bodies
0.090 inch cross section will exhibit the following properties:
[0104] (a) transmittance of more than 88% at 436 nm; and
[0105] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365=n to 630 nm per electron dosage unit of milli coulomb/cm.sup.2,
said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% of photosensitivity inhibitors and
RS suppressing agents with at least 2.4% TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2.
[0106] The present invention is also directed to a gray scale mask
on a Laser Direct Write glass (LDW-glass) produced by darkening at
least a portion of a High Energy Beam Sensitive-glass (HEBS-glass)
with an electron beam to form a LDW-glass having a uniformly
darkened portion having a uniform optical density, the HEBS-glass
in bodies of 0.090 inch cross section exhibiting the following
properties:
[0107] (a) transmittance of more than 88% at 436 nm; and
[0108] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365 nm to 630 nm per electron dosage unit of mini coulomb/cm.sup.2,
said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% of photosensitivity inhibitors and
RS suppressing agents with at least 2.4% TiO.sub.2; 1.1 to 2.4%
Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2% ZnO; 0.5 to
6% Cl; and 58.2 to 78.8% SiO.sub.2; and exposing a plurality of
areas on the uniformly darkened portion of the. LDW-glass with a
focused laser beam to form a gray scale zone with a plurality of
gray scale levels, the optical density of each gray scale level
differing from the optical density of adjacent gray scale levels,
and the optical density of the darkest gray scale level not
exceeding the optical density of the uniformly darkened portion of
the LDW-glass.
[0109] In an alternative embodiment of the gray scale mark, the
gray scale zone has a continuous gray scale comprising a plurality
of grade scale levels.
[0110] The present invention is also directed to a method of making
a gray scale mask comprising darkening at least a portion of a High
Energy Beam Sensitive-glass (HEBS-glass) with an electron beam to
form a Laser Direct Write-glass having uniformly darkened portion
having a uniform optical density, the HEBS-glass in bodies of 0.090
inch cross section exhibiting the following properties:
[0111] (a) transmittance of more than 88% at 436 nm; and
[0112] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365 nm to 630 nm per electron dosage unit of milli
coulomb/cm.sup.2, said HEBS-glass having a base glass composition
consisting essentially on the mole % oxide basis 11.4 to 17.5% of
one or more alkali metal oxide, 2.4 to 10.2% of photosensitivity
inhibitors and RS suppressing agents with at least 2.4% TiO.sub.2;
1.1 to 2.4% Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2%
ZnO; 0.5 to 6% Cl; and 58.2 to 78.8% SiO.sub.2; and exposing a
plurality of areas on the uniformly darkened portion of the
LDW-glass with a focused laser beam to form a gray scale zone with
a plurality of gray scale levels, the optical density of each gray
scale level differing from the optical density of adjacent gray
scale levels, and the optical density of the darkest gray scale
level not exceeding the optical density of the uniformly darkened
portion of the LDW-glass.
[0113] In one embodiment of the method, the focused laser beam
exposure write time for each area exposed is different. In another
embodiment of the method, the focused laser beam intensity for each
area exposed is different. In still another embodiment of the
method, the number of retraces of the focused laser beam writing
for each area exposed is different.
[0114] The present invention is also directed to a method of making
a three dimensional microstructure with three dimensional surfaces
in a photoresist comprising exposing a photoresist to a gray scale
pattern in a gray scale mask on a Laser Direct Write-glass
((LDW-glass) using an optical lithography tool and developing the
exposed photoresist to form three dimensional microstructures in
the photoresist; A gray scale mask on a Laser Direct Write glass
(LDW-glass) produced by darkening at least a portion of a High
Energy Beam Sensitive-glass (HEBS-glass) with an electron beam to
form a LDW-glass having a uniformly darkened portion having a
uniform optical density, the HEBS-glass in bodies of 0.090 inch
cross section exhibiting the following properties:
[0115] (a) transmittance of more than 88% at 436 nm; and
[0116] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365 nm to 630 nm per electron dosage unit of milli
coulomb/cm.sup.2, said HEBS-glass having a base glass composition
consisting essentially on the mole % oxide basis 11.4 to 17.5% of
one or more alkali metal oxide, 2.4 to 10.2% of photosensitivity
inhibitors and RS suppressing agents with at least 2.4% TiO.sub.2;
1.1 to 2.4% Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2%
ZnO; 0.5 to 6% Cl; and 58.2 to 78.8% SiO.sub.2; and exposing a
plurality of areas on the uniformly darkened portion of the
LDW-glass with a focused laser beam to form a gray scale zone with
a plurality of gray scale levels, the optical density of each gray
scale level differing from the optical density of adjacent gray
scale levels, and the optical density of the darkest gray scale
level not exceeding the optical density of the uniformly darkened
portion of the LDW-glass.
[0117] The present invention is also directed to an analog
photoresist with a three dimensional microstructure produced by
exposing a photoresist to a gray scale pattern in a gray scale mask
on a Laser Direct Write-glass (LDW-glass) using an optical
lithography tool and developing the exposed photoresist to form the
three dimensional microstructure in the photoresist; the gray scale
mask comprising:
[0118] A gray scale mask on a Laser Direct Write glass (LDW-glass)
produced by darkening at least a portion of a High Energy Beam
Sensitive-glass (HEBS-glass) with an electron beam to form a
LDW-glass having a uniformly darkened portion having a uniform
optical density, the HEBS-glass in bodies of 0.090 inch cross
section exhibiting the following properties:
[0119] (a) transmittance of more than 88% at 436 nm; and
[0120] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365 nm to 630 nm per electron dosage unit of milli
coulomb/cm.sup.2, said HEBS-glass having a base glass composition
consisting essentially on the mole % oxide basis 11.4 to 17.5% of
one or more alkali metal oxide, 2.4 to 10.2% of photosensitivity
inhibitors and RS suppressing agents with at least 2.4% TiO.sub.2;
1.1 to 2.4% Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2%
ZnO; 0.5 to 6% Cl; and 58.2 to 78.8% SiO.sub.2; and exposing a
plurality of areas on the uniformly darkened portion of the
LDW-glass with a focused laser beam to form a gray scale zone with
a plurality of gray scale levels, the optical density of each gray
scale level differing from the optical density of adjacent gray
scale levels, and the optical density of the darkest gray scale
level not exceeding the optical density of the uniformly darkened
portion of the LDW-glass.
[0121] The present invention is directed to a method of producing
three dimensional microstructures in substrate material comprising
exposing a substrate through a developed analog photoresist with a
three dimensional microstructure with an ion beam in an ion beam
etching system to transfer the three dimensional microstructure of
the developed analog photoresist on to the surface of the substrate
in a single step exposure; the analog photoresist with three
dimensional microstructure being the product of the process
comprising exposing a photoresist to a gray scale pattern in a gray
scale mask on a Laser Direct Write-glass (LDW-glass) using an
optical lithography tool and developing the exposed photoresist to
form three dimensional microstructures in the photoresist; the gray
scale mask comprising a LDW-glass having at least one gray scale
zone with a plurality of gray scale levels, each gray scale level
having a different optical density, the gray scale mask produced by
darkening at least a portion of a High Energy Beam Sensitive-glass
(HEBS-glass) with an electron beam to form a LDW-glass having a
uniformly darkened portion having a uniform optical density, the
HEBS-glass in bodies of 0.090 inch cross section exhibiting the
following properties:
[0122] (a) transmittance of more than 88% at 436 nm; and
[0123] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365 nm to 630 nm per electron dosage unit of milli
coulomb/cm.sup.2, said HEBS-glass having a base glass composition
consisting essentially on the mole % oxide basis 11.4 to 17.5% of
one or more alkali metal oxide, 2.4 to 10.2% of photosensitivity
inhibitors and RS suppressing agents with at least 2.4% TiO.sub.2;
1.1 to 2.4% Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2%
ZnO; 0.5 to 6% Cl; and 58.2 to 78.8% SiO.sub.2; and exposing a
plurality of areas on the uniformly darkened portion of the
LDW-glass with a focused laser beam to form a gray scale zone with
a plurality of gray scale levels, the optical density of each gray
scale level differing from the optical density of adjacent gray
scale levels, and the optical density of the darkest gray scale
level not exceeding the optical density of the uniformly darkened
portion of the LDW-glass.
[0124] The present invention is directed to a component having a
three dimensional microstructure selected from the group consisting
of tapered structures for microelectronics, micro-optical devices,
integrated optical components, micro-electro-mechanical devices,
micro-opto-electro-mechanical devices, microelectrical devices,
diffractive optical elements (DOE), refractive microlens arrays,
micromirror arrays, and diffractive microlens arrays; the component
comprising a substrate having a three dimensional microstructure
produced by exposing a substrate through a developed analog
photoresist with a three dimensional microstructure with an ion
beam in an ion beam etching system to transfer the three
dimensional microstructure of the developed analog photoresist on
to the surface of the substrate in a single step exposure; the
analog photoresist with three dimensional microstructure being the
product of the process comprising exposing a photoresist to a gray
scale pattern in a gray scale mask on a Laser Direct Write-glass
(LDW-glass) using an optical lithography tool and developing the
exposed photoresist to form three dimensional microstructures in
the photoresist; the gray scale mask comprising a LDW-glass having
at least one gray scale zone with a plurality of gray scale levels,
each gray scale level having a different optical density, the gray
scale mask produced by darkening at least a portion of a High
Energy Beam Sensitive-glass (HEBS-glass) with an electron beam to
form a LDW-glass having a uniformly darkened portion having a
uniform optical density, the HEBS-glass in bodies of 0.090 inch
cross section exhibiting the following properties:
[0125] (a) transmittance of more than 88% at 436 nm; and
[0126] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365 nm to 630 nm per electron dosage unit of milli
coulomb/cm.sup.2, said HEBS-glass having a base glass composition
consisting essentially on the mole % oxide basis 11.4 to 17.5% of
one or more alkali metal oxide, 2.4 to 10.2% of photosensitivity
inhibitors and RS suppressing agents with at least 2.4% TiO.sub.2;
1.1 to 2.4% Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2%
ZnO; 0.5 to 6% Cl; and 58.2 to 78.8% SiO.sub.2; and exposing a
plurality of areas on the uniformly darkened portion of the
LDW-glass with a focused laser beam to form a gray scale zone with
a plurality of gray scale levels, the optical density of each gray
scale level differing from the optical density of adjacent gray
scale levels, and the optical density of the darkest gray scale
level not exceeding the optical density of the uniformly darkened
portion of the LDW-glass.
[0127] The present invention is directed to a component having a
three dimensional microstructure selected from the group consisting
of electrical connections between two metallic layers separated by
tapered structures of thick polyimide, bifocal intraocular lenses,
widely asymmetric DOE, miniature compact disc heads, antireflective
surface, complex imaging optics, grating couples,
polarization-sensitive beam splitters, spectral filters, wavelength
division multiplexers, micro optical elements for head-up and
helmet mounted display, micro optical elements for focal plane
optical concentration and optical efficiency enhancement, micro
optical elements for color separation, beam shaping, and for
miniature optical scanners, microlens arrays, diffraction gratings,
diffractive lenses, laser diode array collimators and correctors,
micro optical elements for aberration correction, hybrid optics,
microprism arrays, micromirror arrays, random phase plates and
Bragg gratings, two dimensional fanout gratings, optical
interconnects, signal switches, fiber pig tailing, DOEs for
coupling laser light into a fiber, micro-electro-mechanical sensors
and actuators, micro valves, inertial micro sensors, micro machined
RF switches, GPS component miniaturization devices, laser scanners,
optical shutters, dynamic micro mirrors, optical choppers and
optical switches; the component comprising a substrate having a
three dimensional microstructure produced by exposing a substrate
through a developed analog photoresist with a three dimensional
microstructure with an ion beam in an ion beam etching system to
transfer the three dimensional microstructure of the developed
analog photoresist on to the surface of the substrate in a single
step exposure; the analog photoresist with three dimensional
microstructure being the product of the process comprising exposing
a photoresist to a gray scale pattern in a gray scale mask on a
Laser Direct Write-glass (LDW-glass) using an optical lithography
tool and developing the exposed photoresist to form three
dimensional microstructures in the photoresist; the gray scale mask
comprising a transparent High Energy Beam Sensitive-glass having at
least one gray scale zone with a plurality of gray scale levels,
each gray scale level having a different optical density, the gray
scale produced by darkening at least a portion of a High Energy
Beam Sensitive-glass (HEBS-glass) with an electron beam to form a
LDW-glass having a uniformly darkened portion having a uniform
optical density, the HEBS-glass in bodies of 0.090 inch cross
section exhibiting the following properties:
[0128] (a) transmittance of more than 88% at 436 nm; and
[0129] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365 nm to 630 nm per electron dosage unit of milli
coulomb/cm.sup.2, said HEBS-glass having a base glass composition
consisting essentially on the mole % oxide basis 11.4 to 17.5% of
one or more alkali metal oxide, 2.4 to 10.2% of photosensitivity
inhibitors and RS suppressing agents with at least 2.4% TiO.sub.2;
1.1 to 2.4% Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2%
ZnO; 0.5 to 6% Cl; and 58.2 to 78.8% SiO.sub.2; and exposing a
plurality of areas on the uniformly darkened portion of the
LDW-glass with a focused laser beam to form a gray scale zone with
a plurality of gray scale levels, the optical density of each gray
scale level differing from the optical density of adjacent gray
scale levels, and the optical density of the darkest gray scale
level not exceeding the optical density of the uniformly darkened
portion of the LDW-glass.
[0130] The present invention is directed to a method of producing a
component having a three dimensional microstructure selected from
the group consisting of tapered structures for microelectronics,
micro optical devices, integrated optical components,
micro-electro-is mechanical devices, micro-opto-electro-mechanical
devices, diffractive optical elements, refractive microlens arrays,
diffractive microlens, and micromirror arrays, the method
comprising exposing a substrate through a developed analog
photoresist with a three dimensional microstructure with an ion
beam in an ion beam etching system to transfer the three
dimensional microstructure of the developed analog photoresist on
to the surface of the substrate in a single step exposure; the
analog photoresist with three dimensional microstructure being the
product of the process of exposing a photoresist to a gray scale
pattern in a gray scale mask on a Laser Direct Write-glass
(LDW-glass) using an optical lithography tool and developing the
exposed photoresist to form three dimensional microstructures in
the photoresist; the gray scale mask comprising a transparent High
Energy Beam Sensitive-glass having at least one gray scale zone
with a plurality of gray scale levels, each gray scale level having
a different optical density, the gray scale mask produced by
darkening at least a portion of a High Energy Beam Sensitive-glass
(HEBS-glass) with an electron beam to form a LDW-glass having a
uniformly darkened portion having a uniform optical density, the
HEBS-glass in bodies of 0.090 inch cross section exhibiting the
following properties:
[0131] (a) transmittance of more than 88% at 436 nm; and
[0132] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365 nm to 630 nm per electron dosage unit of milli
coulomb/cm.sup.2, said HEBS-glass having a base glass composition
consisting essentially on the mole % oxide basis 11.4 to 17.5% of
one or more alkali metal oxide, 2.4 to 10.2% of photosensitivity
inhibitors and RS suppressing agents with at least 2.4% TiO.sub.2;
1.1 to 2.4% Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2%
ZnO; 0.5 to 6% Cl; and 58.2 to 78.8% SiO.sub.2; and exposing a
plurality of areas on the uniformly darkened portion of the
LDW-glass with a focused laser beam to form a gray scale zone with
a plurality of gray scale levels, the optical density of each gray
scale level differing from the optical density of adjacent gray
scale levels, and the optical density of the darkest gray scale
level not exceeding the optical density of the uniformly darkened
portion of the LDW-glass.
[0133] The present invention is also directed to a method of
producing a component having a three dimensional microstructure
selected from the group consisting of electrical connections
between two metallic layers separated by tapered structures of
thick polyimide, bifocal intraocular lenses, widely asymmetric DOE,
miniature compact disc heads, antireflective surface, complex
imaging optics, grating couples, polarization-sensitive beam
splitter, spectral filters, wavelength division multiplexers, micro
optical elements for head-up and helmet mounted display, micro
optical elements for focal plane optical concentration and optical
efficiency enhancement, micro optical elements for color
separations, beam shaping, and for miniature optical scanners,
microlens arrays, diffraction gratings, diffractive lenses, laser
diode array collimators and correctors, micro optical elements for
aberration correction, hybrid optics, microprism arrays,
micromirror arrays, random phase plates and Bragg gratings, two
dimensional fanout gratings, optical interconnects, signal
switches, fiber pig tailing, DOEs for coupling laser light into a
fiber, micro-electro-mechanical sensors and actuators, micro
valves, inertial micro sensors, micro machined RF switches, GPS
component miniaturization devices, laser scanners, optical
shutters, dynamic micro mirrors, optical shoppers and optical
switches; the microlens, and micromirror arrays, the method
comprising exposing a substrate through a developed analog
photoresist with a three dimensional microstructure with an ion
beam in an ion beam etching system to transfer the three
dimensional microstructure of the developed analog photoresist on
to the surface of the substrate in a single step exposure; the
analog photoresist with three dimensional microstructure being the
product of the process of exposing a photoresist to a gray scale
pattern in a gray scale mask on a Laser Direct Write-glass
(LDW-glass) using an optical lithography tool and developing the
exposed photoresist to from three dimensional microstructures in
the photoresist; the gray scale mask comprising a transparent High
Energy Beam Sensitive-glass having at least one gray scale zone
with a plurality of gray scale levels, each gray scale level having
a different optical density, the gray scale mask produced by
darkening at least a portion of a High Energy Beam Sensitive-glass
(HEBS-glass) with an electron beam to form a LDW-glass having a
uniformly darkened portion having a uniform optical density, the
HEBS-glass in bodies of 0.090 inch cross section will exhibit the
following properties:
[0134] (a) transmittance of more than 88% at 436 nm; and
[0135] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, an addressing grid
size selected from 0.1 to 0.4 micrometer, and a value of beam
current selected from 25 to 250 na, an electron beam darkening
sensitivity in the linear portion of the sensitivity curve of at
least 2.454 unit of optical density value in the spectral range of
365 nm to 630 nm per electron dosage unit of milli
coulomb/cm.sup.2, said HEBS-glass having a base glass composition
consisting essentially on the mole % oxide basis 11.4 to 17.5% of
one or more alkali metal oxide, 2.4 to 10.2% of photosensitivity
inhibitors and RS suppressing agents with at least 2.4% TiO.sub.2;
1.1 to 2.4% Al.sub.2O.sub.3; 0 to 4.6% B.sub.2O.sub.3; 3.7 to 13.2%
ZnO; 0.5 to 6% Cl; and 58.2 to 78.8% SiO.sub.2; and exposing a
plurality of areas on the uniformly darkened portion of the
LDW-glass with a focused laser beam to form a gray scale zone with
a plurality of gray scale levels, the optical density of each gray
scale level differing from the optical density of adjacent gray
scale levels, and the optical density of the darkest gray scale
level not exceeding the optical density of the uniformly darkened
portion of the LDW-glass.
[0136] A method of fabricating a three-dimensional micro-optic lens
on a substrate selected from a group consisting of quartz glass,
silicate glass, germanium and an optically transmissive material
coated with a photoresist layer, comprising: providing a gray scale
mask having a body portion and a surface layer formed thereon which
is responsive to electron beam radiation to change the optical
density of the surface layer; exposing the mask to an electron beam
of selected charge density over a grid of discrete locations on the
mask to provide a predetermined gray scale pattern of continuously
varying optical transmissivity on the mask; exposing the
photoresist layer to radiation transmitted through the mask; and
removing material from the photoresist layer and the substrate to
provide a predetermined varying thickness of the substrate as
determined by the gray scale patterns on the mask.
[0137] The above method optionally including the step of generating
said electron beam with a current of at least about 25 nA.
[0138] The above method optionally including the step of applying
an electrically conductive coating to the mask prior to exposing
the mask to said electron beam and removing said coating from the
mask after exposing the mask to said electron beam.
[0139] The above method optionally including the step of removing
material from said photoresist layer and said substrate by
chemically assisted ion beam etching.
[0140] The above method optionally including the step of comparing
a thickness of said photoresist layer which may be exposed to
radiation with a corresponding electron beam charge density value
required to darken said layer of the mask to provide a
predetermined depth level in said substrate; and exposing the mask
to said electron beam at a preselected charge density corresponding
to the desired thickness of exposure of said photoresist layer.
[0141] Another method for producing various depth levels in a layer
of photoresist material includes the steps of exposing a layer of
photoresist material to radiation through a gray scale mask having
areas of continuously varying transmissivity; removing photoresist
material from said photoresist layer to depth in said photoresist
layer at a predetermined position thereon corresponding to a
predetermined transmissivity of said gray scale Mask at a
corresponding predetermined position on said gray scale mask; and
providing said gray scale mask as a glass article comprising a body
portion and an integral ion exchanged surface layer which, upon
exposure to a high energy electron beam, becomes darkened and is
substantially insensitive to actinic radiation.
[0142] The above method optionally including the step of exposing
said gray scale mask to selected discrete charge densities of
electron beam radiation over a grid of preselected grid spacings
and varying the electron beam charge density from one spacing to
the next in accordance with a predetermined depth level desired to
be produced in said photoresist layer.
[0143] The above method optionally including the step of comparing
a thickness of said photoresist layer which may be exposed to
radiation with a corresponding electron beam charge density value
required to darken said gray scale mask to provide a predetermined
depth level in said photoresist layer, and exposing said gray scale
mask to said electron beam at a preselected charge density
corresponding to the desired thickness of exposure of said
photoresist layer.
[0144] The above method optionally including the step of
selectively darkening a surface layer of said gray scale mask by
generating an electron beam at discrete, predetermined positions
thereon and at an acceleration voltage of at least about 20 kV.
[0145] Another method of fabricating a three-dimensional
micro-element on a substrate to various depth levels comprising one
of discrete depth levels and a continuous depth profile through a
photoresist layer, comprises the steps of exposing said photoresist
layer to radiation transmitted through a gray scale mask having a
gray scale pattern thereon comprising image areas having a
continuously varying transmissivity corresponding to a depth of
material to be removed from said substrate to provide said element;
removing material from said photoresist layer and said substrate in
a predetermined pattern as determined by said gray scale pattern on
said mask; providing said gray scale mask characterized as a glass
article comprising a body portion and an integral radiation
absorbing surface layer which is substantially insensitive to
actinic radiation; and providing said glass article with said ion
exchanged surface layer having Ag+ ions therein, and/or silver
halide containing and/or Ag.sub.2 O containing and/or Ag+ ion
containing micro-crystals and/or micro-phases therein.
[0146] The above method optionally including the step of exposing
the mask to an electron beam at a predetermined dosage
corresponding to a degree of darkening of the mask required to
produce a predetermined depth level in said photoresist layer.
[0147] The above method optionally including the step of darkening
the mask by generating an electron beam at an acceleration voltage
in the range of 20 kV to 30 kV.
[0148] The above method optionally including the step of exposing
the mask to an electron beam charge density of 0 mC/cm.sup.2 to
about 400 mC/cm.sup.2. The above method optionally including the
step of generating said electron beam with a current of at least
about 25 nA.
[0149] The above method optionally including the step of applying
an electrically conductive coating to the mask prior to exposing
the mask to said electron beam.
[0150] The above method optionally including the step of removing
said coating from the mask after exposing the mask to said electron
beam The above method optionally including the step of comparing a
thickness of said photoresist layer which may be exposed to
radiation with a corresponding electron beam charge density value
required to darken the mask to provide a predetermined depth level
in said substrate; and exposing the mask to said electron beam at a
preselected charge density corresponding to the desired thickness
of exposure of said photoresist layer.
[0151] The above method optionally including the step of: exposing
the mask to selected discrete charge densities of electron beam
radiation over a grid of preselected grid spacings and varying the
electron beam charge density from one spacing to the next in
accordance with a predetermined depth level desired to be produced
in said substrate.
[0152] Another method of fabricating a three-dimensional
micro-element on a substrate and to various depth levels comprising
one of discrete depth levels and a continuously depth profile
through a photoresist layer, comprises the steps of providing a
gray scale mask characterized as a glass article comprising a body
portion and an internal radiation absorbing surface layer which is
substantially insensitive to actinic radiation; and providing said
glass article as a silicate glass having a silicon dioxide content
in mole percent of from 30 to 95 and essentially no transition
metals having 1-4 d electrons in the atomic state and at least one
surface of said article having a substantially continuous silver
and hydration content over its area, effective to render said
surface darkenable upon exposure to electron beam radiation.
[0153] The present invention provides an improved method for
producing micro-elements, including diffractive optical elements
and the like, using a gray scale mask.
[0154] The present invention also provides an improved method for
producing a gray scale mask comprising a glass article which is
sensitive to exposure to a high energy electron beam, for example,
to provide a pre-determined pattern on the article by varying the
optical density of the glass as a result of exposure to the high
energy electron beam.
[0155] In accordance with one aspect of the present invention
micro-elements, such as diffractive optical elements,
computer-generated holograms and other three dimensional
micro-elements, may be produced with greater accuracy of the
prescribed geometry of the element and in large quantities or large
arrays by providing a gray scale mask having a masking pattern
developed on a durable glass substrate comprising a high energy
beam sensitive (HEBS) glass. The glass substrate or article
includes a body portion and an integral ion exchanged surface layer
which, upon exposure to high energy electron beams, becomes
darkened to a selected degree to provide the gray levels required
for developing the various depths or phase levels in the three
dimensional elements to be manufactured using the mask. In
particular, the mask glass article preferably comprises a plate of
a high energy beam-sensitive glass having an integral ion exchanged
surface layer containing a high concentration of Ag.sup.+ ions
and/or a large number density of AgCl-containing and/or Ag.sub.2
O-containing and/or Ag.sup.+ion-containing micro-crystals and/or
micro-phases, and also containing silanol groups and/or water in
the concentration range of about 0.01% to 12.0% by weight water.
The gray scale mask may also be formed of a glass such as a
silicate glass composition hydrated and containing silver and which
can be effectively written with high energy beams, such as electron
beams, to produce high optical density images thereon.
[0156] In accordance with another aspect of the present invention a
method for generating a gray scale mask is provided wherein a glass
mask element is provided with a pre-determined masking pattern
formed directly thereon to provide a durable mask structure which
eliminates the need for thin film coatings and ablative thin film
materials. The particular method for producing a mask structure
contemplated by the present invention comprises exposing a high
energy beam-sensitive glass plate directly to an electron beam,
using a commercially available electron beam writing device, at a
relatively low acceleration voltage to provide a more precise
configuration of the mask image pattern and the variations of
optical density required to generate the various gray levels. In
particular, acceleration voltage is controlled to produce
sufficient penetration depth in the mask material without extending
the electron trajectories unnecessarily with the resultant loss in
resolution of the mask pattern.
[0157] In accordance with still another aspect of the present
invention micro-elements, such as diffractive optical elements, are
fabricated with improved geometries using a gray scale mask formed
of a glass composition which is operable to provide stable images
generated by exposure to an electron beam which may be controlled
to generate a Is precise image on the glass. A gray scale mask in
accordance with the invention may be reused many times, is
relatively insensitive to exposure to environmental factors and is
capable of providing high resolution and the resultant precise
contour or dimensional control over the workpiece.
[0158] The present invention further provides an improved method of
fabricating micro-optic devices, such as diffractive optical
elements, with a gray scale mask which is simplified and cost
effective, and wherein only a single mask needs to be exposed in an
electron beam writer and wherein no multiple resist processing
steps are required to generate the mask. Since the multiple levels
or contour shading of the gray levels are written in a single step
on a single mask the inevitable misregistrations between multiple
lithography steps used in prior art mask fabricating methods are
avoided.
[0159] Still further, the number of processing steps for
fabrication of micro-elements compared to the steps required in
fabrication methods using binary masks is substantially reduced in
the method of the present invention wherein the element workpiece
material may be optimized, that is the material which is best
suited for the application can be chosen without being limited by
the constraints of a molding material used in molded element
fabrication methods.
[0160] Moreover, the method of the invention utilizes certain
materials, tools and equipment compatible with the fabrication of
large scale integrated electronic circuits. In this regard, the
development of new fabrication techniques, environments and
computer programs, for example, are not required to be established.
The reduction in the number of steps involved in the fabrication
method of the present invention will improve the efficiency and
speed of the fabrication process. In this regard, mass production
may be carried out based on a step and repeat photoresist exposure
process followed by a chemically assisted ion beam etching batch
process, for example.
[0161] Those skilled in the art will further appreciate the
above-mentioned advantages and superior features of the invention
together with other important aspects thereof upon reading the
detailed description which follows in conjunction with the
drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0162] FIG. 1 illustrates a qualitative representation of the
silver concentration profile in HEBS-glass FIG. 2 records
absorbance spectra of HEBS-glass No. 3 after flood exposure with
e-beam at 29 kV acceleration voltage.
[0163] FIG. 3 records absorbance spectra of HEBS-glass No. 3 after
flood exposure with e-beam at 25 kV acceleration voltage.
[0164] FIG. 4 records absorbance spectra of HEBS-glass No. 3 after
flood exposure with e-beam at 20 kV acceleration voltage.
[0165] FIG. 5 record absorbance spectra of HEBS-glass No. 3 after
flood exposure with e-beam at 15 kV acceleration voltage.
[0166] FIG. 6 depicts optical density at 436 nm of HEBS-glass No. 3
verses electron dosage. Electron beam exposure was done with EVC
flood exposure system at 29 kV, 20 kV, and 15 kV.
[0167] FIG. 7(a) records net optical density at 435 nm versus
electron dosage at 30 kV. Curve A--250 na, 0.4 .mu.m address size,
Curve B--75 na, 0.2 .mu.m address size, EVC--e-beam flood
exposure.
[0168] FIG. 7(b) records net optical density at 530 nm verses
electron dosage at 30 kV. Curve A--250 na, 0.4 .mu.m address size,
Curve B--75 na, 0.2 .mu.m address size, EVC--e-beam flood
exposure.
[0169] FIG. 7(c) net optical density at 630 nm verses electron
dosage at 30 kV. Curve A--250 na, 0.4 .mu.m address size, Curve
B--75 na, 0.2 .mu.m address size, EVC--e-beam flood exposure.
[0170] FIG. 7(d) records data points of the net optical density at
365 nm vs. electron dosage, depicts the best fit curve and displays
the equation describing the best fit curve; the electron beam
exposure was done with Cambridge EBMF 10.5 e-beam writer operated
at 30 kV ha a beam current of 250 na and an addressing grid spacing
of 0.4 .mu.m. In the equation, Y represents the net optical density
at 365 nm and X represents values of electron dosage in
milli-coulomb/cm.sup.2.
[0171] FIG. 7(e) records data points of the net optical density at
435 nm vs. electron dosage, depicts the best fit curve and displays
the equation describing the best fit curve; the electron beam
exposure was done with Cambridge EBMF 10.5 e-beam writer operated
at 30 kV having a beam current of 250 na and an addressing grid
spacing of 0.4 m In the equation, Y the net optical density at 435
nm and X represents values of electron dosage in
milli-coulomb/cm.sup.2.
[0172] FIG. 7(f) data points of the net optical density at 530 mm
vs. electron dosage, depicts the best fit curve and displays the
equation describing the best fit curve; the electron beam exposure
was done with Cambridge EBMF 10.5 e-beam writer opera at 30 kV
having a beam cut of 250 na and an addressing grid spacing of 0.4
.mu.m In the equation, Y represents the net optical at density at
530 nm and X b values of electron dosage in
milli-coulomb/cm.sup.2.
[0173] FIG. 7(g) records data points of the not optical destiny at
630 mm vs. electron dosage, depict the best fit cue and displays
the equation describing the best fit curve; the electron beam
exposure was done with Cambridge EBMF 10.5 e-beam writer operated
at 30 kV having a beam current of 250 na and an addressing grid
spacing of 0.4 .mu.m. In the equation, Y the net optical density at
630 nm and X values of electron douse in
milli-coulomb/cm.sup.2.
[0174] FIG. 8 records the optical density at 436 nm verses electron
dosage at 20 kV. Curve A--MEBES III, 4000 na, 0.5 .mu.m address
size, 40 MHz. Curve B--Cambridge EBMF 10.5, 25 na, 0.1 .mu.m
address size. EVC--e-beam flood exposure.
[0175] FIG. 9 depicts the transmittance spectra of exemplary
HEBS-glass No. 3. A--a base glass plate 0.090" thick; B--a HEBS
plat 0.086" thick having one ion-exchanged surface glass layer,
C--a HEBS-glass plate 0.090" thick having two ion-exchanged surface
glass layer.
[0176] FIG. 10 exhibits an optical micrograph of a gray scale mask
which is a grating in HEBS-glass No. 3. The grating has 250 gray
levels within a period of 200 .mu.m.
[0177] FIG. 11 exhibits an optical micrograph of a portion of a
gray scale mask which is a diffractive optical lens having ten gray
levels in each zone.
[0178] FIG. 12 illustrates that the processing steps necessary to
generate Diffractive Optical Elements consisting of (a) a
HEBS-glass photo mask blank being exposed in e-beam writer (b) gray
level mask generated in HEBS-glass (c) photoresist exposure to in
optical lithography tool (d) resist surface profile after
development (e) surface profile in substrate material after CAIBE
transfer step.
[0179] FIG. 13 illustrates that the processing steps to fabricate
refractive lens arrays consisting of (a) a HEBS-glass photo mask
blank being exposed in e-beam writer (b) gray level mask generated
in HEBS-glass (c) photoresist exposure in mask aligner (d) resist
surface profile after development (e) lens profile after etching
transfer step.
[0180] FIG. 14 depicts the thickness of Shipley S1650 Photoresist
verses optical density at 436 nm of HEBS-glass mask; photoresist
was exposed in an optical contact aligner.
[0181] FIG. 15 records the calibration curve "net optical density
at 435 nm versus clock rate" of e-beam exposure at 30 kv using
Cambridge EBMF 10.5 e-beam writer with 250 na beam current and 0.4
.mu.m addressing grid size.
[0182] FIG. 16 records the calibration curve "net optical density
at 435 nm versus clock rate" of e-beam exposure at 30 kv using
Cambridge EBMF 10.5 e-beam writer with 75 na beam current and 0.2
.mu.m addressing grid size.
[0183] FIG. 17 records the calibration curve "1/(clock rate) verses
net optical density at 435 nm" of e-beam exposure at 30 kv
Cambridge EBMF 10.5 e-beam writer with 250 na beam current and 0.4
.mu.m addressing grid size.
[0184] FIG. 18 the calibration curve "1/(clock rate) verses net
optical density at 435 nm" of o-be exposure at 30 kv using
Cambridge EBMF 10.5 e-beam writer with 75 na beam current and 0.2
.mu.m addressing grid size.
[0185] FIG. 19 depicts absorption spectra of LDW-HR plates-Type I,
-Type II and Type III.
[0186] FIG. 20 depicts absorption spectra of LDW-IR plates-Type I,
-Type II and Type III;
[0187] FIG. 21 is a diagram showing the variation in optical
density of a gray scale mask formed of high energy beam sensitive
glass after exposure with an electron beam of a particular
acceleration voltage;
[0188] FIG. 22 is a diagram similar to FIG. 1 showing the variation
in optical density of a mask formed of the same material after
exposure to a beam of higher acceleration voltage;
[0189] FIG. 23 is a diagram showing photoresist thickness versus
electron charge density or dosage used to expose a gray scale mask
in accordance with the present invention;
[0190] FIG. 24 is a transverse section view of a portion of a
micro-lens fabricated in accordance with the method of the present
invention;
[0191] FIG. 25A is a partial plat of a grid showing darkened areas
corresponding to changes in contour of portions of the lens shown
in FIG. 4;
[0192] FIG. 25B is intended to be read in conjunction with FIG. 5A
and shows a partial transverse section on a larger scale of the
micro-lens shown in FIG. 4;
[0193] FIG. 26 is a perspective view, greatly enlarged, of a gray
scale mask and a photoresist coated substrate for fabricating an
array of micro-lenses in accordance with the present invention;
and
[0194] FIG. 27 is a diagram showing the geometry of a micro-lens
fabricated in accordance with the method of the invention.
DESCRIPTION OF THE INVENTION
[0195] High energy beam sensitive glasses used to generate the gray
level mask, consist of a low expansion zinc-silicate glass, a white
crown glass. The base glass can be produced from glass melting just
like the conventional white crown optical glasses. The base glass
contains alkali to facilitate the following ion-exchange reactions
which achieve the sensitivity of the HEBS-glass toward high energy
beams, e-beam in particular. After ion-exchange HEBS-glass is
essentially alkali free as a result of the ion-exchange process and
the concurrent leaching process carried out in an acidic aqueous
solution at temperatures above 320.degree. C. The base glass
composition consists of silica, metal oxides, halides and photo
inhibitors. Typically TiO.sub.2, Nb.sub.2O.sub.5 or Y.sub.2O.sub.3
are used as photo inhibitors. The photo inhibitors are used to dope
the silver ion containing complex crystal silver-alkali-halide.
These (AgX).sub.m (MX).sub.n complex crystals are the beam
sensitive material and the doping of the photo inhibitors increases
the energy band gap of the otherwise photosensitive glass.
[0196] The exemplary glass compositions that are optimised for
making HEBS-glass gray level mark are Listed in Exhibit A.
Photosensitivity inhibitors and RS-suppression agents: other than
TiO.sub.2, selected from the group consisting of Ta.sub.2O.sub.5,
ZrO.sub.2, Nb.sub.2O.sub.5, La.sub.2O.sub.3, Y.sub.2O.sub.3 and
WO.sub.3 may optionally be added to the glass batch or replaces
portions of TiO.sub.2 in the base glass compositions of Exhibit A.
More than about 1% of Cl is addled in the forms of Alkali Chloride
to the glass batch to ensure that the glass melt is saturated with
chlorides. The Chlorides also function as a fining agent for the
glass melt.
[0197] The base glass compositions of the present invention consist
in the glass batch essentially of in mole percent on the oxide
basis, 11.4 to 17.5% of one or more alkali metal oxides, 2.4 to
10.2% total of photo sensitivity inhibitors and RS suppression
agents including 2.4 to 10.2% TiO.sub.2, 1.1 to 2.4%
Al.sub.2O.sub.3, O to 4.6% B.sub.203, 3.7 to 13.2% ZnO, 0.5 to 6%
Cl, and 58.2 to 78.8% SiO.sub.2.
[0198] After the glass is melted, drawn, ground and polished the
base glass plates are ion-exchanged in an acidic aqueous solution
containing soluble ionic silver. The ion exchange process is
carried out at tem t in excess of 320.degree. C. for a duration
sufficient to cause silver ions to diffuse into the glass plates 3
.mu.m, i.e., (x.sub.2-x.sub.1) in the thickness dimension of FIG.
1. As a result silver ions are present in the form of
silver-alkali-halide (AgX).sub.m(MX).sub.n complex crystals that
are about 10 nm in each dimension within the cavity of the
SiO.sub.4 tetrahedron network.
[0199] Ground and polished glass plates of the exemplary glass
compositions of Exhibit A were ion exchanged in aqueous solution
containing ionic silver. The aqueous ion exchange solution
consists, on the weight percent basis, 7.5% or more of AgNO.sub.3
and 0.5% or more of HNO.sub.3. HEBS-glass No. 1 to No. 20 are the
glass plates of the exemplary base glass compositions No. 1 to
No.20 respectively having been ion exchanged in the aqueous ion
exchange solution.
[0200] Doping of the base glass with the photo inhibitors causes an
increased energy is band gap, making the ion exchanged glasses
inert to UV and actinic radiation of shorter wavelengths as the
concentration of the doping with photo inhibitors increases.
Nevertheless the chemical reduction of silver ions in the
silver-alkali-halide containing complex crystals to produce
coloring specks of silver atoms can be accomplished by exposing the
HEBS to high era beams, e.g., .gtoreq.10 kV electron beams. This
property of the material can be utilized to generate the necessary
change in transmission for a gray level mask.
[0201] FIG. 2 to 5 exhibit the resulting optical density of the
HEBS-glass No. 3 of the exemplary base glass composition No. 3
after exposure with a flood electron beam exposure system using a
29 kV, a 25 kV, a 20 kV and a 15 kV electron beam respectively at a
number of dosage levels. The flood e-beam exposure system
manufactured and marketed by EVC Corporation, San Diego, Calif.,
has a beam diameter of 8 inches and was operated at a beam current
of 2 milli amp. The absorption data was collected using a Hitachi
U2000 spectrophotometer.
[0202] Optical density values of HEBS-glass No. 3 at 436 nm as a
function of e-beam dosage is plotted in FIG. 6 for e-beam
acceleration voltages of 29 kV, 20 kV and 15 kV. In this plot the
finite optical density value at zero electron dosage is due to
reflection loss of probing light beam at two surfaces of glass
plate samples. To
1 Exhibit A Exemplary Glass Compositions GLASS NO. 1 2 3 4 5 6 7 8
9 10 SiO.sub.2 71.5 78.8 68.5 72.7 70.9 68.9 67.4 67.1 66.1 63.8
Li.sub.2O 3.3 3.4 3.8 3.6 3.7 3.9 3.9 4.2 4.2 4.5 Na.sub.2O 5.3 5.4
6.4 5.7 5.6 6.2 6.2 6.7 6.7 7.2 K.sub.2O 2.8 2.7 3.2 3.1 3.1 3.3
3.3 3.5 3.5 3.8 TiO.sub.2 2.4 4.3 4.6 3.4 4.5 5.6 4.5 5.4 5.4 6.7
Al.sub.2O.sub.3 1.3 1.2 1.3 1.4 1.2 1.1 1.3 1.2 1.1 1.6 ZnO 7.2 3.7
7.4 7.1 6.0 7.0 9.0 7.1 8.2 7.6 Ta.sub.2O.sub.5 Nb.sub.2O.sub.3
ZrO.sub.2 WO.sub.3 B.sub.2O.sub.3 3.2 1.8 2.0 1.0 1.4 1.8 0.8 1.8
Cl 3.0 0.5 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 11 12 13 14 15 16 17 18
19 20 SiO.sub.2 64.8 64.0 60.1 60.5 58.2 69.7 64.2 64.5 66.3 67.8
Li.sub.2O 4.5 4.7 4.3 5.1 5.1 3.9 3.8 3.8 3.8 3.8 Na.sub.2O 7.4 7.6
7.8 8.1 8.1 6.2 6.4 6.4 6.4 6.4 K.sub.2O 3.6 4 4.2 4.3 4.3 3.3 3.2
3.2 3.2 3.2 TiO.sub.2 5.4 7.4 6.1 10.2 5.7 4.4 4.6 4.6 4.6 4.6
Al.sub.2O.sub.3 1.2 1.2 1.5 1.2 2.4 1.2 1.3 1.3 1.3 1.3 ZnO 10.1
8.1 11.0 7.1 13.2 7.1 7.4 7.4 7.4 7.4 Ta.sub.2O.sub.5 1.6
Nb.sub.2O.sub.3 1.2 ZrO.sub.2 2.0 WO.sub.3 0.5 B.sub.2O.sub.3 1.8
2.0 0.5 2.0 4.6 2.0 2.0 Cl 1.2 3.0 3.0 3.0 3.0 2.2 6.0 3.0 3.0
3.0
[0203] obtain an optical density value of 1.0 at 436 nm in
HEBS-glass the required electron dosage is 75 .mu.C/cm.sup.2, 155
.mu.C/cm.sup.2 and 270 .mu.C/cm.sup.2 using EVC e-beam exposure
system that 29 kV, 20 kV and 15 kV respectively.
[0204] The e-beam exposure-induced optical density i.e. net optical
density in HEBS-glass is a function of e-beam exposure scheme and
write parameters which include e-beam energy (i.e. e-beam
acceleration voltage), beam spot size, beam current and addressing
grid. The net optical density is defined he as the optical density
of the e-beam darkened area minus the optical density of the clear
(unexposed) area. The net optical density in the visible spectral
range was measured as a function of electron dosage using
HEBS-glass No.3 having been exposed in a number of 3 mm.times.3 mm
square areas with the following e-beam pattern generators:
[0205] (1) MEBES of ETEC Systems Inc., (2) Cambridge EBMF 10.5
e-beam writer. Results of exemplary exposure schemes are
immediately below.
[0206] FIG. 7(a) exhibits net optical density values of HEBS-glass
No. 3 at 435 nm vs. electron dosage at 30 kv. The e-beam exposure
was done using the vector scan e-beam writer, Cambridge EBMF 10.5.
The e-beam parameters ae as follows:
[0207] Curve A--30 kv, 250 na beam current, 0.4 .mu.m addressing
grid spacing.
[0208] Curve B--30 kv, 75 na beam current, 0.2 .mu.m addressing
grid spacing.
[0209] The data points of the net optical density values at 435 nm
resulting from EVC flood gum exposure at 30 kV am shown in the
figure for comparison.
[0210] FIG. 7(b) displays the corresponding net optical density
values at 530 nm as a function of electron dosage at 30 kv.
[0211] FIG. 7(c) exhibits the corresponding net optical density
values at 630 nm as a function of electron dosage at 30 kv.
[0212] The data points of curve A in Figure 7 aro listed in Table
1. Also listed in Table 1 is the net optical density values at 365
nm. The electron dosage in .mu. Coulomb/cm.sup.2 and in milli
Coulomb/cm.sup.2, the clock rates and the corresponding e-beam
exposure durations per address to result in the tabulated electron
dosages are also listed in the table.
[0213] Th best fit polynomial eons that depict the experimental
data of net optical density vs. electron dosage in milli
coulomb/cm.sup.2 of Table 1 are shown in FIG. 7(d), FIG. 7(e), FIG.
7(f) and FIG. 7(g) respectively for the net optical density values
at 365 nm, 435 nm, 530 nm and 630 nm Lively. In the equations, y
represents net optical density values and x represents values of
electron dosage in milli coulomb/cm.sup.2. The experimental data
points and the best fitted curves are also shown in FIGS. 7(d),
7(e), 7(f), and 7(g).
[0214] As shown in FIG. 7(d), a large portion of the best fit curve
is a straight line. The linear portion ranges in net optical
density values from 0 to 0.9. The slope of the linear portion
representing the e-beam sensitivity of HEBS-glass No. 3 darkening
at the spectral wavelength of 365 nm upon e-beam exposure with
write parameters of 30 kV acceleration voltage, 250 nano-amp beam
cunt, and 0.4 .mu.m addressing grid size, is 6.2767 unit of optical
density value per milli coulomb/cm.sup.2. Namely to obtain a net
optical density value of 0.62767 at 365 nm, the required electron
dosage is 100 micro-coulomb/cm.sup.2.
[0215] As shown in FIG. 7(e), a large portion of the best fit curve
is a straight line. The linear portion ranges in net optical
density values from 0 to 1.65. The slope of is the straight line
portion representing the e-beam sensitivity of HEBS-glass No. 3
darkening at the spectral wavelength of 435 nm upon e-beam exposure
with write parameters of 30 kV acceleration voltage, 250 nano-amp
beam current, and 0.4 .mu.m addressing grid size, is 9.2113 unit of
optical de value per milli coulomb/cm.sup.2. Namely to obtain a not
optical density value of 0.92113 at 435 nm, the required electron
dosage is 100 micro-coulomb/cm.sup.2.
[0216] As shown in FIG. 7(f), a large portion of the bet fit curve
is a straight line. The linear portion ranges in net optical
density values from 0 to 2.05. The slope of the linear portion
representing the e-beam sensitivity of HEBS-glass No. 3 darkening
at the spectral wavelength of 530 nm upon e-beam exposure with
write parameters of 30 kV acceleration voltage, 250 nano-amp beam
current, ad 0.4 .mu.m addressing grid size, is 12.507 unit of
optical density value per milli coulomb/cm.sup.2. Namely to obtain
a net optical density value of 1.2507 at 530 nm, the required
electro dosage is 100 micro-coulomb/cm.sup.2.
[0217] As shown in FIG. 7(g), a large portion of the best fit curve
is a straight line. The linear portion ranges in not optical
density values from 0 to 1.7. The slope of the linear portion
representing the e-beam sensitivity of HEBS-glass No. 3 darkening
at the spectral wavelength of 630 nm upon e-beam exposure with
white parameters of 30 kV acceleration voltage, 250 nano-amp beam
cur, and 0.4 .mu.m addressing grid size, is 9.5929 unit of optical
density value per milli coulomb/cm.sup.2. Namely to obtain a net
optical density value of 0.95929 at 630 nm, the required electron
dosage is 100 micro-coulomb/cm.sup.2.
[0218] Electron beam pattern generators were employed to darken
HEBS-glass No. 3 at a number of electron dosage levels using beam
acceleration voltages, beam current, beam spot size and addressing
grid size as variable parameters. Beam acceleration voltages
ranging from 10 kV to 50 kV, beam spot size ranging from 0.1 .mu.m
to 1 .mu.m, beam current ranging from 10 na to 8000 na, and
addressing grid size ranging from 0.05 .mu.m to 1 .mu.m were
studied to determine the practical and cost effective write schemes
for HEBS-glass compositions. Experimental at of not optical density
in the spectral range of 350 nm to 1100 nm and polynomial equations
together with the best fit curves resembling FIGS. 7(d) to 7(g) as
well as the slope of the linear portion of the best fit curves were
obtained for a number of combinations of e-beam writer parameters.
It has been determined that the exemplary write schemes using EBMF
10.5 e-beam writer, which are practical and cost effective to make
HEBS-glass gray level masks include (1) 30 kV, 0.4 m=, 250 na; (2)
30 kV, 0.2 .mu.m address 150 na; (3) 30 kV, 0.2 .mu.m address, 125
a (4) 30 kV, 0.2 .mu.m address, 100 na; (5) 30 kV, 0.2 .mu.m
address, 75 na; (6) 20 k V, 0.2 .mu.m address, 175 na; (7) 20 kV,
0.2 .mu.m address 150 na; (8) 20 kV, 0.2 .mu.m address, 125 na; (9)
20 kV, 0.2 .mu.m address, 100 na; and (10) 20 kV, 0.1 .mu.m, 25 na.
Using each of the ten write schemes listed immediately above net
optical de values of HEBS-glass NO. 3 at wavelengths from 350 nm to
1100 nm were obtained as a function of the electron dosages. The
bed fit polynomial equations and the slope of the linear portion of
each of the best fit curve of net optical density values at 365 nm,
at 435 nm, at 530 nm and 630 nm vs. electron dosage ae represented
in Table 2.
[0219] FIG. 8 exhibits net optical density values of HEBS-glass No.
3 at 436 nm vs. electron dosage at 20 kv. Curve A displays the data
of e-beam exposure curve using the raster scan e-beam pattern
generator, MEBES III. MEBES III was operated at 20 kv. 40 MHz rate,
using a spot size of 1 .mu.m, a beam greet of 4000 na and an
addressing grid size of 0.5 .mu.m. These write parameters result in
on exposure dosage of 40 .mu.C/cm.sup.2 per scan count. Electron
dosage having multiples of 40 .mu.C/cm.sup.2 were
2TABLE 1 Net optical density in HEBS-glass having been exposed to
e-beam at 30 kv, 250 na beam current, 0.4 .mu.m addressing grid
size using Cambridge EBMF 10.5 e-beam writer at various clock
rates. Exposure Net Net Net Net Duration Optical Optical Optical
Optical per pixel Clock Rate Electron Dosage Density at Density at
Density at Density at (micro sec) (MHz) (micro C/cm.sup.2) (milli
C/cm.sup.2) 365 nm 435 nm 530 nm 630 nm 0.1039 9.625 16.23 0.01623
0.170 0.172 0.149 0.100 0.2091 4.782 32.67 0.03267 0.275 0.317
0.336 0.242 0.2984 3.351 46.63 0.04663 0.362 0.445 0.514 0.377
0.4126 2.424 64.47 0.06447 0.472 0.613 0.744 0.553 0.4956 2.018
77.44 0.07744 0.547 0.729 0.909 0.681 0.5966 1.676 93.22 0.09322
0.651 0.883 1.120 0.846 0.7236 1.382 113.06 0.11306 0.779 1.068
1.373 1.041 0.8248 1.212 128.88 0.12888 0.835 1.202 1.563 1.180
0.8855 1.129 138.36 0.13836 0.894 1.297 1.689 1.273 0.9870 1.013
154.22 0.15422 0.950 1.427 1.862 1.401 1.0900 0.917 170.31 0.17031
1.041 1.574 2.045 1.566 1.1940 0.838 186.56 0.18656 1.111 1.706
2.203 1.690 1.3445 0.744 210.08 0.21008 1.189 1.892 2.404 1.859
1.4430 0.693 225.47 0.22547 1.212 1.998 2.500 1.955 1.5474 0.646
241.78 0.24178 1.258 2.095 2.583 2.042 1.6485 0.607 257.58 0.25758
1.272 2.180 2.652 2.126
[0220] exposed on HEBS-glass using the number of scan court as a
variable parameter. The data points of Curve A corresponds to 1, 6,
8, 10, 12, and 14 scan counts. Curve B displays the data of e-beam
exposure using Cambridge EBMF 10.5 e-beam writer operated at 20 kv,
25 na and 0.1 .mu.m addressing grid spacing. Also shown in FIG. 8
for comparison is the net optical density values at 436 nm
resulting from EVC flood gun exposure at 20 kv.
[0221] The effect of retraces as well as the dependence of e-beam
induced optical density on the variable write parameters of Table 2
are explained in the section "Heat effect of the Write e-beam" in
light of a postulated mechanism of e-beam darkening. FIG. 9
exhibits the transmittance spectra of the base glass plate 0.090
inch thick of the exemplary glass composition No. 3. The cut off in
transmittance i.e., the absorption edge of the base glass is due to
electronic transitions of the constituting chemical elements of the
base glass. As the concentration of the doping with photo
inhibitors increases, the absorption edge of the base glass shifts
to longer wavelengths; namely % T of the base glass reduces in the
spectral range of uv, then near uv and then blue light as the
doping con on of photo inhibitors increases. The concentration of
photo inhibitors in the exemplary base glass compositions of
Exhibit A was optimized for use at mercury G-line so that the
HEBS-glass is totally inert to actinic radiation having wavelengths
.lambda. eq to or longer than 436 mm, and has a % T value of more
than 88%. The % T values of the exemplary HEBS-glass No. 3 is shown
in FIG. 9 and Table 3. A value of 88% transmittance corresponds to
96% internal transmission, since reflection less from two glass is
8%. The values of % T and the internal transmission of the
corresponding base glass 0.090 inch thick are more than 90% and
more than 98% respectively for .lambda..gtoreq.436 nm.
[0222] A HEBS-glass plate in general consists of two ion-exchanged
surface glass layers, since both surfaces of a base glass plate
were ion exchanged during an ion exchange process. To increase the
transmittance of the HEBS-glass plate at .lambda.<436 nm one may
grind off one ion-exchanged surface glass layer and polish the now
anhydrous surface to photomask quality. The transmittance spectra
of HEBS-glass No. 3, 0.086" thick having only one ion-exchanged
surface is also shown in FIG. 9.
3TABLE 2 The best polynomial fit equation and the slope of the
linear portion of an electron beam darkening sensitivity curve
linear portion parameters of write schemes of the Write Scheme
Acceleration Addressing Beam Wave- Electron Beam Darkening
Sensitivity Curve Slope of the No. and voltage grid size Current
length Y = Optical Density Sensitivity Equation No. (kV) (micron)
(nm) (nm) X = Electron Dosage in milli coulomb/cm2 Curve 1 30 0.4
250 365 y = 19708x.sup.6 - 17787x.sup.5 + 6181.2x.sup.4 -
1063.8x.sup.3 + 85.688x.sup.2 + 3.3806x 6.2767 2 30 0.4 250 435 y =
-15440x.sup.6 + 12062x.sup.5 - 3761.5x.sup.4 + 555.15x.sup.3 -
40.414x.sup.2 + 10.637x 9.2113 3 30 0.4 250 530 y = 46062x.sup.6 -
38146x.sup.5 + 12229x.sup.4 - 2013.9x.sup.3 + 173.69x.sup.2 -
5.8097x 12.507 4 30 0.4 250 630 y = 51961x.sup.6 - 43905x.sup.5 +
14402x.sup.4 - 2361.2x.sup.3 + 197.27x.sup.2 + 2.2436x 9.5929 5 30
0.2 75 365 y = 4788.8x.sup.6 - 4881.1x.sup.5 + 1822.8x.sup.4 -
308.43x.sup.3 + 19.251x.sup.2 + 4.098x 4.3024 6 30 0.2 75 435 y =
3780.7x.sup.6 - 4395.5x.sup.5 + 1959x.sup.4 - 421.14x.sup.3 +
40.268x.sup.2 + 4.882x 6.1553 7 30 0.2 75 530 y = 4227.3x.sup.6 -
4897.4x.sup.5 + 2192.6x.sup.4 - 490.42x.sup.3 + 50.025x.sup.2 +
6.8341x 8.6203 8 30 0.2 75 630 y = 3750.9x.sup.6 - 4226.7x.sup.5 +
1854.8x.sup.4 - 408.5x.sup.3 + 41.902x.sup.2 + 4.8131x 3.4022 9 30
0.2 100 365 y = -355.78x.sup.6 + 466.62x.sup.5 - 243.17x.sup.4 +
62.851x.sup.3 - 12.485x.sup.2 + 5.5571x 4.424 10 30 0.2 100 435 y =
-692.18x.sup.6 + 804.39x.sup.5 - 358.96x.sup.4 + 75.143x.sup.3 -
10.535x.sup.2 + 6.9982x 6.1269 11 30 0.2 100 530 y = -175.37x.sup.6
+ 38.823x.sup.5 + 112.01x.sup.4 - 80.56x.sup.3 + 14.073x.sup.2 +
7.6867x 8.3914 12 30 0.2 100 630 y = -839.24x.sup.6 + 947.64x.sup.5
- 359.07x.sup.4 + 40.139x.sup.3 - 0.7855x.sup.2 + 6.4234x 6.3643 13
30 0.2 125 365 y = -664.62x.sup.6 + 932.44x.sup.5 - 464.2x.sup.4 +
95.04x.sup.3 - 13.314x.sup.2 + 6.4665x 5.392 14 30 0.2 125 435 y =
-900.79x.sup.6 + 1480.9x.sup.5 - 905.98x.sup.4 + 243.25x.sup.3 -
32.801x.sup.2 + 9.8528x 7.7152 15 30 0.2 125 530 y = -1283.3x.sup.6
+ 1929.4x.sup.5 - 1020x.sup.4 + 210.47x.sup.3 - 22.431x.sup.2 +
12.109x 10.672 16 30 0.2 125 630 y = 111.03x.sup.6 - 345.7x.sup.5 +
352.69x.sup.4 - 158.9x.sup.3 + 24.867x.sup.2 + 6.7982x 8.1056 17 30
0.2 150 365 y = -104.68x.sup.6 + 149.86x.sup.5 - 51.158x.sup.4 -
8.925x.sup.3 - 0.3208x.sup.2 + 5.866x 5.4107 18 30 0.2 150 435 y =
-341.18x.sup.6 + 643.91x.sup.5 - 430.4x.sup.4 + 115.13x.sup.3 -
16.314x.sup.2 + 9.1502x 7.8427 19 30 0.2 150 530 y = -237.51x.sup.6
+ 304.15x.sup.5 - 52.05x.sup.4 - 65.071x.sup.3 + 15.235x.sup.2 +
10.164x 11.048 20 30 0.2 150 630 y = 225.42x.sup.6 - 507.45x.sup.5
+ 442.41x.sup.4 - 182.81x.sup.3 + 27.586x.sup.2 + 6.9154x 3.8774 30
20 0.2 100 365 y = 1165x.sup.6 - 1729.1x.sup.5 + 969.72x.sup.4 -
255.38x.sup.3 + 28.215x.sup.2 + 1.9949x 3.1561 22 20 0.2 100 435 y
= 321.26x.sup.6 - 495.79x.sup.5 + 299.53x.sup.4 - 93.047x.sup.3 +
11.878x.sup.2 + 3.99x 4.4463 23 20 0.2 100 530 y = 530.82x.sup.6 -
893.24.sub.x.sup.5 + 604.38x.sup.4 - 205.16x.sup.3 - 28.195x.sup.2
+ 4.3652x 5.7739 24 20 0.2 100 630 y = 747.21x.sup.6 -
1197.4x.sup.5 + 741.5x.sup.4 - 217.47x.sup.3 + 24.784x.sup.2 +
2.8845x 3.8774 25 20 0.2 125 365 y = -454.78x.sup.6 + 748.41x.sup.5
- 467.28x.sup.4 + 137.8x.sup.3 - 22.463x.sup.2 + 4.8643x 3.0043 26
20 0.2 125 435 y = -399.43x.sup.6 + 659.66x.sup.5 - 409.6x.sup.4 +
113.52x.sup.3 - 15.916x.sup.2 + 5.6722x 4.5474 27 20 0.2 125 530 y
= -46.317x.sup.6 - 22.296x.sup.5 + 112.29x.sup.4 - 77.504x.sup.3 +
13.876x.sup.2 + 5.0038x 5.7824 28 20 0.2 125 630 y = 417.51x.sup.6
- 711.04x.sup.5 + 469.27x.sup.4 - 145.5x.sup.3 + 16.454x.sup.2 +
3.218x 3.8464 29 20 0.2 150 365 y = -74.993x.sup.6 + 118.24x.sup.5
- 57.174x.sup.4 + 5.249.2x.sup.3 - 0.6172x.sup.2 + 3.3699x 3.2267
30 20 0.2 150 435 y = -278.14x.sup.6 + 503.66x.sup.5 -
329.14x.sup.4 + 89.552x.sup.3 - 11.422x.sup.2 + 5.4742x 4.7421 31
20 0.2 150 530 y = 3.461x.sup.6 - 102.55x.sup.5 + 172.08x.sup.4 -
102.48x.sup.3 + 18.951x.sup.2 + 4.8104x 5.872 32 20 0.2 150 630 y =
161.84x.sup.6 - 348.51x.sup.5 + 286.3x.sup.4 - 107.41x.sup.3 +
13.817x.sup.2 + 3.2921x 3.8027 33 20 0.2 175 365 y = 7.7262x.sup.6
- 37.019x.sup.5 + 56.546x.sup.4 - 35.995x.sup.3 + 6.9532x.sup.2 +
2.7738x 3.1017 34 20 0.2 175 435 y = 45.959.sub.x.sup.6 -
160.56x.sup.5 + 213.4x.sup.4 - 135.06x.sup.3 + 37.556x.sup.2 +
0.3871x 4.6256 35 20 0.2 175 530 y = 82.35x.sup.6 - 237.03x.sup.5 +
259.77x.sup.4 - 130.11x.sup.3 + 23.171x.sup.2 + 4.6292x 6.0434 36
20 0.2 175 630 y = 138.78x.sup.6 - 316.52x.sup.5 + 272.92x.sup.4 -
106.53x.sup.3 + 14.299x.sup.2 + 3.2743x 3.7417 37 20 0.1 25 365 y =
-257.78x.sup.6 + 493.22x.sup.5 - 357.35x.sup.4 + 125.26x.sup.3 -
24.07x.sup.2 + 4.2726x 2.454 38 20 0.1 25 435 y = -421.26x.sup.6 +
736.88x.sup.5 - 503.36x.sup.4 + 168.42x.sup.3 - 30.486x.sup.2 +
5.7851x 3.5813 39 20 0.1 25 530 y = 55.321x.sup.6 - 40.121x.sup.5 -
7.75x.sup.4 + 13.643x.sup.3 - 8.1316x.sup.2 + 5.4291x 4.7759 40 20
0.1 25 630 y = -199.22x.sup.6 + 369.63x.sup.5 - 264.28x.sup.4 +
94.119x.sup.3 - 20.554x.sup.2 + 4.7848x 2.9976
[0223] The internal transmittance of one ion exchanged surface
glass layer was measured by placing the HEBS-glass plate 0.086"
thick with one ion exchanged surface in the sample beam of the
U2000 spectrophotometer and placing a base glass plate 0.090 inch
thick in the reference beam. The internal transmittance from 350 nm
to 500 nm of the ion exchanged glass layer of the exemplary
HEBS-glass No. 3 is listed in Table 3.
[0224] Also listed in Table 3 are the corresponding transmittance
values of the base glass plate 0.090 inch thick, the HEBS-glass
plate 0.090 inch thick having two ion exchanged surface glass
layers (i.e. 2 IEed surfaces) and the HEBS-glass plate 0.086" thick
having one ion exchanged surface glass layers (i.e. 1 IEed
surface).
[0225] Accelerated test on stability of HEBS-glass No. 3 under
intense actinic exposure at 436 nm was carried out. HEBS-glass No.
3, 0.090 inch thick, having a transmittance value of 89.2% was
exposed for a duration of 30 days to 586 milli watt/cm.sup.2 light
intensity at 436 nm from the output actinic radiation of a 200 watt
mercury arc lamp, the actinic radiation being filtered within an
interference filter and focused to a spot of 5 mm diameter. The
transmittance value remains constant at 89.2% before and after the
intense G-line exposure for 30 days.
[0226] From accelerated tests using focused 365 nm radiation from
the 200 watt mercury arc lamp, it has been determined that the
residual sensitivity of the exemplary HEBS-glass No. 3 to I-line at
365 nm is not detectable for optical lithographic exposure of less
than about one million I-line stepper exposures.
[0227] The grayscale mask made of HEBS-glass No. 3 can in general
be employed in I-line as well as G-line optical lithographic
exposure systems.
[0228] An exchange of H.sup.+ and/or H.sub.3O.sup.+ ions for alkali
metal ions takes place concurrently with the exchange of Ag.sup.+
ions for alkali-metal ions when HEBS-glass is ion exchanged in an
acidic aqueous solution containing silver ions. As a result,
H.sup.+ and/or H.sub.3O.sup.+ ions entered into the silicate glass
network and silanol groups SiOH formed in the glass network. The
formation of the silanol groups in a silicate glass network is
referred to as hydration of glass. HEBS glass was hydrated, and a
moving boundary type concentration profile formed. When water
species are among the diffusion species in glass, the diffusion of
water species (i.e.,H.sup.+ and/or H.sub.3O.sup.+) and Ag.sup.+
ions through a hydrated layer is accompanied by an instantaneous
and irreversible immobilization of the diffusion species at the
boundary surface. The moving boundary type diffusion profile is due
to the fact that the diffusion coefficient of H.sup.+,
H.sub.3O.sup.+ and Ag.sup.+ in the hydrated layer is many order of
magnitude larger than that in the anhydrous base glass.
[0229] An essential feature of diffusion accompanied by an
instantaneous and irreversible immobilization of the diffusion
species is that a sharp boundary surface moves through the medium,
separating a region in which all of the sites are occupied from one
in which none are occupied. In front of the advancing boundary the
concentration of freely diffusing species is zero whereas behind it
immobilization is complete.
[0230] FIG. 1 is a qualitative representation of the result of
silver ion exchange of HEBS-glass in an acidic aqueous solution
contain soluble ionic silver. There exists a leached surface glass
layer, x.sub.1 in thickness, wherein essentially all of the alkali
ions are leached out instead of being exchanged by Ag.sup.+ ions.
The leached surface glass layer is essentially fused silica in
composition and contains little or no mobile ions such a sodium,
potassium and lithium ions. The exemplary HEBS-glass No. 3 have a
leached surface glass layer of less than about 0.5 .mu.m, i.e.,
x.sub.1<0.5 .mu.m and has an e-beam sensitized glass layer of 3
.mu.m, i.e., x.sub.2-x.sub.1=3 .mu.m, HEBS-glass photomask blanks
having an e-beam sensitized glass layer (x.sub.2-x.sub.1) of 2
.mu.m, 4 .mu.m, 5 .mu.m and other thickness' were fabricated by
controlling the ion exchange duration and/or heat schedules.
[0231] By controlling the operation parameters of the solution ion
exchange reactions, the thickness of the e-beam sensitized glass
layer can be controlled precisely.
Heat Effect of the Write E-Beam
[0232] The net optical density is a function of the e-beam exposure
scheme and the e-beam write parameters. This is because the e-beam
sensitivity of HEBS-glass is enhanced by the heating effect of the
write beam. Listed in Exhibit B is the input-power density from
e-beam exposure for the three exposure schemes of FIG. 8, where
input-power density is equal to (beam current).times.(beam
acceleration voltage)/(beam spot size).
[0233] The rate of temperature increase at the beam exposure spot
i.e. the e-beam exposed volume of HEBS-glass is proportional to the
net power density which is defined herein as the rate of
input-power density minus the rate of heat dissipation. The rate of
heat dissipation is larger for a smaller exposed volume
corresponding to a smaller beam spot size. This is because the
ratio of surface area to mass is larger for a smaller volume. The
rate of heat dissipation relative to the rate of input-power
density, together with the corresponding beam spot size are also
listed in Exhibit B.
[0234] Comparing the write parameters that we employed using MEBES
III with those of Cambridge EBMF 10.5. It is apparent from Exhibit
B that the net power density of the MEBES exposure scheme is a
factor of 10 to 100 times that of the Cambridge exposure scheme (20
kV, 0.1 .mu.m address, 0.25 .mu.m spot size, 25 na). The very big
difference in heat accumulation between the above described
exposure parameters of MEBES III and Cambridge EBMF 10.5 should
contribute to the observed difference in the e-beam induced optical
density.
[0235] The following hypothesis explains the ream why the e-beam
sensitivity of HEBS-glass is enhanced by the heat effect of the
write beam. During e-beam exposure, silver specks of atomic
dimensions were formed from silver halide-alkali halide complex
crystals. The formation of a silver speck consisting of 2, 3, or
more atoms requires the deformation of silver halide lattice to
silver lattice. Cycles of lattice vibration of sufficient amplitude
is necessary to cause the formation of the silver specks. Since
larger amplitudes of lattice vibrational modes exist at higher
temperatures, silver specks are formed more quickly at a higher
temperature. Each retrace (i.e. ea scan count) allows an extended
time period for the formation of the silver specks.
[0236] The e-beam sensitivity of HEBS-glass using the exposure
scheme of the EVC flood exposure system is further elaborated
below. Although the input-power density of EVC exposure scheme is
very little compared to that of Cambridge EBMF 10.5, the rate of
heat dissipation during EVC exposure is very small relative to the
input-power density, due to the enormous beam spot size of 8
inches. Therefore, a large fraction of the input-power den is
accumulated throughout the
4TABLE 3 Transmittance Values (% T) of HEBS-glass No. 3 Internal
base Transmittance glass HEBS-glass HEBS-glass of an IEed
Wavelength 0.090" 2 IEed Surface 1 IEed Surface glass layer (nm) (%
T) (% T) (% T) (% T) 500.0 91.2 90.6 90.5 100 495.0 91.0 90.5 90.2
100 490.0 91.0 90.6 90.2 100 485.0 91.0 90.4 90.3 100 480.0 90.9
90.2 90.0 100 475.0 90.8 90.4 90.0 100 470.0 90.7 89.9 89.9 100
465.0 90.7 89.9 89.7 100 460.0 90.6 89.9 89.7 100 455.0 90.6 89.6
89.7 100 450.0 90.5 89.6 89.4 100 445.0 90.4 89.4 89.4 100 440.0
90.4 89.2 89.3 100 435.0 90.4 89.2 89.1 99.9 430.0 90.2 88.6 89.0
99.9 425.0 90.2 88.6 88.8 99.6 420.0 90.1 88.0 88.7 99.6 415.0 90.0
87.6 88.3 99.3 410.0 89.9 86.9 88.0 99.0 405.0 89.9 86.1 87.6 98.7
400.0 89.9 84.9 87.0 98.1 395.0 89.7 83.3 86.3 97.4 390.0 89.7 81.3
85.3 96.3 385.0 89.5 78.7 83.9 94.9 380.0 89.4 75.0 82.1 92.7 375.0
89.1 71.2 79.9 90.5 370.0 88.4 65.7 76.8 87.6 365.0 87.1 59.1 72.3
83.7 360.0 84.7 51.2 66.7 79.1 355.0 80.0 41.9 58.8 73.6 350.0 71.6
31.3 48.2 66.9
[0237] flood exposure duration. Moreover, HEBS-glass was under EVC
flood gun exposure for a long duration of e.g. 10 minutes which
corresponds to 600.times.10.sup.12 periods of lattice vibration.
There is thus plenty of time for the deformation of silver halide
lattice into silver lattice.
[0238] For the choice of write parameters using any e-beam writer
to write a gray level mask it is helpful to consider the HEBS-glass
properties which are summarized immediately below.
[0239] HEBS-glass is more sensitive using a larger beam current
density and a larger beam spot size, since the sensitivity is
enhanced by the he effect of the write beam. At a given current
density, a larger spot size is beneficial since heat dissipation is
slower. Using a high kV beam and a spot size of up to about 0.2
.mu.m, the resolution of the recorded image in HEBS-glass is
primarily determined by the scattering of the electrons in glass.
To a certain extent, one can increase both the spot size and the
beam current to maximize the throughput without the adverse effect
of reducing resolution.
[0240] A much larger beam current density than that normally used
in exposing photoresist can be employed and is recommended for
e-beam write on HEBS-glass.
[0241] Using a vector scan e-beam writer, a large range of
available clock rates is the key factor to produce a large optical
density range of gray levels. The maximum clock rate of an e-beam
writer is employed to produce the minimum optical density level of
the gray levels. The larger the maximum clock rate the higher the
current density that can be employed and therefore higher
throughput.
[0242] When a vector scan e-beam writer has a limited range of
useful clock rates, one retrace (i.e. two scan counts) can be
utilized to double the optical density values for all phase levels
provided the linear region of the sensitivity curve is
utilized.
[0243] Number of can be employed as a variable parameter using a
raster scan e-beam writer. For example, 16 phase levels can be
obtained using 1 to 16 scan counts, namely, using 1 scan count to
expose the lowest optical density level and using 16 scan counts to
write the highest optical duty level.
[0244] Although the e-beam sensitivity of HEBS-glass is a function
of the exposure scheme and write parameters, e-beam induced optical
density in the HEBS-glass is a unique function of electron dosage
for a given set of write parameters. Therefore, the net optical
density versus electron dosage is very reproducible.
5 Exhibit B Input-power density and rate of heat dissipation.
Input-Power Relative Density Rate of Heat (Watt/cm.sup.2) Beam Spot
Size Dissipation MEBES III 8 .times. 10.sup.6 1 .mu.m Small 1
scancount Cambridge EBMF 10.5 8 .times. 10.sup.5 0.25 .mu.m Large
EVC 0.1 8 inch Very small
Coloring Speck of Silver
[0245] Upon e-beam exposure coloring specks of silver are formed in
the HEBS-glass. Since there ae no chemical or physical development
steps, the silver specks are of atomic dimensions and the image has
no graininess. The recorded image has a continuous tone even when
observed at the highest magnification under microscope e.g.
1500.times.. On the contrary, at this high magnification the image
in a conventional high resolution photographic emulsion plate is
intrinsically halftone, because isolated grains of photographic
emulsion plates resembling dispersed halftone dots exist at gray
level of low optical density values.
Sub 0.25 Micrometer Resolution
[0246] Since the is no graininess, HEBS-glass is capable of very
high resolution. Sub 0.25 .mu.m features were written in the
exemplary HEBS-glass of Exhibit A.
[0247] Vertical resist profile exists at the boundary of sub micron
resist features which were printed using HEBS-glass mask.
HEBS-Glass Gray Scale Masks with Multi-Gray Levels
[0248] FIG. 10 exhibits an optical micrograph of a gray scale mask
which is a grating in HEBS-glass No.3. The grating has 250 gray
levels within a period of 200 micrometers. A Cambridge EBMF 10.5
e-beam writer operated at 20 kV, 0.2 .mu.m addressing grid size and
100 na beam current, was employed to fabricate the grating with 250
predetermined optical density values. The maximum and minimum
optical density value are 1.6 and 0.149 respectively. The gray
levels have an equal interval of transmittance, namely the values
of the transmittance T corresponding to 250 gray levels are
Ti=0.709578-(0.684459/249)i
[0249] Where i=0, 1, 2, . . . to 249
[0250] The gradual and smooth increase in the transmittance within
each grating period seen in FIG. 10 should result in analog resist
profile having smooth continuous blaze surfaces.
[0251] FIG. 11 exhibits an optical micrograph of a portion of a
gray scale mask made of HEBS-glass No. 3. The primary mask pattern
is a diffractive optical lens having ten gray levels in each zone.
The width of 5 complete zones represented in the photo at 920 m 500
m 390 .mu.m, 330 .mu.m and 290 .mu.m. Ten gray levels in the range
of 0 to 1.0 unit of optical density values, were written in
HEBS-glass No. 3 using Cambridge EBMF 10.5 e-beam writer operated
at 20 kv acceleration voltage, 0.2 .mu.m addressing grid size and
150 na beam current. It is seen in FIG. 11, as the zone width
reduces from 920 .mu.m the discreet gray levels become less
apparent.
[0252] A second pattern which consists of parallel lines with a 42
.mu.m pitch was write within the lens pattern to demonstrate that a
predetermined optical density value can be added to the existing
mask pattern in HEBS-glass. Since the parallel lint was written
with a constant e-beam dosage, the optical density along each lines
increases as it enters into a darker gray level of the lens
pattern.
[0253] One of the products of the present invention is a HEBS-glass
which in bodies of 0.090 inch cross section will exhibit the
following properties:
[0254] (a) the transmittance is more than 88% at 436 nm
[0255] (b) upon exposure to an electron beam with an electron beam
pattern generator operated at a value of acceleration voltage
selected from 20 to 30 kV, a value of addressing grid size selected
from 0.1 to 0.4 micrometer, and a value of beam current selected
from 25 to 250 na, the electron beam darkening sensitivity in the
linear portion of the sensitivity curve, is at least 2.454 unit of
optical density value in the spectra range of 365 nm to 630 nm per
milli coulomb/cm.sup.2. Said HEBS-glass having a base glass
composition consisting essentially Rn the mole % oxide basis 11.4
to 17.5% of one or more alkali metal oxide, 2.4 to 10.2% total of
photosensitivity inhibitors and RS suppressing agents including 2.4
to 10.2% TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6%
B.sub.2O.sub.3, 3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8%
SiO.sub.2.
[0256] Another of the product of the present invention is a
transparent HEBS-glass which in bodies of 0.090 inch cross section
will exhibit the following properties:
[0257] (a) the transmittance is more than 88% at 436 nm
[0258] (b) upon exposure to an electron beam using an electron beam
pattern generator operated with a write scheme having a value of
acceleration voltage selected from 20 to 30 kV, a value of
addressing grid size selected from 0.1 to 0.4 micrometer, and a
value of beam current selected from 25 to 250 na, the electron beam
darkening sensitivity in the linear portion of the sensitivity
curve, is at least 2.454 unit of optical density value in the
spectral range of 365 nm to 630 nm per milli coulomb/cm.sup.2. The
write scheme is selected from the write schemes of Table 2, said
electron beam darkening sensitivity of the HEBS-glass is
substantially represented by the sensitivity curve corresponding to
that of the chosen write scheme of Table 2.
[0259] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O, 0 to 4.6% B.sub.2O.sub.3, 3.7 to
13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0260] Another product of the preset invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0261] (a) the transmittance is more than 88% t 436 nm
[0262] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.4
micrometer and a beam current of 250 na will darken to a net
optical density value Y at 365 mm substantially in accordance with
the equation stated immediately below;
Y=19708x.sup.6-17787x.sup.5+6181.2x.sup.4-1063.8x.sup.3+85.688x.sup.2+3.38-
06x
[0263] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0264] Another product of the present invention is a HEBS-glass
which in bodies of 0.090 inch cross section will exhibit the
following properties:
[0265] (a) the transmittance is more than 88% at 436 nm
[0266] (b) upon exposure to a value X in mini coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.4
micrometer and a beam current of 250 na will darken to a net
optical density value Y at 435 nm substantially in accordance with
the equation stated immediately below;
Y=-15440x.sup.6+12082x.sup.5-3761.5x.sup.4+555.15x.sup.3-40.414x.sup.2+10.-
637x
[0267] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0268] Another pro of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0269] (a) the transmittance is more than 88% at 436 nm
[0270] (b) upon expose to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.4
micrometer and a beam current of 250 na will darken to a net
optical density value Y at 530 nm substantially in accordance with
the equation stated immediately below;
Y=46062x.sup.6-38146x.sup.5+12229x.sup.4-2013.9x.sup.3+173.69x.sup.2+5.809-
7x
[0271] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0272] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0273] (a) the transmittance is more than 88% at 436 nm
[0274] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.4
micrometer and a beam current of 250 na will darken to a net
optical density value Y at 630 nm substantially in accordance with
the equation stated immediately below;
Y=51961x.sup.6-43905x.sup.5+14402x.sup.4-2361.2x.sup.3+197.27x.sup.2+2.243-
6x
[0275] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0276] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0277] (a) the transmittance is more than 88% at 436 nm
[0278] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
elect dosage with an electron beam writer operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.1
micrometer and a beam current of 25 na will darken to a net optical
density value Y at 365 nm substantially in accordance with the
equation stated immediately below;
Y=-257.78x.sup.6+493.22x.sup.5-357.35x.sup.4+125.26x.sup.3-24.07x.sup.2+4.-
2726x
[0279] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0280] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0281] (a) the transmittance is more than 88% at 436 nm
[0282] (b upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.1
micrometer and a beam current of 25 na will darken to a net optical
density value Y at 435 nm substantially in accordance with the
equation stated immediately below;
Y=-421.26x.sup.6+736.88x.sup.5-503.36x.sup.4+168.42x.sup.3-3.486x.sup.2+5.-
785x
[0283] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 0.10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0284] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0285] (a) the transmittance is more than 88% at 436 nm
[0286] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.1
micrometer and a beam current of 25 na will darken to a net optical
density value Y at 530 nm substantially in accordance with the
equation stated immediately below;
Y=55.321x.sup.6-40.121x.sup.5-7.75x.sup.4+13.643x.sup.3-8.1316x.sup.2+5.42-
91x
[0287] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0288] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0289] (a) the transmittance is more than 88% at 436 m
[0290] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.1
micrometer and a beam current of 25 na will darken to a net optical
density value Y at 630 nm substantially in accordance with the
equation stated immediately below;
Y=-199.22x.sup.6+369.63x.sup.5-264.28x.sup.4+94.119x.sup.3-20.554x.sup.2+4-
.7848x
[0291] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0292] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0293] (a) the transmittance is more than 88% at 436 m
[0294] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.2
micrometer and a beam current of 75 na will darken to a net optical
density value Y at 365 nm substantially in accordance with the
equation stated immediately below;
Y=4788.8x.sup.6-4881.1x.sup.5+1822.8x.sup.3+19.251x.sup.2+4.098x
[0295] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0296] Another product of the present invention is a HEBS-glass
which in bodies of 0.090 inch cross section will exhibit the
following properties:
[0297] (a) the transmittance is more than 88% at 436 am
[0298] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.2
micrometer and a beam current of 75 na will darken to a net optical
density value Y at 435 mm substantially in accordance with the
equation stated immediately below;
Y=3780.7x.sup.6-4395.5x.sup.5+1959.1x.sup.4-421.14x.sup.3+40.268x.sup.2+4.-
882x
[0299] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0300] Another product of the present invention is a band
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0301] 15 (a) the transmittance is more than 88% at 436 nm
[0302] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.2
micrometer and a beam current of 100 na will darken to a net
optical density value Y at 365 nm substantially in accordance with
the equation state immediately below;
Y=-355.78x.sup.6+466.62x.sup.5-243.17x.sup.4+62.851x.sup.3-12.485x.sup.2+5-
.5571x
[0303] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0304] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0305] (a) the transmittance is more than 88% at 436 nm
[0306] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.2
micrometer and a beam current of 100 na will darken to a net
optical density value Y at 435 nm substantially in accordance with
the equation stated immediately below;
Y=-692.18x.sup.6+804.39x.sup.5-358.96x.sup.4+75.143x.sup.3-10.535x.sup.2+6-
.9982x
[0307] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% C1 and 58.2 to 78.8% SiO.sub.2.
[0308] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0309] (a) the transmittance is more than 88% at 436 nm
[0310] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.2
micrometer and a beam current of 125 na will darken to a net
optical deity value Y at 365 nm substantially in accordance with
the equation stated immediately below;
Y=-664.62x.sup.6+932.44x.sup.5-464.2x.sup.4+95.04x.sup.3-13.314x.sup.2+6.4-
665x
[0311] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing a including 2.4 to 10.2% TiO.sub.2,
1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3, 3.7 to 13.2%
ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0312] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0313] (a) the transmittance is more than 88% at 436 nm
[0314] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.2 mic
and a beam current of 125 na will darken to a net optical density
value Y at 435 nm substantially in accordance with the equation
stated immediately below;
Y=-900.79x.sup.6+1480.9x.sup.5-905.98x.sup.4+243.25x.sup.3-32.801x.sup.2+9-
.8528x
[0315] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0316] Another product of the present invention is a HEBS-glass
which in bodies of 0.090 inch cross section will exhibit the
following properties:
[0317] (a) the transmittance is more than 88% at 436 nm
[0318] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 30 kV, an addressing grid size of 0.2
micrometer and a beam current of 150 na will darken to a net
optical density value Y at 365 nm substantially in accordance with
the equation stated immediately below;
Y=-104368x.sup.6+149.86x.sup.5-51.158x.sup.4-8.925x.sup.3-0.3208x.sup.2+5.-
866x
[0319] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0320] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0321] (a) the is more than 88% at 436 nm
[0322] (b) up on to a value X in milli coulomb/cm.sup.2 of electron
dosage with an electron beam writer operated at a beam acceleration
voltage of 30 kV, an addressing grid du of 0.2 micrometers and a
beam current of 150 na will to a net optical density value Y at 435
nm substantially in accordance with the equation stated immediately
below;
Y=-341.18x.sup.6+643.91x.sup.5-430.4x.sup.4+115.13x.sup.3-16.314x.sup.2+9.-
1502x
[0323] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0324] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0325] (a) the transmittance is more than 88% at 436 nm
[0326] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.2
micrometer and a beam current of 100 na will darken to a net
optical density value Y at 365 nm substantially in accordance with
the equation stated immediately below;
Y=1165x.sup.6-1729.1x.sup.5+969.72x.sup.4-255.38x.sup.3+28.215x.sup.3+1.99-
49x
[0327] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0328] Another product of the present invention is a at HEBS-glass
which in bodies of 0.090 inch cross section will exhibit the
following properties:
[0329] (a) the transmittance is more than 88% at 436 nm
[0330] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.2
micrometer and a beam current of 100 na will darken to a net
optical density value Y at 435 nm substantially in accordance with
the equation stated immediately below;
Y=321.26x.sup.6-495.78x.sup.5+299.53x.sup.4-93.047x.sup.3+11.878x.sup.3+3.-
99x
[0331] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 132% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0332] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0333] (a) the transmittance is more than 88% at 436 nm
[0334] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.2
micrometer and a beam current of 125 na will darken to a not
optical density value Y at 365 nm substantially in accordance with
the equation stated immediately below;
Y=-454.78x.sup.6+748.41x.sup.5-467.28x.sup.4+137.8x.sup.3-22.463x.sup.2+4.-
8643x
[0335] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents a including 2.4 to 10.2% Tile,
1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3, 3.7 to 13.2%
ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0336] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0337] (a) the transmittance is more than 88% at 436 nm
[0338] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam write operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.2
micrometer and a beam current of 125 na will darken to a net
optical density value Y at 435 nm substantially in accordance with
the equation stated immediately below;
Y=-399.43x.sup.6+659.66x.sup.5-409.6x.sup.4+113.52x.sup.3-15.916x.sup.2+5.-
6722x
[0339] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0340] Another product of the present invention is a HEBS-glass
which in bodies of 0.090 inch cross section will exhibit the
following properties:
[0341] (a) the transmittance is more than 88% at 436 nm
[0342] (b) upon expose to a value X in milli coulomb/cm of electron
dosage with an electron beam writer operated at a beam acceleration
voltage of 20 kV, an addressing grid size of 0.2 micrometer and a
beam current of 150 na will darken to a net optical density value Y
at 365 nm substantially in accordance with the equation stated
immediately below;
Y=-74.993x.sup.6+118.24x.sup.5-57.174x.sup.4+5.2492x.sup.3-0.6172x.sup.2+3-
.3699x
[0343] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS ing a including 2.4 to 10.2% TiO.sub.2, 1.1 to
2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3, 3.7 to 13.2% ZnO,
0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0344] Another product of the present invention is a HEBS-glass
which in bodies of 0.090 inch cross section will exhibit the
following properties:
[0345] (a) the transmittance is more than 88% at 436 nm
[0346] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.2
micrometer and a beam current of 150 na will darken to a net
optical density value Y at 435 nm substantially in accordance with
the equation stated immediately below;
Y=-278.14x.sup.6+503.66x.sup.5-329.14x.sup.4+89.552x.sup.3-11.422x.sup.2+5-
.4742x
[0347] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0348] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0349] (a) the transmittance is more than 88% at 436 nm
[0350] (b) upon exposure to a value X in milli coulomb/cm.sup.2 of
electron dosage with an electron beam writer operated at a beam
acceleration voltage of 20 kV, an addressing grid size of 0.2
micrometer and a beam current of 175 na will darken to a net
optical density value Y at 365 nm substantially in accordance with
the equation stated immediately below;
Y=7.7262x.sup.6-37.019x.sup.5+56.546x.sup.4-35.995x.sup.3+6.9532x.sup.2+2.-
7738x
[0351] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0352] Another product of the present invention is a transparent
HEBS-glass which in bodies of 0.090 inch cross section will exhibit
the following properties:
[0353] (a) the transmittance is more than 88% at 436 nm
[0354] (b) upon exposure to a value X in milli coulomb/cm of elect
dosage with an electron beam writer operated at a beam acceleration
voltage of 20 kV, an addressing grid size of 0.2 micrometer and a
beam current of 175 na will darken to a net optical density value Y
at 530 nm substantially in accordance with the equation stated
immediately below;
Y=82.35x.sup.6-237.03x.sup.5+259.77x.sup.4-130.11x.sup.3+23.171x.sup.2+4.6-
292x
[0355] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2.
[0356] The products of the present invention described above have
utility in making a gray scale mask with multi-gray levels, each of
said gray levels having a predetermined optical density value which
is obtained through exposure to a predetermined electron dosage,
said gray scale mask can be utilized in making three dimensional
microstructures with general three dimensional surfaces in
photoresist through a single optical exposure in a
photolithographic process.
[0357] The profile of a three dimensional surface is transformed
into a substrate material using an etching process.
[0358] For example, one of the products of the invention is a
transparent HEBS-glass which in bodies of 0.090 inch cross section
will exhibit the following properties:
[0359] (a) the transmittance is more than 88% at 436 nm
[0360] (b) upon exposure to an electron beam with an electron beam
pattern generator operated at a value of acceleration voltage
selected from 20 to 30 kV, a value of addressing grid size selected
from 0.1 to 0.4 micrometer, and a value of beam current selected
from 25 to 250 na, the electron beam darkening sensitivity in the
linear portion of the sensitivity curve, is at least 2.454 unit of
optical density value in the spectral range of 365 nm to 630 nm per
milli coulomb/cm.sup.2.
[0361] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali: metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 582 to 78.8% SiO.sub.2 has
utility in making a gray scale mask with multi-gray levels, each of
said gray levels having a predetermined optical density value which
is obtained through exposure to a predetermined electron dosage,
said gray scale mask can be utilized in making three dimensional
microstructures with general three dimensional surfaces in
photoresist through a single optical exposure in a
photolithographic process.
Cost Efficient Mass Fabrication of Diffractive Optical Elements
(DOEs)
[0362] HEBS-glass is a mask material sensitive towards e-beam
exposure, and exposure with a certain electron beam dosage changes
the optical density of the material. After e-beam exposure the mask
needs no further development or fixation process. The mask with
multi levels of optical densities can then be used to expose a
photo resist in a contact aligner or in a reduction stepper this
allows to associate a certain resist thickness after development
with each optical density. The information was used to determine
the e-beam dosages for each of the (e.g. 32) phase levels necessary
to generate a Diffractive Optical Elements (DOE herein after). The
so generated HEBS-glass gray level mask can be used to expose
numerous DOEs using an optical lithography tool. After many copies
of the mask on the photo resist ae developed, many substrates with
the developed photo resist are placed in a Chemically Assisted Ion
Beam Etching (CAIBE) system, to simultaneously transfer the
microstructures from the analog resists onto the surfaces of the
substrates. An overview of these processing steps is shown in FIG.
12.
[0363] The fabrication of DOE arrays using a HEBS-glass gay scale
mask with multi gray levels and the process steps of FIG. 12 was
described in "cost-effective mass fabrication of multi-level
diffractive optical elements by use of a single optical exposure
with a gray scale mask on high-energy beam sensitive glass" Applied
Optics, Jul. 10, 1997/Vol. 36, No. 20 by Walter Daschner, Pin Ling,
Robert Stein, Che-Kuang (Chuck) Wu and S. H. Lee.
[0364] The described fabrication method shows the cost effective
mass fabrication of DOEs. There are a number of advantages:
[0365] The mass fabrication is simplified and more cost-effective.
Instead of a set of masks (i.e. 5 masks for 32 phase levels) with
all the associated resist processing, only a single mask needs to
be exposed in the e-beam writer and no resist processing is
associated with the mask generation. Phase levels of DOE are
immediately visible as gray levels in HEBS-glass upon e-beam
exposure.
[0366] All phase levels are written in a single step on a single
mask. The inevitable mis-registrations and associated efficiency
losses between subsequent exposures are avoided.
[0367] Third, the number of processing steps for the DOE
fabrication compared to binary mask fabrication of e.g. 32 phase
levels is reduced by a actor of 5. This will reduce the cost for
high quality monolithic DOEs substantially.
[0368] Fourth, am with a binary fabrication method for master
fabrication and a following replication step based on injection
molding this replication method only becomes economic with a number
of DOEs to be fabricated in the 10's of thousands. Since the
proposed fabrication method greatly reduces the involved
fabrication steps resulting in a cost reduction, the number at
which molding based methods become economically feasible will grow
considerably. This will allow to avoid the problems associated with
the molding approach. The material which is best suited for the
application, can be chosen without being limited by the constraints
of the molding material (i.e. limited temperature range of
operation or limited wavelength range). Also all the involved
materials and tools are compatible with VLSI fabrication so that no
new fabrication or software tools need to be established unlike in
the case of replication by injection molding or casting.
[0369] There is a considerable gain in turn around time since the
number of production steps has been reduced and the mask
fabrication steps have been simplified.
Cost Efficient Mass Fabrication of Asymmetric Irregularly Shaped
Micro-Lens Arrays
[0370] A cost-effective way of fabricating large arrays of
refractive micro lenses becomes more and more important. Gray level
mask fabrication offers the possibility to shape arbitrary resist
profiles and therefore produce arrays of general aspheric non
rotationally symmetric refractive lenses with different
functionality, complete aberration correction and a 100%
fill-factor. The fabrication method based on HEBS-glass gray level
mask allows for complete freedom in terms of the shapes e.g.
asymmetric, irregularly shaped lenses, and location of the lenses
e.g. with accurate center to center spacing.
[0371] As the resist for the lithography step a comparatively thick
photoresist can be employed in order to achieve a resist thickness
in the range of up to 30 microns. This feature depth in resist will
allow for a total les sag after the etching transfer of up to about
120 microns, since a magnification of the feature depth of about a
factor of 3 to 5 can be achieved during the transferring step of
resist profiles into their respective substrates via chemically
Assisted Ion Beam Etching (CAIBE). The described fabrication steps
are shown in FIG. 13.
[0372] For the analog transfer scheme of FIG. 13, i.e. from an
optical density profile in the gray-level mask into a surface
height profile in the photoresist, it is necessary that the number
of gray levels be increased as the aperture of the reactive lens
increases; for example, HEBS-glass masks having a minimum of 32,
64, and 96 gray levels are desirable to fabricate refractive micro
lenses having apertures of 50 .mu.m, 100 .mu.m and 200 .mu.m,
respectively.
[0373] The fabrication of refractive microlens arrays using a
HEBS-glass gray level mask and the processing steps of FIG. 13 was
described in "General aspheric refractive micro-optics cs
fabricated by optical lithography using a high energy beam
sensitive glass gray-level mask" J. Vac. Sci. Technol. B 14 (6),
November/December 1996 by Walter Daschner, Pin Long, Robert Stein,
Che-kuang (Chuck) Wu and S. H. Lee.
The Analog Transfer Scheme Using HEBS-glass Gray Scale Masks
[0374] It has been determined that the pros of processing
photoresist to produce analog resist profile can be derived from
those normally used for binary photo lithography with the following
modifications and provisions:
[0375] 1. positive and non chemically amplified Novalac based
photoresist is preferred
[0376] 2. prebake photoresist at a low temperature and for a
shortened time duration from that is normally used for binary
lithography
[0377] 3. use a weak developer, or dilute the usual developers for
example, by a factor of 4.
Exemplary Calibration Curves
[0378] (a) Surface height versus optical density, i.e. the
calibration curve of the analog transfer scheme
[0379] FIG. 14 shows the remaining thickness after development of
Shipley S1650 photoresist as a function of the optical density at
436 mm of the gray levels in a HEBS-glass mask. The initial (i.e.
as coated) thickness of the Shipley S1650 photoresist was 4.0
.mu.m. The range of resist thickness in the depth versus optical
density calibration curve can be altered through the choice of a
photoresist and/or resist parameters, the initial thickness of the
photoresist in particular. In the plots of resist thickness versus
optical density, the slope of the calibration curve reduces as the
developed resists thickness approaches the initial (as coated)
resists thickness. Therefore, to produce an analog resist profile
of a given feature depth, it is necessary to start with an as
coated resist thickness which is more than that of its required
feature depth.
[0380] To transfer multilevel resist structure of DOE into qua
through a dry etching process, the relative etch rate between
photoresist and quartz substrate can be so chosen to achieve the
final needed etch depth 3 to 6 times that in the resist. Therefore,
for the fabrication of DOE in quartz, a surface height variation of
e.g. 500 nm in the resist results in a depth modulation in quartz
of up to 3000 nm.
[0381] (b) Electron beam darkening sensitivity curve (Optical
density versus electron dosage).
[0382] Table 2 list, FIG. 7 and FIG. 8 depict the exemplary e-beam
darkening sensitivity curves of HEBS-glass No. 3. For DOE
fabrication the required optical density values of a HEBS-glass
gray level mask are typically in the range of 0.1 to 1.2.
[0383] For the fabrication of refractive micro lens arrays the
optical density levels in a HEBS-glass gray level mask is in
general in the range of 0 to more than 1.2. The maximum optical
density value is larger to produce a larger lens-sag.
[0384] (c) Optical density versus clock rate, i.e. the calibration
curve of e-beam exposure.
[0385] The electron dos D in micro coulomb/cm.sup.2 is calculation
as follow:
D(.mu.c/cm.sup.2)=I.multidot.t.multidot.N=I.multidot.N/f
[0386] Where I is bean current in amp., t is exposure duration i.e.
dwell time per pixel in .mu.sec, and N is number of pixels in 1
cm.sup.2. The exposure duration per pixel is equal to 1/f where f
is the clock rate i.e. the write frequency. Since the clock rate
can be varied on the fly using a vector scan e-beam writer, the
calibration curve of e-beam exposure "optical density versus clock
rate" is a practical one for a vector scan e-beam writer. The
calibration curve was determined experimentally for each
combination of write parameters which include beam acceleration
voltage, beam current addressing grid size.
[0387] The net optical density values at 435 nm and the
corresponding clock rates are plotted in FIG. 15 and FIG. 16 for
two write scheme using the daft of Table 1 and Table 2. FIG. 15
exhibits the calibration curve "net optical density verses clock
rate" for the e-beam write scheme of 30 kv, 250 na beam current and
0.4 .mu.m addressing grid size. FIG. 16 displays the calibration
curve "net optical density verses clock rate" for the e-beam write
scheme of 30 kv, 75 na beam current and 0.2 .mu.m and grid
size.
Fabrication of HEBS-glass Gray Level Masks
[0388] A HEBS-glass photomask with multi-gray levels is ideally
suited for fabrication of diffractive optical elements (DOE),
refractive micro optics, micro-electro-mechanical (MEM) devices,
micro-opto-electro-mechan- ical (MOEM) devices and integrated
optical components, and for beam shaping optics.
[0389] A mask for multi phase levels of DOE is made by exposing in
an e-beam writer with predetermined dosages according to a
calibration curve of the analog transfer scheme such as that shown
in FIG. 14 together with the e-beam darkening sensitivity curve,
examples of which are listed in Table 2.
[0390] To make a HEBS-glass gray level mask using a vector scan
e-beam writer, optical density levels which will achieve evenly
spaced multi depth levels over the thickness range of photoresist
needed for a subsequent dry etching, are determined from a
calibration curve of the analog transfer scheme e.g. FIG. 14. Each
optical density level in the mask is then written with a clock rate
corresponding to the predetermined optical density value. The clock
rate is determined from the calibration curve of e-beam exposure
such as that shown in FIG. 15 and FIG. 16. The calculation of the
clock rate is further elaborated below.
[0391] The clock rata f were calculated from polynomial eons such
as eq. A and eq. B for a large number of the predetermined optical
density levels of gray level mask designs. Eq. A and eq. B are the
best polynomial fit equations of the experimental data.
1/f=0.0692D.sup.6-0.4299D.sup.5+1.0403D.sup.4-1.2009D.sup.3+0.666D.sup.2+0-
.5339D eq. A
1/f=0.012D.sup.6-0.0862D.sup.5+0.304D.sup.4-0.5256D.sup.3+0.5491D.sup.2+0.-
5622D eq. B
[0392] Plotted th experimental data of Table 1, FIG. 17 exhibits
the calibration curve "1/(clock rate) versus net optical density at
435 nm" for the e-beam write scheme of 30 kv, 256=beam current and
0.4 .mu.m addressing grid size. Eq. A is the best polynomial fit
equation of the data points of FIG. 17.
[0393] FIG. 18 displays the calibration curve "1/(clock rate)
versus net optical density at 435 nm" for the e-beam write scheme
of 30 kv, 75 na beam current and 0.2 .mu.m addressing grid size.
Eq. B is the best fit polynomial on of the data points of FIG.
18.
[0394] HEBS-glass masks having gray levels from just a few to many
hundred were fabricated via e-beam direct write HEBS-glass. For
example, a very high quality, sinusoidal absorption 2 cm.times.2 cm
in size having 625 gray levels within each period of 250
.mu.m.+-.0.2 .mu.m was fabricated using Cambridge EBMF 10.5 e-beam
writer. The grating is a series of linear strips, 2 cm long whose
absorbance varies sinusoidally along the direction perpendicular to
the strips. The linear strip which is the lines of constant optical
density, has a requirement of better than .+-.0.1 .mu.m in
linearity. Within each period, the minimum transmission at the
wavelength of 435 nm is 1% of the maximum transmission. 625 clock
rates were determined from the eq. As for the grating fabricated
using the write scheme of Table 1. A different set of 625 clock
rates were determined from eq. B for a second grating fabricated
using a second set of write parameters. To minimum and the maximum
optical density values of the 625 gray levels are 0.172 and 2.172
using the write scheme of FIG. 17, and are 0.178 and 2.178 using
the write parameters of FIG. 18.
[0395] Using a gray level mask in an optical exposure system, the
throughput of resist exposure in DOE fabrication increases with a
lower value of the minimum optical density level in th gray level
mask. It is thereof desirable to have the optical density value of
the lowest gray level being about or below 0.1.
[0396] A vector scan e-beam writer having the capability of higher
clock rates can be employed to increase the throughput of mask
making an also to reduce the minimum optical density value toward
zero. The capability of focusing a larger beam current to a given
e-beam spot size is an important feature to take full advantage of
a larger clock rate.
[0397] It has been determined that the sensitivity of HEBS-glass is
enhanced by the heat effect of a larger beam current. The
throughput of writing a HEBS-glass gray level mask increases by a
factor of 7.5 instead of 4 when the addressing grid size is
increased from 0.2 .mu.m to 0.4 .mu.m, and at the same time the
beam current is increased from 75 na to 300 na.
[0398] A grounding layer in the form of a 10 nm (or thicker) chrome
layer should be applied to the HEBS-glass photomask blank. The only
purpose of this thermally evaporated layer is to avoid local
charging of the mask plate during the e-beam writing process. The
mask is then exposed in the e-beam writer.
[0399] After the e-beam exposure the only necessary processing step
is the wet etching of the Cr grounding layer to make the mask ready
for exposure in an optical lithography exposure tool. Besides the
removal of the grounding layer no processing of the mask is
necessary.
Microscope Observation
[0400] Phase levels of DOE are immediately visible as gray a levels
in HEBS-glass upon e-beam exposure. The pattern data or image
should be observed in a transmission mode. Since the pattern data
or image in HEBS-glass do not scatter or reflect light, they are
essentially not visible in a reflection mode.
DOE Made of An E-Beam Direct-Writ HEBS-Glass Plate Or Made of A
Laser Beam Direct-Write LDW-Glass Plate
[0401] The multi-gray levels in HEBS-glass were transformed into
multi-phase levels, i.e., depth variation of surface relief in
HEBS-glass upon a wet chemical etching or a dry etching process. An
exemplary etching process consists of dipping an e-beam patterned
HEBS-glass plate in 1.25% HF solution for 40 minutes. Before the
etching process the image in HEBS-glass causes an absorption or
amplitude modulation of an incoming light beam, whereas after the
etching process the image in HEBS-glass effects a phase modulation
of the incoming light beam.
[0402] Under microscope observation, the e-beam pattern is
essentially not visible in a refection mode. After the selective
etching process the pattern becomes visible in the reflection
mode.
[0403] HEBS-glasses having been uniformly darkened with a high
energy beam, electron beam in particular, is a laser beam direct
write g, LDW glass herein after.
[0404] The laser beam direct write LDW-glass has a much superior
selective etch ratio than the e-beam direct write HEBS-glass. Due
to a very large etch ratio of the laser exposed area vs. unexposed
area within a LDW-glass mask DOE as well as refractive micro les
arrays and general three dimensional surfaces can be fabricated in
LDW-glass with the laser direct write approach to result in a
LDW-glass mask and followed by an etching step.
LDW-Glass Mask Fabrication
[0405] One of the products of the present invention is an LDW-glass
which is a HEBS-glass having been uniformly darkened to a
predetermined optical density value. Said predetermined optical
density value is at least the maximum optical density value of a
pre-designed gray scale mask with multi-gray levels, said LDW-glass
prior to being darkened with an electron beam or a flood electron
gun is a transparent HEBS-gas which in bodies of 0.090 inch cross
section will exhibit the following properties:
[0406] (a) the transmittance is more than 88% at 436 nm
[0407] (b) upon exposure to an electron beam with a flood electron
gun or with an electron beam pattern generator operated at a value
of acceleration voltage selected from 20 to 30 kV, the electron
beam darkening sensitivity in the linear portion of the sensitivity
curve, is at least 2.454 unit of optical density value in the
spectral range of 365 nm to 630 nm pot milli coulomb/cm.sup.2.
[0408] Said HEBS a base glass composition consisting essentially on
the mole % oxide basis 11.4 to 17.5% of on or more a metal oxide,
2.4 to 10.2% total of photo sensitivity inhibitors and RS
suppressing agents including 2.4 to 10.2% TiO.sub.2, 1.1 to 2.4%
Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3, 3.7 to 13.2% ZnO, 0.5 to
6% Cl and 58.2 to 78.8% SiO.sub.2, said gray scale mask is made by
exposure to a focused laser beam, said multi-gray levels an made
using laser write speed and/or laser beam intensity and/or number
of retraces as variable write parameters.
[0409] Another products of the present invention is an LDW-glass
which is a HEBS-glass having been uniformly darkened to a pr mined
optical density value, said predetermined optical density value is
at least the maximum optical density value of a pre-designed gray
scale mask with multi-gray levels, said LDW-glass prior to being
darkened with an electron beam or a flood electron gun is a
transparent HEBS-glass which in bodies of 0.090 inch cross section
will exhibit the following properties:
[0410] (a) the transmittance is more than 88% at 436 nm
[0411] (b) upon exposure to an electron beam with a flood electron
gun or with an electron beam pattern generator operated at a value
of acceleration voltage selected from 10 to 100 kV, the HEBS-glass
is darkened to a predetermined optical density value which is at
least the maximum optical density value of a pre-designed gray
scale mask with multi-gray levels.
[0412] Said HEBS-glass having a base glass composition consisting
essentially on the mole % oxide basis 11.4 to 17.5% of one or more
alkali metal oxide, 2.4 to 10.2% total of photosensitivity
inhibitors and RS suppressing agents including 2.4 to 10.2%
TiO.sub.2, 1.1 to 2.4% Al.sub.2O.sub.3, 0 to 4.6% B.sub.2O.sub.3,
3.7 to 13.2% ZnO, 0.5 to 6% Cl and 58.2 to 78.8% SiO.sub.2, said
gray scale mask is made by exposure to a focused laser beam, said
multi-gray levels are made using laser write speed and/or laser
beam intensity and/or number of retraces as a variable write
parameters.
[0413] The LDW-glass gray scale mask can be utilized in making
three dimensional microstructures with general three dimensional
surfaces in photoresist through a single optical exposure in a
photolithographic process.
[0414] The profile of a thee dimensional surface in photoresist is
transformed into a substrate material using an etching process.
[0415] Laser Direct Write glass (LDW-glass) also offers the
advantages of a one step fabrication of a true gray level mask. The
exposure of this gray level mask is done in a laser writing tool.
This also allows the use of the existing software previously
written to support mask making and direct write on resist
approaches for the fabrication of diffractive optical elements
(DOEs). The so generated gray level mask can be used in an optical
lithographic exposure tool (e.g., a G-line or a I-line war stepper,
or a contact aligner) to mass fabricate resist profiles.
[0416] Using the LDW gray level mask fabrication and a following
optical lithographic exposure, alignment errors are avoided, since
the mask is written in a single step using different energy
densities of a laser beam to generate multi-gray levels. This new
approach also allows a very economical mask fabrication. Instead of
fabricating a set of 5 binary chrome masks with all the involved
resist processing and wet etching, a single writing step without
the need for any processing is needed. This single mask then
contains all the necessary information previously contained in a
set of 5 binary masks. Misalignment due to sequential printing of 5
binary masks in a set is completely avoided. After the LDW gray
level mask is fabricated a series of single exposure in a
step-and-repeat system can generate hundreds of DOEs on the same
wafer. This wafer can then be processed with a single CAIBE step to
transfer the DOE structure of a large number of different elements
simultaneously into the substrate. Since the complete DOE structure
is transferred into the substrate there is no need for a resist
stripping step after the etching process. After dicing the wafer
hundreds of monolithic multilevel DOEs can be generated by a
process which cut the involved processing steps by more than a
factor of 5.
[0417] The optical density specter of exemplary LDW a are shown in
FIG. 19 and FIG. 20. FIG. 19 exhibits the optical density spectra
of LDW-HR plates-Type 1. -Type II and -Type III. FIG. 20 exhibits
the optical density spectra of LDW-IR plates-Type I, -Type II and
-Type III. LDW-HR plates type I, -Type II and -Type III as well as
LDW-IR plates-Type I, -Type II and -Type III are HEBS-glass No. 3
having been darkened with flood electron gun, using the
acceleration voltage and electron dosage of the electron beam
exposure as variable parameters.
[0418] LDW-glass photomask blanks are monolithic silicate glass
plates with no coating of any kind LDW-glasses contain a large
number density of coloring specks of silver within 1 um in the
thickness dimension into the glass surface. A focused laser beam of
any wavelength in the spectral range of near uv, visible (e.g., 514
nm. 632 nm and 647 nm), near infrared (e.g. 820 nm ad 1060 nm) and
infrared (e.g. 10.6 .mu.m) can be used to heat erase these coloring
specks, causing a portion or all of the coloring specks of silver
in glass to become colorless silver ions. The transmittance of
LDW-glass plates increases with increasing writing-energy density
of a focused laser beam. The required writing energy density is a
function of the wavelength of write beam, writing velocity, i.e.,
the speed of laser sweep, the intensity profile of the focused
laser beam and the value of % T at the desired gray level. For
example, having been exposed to an energy density of 2
joule/cm.sup.2 a write beam at the wavelength of 514 nm and a
writing velocity of 4 meters/sec, LDW-HR plate-type I becomes
totally transparent.
[0419] At any given writing velocity, there exits an erasure
threshold-intensity I.sub.ETh below which there is no change in
optical density of LDW-glass pates even with multiple retraces.
Using a write-beam intensity above the erasure-threshold-intensity
I.sub.ETh, the optical density of LDW-glass pates reduces with each
additional retrace and the LDW-g plates can be erased to a
transparent state with multiple retraces. As the write-beam
intensity increases further above the erasure threshold-intensity
I.sub.ETh, retraces needed to bring about the transparent state
decrease in number. LDW-glass plates a made transparent in one
laser sweep i.e., no retraces at a full erasure intensity
I.sub.FE.
[0420] At any given writing velocity, the also exists an
abrasion-threshold-into I.sub.ATh at an above which the LDW-glass
plates are abraded or damaged on the glass surface due to excessive
temperature (>800.degree. C.) at the laser focused spot.
However, the abrasion is not a pure thermal effect since the
abrasion-threshold-intensity I.sub.ATh is lower using a write beam
of a shorter wavelength.
[0421] At a given writing velocity, the write latitude is defined
as the difference I.sub.ATh-I.sub.FE between the abrasion threshold
intensity and the full-erasure-intensity. The write-latitude
increases with decreasing writing velocity and also increases with
a write beam of a longer wavelength.
[0422] At a writ velocity of 1 to 4 meter/sec the required writing
energy density for full erasure is 2 to 4 joule/cm.sup.2 using a
write-beam whose wavelength in the spectral range of 488 nm to 1060
nm, provided the optical density of the LDW-glass plate is in
excess of about 0.5 at the wavelength of the write-beam.
[0423] The values of the writing energy density cited are based on
experimental data using write-beams having a Gaussian intensity
profile at the fed laser spot. One can expect the required writing
energy density to reduce by a factor of more than 2 and the
write-latitude increases, when a flat top intensity profile is
utilized.
[0424] Multigray levels were written in LDW-glass plates using the
writing velocity or laser beam intensity or multiple retraces or a
combination thereof as variable parameters.
[0425] A LDW-glass photomask with multi-gray levels is ideally
suited for fabrication of diffractive optical elements (DOE),
Micro-electro-mechanical (MEM) devices,
Micro-Opto-electro-mechanical (MOEM) devices. A mask for 32 phase
levels of DOE is made by exposing in a laser beam writer with
predetermined energy density levels according to a depth verses
optical density calibration curve.
[0426] To transfer a multilevel resist structure of DOE into qua
through a dry etching process, the relative etch rate between
photoresist and quartz substrate can be so chosen to achieve the
final needed etch depth 3 to 6 times that in the resist Therefore
for the fabrication of DOE in quartz a substrate height variation
of 1 im in the resist results in a depth modulation in the quartz
of up to 6 .mu.m.
[0427] The optical density at the wavelength of optical
lithographic exposure tool, e.g., 436 nm (G line of mercury arc) is
1.4, 2.4 and 3.0 for LDW-HR plates type 1, type II and type III
respectively. The corresponding optical density at 365 nm (I line)
is 1.0, 1.6 and 2.0 for type L type II and type III plates
respectively. The optical density at 405 nm (H line) is 1.2, 2.0
and 2.7 for type I type II and type III plates respectively. The
optical density of type III plates exceeds 3.0 in the spectral
range of 430 nm to 615 nm. Depending on the photoresist and its
thickness requirement, one can select among type I type II and type
III of LDW-HR plates for the required optical density at the
wavelength of lithographic exposure tool. LDW-HR plates having
optical density of any specified value that is the same or
different from those of type I type II an type III plates are
fabricated by controlling the variable parameter in the darkening
process using a high energy beam. The increased optical density
values from type I to type II to type III plates due primarily to
an increased thickness of the colored glass layer.
[0428] LDW-HR plate-type I has a larger write-latitude than the
type II plat which in turn has a better write-latitude than the
type III plate.
[0429] LDW-HR plats arm recommended for write-wavelengths shorter
than about 900 nm and is also good for a write beam using CO.sub.2
laser at 10.6 .mu.m wavelength. For write-wavelengths longer than
about 750 nm LDW-IR plates are preferred.
[0430] The optical density values at the wavelength of optical
lithographic exposure tool, e.g. 436 m are 1.2, 1.8 and 2.6 for
LDW-IR plates type I type II and type III respectively. The
corresponding optical density values at 365 nm are 1.4, 1.8 and 2.1
for type I, type II and type III plates respectively. The optical
density values at 405 mm are 1.2, 1.8 and 2.4 for type I type II
and type III plates respectively. The optical density of type II
plates exceeds 3.0 in the spectral range of 570 nm to 805 nm. The
optical density of type III plates exceeds 3.0 in the to range of
490 n to 915 nm. Depending on the wavelength of a laser writer and
on the photoresist thickness requirement, one can select type I
type II and type III of LDW-IR plates. LDW-IR plates having optical
density values that are the same or different from those of type I
type II and type III plates fabricated by controlling the variable
parameters in the darkening process using a high energy beam. The
increased optical density values from type I to type II to type III
plan are due primarily to an increased thickness of the colored
glass layer. The type I plate has a larger write latitude than type
II plate which in turn has a better write-latitude than the type
III plate.
[0431] Due to the effect of the erasure-threshold intensity, there
is little or no soft line-edges in the laser direct write patterns
recorded in LDW-glass plates using a focused laser beam with a
Gaussian intensity profile. The recorded spot size in LDW-glass
plates is substantially smaller than the size of the airy disc of
the focused laser spot in air. Moreover, the grain size of coloring
specks of silver in the LDW-glass is of atomic dimension, and
LDW-glass plates have no graininess. Submicron features were
recorded in LDW-glass plates using laser beams of various visible
wavelengths focused with an objective lens which has a numerical
aperture as low as 0.25.
Absorption-Phase-Shift Mask
[0432] A binary absorption HEBS-glass mask becomes a binary
phase-shift mask upon a selective wet chemical etching or a dry
etching process. Starting with a HEBS-glass blank having an e-beam
sensitized glass layer which is sufficiently thick so that the
binary phase shift mask is still sensitive to e-beam, a second
e-beam exposure products an absorption-phase-shift mask.
Advantages of Direct Write All-Glass Photomasks
[0433] Direct write all-glass photomask blanks includes HEBS-glass
photomask blanks and LDW-glass photomask blanks.
[0434] Direct write on HEBS-glass or LDW-glasses create instant
photomasks, and eliminate chrome and photoresist, and their
processing chemicals. This is a zero-waste, inexpensive solution
for mask making. By employing the all-glass photomask blanks,
photomasks meeting specifications containing the most stringent
defect levels can be prepared consistently. Advantages gained in
using all-glass photomask blob include the following:
[0435] 1. Photomasks can be patterned from all-glass blanks without
a number of processing steps.
[0436] 2. The advantages that can be expected from eliminating the
post exposure processing steps include faster turnaround, better
line width control an much lower defect densities.
[0437] 3. Defects such as intrusion, extrusion, lack of adhesion,
excess material/chrome spots and scratches in chrome are eliminated
due to the elimination of chrome and resist as well as the
associated processing steps.
[0438] 4. No post exposure process-induced CD variation. No process
induced image quality problems (e.g. line distortion) due to resist
swelling during baking.
[0439] 5. The direct write all-glass photomasks are non-reflective,
and have near zero difference in reflectivity between darkened and
undarkened areas. Reflectivity is 4% which is much los than that of
the anti-reflective chrome at all wavelengths.
[0440] 6. White light is a safe light for the all-glass photomask
blanks enabling inspection of the mask-blanks with intense white
light before, during and after the pattern is generated.
[0441] 7. The all-glass mask is more durable than a chrome mask
since the all-glass mask is less sensitive to surface scratching
due to its volume effect, i.e., the masking pattern is within the
glass surface rather than on the surface.
[0442] 8. For contact printing, the all-glass masks have long life
times and more wafers produced per mask.
[0443] 9. The sensitivity of an all-glass blank is very uniform
throughout the whole blank surface. Therefore, good CD control is
not limited to the center of the mask. In contrast, chrome blanks
often have the non-uniform photoresist coating thickness near the
edges of the chrome plate.
[0444] 10. Easy re-inspection of accepted mask; since there exists
no scattered light from a clean all-glass photomask (widow the
chrome features which scatter light in the image plane), defects
such as dust particles, fingerprints, and scratches are readily
observable/detected in the passage of an intense light beam in a
dark room. No expensive inspection equipment are needed to
re-inspect used masks, or could-be contaminated masks.
[0445] 11. Unlike chrome blanks, there is no chemical waste
problems.
Applications of The Direct Write All-glass Photomask Blanks
[0446] Surfaces with three dimensional structures are required in
several fields of micro technology. Structures with sawtooth
profile (blaze) in the efficiency of DOE. Tapered structures offer
more flexibility in the design of micro-electronics and micro
mechanical components. Examples of 3D shaping using HEBS-glass gray
level masks and/or LDW-glass gray level masks are:
[0447] 1. Tapered structures for microelectronics, e.g. tapered
structures in thick polyimide to realize electrical connection two
metallic layers separated by the thick polyimide,
[0448] 2. Micro optical devices such diffractive and refractive
micro lenses, bifocal intraocular lenes, widely symmetric DOE,
miniature compact disc heads anti reflective surface complex
imaging optics grating couples, polarization, sensitive beam
splitter, spectral filters, wavelength division multiplexer,
element for head-up and helmet mounted display, for focal plane
optical concentration and optical efficiency enhancement, for color
separation beam shaping, and for miniature optical scanners,
microlens arrays, diffraction gratings, laser diode array
collimators and correctors, aberration correction, hybrid optics,
microprism arrays, micromirror arrays and Bragg gratings.
[0449] 3. Integrated optical components, two dimensional fanout
gratings, optical interconnect, signal switching, fiber pig
tailing, DOE to couple light from a laser into a fiber,
[0450] 4. Microelectrical-mechanical (MEM) devices for sensors and
actuators in automotive, machine tools, robotics and medical
instrumentation, also devices for applications micro valves,
inertial micro sensors, micro machined RF switches, GPS component
minaturization, and a host of other sensors and actuators for
applications to space, air, land, and sea vehicles, as well as
industrial, biotechnology and future consumer electronics,
[0451] 5. Micro-opto-electrical-mechanical (MOEM) devices such as
laser scanners, optical shutter, dynamic micro mirrors, optical
choppers and optical switches.
[0452] In the description which follows like elements are marked
throughout the specification and drawing with the same reference
numerals, respectively. Drawing figures showing actual physical
elements are not intended to be to scale.
[0453] Several types of micro-elements are required to be of a
three dimensional configuration which includes a variable surface
contour or geometry and which may be symmetric or non-symmetric.
Micro-optic devices such as micro-lenses, wave guides and computer
generated holograms, for example, often require a geometry which is
preferably a continuously curved surface or which has a profile of
continuously varying depth from a reference point Examples are
diffractive optical elements such as spherical micro-lenses,
Fresnel lenses and certain optical waveguide and coupling devices.
The fabrication of such elements may be carried out, generally,
using methodology similar to that used for the fabrication of very
large scale integrated circuits (VLSI) wherein a photoresist
material is placed on a substrate and is etched to produce a
replica of the micro-element, preferably to a finely detailed and
precise geometry. This precision geometry is particularly important
for micro-optic devices and micro-machines, for example.
[0454] Gray scale masks (also known as gray "level" masks) have
been developed, as mentioned hereinabove, to provide the necessary
surface contours of micro-elements, including micro-lens devices,
to replace the multi-step binary fabrication methods for these
devices. However, the shortcomings of prior art gray scale masks
mentioned hereinabove have inhibited the development of a method
for volume production of micro-optic elements and other
micro-elements. In accordance with this invention it has been
discovered that an improved gray scale mask suitable for use in the
fabrication of precise, highly efficient micro-optic elements can
be provided using, as the mask structure, glass plates which have
been composed to be sensitive to controlled electron beams to
generate a darkened image in the glass having a precise
configuration and having a substantially continuously varying light
transmissivity capability over a pre-determined area.
[0455] The present invention contemplates the provision of a gray
scale mask comprising a structure formed of a base glass such as a
low expansion zinc-boro-silicate glass or so-called white crown
glass. The base glass composition also contains alkali to
facilitate an ion exchange reaction which achieves the sensitivity
of the glass composition to high energy beams. After ion exchange
the glass material becomes alkali-free as a result of the ion
exchange process, which is typically carried out in an acidic
aqueous solution at temperatures above 320.degree. C. The base
glass composition comprises silica, metal oxides, nitrates, halides
and photo inhibitors. Typically, TiO.sub.2, Nb.sub.2 O.sub.5 or
Y.sub.2 O.sub.3 are used as photo inhibitors. The photo inhibitors
are used to dope silver-alkali-halide complex crystals, for
example. The (AgX).sub.m (MX).sub.n complex crystals are beam
sensitive and the doping process increases the energy band gap of
the otherwise photosensitive material.
[0456] The beam sensitive glass used in the present invention may
be of a type may be such as described in U.S. Pat. No. 5,078,771
issued Jan. 7, 1992 to Che-Kuang Wu, which is incorporated by
reference herein. Other glasses which are beam sensitive and which
may be used to fabricate a gray level mask in accordance with the
invention are described in U.S. Pat. No. 5,114,813 issued May 19,
1992 and U.S. Pat. No. 5,145,757 issued Sep. 8, 1992, both to
Steven W. Smoot, et al., which are also incorporated herein by
reference. However, the invention is not necessarily limited to the
particular glass compositions described hereinabove for fabrication
of the gray scale masks and other materials which are darkenable in
different degrees in accordance with the invention may be used.
[0457] Accordingly, a gray scale mask in accordance with the
present invention may be fabricated from a glass structure or
similar material comprising a relatively thin plate which, after
being drawn, ground and polished is treated in such a way that at
least one surface of the plate (or a similar glass article) becomes
effective to render the surface darkenable upon exposure to
electron beam radiation over at least a portion of the surface and
wherein the plate or article is preferably substantially not
alterable by or sensitive to actinic radiation. Preferably, the
gray scale mask article is exposed to a high energy beam, such as
an electron beam, preferably at an acceleration voltage of greater
than about 20 kV (kilovolts) whereby the necessary change in
transmissivity or optical density of the article is such that a
gray scale mask can be produced while maintaining good resolution
of the image produced on the glass.
[0458] Referring to FIGS; 21 and 22, and by way of example,
diagrams of the optical density or optical transmissivity of a gray
scale mask in accordance with the invention are illustrated showing
the variation in optical density for light of wavelengths between
about 350 nm (nanometers) and 550 nm for electron beam acceleration
voltages of 20 kV (FIG. 21) and 30 kV (FIG. 22) for electron charge
densities or "dosages" ranging from 0 to 367.mu.C/cm.sup.2
(micro-coulombs per centimeter squared). A writing current of about
25 nA (nanoamperes) was used in obtaining the data for FIGS. 21 and
22.
[0459] A gray scale mask comprising a glass article of a
composition in accordance with the teachings of U.S. Pat. No.
5,078,771 can be produced using a commercially available electron
beam writing device. These devices can be controlled to expose the
glass article, such as a plate, to an electron beam to generate
images of varying optical density wherein the image is generated on
a grid having grid spacings of about 0.1 mm, for example. The grid
spacings may be smaller if desired but the writing time is
increased accordingly. Larger grid spacings will tend to reduce
image resolution. The lower of the two acceleration voltages used
to generate the data in FIGS. 21 and 22 is preferable to minimize
the spreading of the darkened spacings on the grid by the electron
beam. Since the size of the interaction volume of the electron beam
with the glass material depends on the energy of the incident beam
the lowest acceleration voltage which still achieves a high enough
penetration depth for sufficient optical density is preferred. An
acceleration voltage of 20 kV produces enough penetration in the
glass material of a gray scale mask as described herein without
extending the electron trajectories unnecessarily in a way which
would result in the loss of image resolution. The operating
parameters of the beam writer or a similar device may be varied
with the particular beam sensitive material being used to fabricate
the gray scale mask and the values given herein are for an
exemplary embodiment of the invention.
[0460] Preparation of a glass plate utilizing the electron
beam-sensitive glass for generating the pre-determined gray scale
darkened areas preferably includes depositing a so-called grounding
layer of material on the surface of the glass. The purpose of this
layer is to avoid local electrical charging of the mask plate
during the electron beam writing process. A grounding layer in the
form of a layer of chromium of a thickness of about 10.0 nm may be
applied to the glass plate surface adjacent to the ion exchanged
surface layer of the glass containing the high concentration of
silver ions. The chromium grounding layer may be removed by wet
etching after the mask plate is darkened to the predetermined gray
level pattern desired.
[0461] In the fabrication of a diffractive optical element as well
as other micro-elements using a photoresist material on the surface
of a substrate and an etching process to develop the photoresist
and the substrate, a correlation must be obtained between the
electron charge density or dosage (in coulombs per centimeter
squared, for example) which will be applied to the gray scale mask
and the corresponding thickness of penetration of the photoresist
during the resultant exposure of the photoresist through the gray
level mask. FIG. 23 shows, by way of example, a calibration curve
for depth of penetration in a photoresist, such as a type OeBR-514
photoresist available from Olin-Ciba-Geigy Corporation, for
example, compared with electron beam charge density applied to the
mask grid spacings, respectively. In other words if a depth contour
in the substrate such as a diffractive optical element is to be
correlated with the thickness of a photoresist which is to be
altered by exposure through the gray level mask, then a
corresponding degree of darkening of the mask must be achieved and
the electron dosage which will achieve this darkening can be
correlated directly with the degree of penetration or exposure of
the photoresist. For the sake of discussion herein it will be
assumed that, if a large amount of exposure light is transmitted
through a particular mask to the photoresist, then the height of
the processed photoresist is limited and the thickness of the
micro-element produced in the etching process is correspondingly
small. If the amount of light transmitted through a particular mask
opening is small, then the height of the processed photoresist is
large and the corresponding thickness or height of the processed
substrate article is also correspondingly large. Photoresist
materials which, upon exposure to varying light intensities,
respond in the opposite manner upon processing, may, of course, be
used in conjunction with the method of the present invention.
[0462] In designing a surface profile for a particular diffractive
optical element, a particular number of evenly spaced depth levels
may be selected. For example, for a photoresist thickness of about
350 nm, thirty-two depth levels of penetration of light which will
alter the characteristics of the photoresist may be selected and
these different depth levels may then be correlated with a
particular electron beam dosage to cause the appropriate darkening
of the gray level mask. In other words, thirty-two different gray
levels are generated.
[0463] For the particular gray level mask discussed herein, an
acceleration voltage for the electron beam of 20 kV may be
selected, so as to avoid substantial exposure time of the beam at
each grid spacing. For the production of diffractive optical
elements such as spherical lenses having a focal length of about
4.4 mm and a lens size of about 100 m.times. 100 m a grid spacing
of about 0.1 m may be selected, for example. A photoresist having a
thickness of about 350-500 nm will produce a depth in the
micro-element substrate in the range of three to six times the
depth of the photoresist so that, for example, the substrate
profile may have a total depth of up to about 2100 nm, by way of
example. Again, by way of example, the design of the surface
profile is spaced out over thirty-two evenly spaced depth levels
over a 350 ran thickness range of the photoresist. With a grid
spacing of 0.1 m the different depth levels may then be written
into a computer program for controlling the electron beam writer in
a way wherein the program controls the writer to dwell for a
predetermined period of time at each grid spacing.
[0464] FIG. 24 illustrates a cross sectional profile for a
generally circular lens 9 having a hub portion 10, concentric
circumferential lens surfaces 12a, 12b, 12c and 12d and
corresponding concentric contoured lens surfaces 14a, 14b, 14 and
14d. These lens surfaces may be repeated at selected radii from the
hub portion 10 in accordance with known practices for spherical or
Fresnel lens design, for example. Referring to FIG. 25B, a portion
of the cross-sectional profile of the lens 9 is shown on a
processed photoresist layer 16 disposed on a substrate 18 of a
suitable light transmissive material, such as quartz glass, silica
glass or germanium to be used as the lens itself. Quartz glass is
used in an example described hereinbelow.
[0465] In FIG. 25B, the layer of photoresist 16 is shown with the
contour or profile of the lens 9 formed therein for the sake of
clarity. Accordingly, a portion of the hub 10 of lens 9 is
indicated at 10r, the contoured lens surface 14a is indicated at
14ar, the circumferential lens surface 12a is indicated at surface
12ar and the contoured surface 14b is indicated at 14br, for
example.
[0466] FIG. 25A is intended to be read in conjunction with FIG. 25B
and shows a portion of a grid 20 having the spacings mentioned
above and showing, for example, grid spacings 21, of equal area,
that is, squares of 0.1.mu.m, exemplary ones of which are shown
darkened to varying degrees to provide the thirty-two depth or
phase levels in the photoresist 16 and eventually in the lens 9. Of
course, the grid 20 exists only in the micro-processor which
controls the electron beam writer and the spacing of the writing
mechanism as it moves from one spacing 21 on the grid to the next
spacing and the electron beam is then generated to darken the
spacings, accordingly. Representative darkened grid spacings are
indicated at 22 defining the edge of the circumferential surface
12a, for example. Representative grid spacings 21 which have been
slightly darkened, as indicated at 24, show the contour of the
periphery of hub portion 10 of the lens as represented on the
contour of the etched photoresist 16. Darkened grid spacings
indicated at 25 define the edge or juncture of surfaces 12br and
14br, for example.
[0467] Accordingly, for a particular photoresist material, the
thickness of the photoresist which is to remain after exposure and
etching may be correlated with the electron beam dosage required to
darken a high energy beam-sensitive glass of the type described
herein and the contour or profile of a micro-optic element or other
micro-element may be correlated with the dosages or beam charge
density required for each subdivided space in a grid. The electron
beam writing device may be controlled to index to each of the
spaces 21 in the grid and apply a pre-determined electron beam
dosage to that space corresponding to the degree of darkening of
the gray level mask desired. Of course, the size of the grid spaces
may be varied, the acceleration voltage may be varied and the
electron beam charge density-may be varied depending on the
characteristics of the particular mask material and the photoresist
material being used.
[0468] Electron beam dosing of the gray scale mask plate at each of
the grid spacings 21 will darken the glass across the grid to
produce the gray levels desired. After removal of the
aforementioned electrical charge grounding layer no further
treatment of the gray scale mask is necessary, the gray levels are
visible and repairs or additional image configurations or other
features may be provided by additional writing operations with the
electron beam writer.
[0469] Fabrication of micro-elements, such as diffractive optical
elements, may then be carried out using a gray scale mask
fabricated in accordance with the description hereinabove. For
example, a gray scale mask 30 is shown in FIG. 26 comprising a
glass plate formed of a glass of the type described above and in
the patents referenced herein and which has been exposed to an
electron beam writer to generate gray level images of an array of
generally spherical micro-lenses, as indicated by the images 31 in
FIG. 26. These images are in the surface layer 30a facing surface
16a of the photoresist layer 16. The gray scale mask 30 may then be
brought into contact or close proximity with surface 16a of
photoresist 16 which is disposed on a quartz glass plate 18.
[0470] Equipment used in the production of micro-electronic devices
by exposure of photomasks to photoresist coated substrates may be
used to produce diffractive optical elements in accordance with
this invention. For example, the gray scale mask 30 may be placed
in contact with or close proximity to the layer of photoresist 16
in a commercially available aligner and the photoresist of the type
mentioned above is then exposed to light in a range of wavelengths
of 327 nm-400 nm, for example. The mask 30 may also be disposed
remote from the photoresist and the mask image projected onto the
photoresist using an optical imaging or scanning system.
Accordingly, photo reduction (demagnification) or photo enlargement
(magnification) of the image in the gray scale mask may be carried
out on photoresist, if desired.
[0471] Preparation of the substrate and photoresist, using a
photoresist of the type mentioned hereinabove (OeBr-514) or another
ultraviolet curable polymer may be carried out by spinning a layer
of photoresist onto the substrate at a speed of about 4,000 rpm,
for about 30 seconds, for example. A 0.8.mu.m thick layer applied
to a quartz glass substrate may be obtained and, the photoresist
coated substrate baked for about 30 minutes at 90.degree. C. prior
to exposure of the resist through the gray level mask.
[0472] After exposure of the photoresist 16 with the gray scale
mask 30, development of the photoresist may be carried out by
post-baking the resist for a predetermined period and at a
relatively low temperature so as to avoid reflow of the resist
during the post-baking procedure which might result in a degraded
profile of the micro-element. Alternatively, the photoresist may be
developed in a metal ion-free developer such as a type made by
Shipley Corporation. The photoresist-coated substrate may then be
subjected to a conventional etching process such as an ion beam
milling procedure. A Veeco Instruments Microtech 301-type milling
system may be used, for example.
[0473] The ion milling system may be modified to accommodate the
introduction of reactive gasses to provide chemically assisted ion
beam etching. Chemically assisted ion beam etching is advantageous
because it allows for the accurate control of the energy, number
and incidence angle of ions during the milling process. Moreover,
the amount of released reactive gas can be chosen freely which
allows for control of the q-factor. The q-factor is defined as the
substrate etch rate to the resist etch rate. Varying the q-factor
provides for varying the feature depth in the final micro-element
to fit a specific application. For example, in the fabrication of
diffractive optical elements, the feature depth in the final
configuration will be dictated by the specific application, wave
length of light to be terminated, the refractive index of the
substrate material, the refractive index of the surrounding
environment, or dimensional constraints on the substrate structure.
Variation in the amount of reactive gas, such as CHF.sub.3,
introduced into the etching system will allow a change in the
q-factor ranging from 1.8 to 4.3, for example. A higher q-factor is
usually necessary to achieve a high etch depth required for
elements transmitting longer wave-length light and also allows the
reduction in the resist thickness which will result in enhanced
resolution. Lower q-factors may be useful in achieving low feature
depth and high accuracy needed for reflection type optical
elements.
[0474] FIG. 27 illustrates a portion of the actual profile of a
micro-spherical lens substantially like lens 9 and fabricated in
accordance with the present invention wherein an overall height of
the lens profile in the range of about 2000-2100 nm was achieved.
The previously described technique was used to produce a 2.times.2
array of spherical lenses having an f number of nineteen and a
focal length of 96 mm. A gray scale mask was fabricated of a high
energy beam sensitive glass plate having a thickness of
approximately 90 mils. The mask was exposed in a Cambridge Model
EBMF 10.5 Electron Beam Writer which was controlled in accordance
with aforedescribed procedure to produce thirty-two discrete levels
of darkening of the mask in a predetermined pattern on 0.1.mu.m
spacing. The electron beam writer was controlled by a
computer-aided design program developed for the University of
California at San Diego to facilitate data generation necessary for
direct write procedures with the electron beam writer. Electron
beam charge density level for each depth or phase level in the
final etched element profile can be included in data files used to
operate the electron beam writer. This may be carried out by
changing the writing frequency for different areas of the produced
micro-element. Substrate material for the diffractive optical
elements was fused silica. The diffractive optical element was, in
particular, designed for an operational wavelength of 830 nm. The
optical efficiency of the lens produced showed a 94% efficiency
which is comparable to an efficiency measurement taken for a
substantially identical lens fabricated by direct write
methods.
[0475] A 10.times.10 array of spherical lenses of 100 mm by 100 mm
size, an f number of 3.10 and a focal length of 4.4 mm was also
fabricated using the above mentioned process for fabrication of the
gray scale mask and the subsequent fabrication of the optical
elements utilizing chemically assisted ion beam etching to transfer
the resist profile into a quartz glass substrate.
[0476] As mentioned previously, a gray scale mask in accordance
with the present invention may be advantageously used for mass
production of diffractive optical elements, computer generated
holograms and other micro-elements in a step and repeat fabrication
system. In particular, a relatively large substrate member,
suitably coated with photoresist may be exposed through a gray
scale mask, such as the mask 30 in a commercially available aligner
of a demagnification type or a contact type wherein the geometry of
plural diffractive optical elements may be imprinted on the
photoresist, the substrate member may be moved relative to the gray
scale mask and the exposure step repeated so that a large array of
micro-elements is imprinted on the photoresist step by step. This
relatively large array of micro-elements may then be fabricated in
a batch by a chemically assisted ion beam etching process, as
described above, to transfer the geometry of the-micro-elements in
the photoresist to the substrate member. Step and repeat or
so-called stepper processes may, thus, be carried out with gray
scale masks in accordance with the invention. Accordingly, the
manufacture of various types of micro-elements as described herein,
may be more efficiently and economically carried out.
[0477] Although preferred embodiments of the present invention have
been described in detail herein, those skilled in the art will
recognize that various substitutions and modifications may be made
to the invention without departing from the scope and spirit of the
appended claims.
* * * * *