U.S. patent application number 09/386358 was filed with the patent office on 2002-01-17 for optical article, exposure apparatus or optical system using it, and process for producing it.
Invention is credited to HARADA, KAZUYUKI, OHMI, TADAHIRO, TANAKA, NOBUYOSHI.
Application Number | 20020006713 09/386358 |
Document ID | / |
Family ID | 12138323 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020006713 |
Kind Code |
A1 |
OHMI, TADAHIRO ; et
al. |
January 17, 2002 |
OPTICAL ARTICLE, EXPOSURE APPARATUS OR OPTICAL SYSTEM USING IT, AND
PROCESS FOR PRODUCING IT
Abstract
An optical article is formed in such structure that an optical
thin film is laminated on a surface of a substrate and that the
optical thin film comprises atoms of at least one selected from the
group consisting of krypton, xenon, and radon. An exposure
apparatus has a plurality of optical articles as described above in
an illumination optical system and/or a projection optical
system.
Inventors: |
OHMI, TADAHIRO; (MIYAGI-KEN,
JP) ; HARADA, KAZUYUKI; (TOKYO, JP) ; TANAKA,
NOBUYOSHI; (TOKYO, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
12138323 |
Appl. No.: |
09/386358 |
Filed: |
August 31, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09386358 |
Aug 31, 1999 |
|
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08598807 |
Feb 9, 1996 |
|
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5981075 |
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Current U.S.
Class: |
438/484 |
Current CPC
Class: |
C23C 14/10 20130101;
G02B 1/115 20130101; C23C 14/081 20130101; C23C 14/0694 20130101;
C23C 14/083 20130101 |
Class at
Publication: |
438/484 |
International
Class: |
H01L 021/36 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 1995 |
JP |
7-24444 |
Claims
What is claimed is:
1. An optical article in which an optical thin film is laminated on
a surface of a substrate, wherein said optical thin film comprises
atoms of at least one selected from the group consisting of
krypton, xenon, and radon.
2. An optical article in which an antireflection film comprising a
first optically transparent thin layer and a second optically
transparent thin layer having a higher refractive index than that
of said first optically transparent thin layer are formed on a
surface of an optically transparent substrate, wherein at least
either one of said first and second optically transparent thin
layers comprises atoms of at least one selected from the group
consisting of krypton, xenon, and radon.
3. The optical article according to claim 2, further comprising a
third optically transparent thin layer having a refractive index
different from those of said first and second optically transparent
thin layers.
4. The optical article according to claim 2, wherein said first
optically transparent thin layer comprises silicon oxide.
5. The optical article according to claim 2, wherein said second
optically transparent thin layer comprises aluminum oxide.
6. The optical article according to claim 2, wherein said second
optically transparent thin layer comprises tantalum oxide.
7. The optical article according to claim 2, wherein a content of
said atoms in said optically transparent thin layer is not more
than 5 atomic %.
8. The optical article according to claim 2, wherein contents of
said atoms in said first and second optically transparent thin
layers are different from each other.
9. The optical article according to claim 2, wherein said substrate
comprises either silica or fluorite.
10. The optical article according to claim 2, which selectively
transmits excimer laser light.
11. An optical article in which a reflection-enhanced film
comprising a first optically transparent thin layer and a second
optically transparent thin layer having a higher refractive index
than that of said first optically transparent thin layer are formed
on a surface of a substrate, wherein at least either one of said
first and second optically transparent thin layers comprises atoms
of at least one selected from the group consisting of krypton,
xenon, and radon.
12. The optical article according to claim 11, further comprising a
third optically transparent thin layer having a refractive index
different from those of said first and second optically transparent
thin layers.
13. The optical article according to claim 11, wherein said first
optically transparent thin layer comprises silicon oxide.
14. The optical article according to claim 11, wherein said second
optically transparent thin layer comprises aluminum oxide.
15. The optical article according to claim 11, wherein said second
optically transparent thin layer comprises tantalum oxide.
16. The optical article according to claim 11, wherein a content of
said atoms in said optically transparent thin layer is not more
than 5 atomic %.
17. The optical article according to claim 11, wherein contents of
said atoms in said first and second optically transparent thin
layers are different from each other.
18. The optical article according to claim 11, wherein said
substrate comprises either silica or fluorite.
19. The optical article according to claim 11, which selectively
reflects excimer laser light.
20. An exposure apparatus having an illumination light source and a
stage for an exposed object to be mounted thereon, in which an
illumination optical system and/or a projection optical system
comprises a plurality of optical articles in each of which a first
optically transparent thin layer and a second optically transparent
thin layer having a higher refractive index than that of said first
optically transparent thin layer are laminated on a surface of a
substrate, wherein at least either one of said first and second
optically transparent thin layers comprises atoms of at least one
selected from the group consisting of krypton, xenon, and
radon.
21. The exposure apparatus according to claim 20, wherein said
illumination light source is an excimer laser light source.
22. The exposure apparatus according to claim 20, wherein said
optical article has a property to selectively transmit a plurality
of laser light beams of different wavelengths from each other.
23. A process for producing an optical article in which a first
optically transparent thin layer and a second optically transparent
thin layer having a higher refractive index than that of said first
optically transparent thin layer are laminated on a surface of a
substrate, wherein at least either one of said first and second
optically transparent thin layers is deposited by sputtering using
a sputtering gas comprising atoms of at least one selected from the
group consisting of krypton, xenon, and radon.
24. The process for producing the optical article according to
claim 23, wherein a gas for oxidation is used as a reaction gas in
addition to said sputtering gas.
25. The process for producing the optical article according to
claim 23, wherein said substrate is held at 100.degree. C. or less
in said sputtering.
26. The process for producing the optical article according to
claim 23, wherein before said sputtering at least a film-forming
surface of said substrate is held at 100.degree. C. or less under a
nitrogen gas atmosphere.
27. An optical system having a plurality of lenses in each of which
an optical thin film comprising atoms of at least one selected from
the group consisting of krypton, xenon, and radon is formed on a
surface of an optically transparent substrate.
28. An optical system having a mirror in which an optical thin film
comprising atoms of at least one selected from the group consisting
of krypton, xenon, and radon is formed on a surface of a
substrate.
29. A process for producing a semiconductor device, using the
exposure apparatus of claim 20 to effect exposure of a resist
pattern corresponding to a wiring or electrode pattern having a
minimum line width of 1 .mu.m or less.
30. The process for producing the semiconductor device according to
claim 29, wherein an excimer laser is used as an exposure light
source.
31. A process for producing a semiconductor device, comprising
steps: using the exposure apparatus of claim 20 to partially expose
a photosensitive coating on a substrate, leaving only a coating
pattern of exposed portions or non-exposed portions as an etching
mask, and etching the surface of the substrate exposed through said
etching mask.
32. The process for producing the semiconductor device according to
claim 31, wherein an excimer laser is used as an exposure light
source.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention concerns an optical article such as a
lens or a mirror, an exposure apparatus or optical system such as a
stepper having it, and a process for producing the optical article.
More particularly, the invention relates to an optical thin film
for optical article suitably applicable to an exposure apparatus or
optical system using an excimer laser, and a process for producing
it.
[0003] 2. Related Background Art
[0004] Optical articles, including lenses, mirrors, and optical
filters, are used, for example, in optical apparatus such as
cameras, telescopes, and microscopes. These optical articles have
an antireflection film or a reflection-enhanced film on the surface
thereof for prevention of reflection or for enhancement of
reflection.
[0005] An exposure apparatus is a kind of an optical apparatus
equipped with such an optical article. The exposure apparatus is
used in the fabrication steps of semiconductor integrated circuits
or photomasks for fabricating them. A typical example of the
exposure apparatus in this field is an exposure apparatus as called
a stepper.
[0006] An illumination light source in such exposure apparatus,
conventionally used, was a super-high pressure mercury lamp, a
xenon-mercury arc lamp, or the like for emitting the g-line (435.8
nm), the h-line (404.7 nm), and the i-line (365 nm). However,
attempt has recently been made to use lasers emitting
far-ultraviolet rays (200 to 260 nm) or emitting a beam of high
power and narrow spectral width in order to realize high exposure
processing capability per unit time (throughput) and uniform
illumination characteristics on an exposed body such as a wafer.
Among others an excimer laser is one of desirable light sources,
because it emits light in very narrow spectral width and at high
output power.
[0007] One of known optical articles for excimer laser is the one
having an antireflection film deposited by vacuum vapor deposition
as disclosed in Japanese Laid-open Patent Application No. 63-113501
or Japanese Laid-open Patent Application No. 63-113502.
[0008] However, for example, if a lens having sufficient optical
characteristics in the optical system for visible light was used in
an optical system for excimer laser, it was sometimes difficult to
maintain optical characteristics enough to be applied to practical
use. Specifically speaking, transmission characteristics,
particularly, of the optical thin film provided over the surface of
lens or mirror were not sufficient to make the best use of the
advantages of excimer laser, and there was a problem in durability
thereof.
[0009] In addition, since the optical articles for exposure
apparatus were required to have a surface formed at very high
accuracy, strict control of temperature condition was necessary in
forming the optical thin film. Thus, film forming techniques
generally regarded as preferable were not able to be used as they
were in fabricating such optical articles.
[0010] As explained above, in order to fabricate an optical article
durable against use of excimer laser, the optical article must be
designed based on a novel idea and a novel approach.
SUMMARY OF THE INVENTION
[0011] The present invention has been accomplished in view of the
technical problems as discussed above, and an object of the
invention is to provide an optical article having optical
characteristics fully durable against such hard operation
conditions as in applications with excimer laser.
[0012] Another object of the present invention is to provide an
optical article with an optical thin film having little unnecessary
light absorption and having uniform physical properties over a
large area.
[0013] Still another object of the present invention is to provide
an optical article with an optical thin film which can be formed at
low temperature and which is free from the negative effect of
stress such as film separation.
[0014] A further object of the present invention is to provide an
optical system and an exposure apparatus having the above optical
article excellent in characteristics.
[0015] Of course, the one durable to the excimer laser must exhibit
adequately good characteristics also in optical systems using the
other light.
[0016] The optical article of the present invention is an optical
article in which an optical thin film is laminated on a surface of
a substrate, wherein the optical thin film comprises atoms of at
least one selected from the group consisting of krypton, xenon, and
radon.
[0017] The optical article of the present invention is an optical
article in which an antireflection film comprising a first
optically transparent thin layer and a second optically transparent
thin layer having a higher refractive index than that of the first
optically transparent thin layer are formed on a surface of an
optically transparent substrate, wherein at least either one of the
first and second optically transparent thin layers comprises atoms
of at least one selected from the group consisting of krypton,
xenon, and radon.
[0018] Further, the optical article of the present invention is an
optical article in which a reflection-enhanced film comprising a
first optically transparent thin layer and a second optically
transparent thin layer having a higher refractive index than that
of the first optically transparent thin layer are formed on a
surface of a substrate, wherein at least either one of the first
and second optically transparent thin layers comprises atoms of at
least one selected from the group consisting of krypton, xenon, and
radon.
[0019] The optical article of the present invention may be adaptive
to the arrangement further having a third optically transparent
thin layer having a different refractive index from those of the
first and second optically transparent thin layers. The first
optically transparent thin layer is preferably silicon oxide, and
the second optically transparent thin layer is preferably aluminum
oxide or tantalum oxide. The content of the atoms of the selected
element in the optically transparent thin layer is not more than 5
atomic %, and the contents of the element in the first and second
optically transparent thin layers are different from each other.
The article is characterized in that the substrate comprises silica
or fluorite. Further, the optical article of the present invention
is characterized in that it selectively transmits or reflects the
excimer laser light.
[0020] The exposure apparatus of the present invention is an
exposure apparatus having an illumination light source and a stage
for an exposed object to be mounted thereon in which an
illumination optical system and/or a projection optical system
comprises a plurality of optical articles in each of which a first
optically transparent thin layer and a second optically transparent
thin layer having a higher refractive index than that of the first
optically transparent thin layer are laminated on a surface of a
substrate, wherein at least either one of the first and second
optically transparent thin layers comprises atoms of at least one
selected from the group consisting of krypton, xenon, and radon.
The apparatus is characterized in that the illumination light
source is an excimer laser light source. Further, the apparatus is
characterized in that the optical article has a characteristic to
selectively transmit a plurality of laser light beams of different
wavelengths from each other.
[0021] The process for producing the optical article of the present
invention is a process for producing an optical article in which a
first optically transparent thin layer and a second optically
transparent thin layer having a higher refractive index than that
of the first optically transparent thin layer are laminated on a
surface of a substrate, wherein at least either one of the first
and second optically transparent thin layers is deposited by
sputtering using a sputtering gas comprising atoms of at least one
selected from the group consisting of krypton, xenon, and radon.
The process is characterized in that a gas for oxidation is used as
a reaction gas in addition to the sputtering gas. Further, it is
preferred that the substrate be held at 100.degree. C. or less in
the sputtering and that before the sputtering at least a
film-forming surface of the substrate be held at 100.degree. C or
less under a nitrogen gas atmosphere.
[0022] The present inventors have accomplished the present
invention by finding out that, as compared with films not
containing krypton, xenon, or radon, obtained by vacuum vapor
deposition or sputtering with Ar gas, films containing atoms of at
least one of these three elements can maintain good transmittances
for a longer period.
[0023] The invention can provide the optical article having the
optical thin film which is less in unnecessary light absorption,
uniform over a large area, free of film separation, and excellent
in durability.
[0024] The invention can provide the optical article having
excellent transmission characteristics of light used, because the
optical thin film is used as an antireflection film.
[0025] The invention can provide the optical article having
excellent reflection characteristics of light used, because the
optical thin film is used as a reflection-enhanced film.
[0026] The invention can achieve the optical article having better
transmittance stability, and particularly having excellent
applicability to the excimer laser optical system.
[0027] The invention can achieve the optical article having better
transmittance stability, and particularly having excellent
applicability to the i-line optical system.
[0028] The invention makes a non-monocrystalline film finer and
reduces degradation of transmission characteristics more by the
feature that the content of xenon, krypton, or radon is not more
than 5 atomic %.
[0029] The invention improves adhesion and enhances the
antireflection or reflection-enhancing effect.
[0030] The invention can provide an excellent excimer laser optical
system.
[0031] The invention can provide an excellent excimer laser
reflection optical system.
[0032] The invention hardly causes an error in exposure parameters,
and it enables good photolithography and enhances reliability.
[0033] The invention enables high-definition and high-accuracy
photolithography.
[0034] The invention enables automatic alignment with high accuracy
and high reliability.
[0035] The invention enables formation of uniform plasma, whereby
the optical article with uniform characteristics and in a large
area can readily be produced at the low temperature of not more
than 150.degree. C., preferably not more than 100.degree. C.
[0036] The invention has the feature that the gas having the
oxidation effect is introduced as a reaction gas, which enables to
obtain an oxide film with more excellent characteristics in a
stoichiometric composition or in a composition very approximate
thereto, even though it is a non-monocrystalline film.
[0037] The invention can suppress a change of the surface shape of
the optical article. Further, gas emission becomes less during
formation of film, which can suppress occurrence of film separation
or unnecessary products.
[0038] The invention can suppress gas emission during formation of
film by exposing the substrate to the nitrogen gas atmosphere
before sputtering.
[0039] The invention can provide an optical system having excellent
transmission characteristics of light used.
[0040] The invention can provide an optical system excellent in
reflection characteristics of light used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIGS. 1A to 1F are diagrammatic, sectional views of optical
articles, each having an optical thin film;
[0042] FIG. 2 is a diagrammatic drawing to show a basic setup of a
producing apparatus used for forming the optical thin film of the
present invention;
[0043] FIG. 3 is an example of a graph to show changes of
reflectivity against ion irradiation energy in the present
invention;
[0044] FIG. 4 is a schematic drawing to show a setup of the
exposure apparatus of the present invention;
[0045] FIG. 5 is a diagrammatic, sectional view to show an example
of the optical article used in the exposure apparatus of the
present invention;
[0046] FIG. 6 is a schematic drawing of a sputtering apparatus in
Example 1;
[0047] FIG. 7 is a diagrammatic drawing to show a chamber of
another producing apparatus used for forming the optical thin film
of the present invention;
[0048] FIG. 8 is a graph to show energy distributions of ions
impinging on a substrate surface earthed, against frequency of
high-frequency power supplied to a target;
[0049] FIG. 9 is a graph to show relations between sputter rate and
energy of Ar ions and Xe ions according to the present invention,
incident to the Si target;
[0050] FIG. 10 is a graph to show time changes of water molecule
layers on a lens surface according to the present invention;
[0051] FIG. 11 is a schematic drawing to show a clean nitrogen
supply system according to the present invention;
[0052] FIG. 12 is a graph to show a change of transmittance with
time according to Example 1;
[0053] FIG. 13 is a graph to show transmittance stability according
to Example 2;
[0054] FIG. 14 is a graph to show transmittance stability according
to Example 3;
[0055] FIG. 15 is a graph to show transmittance stability according
to Example 4;
[0056] FIG. 16 is a diagrammatic, sectional view to show a layer
structure of the optical thin film according to Example 7;
[0057] FIG. 17 is a graph to show reflection characteristics of the
optical thin film according to Example 7;
[0058] FIG. 18 is a graph to show a time change of transmittance of
the optical thin film according to Example 7;
[0059] FIG. 19 is a diagrammatic, sectional view to show a layer
structure of the optical thin film according to Example 8;
[0060] FIG. 20 is a graph to show reflection characteristics of the
optical thin film according to Example 8;
[0061] FIG. 21 is a graph to show a time change of transmittance of
the optical thin film according to Example 8;
[0062] FIG. 22 is a graph to show a time change of reflectivity of
the optical thin film according to Example 9;
[0063] FIG. 23 is a graph to show transmittance stability according
to Example 10; and
[0064] FIG. 24 is a flowchart to show fabrication steps of IC,
using the exposure apparatus of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0065] The embodiments of the present invention will be explained
with reference to the drawings. It should be noted that the present
invention is by no means limited to these embodiments, but the
present invention may have various modifications and arrangements
including replacement of constituent elements into substitutes or
equivalents or change of materials employed, as long as the object
of the present invention can be achieved. (Optical articles in
which the optical thin film is laminated on the surface of
substrate)
[0066] FIGS. 1A-1F are diagrammatic cross sections of optical
articles having various optical thin films according to an
embodiment of the present invention.
[0067] FIG. 1A shows a transmission type optical article in which
an antireflection film 2 is formed on the surface of a transparent
substrate 1, which is used as a lens or a light transmitting
window.
[0068] The antireflection film 2 may be a single thin layer film or
a laminate structure of optically transparent thin layers having
mutually different refractive indices as shown in FIG. 1B. Here,
the thin film 2H is a high-index thin layer and the thin film 2L is
a low-index thin layer. The low-index thin layer is disposed on the
surface (air) side, thereby giving the antireflection effect.
[0069] FIG. 1C shows a structure in which two optically transparent
thin layers with mutually different refractive indices are
alternately laminated two layers each (in four layers in
total).
[0070] FIG. 1D shows a structure having three types of optically
transparent thin layers with mutually different refractive indices
and one low-index thin layer. This example employs the high-index
thin layer 2H, the low-index thin layer 2L, and the thin layer 2M
having an intermediate refractive index between them.
[0071] FIG. 1E shows a structure in which two optically transparent
thin layers with mutually different refractive indices are
alternately laminated three layers each (in six layers in
total).
[0072] FIG. 1F shows an optical article having a
reflection-enhanced film 4 on either an optically transparent or a
non-transparent substrate 3, and the reflection-enhanced film 4 is
formed in a laminate structure of optically transparent thin layers
with mutually different refractive indices. In this example
reflection is enhanced by placing the high-index thin layer 4H on
the surface side. Symbol 4L represents the low-index thin layer.
Although not shown, the reflection-enhanced film 4 may be a
laminate structure of repetitive multiple layers (for example, 10
to 100 layers) of the thin layer 4L and thin layer 4H.
[0073] Materials for the substrate 1, 3 and for the thin layers are
properly selected depending upon the wavelength of light used and
the structure of the optical thin film. The same can be applied to
the thickness of substrate 1, 3 and the thicknesses of the
respective thin layers. The thickness of each thin layer is
selected in the range of about 0.1 nm to 1 .mu.m.
Substrate
[0074] A material for the substrate 1 in the present invention may
be an optically transparent substrate, for example such as fused
silica (SiO.sub.2) or fluorite (CaF.sub.2). The material may
contain a small amount of an adjusting material for adaptation for
the light used. Specifically, the material may contain
B.sub.2O.sub.3, Na.sub.2O, K.sub.2O, PbO, or Al.sub.2O.sub.3 in
addition to the main ingredient of SiO.sub.2. The substrate 3 for
the reflection-enhanced film such as a mirror may be a substrate
formed by putting a high-reflection metal film on the optically
transparent surface as described above, or a metal.
Transparent thin layers
[0075] Materials for the optically transparent thin layers for
constituting the optical thin film in the present invention are
properly selected from the same group including the following
materials either in the case of the antireflection film 2 or in the
case of the reflection-enhanced film 4. The materials included in
the group are, for example, non-monocrystalline oxides including
silicon oxide (1.44), tantalum oxide (2.17), aluminum oxide (1.72),
zirconium oxide (2.25), hafnium oxide (2.25), yttrium oxide (2.10),
and scandium oxide (2.11), and non-monocrystalline fluorides
including magnesium fluoride (1.43), neodymium fluoride (1.66),
calcium fluoride (1.46), lithium fluoride (1.37), sodium aluminum
fluoride (1.35), thorium fluoride (1.59), and lanthanum fluoride
(1.59). The numerals in the parentheses are examples of refractive
indices at the light of wavelength 248 nm corresponding to the KrF
excimer laser.
Atoms which the optical thin film contains
[0076] The atoms which the optical thin film in the present
invention contains were found out through many repetitive
experiments by the inventors.
[0077] If an optical article used in the excimer laser optical
system should have even a little quantity of absorption of laser
light, heat would be generated because of its high power and the
heat would be accumulated while used. It was found that the heat
could degrade the surface property of the optical article and could
degrade the optical transparency of the optical thin film.
[0078] The inventors found that when the optical thin film
contained the atoms in the present invention as a countermeasure,
light absorption of the optical thin film became nearly zero. When
a lot of lenses were combined to form an optical system, it became
possible to make even overall light absorption almost zero. Use of
such an optical article remarkably improved reliability of the
exposure apparatus.
[0079] The optical thin film used in the present invention is a
non-monocrystalline thin film containing atoms of at least one
selected from the group consisting of xenon (Xe), krypton (Kr), and
radon (Rn). When the optical thin film is constructed of many thin
layers, a necessary condition is that at least one thin layer out
of them contains the above atoms. Among others, the effect is
remarkable when the thin film is made of an oxide. When the thin
film contains the above atoms in the content not exceeding 5 atomic
%, packing of the amorphous film is improved to achieve excellent
durability. More preferably, the content is not more than 3 atomic
%, and most preferably, not more than 1 atomic %. The optimum
minimum value of the content is 0.5 atomic ppm. In the case where
the optical thin film is made of a lot of thin layers, a preferred
arrangement is such that contents of the above atoms in the
respective films are made different from each other, which enhances
adhesion to each other. If the film contains two or more out of the
above three elements, the total content is to be controlled below
10 atomic %, whereby packing of the amorphous film can be improved
so as to achieve excellent durability. The contents of these
elements can be measured by the Rutherford backscattering analysis
(RBS), the secondary ion mass spectrometry (SIMS), or the total
reflection fluorescence X-ray diffractometry.
[0080] Further, if the thin layer contains the above three
elements, it is more preferred in order to obtain a good-quality
film that the content of argon (Ar), helium (He), or neon (Ne) be
controlled to be not more than 0.1 atomic %.
Light used in the Optical System to Which the Optical Article is
Applied
[0081] The light used in the optical system to which the optical
article of the present invention is applied is ultraviolet light
such as the i-line, far-ultraviolet light, or laser light. Lasers
for emitting such light are, for example, He--Cd laser (442 nm),
Ar.sup.30 laser (488 nm, 515 nm), He--Ne laser (544 nm, 633 nm),
and semiconductor laser (780 nm).
[0082] Particularly, the optical article of the present invention
is suitable for optical systems of the i-line or excimer lasers,
and among others, it is most suitable for excimer laser optical
systems. Excimer lasers include, for example, those of F.sub.2 (157
nm), ArF (193 nm), KrCl (222 nm), KrF (248 nm), ClF (284 nm), XeCl
(308 nm), I.sub.2 (342 nm), and XeF (351 nm, 353 nm). Among them
the KrF excimer laser, XeCl laser, or ArF excimer laser may be
suitably applicable to the exposure apparatus.
[0083] More desirably, the optical article also has good
transmission characteristics for light of a relatively long
wavelength such as He--Ne laser for alignment in addition to the
above excimer lasers for exposure. Such an optical article can be
applied to the exposure apparatus employing the TTL (Through The
Lens) alignment method by which high-accuracy alignment can be made
by letting alignment light pass through a projection optical
system. Thus, the range of applications can be further widened,
which is more preferable.
Production Method and Producing Apparatus)
[0084] Below described are the production process and producing
apparatus for producing the optical thin film containing the atoms
of at least one selected from the group consisting of xenon (Xe),
krypton (Kr), and radon (Rn).
[0085] The production process of the optical thin film used in the
present invention may be chemical vapor deposition (CVD) or
physical vapor deposition (PVD) using the above rare gas. From the
finding of the inventors, it is desired to deposit at least one of
the thin layers forming the optical thin film by sputtering with a
sputtering gas containing atoms of at least one selected from the
group consisting of krypton, xenon, and radon.
[0086] FIG. 2 is a diagrammatic drawing to show a basic layout of
the producing apparatus of the optical thin film used in the
present invention. The producing apparatus has a film-forming
chamber 12 in which sputtering is carried out, a load-lock chamber
13 which is provided if necessary and which is a preparation
chamber for a film-forming substrate 1 to be carried into or out of
the chamber 12 and for the substrate 1 to be kept in, an exhaust
means 14, and a gas supply means 15. Inside the film-forming
chamber 12 there are a target 12a, a substrate holder 12b, a magnet
12c, and electrodes 12d disposed, and the electrode 12d is
connected to a high-frequency power supply. A gate valve 13a is set
between the load-lock chamber 13 and the film-forming chamber 12 to
separate atmospheres of these two chambers from each other.
[0087] The exhaust means 14 is at least one properly selected from
various pumps including a turbo molecular pump, a cryo-pump, a
mechanical booster pump, and an oil diffusion pump, as installed
together with a valve and pipes.
[0088] The gas supply means is composed of a gas bomb for storing
either krypton, xenon, or radon, a valve, a gas flow controller,
and pipes. Of course, the apparatus may be arranged to supply an
oxidizing gas such as oxygen if necessary.
[0089] Production procedures are as follows. A substrate set in the
load-lock chamber 13 is carried into the chamber 12 as opening the
gate valve 13a and is set on the holder 12b in the chamber 12. The
substrate may be heated in the temperature range not exceeding
100.degree. C. under a nitrogen atmosphere with necessity in the
load-lock chamber 13.
[0090] Then the gate valve 13a is closed and the chamber 12 is
evacuated. After that, krypton or xenon is supplied as a gas for
sputtering. Of course, a reaction gas such as oxygen is further
supplied if reactive sputtering is carried out. Power of radio
frequency is supplied to the electrode 12d to generate glow
discharge plasma of the above rare gas. In this arrangement, the
constituent atoms of the target 12a are beaten and driven out
therefrom by the rare gas, thereby depositing over the substrate
surface. In order to avoid a change of the surface shape on this
occasion, it is desired to control the substrate temperature so as
not to exceed 100.degree. C. due to the plasma by providing the
holder 12b with a heating and cooling means and a temperature
sensor. Such a controller may be omitted, of course, if the
temperature does not exceed 100.degree. C. even without
cooling.
[0091] If the optical thin film is made of two or more types of
thin layers, the above steps are repeated as changing the target
materials. An arrangement for improving the throughput is such that
a plurality of targets are disposed in one chamber and a target to
be exposed to the plasma is selected. Another arrangement may be
such that a plurality of film-forming chambers are prepared
independently of each other and each chamber is dedicated for film
formation of one thin layer.
[0092] In order to control an amount of krypton, xenon, or radon
contained in the thin layer, attention must be paid to keep the
content not more than 5 atomic % by controlling a supply amount of
gas, the temperature of substrate, and the pressure upon formation
of film. A method for forming the thin film of oxide may be
reactive sputtering using a target of a pure metal such as aluminum
or tantalum and oxygen as a reaction gas, or simple sputtering with
an oxide target. A preferred process is reactive sputtering which
is carried out with a target of an oxide as supplying oxygen gas
together with the above rare gas.
[0093] Sputtering using the above rare gas can generate a large
plasma region having a uniform energy distribution and also improve
an energy dependence of film quality. FIG. 3 is an example of graph
to show changes of reflectivity against ion irradiation energy,
which confirms that the thin film exhibits excellent transmittances
(low reflectivities) in a wide region of energy. It is seen that
the film from 100% argon can exhibit good transmittances only in a
very limited range. This result means that reproducibility of film
formation is good and adjusting ranges of parameters upon film
formation become wide, thus facilitating film formation.
[0094] Conditions employed in the sputtering of the present
invention are as follows.
[0095] The pressure during sputtering may be one that can stably
maintain discharge, specifically between 1 and 5 mTorr.
[0096] A value of the RF power may be selected so as not to damage
the thin layer and so as to be capable of removing adsorbed
impurities, specifically between 5 W and 50 W. From the same
reason, an appropriate time is between 1 minute and 20 minutes.
[0097] The rare gas for sputtering may be not only one of Kr, Xe,
and Rn atoms, but also a mixture gas thereof or a mixture gas with
Ar, He, or Ne. Any volume ratio may be applied in the case of the
mixture gas of Kr, Xe, and Rn, but a preferred example is a volume
ratio of Xe:Kr=1:1. When mixed with Ar, He, or Ne, these atoms had
better be controlled in an amount less than the gas of Kr, Xe, or
Rn in order to prevent excessive atoms from being taken into the
thin layer.
[0098] As the frequency of applied power becomes lower, a self bias
of the target becomes greater in the negative region. In that case,
the sputter rate increases, but, on the other hand, variations
appear in irradiation energy. Thus, an appropriate range is between
10 MHz and 500 MHz.
[0099] According to another experiment of the inventors, when a
non-transparent film of silicon (Si) or aluminum (Al) was formed by
sputtering and when sputtering was carried out using Xe, no content
of Xe was recognized in a Si film or Al film deposited. This is in
contrast with the fact that Ar is readily taken into the film in
sputtering with Ar.
[0100] Accordingly, in order to form the optical thin film in which
the atoms of Xe, Kr, or Rn are contained in the range of not more
than 5 atomic t using the sputtering process of the present
invention, preferred conditions are such that the substrate
temperature is set at a relatively low temperature, the frequency
of power for generating the plasma is set relatively low, and
deposition is effected at a relatively slow deposition rate under a
mixture atmosphere with oxygen gas. Specific setting values will be
described later. This permits a fine amount of Xe, Kr, or Rn to be
taken into the transparent optical thin film.
[0101] Mixture of oxygen in these gases is preferred even in
formation of a metal oxide. This has an effect to restore the metal
oxide damaged, by oxidizing bonds at broken bonding for the metal
oxide from the target. A preferred rate of oxygen is not more than
20 volume % to the rare gas. Too much oxygen makes the film-forming
rate extremely lower and decreases the effect of surface activity
by the rare gas ions, which does not permit a fine film to be
formed. In the case where the target is a metal and a film of a
metal oxide is formed, an amount of oxygen to the rare gas becomes
greater than in the case of the metal oxide target. However, the
method using the target of a high-purity metal oxide and partially
reinforcing weak portions by oxidation is more preferred rather
than the method for forming the metal oxide by oxidizing a metal on
a lens, and can form a fine film with little damage.
[0102] Next described is another example of the producing apparatus
of the optical thin film used in the present invention.
[0103] This apparatus is a sputtering apparatus capable of
supplying deposit atoms as controlling energy of ions impinging on
the lens surface.
[0104] The apparatus of FIG. 6 is an rf-dc combination type bias
sputtering apparatus. In FIG. 6, numerals 91, 911 designate vacuum
chambers, wherein 911 is a load-lock chamber. Numeral 920 is a lens
stocker which is connected to the load-lock chamber and in which
clean N.sub.2 always flows. Numeral 912 denotes a halogen lamp,
which enables pre-heating in the load-lock chamber 911. Numeral 92
denotes a target, 93 a magnet for generating the plasma with good
efficiency, and 94 a convex lens mounted on a lens support member
1002 by lens stopper, and this lens support member is mounted on a
lens holder. This lens holder has a rotating system. Numeral 96
represents a high-frequency power supply arranged capable of
changing the frequency, 97 a matching circuit, 98 a DC power supply
for determining the DC potential of the target, and 100 a low-pass
filter of the target. Although not shown, a second high-frequency
power supply may be provided on the lens side to control the energy
or the like of ions impinging on the lens with better accuracy. In
this example, the lens holder is made of SUS 316, and the potential
is the floating potential.
[0105] The vacuum chambers 91, 911, 920 are made of a material with
less gas emission, for example of SUS 316. The inside surfaces of
the chambers are surfaces subjected to electropolishing or
electrochemical buffing as a surface treatment and mirror-finished
in the smoothness of surface Rmax <0.1 .mu.m, and a passivation
oxide film is formed with high-purity oxygen on each surface (T.
Ohmi et al., Extended Abstracts, 174th Electrochemical Society,
Fall Meeting, 396, 579-580, October 1988). Thus, the surfaces have
the structure resistant to adsorption of gas and avoiding pollution
with impurity as much as possible.
[0106] The entire gas supply system, including the mass flow
controller and filter, is made of SUS 316, which is subjected to
electropolishing and passivation oxidation so as to keep an amount
of impurities upon introducing the gas in the process into the
chamber as small as possible. The exhaust system is constructed as
follows. A main pump is a magnetic levitation type and tandem type
turbo molecular pump, and a dry pump is used as an auxiliary pump.
This exhaust system is an oil free system, which is so constructed
as to little be polluted with impurities. The second-stage turbo
molecular pump is a large-flow type pump, which can maintain the
exhaust rate even for the vacuum degree of the mTorr order during
generation of plasma. The lens 94 is introduced into the vacuum
chamber 91 through the load-lock chamber arranged next to the
chamber 91, thereby preventing impurities from intruding into the
vacuum chamber 91.
[0107] As a result, an amount of impurities upon introduction of
lens into the chamber is small; even water mixed in a largest
amount is not more than some ppb. The background vacuum degree of
the vacuum chamber is 10.sup.-8 or less. Since the target is
equipped with a variable high-frequency power supply variable up to
some hundred MHz, the plasma can be generated in a high density,
and the self bias and the plasma potential can be changed. The
apparatus is also arranged in such a manner that the DC power
supply for applying a DC potential is connected through the
low-pass filter to the target and that in the case of a conductive
target, the potential of the target can be controlled also by the
DC power supply. This arrangement makes it possible to control the
film-forming conditions, including:
[0108] (a) the film-forming rate,
[0109] (b) the energy of ions impinging on the substrate,
[0110] (c) the plasma density.
[0111] FIG. 7 is a drawing to show a chamber of another sputtering
apparatus used in the present invention.
[0112] In this chamber 91 there are two triangular-prism target
holders. This arrangement of the target holders is a different
point from the apparatus shown in FIG. 6, and the other arrangement
is the same as that of the apparatus of FIG. 6.
[0113] In this target arrangement, sputtering can be carried out by
selecting one of three types of targets by rotating the holders
92a, 92b.
[0114] The example of FIG. 7 illustrates a case using the targets
of tantalum oxide, aluminum oxide, and silicon oxide.
[0115] During sputtering angles of rotation of the holders are
adjusted so that the surfaces of the targets may become inclined
relative to the surface of substrate. This arrangement facilitates
formation of a uniform film on the substrate having any surface
shape and size, for example on a concave lens, a convex lens, and a
concave mirror.
[0116] FIG. 8 is a graph to show energy distributions of ions
impinging upon the substrate surface earthed, against frequency of
the high-frequency power supplied to the target. This figure shows
cases where the pressure is 7 mTorr and Ar ions and Xe ions are
used, and shows that as the frequency increases, the energy
distribution becomes sharper and that two peaks appearing in the
case of low frequency change into a distribution having one energy
peak. This is because with an increase of the frequency the ions
become unlikely to be vibrated by the high-frequency waves, namely,
because they come to have a stabler plasma potential. The frequency
is preferably as high as possible in view of controllability, but
too high frequency would be a cause to produce an in-plane
distribution because the wavelength becomes comparable to the
substrate.
[0117] As for ion species, heavier atoms are more preferable in
order to obtain a further stabler plasma potential, because heavier
atoms are less vibrated by high-frequency waves; the energy
distribution becomes smaller with an increase of weight of atoms,
specifically in the order of Kr, Xe, and Rn, achieving a good
in-plane distribution of characteristics of film. An optimum use
range of frequency differs depending upon the atoms used, but a
preferred range is approximately 10 to 500 MHz in the use of Kr,
Xe, or Rn. As for the energy supply to the surface of deposit film
by ion irradiation, as comparing ions with same energy, heavier
atoms can give energy with efficiency only to the vicinity of the
surface. In addition, heavier atoms decrease chances to intrude
into the film deeply to damage it. Accordingly, there are effects
to form a fine film and to improve surface flatness.
[0118] FIG. 9 shows input energy dependencies of Ar gas and Xe gas
with normalized values of sputter rate to the Si target. Even with
the same energy value, Ar intrudes deeper into the Si target to
effect sputtering, and it is seen that the sputter rate thereof is
greater than that of Xe (larger in inclination of graph).
[0119] Next explained is the lens stocker used for the optical
article of the present invention.
[0120] Generally, water molecules adsorb in some 10 layers on the
substrate surface kept in the air (Nakagawa, Izumi, and Ohmi
"Measurement of amount of adsorbing water on solid surface using HF
anhydride" 19th super-ultraclean technology symposium, pp 41,
1993). Therefore, the water molecules would be presumably a big
cause to degrade the film quality, for example as being taken as a
pollutant into the film, when the film such as an antireflection
film is deposited over the lens surface. It is also reported that
activation energy of water molecules adhered to the lens surface,
which is a surface mainly containing SiO.sub.2, is 0.09 eV, which
is obtained from the surface temperature thereof and surface
density of molecules adsorbing, and activation energy of the second
layer and further layers is 0.12 eV, because bonding is between
water molecules (M. Nakamura et al., Extended Abstracts, 180th
Electrochemical Society Meeting, Phoenix, Abstract No. 534, pp.
798-799, October 1991). In order to eliminate the water molecules,
clean nitrogen with little water molecules is always let to flow in
the lens stocker.
[0121] FIG. 10 shows time changes of water molecule layers on the
lens surface in this case. It is seen that water molecules on the
surface are being eliminated with a lapse of time. When the lens
temperature is kept at about 90.degree. C., the removing rate
increases, which is efficient. In the case of the ordinary
temperature, the lens is kept in the lens stocker, for example, for
a week, clean nitrogen is kept to flow therein, thereafter the lens
is introduced into the load-lock chamber, and the chamber is
evacuated to a vacuum. Most water molecules on the lens surface can
be removed through the above process.
[0122] Next explained referring to FIG. 11 is a clean nitrogen
supply system for supplying clean nitrogen to the lens stocker.
Reference numeral 301 designates a liquid nitrogen gas tank, 302 an
evaporator, 303 a purifier, 304 a SUS pipe, 305, 306, 310 SUS pipes
passivation-oxidized, 307 a pressure controller, 308 a mass flow
controller, 309 a tandem type cross valve for introducing nitrogen
gas, 311 the lens stocker, 313 a valve, 314 an exhaust pump, and
315, 312 SUS pipes.
[0123] The liquid nitrogen gas is supplied from 301 to pass the
purifier so that an amount of water may be not more than 0.1 ppb
and the number of particles not less than 0.1 .mu.m may be below
the detection limit. The purifier is PEGASUS 200E available from
Nippon Sanso, which is a purifier serving as both an adsorption
type one and a getter type one. The clean nitrogen gas is
introduced through the pressure controller and mass flow controller
to the lens stocker, and six inlet portions are provided so as to
circulate the gas inside the lens stocker. To remove water on the
lens surface, the lens surface may be set near a gas introducing
portion so as to blow the gas thereto, but there is no specific
limitation on the method. Nitrogen introduced into the lens stocker
is exhausted through the valve 313 by the exhaust pump. The exhaust
pump is highly effective to replacing the ordinary air with
nitrogen, but the exhaust pump does not have to be used for
evacuation after that; for example, pushing exhaust or the like may
be employed.
Exposure Apparatus
[0124] Next explained is the exposure apparatus in which the
optical article of the present invention is used.
[0125] The exposure apparatus may be one of reduction projection
exposure apparatus and lens type 1:1 projection exposure apparatus
using a lens optical system.
[0126] Particularly, desired is a stepper employing the
step-and-repeat method for performing such exposure that one small
section (field) of a wafer is first exposed, the wafer is then
stepped to the next field, and the next field is then exposed, in
order to expose the entire wafer. Of course, the optical article of
the present invention can also be suitably applicable to the
microscan type exposure apparatus.
[0127] FIG. 4 is a schematic structural drawing of the exposure
apparatus according to the present invention. In the drawing,
numeral 21 designates an illumination light source section and 22
an exposure mechanism section. The two sections 21, 22 are
constructed separately and independently. Namely, they are in a
physically separated state. Numeral 23 denotes an illumination
light source, which is a large-scale light source of a high output,
for example such as an excimer laser. Numeral 24 represents a
mirror, 25 a concave lens, and 26 a convex lens. The lenses 25, 26
have a role as a beam expander, which expands the beam size of
laser to the size of an optical integrator. Numeral 27 stands for a
mirror, and 28 for an optical integrator for uniformly illuminating
an area on a reticle. The illumination light source section 21 is
composed of the elements of from the laser 23 to the optical
integrator 28. Numeral 29 denotes a mirror, and 30 a condenser lens
for collimating beams emerging from the optical integrator 28.
Numeral 31 is a reticle on which a circuit pattern is written, 31 a
is a reticle holder for holding the reticle by suction, 32 is a
projection optical system for projecting the pattern on the
reticle, and 33 a wafer on which the pattern on the reticle 31 is
to be printed through the projection lens 32. Numeral 34 designates
an XY stage for holding the wafer 33 by suction and for moving the
wafer in the X, Y directions during printing in the step-and-repeat
method. Numeral 35 is a base of the exposure apparatus.
[0128] The exposure mechanism section 22 is composed of the
elements of from the mirror 29, which is a part of the illumination
optical system, to the base 35. Numeral 36 is an alignment means
used for TTL alignment. Normally, the exposure apparatus further
has an autofocusing mechanism, a wafer carrying mechanism, etc.,
which are also included in the exposure mechanism section 22.
[0129] FIG. 5 shows an example of the optical article used in the
exposure apparatus of the present invention, which is a lens
assembly used in the projection optical system in the exposure
apparatus shown in FIG. 4. This lens assembly is composed of eleven
lenses L.sub.1 to L.sub.11 not cemented to each other. The optical
thin film of the present invention may be provided as an
antireflection film or a reflection-enhanced film on the lenses or
the mirrors shown in FIG. 4 and FIG. 5, or on surfaces of mirrors
and lenses in a mirror type exposure apparatus, though not
shown.
EXAMPLE 1
[0130] Specifically explained in the following is a process for
forming a thin film of Ta.sub.2O.sub.5 on a silica substrate, for
example of the diameter 120 mm, by the sputtering apparatus shown
in FIG. 6. The target was made of tantalum in the size of 5
inches.times.15 inches and in the thickness of 6 mm. It was a
high-purity product with the purity of not less than 0.9999.
Pollutants adhering in a very small amount to the substrate surface
were first removed by ion irradiation of weak energy (called as a
surface cleaning step). The introducing gas was Xe of 5 mTorr as an
example.
[0131] Clean nitrogen was first introduced to the load-lock chamber
up to the atmospheric pressure, and then the substrate was carried
together with the supporting member thereof from the lens stocker
into the load-lock chamber. After the gate valve was closed between
the load-lock chamber and the stocker, the inside of the load-lock
chamber was evacuated. The vacuum degree reached was
3.times.10.sup.-8 Torr. At this stage it is also possible to
provide the apparatus with a heating mechanism such as a halogen
lamp and to heat the substrate at about 80.degree. C. to 99.degree.
C. by the heating mechanism to drive the gas out thereof. Next, the
gate valve was opened between the load-lock chamber and the sputter
chamber, and the lens was carried together with the support member
into the sputter chamber to be set on the holder. The Xe gas was
introduced into the sputter chamber as rotating the substrate by
the rotating mechanism connected to the holder, so that the
pressure reached 5 mTorr. After stabilized, high-frequency waves of
the frequency 100 MHz and the power 20 W of RF power were applied
to generate plasma, and Xe ion irradiation of weak energy was
continued for five minutes to remove pollutants adhered in a very
small amount on the lens surface.
[0132] At this point the substrate surface was at the floating
potential, and the lens surface was irradiated with Xe ions of
about 3 eV, which was a potential difference from the plasma
potential. This potential difference can be made uniform by using a
heavier gas than the Ar gas, which increases uniformity of energy
of irradiated ions. Too high irradiation energy would leave a
damage on the surface, which would result in failing to form a fine
Ta.sub.2O.sub.5 film in the subsequent film-forming process. The
temperature of the substrate was the ordinary temperature, and a
little temperature rise was observed upon ion irradiation. It
should be noted that the temperature needs to be controlled so as
not to change the microstructure of the lens surface within the
range not exceeding 100.degree. C.
[0133] After that, the Ta.sub.2O.sub.5 film was formed by the
sputtering process. After the plasma was once stopped by
interrupting application of high-frequency waves, the Xe gas and
O.sub.2 gas were introduced this time into the sputter chamber to
achieve the volume ratio Xe/O.sub.2 -10/1 of the gas flow and the
total pressure 5 mTorr. After stabilized, high-frequency waves of
the frequency 15 MHz and the power 1 kW of RF power were applied to
generate plasma and to carry out film formation. The film-forming
rate was 0.5 nm/sec, and film formation was continued up to the
film thickness 250 nm by a quartz oscillation type film thickness
gage. A rate of Xe ions impinging on one Ta.sub.2O.sub.5 was 9.2.
The energy of Xe ions impinging on the substrate surface at this
moment was 8 eV. It was checked by RBS analysis that Xe taken into
the Ta.sub.2O.sub.5 film at this time was 0.1 atomic %.
[0134] Another film not containing Xe was formed in the same manner
as the Ta.sub.2O.sub.5 film formed under the above conditions
except that the Xe gas was replaced by Ar gas. The two films were
subjected to irradiation with the i-line of the doubled power for
500 hours, and thereafter transmittance and reflectivity were
measured for each of them by spectrophotometry. Then optical
absorption was calculated and expressed by extinction
coefficient.
[0135] The extinction coefficient of Ar was 4.5 and that of Xe was
0.1.
[0136] Since the purpose of this example was to fabricate the
antireflection film against the i-line, the measurement wavelength
was 365 nm. It is thus understood that when Xe is used as a
sputtering gas rather than Ar, a good-quality film with little
optical absorption can be formed as a film with a small extinction
coefficient.
[0137] Setting the article thus obtained in the i-line optical
system, a time change of transmittance of the lens was measured as
irradiating it with the i-line in an irradiation amount two times
larger than that used in the ordinary exposure apparatus. The
result is shown in FIG. 12. The article having the film obtained by
sputtering with Ar not using Xe showed extreme degradation of
transmittance after a lapse of a predetermined time T1 of
irradiation time, whereas the article of this example showed little
degradation of transmittance.
[0138] The in-plane distribution of refractive index was improved
by about 10% as compared with the comparative sample obtained using
the Ar gas and not using Kr, Xe, or Rn.
EXAMPLE 2
[0139] This example is different from Example 1 in that several
types of optical thin films of tantalum oxide were made by changing
the energy amount of ion irradiation. The other matters were the
same as in Example 1.
[0140] Time changes of transmittances were measured for the optical
thin films of this example in the same manner as in FIG. 12 in
Example 1. FIG. 13 is a graph to show quantities of degradation of
transmittance to an initial value after a lapse of time T2,
similarly as in FIG. 12.
[0141] It is seen that the range of ion irradiation energy to form
a good-quality film with little time change is wider than that of
the comparative data of Ar obtained by the same method as the
method for producing the film using the Ar gas for comparison in
Example 1. This means that use of Xe as a sputtering gas permits a
good-quality film to be produced very easily and with good
reproducibility.
EXAMPLE 3
[0142] This example is different from Example 1 in that several
types of optical thin films of tantalum oxide were produced using
the following gases instead of the Xe/O.sub.2 gas in Example 1.
[0143] The gases used in this example were ten types of gases,
including a Kr gas of 100% by volume, mixture gases in volume
ratios of Kr and Xe being 2:8, 1:1, 8:2, mixture gases in volume
ratios of Xe and Ar being 2:8, 1:1, and 8:2, and mixture gases in
volume ratios of Kr and Ar being 2:8, 1:1, and 8:2. The ion
irradiation energy was also changed to obtain many samples. The
other matters were the same as in Example 1.
[0144] To evaluate the samples, time changes of transmittances were
measured in the same manner as in Example 2. FIG. 14 is a graph to
show the results. From comparison with the comparative data of Ar,
it is seen that the optical thin films of this example have a wide
range of ion irradiation energy to form a good-quality film with
little time change. This means that use of Kr or Xe can produce a
good-quality film very easily and with good reproducibility.
EXAMPLE 4
[0145] This example is different from Example 1 in that several
types of optical thin films of tantalum oxide were produced using
mixture gases in different volume ratios of Xe and O.sub.2, and
employing the deposition rates between 0.1 nm/sec and 1 nm/sec by
controlling the temperature upon film formation with a temperature
controller set on the substrate holder in the range of 150.degree.
C. to 20.degree. C. and controlling the frequency of power supply
in the range of 200 MHz to 10 MHz. The ion irradiation energy was
also changed to obtain many samples. The other matters were the
same as in Example 1
[0146] To evaluate the samples, RBS analysis was conducted to
measure amounts of Xe contained in the samples. FIG. 15 is a graph
to show degrees of time changes of transmittances against a
parameter of amount of Xe. The ordinate of FIG. 15 represents
normalized values as setting the case using only Ar gas to 1.0.
[0147] As seen from FIG. 15, preferable samples have an amount of
Xe dropping in the range of 0.5 atomic ppm to 5 atomic %, more
preferable samples have an amount of Xe in the range of 0.5 atomic
ppm to 3 atomic %, and most preferable samples have an amount of Xe
in the range of 0.5 atomic ppm to 1 atomic %.
EXAMPLE 5
[0148] This example is different from Example 4 in that mixture
gases in variable volume ratios of Kr and O.sub.2 were used instead
of the mixture gases in the variable volume ratios of Xe and
O.sub.2 used in Example 4. The other matters were the same as in
Example 4.
[0149] SIMS analysis was conducted for the samples in the same
manner as in Example 4. Checking degrees of time changes of
refractive indices against a parameter of amount of Kr, it was
found, similarly as in Example 4, that preferable samples had an
amount of Kr in the range of not more than 5 atomic %, more
preferable samples had amounts of Kr being 0.5 atomic ppm and 3
atomic %, and the most preferable sample had an amount of Kr being
1 atomic %%.
EXAMPLE 6
[0150] This example is different from Example 4 in that mixture
gases in various volume ratios of Xe, Kr, and O.sub.2 were used
instead of the mixture gases in various volume ratios of Xe and
O.sub.2 used in Example 4. The other matters were the same as in
Example 4.
[0151] RBS analysis was conducted for the samples in the same
manner as in Example 4. Checking degrees of time changes of
transmittances against a parameter of total content of Kr and Xe,
preferable samples had a total amount of not more than 10 atomic %,
and most preferable samples had a total amount of not more than 5
atomic %.
EXAMPLE 7
[0152] This example is different from Example 1 in that the
antireflection film formed on the lens is formed of the first,
third, and fifth layers of low-index layers mainly containing
SiO.sub.2 and the second, fourth, and sixth layers of high-index
layers mainly containing Al.sub.2O.sub.3 in order from the air side
to the lens side. Silica glass was used for the substrate and a
lens for KrF excimer laser was produced. FIG. 16 is a diagrammatic,
sectional view to show the layer structure of the optical thin film
according to this example.
[0153] Deposition conditions for bias sputtering are listed below,
and the steps up to the surface cleaning step were the same as in
Example 1.
[0154] After that, discharge was caused against the Al.sub.2O.sub.3
target, thereby depositing Al.sub.2O.sub.3 containing Xe on the
lens. The film-forming conditions at this time were as follows.
[0155] RF frequency: 20 MHz
[0156] High-frequency power: 1.5 kW
[0157] Xe/O.sub.2 gas=10:1, pressure: 5 mTorr
[0158] Growth rate: 0.2 nm/sec
[0159] Next, the target holder was rotated to change the target to
the SiO.sub.2 target, and deposition of SiO.sub.2 was carried out.
The film-forming conditions at this time were as follows.
[0160] RF frequency: 13.56 MHz
[0161] High-frequency power: 1.5 kW
[0162] Xe/O.sub.2 gas=5:1, pressure: 5 mTorr
[0163] Growth rate: 0.7 nm/sec
[0164] Under the above conditions, the antireflection film against
ultraviolet light of excimer laser of 248 nm was formed with the
refractive indices and optical film thicknesses as listed in Table
1 below. The refractive indices in the table were those to
ultraviolet light of 248 nm.
1 TABLE 1 Optical Material Index Thickness Entrance medium Air
1.000 1st layer SiO.sub.2 1.488 62.308 2nd layer Al.sub.2O.sub.3
1.684 60.575 3rd layer SiO.sub.2 1.488 56.110 4th layer
Al.sub.2O.sub.3 1.684 63.882 5th layer SiO.sub.2 1.488 97.598 6th
layer Al.sub.2O.sub.3 1.684 101.324 Exit medium synthetic silica
1.509
[0165] FIG. 17 is a graph to show reflection characteristics of
this film. FIG. 18 is a graph to show a time change of
transmittance of the film as normalized with respect to a film
formed in the same manner using Ar instead of the part of the above
Xe gas, as defined to 1.0. It is clearly seen from FIG. 18 that the
film using the Xe gas has a longer life.
[0166] The above evaluation was obtained by an accelerated
durability test for an optical system shown in FIG. 5, using the
lens produced in this example, in which the excimer laser light was
applied for 1000 hours in a light quantity two times greater than
the irradiation light quantity used in the normal excimer laser
stepper.
EXAMPLE 8
[0167] This example is different from Example 1 in that the
antireflection film formed on the lens is composed of the first and
third layers of low-index layers mainly containing SiO.sub.2, the
second, fourth, and sixth layers of high-index layers mainly
containing Ta.sub.2O.sub.5, and the fifth layer of a layer
containing Al.sub.2O.sub.3 in order from the air side to the lens
side. The substrate was a lens made of silica glass. FIG. 19 is a
diagrammatic, sectional view to show the layer structure of the
optical thin film according to this example.
[0168] The deposition conditions for bias sputtering are listed
below, and the steps up to the surface cleaning step were the same
as in Example 1.
[0169] After that, discharge was caused against the Ta.sub.2O.sub.5
target, then depositing Ta.sub.2O.sub.5 containing Xe and Kr on the
lens. The film-forming conditions at this time were as follows.
[0170] RF frequency: 100 MHz
[0171] High-frequency power: 2 kW
[0172] Xe/Kr/O.sub.2 gas=5:5:1, pressure: 5 mTorr
[0173] Growth rate: 0.2 nm/sec
[0174] Next, the target holder was rotated to change the target to
the SiO.sub.2 target, and deposition of SiO.sub.2 was carried out.
The film-forming conditions at this time were as follows.
[0175] RF frequency: 100 MHz
[0176] High-frequency power: 2 kW
[0177] Xe/Kr/O.sub.2 gas=5:5:1, pressure: 5 mTorr
[0178] Growth rate: 0.4 nm/sec
[0179] In film formation of Al.sub.2O.sub.3, the target holder was
rotated in the same manner to change the target to the
Al.sub.2O.sub.3 target, and deposition of Al.sub.2O.sub.3 film
containing Xe and Kr was carried out. The film-forming conditions
at this time were as follows.
[0180] RF frequency: 100 MHz
[0181] High-frequency power: 2 kW
[0182] Xe/Kr/O.sub.2 gas=5:5:1, pressure: 5 mTorr
[0183] Growth rate: 0.1 nm/sec
[0184] Under the above conditions, the antireflection film was
formed against both ultraviolet light of the center wavelength 365
nm and visible light of center wavelengths 550 to 650 nm so as to
have the refractive indices and optical film thicknesses as listed
in Table 2 below. The refractive indices in the table are those to
the light of 365 nm.
2 TABLE 2 Optical Material Index Thickness Entrance medium Air
1.000 1st layer SiO.sub.2 1.449 105.609 2nd layer Ta.sub.2O.sub.5
2.171 72.609 3rd layer SiO.sub.2 1.449 13.990 4th layer
Ta.sub.2O.sub.5 2.171 140.874 5th layer Al.sub.2O.sub.3 l..614
28.952 6th layer Ta.sub.2O.sub.5 2.171 32.130 Exit medium F8
1.633
[0185] FIG. 20 is a drawing to show reflection characterisics of
this film. FIG. 21 is a graph to show a time change of
transmittance of the film as normalized with respect to a film
obtained by changing the part of the above Xe gas and Kr gas to Ar,
as defined to 1.0. It is clearly seen from FIG. 21 that the film
using the Xe and Kr mixture gas has a longer life.
[0186] The above evaluation was obtained by the same test as in
Example 7 by forming the optical system of FIG. 5 using the lens of
this example and using the i-line light source for emitting the
ultraviolet light of 365 nm instead of the excimer laser.
EXAMPLE 9
[0187] This example is different from Example 1 in that a
reflection-enhanced film formed on the lens is composed of the
first, third , . . . , 49th layers of high-index layers mainly
containing Ta.sub.2O.sub.5 and the second, fourth, sixth , . . . ,
50th of low-index layers mainly containing SiO.sub.2 in order from
the air side to the lens side. A lens made of silica glass was used
as a substrate.
[0188] The deposition conditions for bias sputtering are listed
below, and the steps up to the surface cleaning step were the same
as in Example 1.
[0189] After that, discharge was caused against the Ta.sub.2O.sub.5
target, and deposition of Ta.sub.2O.sub.5 was carried out on the
silica glass. The film-forming conditions at this time were as
follows.
[0190] RF frequency: 100 MHz
[0191] High-frequency power: 2 kW
[0192] Xe/Kr/Ar/O.sub.2 gas=5:5:1:1, pressure: 5 mTorr
[0193] Growth rate: 0.3 nm/sec
[0194] Next, the target holder was rotated to change the target to
the SiO.sub.2 target, and deposition of the SiO.sub.2 film was
carried out. The film-forming conditions at this time were as
follows.
[0195] RF frequency: 100 MHz
[0196] High-frequency power: 2 kW
[0197] Xe/Kr/Ar/O.sub.2 gas=5:5:1:1, pressure: 5 mTorr
[0198] Growth rate: 0.5 nm/sec
[0199] Under the above conditions, the reflection-enhanced film was
formed to the near-ultraviolet light of the center wavelength 365
nm.
[0200] FIG. 22 is a graph to show a time change of reflectivity of
the film with respect to a film formed in the same manner except
that the portion of the above Xe gas and Kr gas was changed to Ar.
It is clearly seen from FIG. 22 that the film using the Xe, Kr
gases has a longer life.
[0201] The above test was conducted for the optical system shown in
FIG. 4 assembled using the lens produced in this example.
EXAMPLE 10
[0202] In this example, several types of optical thin films of
aluminum oxide were produced by using mixture gases in various
volume ratios of Xe and O.sub.2 and setting the deposition rate to
0.1 nm/sec to 1 nm/sec by controlling the temperature upon film
formation with a temperature controller mounted to the substrate
holder in the range of 150.degree. C. to 20.degree. C. and
controlling the frequency of power supply in the range of 200 MHz
to 10 MHz. The other matters were the same as in Example 4.
[0203] FIG. 23 is a graph to show transmittance stability against
amount of Xe.
[0204] Using the exposure apparatus with an illumination system
including the optical article as explained above, a pattern can be
formed by photolithography in the minimum line width of not more
than 1 .mu.m (in the submicron order), as shown in FIG. 24.
[0205] At step S1 a base coating film, such as silicon oxide,
silicon nitride, polycrystal silicon, aluminum, tungsten, titanium
nitride, or the like, is formed on the substrate.
[0206] At step S2 the resultant is coated with a negative resist or
a positive resist of a photosensitive resin.
[0207] At step S3 the resist is exposed through an exposure mask
(reticle) using the KrF excimer laser, thereby forming a latent
image of the pattern in the resist.
[0208] At step S4 the resist is developed with a developer to leave
exposed portions or non-exposed portions. The left portions become
a resist pattern.
[0209] At step S5 the base layer is etched with the resist pattern
as an etching mask, thereby forming a coating pattern corresponding
to the etching mask. If the coating layer is polycrystal silicon,
the line width can be formed below 1 .mu.m. Thus, transistors can
be formed with the gate length of the submicron order.
[0210] At step S6 ashing is carried out to remove the resist.
[0211] An insulating film such as SiO.sub.2 is formed by the CVD
process or the like on the coating layer pattern thus obtained
(step S7).
[0212] According to the present invention, even if many
semiconductor integrated circuits (ICs) are fabricated by repeating
the above steps, the resist patterns corresponding to the exposure
mask pattern can be obtained with good reproducibility, because
there is no deterioration of the antireflection film of lens. The
yield of ICs can be improved accordingly.
* * * * *