U.S. patent application number 09/385929 was filed with the patent office on 2001-11-15 for method of forming resist images by periodic pattern removal.
Invention is credited to COLE, DANIEL C., CONRAD, EDWARD W., HORAK, DAVID V., MANN, RANDY W., PASTEL, PAUL W., RANKIN, JED H., WATTS, ANDREW J..
Application Number | 20010041306 09/385929 |
Document ID | / |
Family ID | 23523473 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041306 |
Kind Code |
A1 |
COLE, DANIEL C. ; et
al. |
November 15, 2001 |
METHOD OF FORMING RESIST IMAGES BY PERIODIC PATTERN REMOVAL
Abstract
The present invention provides a method of forming nested and
isolated images in a photosensitive resist. In the disclosed
method, the entire surface of the photosensitive resist or selected
regions thereof is exposed to a first mask having a set of nested,
i.e. repeating pattern or grid images thereon, and then exposed to
a second mask in order to remove unwanted portions of the nested
image, so as to provide regions of nested and regions of isolated
images in said photosensitive resist. The method may also be used
to form regions having images in proximity to one another and
regions having isolated images by exposing the entire surface of
the photosensitive resist to a first mask having repeating
patterns, and then removing entire or portions of the repeating
patterns by exposure of the photosensitive resist with a second
mask.
Inventors: |
COLE, DANIEL C.; (JERICHO,
VT) ; CONRAD, EDWARD W.; (JEFFERSONVILLE, VT)
; HORAK, DAVID V.; (ESSEX JUNCTION, VT) ; MANN,
RANDY W.; (JERICHO, VT) ; PASTEL, PAUL W.;
(ESSEX JUNCTION, VT) ; RANKIN, JED H.;
(BURLINGTON, VT) ; WATTS, ANDREW J.; (ESSEX
JUNCTION, VT) |
Correspondence
Address: |
RICHARD L CATANIA ESQ
SCULLY SCOTT MURPHY & PRESSER
400 GARDEN CITY PLAZA
GARDEN CITY
NY
11530
|
Family ID: |
23523473 |
Appl. No.: |
09/385929 |
Filed: |
August 30, 1999 |
Current U.S.
Class: |
430/312 ;
430/311; 430/5 |
Current CPC
Class: |
G03F 7/203 20130101;
G03F 7/70466 20130101; G03F 7/70125 20130101 |
Class at
Publication: |
430/312 ; 430/5;
430/311 |
International
Class: |
G03F 007/20 |
Claims
Having thus described our invention in detail, what we claim as new
and desire to secure by the letters Patent is:
1. A method of forming resist images in a photosensitive resist
comprising the steps of: (a) exposing a photosensitive resist to a
first mask having a grid pattern image thereon so as to form a
repeating pattern image on said photosensitive resist; and (b)
exposing the photosensitive resist containing said repeating
pattern image to a trim mask having a predetermined pattern thereon
so as to remove unwanted portions of the repeating pattern image in
said photosensitive resist.
2. The method of claim 1 wherein said photosensitive resist is
formed on a substrate.
3. The method of claim 2 wherein said substrate is a semiconductor
chip, wafer, interconnect structure or circuit board.
4. The method of claim 2 wherein said substrate is composed of, or
contains, a semiconducting material selected from the group
consisting of Si, Ge, GaAs, InAs, InP and other like III/V
compounds.
5. The method of claim 1 wherein said photosensitive resist is a
dry or liquid photosensitive material.
6. The method of claim 1 wherein said photosensitive resist is a
radiation sensitive material selected from the group consisting of
a negative working resist, a positive working resist and mixtures
thereof.
7. The method of claim 1 wherein step (a) is carried out under
conditions effective to provide harden areas in said photosensitive
resist.
8. The method of claim 1 wherein step (a) is carried out using
off-axis illumination.
9. The method of claim 8 wherein said off-axis illumination is
annular.
10. The method of claim 1 wherein step (a) is carried out at an
energy of from about 10 millijoules/cm.sup.2 to about 30
millijoules/cm.sup.2 using a 193 nm or 248 nm light source.
11. The method of claim 1 wherein said first mask comprises light
blocking regions corresponding to features to be printed and open,
light transmitting areas surrounding the features.
12. The method of claim 11 wherein said features comprise an opaque
layer of chrome formed on quartz.
13. The method of claim 1 wherein step (b) is carried using
off-axis illumination.
14. The method of claim 13 wherein said off-axis illumination is
annular.
15. The method of claim 1 wherein said step (b) exposure is
substantially less than said step (a) exposure.
16. The method of claim 1 further comprises a postbake step after
step (b).
17. The method of claim 1 wherein said predetermined pattern is a
repeating pattern.
18. The method of claim 1 wherein a portion of said predetermined
pattern is a repeating pattern.
19. The method of claim 1 further comprising a development step
after step (b) which removes unexposed areas of said photosensitive
resist.
20. The method of claim 1 wherein said trim mask has larger
features than said first mask.
21. The method of claim 1 wherein a common grid mask is used for
making multiple part numbers.
22. A method of forming resist images in a photosensitive resist
comprising the steps of: (a) exposing a photosensitive resist to a
first mask having a grid pattern image thereon so as to form a
nested image on said photosensitive resist; and (b) exposing the
photosensitive resist containing said nested image to a trim mask
having a predetermined pattern thereon so as to remove unwanted
portions of the nested image providing an isolated image in said
photosensitive resist.
23. A method of forming resist images in a photosensitive resist
comprising the steps of: (a) exposing a photosensitive resist to a
first mask having a grid pattern image having a first periodicity
thereon so as to form a nested image on said photosensitive resist;
and (b) exposing the photosensitive resist containing said first
periodicity to a trim mask having a predetermined pattern having a
second periodicity thereon so as to remove unwanted portions of the
first periodicity providing a semi-nested image having a third
periodicity in said photosensitive resist, said second and third
periodicities being the same but different from said first
periodicity.
Description
DESCRIPTION
[0001] 1. Field of the Invention
[0002] The present invention relates to photolithography, and more
specifically to a method of forming resist images by utilizing a
grid mask containing a periodic set of images to produce a nested
set of identical images over an entire chip surface or selected
regions thereof and then removing any unwanted portions of said
nested set of identical images with a trim mask.
[0003] 2. Background of the Invention
[0004] As the minimum feature size in semiconductor integrated
circuit technology is pushed near or below the wavelength of light
used in micro-lithographic projection printing, diffraction effects
introduce significant differences between the patterns used on
micro-lithographic reticles and the resulting printed structures on
a semiconductor wafer. Similarly, the smaller the circuit elements
become, the more difficult it is to create the desired pattern
shapes on the wafer due to factors such as localized etch
variations, mask distortions, lens distortions, topography
variations, and non-uniform material composition.
[0005] These physical factors introduce deviations in isolated
versus nested printed structures, with the degree of variation
being highly dependent on the degree of proximity of nearby shapes.
In order to maximize circuit performance and speed, it has been
found highly desirable to make the device structure dimensions as
identical as possible, e.g. to try to make isolated gates and
nested gates print as identically as possible. These effects become
increasing important as the physical dimensions of the circuit
elements decrease.
[0006] Across Chip Linewidth Variation (ACLV) is one major problem
in semiconductor device manufacturing. Image size variations can
affect transistor speed matching and resistivity and conductance
matching from one portion of the chip to another. One significant
cause of printed pattern size variation is the diffraction
component of imaging, which results in structures on a reticle
being imaged differently depending upon what other structures are
present in the local neighborhood.
[0007] A common form of this is differences between nested and
isolated images. FIG. 1 shows a prior art mask intended to produce
holes in a negative resist. FIG. 2 shows the resultant resist
images with the isolated images being overexposed and smaller. In
actuality, the printed shapes in FIG. 2 occur as rounded structures
because each corner on a mask ends up as a printed rounded corner
on the wafer. The isolated structure prints much differently than a
nested structure. The degree that they print differently depends on
the degree of proximity of nearby structures, as well as the size
of nearby structures, the periodicity of nearby structures, and
exposure tool illumination conditions.
[0008] It should be further appreciated that prior art
photolithographic techniques require multiple custom masks to
provide a nested and isolated image on the surface of a
semiconductor wafer having improved ACLV. An example of such a
technique, is described, for example, in U.S. Pat. No. 5,424,154
which discloses a method of enhancing the lithographic resolution
of randomly laid out isolated structures, wherein a first mask
comprising an active layer with isolated features such as gates is
used. Portions of the active layer have a reduced dimension typical
of periodic structures. The first mask disclosed in the '154 patent
additionally has complementary features provided along side the
reduced active features to provide periodicity. Accordingly, the
resolution of the lithographic process is enhanced, and other
enhanced resolution technologies additionally can be used to best
advantage to form a patterned photosensitive layer having isolated
features of reduced width. The photosensitive resist is then
exposed to a second mask which exposes the complementary features
so that they are removed from the latent image in the
photosensitive resist. This second exposure reportedly improves
resolution by enhancing contrast between exposed and unexposed
regions.
[0009] While such prior art techniques can be used in printing
resist images, it would be highly desirable to provide a method of
forming resist images using a non-custom first mask (or a
non-custom common grid mask useable for many designs) and a single
custom trim mask to provide the nested and isolated images. This
provides a significant reduction in manufacturing cost.
SUMMARY OF THE INVENTION
[0010] The present invention provides a method of overcoming the
problems associated with prior art photolithographic techniques,
especially those caused by ACLV, by first printing a set of nested
images using a grid mask over the entire surface of a semiconductor
chip or critical regions thereof; and then removing unwanted images
with a trim mask. The grid mask can be fabricated and selected to
be a nearly perfect mask for each chip size, so only the less
critical trim mask is personalized for a given chip design.
[0011] Specifically, the method of the present invention comprises
the steps of:
[0012] (a) exposing a photosensitive resist to a first mask having
a grid pattern image thereon so as to form a repeating pattern
image on said photosensitive resist; and
[0013] (b) exposing the photosensitive resist containing said
repeating pattern image to a trim mask having a predetermined
pattern thereon so as to remove unwanted portions of the repeating
pattern image in said photosensitive resist.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 represents a prior art mask used for forming holes in
a negative resist layer.
[0015] FIG. 2 shows the resultant resist image produced using the
mask shown in FIG. 1.
[0016] FIGS. 3A-G show the various processing steps and masks that
are employed in the present invention in printing a nested and
isolated resist image when a negative working resist is used.
[0017] FIG. 4 shows a grid mask for fabricating lines when a
positive working resist is used.
[0018] FIG. 5 shows the trim mask that is employed to remove
unwanted portions of the grid provided using the grid mask shown in
FIG. 4.
[0019] FIG. 6 shows the resultant nested and isolated resist image
produced using the masks shown in FIGS. 4 and 5.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention, which provides a method of forming
nested and isolated resist images by periodic pattern removal, will
now be described in greater detail by referring to the drawings
that accompany this application. It should be noted that in the
drawings like and corresponding elements are referred to by like
reference numerals.
[0021] Reference is made first to FIG. 3A which shows a structure
comprising a substrate 10 having a layer of photosensitive resist
12 formed on the surface thereof.
[0022] Substrate 10 employed in the present invention is typically
a semiconductor chip, wafer, interconnect structure, circuit board
or other like semiconductor structures. The substrate is typically
composed of, or contains, a semiconducting material such as Si, Ge,
GaAs, InAs, InP or other like III/V compounds. The substrate may
contain active device regions, wiring regions or other like
regions. For clarity these regions are not shown in the drawings of
the present application, but nevertheless, may be present
therein.
[0023] Photosensitive resist 12 is composed of any conventional
photosensitive material including dry resists and liquid resists
which is capable of receiving an image during exposure. Examples of
some suitable photosensitive resists that can be employed in the
present invention include Shipley CGR2205 negative resist and
Shipley UV5 positive resist as examples. Other negative or positive
resists can also be employed in the present invention. Mixtures of
negative and positive resists are also contemplated in the present
invention.
[0024] The photosensitive resist is formed on the surface of
substrate 10 using conventional deposition processes well known to
those skilled in the art. Suitable deposition processes that can be
employed in the present invention in forming photosensitive resist
12 on the surface of substrate 10 include: spin-on coating, dip
coating, chemical vapor deposition, sputtering and other like
deposition techniques.
[0025] Next, a suitable first mask having a desired grid image
thereon is selected. The mask having the desired grid image
(hereinafter "grid mask") comprises light blocking regions
corresponding to features to be printed and open, light
transmitting areas surrounding the features. Typically, the
features of the grid mask comprise an opaque layer of, for example,
chrome formed on a reticle base of quartz.
[0026] One such mask is shown in FIG. 3B, wherein reference
numerals 14 are the feature regions composed of chrome and
reference numeral 16 is the light transmitting area surrounding
features 14. The grid mask of FIG. 3B would be used with a negative
resist to form, for example, via images. The grid in FIG. 3B is
shown as an array of square features 14. Feature 14 may be other
shapes, and may even be comprised of combinations of two or more
sub-features.
[0027] An alternative grid mask that can be employed in the present
invention is shown in FIG. 4. In FIG. 4, feature 14 is a lattice.
The grid mask of FIG. 4 would be used with a positive resist to
form, for example, line images. It is noted that the grid mask
employed in the present invention is one which is capable of
forming nested images in the photosensitive resist during grid
exposure.
[0028] The photosensitive resist is exposed to radiation through
the grid mask structure using a commercially available exposure
device to form a latent nested image of the grid mask in the
photosensitive resist. Exposure conditions can be conventional
circular illumination or off-axis illumination such as annular,
dipole or quadrupole illumination. Exposure is typically carried in
the present invention at an energy of from about 10 to about 30
millijoules/cm.sup.2 using a 193 nm or 248 nm light source; i.e.
laser, arc lamp and etc.
[0029] The above exposure process causes the formation of latent
nested images 12' in photosensitive resist 12 that are harder than
the adjacent areas which were not subjected to exposure. The
structure containing the latent nested image on the photosensitive
resist is shown in FIG. 3C.
[0030] Next, a trim mask is selected containing features of a
desired pattern thereon so as to isolate certain regions of the
nested image. The trim mask, like the grid mask disclosed above, is
composed of light blocking regions corresponding to features to be
printed and open, light transmitting areas surrounding the
features. Typically, the features comprise an opaque layer of, for
example, chrome formed on a reticle base of quartz.
[0031] A typical trim mask that can be employed in the present
invention is shown in FIG. 3D, wherein reference numerals 14
represent feature regions composed of chrome and reference numeral
16 represents light transmitting areas surrounding features 14. The
trim mask of FIG. 3D would be used with a negative resist to form,
for example, via images.
[0032] An alternative trim mask that can be employed in the present
invention is shown in FIG. 5. The trim mask of FIG. 5 would be used
with a positive resist to form, for example, line images. As is
seen in those figures, the trim mask employed in the present
invention has larger features than those of the grid mask, so as to
be able to provide an isolated image on the surface of the
photosensitive resist. However the exact relationship in size and
overlay between the grid and trim masks may be adjusted based on
the final image desired. For example, the trim mask of FIG. 5 may
be adjusted to compensate for the intersections of the grid mask
image in FIG. 4 so the resist images illustrated in FIG. 6 are
uniform rather than variable in width along their lengths.
[0033] The photosensitive resist is exposed through the trim mask
to radiation using a commercially available device using exposure
conditions to modify the latent grid image in the photosensitive
resist so as to remove unwanted portions of the nested latent image
creating a latent isolated image in the photosensitive resist.
Exposure conditions can be conventional circular illumination or
off-axis illumination such as annular, dipole and quadrupole
illumination. Exposure is typically carried in the present
invention at an energy of from about 5 to about 30
millijoules/cm.sup.2 using a 193 nm or 248 nm light source.
[0034] The trim mask exposure step also causes the formation of
areas 12' on photosensitive resist layer 12 that are harder than
the adjacent areas which were not subjected to exposure. The
patterned structure may, if required, be subjected to additional
trim exposure steps.
[0035] After trim exposure, the photosensitive resist may
optionally be postbaked at a temperature of from about 70.degree.
to about 160.degree. C. for a time period of from about 30 to about
120 seconds for Shipley CGR 2205 or at a temperature of from about
100.degree. to about 160.degree. C. for a time period of from about
30 to about 120 seconds for Shipley UV5. Other baking temperatures
and times are also contemplated by the present invention.
[0036] Areas of photosensitive resist 12 that were not exposed in
either grid or trim mask exposure steps are then developed, i.e.
removed, using a suitable solvent that is capable of removing the
non-exposed regions of the photosensitive resist, yet selective
enough to leave behind the harden areas 12' containing the desired
nested and isolated image pattern therein when the resist is a
positive working resist. When the resist is a positive working
resist, the developer is usually an aqueous basic solution capable
of removing the exposed regions of the photosensitive layer, yet
selective enough to leave behind the unexposed areas.
[0037] The final structure after exposing thru the trim mask and
development is shown in FIGS. 3F and 3G for the case of a negative
resist. FIG. 3F is a side view and FIG. 3G is a top view of a
portion of the substrate containing the developed resist layer.
Alternatively, FIG. 6. is a top view of a portion of the substrate
containing the developed resist layer when a positive resist is
used. As are shown therein, the substrate 10 contains a resist
image 12' thereon which may have nested regions and isolated
regions.
[0038] In some cases it may be useful to leave every other or every
third or similar groupings of grid images. This can be achieved by
exposing the photosensitive resist to the grid mask where the
images are arranged in a first periodic pattern and then exposing
the photosensitive resist to a trim mask having images arranged in
a second periodic pattern. This results in unwanted portions of the
grid mask images being removed in a third periodic pattern. The
second and third periodicities are the same but different from the
first periodicity.
[0039] It should be noted that by employing the method of the
present invention it is possible to print images having nearly the
same size as the masks utilized. Moreover, there are no gross image
size differences using the method of the present invention. More
specifically, some of the minor pattern dependent effects, such as
those due to diffraction from the edge of the trim mask will still
remain after employing the method of the present invention. These
minor effects are, however, greatly offset by the fact that the
present method removes the major contributor to proximity effects.
In general, the trim mask has much larger dimensions than the
dimension of the single structures so edge to edge proximity
diffraction effects will be a much smaller contributor using the
method of the present invention.
[0040] While the present invention has been particularly shown and
described with respect to preferred embodiments thereof, it will be
understood by those skilled in the art that the foregoing and other
changes in form and detail may be made without departing from the
scope and spirit of the invention.
* * * * *