U.S. patent application number 11/105862 was filed with the patent office on 2005-11-17 for anti-reflective coatings using vinyl ether crosslinkers.
Invention is credited to Cox, Robert Christian, Guerrero, Douglas J., Weimer, Marc W..
Application Number | 20050255410 11/105862 |
Document ID | / |
Family ID | 35309829 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050255410 |
Kind Code |
A1 |
Guerrero, Douglas J. ; et
al. |
November 17, 2005 |
Anti-reflective coatings using vinyl ether crosslinkers
Abstract
Novel, wet developable anti-reflective coating compositions and
methods of using those compositions are provided. The compositions
comprise a polymer and/or oligomer having acid functional groups
and dissolved in a solvent system along with a crosslinker and a
photoacid generator. The preferred acid functional group is a
carboxylic acid, while the preferred crosslinker is a vinyl ether
crosslinker. In use, the compositions are applied to a substrate
and thermally crosslinked. Upon exposure to light, the cured
compositions will decrosslink, rendering them soluble in typical
photoresist developing solutions (e.g., alkaline developers).
Inventors: |
Guerrero, Douglas J.;
(Rolla, MO) ; Cox, Robert Christian; (Rolla,
MO) ; Weimer, Marc W.; (Rolla, MO) |
Correspondence
Address: |
HOVEY WILLIAMS LLP
2405 GRAND BLVD., SUITE 400
KANSAS CITY
MO
64108
US
|
Family ID: |
35309829 |
Appl. No.: |
11/105862 |
Filed: |
April 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60566329 |
Apr 29, 2004 |
|
|
|
Current U.S.
Class: |
430/311 ;
430/271.1 |
Current CPC
Class: |
G03F 7/039 20130101;
Y10T 428/31667 20150401; G03F 7/40 20130101; C07C 43/166 20130101;
G03F 7/094 20130101; Y10T 428/31699 20150401; G03F 7/091 20130101;
G03F 7/0392 20130101; Y10S 438/952 20130101; G03F 7/11 20130101;
G03F 7/168 20130101; Y10T 428/31935 20150401 |
Class at
Publication: |
430/311 |
International
Class: |
G03C 001/492; G03C
001/494 |
Goverment Interests
[0002] This invention was made with government support under
contract number DASG60-01-C-0047 awarded by the U.S. Army Space and
Missile Defense Command. The United States government has certain
rights in the invention.
Claims
We claim:
1. A composition useful for forming microelectronic devices, said
composition comprising: a compound selected from the group
consisting of polymers, oligomers, and mixtures thereof, said
compound comprising an acid group other than a phenolic group; a
vinyl ether crosslinker; and a solvent system, said compound and
crosslinker being dissolved or dispersed in said solvent system,
said composition being wet developable.
2. The composition of claim 1, said composition further comprising
an acid generator.
3. The composition of claim 2, wherein said acid generator is a
photoacid generator.
4. The composition of claim 1, wherein said compound is not
acid-sensitive.
5. The composition of claim 1, wherein said acid group is free of
protective groups.
6. The composition of claim 1, wherein said compound comprises
protected acid groups and unprotected acid groups, and the molar
ratio of protected acid groups to unprotected acid groups is from
about 1:3 to about 3:1.
7. The composition of claim 1, wherein said composition further
comprises a chromophore.
8. The composition of claim 7, wherein said chromophore is bonded
with said compound.
9. The composition of claim 7, wherein said chromophore is present
in said composition at a level of from about 5-50% by weight, based
upon the total weight of the compound taken as 100% by weight.
10. The composition of claim 1, wherein said vinyl ether
crosslinker has the formula R--(X--O--CH.dbd.CH.sub.2).sub.n,
where: R is selected from the group consisting of aryls and alkyls;
each X is individually selected from the group consisting of
alkyls, alkoxys, carboxys, and combinations of two or more thereof;
and n is 2-6.
11. The composition of claim 10, wherein said vinyl ether
crosslinker is selected from the group consisting of ethylene
glycol vinyl ether, trimethylolpropane trivinyl ether,
1,4-cyclohexane dimethanol divinyl ether, 6and mixtures
thereof.
12. The composition of claim 1, wherein said acid group is a
carboxylic acid.
13. The composition of claim 1, wherein said polymer is selected
from the group consisting of aliphatic polymers, acrylates,
methacrylates polyesters, polycarbonates, novolaks, polyamic acids,
and mixtures thereof.
14. A method of forming a microelectronic structure, said method
comprising the steps of: providing a substrate having a surface;
applying a composition to said surface, said composition
comprising: a compound selected from the group consisting of
polymers, oligomers, and mixtures thereof, said compound comprising
an acid group other than a phenolic group; a vinyl ether
crosslinker; and a solvent system, said compound and crosslinker
being dissolved or dispersed in said solvent system, crosslinking
the compound in said composition; exposing said composition to
light to yield an exposed portion of said composition; and
contacting said composition with a developer so as to remove said
exposed portion from said surface.
15. The method of claim 14, wherein said crosslinking step
comprises thermally crosslinking said compound.
16. The method of claim 14, wherein said crosslinking step yields a
layer of composition that is substantially insoluble in photoresist
solvents.
17. The method of claim 16, wherein said crosslinking step yields
crosslinked compounds comprising linkages having the formula 7
18. The method of claim 14, where said exposing step yields a layer
of composition that is substantially soluble in photoresist
developers.
19. The method of claim 17, wherein said exposing step results in
the breaking of the bond (*) of the linkage having the formula
8
20. The method of claim 14, wherein said substrate is a
microelectronic substrate.
21. The method of claim 20, wherein said substrate is selected from
the group consisting of silicon, aluminum, tungsten, tungsten
silicide, gallium arsenide, germanium, tantalum, tantalum nitrite,
SiGe, ion implant layers, low k dielectric layers, and dielectric
layers.
22. The method of claim 14, wherein: said substrate further
comprises structure defining a hole, said structure including
sidewalls and a bottom wall; and said applying step comprises
applying the composition to at least a portion of said hole
sidewalls and bottom wall.
23. The method of claim 14, wherein said substrate comprises an ion
implant layer, and said applying step comprises forming a layer of
said composition adjacent said ion implant layer.
24. The method of claim 14, further comprising the step of applying
a photoresist layer prior to said exposing step.
25. A method of forming a microelectronic structure, said method
comprising the steps of: providing a substrate having a surface;
applying a composition to said surface, said composition comprising
a compound dissolved or dispersed in a solvent system, said
compound being selected from the group consisting of polymers,
oligomers, and mixtures thereof, said compound comprising a
carboxylic acid group; crosslinking the compound in said
composition; and exposing said composition to light so as to
decrosslink said compound.
26. The method of claim 25, wherein said crosslinking step
comprises thermally crosslinking said compound.
27. The method of claim 25, wherein said crosslinking step yields a
layer of composition that is substantially insoluble in photoresist
solvents.
28. The method of claim 25, wherein crosslinking step yields
crosslinked compounds comprising linkages having the formula 9
29. The method of claim 25, where said exposing step yields a layer
of composition that is substantially soluble in photoresist
developers.
30. The method of claim 28, wherein said exposing step results in
the breaking of the bond (*) of the linkage having the formula
10
31. The method of claim 25, wherein said substrate is a
microelectronic substrate.
32. The method of claim 31, wherein said substrate is selected from
the group consisting of silicon, aluminum, tungsten, tungsten
silicide, gallium arsenide, germanium, tantalum, tantalum nitrite,
SiGe, ion implant layers, low k dielectric layers, and dielectric
layers.
33. The method of claim 25, wherein: said substrate further
comprises structure defining a hole, said structure including
sidewalls and a bottom wall; and said applying step comprises
applying the composition to at least a portion of said hole
sidewalls and bottom wall.
34. The method of claim 25, wherein said substrate comprises an ion
implant layer, and said applying step comprises forming a layer of
said composition adjacent said ion implant layer.
35. The method of claim 25, further comprising the step of applying
a photoresist layer prior to said exposing step.
36. The combination of: a substrate; and a layer adjacent said
substrate, said layer comprising a crosslinked compound comprising
linkages having the formula 11
37. The combination of claim 36, wherein said substrate is
amicroelectronic substrate.
38. The combination of claim 37, wherein said substrate is selected
from the group consisting of silicon, aluminum, tungsten, tungsten
silicide, gallium arsenide, germanium, tantalum, tantalum nitrite,
SiGe, ion implant layers, low k dielectric layers, and dielectric
layers.
39. The combination of claim 36, wherein said layer is
substantially insoluble in photoresist solvents.
40. The combination of claim 36, further comprising a photoresist
adjacent said layer.
41. The combination of: a substrate; and a layer adjacent said
substrate, said layer comprising a mixture of: a compound selected
from the group consisting of polymers, oligomers, and mixtures
thereof, said compound comprising an acid group; an alcohol; and
acetylaldehyde.
42. The combination of claim 41, wherein said substrate is a
microelectronic substrate.
43. The combination of claim 42, wherein said substrate is selected
from the group consisting of silicon, aluminum, tungsten, tungsten
silicide, gallium arsenide, germanium, tantalum, tantalum nitrite,
SiGe, ion implant layers, low k dielectric layers, and dielectric
layers.
44. The combination of claim 41, wherein said layer is
substantially soluble in photoresist developers.
45. The combination of claim 41, further comprising a photoresist
adjacent said layer.
46. A compound having the formula 12
Description
RELATED APPLICATIONS
[0001] This application claims the priority benefit of a
provisional application entitled ANTI-REFLECTIVE COATING USING
VINYL ETHER CROSSLINKERS, Ser. No. 60/566,329, filed Apr. 29, 2004,
incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention is concerned with novel wet
developable anti-reflective coating compositions and methods of
using the same.
[0005] 2. Description of the Prior Art
[0006] As feature sizes shrink to less than 110 nm, new and more
advanced materials will be needed to achieve the goals set by the
semiconductor industry. Improvements in both photoresists and
bottom anti-reflective coatings are needed to achieve
high-resolution lithography targets. For example, resist thickness
loss that occurs during the bottom anti-reflective coating and
substrate etch steps becomes a critical issue because new resists
are much thinner than older generation materials. While resist
thickness is being reduced, bottom anti-reflective coating
thickness is not expected to decrease at the same rate, which
further complicates the problem of resist loss. A solution to this
problem is to eliminate the bottom anti-reflective coating etch
step by using a wet-developable bottom anti-reflective coating.
[0007] Wet-developable bottom anti-reflective coatings have
typically utilized a polyamic acid soluble in alkaline media as a
polymer binder, thus allowing the bottom anti-reflective coating to
be removed when the resist is developed. These traditional
wet-developable bottom anti-reflective coatings are rendered
insoluble in resist solvents taking advantage of a thermally driven
amic acid-to-imide conversion. This process works well, however, it
has two limitations: (1) the bake temperature window can be narrow
(less than 10.degree. C.) where the bottom anti-reflective coating
remains insoluble in organic solvents but soluble in alkaline
developer; and (2) the wet-develop process is isotropic, meaning
the bottom anti-reflective coating is removed vertically at the
same rate as horizontally, which leads to undercutting of the
resist lines. While this is not a problem with larger geometries
(greater than 0.2 micron), it can easily lead to line lifting and
line collapse at smaller line sizes.
SUMMARY OF THE INVENTION
[0008] The present invention overcomes the problems of prior art
wet developable anti-reflective coatings by providing new wet
developable compositions that are useful in the manufacture of
microelectronic devices.
[0009] In more detail, the inventive compositions comprise a
compound selected from the group consisting of polymers, oligomers,
and mixtures thereof dissolved or dispersed in a solvent system.
The compound is preferably present in the composition at a level of
from about 0.5-10% by weight, preferably from about 0.5-5% by
weight, and even more preferably from about 1-4% by weight, based
upon the total weight of all ingredients in the composition taken
as 100% by weight.
[0010] If the compound is a polymer, it is preferred that the
average molecular weight be from about 1,000-100,000 Daltons, and
more preferably from about 1,000-25,000 Daltons. Preferred polymers
include those selected from the group consisting of aliphatic
polymers, acrylates, methacrylates, polyesters, polycarbonates,
novolaks, polyamic acids, and mixtures thereof.
[0011] If the compound is an oligomer, it is preferred that the
molecular weight be from about 500-3,000 Daltons, and more
preferably from about 500-1,500 Daltons. Preferred oligomers
include substituted and unsubstituted acrylates, methacrylates,
novolaks, isocyanurates, glycidyl ethers, and mixtures thereof.
[0012] Regardless of whether the compound is an oligomer or
polymer, and regardless of the structure of the polymer backbone or
oligomer core, it is preferred that the compound comprise an acid
functional group. The acid group is preferably present in the
compound at a level of at least about 5% by weight, preferably from
about 5-90% by weight, and even more preferably from about 5-50% by
weight, based upon the total weight of the compound taken as 100%
by weight. Preferred acid groups are groups other than phenolics,
such as carboxylic acids (--COOH).
[0013] Unlike prior art compositions, the acid group is preferably
not protected by a protective group. That is, at least about 95%,
preferably at least about 98%, and preferably about 100% of the
acid groups are free of protective groups. A protective group is a
group that prevents the acid from being reactive.
[0014] Because protective groups are not necessary with the present
invention, it is also preferred that the compound is not
acid-sensitive. An acid-sensitive polymer or oligomer is one that
contains protective groups that are removed, decomposed, or
otherwise converted in the presence of an acid.
[0015] In another embodiment, a combination of protected acid
groups and unprotected acid groups could be utilized. In these
embodiments, the molar ratio of protected acid groups to
unprotected acid groups is from about 1:3 to about 3:1, and more
preferably from about 1:2 to about 1:1.
[0016] It is also preferred that the inventive compositions
comprise a chromophore (light attenuating compound or moiety). The
chromophore can be bonded with the compound (either to a functional
group on the compound or directly to the polymer backbone or
oligomer core), or the chromophore can simply be physically mixed
in the composition. The chromophore should be present in the
composition at a level of from about 5-50% by weight, and
preferably from about 20-40% by weight, based upon the total weight
of the compound taken as 100% by weight. The chromophore is
selected based upon the wavelength at which the compositions will
be processed. For example, at wavelengths of 248 nm, preferred
chromophores include naphthalenes (e.g., naphthoic acid
methacrylate, 3,7-dihydroxynaphthoic acid), heterocyclic
chromophores, carbazoles, anthracenes (e.g., 9-anthracene methyl
methacrylate, 9-anthracenecarboxylic acid), and functional moieties
of the foregoing. At wavelengths of 193 nm, preferred chromophores
include substituted and unsubstituted phenyls, heterocyclic
chromophores (e.g., furan rings, thiophene rings), and functional
moieties of the foregoing. The preferred inventive compositions
will also include a crosslinker.
[0017] Preferred crosslinkers are vinyl ether crosslinkers. It is
preferred that the vinyl ether crosslinkers be multi-functional,
and more preferably tri- and tetra-functional.
[0018] Preferred vinyl ether crosslinkers have the formula
R--(X--O--CH.dbd.CH.sub.2).sub.n,
[0019] where R is selected from the group consisting of aryls
(preferably C.sub.6-C.sub.12) and alkyls (preferably
C.sub.1-C.sub.18, and more preferably C.sub.1-C.sub.10), each X is
individually selected from the group consisting of: alkyls
(preferably C.sub.1-C.sub.18, and more preferably
C.sub.1-C.sub.10); alkoxys (preferably C.sub.1-C.sub.18, and more
preferably C.sub.1-C.sub.10); carboxys; and combinations of two or
more of the foregoing, and n is 2-6. The most preferred vinyl ether
crosslinkers include those selected from the group consisting of
ethylene glycol vinyl ether, trimethylolpropane trivinyl ether,
1,4-cyclohexane dimethanol divinyl ether, and mixtures thereof.
Another preferred vinyl ether crosslinker has a formula selected
from the group consisting of 1
[0020] The preferred compositions also contain a catalyst. The
preferred catalyst is an acid generator, and particularly a
photoacid generator ("PAG," both ionic and/or non-ionic). Any PAG
that produces an acid in the presence of light is suitable.
Preferred PAGs include onium salts (e.g., triphenyl sulfonium
perfluorosulfonates such as triphenyl sulfonium nonaflate and
triphenyl sulfonium triflate), oxime-sulfonates (e.g., those sold
under the name CGI.RTM. by CIBA), and triazines (e.g., TAZ108.RTM.
available from Midori Kagaku Company).
[0021] The compositions preferably comprise from about 0.1-10% by
weight of catalyst, and more preferably from about 1-5% by weight
of catalyst, based upon the total weight of the polymer and
oligomer solids in the composition taken as 100% by weight.
[0022] It will be appreciated that a number of other optional
ingredients can be included in the compositions as well. Typical
optional ingredients include surfactants, amine bases, and adhesion
promoters.
[0023] Regardless of the embodiment, the anti-reflective
compositions are formed by simply dispersing or dissolving the
polymers, oligomers, or mixtures thereof in a suitable solvent
system, preferably at ambient conditions and for a sufficient
amount of time to form a substantially homogeneous dispersion. The
other ingredients (e.g., crosslinker, PAG) are preferably dispersed
or dissolved in the solvent system along with the compound.
[0024] Preferred solvent systems include a solvent selected from
the group consisting of propylene glycol methyl ether acetate
(PGMEA), propylene glycol methyl ether (PGME), propylene glycol
n-propyl ether (PnP), ethyl lactate, and mixtures thereof.
Preferably, the solvent system has a boiling point of from about
50-250.degree. C., and more preferably from about 100-175.degree.
C. The solvent system should be utilized at a level of from about
80-99% by weight, and preferably from about 95-99% by weight, based
upon the total weight of the composition taken as 100% by
weight.
[0025] The method of applying the compositions to a substrate (such
as a microelectronic substrate) simply comprises applying a
quantity of a composition hereof to the substrate surface by any
known application method (including spin-coating). The substrate
can be any conventional circuit substrate, and suitable substrates
can be planar or can include topography (e.g., contact or via
holes, trenches). Exemplary substrates include silicon, aluminum,
tungsten, tungsten silicide, gallium arsenide, germanium, tantalum,
tantalum nitrite, SiGe, low k dielectric layers, dielectric layers
(e.g., silicon oxide), and ion implant layers.
[0026] After the desired coverage is achieved, the resulting layer
should be heated to a temperature of from about 100-250.degree. C.,
and preferably from about 120-200.degree. C., to induce
crosslinking of the compound in the layer. In embodiments where the
polymer or oligomer includes a carboxylic acid group, and the
crosslinker is a vinyl ether crosslinker, the crosslinked polymers
or oligomers will comprise acetal linkages having the formula 2
[0027] The crosslinked layer will be sufficiently crosslinked that
it will be substantially insoluble in typical photoresist solvents.
Thus, when subjected to a stripping test, the inventive coating
layers will have a percent stripping of less than about 5%,
preferably less than about 1%, and even more preferably about 0%.
The stripping test involves first determining the thickness (by
taking the average of measurements at five different locations) of
a cured layer. This is the average initial film thickness. Next, a
solvent (e.g., ethyl lactate) is puddled onto the cured film for
about 10 seconds, followed by spin drying at about 2,000-3,500 rpm
for about 20-30 seconds to remove the solvent. The thickness is
measured again at five different points on the wafer using
ellipsometry, and the average of these measurements is determined.
This is the average final film thickness.
[0028] The amount of stripping is the difference between the
initial and final average film thicknesses. The percent stripping
is: 1 % stripping = ( amount of stripping initial average film
thickness ) .times. 100.
[0029] The crosslinked layers will also have superior light
absorbance. The n value of this cured anti-reflective layer or
coating will be at least about 1.3, and preferably from about
1.4-2.0, while the k value will be least about 0.1, and preferably
from about 0.2-0.8, at the wavelength of use (e.g., 157 nm, 193 nm,
248 nm, 365 nm). The OD of the cured layers will be at least about
5/.mu.m, preferably from about 5-15/.mu.m, and even more preferably
from about 10-15 .mu.m, at the wavelength of use (e.g., 157 nm, 193
nm, 248 nm, 365 nm).
[0030] After the layers are cured, further steps can be carried out
as necessary for the particular manufacturing process. For example,
a photoresist can be applied to the cured layer and subsequently
patterned by exposure to light of the appropriate wavelength
followed by development of the exposed photoresist. Advantageously,
as the photoresist is exposed to light, so is the inventive
coating. Upon exposure to light, an acid is generated from the PAG,
and this acid "decrosslinks" the compound in the layer. That is,
the acid breaks the bond that was formed between the compound and
the crosslinker upon thermal crosslinking. When a carboxylic acid
is the acid group on the polymer or oligomer, decrosslinking
results in the formation of the same polymer or oligomer originally
present in the composition as well as an alcohol and an
acetylaldehyde. This reaction is demonstrated in the scheme below
(where R represents the polymer backbone or oligomer core, and R'
represents the remainder of the vinyl ether crosslinker). 3
[0031] It will be appreciated that after this decrosslinking has
occurred, the inventive coatings are rendered wet developable. That
is, the cured compositions that have been exposed to light can be
substantially (and preferable completely) removed with conventional
aqueous developers such as tetramethyl ammonium hydroxide and KOH
developers. Some of these developers are commercialized under the
names PD523AD (available from JSR Micro), MF-319 (available from
Shipley, Mass.), and NMD3 (available from TOK, Japan) developers.
At least about 95%, preferably at least about 99%, and even more
preferably 100% of the inventive coatings will be removed by a base
developer such as tetramethyl ammonium hydroxide and/or KOH
developers. This high percent solubility in commercially-available
developers after light exposure is a significant advantage over the
prior art as this shortens the manufacturing process and makes it
less costly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] The following examples set forth preferred methods in
accordance with the invention. It is to be understood, however,
that these examples are provided by way of illustration and nothing
therein should be taken as a limitation upon the overall scope of
the invention.
Material and Methods
[0033]
1 1. In-house Preparation of Tetrafunctional Vinyl Ether
Crosslinker 4
[0034] The reaction was carried out under N.sub.2 in a 250-ml,
3-neck, round bottom flask. The Na cube was rinsed with hexane
prior to use to remove mineral oil, placed quickly in a vial for
weighing, and then transferred to the flask, which contained 50 ml
THF. An alcohol solution in THF (20 ml) was added dropwise through
an addition funnel (about 15 minutes), and then heated to reflux
until all of the Na was dissolved (about 30 minutes). The solution
was light yellow and homogeneous. Tetrabromo durene dissolved in
THF (15 ml) was added to the reaction flask dropwise (about 30
minutes), and allowed to reflux overnight. Upon addition, the
mixture became heterogenous (NaBr precipitates).
[0035] After cooling, the salts were filtered and rinsed with THF.
The THF was removed in a rotary evaporator, and the remaining oil
was redissolved in CHCl.sub.3 (25 ml). The chloroform solution was
washed with water (2.times.25 ml), and then with brine (saturated
NaCl, 25 ml). The organic layer was dried by passing it over a bed
of silica gel. The solvent was removed. The product was left under
vacuum for further drying. 5
[0036] Ethylene glycol vinyl ether (6 grams) and triethyl amine
(7.5 ml) were mixed in ether (40 ml) and treated dropwise with a
solution of trimesic acid chloride (6 grams) in ether (40%). After
addition, the mixture was heated to reflux for 1.5 hours. Residual
salts were removed by filtration, and the ether solution was washed
with 10% NaOH (2.times.25 ml), washed with water (25 ml), and then
dried over anhydrous magnesium sulfate. After removal of the
solvent under pressure, light yellow oil was collected (69%
yield).
EXAMPLE 1
Polymer Composition Without Acid Sensitive Groups
[0037] A homopolymer of methacryloyloxy ethyl phthalate (28.9 mmol,
obtained from Aldrich) and 2,2'-azobisisobutyronitrile ("AIBN,"
0.58 mmol radical initiator, obtained from Aldrich) were mixed in
50 ml tetrahydrofuran ("THF," obtained from Aldrich) under a
nitrogen atmosphere and heated to reflux for 15 hours. The reaction
was allowed to cool, concentrated to about 25 ml, and then
precipitated into 200 ml hexane. After filtration and drying, about
8 grams of the remaining white powder were collected. The polymer
molecular weight ("Mw") was measured by using polystyrene standards
and gel permeation chromatography ("GPC") and was determined to be
68,400.
[0038] A 193-nm bottom anti-reflective coating was prepared as
follows: A 3% solids formulation containing ethyl lactate ("EL,"
obtained from General Chemical), the polymer prepared above, 28% by
weight Vectomer 5015 (a vinyl ether crosslinker obtained from
Aldrich), and 4% by weight triphenyl sulfonium nonaflate (a PAG,
obtained from Aldrich) was prepared and filtered through 0.1-micron
endpoint filter. The crosslinker and PAG amounts were based on the
weight of the polymer.
[0039] The above formulation was spin coated at 1,500 rpm on a
silicon substrate and then baked at 160.degree. C. The films were
rinsed with EL to determine resistance to the resist solvent,
exposed to light for 2 seconds, heated in a post-exposure bake
("PEB") at 130.degree. C., and immersed in developer
(tetramethylammonium hydroxide or "TMAH," sold under the name
PD523AD, obtained from JSR Micro) for 60 seconds to decrosslink and
remove the bottom anti-reflective coating. Table 1 below shows that
the bottom anti-reflective coating had good solvent resistance, and
that it could only be removed by an alkaline developer after
exposure. This example shows that a polymer having an
acid-sensitive group is not required for the
crosslinking/decrosslinking process.
2TABLE 1 Thickness After Thickness After Initial Thickness After
Development Exposure, PEB.sup.a, Thickness 20 sec. EL Rinse % (No
Exposure) % and Development % (.ANG.) (.ANG.) Loss (.ANG.) Loss
(.ANG.) Loss 619 590 4.7 712 0 65 90 .sup.aPost-exposure bake
EXAMPLE 2
Bottom Anti-Reflective Coating Containing Chromophore, Acid, and
Dissolution Enhancer
[0040] Methacrylic acid ("MAA," 31.2 mmol, obtained from Aldrich),
tert-butyl methacrylate ("tBMA," 26.0 mmol, obtained from Aldrich),
9-anthracene methyl methacrylate ("9-AMMA," 14.5 mmol, obtained
from St-Jean Photochemicals Inc.), and AIBN (1.4 mmol) were mixed
in 60 ml THF under nitrogen atmosphere and heated to reflux for 19
hours. The reaction was allowed to cool, was concentrated to about
35 ml, and was then precipitated into 150 ml hexane. After
filtration and drying, about 10 grams of a light yellow powder were
collected. The polymer Mw, measured by using polystyrene standards
and GPC, was determined to be 23,800.
[0041] A 3% solids formulation containing the polymer, PGME
(obtained from General Chemical), PGMEA (obtained from General
Chemical), 10% tetrafunctional vinyl ether crosslinker prepared
in-house as described above, and 4% triphenyl sulfonium triflate (a
PAG obtained from Aldrich) was prepared and filtered through a
0.1-micron endpoint filter. The crosslinker and PAG amounts were
based on polymer weight. The above formulation was spin coated at
1,500 rpm onto a silicon substrate and then baked at 160.degree. C.
The optical constants at 248 nm were measured using a variable
angle spectroscopic ellipsometer ("VASE") and were determined to be
k=0.42 and n=1.4589. The film was rinsed with EL to test resistance
to a resist solvent. After a rinse and spin dry cycle, no change in
film thickness occurred. The cured film was immersed in 0.26N TMAH
solution, and no thickness loss occurred. However, after the film
was exposed to light from a mercury-xenon lamp for 2 seconds and
underwent a subsequent post-exposure bake at 130.degree. C. for 90
seconds, the film became soluble in developer.
EXAMPLE 3
Control of Optical Properties by Polymer Composition
[0042] Several polymers were prepared using the procedure in
Example 2 and using varying amounts of chromophore (9-AMMA) in
order to demonstrate control of the optical properties of the
bottom anti-reflective coating while maintaining dissolution
properties. A 3% solids formulation containing PGME, PGMEA, 10%
tetrafunctional vinyl ether crosslinker prepared in-house as
described above, and 4% triphenyl sulfonium triflate PAG was
prepared and filtered through a 0.1-micron endpoint filter.
[0043] Table 2 shows that by increasing chromophore loading in the
polymer, optical density, and substrate reflectivity can be
controlled.
3TABLE 2 Reflectivity 9-AMMA n 1st Minimum at 1st Minimum (Mole
%).sup.a k value value OD/.mu.m Thickness (.ANG.) Thickness (%) 10
0.27 1.52 6.1 660 2.6 20 0.42 1.459 10.8 660 0.08 30 0.54 1.462
13.3 620 0.87 .sup.abased upon total moles of solids in
composition
EXAMPLE 4
Comparative Example with Phenolic Polymer
[0044] A comparative example was prepared to demonstrate that vinyl
ether crosslinking with a phenolic resin does not provide
sufficient crosslinking density to prevent stripping by photoresist
solvent.
[0045] In this procedure, 0.5 grams of polyhydroxystyrene ("PHS,"
obtained from DuPont), 0.02 grams of a triazine PAG (TAZ107,
obtained from Midori Kagaku Company), 8.5 grams of EL, and various
amounts of triscarboxyphenyl trivinyl ether prepared in-house were
mixed and filtered through a 0.1-micron endpoint filter. Two
additional formulations were also prepared in which 9-anthracene
carboxylic acid ("9-ACA," a chromophore obtained from Aldrich) were
added to the composition to form a bottom anti-reflective coating
for 248-nm lithography. Films were spin coated onto silicon
substrates and then baked at varying temperatures up to 205.degree.
C. Table 3 shows the results obtained. In all cases, the bottom
anti-reflective coating stripped completely when rinsed with
EL.
4TABLE 3 Bake EL Stripping (% Crosslinker:PHS Temperature change in
film Polymer Ratio (.degree. C.) PAG Chromophore thickness) PHS 2:1
150, 205 TAZ107 -- 100 PHS 4:1 150, 205 TAZ107 -- 100 PHS 2:1
100-205.sup.a TAZ107 9-ACA 100 PHS 4:1 100-205 TAZ107 9-ACA 100
.sup.atests were carried out at 10-degree intervals through this
temperature range.
* * * * *