U.S. patent application number 09/422633 was filed with the patent office on 2001-12-06 for highly sensitive positive photoresist compositions.
This patent application is currently assigned to David Paul Merritt. Invention is credited to MERRITT, DAVID PAUL, MOREAU, WAYNE MARTIN, WOOD, ROBERT LAVIN.
Application Number | 20010049071 09/422633 |
Document ID | / |
Family ID | 25463947 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010049071 |
Kind Code |
A1 |
MERRITT, DAVID PAUL ; et
al. |
December 6, 2001 |
HIGHLY SENSITIVE POSITIVE PHOTORESIST COMPOSITIONS
Abstract
Positive resists sensitive to UV, electron beam, and x-ray
radiation which are alkaline developable are formulated from a
polymer material comprising recurrent structures having alkaline
soluble groups pendent to the polymer backbone, a portion of which
groups are substituted with acid labile groups.
Inventors: |
MERRITT, DAVID PAUL; (COLD
SPRING, NY) ; MOREAU, WAYNE MARTIN; (WAPPINGERS
FALLS, NY) ; WOOD, ROBERT LAVIN; (POUGHKEEPSIE,
NY) |
Correspondence
Address: |
STEVEN CAPELLA
IBM CORPORATION
INTELLECTUAL PROPERTY LAW
BLDG. 300-482, 2070 ROUTE 52
HOPEWELL JUNCTION
NY
12533-6531
US
|
Assignee: |
David Paul Merritt
|
Family ID: |
25463947 |
Appl. No.: |
09/422633 |
Filed: |
October 21, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09422633 |
Oct 21, 1999 |
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08961186 |
Oct 30, 1997 |
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6051659 |
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08961186 |
Oct 30, 1997 |
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07933432 |
Aug 20, 1992 |
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07933432 |
Aug 20, 1992 |
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07264407 |
Oct 28, 1988 |
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Current U.S.
Class: |
430/270.1 |
Current CPC
Class: |
C08F 8/00 20130101; C08F
8/00 20130101; G03F 7/039 20130101; C08F 12/14 20130101 |
Class at
Publication: |
430/270.1 |
International
Class: |
G03F 007/038 |
Claims
We claim:
1. An improved positive working resist composition comprising a
polymeric material having functional groups pendent thereto which
contribute to the solubility of the polymer in alkaline developers
and a portion of which functional groups are substituted with acid
labile groups which inhibit the alkaline solubility of the polymer,
and a photoinitiator which generates a strong acid upon radiolysis
to remove the acid labile groups from the functional groups in the
exposed areas of the polymer.
2. The resist composition of claim 1 wherein the polymeric material
comprises an aromatic polymer.
3. The resist composition of claim 2 wherein the aromatic material
is a polystyrene.
4. The resist composition of claim 1 wherein the alkaline soluble
functional groups are selected from the group consisting of
hydroxyl, amine, carboxyl, and imide NH.
5. The resist composition of claim 4 wherein the alkaline soluble
functional group is hydroxyl.
6. The resist composition of claim 1 wherein the acid labile group
is selected from the group of alkyloxycarbonyl, aryloxycarbonyloxy,
and alkyloxycarbonyloxy.
7. The resist composition of claim 6 wherein the alkyl portion of
the acid labile group has an available hydrogen on an a carbon
atom.
8. The resist composition of claim 7 where the alkyl portion of the
acid labile group is secondary alkyl or tertiary alkyl.
9. The resist composition of claim 1 wherein from about 20% to
about 50% of the pendent groups are substituted with acid labile
groups.
10. The resist composition of claim 1 wherein the polymer is a
polystyrene, the functional group is hydroxyl, and the acid labile
group is a secondary or tertiary alkyloxy carbonyloxy group.
11. The resist composition of claim 11 wherein the polymer is a
p-hydroxystyrene and the acid labile group is
t-butyloxycarbonyloxy.
12. The method of making a substituted polymeric material for use
in resist compositions, comprising the steps of: (a) dissolving a
polymer having acid labile groups pendent to the polymer backbone
thereof in an acid stable solvent, (b) heating the solution with
stirring under an unreactive atmosphere to a temperature in the
range 20 to 70.degree. C., (c) adding concentrated mineral acid to
the stirred solution in an amount sufficient to remove acid labile
groups from the polymer, (d) continuing the reaction until the
desired degree of substitution is achieved, (e) quenching the
reaction with base, and (f) precipitating the substituted polymeric
material.
13. The method of claim 12 wherein the polymer is polystyrene.
14. The method of claim 12 wherein the acid labile groups are
selected from the group consisting of alkyloxycarbonyl,
aryloxycarbonyloxy and alkyloxycarbonyloxy.
15. The method of claim 14 wherein the alkyl portion of the acid
labile group has an available hydrogen on an .alpha. carbon
atom.
16. The method of claim 15 wherein the alkyl portion of the acid
labile group is secondary alkyl or tertiary alkyl.
17. The method of claim 16 wherein the acid labile group is
t-butyloxycarbonyloxy.
18. The method fo claim 12 wherein the pKa of the acid is less than
about 4.
19. The method of claim 18 wherein the mineral acid is sulfuric
acid.
20. The method of claim 12 wherein the reaction temperature is in
the range of 50-60.degree. C.
21. The method of claim 12 wherein the reaction is quenched with
ammonium hydroxide.
22. The method of claim 12 wherein the substituted polymeric
material is precipitated in ammonium acetate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to highly sensitive positive
photoresist compositions which are mixtures of certain partially
substituted polymeric materials and cationic photoinitiators. In
particular, there are provided photoresist compositions with
greatly improved sensitivity without deterioration of their
processability. These compositions which may be conveniently
developed with alkaline developers display increased sensitivity to
ultraviolet (UV), electron beam (E-beam) and X-ray radiation, are
thermally stable at temperatures up to about 165.degree. C, adhere
readily to silicon dioxide and silicon nitride layers on a
substrate, and may be treated with organometallic reagents (e.g.,
silylating agents) without the necessity of any post development
baking. The films formed may be processed with very little image
shrinkage on exposure and development and provide essentially
crack-free resist layers. The partially substituted polymeric
materials comprise recurrent structures having alkaline soluble
groups pendent to the polymeric backbone, a portion of which groups
have been substituted with (protected by) acid labile groups.
[0003] 2. Background of the Invention
[0004] The fabrication of semiconductor devices requires the use of
resist compositions which maintain imaged patterns during a
processing. As the need to increase semiconductor circuit density
has dictated a movement from very large scale integration (VLSI)
devices to ultra-large scale integration (ULSI) devices, the
demands for submicron photolithography with sensitivity to produce
and maintain ultra-fine tolerances become more critical.
[0005] Chemically amplified resist systems having a polymer and
sensitizer combination which generate an initial acid from the
sensitizer and additional acid from the polymer provide increased
sensitivity to UV, e-beam and x-ray radiation.
[0006] In Ito et al., U.S. Pat. No. 4,491,628, resists sensitive to
ultraviolet (UV), electron beam and X-ray radiation capable of
forming either positive or negative tone patterns dependent upon
the choice of developers were disclosed. Such resist compositions
are formulated from a polymer having recurrent acid labile groups
(such as tertbutyl esters and tertbutyl carbonates) which undergo
efficient acidolysis to effect a change in polarity (solubility)
and a photo-initiator which generates acid upon radiolysis. The
polymer may be a copolymer which includes polymers having recurrent
acid labile groups. When being used to form positive images the Ito
materials have possibility drawbacks that are directly related to
the completeness of removal of the acid labile group on the film
composition. These factors relate to skin formation, shrinkage,
cracking and poor adhesion which require delicate control to
overcome.
[0007] In Ito et al., U.S. Pat. No. 4,552,833, there is provided a
process for generating negative images wherein a film of a polymer
having masked functionalities is coated onto a substrate, the film
is imagewise exposed, the exposed film is treated with an
organometallic reagent, and the treated film is developed with an
oxygen plasma. That disclosure contemplates the dry development of
polymers similar to those disclosed in U.S. Pat. No. 4,491,628. The
dry development process avoids changes in film compositions that
lead to processing complications in Chiong et al., U.S. Pat. No.
4,613,398, still other processes are disclosed entailing the
removal of acid labile protecting groups from pendent alkaline
soluble groups on a resist polymer such as hydroxyl, amine,
carboxyl, phenol, or imide NH which are capable of reacting with
the organometallic reagent. Upon silylation and further processing
negative images are obtained.
[0008] In U.S. Ser. No. 922,657, filed Oct. 24, 1986 and assigned
to the assignee of the present application, there are described
certain highly sensitive resists that achieve high
autodecomposition temperatures due to the presence of secondary
carbonium ion forming acid labile substituent groups on polymers
having pendent carbonate or carbonate-like groups.
[0009] Ito, J. Polymer Science Part A, 24, 2971-80 (1986) discloses
effects of p-hydroxystyrene groups in the thermolysis of
poly(p-t-butyloxycarbonyloxy styrene) and devises a method to make
such substituted polymer via a copolymerization of
butyloxycarbonyloxy styrene with formyloxy styrene followed by
photo-fries decomposition to convert the formyloxystyrene units to
hydroxystyrene units.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, highly sensitive
positive photoresist compositions are made by combining a polymeric
material having functional groups pendent thereto which contribute
to the solubility of the polymer in alkaline developers, a portion
of which functional groups are substituted with masking or
protecting acid labile groups which inhibit the solubility of the
polymer, and a photoinitiator compound which generates a strong
acid upon radiolysis which is able to cleave or remove the acid
labile groups from the polymer to unmask or deprotect functional
sites. From 15 to 40 percent of the pendent functional groups are
masked or protected with acid labile groups. The preferred
protecting groups will also generate acid when they are cleaved or
removed and cause additional cleavage or removal of masking as
protecting groups, furthering the formation of a latent image. The
most preferred protecting group-functional group structure is
tert-butyl carbonate of a phenol. On acid generated decomposition,
it is believed that the mechanism includes formation of a
phenoxycarbonyloxy ion and a tertiary carbonium ion which further
decompose to provide phenol, carbon dioxide, isobutene and proton
(H+) fragments, the latter being available for further deprotecting
of the polymer. Other protecting groups which generate a proton
such as the secondary alkyl substituted moieties as disclosed in
U.S. Ser. No. 922,657, the disclosure of which is hereby
incorporated by reference into this application, may also be used,
however, such groups are generally more tightly bound to the groups
on the polymeric material functional groups and do not provide as
much sensitivity as do the tert-butyl carbonates of phenols.
[0011] It has been surprisingly found that a polymer having from 15
to 40 percent substitution with acid labile protecting groups
exhibits far more sensitivity than a polymer which is essentially
fully protected. This is especially surprising since the fully
unprotected polymer provides very limited resolution and image
discrimination to a positive tone.
[0012] Polymer backbones having pendent aromatic groups provide the
thermal and dimensional stability which are desired in order to
provide a material which may be applied to a substrate in a
uniformly thin coating, which may be baked to remove solvent and
which after imaging and patterning provides chemical resistance in
subsequent process steps.
[0013] The preferred polymer backbone is polystyrene having
substituent functional groups on the aromatic ring to impart
aqueous alkaline solubility to the polymer. These groups not only
must provide solubility, but they must be maskable with a blocking
or protective group that is acid removable in response to the
radiolysis of the acid generating sensitizer. The functional groups
ideally should be one which does not adversely interact with the
semiconductor processing environment. For that reason phenolic
groups are most preferred.
[0014] The partially substituted polymeric materials are not the
result of a copolymerization of monomeric materials, but rather
result from side chain substitution of homopolymers.
[0015] The homopolymers may be prepared in accordance with the
methods set forth in Ito et al. U.S. Pat. No. 4,491,628, the
disclosure of which is incorporated herein by reference. Those
methods include phase transfer reactions, free radical
polymerization and cationic polymerization to provide
p-tert-butyloxy-carbonyloxy styrene and p-tert-butyloxycarbonylox-
-.alpha.-methyl styrene.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a infrared spectrum showing the progress of
decarbonation of the polymer.
[0017] FIG. 2 is a correlation between infrared absorbance and mole
percent p-hydroxystyrene in the polymer.
[0018] FIG. 3 is a graph of absorbance in a 1 cm path-length cell
of a 0.02% diglyme solution made with the polymer of the
invention.
[0019] FIG. 4 is a comparative spectral representation of 1.4 .mu.m
resist films of various composition.
DETAILED DESCRIPTION
[0020] In accordance with the present invention the substituted
polymers were prepared as follows:
EXAMPLE 1
[0021] Synthesis of
poly-(p-Hydroxystyrene-p-tertbutoxycarbonyloxystyrene)
[0022] 300 grams of poly p-tertbutoxycarbonyloxystyrene with a
molecular weight of 15,000 was dissolved in 1500 ml of 1,2
dimethoxyethane and the solution was heated to 60.0.degree. C. To
the stirred solution was added dropwise 20.0 g of concentrated
H.sub.2SO.sub.4. The solution is kept at 60.degree. C. for 3-4
hours to convert 75 mole percent of the
p-tertbutoxycarbonyloxystyrene groups to p-hydroxystyrene. The
reaction was followed by IR of the reaction liquid. The IR peak
ratio of the hydroxyl (OH) group peak (3400 cm.sup.-1)to the
carbonate group peak (1750 cm.sup.-1)was used as the monitor to
obtain the desired ratio for conversion to a 75 mole percent
p-hydroxystyrene (see FIGS. 1 and 2). The mole percent of
p-hydroxystyrene can also be determined on the final product by UV
286 nm absorbance of a 0.02 weight percent solution in diglyme
(corrected for diglyme absorbance). The ratio of the absorbance of
the partially substituted to the absorbance of a 0.01%
p-hydroxystyrene at 286 nm is used, see FIG. 3. The
p-hydroxystyrene is made by the complete conversion (acidolysis) of
the initial tertbutoxycarbonyloxystyrene polymer. After the desired
tertbutoxycarbonyloxystyrene conversion was determined from the IR
monitor, the reaction is quenched by the addition of a solution of
potassium carbonate (125 g/250 ml water). The decanted liquid from
the reaction is precipitated into a ten-fold ratio of water
containing 0.05 M ammonium acetate and the product washed several
times with water. The product was dried overnight in vacuum at
50.degree. C. and checked for p-hydroxystyrene content by UV
analysis.
EXAMPLE 2
[0023] Two substituted polymer compositions were prepared by
solution phase acidolysis of the tertbutoxycarbonyloxystyrene
polymer having a weight-average molecular weight of about 15000 as
described in Example 1.
[0024] The first composition contained about 60 mole %
tertbutoxycarbonyloxystyrene and 40 mole % p-hydroxystyrene and the
second composition was about 23 mole % tertbutoxycarbonyloxy
styrene and 77 mole % p-hydroxystyrene as determined by UV
spectroscopy. These substituted polymers were formulated in
propylene glycol methyl ether acetate with 5% (based on weight of
solids) triphenylsulfonium hexafluroantimonate salt and were spin
coated on silicon wafers to give film thicknesses of about 1.3
microns. Following a 115.degree. C. 15 minute bake, the resists
were imagewise exposed on a Perkin Elmer projection aligner in the
UV-2 mode (240-300 nm) at doses ranging from 1-100 mJ/cm.sup.2.
Post exposure conversion was done at 90.degree. C. for 90 seconds
on a hot plate. The resists were developed at times ranging from 30
seconds to 5 minutes in an aqueous 0.27 N tetramethyl ammonium
hydroxide developer solution at room temperature. Alpha step
surface profile measurements of undeveloped films showed that the
first film had 18% film shrinkage while the second resist gave only
7% shrinkage. The tertbutoxycarbonyloxystyrene homopolymer control
gave 33% film shrinkage. Inspection of the developed images showed
that the tertbutoxycarbonyloxy styrene polymer control had cracked
extensively after only 30 seconds of development. Gross adhesion
loss was also noted. The first resist showed a low level of
cracking failure after 30 seconds and no adhesion failure. The
second resist showed neither cracking nor adhesion failure for up
to 5 minutes developing time.
[0025] Scanning electron microscope inspection of final images
showed that the control was underdeveloped at 60 seconds. Longer
developed times could not be evaluated due to poor adhesion and
cracking. The first resist gave nearly 1 to 1 mask replication
after 30 mJ exposure with 30 second development time. Nearly
vertical profiles were obtained, with a slight bread-loaf
appearance. The second resist required a higher exposure dose due
to the higher optical density in the 240-300 nm range. At 100 mJ
for 120 seconds development time, the second resist gave sidewall
having 70-80.degree. angles and no trace of bread-loaf. The first
and second resists were capable of resolving the smallest masked
feature of 0.75 micron.
[0026] FIG. 4 shows UV spectra at 1.4 micron films of the first and
second resists as well as of a fully protected control resist.
These curves show that the incorporation p-hydroxystyrene into the
film increases its optical density in the 240-300 nm range. Such
incorporation accounts for increased sensitivity and shallower
image profiles obtained with the 77% substituted polymers of the
second resist.
EXAMPLE 3
[0027] One mole of a p-tert-butyloxycarbonyloxy styrene polymer
(BCS) having a molecular weight of 15,000 was dissolved in a 20
weight percent solution of glyme. The solution was then heated
under a nitrogen atmosphere to 60.degree. C. To the stirred
solution, 0.25 mole of concentrated sulfuric acid was added
dropwise and the progress of the reaction was monitored by IR
spectroscopy until 78 mole percent of the tert-butyloxycarbonyl
(BC) groups were removed and the polymer had 22 percent BC
substitution and 78 percent hydroxyl substitution. The reaction was
quenched with an excess of ammonium hydroxide and ammonium sulfate
was filtered off. The polymer solution was precipitated from a
solution of excess ammonium acetate, was washed with water,
filtered and dried overnight at 60.degree. C. in a vacuum.
EXAMPLE 4
[0028] A p-tert-butyloxycarbonyloxy styrene (BCS) polymer having a
molecular weight of 15,000 was heated in nitrogen at 160.degree. C.
for two hours. Samples were taken and analyzed for t-butylcarbonyl
(BC) content from between 50 mole and 0 mole percent BC remaining.
In all cases, the polymer solution in propylene glycol acetate was
cloudy and could not be filtered through a 0.2 .mu.m Millipore
filter. A sample having 22 mole % tert-butyloxycarbonyloxy styrene
and 78 mole % p-hydroxy styrene was isolated.
EXAMPLE 5
[0029] A poly p-hydroxystyrene polymer having a molecular weight of
11,000 reacted with a solution of ditertiarybutylcarbonate in glyme
with triethylamine as a catalyst. The reaction product was
precipitated in hydrochloric acid, was stirred with ammonium
acetate and was washed with water. IR and UV analysis characterized
the polymer as containing 22 mole percent of tert-butyloxy carbonyl
groups.
EXAMPLE 6
[0030] Preparation of the substituted polymer by copolymerization
of p-hydroxystyrene and p-t-butyloxycarbonyloxystyrene monomers was
not attempted due to inherent instability of p-hydroxystyrene
monomers.
EXAMPLE 7
[0031] Polymers having an average mole % composition of 22%
tert-butyloxycarbonyloxy styrene and 78% p-hydroxystyrene derived
by the synthetic methods of Examples 3-5 and a control using the
BCS starting material of Example 3 were formulated into resists
with 7 percent triphenyl sulfonium hexafluoroantimonate sensitizer
in a propylene glycol methyl ether acetate. The films were cast
onto substrates, were baked at 95.degree. C. for five minutes, were
exposed in deep UV radiation at 254 nm, were post exposure baked at
95.degree. C. for ninety seconds, and were developed in an aqueous
0.27 N tetramethylammonium hydroxide developer solution.
[0032] The sensitivity of each resist was determined by measuring
step wedge thickness remaining using a criterion of 95 percent of
unexposed film remaining while the exposed area was developed at a
given dose. The results are shown in Table I.
1 TABLE I Source of UV Sensitivity, Polymer in Resist Dose in
mJ/cm.sup.2 Example 3 5 Example 4 25* Example 5 45 Control 30**
*Many insoluble particles or residues in image **Images were
cracked and unusable
[0033] The causes for differences in sensitivity of the resist
compositions have polymers having the same ratio of
t-butyloxycarbonyloxy groups to hydroxy groups is not understood.
The noted differences are reproducible.
[0034] Further comparison between the resist made from the Example
3 polymer and a control polymer of p-tertbutyloxycarbonyloxystyrene
prepared in accordance with U.S. Pat. No. 4,491,628 yielded the
following data:
2 TABLE II Polymer in Resist Property Control Example 3 Sensitivity
UV photo speed 30 mJ/cm.sup.2 5 mJ/cm.sup.2 E-beam dose 10
.mu.c/cm.sup.2 3 .mu.c/cm.sup.2 X-ray dose 150 mJ/cm.sup.2 100
mJ/cm.sup.2 On set of thermal flow 90.degree. C. 165.degree. C.
Post silylatable No* Yes Image shrinkage 37% 7% (after DUV
hardening) Cracking in developer Yes No Adhesion to Si,
Si.sub.3N.sub.4 surfaces Poor Good RIE erosion 35% 10% Base
developable Cracked Excellent, no cracks UV hardenable Yes with Yes
shrinkage *requires flood UV exposure/baking before silylation
EXAMPLE 8
[0035] Another series of polymers were prepared in accordance with
the method of Example 3 and were incorporated into resists in
accordance with the method of Example 7. The properties resists
containing these polymers and the control were compared.
3TABLE III Mole % BC in Polymer 100 (control) 64 36 20 16 Shrinkage
37 18 8 7 7 (percent) Crack Devel- Severe Moder. None None None
opment Adhesion Poor Fair Excel. Excel. Excel. Resistance Excel.
Excel. Excel. Excel. Poor to Alkali Image Dis- Severe Severe Slight
Unde- Unde- tortion tect- tect- able able
[0036] Only the preferred embodiments of the invention have been
described above and one skilled in the art will recognize that
numerous substitutions, modifications and alterations are
permissible without departing from the spirit and the scope of the
invention, as set forth in the following claims.
* * * * *