U.S. patent application number 12/058967 was filed with the patent office on 2008-10-02 for chemically amplified negative resist composition and patterning process.
This patent application is currently assigned to SHIN-ETSU CHEMICAL CO., LTD.. Invention is credited to Ryuji KOITABASHI, Keiichi MASUNAGA, Takanobu TAKEDA, Akinobu TANAKA, Osamu WATANABE, Tamotsu WATANABE.
Application Number | 20080241751 12/058967 |
Document ID | / |
Family ID | 39642741 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080241751 |
Kind Code |
A1 |
TAKEDA; Takanobu ; et
al. |
October 2, 2008 |
CHEMICALLY AMPLIFIED NEGATIVE RESIST COMPOSITION AND PATTERNING
PROCESS
Abstract
A chemically amplified negative resist composition comprises a
polymer comprising recurring hydroxystyrene units and recurring
styrene units having electron withdrawing groups substituted
thereon. In forming a pattern having a fine feature size of less
than 0.1 .mu.m, the composition exhibits a high resolution in that
a resist coating formed from the composition can be processed into
such a fine size pattern while the formation of bridges between
pattern features is minimized.
Inventors: |
TAKEDA; Takanobu;
(Joetsu-shi, JP) ; WATANABE; Tamotsu; (Joetsu-shi,
JP) ; KOITABASHI; Ryuji; (Joetsu-shi, JP) ;
MASUNAGA; Keiichi; (Joetsu-shi, JP) ; TANAKA;
Akinobu; (Joetsu-shi, JP) ; WATANABE; Osamu;
(Joetsu-shi, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
SHIN-ETSU CHEMICAL CO.,
LTD.
Tokyo
JP
|
Family ID: |
39642741 |
Appl. No.: |
12/058967 |
Filed: |
March 31, 2008 |
Current U.S.
Class: |
430/286.1 ;
430/296; 430/322 |
Current CPC
Class: |
G03F 7/0382 20130101;
G03F 7/20 20130101 |
Class at
Publication: |
430/286.1 ;
430/296; 430/322 |
International
Class: |
G03F 7/027 20060101
G03F007/027; G03F 7/20 20060101 G03F007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2007 |
JP |
2007-087243 |
Claims
1. A chemically amplified negative resist composition comprising a
polymer comprising recurring units having the general formulae (1)
and (2): ##STR00010## wherein R.sup.1 and R.sup.2 are each
independently hydrogen or methyl, X is an electron withdrawing
group, m is 0 or an integer of 1 to 4, and n is an integer of 1 to
5, said polymer having a weight average molecular weight of 1,000
to 50,000.
2. The resist composition of claim 1 wherein the electron
withdrawing group represented by X has an active structure directly
bonded to the benzene ring, the active structure being at least one
member selected from the group consisting of a halogen atom,
carbonyl group, nitro group, cyano group, sulfinyl group, and
sulfonyl group.
3. The resist composition of claim 2 wherein the electron
withdrawing group represented by X is at least one member selected
from the group consisting of chlorine, bromine, and iodine.
4. The resist composition of claim 1 wherein said polymer further
comprises recurring units having the general formula (3):
##STR00011## wherein R.sup.3 and R.sup.4 are each independently
hydrogen, optionally substituted hydroxyl, or halogen, and u is 0
or an integer of 1 to 5.
5. The resist composition of claim 1 wherein said polymer has a
weight average molecular weight of 2,000 to 8,000.
6. The resist composition of claim 1 wherein said polymer has a
dispersity Mw/Mn equal to or less than 1.7.
7. A pattern forming process comprising the steps of: applying the
resist composition of claim 1 onto a substrate to form a coating,
heating the coating, exposing the coating to light, soft x-ray or
electron beam, post-exposure heating the coating, and developing
the coating with an aqueous alkaline solution.
8. A resist pattern forming process comprising providing a
substrate having a surface composed mainly of a transition metal
compound, providing a chemically amplified negative resist
composition comprising a polymer comprising recurring units having
the general formulae (1) and (2): ##STR00012## wherein R.sup.1 and
R.sup.2 are each independently hydrogen or methyl, X is an electron
withdrawing group, m is 0 or an integer of 1 to 4, and n is an
integer of 1 to 5, said polymer having a weight average molecular
weight of 1,000 to 50,000, and forming a resist pattern on the
substrate surface using the chemically amplified negative resist
composition.
9. The process of claim 8 wherein the electron withdrawing group
represented by X has an active structure directly bonded to the
benzene ring, the active structure being at least one member
selected from the group consisting of a halogen atom, carbonyl
group, nitro group, cyano group, sulfinyl group, and sulfonyl
group.
10. The process of claim 8 wherein said polymer further comprises
recurring units having the general formula (3): ##STR00013##
wherein R.sup.3 and R.sup.4 are each independently hydrogen,
optionally substituted hydroxyl, or halogen, and u is 0 or an
integer of 1 to 5.
11. The process of claim 8 wherein said transition metal compound
comprises at least one transition metal selected from the group
consisting of chromium, molybdenum, zirconium, tantalum, tungsten,
titanium, and niobium, and optionally, at least one element
selected from the group consisting of oxygen, nitrogen and carbon.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This non-provisional application claims priority under 35
U.S.C. .sctn.119(a) on Patent Application No. 2007-087243 filed in
Japan on Mar. 29, 2007, the entire contents of which are hereby
incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to a chemically amplified negative
resist composition and more particularly, to a chemically amplified
negative resist composition comprising a polymer having aromatic
rings for use in processing of semiconductor and photomask
substrates, and a patterning process using the same.
BACKGROUND ART
[0003] To meet the recent demand for higher integration in
integrated circuits, pattern formation to a finer feature size is
required. In forming resist patterns with a feature size of 0.2
.mu.m or less, chemically amplified resist compositions utilizing
photo-generated acid as the catalyst are typically used in the art
because of their high sensitivity and resolution. Often,
high-energy radiation such as UV, deep UV or electron beam (EB) is
used as the light source for exposure of these resist compositions.
Among others, the EB or EUV lithography is recognized most
attractive because patterns of the finest size are expectable.
[0004] Resist compositions include positive ones in which exposed
areas become soluble and negative ones in which exposed areas are
left as a pattern. A suitable composition is selected among them
depending on the desired resist pattern. In general, the chemically
amplified negative resist composition comprises a polymer which is
normally soluble in an aqueous alkaline developer, an acid
generator which is decomposed to generate an acid when exposed to
light, and a crosslinker which causes the polymer to crosslink in
the presence of the acid serving as a catalyst, thus rendering the
polymer insoluble in the developer (sometimes, the crosslinker is
incorporated in the polymer). Typically a basic compound is added
for controlling the diffusion of the acid generated upon light
exposure.
[0005] A number of negative resist compositions of the type
comprising a polymer which is soluble in an aqueous alkaline
developer and includes phenolic units as the alkali-soluble units
were developed, especially as adapted for exposure to KrF excimer
laser light. These compositions have not been used in the ArF
excimer laser lithography because the phenolic units are not
transmissive to exposure light having a wavelength of 150 to 220
nm. Recently, these compositions are recognized attractive again as
the negative resist composition for the EB and EUV lithography
capable of forming finer size patterns. Exemplary compositions are
described in JP-A 2006-201532 (corresponding to US 20060166133, EP
1684118, CN 1825206) and JP-A 2006-215180.
[0006] As the required pattern size is reduced, more improvements
are made on the negative resist composition of the type using
hydroxystyrene units typical of the phenolic units. Now that the
pattern reaches a very fine size of 0.1 .mu.m or less, there is a
likelihood that the resist layer is left like thin strings between
features of a fine size pattern, which is known as "bridge
problem." The prior art compositions fail to solve the problem.
[0007] Also known in the art is the problem of pattern's substrate
dependence, that is, the profile of a pattern alters near a
processable substrate, depending on the material of which the
substrate is made. As the desired pattern size is reduced, even a
minor profile alteration becomes significant. Particularly in
processing a photomask blank having the outermost surface made of
chromium oxynitride, if a pattern is formed on the chromium
oxynitride using a chemically amplified negative resist
composition, then an "undercut" problem arises, that is, the
pattern is notched at positions in contact with the substrate. The
prior art compositions fail to fully solve the undercut
problem.
DISCLOSURE OF THE INVENTION
[0008] An object of the present invention is to provide a
chemically amplified negative resist composition which can form a
pattern having few bridges without substantial substrate
dependence, and a patterning process using the same.
[0009] Assuming that the cause of bridging is a low contrast of
crosslinking reaction, the inventors attempted to improve the
contrast by introducing a greater number of electron donative
groups into constituent units of a polymer for increasing the
number of active sites in the polymer which are reactive with a
crosslinker.
[0010] In JP-A 2006-201532, cited above, the polymer used contains
hydroxystyrene units and carbonyloxystyrene units as styrene
derivative units. When styrene units having substituted thereon
alkoxy groups, which are electron donative groups, were used
instead of the carbonyloxystyrene units, then the number of active
sites in the polymer which are reactive with a crosslinker could be
increased without significantly altering the alkali dissolution
rate of the polymer. To verify the effect of electron donative
groups, on the other hand, a polymer comprising styrene units
having electron withdrawing groups was prepared as a control. A
comparison was made in resist performance between these polymers.
Quite unexpectedly, we have found that the resist using the polymer
comprising styrene units having electron withdrawing groups
substituted thereon is unlikely to leave bridges, as compared with
the prior art polymers and polymers having electron donative groups
substituted thereon, and is minimized in pattern's substrate
dependence.
[0011] In one aspect, the invention provides a chemically amplified
negative resist composition comprising as a base resin a polymer
comprising recurring units having the general formulae (1) and
(2):
##STR00001##
wherein R.sup.1 and R.sup.2 are each independently hydrogen or
methyl, X is an electron withdrawing group, m is 0 or an integer of
1 to 4, and n is an integer of 1 to 5, the polymer having a weight
average molecular weight of 1,000 to 50,000. The resist composition
is used to form a resist coating which has a high resolution and
gives rise to little bridge problem when patterned.
[0012] The electron withdrawing group represented by X has an
active structure directly bonded to the benzene ring, examples of
which include a halogen atom due to the inductive effect, and a
carbonyl group, nitro group, cyano group, sulfinyl group, and
sulfonyl group due to the mesomeric effect.
[0013] The most preferred examples of the electron withdrawing
group include chlorine, bromine and iodine. When these elements are
incorporated into a polymer, the undercut problem of resist pattern
near substrate and the bridge problem between fine pattern features
are significantly mitigated.
[0014] In one preferred embodiment of the resist composition, the
polymer may further comprise recurring units having the general
formula (3):
##STR00002##
wherein R.sup.3 and R.sup.4 are each independently hydrogen,
optionally substituted hydroxyl, or halogen, and u is 0 or an
integer of 1 to 5. Inclusion of these units provides high etch
resistance, enabling to reduce the thickness of resist coating.
[0015] Preferably the polymer has a weight average molecular weight
(Mw) of 2,000 to 8,000. With too low a Mw, the resulting pattern
may be prone to thermal deformation. With too high a Mw, a bridge
problem is likely to occur during development, depending on a
particular composition.
[0016] In a preferred embodiment, the polymer is obtained by
removing a low molecular weight fraction from a polymer product as
polymerized, so that the polymer has a dispersity Mw/Mn equal to or
less than 1.7. Note that the dispersity is a weight average
molecular weight divided by a number average molecular weight,
Mw/Mn, and represents a molecular weight distribution. By removing
the low molecular weight fraction so as to achieve a dispersity of
1.7 or less, the profile of a resist pattern is improved, and
especially the undercut problem associated with substrate
dependence is ameliorated.
[0017] In another aspect, the invention provides a pattern forming
process comprising the steps of applying the resist composition
defined above onto a substrate to form a coating, heating the
coating prior to exposure, exposing the coating to light, soft
x-ray or electron beam, post-exposure heating the coating, and
developing the coating with an aqueous alkaline solution.
[0018] In a further aspect, the invention provides a resist pattern
forming process comprising the steps of providing a substrate
having a surface composed mainly of a transition metal compound,
providing a chemically amplified negative resist composition
comprising a polymer comprising recurring units having the general
formulae (1) and (2) and having a weight average molecular weight
of 1,000 to 50,000, and forming a resist pattern on the substrate
using the chemically amplified negative resist composition. Typical
of the material of which a photomask blank surface is made is a
material containing a transition metal and oxygen and/or nitrogen.
When a resist pattern is formed on the surface of transition metal
compound substrate, there is a likelihood that the pattern profile
becomes defective near the substrate surface. The resist
composition of this embodiment ensures to form a pattern of a good
profile even when applied to the transition metal compound
surface.
[0019] The electron withdrawing group represented by X has an
active structure directly bonded to the benzene ring, examples of
which include a halogen atom, carbonyl group, nitro group, cyano
group, sulfinyl group, and sulfonyl group.
[0020] In a preferred embodiment of the process, the polymer may
further comprise recurring units having the general formula (3).
Inclusion of the units of formula (3) enables to form a thinner
resist coating even when the transition metal compound, which is
difficult to establish a selectivity ratio during etching, is to be
etched through the resist.
[0021] The transition metal compound may comprise at least one
transition metal selected from chromium, molybdenum, zirconium,
tantalum, tungsten, titanium, and niobium, and optionally, at least
one element selected from oxygen, nitrogen and carbon. These
compounds are generally used as a material to form a surface layer
of a photomask blank and specifically serve as an etch mask,
light-shielding film, antireflective coating or the like.
BENEFITS OF THE INVENTION
[0022] The chemically amplified negative resist composition
comprising a polymer comprising recurring hydroxystyrene units and
recurring styrene units having electron withdrawing groups
substituted thereon has many advantages. When it is desired to form
a pattern having a fine feature size of less than 0.1 .mu.m, the
composition exhibits a high resolution in that a resist coating
formed from the composition can be processed into such a fine size
pattern while the formation of bridges between pattern features is
minimized.
[0023] In the processing of a photomask substrate wherein a
substrate surface is of a transition metal compound, an undercut
problem often arises in a resist pattern formed on the surface. The
use of the negative resist composition of the invention ensures to
define a resist pattern of good profile even on the transition
metal compound because the dependence of the pattern on the
substrate is minimized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a photomicrograph of a resist pattern in Example
1.
[0025] FIG. 2 is a photomicrograph of a resist pattern in
Comparative Example 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] The polymer or high molecular weight compound used in the
chemically amplified negative resist composition of the invention
comprises recurring units having the general formulae (1) and (2)
and has a weight average molecular weight of 1,000 to 50,000.
##STR00003##
Herein R.sup.1 and R.sup.2 are each independently a hydrogen atom
or methyl group, X is an electron withdrawing group, m is 0 or an
integer of 1 to 4, and n is an integer of 1 to 5.
[0027] The polymer may further comprise recurring units having the
general formula (3).
##STR00004##
Herein R.sup.3 and R.sup.4 are each independently a hydrogen atom,
optionally substituted hydroxyl group, or halogen atom, and u is 0
or an integer of 1 to 5.
[0028] Although the polymers used in the resist composition of the
invention may comprise additional recurring units other than the
units of formulae (1) to (3), the polymers are represented by the
following general formulae (4) and (5) provided that no additional
recurring units are included.
[0029] Polymer I of general formula (4):
##STR00005##
Herein R.sup.1 and R.sup.2 are each independently hydrogen or
methyl, X is an electron withdrawing group, m is 0 or an integer of
1 to 4, n is an integer of 1 to 5, p and q are positive numbers
satisfying p+q.ltoreq.1.
[0030] Polymer II of general formula (5):
##STR00006##
Herein R.sup.1 and R.sup.2 are each independently hydrogen or
methyl, R.sup.3 and R.sup.4 are each independently hydrogen,
optionally substituted hydroxyl, or halogen, X is an electron
withdrawing group, m is 0 or an integer of 1 to 4, n is an integer
of 1 to 5, u is 0 or an integer of 1 to 5, p, q and r are positive
numbers satisfying p+q+r.ltoreq.1.
[0031] It is noted that the meaning of p+q+r=1 is that in a polymer
comprising recurring units p, q, and r, the sum of recurring units
p, q and r is 100 mol % based on the total amount of entire
recurring units. The meaning of p+q+r<1 is that the sum of
recurring units p, q, and r is less than 100 mol % based on the
total amount of entire recurring units, indicating the inclusion of
other recurring units.
[0032] X stands for an electron withdrawing group. The electron
withdrawing group which is bonded to the benzene ring is effective
for reducing the electron density of the benzene ring. It may have
either the inductive effect or the mesomeric effect. A mixture of
two or more electron withdrawing groups is acceptable. The electron
withdrawing group has an active structure directly bonded to the
benzene ring, examples of which include a halogen atom exhibiting
the inductive effect, and a carbonyl group, nitro group, cyano
group, sulfinyl group, and sulfonyl group exhibiting the mesomeric
effect. Of these active structures, the carbonyl, sulfinyl and
sulfonyl groups are divalent and have the other end, examples of
which include optionally substituted alkyl, aryl, alkoxy, and
aryloxy groups of up to 15 carbon atoms.
[0033] Specifically, suitable electron withdrawing groups X include
halogen atoms, nitro groups, nitrile groups, optionally substituted
alkylcarbonyl groups of 1 to 15 carbon atoms, optionally
substituted alkoxycarbonyl groups of 1 to 15 carbon atoms,
optionally substituted arylcarbonyl groups of 7 to 20 carbon atoms,
optionally substituted aryloxycarbonyl groups of 7 to 20 carbon
atoms, optionally substituted alkylsulfinyl groups of 1 to 15
carbon atoms, optionally substituted alkoxysulfinyl groups of 1 to
15 carbon atoms, optionally substituted arylsulfinyl groups of 7 to
20 carbon atoms, optionally substituted aryloxysulfinyl groups of 7
to 20 carbon atoms, optionally substituted alkylsulfonyl groups of
1 to 15 carbon atoms, optionally substituted alkoxysulfonyl groups
of 1 to 15 carbon atoms, optionally substituted arylsulfonyl groups
of 7 to 20 carbon atoms, and optionally substituted aryloxysulfonyl
groups of 7 to 20 carbon atoms. Each of the carbonyl (--CO--),
sulfinyl (--SO--), and sulfonyl (--SO.sub.2--) moieties in the
foregoing groups is directly bonded to the benzene ring of styrene
unit. Where the foregoing groups are substituted groups, exemplary
substituent groups include halogen, alkoxy, alkyl- or
aryl-carbonyl, alkyl- or aryl-carbonyloxy, and epoxy groups.
[0034] Among others, chlorine, bromine, iodine and alkoxycarbonyl
groups of the general formula (6):
--CO--OR.sup.5 (6)
wherein R.sup.5 is an optionally substituted, straight, branched or
cyclic alkyl group of 1 to 15 carbon atoms, are advantageous for
the ease of synthesis and better characteristics. Exemplary
straight, branched or cyclic alkyl groups represented by R.sup.5
include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,
tert-butyl, cyclopentyl, cyclohexyl, norbornyl, and adamantyl.
Where substituted, exemplary substituent groups include halogen,
alkoxy, hydroxyl, and epoxy groups.
[0035] Of the electron withdrawing groups exemplified above,
chlorine, bromine, and iodine are particularly effective in
improving a pattern profile and inhibiting bridge formation.
[0036] Since the units of formula (3) are incorporated for the
purpose of improving etch resistance as described above, R.sup.3
and R.sup.4 may or may not have an additional function. Examples of
optionally substituted hydroxyl groups exemplified for R.sup.3 and
R.sup.4 include hydroxyl, alkoxy groups of 1 to 15 carbon atoms,
alkylcarbonyloxy groups of 2 to 15 carbon atoms, arylcarbonyloxy
groups of 7 to 15 carbon atoms, alkylsulfonyloxy groups of 1 to 15
carbon atoms, and arylsulfonyloxy groups of 6 to 15 carbon
atoms.
[0037] The compositional ratio (molar ratio) of constituent units
in Polymer I is preferably selected in view of characteristics of
resist material, such that p and q in formula (4) are positive
numbers, and the compositional ratio of p satisfies
0.3.ltoreq.p/(p+q).ltoreq.0.9, and more preferably
0.5.ltoreq.p/(p+q).ltoreq.0.8. If the value of p/(p+q) is too
small, fine size patterns cannot be formed. If the value of p/(p+q)
is too large, there is an increased likelihood of pattern collapse
due to swelling.
[0038] Besides the units of formula (3), Polymer I may have further
incorporated therein recurring units which are commonly used in
resist polymers (see JP-A 2006-201532). The acceptable
compositional ratio of recurring units other than the units of
formulae (1) to (3) is set to meet the following requirements. In
one embodiment wherein the other recurring units are free of
alkali-soluble groups, for example, alkyl-substituted styrene units
and (meth)acrylate units as disclosed in the literature are used,
the compositional ratio of recurring units of formula (1) is in a
range of 30 to 90 mol %, and more preferably 50 to 80 mol % of the
entire recurring units. To accomplish the advantages of the
invention, the recurring units of formula (2) must be included in
an amount of at least 3 mol %, and preferably at least 5 mol %
relative to the entire recurring units. In another embodiment
wherein the recurring units other than the units of formulae (1) to
(3) have alkali-soluble groups, an empirical study of previously
preparing model polymers having different molar ratios and
determining a compositional ratio that affords an appropriate
dissolution rate is necessary. In the other embodiment as well, to
obtain an acid-catalyzed crosslinking reaction activity, the
compositional ratio of recurring units of formula (1) is preferably
in a range of at least 30 mol %, and more preferably at least 50
mol % of the entire recurring units. To accomplish the advantages
of the invention, the recurring units of formula (2) must be
included in an amount of at least 3 mol %, and preferably at least
5 mol % relative to the entire recurring units of the polymer.
[0039] As for Polymer II, p, q and r in formula (5) are positive
numbers, the compositional ratio of p satisfies preferably
0.3.ltoreq.p/(p+q+r).ltoreq.0.9, and more preferably
0.6.ltoreq.p/(p+q+r).ltoreq.0.8, and the compositional ratio of r
satisfies preferably 0<r/(p+q+r).ltoreq.0.3, and more preferably
0.05.ltoreq.r/(p+q+r).ltoreq.0.3. Notably the recurring units of
formula (3) are incorporated for the main purpose of improving etch
resistance. If the value of r/(p+q+r) is too large, resolution is
reduced. If the value of r/(p+q+r) is too small, the effect of
improving etch resistance is not exerted.
[0040] Likewise, recurring units other than the units of formulae
(1) to (3) may be incorporated in Polymer II. A number of recurring
units which can constitute polymers for use in resist compositions
are known in the art as previously pointed out. The design
procedure taken for incorporating recurring units other than the
units of formulae (1) to (3) is essentially the same as in Polymer
I. To accomplish the advantages of the invention, the recurring
units of formula (2) must be included in an amount of at least 3
mol %, and preferably at least 5 mol % relative to the entire
recurring units of the polymer.
[0041] The polymers should have a weight average molecular weight
(Mw) of 1,000 to 50,000, preferably 2,000 to 8,000, as measured by
gel permeation chromatography (GPC, HLC-8120GPC by Tosoh Corp.)
versus polystyrene standards. With too low a Mw, the resist pattern
is susceptible to thermal deformation. Too high a Mw increases the
tendency for a bridging phenomenon to occur during pattern
formation.
[0042] In a preferred embodiment, the polymer is obtained by
removing a low molecular weight fraction from a polymer product as
polymerized, so that the polymer has a dispersity Mw/Mn equal to or
less than 1.7. Note that the dispersity is a weight average
molecular weight divided by a number average molecular weight,
Mw/Mn, and represents a molecular weight distribution. When a
dispersity of 1.7 or less is achieved by removing the low molecular
weight fraction, the resist pattern formed on a mask blank is
improved in profile, the undercut problem is significantly
ameliorated, and substantial resolution is improved.
[0043] For the synthesis of the polymers, one suitable method
involves feeding acetoxystyrene monomer, a styrene monomer having
an electron withdrawing group substituted thereon, and an optional
indene or other monomer to an organic solvent, adding a radical
initiator thereto, effecting thermal polymerization, subjecting the
resulting polymer to alkaline hydrolysis in the organic solvent for
deprotection of acetoxy groups, thus yielding a multi-component
copolymer comprising hydroxystyrene and electron withdrawing
group-substituted styrene. Suitable organic solvents used for
polymerization include toluene, benzene, tetrahydrofuran, diethyl
ether, and dioxane. Suitable polymerization initiators include
2,2'-azobisisobutyronitrile,
2,2'-azobis(2,4-dimethylvaleronitrile), dimethyl
2,2'-azobis(2-methyl propionate), benzoyl peroxide, and lauroyl
peroxide. Preferably polymerization may be effected by heating at a
temperature of 40.degree. C. to 80.degree. C. and for a time of 2
to 100 hours, and more preferably 5 to 40 hours. For the alkaline
hydrolysis, exemplary bases are aqueous ammonia and triethylamine;
the reaction temperature is -20.degree. C. to 100.degree. C., and
preferably 0.degree. C. to 60.degree. C.; and the time is 0.2 to
100 hours, and preferably 0.5 to 40 hours.
[0044] The polymer product obtained by the abovementioned
polymerization method may be adjusted to a dispersity of 1.7 or
less by dissolving the polymer product in a good solvent, admitting
the polymer solution into a bad solvent with stirring, and
fractionating off the low molecular weight fraction in the bad
solvent. Examples of the good and bad solvents used in this
fractionation step include acetone, ethyl acetate, methyl acetate,
propylene glycol monomethyl ether, propylene glycol monoethyl
ether, propylene glycol methyl ether acetate, propylene glycol
ethyl ether acetate, tetrahydrofuran, diethyl ether, water,
methanol, ethanol, isopropanol, hexane, pentane, toluene, and
benzene. Of these solvents, a choice may be made depending on
whether the polymer subject to fractionation is lipophilic or
hydrophilic. Other fractionation methods include precipitation of a
polymer in a bad solvent, and separation into two layers of a good
solvent (containing a polymer component to be collected) and a bad
solvent (containing a low molecular weight fraction to be
removed).
[0045] It is understood that the synthesis method is not limited to
the foregoing.
Photoacid Generator
[0046] While the aforementioned polymer is compounded as a base
resin in a chemically amplified negative resist composition, an
acid generator which is decomposed to generate an acid upon
exposure to high-energy radiation, referred to as "photoacid
generator," may be compounded as well. It is noted that an acid
generator which is sensitive to EB exposure is also referred to as
"photoacid generator" in a sense to distinguish from a thermal acid
generator capable of generating an acid by heat. A number of
photoacid generators are known in the art including those described
in JP-A 2006-201532 and JP-A 2006-215180 cited above. Generally,
any of well-known photoacid generators may be used herein.
[0047] Suitable photoacid generators include sulfonium salts,
iodonium salts, sulfonyldiazomethane and N-sulfonyloxyimide
photoacid generators. Exemplary photoacid generators are given
below while they may be used alone or in admixture of two or
more.
[0048] Sulfonium salts are salts of sulfonium cations with
sulfonate anions. Exemplary sulfonium cations include
triphenylsulfonium, (4-tert-butoxyphenyl)diphenylsulfonium,
bis(4-tert-butoxyphenyl)phenylsulfonium,
tris(4-tert-butoxyphenyl)sulfonium,
(3-tert-butoxyphenyl)diphenylsulfonium,
bis(3-tert-butoxyphenyl)phenylsulfonium,
tris(3-tert-butoxyphenyl)sulfonium,
(3,4-di-tert-butoxyphenyl)diphenylsulfonium,
bis(3,4-di-tert-butoxyphenyl)phenylsulfonium,
tris(3,4-di-tert-butoxyphenyl)sulfonium,
diphenyl(4-thiophenoxyphenyl)sulfonium,
(4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium,
tris(4-tert-butoxycarbonylmethyloxyphenyl)sulfonium,
(4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium,
tris(4-dimethylaminophenyl)sulfonium, 2-naphthyldiphenylsulfonium,
dimethyl-2-naphthylsulfonium, 4-hydroxyphenyldimethylsulfonium,
4-methoxyphenyldimethylsulfonium, trimethylsulfonium,
2-oxocyclohexylcyclohexylmethylsulfonium, trinaphthylsulfonium, and
tribenzylsulfonium. Exemplary sulfonate anions include
trifluoromethanesulfonate, nonafluorobutanesulfonate,
heptadecafluorooctanesulfonate, 2,2,2-trifluoroethanesulfonate,
pentafluorobenzenesulfonate, 4-trifluoromethylbenzenesulfonate,
4-fluorobenzenesulfonate, toluenesulfonate, benzenesulfonate,
4-(4-toluenesulfonyloxy)benzenesulfonate, naphthalenesulfonate,
camphorsulfonate, octanesulfonate, dodecylbenzenesulfonate,
butanesulfonate, and methanesulfonate. Sulfonium salts based on
combination of the foregoing examples are included.
[0049] Iodinium salts are salts of iodonium cations with sulfonate
anions. Exemplary iodonium cations are aryliodonium cations
including diphenyliodinium, bis(4-tert-butylphenyl)iodonium,
4-tert-butoxyphenylphenyliodonium, and
4-methoxyphenylphenyliodonium. Exemplary sulfonate anions include
trifluoromethanesulfonate, nonafluorobutanesulfonate,
heptadecafluorooctanesulfonate, 2,2,2-trifluoroethanesulfonate,
pentafluorobenzenesulfonate, 4-trifluoromethylbenzenesulfonate,
4-fluorobenzenesulfonate, toluenesulfonate, benzenesulfonate,
4-(4-toluenesulfonyloxy)benzenesulfonate, naphthalenesulfonate,
camphorsulfonate, octanesulfonate, dodecylbenzenesulfonate,
butanesulfonate, and methanesulfonate. Iodonium salts based on
combination of the foregoing examples are included.
[0050] Exemplary sulfonyldiazomethane compounds include
bissulfonyldiazomethane compounds and sulfonyl-carbonyldiazomethane
compounds such as bis(ethylsulfonyl)diazomethane,
bis(1-methylpropylsulfonyl)diazomethane,
bis(2-methylpropylsulfonyl)diazomethane,
bis(1,1-dimethylethylsulfonyl)diazomethane,
bis(cyclohexylsulfonyl)diazomethane,
bis(perfluoroisopropylsulfonyl)diazomethane,
bis(phenylsulfonyl)diazomethane,
bis(4-methylphenylsulfonyl)diazomethane,
bis(2,4-dimethylphenylsulfonyl)diazomethane,
bis(2-naphthylsulfonyl)diazomethane,
4-methylphenylsulfonylbenzoyldiazomethane,
tert-butylcarbonyl-4-methylphenylsulfonyldiazomethane,
2-naphthylsulfonylbenzoyldiazomethane,
4-methylphenylsulfonyl-2-naphthoyldiazomethane,
methylsulfonylbenzoyldiazomethane, and
tert-butoxycarbonyl-4-methylphenylsulfonyldiazomethane.
[0051] N-sulfonyloxyimide photoacid generators include combinations
of imide skeletons with sulfonate skeletons. Exemplary imide
skeletons are succinimide, naphthalene dicarboxylic acid imide,
phthalimide, cyclohexyldicarboxylic acid imide,
5-norbornene-2,3-dicarboxylic acid imide, and
7-oxabicyclo[2.2.1]-5-heptene-2,3-dicarboxylic acid imide.
Exemplary sulfonate skeletons include trifluoromethanesulfonate,
nonafluorobutanesulfonate, heptadecafluorooctanesulfonate,
2,2,2-trifluoroethanesulfonate, pentafluorobenzenesulfonate,
4-trifluoromethylbenzenesulfonate, 4-fluorobenzenesulfonate,
toluenesulfonate, benzenesulfonate, naphthalenesulfonate,
camphorsulfonate, octanesulfonate, dodecylbenzenesulfonate,
butanesulfonate, and methanesulfonate.
[0052] Additionally, other photoacid generators as listed below are
useful. Benzoinsulfonate photoacid generators include benzoin
tosylate, benzoin mesylate, and benzoin butanesulfonate.
[0053] Pyrogallol trisulfonate photoacid generators include
pyrogallol, fluoroglycine, catechol, resorcinol, hydroquinone, in
which all the hydroxyl groups are substituted with sulfonate groups
such as trifluoromethanesulfonate, nonafluorobutanesulfonate,
heptadecafluorooctanesulfonate, 2,2,2-trifluoroethanesulfonate,
pentafluorobenzenesulfonate, 4-trifluoromethylbenzenesulfonate,
4-fluorobenzenesulfonate, toluenesulfonate, benzenesulfonate,
naphthalenesulfonate, camphorsulfonate, octanesulfonate,
dodecylbenzenesulfonate, butanesulfonate, and methanesulfonate.
[0054] Nitrobenzyl sulfonate photoacid generators include
2,4-dinitrobenzyl sulfonate, 2-nitrobenzyl sulfonate, and
2,6-dinitrobenzyl sulfonate, with exemplary sulfonates including
trifluoromethanesulfonate, nonafluorobutanesulfonate,
heptadecafluorooctanesulfonate, 2,2,2-trifluoroethanesulfonate,
pentafluorobenzenesulfonate, 4-trifluoromethylbenzenesulfonate,
4-fluorobenzenesulfonate, toluenesulfonate, benzenesulfonate,
naphthalenesulfonate, camphorsulfonate, octanesulfonate,
dodecylbenzenesulfonate, butanesulfonate, and methanesulfonate.
Also useful are analogous nitrobenzyl sulfonate compounds in which
the nitro group on the benzyl side is substituted with a
trifluoromethyl group.
[0055] Sulfone photoacid generators include
bis(phenylsulfonyl)methane, bis(4-methylphenylsulfonyl)methane,
bis(2-naphthylsulfonyl)methane, 2,2-bis(phenylsulfonyl)propane,
2,2-bis(4-methylphenylsulfonyl)propane,
2,2-bis(2-naphthylsulfonyl)propane,
2-methyl-2-(p-toluenesulfonyl)propiophenone,
2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane, and
2,4-dimethyl-2-(p-toluenesulfonyl)pentan-3-one.
[0056] Photoacid generators in the form of glyoxime derivatives
include bis-O-(p-toluenesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(p-toluenesulfonyl)-.alpha.-diphenylglyoxime,
bis-O-(p-toluenesulfonyl)-.alpha.-dicyclohexylglyoxime,
bis-O-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime,
bis-O-(p-toluenesulfonyl)-2-methyl-2,3-pentanedioneglyoxime,
bis-O-(n-butanesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(n-butanesulfonyl)-.alpha.-diphenylglyoxime,
bis-O-(n-butanesulfonyl)-.alpha.-dicyclohexylglyoxime,
bis-O-(n-butanesulfonyl)-2,3-pentanedioneglyoxime,
bis-O-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,
bis-O-(methanesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(trifluoromethanesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(1,1,1-trifluoroethanesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(tert-butanesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(perfluorooctanesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(cyclohexylsulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(benzenesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(p-fluorobenzenesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(p-tert-butylbenzenesulfonyl)-.alpha.-dimethylglyoxime,
bis-O-(xylenesulfonyl)-.alpha.-dimethylglyoxime, and
bis-O-(camphorsulfonyl)-.alpha.-dimethylglyoxime.
[0057] Of these, sulfonium salt, bissulfonyldiazomethane and
N-sulfonyloxyimide photoacid generators are preferred.
[0058] While the anion of an optimum acid generated varies
depending on the reactivity of crosslinker in the resist
composition, it is generally selected from those anions which are
nonvolatile and not extremely diffusive. Suitable anions include
benzenesulfonate, toluenesulfonate,
4-(4-toluenesulfonyloxy)benzenesulfonate,
pentafluorobenzenesulfonate, 2,2,2-trifluoroethanesulfonate,
nonafluorobutanesulfonate, heptadecafluorooctanesulfonate, and
camphorsulfonate anions.
[0059] In the negative resist composition of the invention, the
photoacid generator is preferably added in an amount of 0 to 30
parts by weight, more preferably 2 to 20 parts by weight per 100
parts by weight of the polymer or base resin. The photoacid
generators may be used alone or in admixture of two or more. The
transmittance of the resist film can be controlled by using a
photoacid generator having a low transmittance at the exposure
wavelength and adjusting the amount of the photoacid generator
added.
Crosslinker
[0060] A crosslinker is an essential component in the chemically
amplified negative resist composition. In some cases, the
crosslinker can be incorporated in the polymer, for example, by
adding epoxy group-bearing units to the units of formulae (1) to
(3) during polymerization. Usually, crosslinking compounds as
described below are separately added to the composition.
[0061] The crosslinker used herein may be any of crosslinkers which
react with the polymer to induce intramolecular and intermolecular
crosslinkage under the catalysis of the acid generated by the
photoacid generator. Typically they are compounds having a
plurality of functional groups which undergo electrophilic reaction
with recurring units of formula (1) in the polymer to form bonds
therewith. A number of such compounds are already known (see JP-A
2006-201532 and JP-A 2006-215180).
[0062] The crosslinker used in the resist composition may be any of
well-known crosslinkers. Suitable crosslinkers include
alkoxymethylglycolurils and alkoxymethylmelamines. Examples of
suitable alkoxymethylglycolurils include
tetramethoxymethylglycoluril,
1,3-bismethoxymethyl-4,5-bismethoxyethylene urea, and
bismethoxymethyl urea. Examples of suitable alkoxymethylmelamines
include hexamethoxymethylmelamine and hexaethoxymethylmelamine.
[0063] In the negative resist composition of the invention, the
crosslinker is preferably added in an amount of 2 to 40 parts by
weight, more preferably 5 to 20 parts by weight per 100 parts by
weight of the base resin. The crosslinkers may be used alone or in
admixture of two or more. The transmittance of the resist film can
be controlled by using a crosslinker having a low transmittance at
the exposure wavelength and adjusting the amount of the crosslinker
added.
Basic Compound
[0064] To the chemically amplified negative resist composition, a
basic compound may be added as a component capable of controlling
the diffusion distance of acid. Controlling the diffusion distance
leads to better resolution, reduces the substrate and environment
dependence, and improves the exposure latitude and pattern
profile.
[0065] Examples of basic compounds include primary, secondary, and
tertiary aliphatic amines, mixed amines, aromatic amines,
heterocyclic amines, nitrogen-containing compounds having carboxyl
group, nitrogen-containing compounds having sulfonyl group,
nitrogen-containing compounds having hydroxyl group,
nitrogen-containing compounds having hydroxyphenyl group, alcoholic
nitrogen-containing compounds, amide derivatives, and imide
derivatives.
[0066] Examples of suitable primary aliphatic amines include
ammonia, methylamine, ethylamine, n-propylamine, isopropylamine,
n-butylamine, isobutylamine, sec-butylamine, tert-butylamine,
pentylamine, tert-amylamine, cyclopentylamine, hexylamine,
cyclohexylamine, heptylamine, octylamine, nonylamine, decylamine,
dodecylamine, cetylamine, methylenediamine, ethylenediamine, and
tetraethylenepentamine. Examples of suitable secondary aliphatic
amines include dimethylamine, diethylamine, di-n-propylamine,
diisopropylamine, di-n-butylamine, diisobutylamine,
di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine,
dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine,
didecylamine, didodecylamine, dicetylamine,
N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, and
N,N-dimethyltetraethylenepentamine. Examples of suitable tertiary
aliphatic amines include trimethylamine, triethylamine,
tri-n-propylamine, triisopropylamine, tri-n-butylamine,
triisobutylamine, tri-sec-butylamine, tripentylamine,
tricyclopentylamine, trihexylamine, tricyclohexylamine,
triheptylamine, trioctylamine, trinonylamine, tridecylamine,
tridodecylamine, tricetylamine,
N,N,N',N'-tetramethylmethylenediamine,
N,N,N',N'-tetramethylethylenediamine, and
N,N,N',N'-tetramethyltetraethylenepentamine.
[0067] Examples of suitable mixed amines include
dimethylethylamine, methylethylpropylamine, benzylamine,
phenethylamine, and benzyldimethylamine. Examples of suitable
aromatic and heterocyclic amines include aniline derivatives (e.g.,
aniline, N-methylaniline, N-ethylaniline, N-propylaniline,
N,N-dimethylaniline, 2-methylaniline, 3-methylaniline,
4-methylaniline, ethylaniline, propylaniline, trimethylaniline,
2-nitroaniline, 3-nitroaniline, 4-nitroaniline, 2,4-dinitroaniline,
2,6-dinitroaniline, 3,5-dinitroaniline, and N,N-dimethyltoluidine),
diphenyl(p-tolyl)amine, methyldiphenylamine, triphenylamine,
phenylenediamine, naphthylamine, diaminonaphthalene, pyrrole
derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole,
2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole),
oxazole derivatives (e.g., oxazole and isooxazole), thiazole
derivatives (e.g., thiazole and isothiazole), imidazole derivatives
(e.g., imidazole, 4-methylimidazole, and
4-methyl-2-phenylimidazole), pyrazole derivatives, furazan
derivatives, pyrroline derivatives (e.g., pyrroline and
2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine,
N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone),
imidazoline derivatives, imidazolidine derivatives, pyridine
derivatives (e.g., pyridine, methylpyridine, ethylpyridine,
propylpyridine, butylpyridine, 4-(1-butylpentyl)pyridine,
dimethylpyridine, trimethylpyridine, triethylpyridine,
phenylpyridine, 3-methyl-2-phenylpyridine, 4-tert-butylpyridine,
diphenylpyridine, benzylpyridine, methoxypyridine, butoxypyridine,
dimethoxypyridine, 1-methyl-2-pyridine, 4-pyrrolidinopyridine,
1-methyl-4-phenylpyridine, 2-(1-ethylpropyl)pyridine,
aminopyridine, and dimethylaminopyridine), pyridazine derivatives,
pyrimidine derivatives, pyrazine derivatives, pyrazoline
derivatives, pyrazolidine derivatives, piperidine derivatives,
piperazine derivatives, morpholine derivatives, indole derivatives,
isoindole derivatives, 1H-indazole derivatives, indoline
derivatives, quinoline derivatives (e.g., quinoline and
3-quinolinecarbonitrile), isoquinoline derivatives, cinnoline
derivatives, quinazoline derivatives, quinoxaline derivatives,
phthalazine derivatives, purine derivatives, pteridine derivatives,
carbazole derivatives, phenanthridine derivatives, acridine
derivatives, phenazine derivatives, 1,10-phenanthroline
derivatives, adenine derivatives, adenosine derivatives, guanine
derivatives, guanosine derivatives, uracil derivatives, and uridine
derivatives.
[0068] Examples of suitable nitrogen-containing compounds with
carboxyl group include aminobenzoic acid, indolecarboxylic acid,
and amino acid derivatives (e.g. nicotinic acid, alanine, alginine,
aspartic acid, glutamic acid, glycine, histidine, isoleucine,
glycylleucine, leucine, methionine, phenylalanine, threonine,
lysine, 3-aminopyrazine-2-carboxylic acid, and methoxyalanine).
Examples of suitable nitrogen-containing compounds with sulfonyl
group include 3-pyridinesulfonic acid and pyridinium
p-toluenesulfonate. Examples of suitable nitrogen-containing
compounds with hydroxyl group, nitrogen-containing compounds with
hydroxyphenyl group, and alcoholic nitrogen-containing compounds
include 2-hydroxypyridine, aminocresol, 2,4-quinolinediol,
3-indolemethanol hydrate, monoethanolamine, diethanolamine,
triethanolamine, N-ethyldiethanolamine, N,N-diethylethanolamine,
triisopropanolamine, 2,2'-iminodiethanol, 2-aminoethanol,
3-amino-1-propanol, 4-amino-1-butanol,
4-(2-hydroxyethyl)morpholine, 2-(2-hydroxyethyl)pyridine,
1-(2-hydroxyethyl)piperazine,
1-[2-(2-hydroxyethoxy)ethyl]piperazine, piperidine ethanol,
1-(2-hydroxyethyl)pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone,
3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol,
8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol,
1-methyl-2-pyrrolidine ethanol, 1-aziridine ethanol,
N-(2-hydroxyethyl)phthalimide, and
N-(2-hydroxyethyl)isonicotinamide.
[0069] Examples of suitable amide derivatives include formamide,
N-methylformamide, N,N-dimethylformamide, acetamide,
N-methylacetamide, N,N-dimethylacetamide, propionamide, and
benzamide. Suitable imide derivatives include phthalimide,
succinimide, and maleimide.
[0070] In addition, one or more of basic compounds of the following
general formula (B)-1 may also be included.
N(Z).sub.n(Y).sub.3-n (B)-1
[0071] In the formula, n is equal to 1, 2 or 3; Y is independently
hydrogen or a straight, branched or cyclic alkyl group of 1 to 20
carbon atoms which may contain a hydroxyl group or ether group; and
Z is independently selected from groups of the following general
formulas (Z)-1 to (Z)-3, and two or three Z may bond together to
form a ring.
##STR00007##
[0072] In the formulas, R.sup.300, R.sup.302 and R.sup.305 are
independently straight or branched C.sub.1-C.sub.4 alkylene groups;
R.sup.301 and R.sup.304 are independently hydrogen or straight,
branched or cyclic C.sub.1-C.sub.20 alkyl groups, which may contain
at least one hydroxyl group, ether group, ester group or lactone
ring; R.sup.303 is a single bond or a straight or branched
C.sub.1-C.sub.4 alkylene group; and R.sup.306 is a straight,
branched or cyclic C.sub.1-C.sub.20 alkyl group, which may contain
at least one hydroxyl group, ether group, ester group or lactone
ring.
[0073] Illustrative examples of the basic compounds of formula
(B)-1 include, but are not limited to,
tris[(2-methoxymethoxy)ethyl]amine,
tris[2-(2-methoxyethoxy)ethyl]amine,
tris[2-(2-methoxyethoxymethoxy)ethyl]amine,
tris[2-(1-methoxyethoxy)ethyl]amine,
tris[2-(1-ethoxyethoxy)ethyl]amine,
tris[2-(1-ethoxypropoxy)ethyl]amine,
tris[2-(2-(2-hydroxyethoxy)ethoxy)ethyl]amine,
4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane,
4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane,
1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane,
1-aza-12-crown-4,1-aza-15-crown-5,1-aza-18-crown-6,
tris(2-formyloxyethyl)amine, tris(2-acetoxyethyl)amine,
tris(2-propionyloxyethyl)amine, tris(2-butyryloxyethyl)amine,
tris(2-isobutyryloxyethyl)amine, tris(2-valeryloxyethyl)amine,
tris(2-pivaloyloxyethyl)amine,
N,N-bis(2-acetoxyethyl)-2-(acetoxyacetoxy)ethylamine,
tris(2-methoxycarbonyloxyethyl)amine,
tris(2-tert-butoxycarbonyloxyethyl)amine,
tris[2-(2-oxopropoxy)ethyl]amine,
tris[2-(methoxycarbonylmethyl)oxyethyl]amine,
tris[2-(tert-butoxycarbonylmethyloxy)ethyl]amine,
tris[2-(cyclohexyloxycarbonylmethyloxy)ethyl]amine,
tris(2-methoxycarbonylethyl)amine,
tris(2-ethoxycarbonylethyl)amine,
N,N-bis(2-hydroxyethyl)-2-(methoxycarbonyl)ethylamine,
N,N-bis(2-acetoxyethyl)-2-(methoxycarbonyl)ethylamine,
N,N-bis(2-hydroxyethyl)-2-(ethoxycarbonyl)ethylamine,
N,N-bis(2-acetoxyethyl)-2-(ethoxycarbonyl)ethylamine,
N,N-bis(2-hydroxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine,
N,N-bis(2-acetoxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine,
N,N-bis(2-hydroxyethyl)-2-(2-hydroxyethoxycarbonyl)ethylamine,
N,N-bis(2-acetoxyethyl)-2-(2-acetoxyethoxycarbonyl)ethylamine,
N,N-bis(2-hydroxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]-ethylamine,
N,N-bis(2-acetoxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]-ethylamine,
N,N-bis(2-hydroxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine,
N,N-bis(2-acetoxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine,
N,N-bis(2-hydroxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)-ethylamine,
N,N-bis(2-acetoxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)-ethylamine,
N,N-bis(2-hydroxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxy-carbonyl]ethyla-
mine,
N,N-bis(2-acetoxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxy-carbonyl]e-
thylamine,
N,N-bis(2-hydroxyethyl)-2-(4-hydroxybutoxycarbonyl)ethylamine,
N,N-bis(2-formyloxyethyl)-2-(4-formyloxybutoxycarbonyl)-ethylamine,
N,N-bis(2-formyloxyethyl)-2-(2-formyloxyethoxycarbonyl)-ethylamine,
N,N-bis(2-methoxyethyl)-2-(methoxycarbonyl)ethylamine,
N-(2-hydroxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,
N-(2-acetoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,
N-(2-hydroxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine,
N-(2-acetoxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine,
N-(3-hydroxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine,
N-(3-acetoxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine,
N-(2-methoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,
N-butyl-bis[2-(methoxycarbonyl)ethyl]amine,
N-butyl-bis[2-(2-methoxyethoxycarbonyl)ethyl]amine,
N-methyl-bis(2-acetoxyethyl)amine,
N-ethyl-bis(2-acetoxyethyl)amine,
N-methyl-bis(2-pivaloyloxyethyl)amine,
N-ethyl-bis[2-(methoxycarbonyloxy)ethyl]amine,
N-ethyl-bis[2-(tert-butoxycarbonyloxy)ethyl]amine,
tris(methoxycarbonylmethyl)amine, tris(ethoxycarbonylmethyl)amine,
N-butyl-bis(methoxycarbonylmethyl)amine,
N-hexyl-bis(methoxycarbonylmethyl)amine, and
.beta.-(diethylamino)-.delta.-valerolactone.
[0074] The basic compounds may be used alone or in admixture of two
or more. The basic compound is preferably formulated in an amount
of 0 to 2 parts, and especially 0.01 to 1 part by weight, per 100
parts by weight of the base resin in the resist composition. The
use of more than 2 parts of the basis compound may result in too
low a sensitivity.
Organic Solvent
[0075] In order that the negative resist composition be coated to
form a resist film, the foregoing components are dissolved in an
organic solvent to formulate the composition in solution form. A
number of organic solvents are known and used to this end.
Illustrative, non-limiting, examples of suitable organic solvents
include butyl acetate, amyl acetate, cyclohexyl acetate,
3-methoxybutyl acetate, methyl ethyl ketone, methyl amyl ketone,
cyclohexanone, cyclopentanone, 3-ethoxyethyl propionate,
3-ethoxymethyl propionate, 3-methoxymethyl propionate, methyl
acetoacetate, ethyl acetoacetate, diacetone alcohol, methyl
pyruvate, ethyl pyruvate, propylene glycol monomethyl ether,
propylene glycol monoethyl ether, propylene glycol monomethyl ether
propionate, propylene glycol monoethyl ether propionate, ethylene
glycol monomethyl ether, ethylene glycol monoethyl ether,
diethylene glycol monomethyl ether, diethylene glycol monoethyl
ether, 3-methyl-3-methoxybutanol, N-methylpyrrolidone, dimethyl
sulfoxide, .gamma.-butyrolactone, propylene glycol alkyl ether
acetates such as propylene glycol methyl ether acetate, propylene
glycol ethyl ether acetate, and propylene glycol propyl ether
acetate, alkyl lactates such as methyl lactate, ethyl lactate, and
propyl lactate, and tetramethylene sulfone.
[0076] Of these, the propylene glycol alkyl ether acetates and
alkyl lactates are especially preferred. The solvents may be used
alone or in admixture of two or more. An exemplary useful solvent
mixture is a mixture of propylene glycol alkyl ether acetates
and/or alkyl lactates. It is noted that the alkyl groups of the
propylene glycol alkyl ether acetates are preferably those of 1 to
4 carbon atoms, for example, methyl, ethyl and propyl, with methyl
and ethyl being especially preferred. Since the propylene glycol
alkyl ether acetates include 1,2- and 1,3-substituted ones, each
includes three isomers depending on the combination of substituted
positions, which may be used alone or in admixture. It is also
noted that the alkyl groups of the alkyl lactates are preferably
those of 1 to 4 carbon atoms, for example, methyl, ethyl and
propyl, with methyl and ethyl being especially preferred.
[0077] When the propylene glycol alkyl ether acetate is used as the
solvent, it preferably accounts for at least 50% by weight of the
entire solvent. Also when the alkyl lactate or propylene glycol
alkyl ether is used as the solvent, it preferably accounts for at
least 50% by weight of the entire solvent. When a mixture of
propylene glycol alkyl ether acetate and alkyl lactate or propylene
glycol alkyl ether is used as the solvent, that mixture preferably
accounts for at least 50% by weight of the entire solvent. In this
solvent mixture, it is further preferred that the propylene glycol
alkyl ether acetate is 5 to 40% by weight and the alkyl lactate or
propylene glycol alkyl ether is 60 to 95% by weight. A lower
proportion of the propylene glycol alkyl ether acetate would invite
a problem of inefficient coating whereas a higher proportion
thereof would provide insufficient dissolution and allow for
particle and foreign matter formation. A lower proportion of the
alkyl lactate or propylene glycol alkyl ether would provide
insufficient dissolution and cause the problem of many particles
and foreign matter whereas a higher proportion thereof would lead
to a composition which has a too high viscosity to apply and loses
storage stability.
[0078] In the negative resist composition, the solvent is
preferably used in an amount of 300 to 2,000 parts by weight,
especially 400 to 1,000 parts by weight per 100 parts by weight of
the base resin. The concentration of the resulting composition is
not limited thereto as long as a film can be formed by existing
methods.
Surfactant
[0079] To the chemically amplified negative resist composition of
the invention, a surfactant may be added for improving coating
characteristics or the like.
[0080] Illustrative, non-limiting, examples of the surfactant
include nonionic surfactants, for example, polyoxyethylene alkyl
ethers such as polyoxyethylene lauryl ether, polyoxyethylene
stearyl ether, polyoxyethylene cetyl ether, and polyoxyethylene
oleyl ether, polyoxyethylene alkylaryl ethers such as
polyoxyethylene octylphenol ether and polyoxyethylene nonylphenol
ether, polyoxyethylene polyoxypropylene block copolymers, sorbitan
fatty acid esters such as sorbitan monolaurate, sorbitan
monopalmitate, and sorbitan monostearate, and polyoxyethylene
sorbitan fatty acid esters such as polyoxyethylene sorbitan
monolaurate, polyoxyethylene sorbitan monopalmitate,
polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan
trioleate, and polyoxyethylene sorbitan tristearate; fluorochemical
surfactants such as EFTOP EF301, EF303 and EF352 (Tohkem Products
Co., Ltd.), Megaface F171, F172 and F173 (Dainippon Ink &
Chemicals, Inc.), Fluorad FC430 and FC431 (Sumitomo 3M Co., Ltd.),
Asahiguard AG710, Surflon S-381, S-382, SC101, SC102, SC103, SC104,
SC105, SC106, Surfynol E1004, KH-10, KH-20, KH-30 and KH-40 (Asahi
Glass Co., Ltd.); organosiloxane polymers KP341, X-70-092 and
X-70-093 (Shin-Etsu Chemical Co., Ltd.), acrylic acid or
methacrylic acid Polyflow No. 75 and No. 95 (Kyoeisha Ushi Kagaku
Kogyo K.K.). Inter alia, Fluorad FC430, Surflon S-381, Surfynol
E1004, KH-20 and KH-30 are preferred. These surfactants may be used
alone or in admixture.
[0081] In the chemically amplified negative resist composition of
the invention, the surfactant is preferably formulated in an amount
of up to 2 parts, and especially up to 1 part by weight, per 100
parts by weight of the base resin.
Process
[0082] A resist pattern is formed from the chemically amplified
negative resist composition of the invention by any ordinary
lithography process including coating step of the resist
composition onto a processable substrate (or substrate to be
processed), pattern-wise exposure step using high-energy radiation,
and development step using an aqueous alkaline developer.
[0083] The material of which the processable substrate or its
outermost surface layer is made is not particularly limited. In the
case of semiconductor wafers, for example, silicon wafers may be
used, and examples of the outermost surface layer include Si,
SiO.sub.2, SiN, SiON, TiN, WSi, BPSG, SOG, and organic
antireflective films.
[0084] In another embodiment, a resist pattern is formed on a
photomask blank, from which a photomask is obtained. Typical
transparent substrates used herein include transparent substrates
of quartz and calcium fluoride. In most cases, necessary functional
films such as a light-shielding film, antireflective coating, phase
shift film, and optionally, etch stop film and etch mask film are
laid in sequence on the substrate, depending on the intended
application. In some special cases, such a functional film is
omitted. Examples of the material of which the functional film is
made include silicon, or transition metals such as chromium,
molybdenum, zirconium, tantalum, tungsten, titanium and niobium,
which may be used to form a layer. Examples of the material of
which the outermost surface layer is made include materials mainly
containing silicon or silicon and oxygen and/or nitrogen, silicon
compound materials mainly containing a transition metal in addition
to the foregoing, and transition metal compound materials mainly
containing a transition metal, specifically at least one of
chromium, molybdenum, zirconium, tantalum, tungsten, titanium, and
niobium, and optionally at least one of oxygen, nitrogen, and
carbon.
[0085] Of these materials, the transition metal compound material
tends to give rise to the undercut problem. Specifically, a
photomask blank includes an outermost surface layer of a transition
metal compound material, specifically a transition metal compound
material containing oxygen and/or nitrogen, and more specifically a
transition metal compound material containing chromium and oxygen
and/or nitrogen. When a pattern is formed on this photomask blank
using a chemically amplified negative resist composition, the
pattern tends to be constricted near the substrate, resulting in a
so-called "undercut" shape. Nevertheless, the chemically amplified
negative resist composition of the invention is successful in
ameliorating the undercut problem, as compared with prior art
resist compositions. Thus the pattern forming process of the
invention is advantageous.
[0086] The process starts with a coating step. In applying the
inventive resist composition, any of well-known application
techniques including spin coating, roll coating, flow coating, dip
coating, spray coating, and doctor coating may be used. Spin
coating is preferred for consistent formation of a thin
coating.
[0087] The thickness of the coating is selected depending on the
minimum line width of the desired pattern and the etching rate of
the processable substrate. Usually a thickness which is equal to or
greater than the minimum line width by a factor of 1 to 8 is
selected.
[0088] The resist coating is then heated (i.e., prebaked) on a hot
plate, heating furnace or the like for removing the unnecessary
organic solvent remaining in the resist coating. The heating
conditions, which vary with the type of substrate, may not be
determined unequivocally. Where a hot plate is used, typical
prebaking conditions include a temperature of 60 to 150.degree. C.
for about 1 to 10 minutes, preferably 80 to 120.degree. C. for
about 1 to 5 minutes.
[0089] The pattern exposure step is imagewise exposure in a
well-known way using high-energy radiation providing a high
transmittance to the benzene ring, for example, deep-UV having a
wavelength equal to or more than 230 nm, typically KrF excimer
laser radiation, EB, EUV, and X-ray. In the processing of a
photomask blank, EB exposure is always used. For the EB exposure,
an exposure dose of about 0.1 to 20 .mu.C/cm.sup.2 is preferred,
with an exposure dose of about 3 to 10 .mu.C/cm.sup.2 being more
preferred.
[0090] After the pattern exposure, the coated substrate is heated
again (or post-exposure baked) for promoting acid-catalyzed
crosslinking reaction. Where a hot plate is used, for example, the
exposed areas of the coating are appropriately cured by heating at
60 to 150.degree. C. for about 1 to 20 minutes, preferably at 80 to
120.degree. C. for about 1 to 10 minutes.
[0091] In the subsequent development step, an aqueous alkaline
developer is used to dissolving away the unexposed areas of the
coating, leaving the desired resist pattern. Development is
typically carried out in an aqueous solution of 0.1 to 5 wt %,
preferably 2 to 3 wt % tetramethylammonium hydroxide (TMAH) for 0.1
to 3 minutes, preferably 0.5 to 2 minutes by a conventional
technique such as dip, puddle or spray technique. In this way, a
desired resist pattern is formed on the substrate.
EXAMPLE
[0092] Synthesis Examples, Comparative Synthesis Examples,
Examples, and Comparative Examples are given below by way of
illustration and not by way of limitation. The average molecular
weights including weight average molecular weight (Mw) and number
average molecular weight (Mn) are determined by gel permeation
chromatography (GPC) versus polystyrene standards.
Synthesis Example 1
[0093] A 3-L flask was charged with 238.0 g of acetoxystyrene, 22.6
g of 4-chlorostyrene, 189.4 g of indene, and 675 g of toluene as a
solvent. The reactor was cooled to -70.degree. C. in a nitrogen
blanket, followed by three repeated cycles of vacuum evacuation and
nitrogen flow. The reactor was warmed to room temperature, fed with
40.5 g of 2,2'-azobis(2,4-dimethylvaleronitrile), V-65 (Wako Pure
Chemical Industries, Ltd.) as a polymerization initiator, and
heated at 45.degree. C. whereupon reaction took place for 20 hours.
The temperature was then raised to 55.degree. C. whereupon reaction
took place for a further 20 hours. The reaction solution was
concentrated to a half volume and precipitated in 15.0 L of
methanol. The resulting white solids were collected by filtration
and dried in vacuum at 40.degree. C., yielding 311 g of a white
polymer.
[0094] The polymer was dissolved again in 488 g of methanol and 540
g of tetrahydrofuran, whereupon 162 g of triethylamine and 32 g of
water were added to the polymer solution. Deprotection reaction
occurred at 60.degree. C. for 40 hours. Then for fractionation, the
reaction solution was concentrated and dissolved in a solvent
mixture of 548 g of methanol and 112 g of acetone. To this
solution, 990 g of hexane was added dropwise over 10 minutes. The
mixed white turbid solution was left at rest for separation,
whereupon the lower (polymer) layer was taken out and concentrated.
The polymer concentrate was dissolved again in a mixture of 548 g
of methanol and 112 g of acetone, after which the solution was
combined with 990 g of hexane for dispersion and separation. The
lower (polymer) layer was taken out and concentrated. The
concentrate was dissolved in 870 g of ethyl acetate, followed by
one cycle of neutralization, separation and washing with a mixture
of 250 g of water and 98 g of acetic acid, one cycle of separation
and washing with 225 g of water and 75 g of pyridine, and four
cycles of separation and washing with 225 g of water. Thereafter,
the upper layer, ethyl acetate solution was concentrated, dissolved
in 250 g of acetone, precipitated in 15 L of water, filtered, and
vacuum dried at 50.degree. C. for 40 hours, yielding 187 g of a
white polymer.
[0095] The polymer, designated Poly-A, was analyzed by
.sup.13C-NMR, .sup.1H-NMR and GPC, from which the composition and
molecular weight were determined.
[0096] Copolymer compositional ratio (molar ratio) [0097]
hydroxystyrene/4-chlorostyrene/indene=76.0/6.5/17.5 [0098] Mw=4,200
[0099] Dispersity Mw/Mn=1.59
Synthesis Example 2
[0100] A 3-L flask was charged with 212.0 g of acetoxystyrene, 20.4
g of 4-bromostyrene, 188.1 g of indene, and 675 g of toluene as a
solvent. The reactor was cooled to -70.degree. C. in a nitrogen
blanket, followed by three repeated cycles of vacuum evacuation and
nitrogen flow. The reactor was warmed to room temperature, fed with
40.5 g of 2,2'-azobis(2,4-dimethylvaleronitrile), V-65 (Wako Pure
Chemical Industries, Ltd.) as a polymerization initiator, and
heated at 45.degree. C. whereupon reaction took place for 20 hours.
The temperature was then raised to 55.degree. C. whereupon reaction
took place for a further 20 hours. The reaction solution was
concentrated to a half volume and precipitated in 15.0 L of
methanol. The resulting white solids were collected by filtration
and dried in vacuum at 40.degree. C., yielding 320 g of a white
polymer.
[0101] The polymer was dissolved again in 488 g of methanol and 540
g of tetrahydrofuran, whereupon 162 g of triethylamine and 32 g of
water were added to the polymer solution. Deprotection reaction
occurred at 60.degree. C. for 40 hours. Then for fractionation, the
reaction solution was concentrated and dissolved in a solvent
mixture of 548 g of methanol and 112 g of acetone. To this
solution, 990 g of hexane was added dropwise over 10 minutes. The
mixed white turbid solution was left at rest for separation,
whereupon the lower (polymer) layer was taken out and concentrated.
The polymer concentrate was dissolved again in a mixture of 548 g
of methanol and 112 g of acetone, after which the solution was
combined with 990 g of hexane for dispersion and separation. The
lower (polymer) layer was taken out and concentrated. The
concentrate was dissolved in 870 g of ethyl acetate, followed by
one cycle of neutralization, separation and washing with a mixture
of 250 g of water and 98 g of acetic acid, one cycle of separation
and washing with 225 g of water and 75 g of pyridine, and four
cycles of separation and washing with 225 g of water. Thereafter,
the upper layer, ethyl acetate solution was concentrated, dissolved
in 250 g of acetone, precipitated in 15 L of water, filtered, and
vacuum dried at 50.degree. C. for 40 hours, yielding 191 g of a
white polymer.
[0102] The polymer, designated Poly-B, was analyzed by
.sup.13C-NMR, .sup.1H-NMR and GPC, from which the composition and
molecular weight were determined.
[0103] Copolymer compositional ratio (molar ratio) [0104]
hydroxystyrene/4-bromostyrene/indene=77.7/5.4/16.9 [0105] Mw=4,100
[0106] Dispersity Mw/Mn=1.58
Synthesis Example 3
[0107] A 3-L flask was charged with 222.0 g of acetoxystyrene, 37.1
g of 4-methoxycarbonylstyrene, 178.3 g of indene, and 675 g of
toluene as a solvent. The reactor was cooled to -70.degree. C. in a
nitrogen blanket, followed by three repeated cycles of vacuum
evacuation and nitrogen flow. The reactor was warmed to room
temperature, fed with 40.1 g of
2,2'-azobis(2,4-dimethylvaleronitrile), V-65 (Wako Pure Chemical
Industries, Ltd.) as a polymerization initiator, and heated at
45.degree. C. whereupon reaction took place for 20 hours. The
temperature was then raised to 55.degree. C. whereupon reaction
took place for a further 20 hours. The reaction solution was
concentrated to a half volume and precipitated in 15.0 L of
methanol. The resulting white solids were collected by filtration
and dried in vacuum at 40.degree. C., yielding 299 g of a white
polymer.
[0108] The polymer was dissolved again in 488 g of methanol and 540
g of tetrahydrofuran, whereupon 162 g of triethylamine and 32 g of
water were added to the polymer solution. Deprotection reaction
occurred at 60.degree. C. for 40 hours. Then for fractionation, the
reaction solution was concentrated and dissolved in a solvent
mixture of 548 g of methanol and 112 g of acetone. To this
solution, 990 g of hexane was added dropwise over 10 minutes. The
mixed white turbid solution was left at rest for separation,
whereupon the lower (polymer) layer was taken out and concentrated.
The polymer concentrate was dissolved again in a mixture of 548 g
of methanol and 112 g of acetone, after which the solution was
combined with 990 g of hexane for dispersion and separation. The
lower (polymer) layer was taken out and concentrated. The
concentrate was dissolved in 870 g of ethyl acetate, followed by
one cycle of neutralization, separation and washing with a mixture
of 250 g of water and 98 g of acetic acid, one cycle of separation
and washing with 225 g of water and 75 g of pyridine, and four
cycles of separation and washing with 225 g of water. Thereafter,
the upper layer, ethyl acetate solution was concentrated, dissolved
in 250 g of acetone, precipitated in 15 L of water, filtered, and
vacuum dried at 50.degree. C. for 40 hours, yielding 165 g of a
white polymer.
[0109] The polymer, designated Poly-C, was analyzed by
.sup.13C-NMR, .sup.1H-NMR and GPC, from which the composition and
molecular weight were determined.
[0110] Copolymer compositional ratio (molar ratio) [0111]
hydroxystyrene/4-methoxycarbonylstyrene/indene=74.9/10.0/15.1
[0112] Mw=4,700 [0113] Dispersity Mw/Mn=1.63
Synthesis Example 4
[0114] A 3-L flask was charged with 254.1 g of acetoxystyrene, 32.0
g of 4-t-butoxycarbonylstyrene, 163.8 g of indene, and 600 g of
toluene as a solvent. The reactor was cooled to -70.degree. C. in a
nitrogen blanket, followed by three repeated cycles of vacuum
evacuation and nitrogen flow. The reactor was warmed to room
temperature, fed with 39.0 g of
2,2'-azobis(2,4-dimethylvaleronitrile), V-65 (Wako Pure Chemical
Industries, Ltd.) as a polymerization initiator, and heated at
45.degree. C. whereupon reaction took place for 20 hours. The
temperature was then raised to 55.degree. C. whereupon reaction
took place for a further 20 hours. The reaction solution was
concentrated to a half volume and precipitated in 15.0 L of
methanol. The resulting white solids were collected by filtration
and dried in vacuum at 40.degree. C., yielding 318 g of a white
polymer.
[0115] The polymer was dissolved again in 488 g of methanol and 540
g of tetrahydrofuran, whereupon 162 g of triethylamine and 32 g of
water were added to the polymer solution. Deprotection reaction
occurred at 60.degree. C. for 40 hours. Then for fractionation, the
reaction solution was concentrated and dissolved in a solvent
mixture of 548 g of methanol and 112 g of acetone. To this
solution, 990 g of hexane was added dropwise over 10 minutes. The
mixed white turbid solution was left at rest for separation,
whereupon the lower (polymer) layer was taken out and concentrated.
The polymer concentrate was dissolved again in a mixture of 548 g
of methanol and 112 g of acetone, after which the solution was
combined with 990 g of hexane for dispersion and separation. The
lower (polymer) layer was taken out and concentrated. The
concentrate was dissolved in 870 g of ethyl acetate, followed by
one cycle of neutralization, separation and washing with a mixture
of 250 g of water and 98 g of acetic acid, one cycle of separation
and washing with 225 g of water and 75 g of pyridine, and four
cycles of separation and washing with 225 g of water. Thereafter,
the upper layer, ethyl acetate solution was concentrated, dissolved
in 250 g of acetone, precipitated in 15 L of water, filtered, and
vacuum dried at 50.degree. C. for 40 hours, yielding 178 g of a
white polymer.
[0116] The polymer, designated Poly-D, was analyzed by
.sup.13C-NMR, .sup.1H-NMR and GPC, from which the composition and
molecular weight were determined.
[0117] Copolymer compositional ratio (molar ratio) [0118]
hydroxystyrene/4-t-butoxycarbonylstyrene/indene=77.8/7.0/15.1
[0119] Mw=5,000 [0120] Dispersity Mw/Mn=1.61
Synthesis Example 5
[0121] A 3-L flask was charged with 354.4 g of acetoxystyrene, 95.6
g of 4-chlorostyrene, and 1500 g of toluene as a solvent. The
reactor was cooled to -70.degree. C. in a nitrogen blanket,
followed by three repeated cycles of vacuum evacuation and nitrogen
flow. The reactor was warmed to room temperature, fed with 23.6 g
of AIBN (Wako Pure Chemical Industries, Ltd.) as a polymerization
initiator, and heated at 65.degree. C. whereupon reaction took
place for 40 hours. The reaction solution was concentrated to a
half volume and precipitated in 20.0 L of methanol. The resulting
white solids were collected by filtration and dried in vacuum at
40.degree. C., yielding 420 g of a white polymer.
[0122] The polymer was dissolved again in 488-g of methanol and 540
g of tetrahydrofuran, whereupon 162 g of triethylamine and 32 g of
water were added to the polymer solution. Deprotection reaction
occurred at 60.degree. C. for 40 hours. Then for fractionation, the
reaction solution was concentrated and dissolved in a solvent
mixture of 822 g of methanol and 168 g of acetone. To this
solution, 1485 g of hexane was added dropwise over 10 minutes. The
mixed white turbid solution was left at rest for separation,
whereupon the lower (polymer) layer was taken out and concentrated.
The polymer concentrate was dissolved again in a mixture of 822 g
of methanol and 168 g of acetone, after which the solution was
combined with 1485 g of hexane for dispersion and separation. The
lower (polymer) layer was taken out and concentrated. The
concentrate was dissolved in 1300 g of ethyl acetate, followed by
one cycle of neutralization, separation and washing with a mixture
of 375 g of water and 98 g of acetic acid, one cycle of separation
and washing with 375 g of water and 75 g of pyridine, and four
cycles of separation and washing with 225 g of water. Thereafter,
the upper layer, ethyl acetate solution was concentrated, dissolved
in 375 g of acetone, precipitated in 20 L of water, filtered, and
vacuum dried at 50.degree. C. for 40 hours, yielding 280 g of a
white polymer.
[0123] The polymer, designated Poly-E, was analyzed by
.sup.13C-NMR, .sup.1H-NMR and GPC, from which the composition and
molecular weight were determined.
[0124] Copolymer compositional ratio (molar ratio) [0125]
hydroxystyrene/4-chlorostyrene=75.8/24.2 [0126] Mw=5,200 [0127]
Dispersity Mw/Mn=1.62
Synthesis Example 6
[0128] A 3-L flask was charged with 238.0 g of acetoxystyrene, 22.0
g of 4-chlorostyrene, 190.7 g of indene, and 675 g of toluene as a
solvent. The reactor was cooled to -70.degree. C. in a nitrogen
blanket, followed by three repeated cycles of vacuum evacuation and
nitrogen flow. The reactor was warmed to room temperature, fed with
40.5 g of 2,2'-azobis(2,4-dimethylvaleronitrile), V-65 (Wako Pure
Chemical Industries, Ltd.) as a polymerization initiator, and
heated at 45.degree. C. whereupon reaction took place for 20 hours.
The temperature was then raised to 55.degree. C. whereupon reaction
took place for a further 20 hours. The reaction solution was
concentrated to a half volume and precipitated in 15.0 L of
methanol. The resulting white solids were collected by filtration
and dried in vacuum at 40.degree. C., yielding 309 g of a white
polymer.
[0129] The polymer was dissolved again in 488 g of methanol and 540
g of tetrahydrofuran, whereupon 162 g of triethylamine and 32 g of
water were added to the polymer solution. Deprotection reaction
occurred at 60.degree. C. for 40 hours. The reaction solution was
concentrated and dissolved in 870 g of ethyl acetate, followed by
one cycle of neutralization, separation and washing with a mixture
of 250 g of water and 98 g of acetic acid, one cycle of separation
and washing with 225 g of water and 75 g of pyridine, and four
cycles of separation and washing with 225 g of water. Thereafter,
the upper layer, ethyl acetate solution was concentrated, dissolved
in 250 g of acetone, precipitated in 15 L of water, filtered, and
vacuum dried at 50.degree. C. for 40 hours, yielding 220 g of a
white polymer.
[0130] The polymer, designated Poly-F, was analyzed by
.sup.13C-NMR, .sup.1H-NMR and GPC, from which the composition and
molecular weight were determined.
[0131] Copolymer compositional ratio (molar ratio) [0132]
hydroxystyrene/4-chlorostyrene/indene=75.6/7.5/16.9 [0133] Mw=4,700
[0134] Dispersity Mw/Mn=1.88
Comparative Synthesis Example
[0135] Polymers, designated Poly-G, Poly-H, Poly-I, and Poly-J,
were synthesized by the same procedure as in the foregoing
Synthesis Examples.
Poly-G
[0136] Copolymer compositional ratio (molar ratio) [0137]
hydroxystyrene/indene=74.5/25.5 [0138] Mw=4,400 [0139] Dispersity
Mw/Mn=1.60
Poly-H
[0140] Copolymer compositional ratio (molar ratio) [0141]
hydroxystyrene/4-isopropyloxystyrene/indene=73.9/11.6/14.5 [0142]
Mw=4,100 [0143] Dispersity Mw/Mn=1.70
Poly-I
[0144] Copolymer compositional ratio (molar ratio) [0145]
hydroxystyrene/3,5-dimethoxystyrene/indene=70.8/15.6/13.6 [0146]
Mw=4,300 [0147] Dispersity Mw/Mn=1.65
Poly-J
[0148] Copolymer compositional ratio (molar ratio) [0149]
hydroxystyrene/4-acetoxystyrene/indene=74.6/10.6/14.8 [0150]
Mw=4,500 [0151] Dispersity Mw/Mn=1.65
[0152] The polymers synthesized are represented by the following
formulae.
##STR00008## ##STR00009##
Examples 1 to 7 and Comparative Examples 1 to 4
[0153] Chemically amplified negative resist compositions were
prepared in accordance with the formulation shown in Tables 1 and
2. The values in Tables are expressed in parts by weight (pbw). The
components used in the resist compositions and shown in Tables 1
and 2 are identified below.
TABLE-US-00001 TABLE 1 Example (pbw) 1 2 3 4 5 6 7 Poly-A 80 80
Poly-B 80 Poly-C 80 Poly-D 80 Poly-E 80 Poly-F 80 Crosslinker 1 8.2
8.2 8.2 8.2 8.2 6.4 8.2 Crosslinker 2 1.8 PAG1 8 8 8 8 8 8 8 PAG2 2
2 2 2 2 2 2 Basic compound 0.4 0.4 0.4 0.4 0.33 0.33 0.33 Solvent A
320 320 320 320 320 320 320 Solvent B 760 760 760 760 760 760 760
Crosslinker 1: tetramethoxymethylglycoluril Crosslinker 2:
hexamethoxymethylmelamine PAG1: triphenylsulfonium
2,5-dimethylbenzenesulfonate PAG2: triphenylsulfonium
2,4,6-triisopropylbenzenesulfonate Basic compound:
tris(2-methoxyethyl)amine Surfactant A: KH-20 (Asahi Glass Co.,
Ltd.) Solvent A: propylene glycol monomethyl ether acetate Solvent
B: ethyl lactate
TABLE-US-00002 TABLE 2 Comparative Example (pbw) 1 2 3 4 Poly-G 80
Poly-H 80 Poly-I 80 Poly-J 80 Crosslinker 1 8.2 8.2 8.2 8.2
Crosslinker 2 PAG1 8 8 8 8 PAG2 2 2 2 2 Basic compound 0.4 0.4 0.4
0.4 Solvent A 320 320 320 320 Solvent B 760 760 760 760
[0154] The resist compositions was filtered through a 0.02-.mu.m
nylon resin filter and then spin-coated onto mask blanks having an
outermost surface of chromium oxynitride to a thickness of 0.15
.mu.m.
[0155] The mask blanks were then baked on a hot plate at
110.degree. C. for 10 minutes. The resist films were exposed to
electron beam using an EB exposure system HL-800D (Hitachi
High-Technologies Corp., accelerating voltage 50 keV), then baked
(PEB) at 120.degree. C. for 10 minutes, and developed with a
solution of 2.38% tetramethylammonium hydroxide in water, thereby
giving negative patterns.
[0156] The resulting resist patterns were evaluated as described
below.
[0157] The optimum exposure dose (sensitivity Eop) was the exposure
dose which provided a 1:1 resolution at the top and bottom of a
0.20-.mu.m line-and-space pattern. The minimum line width (.mu.m)
of a line-and-space pattern which was ascertained separate on the
mask blank without collapse when processed at the optimum dose was
the resolution of a test resist. The shape in cross section of the
resolved resist pattern was observed under a scanning electron
microscope (SEM).
[0158] A cross section of the line-and-space resist pattern was
also examined for bridge margin and undercut. The line width below
which bridges resulting from dissolution residues of the resist
(i.e., resist left undissolved in developer) are observed in spaces
is reported as "bridge margin," with smaller values indicating
better resolution in spaces.
[0159] The dry etch resistance of the resist composition following
development was examined by dry etching a resist film using a
system TE8500S (Tokyo Electron Ltd.) and observing a cross section
of the resist film under SEM. A reduction in thickness of a resist
film after etching is expressed by a relative value provided that a
reduction in thickness of the resist film of Example 5 after
etching is 1.0. Smaller values indicate resist films with better
etch resistance.
[0160] The etching was effected under the following conditions.
[0161] Prees: 250 mJ [0162] RF power: 800 W [0163] Gas: CHF.sub.3
20 sccm+CF.sub.4 20 sccm+Ar 400 sccm [0164] Etching time:
2'30''
[0165] The resist test results are shown in Table 3.
TABLE-US-00003 TABLE 3 Maximum Bridge Dry Eop resolution margin
etch (.mu.C/cm.sup.2) (.mu.m) (.mu.m) resistance Undercut Example 1
9.2 0.06 0.06 0.89 slight 2 9.1 0.07 0.07 0.91 slight 3 10.5 0.08
0.11 0.92 slight 4 10.7 0.06 0.10 0.91 slight 5 8.9 0.06 0.07 1
slight 6 9.1 0.09 0.09 0.89 small 7 8.7 0.05 0.06 0.9 slight
Comparative Example 1 11.3 0.11 0.12 0.87 large 2 10.9 0.12 0.12
0.96 large 3 9.9 0.14 0.14 0.98 large 4 10.2 0.12 0.13 0.97
large
[0166] FIG. 1 is a photomicrograph of the resist pattern
(0.10-.mu.m line-and-space pattern) obtained in Example 1. The side
walls of lines are flat and no traces of bridges are found. Even
though the resist is on the chromium compound which otherwise
provides strong substrate dependence, only slight undercuts are
seen.
[0167] FIG. 2 is a photomicrograph of the resist pattern
(0.10-.mu.m line-and-space pattern) obtained in Comparative Example
2. Some lines have fell down due to extreme undercuts, and some
lines collapse following bridge formation, leaving small horn-like
projections from lines.
[0168] It is seen from Table 3 and the photomicrograph of FIG. 1
that when a chemically amplified negative resist composition is
prepared using a hydroxystyrene based polymer comprising electron
withdrawing group-bearing styrene units represented by formula (2)
as constituent units, applied as a resist coating, and processed to
form a pattern, the pattern profile is significantly improved even
though the resist pattern is on the chromium compound which is
otherwise likely to invite pattern profile defectives near the
substrate. Similarly the problem that bridges form between
microscopic structures is also ameliorated.
[0169] In summary, the negative resist composition of the invention
is defined as comprising as a base resin a polymer which is
obtained by copolymerizing a monomer having a structure capable of
converting to a functional group providing solubility through
deprotection reaction, a styrene monomer having substituted thereon
an electron withdrawing group, typically chlorine, bromine or
iodine, and optionally a substituted or unsubstituted indene
monomer, followed by deprotection reaction. The composition offers
a high contrast of alkaline dissolution rate before and after
exposure, forms a resist pattern of a satisfactory profile on a
mask blank, especially a mask blank having an outermost surface of
transition metal compound material, which indicates a high
resolution, and exhibits satisfactory etch resistance. Accordingly,
the composition is suited as a micro-patterning material for the
fabrication of VLSI and a mask pattern-forming material.
[0170] Japanese Patent Application No. 2007-087243 is incorporated
herein by reference.
[0171] Although some preferred embodiments have been described,
many modifications and variations may be made thereto in light of
the above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
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