U.S. patent application number 15/937080 was filed with the patent office on 2018-09-06 for copolymer and associated layered article, and device-forming method.
The applicant listed for this patent is ROHM AND HAAS ELECTRONIC MATERIALS LLC, THE UNIVERSITY OF QUEENSLAND. Invention is credited to Idriss Blakey, Ke Du, James W. Thackeray, Peter Trefonas, III, Andrew Keith Whittaker.
Application Number | 20180252645 15/937080 |
Document ID | / |
Family ID | 58048757 |
Filed Date | 2018-09-06 |
United States Patent
Application |
20180252645 |
Kind Code |
A1 |
Thackeray; James W. ; et
al. |
September 6, 2018 |
COPOLYMER AND ASSOCIATED LAYERED ARTICLE, AND DEVICE-FORMING
METHOD
Abstract
A copolymer is prepared by the polymerization of monomers that
include an ultraviolet absorbing monomer, and a
base-solubility-enhancing monomer. The copolymer is useful for
forming a topcoat layer for electron beam and extreme ultraviolet
lithographies. Also described are a layered article including the
topcoat layer, and an associated method of forming an electronic
device.
Inventors: |
Thackeray; James W.;
(Braintree, MA) ; Du; Ke; (Queensland, AU)
; Trefonas, III; Peter; (Medway, MA) ; Blakey;
Idriss; (Clayfield, AU) ; Whittaker; Andrew
Keith; (Toowong, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE UNIVERSITY OF QUEENSLAND
ROHM AND HAAS ELECTRONIC MATERIALS LLC |
St. Lucia
Marlborough |
MA |
AU
US |
|
|
Family ID: |
58048757 |
Appl. No.: |
15/937080 |
Filed: |
March 27, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14820699 |
Aug 7, 2015 |
9957339 |
|
|
15937080 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2021/646 20130101;
G01N 2021/8592 20130101; G01N 21/6486 20130101; G01N 21/359
20130101; B07C 2501/0018 20130101; G01N 2021/8411 20130101; C08F
220/28 20130101; G01N 21/84 20130101; G01N 2021/6439 20130101; G01N
21/6428 20130101; A24B 15/10 20130101; G01N 21/55 20130101; C10L
1/003 20130101; G01N 21/94 20130101; G01N 21/95 20130101; G01N
2021/6417 20130101; G01N 2021/845 20130101; C10N 2040/42 20200501;
C08F 2438/03 20130101; B07C 5/366 20130101; C08F 220/281 20200201;
G01N 21/952 20130101; G03F 7/20 20130101; G01N 2021/8466 20130101;
G03F 7/091 20130101; A24B 1/04 20130101; B65G 27/00 20130101; B07C
5/3427 20130101; B05D 1/005 20130101; G03F 7/094 20130101; A24B
13/00 20130101; G01N 21/85 20130101; C08F 220/286 20200201; C08F
220/1807 20200201; C08F 220/22 20130101; C08F 220/286 20200201;
C08F 220/1807 20200201; C08F 220/22 20130101 |
International
Class: |
G01N 21/64 20060101
G01N021/64; G01N 21/84 20060101 G01N021/84; A24B 13/00 20060101
A24B013/00; A24B 15/10 20060101 A24B015/10; B07C 5/342 20060101
B07C005/342; B07C 5/36 20060101 B07C005/36; B65G 27/00 20060101
B65G027/00; C10L 1/00 20060101 C10L001/00; G01N 21/359 20140101
G01N021/359; G01N 21/55 20140101 G01N021/55; G01N 21/95 20060101
G01N021/95; G01N 21/94 20060101 G01N021/94; G01N 21/85 20060101
G01N021/85; A24B 1/04 20060101 A24B001/04 |
Claims
1. A method of forming an electronic device, comprising: (a)
applying a photoresist layer onto a substrate; (b) applying a
topcoat layer comprising a copolymer, onto the photoresist layer;
(c) pattern-wise exposing the photoresist layer through the topcoat
layer to activating radiation; and (d) developing the exposed
photoresist layer to provide a resist relief image, wherein the
copolymer comprises the polymerization product of monomers
comprising: an out-of-band absorbing monomer; and a
base-solubility-enhancing monomer; and wherein a film cast from the
copolymer has an extinction coefficient, k, of 0.1 to 0.5 at a
wavelength in the range of 150 to 400 nanometers.
2. The method of claim 1, wherein the activating radiation
comprises electron beam or extreme ultraviolet radiation.
3. The method of claim 1, wherein the copolymer has a dispersity
(W.sub.w/M.sub.n) of 1.05 to 1.2.
4. The method of claim 1, wherein the out-of-band absorbing monomer
comprises an unsubstituted or substituted C.sub.6-C.sub.18 aryl
group that is free of fluorine, an unsubstituted or substituted
C.sub.2-C.sub.17 heteroaryl group, a C.sub.5-C.sub.12 dienone
group, or a combination thereof.
5. The method of claim 1, wherein the out-of-band absorbing monomer
has the structure ##STR00012## wherein R.sup.1 is hydrogen or
methyl, n is 0, 1, 2, 3, or 4, and Ar.sup.1 is an unsubstituted or
substituted C.sub.6-C.sub.18 aryl group that is free of
fluorine.
6. The method of claim 1, wherein the base-solubility-enhancing
monomer is selected from the group consisting of (meth)acrylate
esters of poly(ethylene oxide)s, (meth)acrylate esters of
poly(propylene oxide)s, base-labile (meth)acrylate esters,
(meth)acrylate esters substituted with a group having a ply of 2 to
12, and combinations thereof.
7. The method of claim 1, wherein the base-solubility-enhancing
monomer comprises a (meth)acrylate ester of a poly(ethylene oxide)
and a (meth)acrylate ester substituted with a
1,1,1,3,3,3-hexafluoro-2-hydroxy-2-propyl group.
8. The method of claim 1, wherein the out-of-band absorbing monomer
has the structure ##STR00013## wherein R.sup.1 is hydrogen or
methyl, n is 0, 1, 2, 3, or 4, and Ar.sup.1 is an unsubstituted or
substituted C.sub.6-C.sub.18 aryl group that is free of fluorine;
wherein the base-solubility-enhancing monomer comprises a
(meth)acrylate ester of a poly(ethylene oxide) and a (meth)acrylate
ester substituted with a 1,1,1,3,3,3-hexafluoro-2-hydroxy-2-propyl
group; wherein the monomers comprise, based on the total moles of
monomer, 30 to 50 mole percent of the out-of-band absorbing
monomer, 30 to 50 mole percent of the (meth)acrylate ester of a
poly(ethylene oxide), and 10 to 30 mole percent of the
(meth)acrylate ester substituted with a
1,1,1,3,3,3-hexafluoro-2-propyl group; and wherein the copolymer
has a dispersity (W.sub.w/M.sub.n) of 1.05 to 1.2.
9. The method of claim 1, wherein the topcoat layer is formed by
spin-coating a polymer solution comprising 0.1 to 3 weight percent
of the copolymer in a solvent selected from the group consisting of
2-methyl-2-butanol, 2-methyl-2-pentanol, combinations of
2-methyl-2-butanol and 2-methyl-2-pentanol, combinations of
dipropylene glycol monomethyl ether and 2-methyl-2-butanol
containing at least 90 weight percent 2-methyl-2-butanol,
combinations of dipropylene glycol monomethyl ether and
2-methyl-2-pentanol containing at least 90 weight percent
2-methyl-2-pentanol, and combinations of dipropylene glycol
monomethyl ether and 2-methyl-2-butanol and 2-methyl-2-pentanol
containing at least 90 weight percent total of 2-methyl-2-butanol
and 2-methyl-2-pentanol.
10. A layered article comprising: a substrate; a photoresist layer
over the substrate; and a topcoat layer comprising a copolymer,
over and in contact with the photoresist layer, wherein the
copolymer comprises the polymerization product of monomers
comprising: an out-of-band absorbing monomer; and a
base-solubility-enhancing monomer; and wherein a film cast from the
copolymer has an extinction coefficient, k, of 0.1 to 0.5 at a
wavelength in the range of 150 to 400 nanometers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/820,699, filed Aug. 7, 2015 in the United
States Patent and Trademark Office (USPTO), the contents of which
is incorporated herein in its entirety by reference.
FIELD
[0002] The present invention relates to a copolymer, a
photolithographic topcoat layer containing the copolymer, a layered
article comprising the topcoat layer, and a method of forming an
electronic device wherein the method utilizes the topcoat
layer.
INTRODUCTION
[0003] Extreme ultraviolet (EUV) lithography and electron-beam
lithography are promising technologies for patterning at scales of
20 nanometers and less. Sources of EUV radiation also produce
longer wavelength radiation--so-called out-of-band (OOB)
radiation--that can significantly deteriorate imaging performance.
There is therefore a need for compositions that can reduce the
negative impact of out-of-band radiation without unduly
compromising other photolithographic responses. Co-filed U.S.
patent application Ser. No. 14/820,647 describes a photoresist
composition comprising a self-segregating OOB radiation-absorbing
block polymer. For circumstances in which it is desirable to avoid
or minimize modification of the photoresist composition, the
present application describes a copolymer useful in an OOB
radiation-absorbing, developer-soluble topcoat layer.
SUMMARY
[0004] One embodiment is a copolymer, wherein the copolymer
comprises the polymerization product of monomers comprising: an
out-of-band absorbing monomer; and a base-solubility-enhancing
monomer; wherein a film cast from the copolymer has an extinction
coefficient, k, of 0.1 to 0.5 at a wavelength in the range of 150
to 400 nanometers.
[0005] Another embodiment is method of forming a polymer layer,
comprising spin-coating a polymer solution comprising 0.1 to 3
weight percent of the copolymer in a solvent selected from the
group consisting of 2-methyl-2-butanol, 2-methyl-2-pentanol,
combinations of 2-methyl-2-butanol and 2-methyl-2-pentanol,
combinations of dipropylene glycol monomethyl ether and
2-methyl-2-butanol containing at least 90 weight percent
2-methyl-2-butanol, combinations of dipropylene glycol monomethyl
ether and 2-methyl-2-pentanol containing at least 90 weight percent
2-methyl-2-pentanol, and combinations of dipropylene glycol
monomethyl ether and 2-methyl-2-butanol and 2-methyl-2-pentanol
containing at least 90 weight percent total of 2-methyl-2-butanol
and 2-methyl-2-pentanol.
[0006] Another embodiment is a layered article comprising: a
substrate; a photoresist layer over the substrate; and a topcoat
layer comprising the copolymer, over and in contact with the
photoresist layer.
[0007] Another embodiment is a method of forming an electronic
device, comprising: (a) applying a photoresist layer onto a
substrate; (b) applying a topcoat layer comprising the copolymer
onto the photoresist layer; (c) pattern-wise exposing the
photoresist layer through the topcoat layer to activating
radiation; and (d) developing the exposed photoresist layer to
provide a resist relief image.
[0008] These and other embodiments are described in detailed
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a reaction scheme for the synthesis of
poly(PEGMA-co-BzMA-co-HFACHOH).
[0010] FIG. 2 is a reaction scheme for RAFT end group removal for
poly(PEGMA-co-BzMA-co-HFACHOH).
[0011] FIG. 3 provides normalized ultraviolet-visible spectra for
poly(PEGMA-co-BzMA-co-HFACHOH) before and after RAFT end group
cleavage (removal).
[0012] FIG. 4 is a .sup.1H NMR spectrum of the topcoat polymer
poly(PEGMA-co-BzMA-co-HFACHOH).
[0013] FIGS. 5A and 5B present plots of film thickness (nm) versus
polymer concentration (weight percent (wt %)) for FIG. 5A a CBP-4
photoresist layer; and FIG. 5B a topcoat layer.
[0014] FIG. 6 is plot of contact angle (.degree.) as a function of
development time (1 or 60 seconds) for a 10 nanometer topcoat, a 30
nanometer topcoat, CBP-4+10 nm topcoat, CBP-4+30 nm topcoat, and
CBP-4.
[0015] FIG. 7 is a plot of extinction coefficient versus wavelength
(nm) for topcoats having 10 and 30 nanometer thicknesses.
[0016] FIG. 8 is a plot of transmittance (%) versus wavelength (nm)
for topcoats having 10 and 30 nanometer thicknesses.
[0017] FIG. 9 is a plot of normalized film thickness (%) as a
function of dose (microCoulomb/centimeter.sup.2 (.mu.C/cm.sup.2)
for (a) CBP-4 photoresist, and (b) CBP-4 photoresist+10 nm
topcoat.
[0018] FIGS. 10A, 10B, 10C, 10D, 10E, and 10F consist of scanning
electron micrographs (SEM) of line patterns for FIG. 10A
photoresist CBP-4 at 51 .mu.C/cm.sup.2; FIG. 10B photoresist CBP-4
at 53 .mu.C/cm.sup.2; FIG. 10C photoresist CBP-4 at 55
.mu.C/cm.sup.2; FIG. 10D photoresist CBP-4+topcoat at 51
.mu.C/cm.sup.2; FIG. 10E photoresist CBP-4+topcoat at 57
.mu.C/cm.sup.2; FIG. 10F photoresist CBP-4+topcoat at 60
.mu.C/cm.sup.2.
DETAILED DESCRIPTION
[0019] The present inventors have determined that a specific
copolymer is useful as the primary or sole component of a topcoat
layer for electron beam or extreme ultraviolet lithography. The
copolymer absorbs out-of-band (OOB) radiation and readily dissolves
in alkaline developer.
[0020] As used herein, the term "copolymer" includes random
copolymers (including statistical copolymers), block copolymers,
and graft copolymers. The random copolymers can include two, three,
four, or more different types of repeat units. The block copolymers
can be multiblock copolymers and can include, for example, diblock
copolymers, triblock copolymers, tetrablock copolymers, or
copolymers having five or more blocks. The blocks can be part of a
linear copolymer, a branched copolymer where the branches are
grafted onto a backbone (these copolymers are also sometimes called
"comb copolymers"), a star copolymer (sometimes called a radial
block copolymer), and the like. In graft copolymers, the
compositions of the main chain and the one or more side chains are
different either in composition or in the sequence of repeat
units.
[0021] As used herein, the term "(meth)acrylate" means acrylate or
methacrylate.
[0022] As used herein, the term "hydrocarbyl", whether used by
itself, or as a prefix, suffix, or fragment of another term, refers
to a residue that contains only carbon and hydrogen unless it is
specifically identified as "substituted hydrocarbyl". The
hydrocarbyl residue can be aliphatic or aromatic, straight-chain,
cyclic, bicyclic, branched, saturated, or unsaturated. It can also
contain combinations of aliphatic, aromatic, straight chain,
cyclic, bicyclic, branched, saturated, and unsaturated hydrocarbon
moieties. When the hydrocarbyl residue is described as substituted,
it can contain heteroatoms in addition to carbon and hydrogen.
[0023] Except where otherwise specified, the term "substituted"
means including at least one substituent such as a halogen (i.e.,
F, Cl, Br, I), hydroxyl, amino, thiol, carboxyl, carboxylate, ester
(including acrylates, methacrylates, and lactones), amide, nitrile,
sulfide, disulfide, nitro, C.sub.1-18 alkyl, C.sub.1-18 alkenyl
(including norbornenyl and adamantyl), C.sub.1-18 alkoxyl,
C.sub.2-18 alkenoxyl (including vinyl ether), C.sub.6-18 aryl,
C.sub.6-18 aryloxyl, C.sub.7-18 alkylaryl, or C.sub.7-18
alkylaryloxyl.
[0024] As used herein, the term "fluorinated" shall be understood
to mean having one or more fluorine atoms incorporated into the
group. For example, where a C.sub.1-18 fluoroalkyl group is
indicated, the fluoroalkyl group can include one or more fluorine
atoms, for example, a single fluorine atom, two fluorine atoms
(e.g., as a 1,1-difluoroethyl group), three fluorine atoms (e.g.,
as a 2,2,2-trifluoroethyl group), or fluorine atoms at each free
valence of carbon (e.g., as a perfluorinated group such as
--CF.sub.3, --C.sub.2F.sub.5, --C.sub.3F.sub.7, or
--C.sub.4F.sub.9).
[0025] As used herein, the term "alkyl" includes linear alkyl,
branched alkyl, cyclic alkyl, and alkyl groups combining two-way
and three-way combinations of linear, branched, and cyclic groups.
The alkyl groups can be unsubstituted or substituted. Specific
examples of alkyl groups include methyl, ethyl, 1-propyl, 2-propyl,
cyclopropyl, 1-butyl, 2-butyl, 2-methyl-1-propyl, tertiary-butyl,
cyclobutyl, 1-methylcyclopropyl, 2-methylcyclopropyl, 1-pentyl,
2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl,
2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl
(neopentyl), cyclopentyl, 1-methylcyclobutyl, 2-methylcyclobutyl,
3-methylcyclobutyl, 1,2-dimethylcyclopropyl,
2,2-dimethylcyclopropyl, 2,3-dimethylcyclopropyl, 1-hexyl, 2-hexyl,
3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl,
2-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl,
3-methyl-2-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl,
3,3-dimethyl-1-butyl, 3,3-dimethyl-2-butyl, 2,3-dimethyl-1-butyl,
2,3-dimethyl-2-butyl, 1,2,2-trimethylcyclopropyl,
2,2,3-trimethylcyclopropyl, (1,2-dimethylcyclopropyl)methyl,
(2,2-dimethylcyclopropyl)methyl, 1,2,3-trimethylcyclopropyl,
(2,3-dimethylcyclopropyl)methyl, 2,2-dimethylcyclobutyl,
2,3-dimethylcyclobutyl, (1-methylcyclobutyl)methyl,
1,2-dimethylcyclobutyl, 2,3-dimethylcyclobutyl,
(2-methylcyclobutyl)methyl, 1,3-dimethylcyclobutyl,
2,4-dimethylcyclobutyl, (3-methylcyclobutyl)methyl,
1-methylcyclopentyl, 2-methylcyclopentyl, cyclopentylmethyl,
cyclohexyl, 1-norbornyl, 2-norbornyl, 3-norbornyl, 1-adamantyl,
2-adamantyl, octahydro-1-pentalenyl, octahydro-2-pentalenyl,
octahydro-3-pentalenyl, octahydro-1-phenyl-1-pentalenyl,
octahydro-2-phenyl-2-pentalenyl, octahydro-1-phenyl-3-pentalenyl,
octahydro-2-phenyl-3-pentalenyl, decahydro-1-naphthyl,
decahydro-2-naphthyl, decahydro-3-naphthyl,
decahydro-1-phenyl-1-naphthyl, decahydro-2-phenyl-2-naphthyl,
decahydro-1-phenyl-3-naphthyl, and
decahydro-2-phenyl-3-naphthyl.
[0026] One embodiment is a copolymer, wherein the copolymer
comprises the polymerization product of monomers comprising: an
out-of-band absorbing monomer; and a base-solubility-enhancing
monomer; wherein a film cast from the copolymer has an extinction
coefficient, k, of 0.1 to 0.5 at a wavelength in the range of 150
to 400 nanometers.
[0027] As used herein, the term "out-of-band absorbing monomer"
means a monomer that absorbs radiation at longer wavelengths than
the radiation intended to expose the photoresist. For example, if
the exposure device uses extreme ultraviolet radiation at a
wavelength of 13.5 nanometers, then a monomer that absorbs
ultraviolet radiation in the wavelength range 150 to 400
nanometers, specifically 190 to 300 nanometers, would be an
out-of-band absorbing monomer. The "out-of-band absorbing monomer"
provides the copolymer with absorbance in the range 150 to 400
nanometers. Specifically, a film cast from the copolymer has an
extinction coefficient, k, of 0.1 to 0.5 at a wavelength (i.e., at
least one wavelength) in the range of 150 to 400 nanometers. In
some embodiments, the maximum value of the extinction coefficient,
k, in the range 150 to 400 nanometers, is 0.1 to 0.5. It will be
understood that the extinction coefficient, k, can be less than 0.1
and even zero at some wavelengths in the range 150 to 400
nanometers. The out-of-band absorbing monomer excludes
fluorine-substituted ester groups. In some embodiments, the
out-of-band absorbing monomer comprises an unsubstituted or
substituted C.sub.6-C.sub.18 aryl group that is free of fluorine,
an unsubstituted or substituted C.sub.2-C.sub.17 heteroaryl group,
a C.sub.5-C.sub.12 dienone group, or a combination thereof.
[0028] In some embodiments, the out-of-band absorbing monomer has
the structure
##STR00001##
wherein R.sup.1 is hydrogen or methyl; n is 0, 1, 2, 3, or 4; and
Ar.sup.1 is an unsubstituted or substituted C.sub.6-C.sub.18 aryl
group, provided that the substituted C.sub.6-C.sub.18 aryl group is
free of fluorine.
[0029] Specific examples of out-of-band absorbing monomers
include
##STR00002##
and combinations thereof.
[0030] The copolymer can comprise 20 to 60 mole percent of repeat
units derived from the out-of-band absorbing monomer, based on 100
mole percent total repeat units in the copolymer. Within the range
of 20 to 60 mole percent, the content of repeat units derived from
the out-of-band absorbing monomer can be 30 to 50 mole percent.
[0031] In addition to repeat units derived from the out-of-band
absorbing monomer, the copolymer comprises repeat units derived
from a base-solubility-enhancing monomer. Base-solubility-enhancing
monomers include (meth)acrylate esters of poly(ethylene oxide)s,
(meth)acrylate esters of poly(propylene oxide)s, base-labile
(meth)acrylate esters, (meth)acrylate esters substituted with a
group having a pK.sub.a of 2 to 12, and combinations thereof.
[0032] (Meth)acrylate esters of poly(ethylene oxide)s and
poly(propylene oxide)s can have the structure
##STR00003##
wherein R.sup.1 is hydrogen (for acrylate) or methyl (for
methacrylate), R.sup.2 is hydrogen (for poly(ethylene oxide)) or
methyl (for poly(propylene oxide)), and n is 3 to 50, specifically
5 to 30.
[0033] Base-labile (meth)acrylate esters include
lactone-substituted monomers, such as, for example,
##STR00004##
and combinations thereof.
[0034] (Meth)acrylate esters substituted with a group having a
pK.sub.a of 2 to 12 include (meth)acrylate esters substituted with
carboxylic acids, phenols, arylsulfonic acids, phthalimides,
sulfonamides, sulfonimides, and alcohols. Those skilled in the art
can readily determine if a particular species comprising one of
these acidic functional groups has a pK.sub.a value in the range of
2 to 12. Specific examples of (meth)acrylate esters substituted
with a group having a pK.sub.a of 2 to 12 include, for example,
##STR00005## ##STR00006##
and combinations thereof.
[0035] In some embodiments, the base-solubility-enhancing monomer
comprises a (meth)acrylate esters of poly(ethylene oxide), and a
(meth)acrylate ester comprising a 1,1,1,3,3,3-hexafluoro-2-propyl
group.
[0036] The copolymer can comprise 40 to 80 mole percent of repeat
units derived from the base-solubility-enhancing monomer, based on
100 mole percent total repeat units in the copolymer. Within the
range of 40 to 80 mole percent, the content of repeat units derived
from the out-of-band absorbing monomer can be 50 to 70 mole
percent. In a very specific embodiment, the copolymer comprises 30
to 50 mole percent of the (meth)acrylate ester of a poly(ethylene
oxide), and 10 to 30 mole percent of the (meth)acrylate ester
substituted with a 1,1,1,3,3,3-hexafluoro-2-propyl group.
[0037] In some embodiments, the copolymer consists of repeat units
derived from the out-of-band absorbing monomer and the
base-solubility-enhancing monomer.
[0038] The copolymer has an extinction coefficient "k" of 0.1 to
0.4 at 193 nanometer wavelength. Within this range, the extinction
coefficient "k" can be 0.15 to 0.35 at 193 nanometer wavelength. A
procedure for determining extinction coefficient "k" is described
in the working examples.
[0039] There is no particular limitation on the molecular weight of
the copolymer. Molecular weight characteristics can be determined
by size exclusion chromatography using polystyrene standards and
tetrahydrofuran solvent. In some embodiments, the copolymer has a
number average molecular weight of 2,000 to 100,000 Daltons. Within
this range, the number average molecular weight can be 3,000 to
60,000 Daltons, specifically 4,000 to 40,000 Daltons. Particularly
when the copolymer is prepared using the RAFT methods described
herein, it can have a narrow molecular weight distribution. The
molecular weight distribution can be characterized by the
dispersity, which is the ratio of the weight average molecular
weight to the number average molecular weight. In some embodiments,
the copolymer has a dispersity (W.sub.w/M.sub.n) of 1.05 to 1.2.
Within this range, the dispersity can be 1.05 to 1.15. However, a
narrow molecular weight distribution is not required for the
copolymer to function as intended. For example, in some
embodiments, the copolymer has a dispersity of 1.05 to 2.
[0040] In some embodiments, the copolymer is purified using a
method selected from the group consisting of precipitation,
filtration, solvent exchange, centrifugation, decantation
(including multiple decantation), ion exchange, and combinations
thereof.
[0041] In a very specific embodiment of the copolymer, the
out-of-band absorbing monomer has the structure
##STR00007##
wherein R.sup.1 is hydrogen or methyl, n is 0, 1, 2, 3, or 4, and
Ar.sup.1 is an unsubstituted or substituted C.sub.6-C.sub.18 aryl
group that is free of fluorine; the base-solubility-enhancing
monomer comprises a (meth)acrylate ester of a poly(ethylene oxide)
and a (meth)acrylate ester substituted with a
1,1,1,3,3,3-hexafluoro-2-propyl group; the monomers comprise, based
on the total moles of monomer, 30 to 50 mole percent of the
out-of-band absorbing monomer, 30 to 50 mole percent of the
(meth)acrylate ester of a poly(ethylene oxide), and 10 to 30 mole
percent of the (meth)acrylate ester substituted with a
1,1,1,3,3,3-hexafluoro-2-propyl group; and the copolymer has a
dispersity (W.sub.w/M.sub.n) of 1.05 to 1.2.
[0042] The copolymer is particularly useful for forming a topcoat
layer for electron beam lithography or extreme ultraviolet
lithography. The copolymer can constitute 50 to 100 weight percent
of the topcoat layer. Optional components of the topcoat layer
include hydrophobic additives to enhance physical separation of the
topcoat layer from an underlying photoresist layer.
[0043] The topcoat layer can have a thickness of 5 to 50
nanometers, specifically 5 to 40 nanometers. Layer thickness can be
controlled by varying the copolymer concentration in a solution for
spin coating.
[0044] One embodiment is a method of forming a polymer layer,
comprising spin-coating a copolymer solution comprising 0.1 to 3
weight percent of the copolymer (in any of its above-described
variations) in a solvent selected from the group consisting of
2-methyl-2-butanol, 2-methyl-2-pentanol, combinations of
2-methyl-2-butanol and 2-methyl-2-pentanol, combinations of
dipropylene glycol monomethyl ether and 2-methyl-2-butanol
containing at least 90 weight percent 2-methyl-2-butanol,
combinations of dipropylene glycol monomethyl ether and
2-methyl-2-pentanol containing at least 90 weight percent
2-methyl-2-pentanol, and combinations of dipropylene glycol
monomethyl ether and 2-methyl-2-butanol and 2-methyl-2-pentanol
containing at least 90 weight percent total of 2-methyl-2-butanol
and 2-methyl-2-pentanol.
[0045] The invention further includes a layered article comprising:
a substrate; a photoresist layer over the substrate; and a topcoat
layer comprising the copolymer, in any of its above-described
variations, over and in contact with the photoresist layer. In this
embodiment, the layer article can, optionally, further comprise one
or more additional layers between the substrate and the photoresist
layer.
[0046] The invention further includes a method of forming an
electronic device, comprising: (a) applying a photoresist onto a
substrate; (b) applying a topcoat layer, in any of its
above-described variations, onto the photoresist layer; (c)
pattern-wise exposing the photoresist layer through the topcoat
layer to activating radiation; and (d) developing the exposed
photoresist layer to provide a resist relief image. The method can,
optionally, further include (e) etching the resist relief pattern
into the underlying substrate. In some embodiments, the activating
radiation is electron beam or extreme ultraviolet radiation.
[0047] The substrate can be of a material such as a semiconductor,
such as silicon or a compound semiconductor (e.g., III-V or II-VI),
glass, quartz, ceramic, copper and the like. Typically, the
substrate is a semiconductor wafer, such as single crystal silicon
or compound semiconductor wafer, having one or more layers and
patterned features formed on a surface thereof. Optionally, the
underlying base substrate material itself may be patterned, for
example, when it is desired to form trenches in the base substrate
material. Layers formed over the base substrate material may
include, for example, one or more conductive layers such as layers
of aluminum, copper, molybdenum, tantalum, titanium, tungsten, and
alloys, nitrides or silicides of such metals, doped amorphous
silicon or doped polysilicon, one or more dielectric layers such as
layers of silicon oxide, silicon nitride, silicon oxynitride or
metal oxides, semiconductor layers, such as single-crystal silicon,
underlayers, antireflective layers such as a bottom antireflective
layers, and combinations thereof. The layers can be formed by
various techniques, for example, chemical vapor deposition (CVD)
such as plasma-enhanced CVD, low-pressure CVD or epitaxial growth,
physical vapor deposition (PVD) such as sputtering or evaporation,
electroplating or spin-coating.
[0048] Any photoresist composition suitable for electron beam or
extreme ultraviolet lithography can be used.
[0049] Applying the photoresist composition to the substrate can be
accomplished by any suitable method, including spin coating, spray
coating, dip coating, and doctor blading. In some embodiments,
applying the layer of photoresist composition is accomplished by
spin coating the photoresist in solvent using a coating track, in
which the photoresist composition is dispensed on a spinning wafer.
During dispensing, the wafer can be spun at a speed of up to 4,000
rotations per minute (rpm), specifically 500 to 3,000 rpm, and more
specifically 1,000 to 2,500 rpm. The coated wafer is spun to remove
solvent, and baked on a hot plate to remove residual solvent and
free volume from the film to make it uniformly dense.
[0050] Pattern-wise exposure is then carried out using an exposure
tool such as a stepper, in which the film is irradiated through a
pattern mask and thereby is exposed pattern-wise. In some
embodiments, the method uses advanced exposure tools generating
activating radiation at wavelengths capable of high resolution
including extreme-ultraviolet (EUV) or electron-beam (e-beam)
radiation. The resolution of such exposure tools can be less than
30 nanometers.
[0051] Developing the exposed photoresist layer is then
accomplished by treating the exposed layer and overlying topcoat
layer with a suitable positive tone developer capable of uniformly
dissolving the topcoat layer and selectively removing the exposed
portions of the photoresist layer. In some embodiments, the
positive tone developer is a metal-ion-free tetraalkylammonium
hydroxide solution, such as, for example, aqueous 0.26 Normal
tetramethylammonium hydroxide.
[0052] The photoresist composition can, when used in one or more
such a pattern-forming processes, be used to fabricate electronic
and optoelectronic devices such as memory devices, processor chips
(including central processing units or CPUs), graphics chips, and
other such devices.
EXAMPLES
[0053] Table 1 provides chemical structures and acronyms of
monomers used in topcoat copolymer and photoresist copolymer
synthesis.
TABLE-US-00001 TABLE 1 PEGMA ##STR00008## BzMA ##STR00009## HFACHOH
##STR00010##
[0054] Synthesis of Poly(PEGMA-co-BzMA-co-HFACHOH) statistical
copolymer by the RAFT technique. A reaction scheme for the RAFT
synthesis of poly(PEGMA-co-BzMA-co-HFACHOH) is presented in FIG. 1.
PEGMA (4.75 gram, 0.01 mole), benzyl methacrylate (BzMA, 1.76 gram,
0.01 mole), HFACHOH (1.67 gram, 0.005 mole),
4-cyano-4-[(dodecylsufanylthiocarbonyl)sulfanyl]pentanoic acid
(CDTPA, RAFT agent, 221.8 milligrams (91% pure), 5.times.10.sup.-4
mole), azoisobutyronitrile (AIBN, initiator, 8.2 milligrams,
5.times.10.sup.-5 mole) and 1,4-dioxane (15 milliliters) were
introduced in a 50 milliliter Schlenk flask equipped with a
magnetic stirrer ([M].sub.0:[mCTA].sub.0:[Init].sub.0=50:1:0.1,
[PEGMA]:[BzMA]:[HFACHOH]=2:2:1). The reaction mixture was purged
with argon for 30 minutes in an ice bath to remove oxygen, and then
heated at 70.degree. C. The monomer conversion was calculated by
.sup.1H NMR and the polymer was recovered by double precipitation
in hexane. The polymer was characterized by proton nuclear magnetic
resonance spectroscopy (.sup.1H NMR), ultraviolet-visible
spectroscopy (UV-VIS) and size exclusion chromatography (SEC) using
polystyrene standards and tetrahydrofuran solvent. SEC indicated a
dispersity (M.sub.w/M.sub.n) of 1.12. Polymer characterization is
summarized in Table 2.
TABLE-US-00002 TABLE 2 Monomer 1 (M1) PEGMA Monomer 2 (M2) BzMA
Monomer 3 (M3) HFACHOH M1 percent conversion (%) 94.6 M2 percent
conversion (%) 97.7 M3 percent conversion (%) 99.2 theoretical
molecular weight (Daltons) 16,200 M1 degree of polymerization 19.1
M2 degree of polymerization 19.9 M3 degree of polymerization 9.6
number average molecular weight, .sup.1H NMR 16,200 (Daltons)
Dispersity, SEC 1.12
[0055] RAFT cleavage of Poly(PEGMA-co-BzMA-co-HFACHOH). A reaction
scheme for end group removal from the RAFT polymer is presented in
FIG. 2. The end-group cleavage of the statistical copolymer was
carried out as follows. Poly (PEGMA-co-BzMA-co-HFACHOH) (3 grams,
1.85.times.10.sup.-4 mole), AIBN (0.912 gram, 5.6.times.10.sup.-3
mole, 30 equivalents) and 1,4-dioxane (25 milliliters) were
introduced in a 100 mL Schlenk flask equipped with a magnetic
stirrer. The reaction mixture was purged with argon for 30 minutes
in an ice bath to remove oxygen, and then heated at 70.degree. C.
After 8 hours, the polymer was purified by dialysis in methanol and
then removed the solvent. The polymer was characterized by .sup.1H
NMR, UV-VIS, and SEC. The .sup.1H NMR spectrum is shown in FIG. 3,
and the UV-VIS spectra of the copolymer before and after end group
removal are presented in FIG. 4.
Thin Film Preparation
[0056] Determination of film thickness as a function of polymer
concentration. The structure of photoresist polymer CBP-4 is shown
in Table 3. A series of photoresist solutions was prepared as with
photoresist polymer CBP-4 solutions at target concentrations 1, 2,
3, 4, and 5 weight percent in ethyl lactate or propylene glycol
monomethyl ether acetate (PGMEA) as solvent. A representative spin
coating process was carried out as follows. First, a silicon wafer
was rinsed with acetone and isopropanol. Then the silicon wafer was
placed on a 100.degree. C. hotplate for 10 minutes. Then the
silicon wafer was further cleaned by O.sub.2 plasma treatment. The
photoresist solution was spin coated onto the silicon wafer at a
speed of 3000 rotations per minute (rpm) for 60 seconds. Following
coating of the photoresist solution onto the wafer, the photoresist
layer was dried by heating at 100.degree. C. for 90 seconds to
remove the solvent until the photoresist layer was tack free. Film
thickness was measured on a SCI Filmtek 4000 spectroscopic
reflectometer. The linear curve of film thickness versus polymer
concentration is presented in FIG. 5a. According to the curve, 2.5
to 3 weight percent was used as final polymer concentration to
achieve the desired photoresist layer thickness of about 50
nanometers.
TABLE-US-00003 TABLE 3 Photoresist Polymer CBP-4 ##STR00011##
[0057] Thickness change of photoresist layer caused by different
topcoat solvents. The purpose of this step was selection of a
topcoat solvent. Generally, the topcoat solvent should not dissolve
the photoresist layer. Otherwise, the solvent will partially
dissolve the resist surface during the topcoat spin coating
process, forming an intermixed layer. An effective method for
evaluating the solvent compatibility between resist and topcoat is
to measure the thickness change of the resist by exposing different
topcoat solvents to the resist film. A typical process was as
follows. First, the photoresist solution was spin coated onto the
silicon wafer. After the post-application bake, the thickness of
the photoresist layer was measured. Then different solvents were
applied by spin coating over photoresist layer. After another
post-application bake, the film thickness was measured. Solvent
properties are summarized in Table 4, where "TMAH" stands for
tetramethylammonium hydroxide. The thickness change caused by
different solvents is presented in Table 5, where "Di(propylene
glycol) monomethyl ether+2-Methyl-2-butanol" refers to an 11:89
weight ratio of di(propylene glycol) monomethyl ether to
2-methyl-2-butanol.
TABLE-US-00004 TABLE 4 Topcoat Polymer Solvent Dissolution Boiling
point (.degree. C.) Acetone 56 Ethanol 78.1 Methanol 64.7
Tetrahydrofuran 66 2.38% TMAH -- Water 100 Isobutanol 107.9
2-Methyl-2-butanol 102 2-Methyl-4-pentanol 131.6 Anisole 154
Di(propylene glycol) monomethyl 190 ether
TABLE-US-00005 TABLE 5 Photoresist layer Photoresist layer
thickness before thickness after Solvent solvent application (nm)
solvent application (nm) 2-Methyl-2-butanol 48.1 .+-. 0.5 47.3 .+-.
0.4 2-Methyl-4-pentanol 47.5 .+-. 3.7 46.7 .+-. 0.3 Anisole 47.5
.+-. 0.8 6.7 .+-. 2.5 Di(propylene glycol) 47.1 .+-. 0.2 9.1 .+-.
1.8 monomethyl ether Di(propylene glycol) 46.6 .+-. 0.5 45.2 .+-.
1.2 monomethyl ether + 2-Methyl-2-butanol
Intermixing Test
[0058] A typical process for the intermixing test was carried out
as follows. First, the photoresist solution was spin coated on the
silicon wafer to form a 50 nanometer layer. After the
post-application bake, the thickness of the photoresist layer was
measured. Then the topcoat solution (poly(PEGMA-co-BzMA-co-HFACHOH)
in 2-methyl-2-butanol) was spin coated over the photoresist layer.
After the post-application bake, the total layer thickness was
measured. The "dark loss" was measured after dissolving the topcoat
layer in developer solution (2.38 weight percent TMAH solution)
followed by rinsing with deionized water. The "dark loss" is the
difference between the photoresist layer thickness before and after
removing the topcoat and is called dark loss because no exposure is
involved in the measurement.
[0059] The results of the intermixing test are shown Table 6.
Coating of Poly(PEGMA-co-BzMA-co-HFACHOH)/2-methyl-2-butanol
solution on a bare silicon substrate gave layer thicknesses of 10
nanometers (0.3 weight percent solution) or 27 nanometers (0.7
weight percent solution). The thicknesses of the photoresist layers
were about 50 nanometers. After the topcoat was coated onto the
photoresist layer, then the total layer thickness was about 60
nanometers (for the 0.3 weight percent topcoat solution) or about
80 nanometers (for the 0.7 weight percent solution). After removing
the topcoat layer using 2.38% TMAH solution and rinsing with
deionized water, the final thickness of the photoresist layer was
similar to its original thickness. These results demonstrate that
the topcoat layer described herein did not form a mixed layer with
the photoresist layer and could be removed using developer
solution.
TABLE-US-00006 TABLE 6 Total thickness Thickness after Photoresist
of photoresist developer layer and topcoat solution Sample
thickness (nm) layers (nm) treatment (nm) Photoresist layer + 54.1
.+-. 0.5 64.6 .+-. 0.7 53.8 .+-. 1.0 10 nm topcoat coated from
ethyl lactate Photoresist layer + 55.1 .+-. 0.4 81.2 .+-. 0.3 53.1
.+-. 0.7 30 nm topcoat coated from ethyl lactate Photoresist layer
+ 51.8 .+-. 0.4 62.0 .+-. 0.7 50.5 .+-. 0.5 10 nm topcoat coated
from PGMEA Photoresist layer + 51.1 .+-. 0.3 77.3 .+-. 0.5 48.6
.+-. 0.4 30 nm topcoat coated from PGMEA
Measurement of Contact Angles
[0060] A typical procedure for preparing samples for contact angle
measurement was as follows. A CBP-4 photoresist solution was spin
coated onto a clean silicon wafer. No adhesion promoter coating was
applied on the wafer prior to the photoresist layer. The topcoat
solution was spin coated on the photoresist layer, forming a
topcoat layer with a thickness of 10 or 30 nanometers. Contact
angles were measured using a Dataphysics OCA20 contact-angle system
at room temperature. Deionized water droplets (2 microliters) were
dropped onto sample surfaces in order to conduct measurements of
the wetting behavior.
[0061] The results, presented in FIG. 6, show that the bare topcoat
layer (10 or 30 nanometers) was quite hydrophilic. The deionized
water contact angle was around 35.degree. and the deionized water
drop was spreading very quickly. After 60 seconds, the deionized
water contact angle became about 11.degree.. However, in the case
of the topcoat coated on the photoresist layer, the water contact
angle differed from that of the bare topcoat coated directly on the
silicon wafer. For a topcoat with a thickness of 30 nanometers, the
water contact angle (WCA) was 55.degree. and became 25.degree.
after 60 seconds. For a topcoat layer with a thickness of 10
nanometers, the WCA was 72.degree. and became 46.degree. after 60
seconds. The WCA was 82.degree. and stayed constant on the bare
photoresist layer surface after 60 seconds. It is known that
silicon readily oxidizes in air and is coated with a layer of
silicon oxide which is a hydrophilic surface. While not wishing to
be bound by any particular hypothesis, the inventors speculate
that, shown in the schematic image in FIG. 6, the hydrophilic
hydroxyl group hydrogen atoms on the wafer surface may hydrogen
bond with the oxygen atoms of the hydroxyl groups of the HFACHOH
repeat units. Consequently, the topcoat layer surface may tend to
be more hydrophilic. However, when the topcoat layer is spin coated
on the photoresist layer, more HFACHOH repeat units may move to
surface because of the low surface energy during the spin coating
process. This may be a reason that a topcoat layer coated on a
photoresist layer tends to be more hydrophobic than a topcoat layer
coated directly on a silicon substrate.
VUV VASE Ellipsometer Characterization
[0062] In order to examine the blocking effect of the topcoat layer
to the out-of-band light, the optical properties of the topcoat
thin films were measured by VUV VASE ellipsometer. Optical
constants, n and k, and film thicknesses were measured on a J. A.
Woollam.TM. VUV VASE.TM. Spectroscopic Ellipsometer. The VUV VASE
measurements were performed using a spectral range from 1.2 to 8.3
electron-volts (eV), corresponding to a wavelength range
.lamda.150-1000 nanometers, and angles of incidence of
65.degree.-75.degree., by 5.degree. as a step. The entire optical
path was enclosed inside a dry nitrogen purge to eliminate
absorption from ambient water vapor and oxygen. The modeling and
fitting procedure in this study consisted of first determining the
thickness and optical constants of transparent region of spectra
from 300 to 1000 nanometers using a Cauchy layer and then using a
point-by-point method to fit the curve ranging from 150 to 300 nm
in order to obtain the optical constants extinction coefficient `k`
and refractive index `n`. Optical properties of topcoat layers are
summarized in Table 7 and presented in FIG. 7 (extinction
coefficient as a function of wavelength and topcoat layer
thickness) and FIG. 8 (percent transmittance as a function of
wavelength and topcoat layer thickness). As shown in Table 7, and
FIGS. 7 and 8, for topcoat layers with thicknesses of 13 and 30
nanometers, the extinction coefficient k is 0.213 and 0.215,
respectively. The transmittance percentage at 193 nanometers was
calculated to be 83.2% and 64%, respectively. The Absorption
coefficients a were 13.9 and 14.0 .mu.m.sup.-1.
TABLE-US-00007 TABLE 7 Topcoat Layer Thickness (nm) 13.24 .+-. 0.03
30.82 .+-. 0.01 extinction coefficient, k, at 193 nm 0.213 0.215
refractive index, n, at 193 nm 1.742 1.720 T (%) at 193 nm 83.2
64.0 Absorption coefficient .alpha. (.mu.m.sup.-1) 13.9 14.0 A/d
Absorbance (.mu.m.sup.-1) 6.03 6.08
Lithographic Performance
[0063] Samples for electron beam lithography (EBL) were prepared as
follows. Photoresist polymer CBP-4 (25 milligrams) and
triisopropanolamine (0.20 milligram, 20 mole percent relative to
photoacid generating repeat units in the CBP-4 copolymer) were
introduced in a 20 milliliter vial. Ethyl lactate (760 microliters,
786 milligrams) was added to make a solution with a CBP-4 polymer
concentration of 3 weight percent. Topcoat polymer
poly(PEGMA-co-BzMA-co-HFACHOH) (10 milligrams) was dissolved in
2-methyl-2-butanol (5 milliliters, 4.02 grams) to make a solution
with a concentration of 0.25 weight percent.
[0064] A representative spin coating process was carried out as
follows. First, the silicon wafer was rinsed with acetone and
isopropanol. Then the silicon wafer was placed on 100.degree. C.
hotplate for 10 minutes. Then the silicon wafer was further cleaned
by O.sub.2 plasma treatment. An adhesion promoter obtained as
TI/HDMS prime from MicroChemicals was spin coated on the clean
silicon wafer at a speed of 3000 rpm for 20 seconds, followed by
baking on a 120.degree. C. hotplate for 5 minutes to remove the
solvent. The photoresist solution was spin coated on the primer
layer at a speed of 3000 rpm for 60 seconds. After coating of the
photoresist solution onto the wafer, it was dried by heating at
100.degree. C. for 90 seconds to remove the solvent until the
photoresist layer was tack free. Then topcoat solution was spin
coated over the photoresist layer at a speed of 3000 rpm for 60
seconds. For the post-application bake step, the coated wafer was
placed on the 100.degree. C. hotplate for 90 seconds to remove
residual solvent.
[0065] The photoresist with topcoat layer was then patterned and
exposed to activating radiation with the exposure energy typically
ranging from about 10 to 100 .mu.C/cm.sup.2. Typically, the
electron beam lithography technique was utilized as an exposure
tool to generate patterns.
[0066] Following exposure, the photoresist with topcoat layer was
baked at a temperature of 100.degree. C. for 60 seconds.
Thereafter, the sample was developed by treatment with an aqueous
alkaline developer such as 0.26 N tetramethylammonium hydroxide
(2.38 weight percent TMAH) for 20 seconds, followed by a water
rinse for 20 seconds.
[0067] Electron beam lithographic analysis was conducted using a
7800 Field Emission Scanning Electron Microscope (FE-SEM) with a
hot (Schottky) electron gun, which has a resolution (sample
dependent) of 0.8 nm at 15 kV and 1.2 nm at 1 kV. It is equipped
with a RAITH.TM. system for electron beam lithography.
[0068] FIG. 9 shows contrast curves for CBP-4 photoresist layer,
and CBP-4 photoresist layer plus 10 nanometer topcoat layer. It can
be seen from the curves that the resist sensitivity did not change
in the presence of topcoat layer. The dose-to-clear values of the
two samples were about 40 .mu.C/cm.sup.2. However, the slope is
higher in the curve for CBP-4 photoresist layer plus 10 nanometer
topcoat layer. Therefore, the contrast was improved with the
addition of the topcoat layer. Scanning Electron Microscopy.
[0069] FIG. 10 presents scanning electron micrographs (SEM) of line
patterns for (a) CBP-4 photoresist layer exposed at 51
.mu.C/cm.sup.2; (b) CBP-4 photoresist layer exposed at 53
.mu.C/cm.sup.2; (c) CBP-4 photoresist layer exposed at 55
.mu.C/cm.sup.2; (d) CBP-4 photoresist layer+10 nm topcoat layer at
exposed at 51 .mu.C/cm.sup.2; (e) CBP-4 photoresist layer+10 nm
topcoat layer at exposed at 57 .mu.C/cm.sup.2; and (f) CBP-4
photoresist layer+10 nm topcoat layer at exposed at 60
.mu.C/cm.sup.2.
* * * * *