U.S. patent application number 14/927354 was filed with the patent office on 2016-05-05 for pattern formation methods.
The applicant listed for this patent is Rohm and Haas Electronic Materials LLC. Invention is credited to Cecily ANDES, Stefan J. CAPORALE, Jason A. DeSISTO, Choong-Bong LEE, Cong LIU, Jong Keun PARK, Cheng-Bai XU.
Application Number | 20160124309 14/927354 |
Document ID | / |
Family ID | 55852525 |
Filed Date | 2016-05-05 |
United States Patent
Application |
20160124309 |
Kind Code |
A1 |
LEE; Choong-Bong ; et
al. |
May 5, 2016 |
PATTERN FORMATION METHODS
Abstract
Methods of forming an electronic device, comprise: (a) providing
a semiconductor substrate comprising one or more layers to be
patterned; (b) forming a photoresist layer over the one or more
layers to be patterned, wherein the photoresist layer is formed
from a composition that comprises: a matrix polymer comprising a
unit having an acid labile group; a photoacid generator; and an
organic solvent; (c) coating a photoresist overcoat composition
over the photoresist layer, wherein the overcoat composition
comprises: a matrix polymer; an additive polymer; a basic quencher;
and an organic solvent; wherein the additive polymer has a lower
surface energy than a surface energy of the matrix polymer, and
wherein the additive polymer is present in the overcoat composition
in an amount of from 1 to 20 wt % based on total solids of the
overcoat composition; (d) exposing the photoresist layer to
activating radiation; (e) heating the substrate in a post-exposure
bake process; and (f) developing the exposed film with an organic
solvent developer. The methods have particular applicability in the
semiconductor manufacturing industry.
Inventors: |
LEE; Choong-Bong;
(Westborough, MA) ; CAPORALE; Stefan J.;
(Marlborough, MA) ; DeSISTO; Jason A.;
(Bellingham, MA) ; PARK; Jong Keun; (Shrewsbury,
MA) ; LIU; Cong; (Shrewsbury, MA) ; XU;
Cheng-Bai; (Southborough, MA) ; ANDES; Cecily;
(Newton, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rohm and Haas Electronic Materials LLC |
Marlborough |
MA |
US |
|
|
Family ID: |
55852525 |
Appl. No.: |
14/927354 |
Filed: |
October 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62073769 |
Oct 31, 2014 |
|
|
|
Current U.S.
Class: |
430/311 |
Current CPC
Class: |
C09D 133/14 20130101;
G03F 7/168 20130101; C08F 220/18 20130101; G03F 7/11 20130101; G03F
7/0752 20130101; G03F 7/38 20130101; G03F 7/0397 20130101; G03F
7/325 20130101; G03F 7/0046 20130101; G03F 7/162 20130101; C08F
220/28 20130101; C08F 220/281 20200201; C09D 133/08 20130101; G03F
7/2041 20130101; C08F 220/283 20200201; G03F 7/038 20130101; G03F
7/327 20130101; G03F 7/039 20130101 |
International
Class: |
G03F 7/20 20060101
G03F007/20; G03F 7/38 20060101 G03F007/38; G03F 7/32 20060101
G03F007/32; G03F 7/16 20060101 G03F007/16 |
Claims
1. A pattern formation method, comprising: (a) providing a
semiconductor substrate comprising one or more layers to be
patterned; (b) forming a photoresist layer over the one or more
layers to be patterned, wherein the photoresist layer is formed
from a composition that comprises: a matrix polymer comprising a
unit having an acid labile group; a photoacid generator; and an
organic solvent; (c) coating a photoresist overcoat composition
over the photoresist layer, wherein the overcoat composition
comprises: a matrix polymer; an additive polymer; a basic quencher;
and an organic solvent; wherein the additive polymer has a lower
surface energy than a surface energy of the matrix polymer, and
wherein the additive polymer is present in the overcoat composition
in an amount of from 1 to 20 wt % based on total solids of the
overcoat composition; (d) exposing the photoresist layer to
activating radiation; (e) heating the substrate in a post-exposure
bake process; and (f) developing the exposed film with an organic
solvent developer.
2. The method of claim 1, wherein the additive polymer comprises a
unit containing a silicon atom.
3. The method of claim 1, wherein the additive polymer comprises a
unit containing a fluorine atom.
4. The method of claim 3, wherein the additive polymer comprises a
unit containing a fluoroalcohol.
5. The method of claim 1, wherein the matrix polymer comprises a
unit formed from a monomer of the following general formula (I):
##STR00046## wherein: R.sub.1 is chosen from hydrogen and
optionally substituted C1 to C3 alkyl; R.sub.2 is chosen from
optionally substituted C1 to C15 alkyl; X.sub.1 is oxygen, sulfur
or is represented by the formula NR.sub.3, wherein R.sub.3 is
chosen from hydrogen and optionally substituted C1 to C10 alkyl;
and Z.sub.1 is a single bond or a spacer unit chosen from
optionally substituted aliphatic and aromatic hydrocarbons, and
combinations thereof, optionally with one or more linking moiety
chosen from --O--, --S--, --COO-- and --CONR.sub.4-- wherein
R.sub.4 is chosen from hydrogen and optionally substituted C1 to
C10 alkyl.
6. The method of claim 1, wherein the additive polymer is formed
from a monomer having the following general formula (II) or (III):
##STR00047## wherein: R.sub.10 is chosen from hydrogen and
optionally substituted C1 to C3 alkyl; R.sub.11 is chosen from
optionally substituted C1 to C15 alkyl; X.sub.2 is oxygen, sulfur
or is represented by the formula NR.sub.12, wherein R.sub.12 is
chosen from hydrogen and optionally substituted C1 to C10 alkyl;
and Z.sub.3 is a single bond or a spacer unit chosen from
optionally substituted aliphatic and aromatic hydrocarbons, and
combinations thereof, optionally with one or more linking moiety
chosen from --O--, --S--, --NHSO.sub.2--, --COO-- and
--CONR.sub.13-- wherein R.sub.13 is chosen from hydrogen and
optionally substituted C1 to C10 alkyl; ##STR00048## wherein:
R.sub.14 is chosen from hydrogen and optionally substituted C1 to
C3 alkyl; R.sub.15 is independently chosen from optionally
substituted C1 to C15 alkyl; X.sub.3 is oxygen, sulfur or is
represented by the formula NR.sub.16, wherein R.sub.16 is chosen
from hydrogen and optionally substituted C1 to C10 alkyl; Z.sub.4
is a single bond or a spacer unit chosen from optionally
substituted aliphatic and aromatic hydrocarbons, and combinations
thereof, optionally with one or more linking moiety chosen from
--O--, --S--, --COO-- and --CONR.sub.17--, wherein R.sub.17 is
chosen from hydrogen and optionally substituted C1 to C10 alkyl;
and n is an integer from 0 to 2.
7. The method of claim 1, wherein the basic quencher comprises a
basic moiety on the matrix polymer.
8. The method of claim 1, wherein the basic quencher comprises an
additive separate from the matrix polymer.
9. The method of claim 1, wherein the additive polymer is present
in the overcoat composition in an amount of from 3 to 15 wt % based
on total solids of the overcoat composition.
10. The method of claim 1, wherein the photoresist layer is exposed
to the activating radiation in an immersion lithography process.
Description
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119(e) to U.S. Provisional Application No. 62/073,769,
filed Oct. 31, 2014, the entire contents of which are incorporated
herein by reference.
BACKGROUND
[0002] The invention relates generally to the manufacture of
electronic devices. More specifically, this invention relates to
photolithographic methods which allow for the formation of fine
patterns using a negative tone development process with a
photoresist overcoat.
[0003] In the semiconductor manufacturing industry, photoresist
materials are used for transferring an image to one or more
underlying layers, such as metal, semiconductor and dielectric
layers, disposed on a semiconductor substrate, as well as to the
substrate itself. To increase the integration density of
semiconductor devices and allow for the formation of structures
having dimensions in the nanometer range, photoresists and
photolithography processing tools having high-resolution
capabilities have been and continue to be developed.
[0004] Positive-tone chemically amplified photoresists are
conventionally used for high-resolution processing using a positive
tone development (PTD) process. In the PTD process, exposed regions
of a photoresist layer become soluble in a developer solution,
typically an aqueous alkaline developer, and are removed from the
substrate surface, whereas unexposed regions which are insoluble in
the developer remain after development to form a positive image. To
improve lithographic performance, immersion lithography tools have
been developed to effectively increase the numerical aperture (NA)
of the lens of the imaging device, for example, a scanner having a
KrF or ArF light source. This is accomplished by use of a
relatively high refractive index fluid (i.e., an immersion fluid)
between the last surface of the imaging device and the upper
surface of the semiconductor wafer.
[0005] Considerable effort has been made to extend the practical
resolution beyond that achieved with positive tone development from
both a materials and processing standpoint. One such example is the
negative tone development (NTD) process. The NTD process allows for
improved resolution and process window as compared with standard
positive tone imaging by making use of the superior imaging quality
obtained with bright field masks for printing critical dark field
layers. NTD resists typically employ a resin having acid-labile
(also referred to herein as acid-cleavable) groups and a photoacid
generator. Exposure to actinic radiation causes the photoacid
generator to form an acid which, during post-exposure baking,
causes cleavage of the acid-labile groups giving rise to a polarity
switch in the exposed regions. As a result, a difference in
solubility characteristics is created between exposed and unexposed
regions of the resist such that unexposed regions of the resist can
be removed by organic solvent developers, leaving behind a pattern
created by the insoluble exposed regions.
[0006] Problems in NTD processing in the form of necking of contact
holes and T-topping of line and trench patterns in the developed
resist patterns are known and described in U.S. Application Pub.
No. US2013/0244438A1. Such problems are believed to be caused by
diffusion of stray light beneath edges of the photomask opaque
pattern, undesirably causing polarity-switching in those "dark"
regions at the resist surface. In an effort to address this
problem, the '438 publication discloses use of a photoresist
overcoat that includes a basic quencher, a polymer and an organic
solvent. For purposes of immersion lithography, the '438
publication further discloses that the overcoat compositions can be
used to form a barrier layer for avoidance of leaching of
photoresist components into the immersion fluid and to provide
desirable contact angle characteristics with the immersion fluid
for increased exposure scan speeds.
[0007] There is a continuing need in the art for improved
photolithographic methods and photoresist overcoat compositions for
the formation of fine patterns with improved contact angle
characteristics between the substrate surface and immersion fluid
which would allow for greater immersion scanner speeds.
SUMMARY OF THE INVENTION
[0008] In accordance with an aspect of the invention, methods of
forming electronic devices are provided. The methods comprise: (a)
providing a semiconductor substrate comprising one or more layers
to be patterned; (b) forming a photoresist layer over the one or
more layers to be patterned, wherein the photoresist layer is
formed from a composition that comprises: a matrix polymer
comprising a unit having an acid labile group; a photoacid
generator; and an organic solvent; (c) coating a photoresist
overcoat composition over the photoresist layer, wherein the
overcoat composition comprises: a matrix polymer; an additive
polymer; a basic quencher; and an organic solvent; wherein the
additive polymer has a lower surface energy than a surface energy
of the matrix polymer, and wherein the additive polymer is present
in the overcoat composition in an amount of from 1 to 20 wt % based
on total solids of the overcoat composition; (d) exposing the
photoresist layer to activating radiation; (e) heating the
substrate in a post-exposure bake process; and (f) developing the
exposed film with an organic solvent developer. The methods have
particular applicability in the semiconductor manufacturing
industry.
[0009] As used herein: "mol %" means mole percent based on the
polymer, unless otherwise specified, and numbers shown with polymer
units are in mol % unless otherwise specified; "Mw" means weight
average molecular weight; "Mn" means number average molecular
weight; "PDI" means polydispersity index=Mw/Mn; "copolymer" is
inclusive of polymers containing two or more different types of
polymerized units; "alkyl" and "alkylene" are inclusive of linear,
branched and cyclic alkyl and alkylene structures, respectively,
unless otherwise specified or indicated by context; the articles
"a" and "an" are inclusive of one or more unless otherwise
indicated by context; and "substituted" means having one or more
hydrogen atoms replaced with one or more substituents chosen, for
example, from hydroxy, fluorine and alkoxy such as C1-C5
alkoxy.
DESCRIPTION OF THE DRAWINGS
[0010] The present invention will be described with reference to
the following drawings, in which like reference numerals denote
like features, and in which:
[0011] FIG. 1A-C illustrates a process flow for forming a
photolithographic pattern by negative tone development in
accordance with the invention.
DETAILED DESCRIPTION
Photoresist Overcoat Compositions
[0012] The photoresist overcoat compositions include a matrix
polymer, an additive polymer, a basic quencher and an organic
solvent. The additive polymer has a lower surface energy than a
surface energy of the matrix polymer. The compositions useful in
the invention when coated over a photoresist layer in a negative
tone development process can provide various benefits, such as one
or more of improved contact angle characteristics with an immersion
fluid, improved focus latitude, improved exposure latitude, reduced
defectivity, effective barrier layer properties for avoidance of
leaching of photoresist and overcoat components into an immersion
fluid, geometrically uniform resist patterns and reduced
reflectivity during resist exposure. The compositions can be used
in dry lithography or immersion lithography processes. The exposure
wavelength is not particularly limited except by the photoresist
compositions, with 248 nm or sub-200 nm such as 193 nm (immersion
or dry lithography) or an EUV wavelength (e.g., 13.4 nm) being
typical.
[0013] The matrix polymer can with the additive polymer impart to
layers formed from the overcoat compositions beneficial barrier
properties to minimize or prevent migration of photoresist
components into an immersion fluid. The additive polymer preferably
can also prevent migration of components within the overcoat
composition such as the basic quencher into an immersion fluid.
Beneficial contact angle characteristics with the immersion fluid
such as a high immersion fluid receding contact angle (RCA) at the
overcoat/immersion fluid interface can be provided, thereby
allowing for faster exposure tool scanning speeds. A layer of the
overcoat composition in a dried state typically has a water
receding contact angle of from 70.degree. to 89.degree., preferably
from 75 to 85.degree.. The phrase "in a dried state" means
containing 8 wt % or less of solvent, based on the overcoat
composition.
[0014] The matrix polymer is soluble in the organic solvent of the
overcoat composition, described herein. In addition, the matrix
polymer should be soluble in for good developability with organic
solvent developers used in negative tone development processes. To
minimize residue defects originated from the overcoat materials,
the dissolution rate of a dried layer of the overcoat composition
is preferably greater than that of the underlying photoresist layer
in the developer used in the patterning process. The matrix polymer
typically exhibits a developer dissolution rate of 100 .ANG./second
or higher, preferably 1000 .ANG./second or higher.
[0015] Matrix polymers useful in the overcoat compositions can be
homopolymers or can be copolymers having a plurality of distinct
repeat units, for example, two, three, four or more distinct repeat
units. The matrix polymer can include units having polymerizable
groups chosen, for example, from one or more of (alkyl)acrylate,
(alkyl)acrylamide, allyl, maleimide styrene, vinyl, polycyclic
(e.g., norbornene) or other group, with (alkyl)acrylate such as
(meth)acrylate being preferred. The matrix polymer can be a random
polymer, a block polymer, or a gradient polymer having a graded
change in composition from one monomer unit-type to another monomer
unit-type along the length of the polymer chain.
[0016] The matrix polymer has a higher surface energy than that of,
and is preferably immiscible with, the additive polymer, to allow
the additive polymer to phase separate from the matrix polymer and
migrate to the upper surface of the overcoat layer. The surface
energy of the matrix polymer is typically from 30 to 60 mN/m. The
matrix polymer is preferably free of silicon and fluorine as these
tend to decrease surface energy and can inhibit phase separation of
the additive polymer from the matrix polymer.
[0017] The matrix polymer is preferably formed from a monomer
having the following general formula (I):
##STR00001##
wherein: R.sub.1 is chosen from hydrogen and optionally substituted
C1 to C3 alkyl, preferably hydrogen or methyl; R.sub.2 is chosen
from optionally substituted C1 to C15 alkyl, preferably C4 to C8
alkyl, more preferably C4 to C6 alkyl; X.sub.1 is oxygen, sulfur or
is represented by the formula NR.sub.3, wherein R.sub.3 is chosen
from hydrogen and optionally substituted C1 to C10 alkyl,
preferably C1 to C5 alkyl; and Z.sub.1 is a single bond or a spacer
unit chosen from optionally substituted aliphatic (such as C1 to C6
alkylene) and aromatic hydrocarbons, and combinations thereof,
optionally with one or more linking moiety chosen from --O--,
--S--, --COO-- and --CONR.sub.4-- wherein R.sub.4 is chosen from
hydrogen and optionally substituted C1 to C10 alkyl, preferably C2
to C6, alkyl. The monomer of general formula (I) is preferably free
of silicon and fluorine. Units of general formula (I) taken
together are typically present in the matrix polymer in an amount
of from 50 to 100 mol %, for example, from 70 to 100 mol %, from 80
to 100 mol %, from 90 to 100 mol % or 100 mol %, based on the
matrix polymer.
[0018] The monomer of general formula (I) is preferably of the
following general formula (I-1):
##STR00002##
wherein R.sub.5 is chosen from hydrogen and optionally substituted
C1 to C3 alkyl, preferably hydrogen or methyl; R.sub.6, R.sub.7 and
R.sub.8 independently represent hydrogen or a C.sub.1 to C.sub.3
alkyl group; and Z.sub.2 is a single bond or a spacer unit chosen
from optionally substituted aliphatic (such as C1 to C6 alkylene)
and aromatic hydrocarbons, and combinations thereof, optionally
with one or more linking moiety chosen from --O--, --S--, --COO--
and --CONR.sub.9--, wherein R.sub.9 is chosen from hydrogen and
optionally substituted C1 to C10 alkyl, preferably C2 to C6, alkyl.
The monomer of general formula (I-1) is preferably free of silicon
and fluorine.
[0019] One or more unit of the matrix polymer can include a basic
moiety. The basic moiety can neutralize acid in the regions of an
underlying photoresist layer intended to be unexposed (dark
region), which acid is generated by stray light in the surface
region of the photoresist layer. Such a basic moiety-containing
matrix polymer can function as the basic quencher in the overcoat
composition in addition to or as an alternative to a basic quencher
additive. Suitable moieties include, for example, a
nitrogen-containing group chosen from: amines such as amino ethers,
pyridines, anilines, indazoles, pyrroles, pyrazoles, pyrazines,
guanidiniums and imines; amides such as carbamates, pyrrolidinones,
maleimides, imidazoles and imides; and derivatives thereof. If
present in the matrix polymer, the content of the basic
moiety-containing unit(s) in the matrix polymer is typically
sufficient to substantially or completely eliminate acid-induced
deprotection reaction in the dark regions of an underlying
photoresist layer while allowing such reaction to occur in the
bright regions (those regions intended to be exposed) of the layer.
The desired content of the basic moiety-containing unit(s) in the
matrix polymer will depend, for example, on the content of the
photoacid generator in the photoresist layer, and on the intended
use of the overcoat, whether in a dry or immersion lithography
process. If present, the content of basic moiety-containing unit(s)
in the matrix polymer for a dry lithography process will typically
be from 0.1 to 100 mole %, from 0.1 to 50 mole % or from 0.5 to 20
mole %, based on the matrix polymer. The pKa (in water) of the
monomer containing the basic moiety is preferably from 5 to 50,
more preferably from 8 to 40 and most preferably from 10 to 35. The
pKa value of the basic moiety-containing monomer and the matrix
polymer as a whole will typically have the same or substantially
the same value.
[0020] Exemplary suitable monomers for use in forming the matrix
polymer are described below, but are not limited to these
structures, with "R.sub.1" and "X.sub.1" are as defined above:
##STR00003## ##STR00004## ##STR00005## ##STR00006## ##STR00007##
##STR00008## ##STR00009## ##STR00010## ##STR00011##
[0021] Suitable matrix polymers for the overcoat compositions
include, for example, homopolymers and copolymers formed from
monomers described above. Exemplary suitable matrix polymers
include the following, wherein unit content is provided in mol
%:
##STR00012## ##STR00013## ##STR00014## ##STR00015##
[0022] The matrix polymer is typically present in the compositions
in an amount of from 70 to 99 wt %, more typically from 85 to 95 wt
%, based on total solids of the overcoat composition. The weight
average molecular weight of the matrix polymer is typically less
than 400,000, preferably from 5000 to 50,000, more preferably from
5000 to 25,000.
[0023] Like the matrix polymer, the additive polymer should have
very good developability before and after photolithographic
treatment, typically exhibits a developer dissolution rate of 100
.ANG./second or higher, preferably 1000 .ANG./second or higher, is
soluble in the organic solvent of the overcoat composition,
described herein, and is soluble in the organic developer used in
the negative tone development process. The additive polymer has a
lower surface energy than the matrix polymer. Preferably, the
additive polymer has a significantly lower surface energy than and
is substantially immiscible with the matrix polymer, as well as
other polymers present in the overcoat composition. In this way,
the overcoat composition can be self-segregating, wherein the
additive polymer migrates to the upper surface of the overcoat
layer apart from other polymers during coating. The resulting
overcoat layer is thereby rich in the additive polymer at the
overcoat layer upper surface at the overcoat/immersion fluid
interface in the case of an immersion lithography process. The
additive polymer surface energy is typically from 15 to 35 mN/m,
preferably from 18 to 30 mN/m. The additive polymer is typically
from 5 to 25 mN/m less than that of the matrix polymer, preferably
from 5 to 15 mN/m less than that of the matrix polymer.
[0024] Additive polymers useful in the overcoat compositions can be
homopolymers or can be copolymers having a plurality of distinct
repeat units, for example, two, three, four or more distinct repeat
units. The additive polymer can include units having polymerizable
groups chosen, for example, from one or more of (alkyl)acrylate,
(alkyl)acrylamide, allyl, maleimide styrene, vinyl, polycyclic
(e.g., norbornene) or other group, with (alkyl)acrylate such as
(meth)acrylate being preferred. The additive polymer can be a
random polymer, a block polymer, or a gradient polymer having a
graded change in composition from one monomer unit-type to another
monomer unit-type along the length of the polymer chain.
[0025] Suitable additive polymers can include, for example, the
units and polymers described above with respect to the matrix
polymer, with the understanding that the surface energy of the
additive polymer is less than that of the matrix polymer to allow
for self-segregation of the additive polymer from the matrix
polymer during the coating process to allow for the formation of a
surface layer rich in the additive polymer. The additive polymer
preferably has a branched structure and/or includes one or more
fluorinated and/or silicon-containing groups, as their inclusion
can result in a polymer having reduced surface energy. It is
particularly preferred that the additive polymer includes one or
more fluorinated and/or silicon-containing groups, and that the
matrix polymer is free of fluorinated and silicon-containing
groups.
[0026] The additive polymer is preferably formed from a monomer
having the following general formula (II) or (III):
##STR00016##
wherein: R.sub.10 is chosen from hydrogen and optionally
substituted C1 to C3 alkyl, preferably hydrogen or methyl; R.sub.11
is chosen from optionally substituted C1 to C15 alkyl, preferably
C4 to C8 alkyl or fluoroalkyl, more preferably C4 to C6 alkyl or
fluoroalkyl and may advantageously include a fluoroalcohol group
such as a hexafluoroalcohol group, or a partially fluorinated or
perfluorinated cycloalkyl structure; X.sub.2 is oxygen, sulfur or
is represented by the formula NR.sub.12, wherein R.sub.12 is chosen
from hydrogen and optionally substituted C1 to C10 alkyl,
preferably C1 to C5 alkyl; and Z.sub.3 is a single bond or a spacer
unit chosen from optionally substituted aliphatic (such as C1 to C6
alkylene) and aromatic hydrocarbons, and combinations thereof,
optionally with one or more linking moiety chosen from --O--,
--S--, --NHSO.sub.2--, --COO-- and --CONR.sub.13-- wherein R.sub.13
is chosen from hydrogen and optionally substituted C1 to C10 alkyl,
preferably C2 to C6, alkyl. The monomer of general formula (I)
preferably contains fluorine for purposes of reducing surface
energy.
##STR00017##
wherein: R.sub.14 is chosen from hydrogen and optionally
substituted C1 to C3 alkyl, preferably hydrogen or methyl; R.sub.15
is independently chosen from optionally substituted C1 to C15
alkyl, preferably C4 to C8 alkyl, more preferably C4 to C6 alkyl,
and may advantageously include fluorine atoms or a fluoroalcohol
group such as a hexafluoroalcohol group, or a partially fluorinated
or perfluorinated cycloalkyl structure; X.sub.3 is oxygen, sulfur
or is represented by the formula NR.sub.16, wherein R.sub.16 is
chosen from hydrogen and optionally substituted C1 to C10 alkyl,
preferably C1 to C5 alkyl; Z.sub.4 is a single bond or a spacer
unit chosen from optionally substituted aliphatic (such as C1 to C6
alkylene) and aromatic hydrocarbons, and combinations thereof,
optionally with one or more linking moiety chosen from --O--,
--S--, --COO-- and --CONR.sub.17-- wherein R.sub.17 is chosen from
hydrogen and optionally substituted C1 to C10 alkyl, preferably C2
to C6, alkyl; and n is an integer from 0 to 2.
[0027] Units of general formula (II) or (III) are typically present
in the additive polymer in an amount of from 50 to 100 mol %, for
example, from 70 to 100 mol %, from 80 to 100 mol %, from 90 to 100
mol % or 100 mol %, based on the additive polymer. Exemplary
suitable monomers for use in forming the additive polymer are
described below, but are not limited to these structures
("R.sub.10", "R.sub.14" and "X.sub.2" and "X.sub.3" are as defined
above):
##STR00018## ##STR00019## ##STR00020## ##STR00021## ##STR00022##
##STR00023##
[0028] Suitable additive polymers for the overcoat compositions
include homopolymers and copolymers formed from monomers described
above, with the following polymers being preferred, wherein unit
content is provided in mol %:
##STR00024## ##STR00025## ##STR00026## ##STR00027##
[0029] The content of the additive polymer may depend, for example,
on whether the lithography is a dry or immersion-type process. For
example, the additive polymer lower limit for immersion lithography
is generally dictated by the need to prevent leaching of the
photoresist components. The additive polymer is typically present
in the compositions in an amount of from 1 to 30 wt %, more
typically from 3 to 20 wt % or 5 to 15 wt %, based on total solids
of the overcoat composition. The weight average molecular weight of
the additive polymer is typically less than 400,000, preferably
from 5000 to 50,000, more preferably from 5000 to 25,000.
[0030] The photoresist overcoat compositions further include a
basic quencher. The basic quencher is present for purposes of
neutralizing acid generated in the surface region of the underlying
photoresist layer by stray light which reaches what are intended to
be unexposed (dark) regions of the photoresist layer. This allows
for improvement in depth of focus in the defocus area and exposure
latitude by controlling unwanted deprotection reaction in the
unexposed areas. As a result, irregularities in the profile, for
example, necking and T-topping, in formed resist patterns can be
minimized or avoided.
[0031] As discussed above, the basic quencher can be present in the
matrix polymer or can be of an additive type. To allow for
effective interaction between the basic quencher and the acid
generated in the dark areas of the underlying photoresist layer,
the basic quencher should be of a non-surfactant-type. That is, the
basic quencher should not be of a type that migrates to the top
surface of the overcoat layer due, for example, to a low surface
free energy relative to other components of the overcoat
composition. In such a case, the basic quencher would not be
appreciably present at the photoresist layer interface for
interaction with the generated acid to prevent acid deprotection.
The basic quencher should therefore be of a type that is present at
the overcoat layer/photoresist layer interface, whether being
uniformly dispersed through the overcoat layer or forming a graded
or segregated layer at the interface. Such a layer can be achieved
by selection of a basic quencher having a high surface free energy
relative to other components of the overcoat composition.
[0032] Suitable basic quenchers include, for example: linear and
cyclic amides and derivatives thereof such as
N,N-bis(2-hydroxyethyl)pivalamide, N,N-Diethylacetamide,
N1,N1,N3,N3-tetrabutylmalonamide, 1-methylazepan-2-one,
1-allylazepan-2-one and tert-butyl
1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylcarbamate; aromatic
amines such as pyridine, and di-tert-butyl pyridine; aliphatic
amines such as triisopropanolamine, n-tert-butyldiethanolamine,
tris(2-acetoxy-ethyl)amine,
2,2',2'',2'''-(ethane-1,2-diylbis(azanetriyl))tetraethanol, and
2-(dibutylamino)ethanol, 2,2',2''-nitrilotriethanol; cyclic
aliphatic amines such as
1-(tert-butoxycarbonyl)-4-hydroxypiperidine, tert-butyl
1-pyrrolidinecarboxylate, tert-butyl
2-ethyl-1H-imidazole-1-carboxylate, di-tert-butyl
piperazine-1,4-dicarboxylate and N (2-acetoxy-ethyl) morpholine. Of
these basic quenchers, 1-(tert-butoxycarbonyl)-4-hydroxypiperidine
and triisopropanolamine are preferred. While the content of the
basic quencher will depend, for example, on the content of the
photoacid generator in the underlying photoresist layer, it is
typically present in an amount of from 0.1 to 5 wt %, preferably
from 0.5 to 3 wt %, more preferably from 1 to 3 wt %, based on
total solids of the overcoat composition.
[0033] The overcoat compositions further include an organic solvent
or mixture of organic solvents. Suitable solvent materials to
formulate and cast the overcoat composition exhibit excellent
solubility characteristics with respect to the non-solvent
components of the overcoat composition, but do not appreciably
dissolve an underlying photoresist layer. Suitable organic solvents
for the overcoat composition include, for example: alkyl esters
such as alkyl propionates such as n-butyl propionate, n-pentyl
propionate, n-hexyl propionate and n-heptyl propionate, and alkyl
butyrates such as n-butyl butyrate, isobutyl butyrate and isobutyl
isobutyrate; ketones such as 2,5-dimethyl-4-hexanone and
2,6-dimethyl-4-heptanone; aliphatic hydrocarbons such as n-heptane,
n-nonane, n-octane, n-decane, 2-methylheptane, 3-methylheptane,
3,3-dimethylhexane and 2,3,4-trimethylpentane, and fluorinated
aliphatic hydrocarbons such as perfluoroheptane; and alcohols such
as straight, branched or cyclic C.sub.4-C.sub.9 monohydric alcohol
such as 1-butanol, 2-butanol, 3-methyl-1-butanol, isobutyl alcohol,
tert-butyl alcohol, 1-pentanol, 2-pentanol, 1-hexanol, 1-heptanol,
1-octanol, 2-hexanol, 2-heptanol, 2-octanol, 3-hexanol, 3-heptanol,
3-octanol and 4-octanol; 2,2,3,3,4,4-hexafluoro-1-butanol,
2,2,3,3,4,4,5,5-octafluoro-1-pentanol and
2,2,3,3,4,4,5,5,6,6-decafluoro-1-hexanol, and C.sub.5-C.sub.9
fluorinated diols such as 2,2,3,3,4,4-hexafluoro-1,5-pentanediol,
2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol and
2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1,8-octanediol; and mixtures
containing one or more of these solvents. Of these organic
solvents, alkyl propionates, alkyl butyrates and ketones,
preferably branched ketones, are preferred and, more preferably,
C.sub.8-C.sub.9 alkyl propionates, C.sub.8-C.sub.9 alkyl
propionates, C.sub.8-C.sub.9 ketones, and mixtures containing one
or more of these solvents. Suitable mixed solvents include, for
example, mixtures of an alkyl ketone and an alkyl propionate such
as the alkyl ketones and alkyl propionates described above. The
solvent component of the overcoat composition is typically present
in an amount of from 90 to 99 wt % based on the overcoat
composition.
[0034] The photoresist overcoat compositions can include one or
more optional materials. For example, the compositions can include
one or more of actinic and contrast dyes, anti-striation agents,
and the like. Of these, actinic and contrast dyes are preferred for
enhancing antireflective properties of layers formed from the
compositions. Such optional additives if used are typically present
in the composition in minor amounts such as from 0.1 to 10 wt %
based on total solids of the overcoat composition. The overcoat
compositions are preferably free of acid generator compounds, for
example, thermal acid generator compounds and photoacid generator
compounds, as such compounds may neutralize the effect of the basic
quencher in the overcoat compositions.
[0035] The photoresist overcoat compositions can be prepared
following known procedures. For example, the compositions can be
prepared by dissolving solid components of the composition in the
solvent components. The desired total solids content of the
compositions will depend on factors such as the particular
polymer(s) in the composition and desired final layer thickness.
Preferably, the solids content of the overcoat compositions is from
1 to 10 wt %, more preferably from 1 to 5 wt %, based on the total
weight of the composition.
[0036] Resist overcoat layers formed from the compositions
typically have an index of refraction of 1.4 or greater at 193 nm,
preferably 1.47 or greater at 193 nm. The index of refraction can
be tuned by changing the composition of the matrix polymer, the
additive polymer or other components of the overcoat composition.
For example, increasing the relative amount of organic content in
the overcoat composition may provide increased refractive index of
the layer. Preferred overcoat composition layers will have a
refractive index between that of the immersion fluid and the
photoresist at the target exposure wavelength.
[0037] Reflectivity of the overcoat layer can be reduced if the
refractive index of the overcoat layer (n.sub.1) is the geometric
mean of that of the materials on either side (n.sub.1=
(n.sub.0n.sub.2)), where n.sub.0 is the refractive index of water
in the case of immersion lithography or air for dry lithography,
and n.sub.2 is the refractive index of the photoresist. Also to
enhance antireflective properties of layers formed from the
overcoat compositions, it is preferred that the thickness of the
overcoat (d.sub.1) is chosen such that the wavelength in the
overcoat is one quarter the wavelength of the incoming wave
(.lamda..sub.0). For a quarter wavelength antireflective coating of
an overcoat composition with a refractive index n.sub.1, the
thickness d.sub.1 that gives minimum reflection is calculated by
d.sub.1=.lamda..sub.0/(4n.sub.1).
NTD Photoresist Compositions
[0038] Photoresist compositions useful in the invention include
chemically-amplified photoresist compositions comprising a matrix
resin that is acid-sensitive, meaning that as part of a layer of
the photoresist composition, the resin and composition layer
undergo a change in solubility in an organic developer as a result
of reaction with acid generated by a photoacid generator following
softbake, exposure to activating radiation and post exposure bake.
The change in solubility is brought about when acid-cleavable
leaving groups such as photoacid-labile ester or acetal groups in
the matrix polymer undergo a photoacid-promoted deprotection
reaction on exposure to activating radiation and heat treatment to
produce an acid or an alcohol group. Suitable photoresist
compositions useful for the invention are commercially
available.
[0039] For imaging at sub-200 nm wavelengths such as 193 nm, the
matrix polymer is typically substantially free (e.g., less than 15
mole %) or completely free of phenyl, benzyl or other aromatic
groups where such groups are highly absorbing of the radiation.
Preferable acid labile groups include, for example, acetal groups
or ester groups that contain a tertiary non-cyclic alkyl carbon
(e.g., t-butyl) or a tertiary alicyclic carbon (e.g.,
methyladamantyl) covalently linked to a carboxyl oxygen of an ester
of the matrix polymer.
[0040] Suitable matrix polymers further include polymers that
contain (alkyl)acrylate units, preferably including acid-labile
(alkyl)acrylate units, such as t butyl acrylate, t-butyl
methacrylate, methyladamantyl acrylate, methyl adamantyl
methacrylate, ethylfenchyl acrylate, ethylfenchyl methacrylate, and
the like, and other non-cyclic alkyl and alicyclic
(alkyl)acrylates. Other suitable matrix polymers include, for
example, those which contain polymerized units of a non-aromatic
cyclic olefin (endocyclic double bond) such as an optionally
substituted norbornene.
[0041] Still other suitable matrix polymers include polymers that
contain polymerized anhydride units, particularly polymerized
maleic anhydride and/or itaconic anhydride units, such as disclosed
in European Published Application EP01008913A1 and U.S. Pat. No.
6,048,662.
[0042] Also suitable as the matrix polymer is a resin that contains
repeat units that contain a hetero atom, particularly oxygen and/or
sulfur (but other than an anhydride, i.e., the unit does not
contain a keto ring atom). The heteroalicyclic unit can be fused to
the polymer backbone, and can comprise a fused carbon alicyclic
unit such as provided by polymerization of a norbornene group
and/or an anhydride unit such as provided by polymerization of a
maleic anhydride or itaconic anhydride. Such polymers are disclosed
in PCT/US01/14914 and U.S. Pat. No. 6,306,554. Other suitable
hetero-atom group containing matrix polymers include polymers that
contain polymerized carbocyclic aryl units substituted with one or
more hetero-atom (e.g., oxygen or sulfur) containing groups, for
example, hydroxy naphthyl groups, such as disclosed in U.S. Pat.
No. 7,244,542.
[0043] Blends of two or more of the above-described matrix polymers
can suitably be used in the photoresist compositions. Suitable
matrix polymers for use in the photoresist compositions are
commercially available and can readily be made by persons skilled
in the art. The matrix polymer is present in the resist composition
in an amount sufficient to render an exposed coating layer of the
resist developable in a suitable developer solution. Typically, the
matrix polymer is present in the composition in an amount of from
50 to 95 wt % based on total solids of the resist composition. The
weight average molecular weight Mw of the matrix polymer is
typically less than 100,000, for example, from 5000 to 100,000,
more typically from 5000 to 15,000.
[0044] The photoresist composition further comprises a photoacid
generator (PAG) employed in an amount sufficient to generate a
latent image in a coating layer of the composition upon exposure to
activating radiation. For example, the photoacid generator will
suitably be present in an amount of from about 1 to 20 wt % based
on total solids of the photoresist composition. Typically, lesser
amounts of the PAG will be suitable for chemically amplified
resists as compared with non-chemically amplified materials.
[0045] Suitable PAGs are known in the art of chemically amplified
photoresists and include, for example: onium salts, for example,
triphenylsulfonium trifluoromethanesulfonate,
(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,
tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,
triphenylsulfonium p-toluenesulfonate; nitrobenzyl derivatives, for
example, 2-nitrobenzyl-p-toluenesulfonate,
2,6-dinitrobenzyl-p-toluenesulfonate, and
2,4-dinitrobenzyl-p-toluenesulfonate; sulfonic acid esters, for
example, 1,2,3-tris(methanesulfonyloxy)benzene,
1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and
1,2,3-tris(p-toluenesulfonyloxy)benzene; diazomethane derivatives,
for example, bis(benzenesulfonyl)diazomethane,
bis(p-toluenesulfonyl)diazomethane; glyoxime derivatives, for
example, bis-O-(p-toluenesulfonyl)-.alpha.-dimethylglyoxime, and
bis-O-(n-butanesulfonyl)-.alpha.-dimethylglyoxime; sulfonic acid
ester derivatives of an N-hydroxyimide compound, for example,
N-hydroxysuccinimide methanesulfonic acid ester,
N-hydroxysuccinimide trifluoromethanesulfonic acid ester; and
halogen-containing triazine compounds, for example,
2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, and
2-(4-methoxynaphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine. One
or more of such PAGs can be used.
[0046] Suitable solvents for the photoresist compositions include,
for example: glycol ethers such as 2-methoxyethyl ether (diglyme),
ethylene glycol monomethyl ether, and propylene glycol monomethyl
ether; propylene glycol monomethyl ether acetate; lactates such as
methyl lactate and ethyl lactate; propionates such as methyl
propionate, ethyl propionate, ethyl ethoxy propionate and
methyl-2-hydroxy isobutyrate; Cellosolve esters such as methyl
Cellosolve acetate; aromatic hydrocarbons such as toluene and
xylene; and ketones such as acetone, methylethyl ketone,
cyclohexanone and 2-heptanone. A blend of solvents such as a blend
of two, three or more of the solvents described above also are
suitable. The solvent is typically present in the composition in an
amount of from 90 to 99 wt %, more typically from 95 to 98 wt %,
based on the total weight of the photoresist composition.
[0047] The photoresist compositions can further include other
optional materials. For example, negative-acting resist
compositions typically also include a crosslinker component.
Suitable crosslinker components include, for example, an
amine-based material such as a melamine resin, that will cure,
crosslink or harden upon exposure to acid on exposure of a
photoacid generator to activating radiation. Preferred crosslinkers
include amine-based materials, including melamine, glycolurils,
benzoguanamine-based materials and urea-based materials.
Melamine-formaldehyde resins are generally most preferred. Such
crosslinkers are commercially available, e.g., the melamine resins
sold by American Cyanamid under the trade names Cymel 300, 301 and
303. Glycoluril resins are sold by American Cyanamid under trade
names Cymel 1170, 1171, 1172, urea-based resins are sold under the
trade names of Beetle 60, 65 and 80, and benzoguanamine resins are
sold under the trade names Cymel 1123 and 1125. For imaging at
sub-200 nm wavelengths such as 193 nm, preferred negative-acting
photoresists are disclosed in WO 03077029 to the Shipley
Company.
[0048] The photoresist compositions can also include other optional
materials. For example, the compositions can include one or more of
actinic and contrast dyes, anti-striation agents, plasticizers,
speed enhancers, sensitizers, and the like. Such optional additives
if used are typically present in the composition in minor amounts
such as from 0.1 to 10 wt % based on total solids of the
photoresist composition.
[0049] A preferred optional additive of the resist compositions is
an added base. Suitable bases include, for example: linear and
cyclic amides and derivatives thereof such as
N,N-bis(2-hydroxyethyl)pivalamide, N,N-Diethylacetamide,
N1,N1,N3,N3-tetrabutylmalonamide, 1-methylazepan-2-one,
1-allylazepan-2-one and tert-butyl
1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylcarbamate; aromatic
amines such as pyridine, and di-tert-butyl pyridine; aliphatic
amines such as triisopropanolamine, n-tert-butyldiethanolamine,
tris(2-acetoxy-ethyl)amine,
2,2',2'',2'''-(ethane-1,2-diylbis(azanetriyl))tetraethanol, and
2-(dibutylamino)ethanol, 2,2',2''-nitrilotriethanol; cyclic
aliphatic amines such as
1-(tert-butoxycarbonyl)-4-hydroxypiperidine, tert-butyl
1-pyrrolidinecarboxylate, tert-butyl
2-ethyl-1H-imidazole-1-carboxylate, di-tert-butyl
piperazine-1,4-dicarboxylate and N (2-acetoxy-ethyl) morpholine.
The added base is typically used in relatively small amounts, for
example, from 0.01 to 5 wt %, preferably from 0.1 to 2 wt %, based
on total solids of the photoresist composition.
[0050] The photoresists can be prepared following known procedures.
For example, the resists can be prepared as coating compositions by
dissolving the components of the photoresist in a suitable solvent,
for example, one or more of: a glycol ether such as 2-methoxyethyl
ether (diglyme), ethylene glycol monomethyl ether, propylene glycol
monomethyl ether; propylene glycol monomethyl ether acetate;
lactates such as ethyl lactate or methyl lactate, with ethyl
lactate being preferred; propionates, particularly methyl
propionate, ethyl propionate and ethyl ethoxy propionate; a
Cellosolve ester such as methyl Cellosolve acetate; an aromatic
hydrocarbon such toluene or xylene; or a ketone such as methylethyl
ketone, cyclohexanone and 2-heptanone. The desired total solids
content of the photoresist will depend on factors such as the
particular polymers in the composition, final layer thickness and
exposure wavelength. Typically the solids content of the
photoresist varies from 1 to 10 wt %, more typically from 2 to 5 wt
%, based on the total weight of the photoresist composition.
[0051] Suitable NTD photoresists are known in the art and include,
for example, those described in US Patent Publications
US20130115559A1, US20110294069A1, US20120064456A1, US20120288794A1,
US20120171617A1, US20120219902A1 and U.S. Pat. No. 7,998,655B2.
Negative Tone Development Methods
[0052] Processes in accordance with the invention will now be
described with reference to FIG. 1A-C, which illustrates an
exemplary process flow for forming a photolithographic pattern by
negative tone development.
[0053] FIG. 1A depicts in cross-section a substrate 100 which may
include various layers and features. 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, and may have one or more layers and patterned features
formed on a surface thereof. One or more layers to be patterned 102
may be provided over the substrate 100. Optionally, the underlying
base substrate material itself may be patterned, for example, when
it is desired to form trenches in the substrate material. In the
case of patterning the base substrate material itself, the pattern
shall be considered to be formed in a layer of the substrate.
[0054] The layers may include, for example, one or more conductive
layers such as layers of aluminum, copper, molybdenum, tantalum,
titanium, tungsten, 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, and combinations thereof. The layers to be
etched 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, or electroplating. The particular
thickness of the one or more layers to be etched 102 will vary
depending on the materials and particular devices being formed.
[0055] Depending on the particular layers to be etched, film
thicknesses and photolithographic materials and process to be used,
it may be desired to dispose over the layers 102 a hard mask layer
and/or a bottom antireflective coating (BARC) over which a
photoresist layer 104 is to be coated. Use of a hard mask layer may
be desired, for example, with very thin resist layers, where the
layers to be etched require a significant etching depth, and/or
where the particular etchant has poor resist selectivity. Where a
hard mask layer is used, the resist patterns to be formed can be
transferred to the hard mask layer which, in turn, can be used as a
mask for etching the underlying layers 102. Suitable hard mask
materials and formation methods are known in the art. Typical
materials include, for example, tungsten, titanium, titanium
nitride, titanium oxide, zirconium oxide, aluminum oxide, aluminum
oxynitride, hafnium oxide, amorphous carbon, silicon oxynitride and
silicon nitride. The hard mask layer can include a single layer or
a plurality of layers of different materials. The hard mask layer
can be formed, for example, by chemical or physical vapor
deposition techniques.
[0056] A bottom antireflective coating may be desirable where the
substrate and/or underlying layers would otherwise reflect a
significant amount of incident radiation during photoresist
exposure such that the quality of the formed pattern would be
adversely affected. Such coatings can improve depth-of-focus,
exposure latitude, linewidth uniformity and critical dimension (CD)
control. Antireflective coatings are typically used where the
resist is exposed to deep ultraviolet light (300 nm or less), for
example, KrF excimer laser light (248 nm) or ArF excimer laser
light (193 nm). The antireflective coating can comprise a single
layer or a plurality of different layers. Suitable antireflective
materials and methods of formation are known in the art.
Antireflective materials are commercially available, for example,
those sold under the AR.TM. trademark by Rohm and Haas Electronic
Materials LLC (Marlborough, Mass. USA), such as AR.TM.40A and
AR.TM.124 antireflectant materials.
[0057] A photoresist layer 104 formed from a composition such as
described herein is disposed on the substrate over the
antireflective layer (if present). The photoresist composition can
be applied to the substrate by spin-coating, dipping,
roller-coating or other conventional coating technique. Of these,
spin-coating is typical. For spin-coating, the solids content of
the coating solution can be adjusted to provide a desired film
thickness based upon the specific coating equipment utilized, the
viscosity of the solution, the speed of the coating tool and the
amount of time allowed for spinning. A typical thickness for the
photoresist layer 104 is from about 500 to 3000 .ANG..
[0058] The photoresist layer can next be softbaked to minimize the
solvent content in the layer, thereby forming a tack-free coating
and improving adhesion of the layer to the substrate. The softbake
can be conducted on a hotplate or in an oven, with a hotplate being
typical. The softbake temperature and time will depend, for
example, on the particular material of the photoresist and
thickness. Typical softbakes are conducted at a temperature of from
about 90 to 150.degree. C., and a time of from about 30 to 90
seconds.
[0059] A photoresist overcoat layer 106 formed from an overcoat
composition as described herein is formed over the photoresist
layer 104. The overcoat composition is typically applied to the
substrate by spin-coating. The solids content of the coating
solution can be adjusted to provide a desired film thickness based
upon the specific coating equipment utilized, the viscosity of the
solution, the speed of the coating tool and the amount of time
allowed for spinning To reduce reflectivity of the overcoat layer,
the thickness is preferably chosen such that the wavelength in the
overcoat is one quarter the wavelength of the incoming wave. A
typical thickness for the photoresist overcoat layer 106 is from
200 to 1000 .ANG.. The basic quencher may be present in the
overcoat layer 106 dispersed homogeneously through the overcoat
layer, or may be present as a segregated or graded quencher region
107 disposed at the overcoat layer-photoresist layer interface.
[0060] The photoresist overcoat layer can next be baked to minimize
the solvent content in the layer. The bake can be conducted on a
hotplate or in an oven, with a hotplate being typical. Typical
bakes are conducted at a temperature of from about 80 to
120.degree. C., and a time of from about 30 to 90 seconds.
[0061] The photoresist layer 104 is next exposed to activating
radiation 108 through a first photomask 110 to create a difference
in solubility between exposed and unexposed regions. References
herein to exposing a photoresist composition to radiation that is
activating for the composition indicates that the radiation is
capable of forming a latent image in the photoresist composition.
The photomask has optically transparent and optically opaque
regions 112, 114 corresponding to regions of the resist layer to
remain and be removed, respectively, in a subsequent development
step. The exposure wavelength is typically sub-400 nm, sub-300 nm
or sub-200 nm, with 248 nm and 193 nm being typical. The methods
find use in immersion or dry (non-immersion) lithography
techniques. The exposure energy is typically from about 10 to 80
mJ/cm.sup.2, dependent upon the exposure tool and the components of
the photosensitive composition.
[0062] Following exposure of the photoresist layer 104, a
post-exposure bake (PEB) is performed. The PEB can be conducted,
for example, on a hotplate or in an oven. Conditions for the PEB
will depend, for example, on the particular photoresist composition
and layer thickness. The PEB is typically conducted at a
temperature of from about 80 to 150.degree. C., and a time of from
about 30 to 90 seconds. Following post exposure bake, it is
believed that the basic quencher diffuses into the surface region
of the photoresist layer 104 as shown by dashed lines 109. A latent
image 116 defined by the boundary (dashed line) between
polarity-switched and unswitched regions (corresponding to exposed
and unexposed regions, respectively) is formed in the photoresist
as shown in FIG. 1B. The diffused basic quencher in the photoresist
is believed to prevent polarity switch in undesired dark regions of
the photoresist layer, resulting in a latent image with vertical
walls.
[0063] The overcoat layer 106 and exposed photoresist layer are
next developed to remove unexposed regions of the photoresist layer
104, leaving exposed regions forming an open resist pattern 104'
with contact hole pattern 120 having vertical sidewalls as shown in
FIG. 1C. The developer is typically an organic developer, for
example, a solvent chosen from ketones, esters, ethers,
hydrocarbons, and mixtures thereof. Suitable ketone solvents
include, for example, acetone, 2-hexanone, 5-methyl-2-hexanone,
2-heptanone, 4-heptanone, 1-octanone, 2-octanone, 1-nonanone,
2-nonanone, diisobutyl ketone, cyclohexanone, methylcyclohexanone,
phenylacetone, methyl ethyl ketone and methyl isobutyl ketone.
Suitable ester solvents include, for example, methyl acetate, butyl
acetate, ethyl acetate, isopropyl acetate, amyl acetate, propylene
glycol monomethyl ether acetate, ethylene glycol monoethyl ether
acetate, diethylene glycol monobutyl ether acetate, diethylene
glycol monoethyl ether acetate, ethyl-3-ethoxypropionate,
3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, methyl
formate, ethyl formate, butyl formate, propyl formate, ethyl
lactate, butyl lactate and propyl lactate. Suitable ether solvents
include, for example, dioxane, tetrahydrofuran and glycol ether
solvents, for example, ethylene glycol monomethyl ether, propylene
glycol monomethyl ether, ethylene glycol monoethyl ether, propylene
glycol monoethyl ether, diethylene glycol monomethyl ether,
triethylene glycol monoethyl ether and methoxymethyl butanol.
Suitable amide solvents include, for example,
N-methyl-2-pyrrolidone, N,N-dimethylacetamide and
N,N-dimethylformamide. Suitable hydrocarbon solvents include, for
example, aromatic hydrocarbon solvents such as toluene and xylene.
In addition, mixtures of these solvents, or one or more of the
listed solvents mixed with a solvent other than those described
above or mixed with water can be used. Other suitable solvents
include those used in the photoresist composition. The developer is
preferably 2-heptanone or a butyl acetate such as n-butyl
acetate.
[0064] Mixtures of organic solvents can be employed as a developer,
for example, a mixture of a first and second organic solvent. The
first organic solvent can be chosen from hydroxy alkyl esters such
as methyl-2-hydroxyisobutyrate and ethyl lactate; and linear or
branched C.sub.5 to C.sub.6 alkoxy alkyl acetates such as propylene
glycol monomethyl ether acetate (PGMEA). Of the first organic
solvents, 2-heptanone and 5-methyl-2-hexanone are preferred. The
second organic solvent can be chosen from linear or branched
unsubstituted C.sub.6 to C.sub.8 alkyl esters such as n-butyl
acetate, n-pentyl acetate, n-butyl propionate, n-hexyl acetate,
n-butyl butyrate and isobutyl butyrate; and linear or branched
C.sub.8 to C.sub.9 ketones such as 4-octanone,
2,5-dimethyl-4-hexanone and 2,6-dimethyl-4-heptanone. Of the second
organic solvents, n-butyl acetate, n-butyl propionate and
2,6-dimethyl-4-heptanone are preferred. Preferred combinations of
the first and second organic solvent include 2-heptanone/n-butyl
propionate, cyclohexanone/n-butyl propionate, PGMEA/n-butyl
propionate, 5-methyl-2-hexanone/n-butyl propionate,
2-heptanone/2,6-dimethyl-4-heptanone and 2-heptanone/n-butyl
acetate. Of these, 2-heptanone/n-butyl acetate and
2-heptanone/n-butyl propionate are particularly preferred.
[0065] The organic solvents are typically present in the developer
in a combined amount of from 90 wt % to 100 wt %, more typically
greater than 95 wt %, greater than 98 wt %, greater than 99 wt % or
100 wt %, based on the total weight of the developer.
[0066] The developer material may include optional additives, for
example, surfactants such as described above with respect to the
photoresist. Such optional additives typically will be present in
minor concentrations, for example, in amounts of from about 0.01 to
5 wt % based on the total weight of the developer.
[0067] The developer can be applied to the substrate by known
techniques, for example, by spin-coating or puddle-coating. The
development time is for a period effective to remove the unexposed
regions of the photoresist, with a time of from 5 to 30 seconds
being typical. Development is typically conducted at room
temperature. The development process can be conducted without use
of a cleaning rinse following development. In this regard, it has
been found that the development process can result in a
residue-free wafer surface rendering such extra rinse step
unnecessary.
[0068] The BARC layer, if present, is selectively etched using
resist pattern 104' as an etch mask, exposing the underlying
hardmask layer. The hardmask layer is next selectively etched,
again using the resist pattern 104' as an etch mask, resulting in
patterned BARC and hardmask layers. Suitable etching techniques and
chemistries for etching the BARC layer and hardmask layer are known
in the art and will depend, for example, on the particular
materials of these layers. Dry-etching processes such as reactive
ion etching are typical. The resist pattern 104' and patterned BARC
layer are next removed from the substrate using known techniques,
for example, oxygen plasma aching.
[0069] Using the hardmask pattern as an etch mask, the one or more
layers 102 are selectively etched. Suitable etching techniques and
chemistries for etching the underlying layers 102 are known in the
art, with dry-etching processes such as reactive ion etching being
typical. The patterned hardmask layer can next be removed from the
substrate surface using known techniques, for example, a
dry-etching process such as reactive ion etching. The resulting
structure is a pattern of etched features. In an alternative
exemplary method, it may be desirable to pattern the layers 102
directly using the resist pattern 104' without the use of a
hardmask layer. Whether direct patterning is employed will depend
on factors such as the materials involved, resist selectivity,
resist pattern thickness and pattern dimensions.
[0070] The negative tone development methods of the invention are
not limited to the exemplary methods described above. For example,
the photoresist overcoat compositions can be used in a negative
tone development double exposure method for making contact holes.
An exemplary such process is a variation of the technique described
with reference to FIG. 1, but using an additional exposure of the
photoresist layer in a different pattern than the first exposure.
In this process, the photoresist layer is exposed to actinic
radiation through a photomask in a first exposure step. The
photomask includes a series of parallel lines forming the opaque
regions of the mask. Following the first exposure, a second
exposure of the photoresist layer is conducted through a second
photomask that includes a series of lines in a direction
perpendicular to those of the first photomask. The resulting
photoresist layer includes unexposed regions, once-exposed regions
and twice-exposed regions. Following the second exposure, the
photoresist layer is post-exposure baked and developed using a
developer as described above. Unexposed regions corresponding to
points of intersection of the lines of the two masks are removed,
leaving behind the once- and twice-exposed regions of the resist.
The resulting structure can next be patterned as described above
with reference to FIG. 1.
[0071] Further refined resolution for features such as contact
holes and trench patterns can be achieved using an NTD overexposure
process. In this process, the photomask has large patterns relative
to those to be printed on the wafer. Exposure conditions are
selected such that light diffuses beneath the edge of the photomask
pattern causing the polarity switch in the resist to extend beneath
these edge regions.
[0072] The following non-limiting examples are provided to further
describe patterning methods and overcoat compositions in accordance
with the invention.
Examples
Photoresist Polymers (PP) Synthesis
##STR00028##
[0073] Poly(IPAMA/IPCPMA/aGBLMA/X-GM-HL-2/HAMA) (PP-1)
[0074] Monomers of IPAMA (20.68 g), IPCPMA (24.72 g), aGBLMA (27.78
g), X-GM-HL-2 (17.26 g) and HAMA (11.46 g) were dissolved in 108.33
g of ethyl lactate/.gamma.-butyrolactone (gBL) (7/3). The monomer
solution was degassed by bubbling with nitrogen for 20 min. Ethyl
lactate/.gamma.-butyrolactone (gBL) (113 g) was charged into a 500
mL Jacket reactor equipped with a condenser and a mechanical
stirrer and was degassed by bubbling with nitrogen for 20 min.
Subsequently, the solvent in the reaction flask was brought to a
temperature of 80.degree. C. V-601 (dimethyl-2,2-azodiisobutyrate)
(3.974 g) was dissolved in 12 g of ethyl lactate/gBL and the
initiator solution was degassed by bubbling with nitrogen for 20
min. The initiator solution was added into the reactor and then
monomer solution was fed into the reactor dropwise over a 3.5 hour
period under rigorous stirring and nitrogen environment. After
monomer feeding was complete, the polymerization mixture was left
standing for an additional 0.5 hour at 80.degree. C. After reaction
was completed, the polymerization mixture was allowed to cool down
to room temperature. Precipitation was carried out in MeOH (3000
g). The powder precipitated was collected by filtration, air-dried
overnight, re-dissolved in 120 g of THF, and re-precipitated into
MeOH (3000 g). The final polymer was filtered, air-dried overnight
and further dried under vacuum at 60.degree. C. for 48 hours to
give Polymer PP-1 (Mw=7785; PDI=1.36; yield=82.75%)
##STR00029##
Overcoat Matrix Polymer (MP) Synthesis
##STR00030##
[0075] Poly(iBMA/nBMA) (75/25) (MP-1)
[0076] 30 g of isobutyl methacrylate (iBMA) and 10 g of n-butyl
methacrylate (nBMA) monomers were dissolved in 60 g of PGMEA. The
monomer solution was degassed by bubbling with nitrogen for 20 min.
PGMEA (32.890 g) was charged into a 500 mL three-neck flask
equipped with a condenser and a mechanical stirrer and was degassed
by bubbling with nitrogen for 20 min. Subsequently the solvent in
the reaction flask was brought to a temperature of 80.degree. C.
V601 (3.239 g) was dissolved in 8 g of PGMEA and the initiator
solution was degassed by bubbling with nitrogen for 20 min. The
initiator solution was added into the reaction flask and then
monomer solution was fed into the reactor dropwise over a 3 hour
period under rigorous stirring and nitrogen environment. After
monomer feeding was complete, the polymerization mixture was left
standing for an additional hour at 80.degree. C. After a total of 4
hours of polymerization time (3 hours of feeding and 1 hour of
post-feeding stirring), the polymerization mixture was allowed to
cool down to room temperature. Precipitation was carried out in
methanol/water (8/2) mixture (1730 g). The precipitated polymer was
collected by filtration, air-dried overnight, re-dissolved in 120 g
of THF, and re-precipitated into methanol/water (8/2) mixture (1730
g). The final polymer was filtered, air-dried overnight and further
dried under vacuum at 25.degree. C. for 48 hours to give 33.1 g of
poly(iBMA/nBMA) (75/25) copolymer (MP-1) (Mw=9,203; Mw/Mn=1.60;
Yield=82.75%). The results of the synthesis are described in Table
1.
##STR00031##
Overcoat Additive Polymer (AP) Synthesis
##STR00032##
[0077] Poly(MA-MIB-HFA/MA-DM-EATf/233-1MBA) (55/25/20) (AP-1)
[0078] 25 g of PGMEA was charged to a 200 ml reactor and heated to
99.degree. C. under nitrogen purge for 30 mins 27.5 g of MA-MIB-HFA
monomer, 12.5 g of MA-DM-EATf monomer and 10 g of 233-tMBA monomer
were dissolved in 7.02 g of PGMEA solvent, and the monomer solution
was degassed by bubbling with nitrogen. 1.80 g of V601
(dimethyl-2,2-azodiisobutyrate) was dissolved in 16.18 g of PGMEA
and the monomer solution was degassed by bubbling with nitrogen.
The initiator solution was fed into the reactor dropwise over 120
min with a feeding rate of 0.150 g/min. The monomer solution was
also fed into the reactor dropwise over 120 min with a feeding rate
0.475 g/min under rigorous stirring and nitrogen environment. After
feeding was complete, the polymerization mixture was left standing
for an additional 2 hours. The polymerization mixture was then
allowed to cool down to room temperature, resulting in a solution
of Poly(MA-MIB-HFA/MA-DM-EATf/tMBA) (55/25/20) copolymer (AP-1)
(Mw=9017; Mw/Mn=1.87; Yield=35.7%). The results of the synthesis
are described in Table 1.
##STR00033##
Poly(MA-MIB-HFA/233-tMBA) (80/20) (AP-2)
[0079] 25 g of PGMEA was charged to 200 ml reactor and heated to
99.degree. C. under nitrogen purge for 30 min. 40 g of MA-MIB-HFA
monomer and 10 g of 233-tMBA monomer were mixed and dissolved in 10
g of PGMEA solvent. 1.50 g of V601 (dimethyl-2,2-azodiisobutyrate)
was dissolved in 13.5 g of PGMEA. The monomer and initiator
solution were degassed by bubbling with nitrogen. The initiator
solution was fed into the reactor dropwise over 110 min. with a
feeding rate of 0.136 g/min. The monomer solution was also fed into
the reactor dropwise over 110 min. at a feeding rate of 0.545 g/min
under rigorous stirring and nitrogen environment. After feeding was
complete, the polymerization mixture was left standing for an
additional 2 hours. The polymerization mixture was then allowed to
cool down to room temperature, resulting in a solution of
Poly(MA-MIB-HFA/233-tMBA) (80/20) copolymer (AP-2) (Mw=8945;
Mw/Mn=1.91; Yield=42.1%). The results of the synthesis are
described in Table 1.
##STR00034##
Poly(MA-MIB-HFA) (AP-3)
[0080] 300 g of isobutyl isobutyrate (IBIB) was charged to a 2 L
reactor and heated to 99.degree. C. under nitrogen purge. 400 g of
MA-MIB-HFA monomer and 14.4 g V601 (dimethyl-2,2-azodiisobutyrate)
were dissolved in 285.7 g of IBIB and the monomer solution was
degassed by bubbling with nitrogen and was subsequently fed into
the reactor dropwise over a 120 min. period under rigorous stirring
and nitrogen environment. After monomer feeding was complete, the
polymerization mixture was left standing for an additional 5 hours
at 99.degree. C. The polymerization mixture was then allowed to
cool down to room temperature, resulting in a solution of
Poly(MA-MIB-HFA) homopolymer (AP-3) (Mw=6768; Mw/Mn=1.658;
Yield=29.83%). The results of the synthesis are described in Table
1.
##STR00035##
Poly(TBMA/MHFPMA) (70/30) (AP-4)
[0081] 53.94 g of PGMEA was charged to 300 ml reactor and heated to
99.degree. C. under nitrogen purge for 30 min. 57.18 g of TBMA
monomer and 50.7 g of MHFPMA monomer were mixed and dissolved in
15.14 g of PGMEA. The monomer solution was degassed by bubbling
with nitrogen. 3.88 g of V601 (dimethyl-2,2-azodiisobutyrate) was
dissolved in 34.91 g of PGMEA and the initiator solution was fed
into the reactor dropwise over 110 min. at a feeding rate of 0.353
g/min. The monomer solution was also fed into the reactor dropwise
over 110 min. at a feeding rate of 1.118 g/min under rigorous
stirring and nitrogen environment. After feeding was complete, the
polymerization mixture was left standing for an additional 2 hours.
The polymerization mixture was then allowed to cool down to room
temperature, resulting in a solution of Poly(TBMA/MHFPMA) copolymer
(AP-4) (Mw=10,944; Mw/Mn=1.74; Yield=45.2%). The results of the
synthesis are described in Table 1.
##STR00036##
TABLE-US-00001 TABLE 1 Poly- mer Monomer(s) Composition* Yield Mw
Mw/Mn MP-1 iBMA/nBMA 75/25 82.75% 9,203 1.60 AP-1 MA-MIB-HFA/
55/25/20 35.7% 9,017 1.87 MA-DM-EATf/ tMBA AP-2 MA-MIB-HFA/ 80/20
42.1% 8,945 1.91 tMBA AP-3 MA-MIB-HFA 100 29.83% 6,768 1.658 AP-4
TBMA/ 70/30 45.2% 10,944 1.74 MHFPMA *Molar feed ratio in the
polymerization
Preparation of Photoresist Composition (PC-1)
[0082] 31.219 g of Polymer PP-1 solution (10 wt %) in PGMEA, 5.415
g of Triphenylsulfonium perfluorobutane sulfonate solution (1 wt %)
in PGMEA, 15.047 g of Triphenylsulfonium
2-(((3r,5r,7r)-adamantane-1-carbonyl)oxy)-1,1-difluoroethanesulfonate
solution (1 wt %) in PGMEA, 3.01 g of
2,2'-(dodecylazanediyl)diethanol solution (1%) in PGMEA, 14.336 g
of Triphenylsulfonium
((1S,4S)-7,7-dimethyl-2-oxobicyclo[2.2.1]heptan-1-yl)methanesulfonate
(1%) in PGMEA, 21.324 g PGMEA and 9.650 g of .gamma.-butyrolactone
were mixed for 4 hours. The mixture was filtered with a 0.2 micron
Nylon filter to provide photoresist composition PC-1.
Preparation of Resist Overcoat Compositions (OC)
[0083] Resist overcoat compositions were prepared by dissolving an
overcoat matrix polymer, additive polymer and basic quencher in a
solvent using the components and amounts set forth in Table 2. The
resulting mixtures were rolled on a mechanical roller for three
hours and then filtered through a Teflon filter having a 0.2 micron
pore size. The compositions were formulated based on target
thicknesses (after spin coating at .about.1500 rpm) of 290 .ANG.,
corresponding to 1/4 the wavelength of the incoming wave to reduce
reflectance at the overcoat surface.
TABLE-US-00002 TABLE 2 Overcoat Additive Basic composition Matrix
Polymer Polymer Quencher Solvent Target thickness OC-1 (Comp) MP-1
0.3109 g -- 0.4095 g IBIB 29.2796 g 290 .ANG. OC-2 MP-1 0.2954 g
AP-1 0.0155 g 0.4095 g IBIB 29.2796 g 290 .ANG. OC-3 MP-1 0.2954 g
AP-2 0.0155 g 0.4095 g IBIB 29.2796 g 290 .ANG. OC-4 MP-1 0.2954 g
AP-3 0.0155 g 0.4095 g IBIB 29.2796 g 290 .ANG. OC-5 MP-1 0.2891 g
AP-3 0.0218 g 0.4095 g IBIB 29.2796 g 290 .ANG. OC-6 MP-1 0.2798 g
AP-3 0.0311 g 0.4095 g IBIB 29.2796 g 290 .ANG. OC-7 MP-1 0.2954 g
AP-4 0.0155 g 0.4095 g IBIB 29.2796 g 290 .ANG. IBIB = Isobutyl
Isobutyrate; Basic Quencher = tert-butyl
4-hydroxypiperidine-1-carboxylate solution (1 wt %) in IBIB.
Contact Angle Measurement
[0084] Static contact angle (SCA), receding contact angle (RCA),
advancing contact angle (ACA) and sliding angle (SA) with respect
to DI water were measured for each resist overcoat composition.
Static and dynamic contact angles were measured using a KRUSS drop
shape analyzer model 100. For dynamic contact angle measurement,
the droplet size of DI water was 50 .mu.l (microliter), and the
wafer stage tilting rate was 1 unit/sec. Once a water droplet was
placed on a test wafer surface, the wafer stage started to tilt
immediately. During wafer stage tilting, video of the droplet was
taken at a rate of 20 frames per second until the droplet slid away
from its original location. Each frame in the video was then
analyzed, and the image of the droplet on the frame when the
droplet just started to slide was used to determine the dynamic
contact angles (receding and advancing) by their corresponding
tangent lines. Sliding angle is the wafer stage tilting angle
corresponding to the frame when the droplet just started to slide.
In static contact angle measurement, the water droplet was 2.5
.mu.l and placed on the test wafer surface without tilting. The
contact angle was determined by the tangent lines on both sides of
the droplet. The reported static contact angle was the average of
the contact angles from left and right sides of the droplet.
Surface energy was calculated based on the static contact angles of
water using the Extended Fowkes theory. The results for contact
angle (SCA), receding contact angle (RCA), advancing contact angle
(ACA), sliding angle (SA) and the difference in RCA with respect to
OC-1 (ARCA from OC-1) are set forth in Table 3.
TABLE-US-00003 TABLE 3 .DELTA.RCA from Sample SCA (.degree.) RCA
(.degree.) ACA (.degree.) SA (.degree.) OC-1 (.degree.) OC-1 (Comp)
83.2 74.8 91.6 14.4 -- OC-2 88.0 78.6 97.4 18.7 3.8 OC-3 88.8 79.8
97.8 17.3 5.0 OC-4 88.9 80.4 97.4 16.5 5.6 OC-5 91.1 82.2 100.0
15.6 7.4 OC-6 92.9 84.5 101.3 14.1 6.7 OC-7 92.7 84.9 100.6 14.2
10.1
As can be seen from Table 3, resist overcoat compositions
OC-2.about.OC-7 containing an additive polymer in accordance with
the invention exhibited favorable SCA, RCA and ACA characteristics
as compared with the comparative overcoat composition OC-1, and
comparable characteristics for SA.
Lithographic Process
[0085] Dry lithography was performed to examine the effect of the
overcoat compositions on lithography performance. On a TEL
CleanTrack ACT 8 linked to an ASML/1100 scanner, 200 mm silicon
wafers were spin-coated with AR.TM.19 bottom-antireflective coating
(BARC) material (Rohm and Haas Electronic Materials, Marlborough,
Mass.) and baked for 60 seconds at 205.degree. C. to yield a film
thickness of 860 .ANG.. Photoresist composition PC-1 was coated on
the BARC-coated wafers and soft-baked at 90.degree. C. for 60
seconds on a TEL CleanTrack ACT 8 coater/developer to provide a
resist layer thickness of 1000 .ANG.. Overcoat compositions if used
were coated on top of the resist and soft-baked at 90.degree. C.
for 60 seconds on a TEL CleanTrack ACT 8 coater/developer to
provide a resist overcoat thickness of 290 .ANG.. The wafers were
exposed using quadrupole illumination condition with 0.75 NA, 0.89
outer sigma and 0.64 inner sigma with an ASML 1100 scanner. The
exposed wafers were post-exposure baked at 90.degree. C. for 60
seconds and developed with n-butyl acetate (NBA) developer for 30
seconds on a TEL CleanTrack ACT 8 coater/developer. The Critical
dimensions (CDs) were targeted at 100 nm for dense contact holes
with a 200 nm pitch at same mask features (6% PSM) and were
measured at diameter of hole pattern on a Hitachi 9380 CD SEM with
200K magnification.
[0086] The following values were determined from the lithographic
results: E.sub.s=exposure energy to print the target CD of 100 nm
for dense contact holes with a 200 nm pitch (CD.sub.t); EL=exposure
latitude of the photoresist, defined by the percent CD change
(.DELTA.CD) per exposure energy within .+-.10% of CD.sub.t
according to the following formula:
EL=(1.1.times.CD.sub.t-0.9.times.CD.sub.t)/(E.sub.opt of
1.1.times.CD.sub.t-E.sub.opt of 0.9.times.CD.sub.t)
wherein EL and CD.sub.t are as defined above, and E.sub.opt is the
optimum exposure energy to print the specified CD; FL at
E.sub.s=focus latitude at E.sub.s, wherein focus latitude is the
range of focus that keeps CD variation within .+-.10% of CD.sub.t;
PW means process window, which is the overlapping region of focus
and exposure that keeps the final CD within specification or
limited data area (PW was determined with KLA/Tencor Prodata.TM.
software); PW at 5% EL=Process window in the range of .+-.5% CD
variation; FL at underdose=focus latitude at an exposure dose of 1
mJ less than E.sub.s; and FL at overdose=focus latitude at an
exposure dose of 1 mJ greater than E.sub.s. The results are
summarized in Table 4. As can be seen from Table 4, the
lithographic performance for the examples using a resist overcoat
in accordance with the invention provided good overall lithographic
performance.
TABLE-US-00004 TABLE 4 Overcoat E.sub.s PW at 5% EL FL at under- FL
at Example Composition (mJ/cm.sup.2) EL % (.mu.m) FL at E.sub.s
(.mu.m) dose (.mu.m) overdose (.mu.m) 1 (Comp) N/A 25.8 9.8 0.31
0.40 0.40 0.30 2 (Comp) OC-1 26.3 13.0 0.46 0.50 0.60 0.30 3 OC-2
27.1 11.9 0.39 0.45 0.50 0.30 4 OC-3 26.5 12.1 0.42 0.45 0.50 0.30
5 OC-4 26.4 11.5 0.43 0.45 0.55 0.30 6 OC-5 26.6 12.3 0.42 0.45
0.60 0.35 7 OC-6 26.5 11.8 0.42 0.45 0.60 0.40 8 OC-7 27.4 11.1
0.39 0.40 0.50 0.30
Preparation of Resist Overcoat Compositions (OC)
[0087] Resist overcoat compositions are prepared by dissolving 9 g
matrix polymer, 0.95 g additive polymer and 0.05 g tert-butyl
4-hydroxypiperidine-1-carboxylate in 990 g of a solvent using the
components set forth in Table 5. The resulting mixtures are rolled
on a mechanical roller for three hours and are then filtered
through a Teflon filter having a 0.2 micron pore size.
TABLE-US-00005 TABLE 5 Overcoat composition Matrix Polymer Additive
Polymer Basic Quencher Solvent OC-9 MP-2 AP-5 TB-4HP IBIB OC-10
MP-3 AP-6 TB-4HP IBIB OC-11 MP-4 AP-6 TB-4HP NHP OC-12 MP-5 AP-7
TB-4HP NHP OC-13 MP-6 AP-3 TIPA IBIB OC-14 MP-7 AP-3 TIPA IBIB
OC-15 MP-8 AP-8 TIPA NHP OC-16 MP-9 AP-3 TIPA NHP OC-17 MP-10 AP-8
TBMA IBIB OC-18 MP-11 AP-9 TBMA IBIB OC-19 MP-12 AP-10 TBMA IBIB
OC-20 MP-13 AP-3 TBMA IBIB OC-21 MP-14 AP-11 TBMA IBIB OC-22 MP-15
AP-12 TBMA IBIB OC-23 MP-16 AP-10 TBDA NHP OC-24 MP-17 AP-11 TBDA
NHP OC-25 MP-18 AP-5 TBDA NHP OC-26 MP-19 AP-13 TBDA IBIB OC-27
MP-20 AP-14 TBDA IBIB TB-4HP = tert-butyl
4-hydroxypiperidine-1-carboxylate; TIPA = triisopropanolamine; TBMA
= N1,N1,N3,N3-tetrabutylmalonamide; TBDA =
n-tert-butyldiethanolamine; IBIB = Isobutyl Isobutyrate; and NHP =
n-heptyl propionate. Matrix Polymers ##STR00037## ##STR00038##
##STR00039## ##STR00040## ##STR00041## Additive Polymers
##STR00042## ##STR00043## ##STR00044## ##STR00045##
Lithographic Process
[0088] 300 mm silicon wafers are spin-coated with AR.TM.19
bottom-antireflective coating (BARC) material (Rohm and Haas
Electronic Materials, Marlborough, Mass.) and baked for 60 seconds
at 205.degree. C. to yield a film thickness of 860 .ANG..
Photoresist composition PC-1 is spin-coated on the BARC-coated
wafers and soft-baked at 90.degree. C. for 60 seconds to provide a
resist layer thickness of 1000 .ANG.. The overcoat compositions in
Table 5 are spin-coated on top of the resist and soft-baked at
90.degree. C. for 60 seconds to provide a resist overcoat layer.
The wafers are exposed on an immersion scanner and then developed
using 2-heptanone for 25 seconds on a spin-coater to give negative
tone patterns.
* * * * *