U.S. patent application number 10/924484 was filed with the patent office on 2005-02-03 for resist compositions including thermal crosslinking agents.
Invention is credited to Choi, Sang-jun, Chung, Jeong-hee, Kang, Yool, Moon, Joo-tae, Woo, Sang-gyun.
Application Number | 20050026078 10/924484 |
Document ID | / |
Family ID | 26634988 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050026078 |
Kind Code |
A1 |
Choi, Sang-jun ; et
al. |
February 3, 2005 |
Resist compositions including thermal crosslinking agents
Abstract
A method for forming a fine pattern in a semiconductor
substrate, by coating a target layer to be etched on a
semiconductor substrate with a resist composition including at
least one compound capable of forming a photoresist pattern by a
photolithography process, and a free radical initiator. The free
radical initiator is capable of being decomposed by a thermal
process at a temperature equal to or higher than the glass
transition temperature of the at least one compound. A lithography
process is performed on the resist compound layer to form a
photoresist pattern. The resist compound layer having the
photoresist pattern formed therein is heated to a temperature equal
to or higher than the glass transition temperature of the at least
one compound, and wherein a partial cross-linking reaction in the
resist composition occurs.
Inventors: |
Choi, Sang-jun; (Seoul,
KR) ; Kang, Yool; (Kyungki-do, KR) ; Moon,
Joo-tae; (Kyungki-do, KR) ; Chung, Jeong-hee;
(Kyungki-do, KR) ; Woo, Sang-gyun; (Kyungki-do,
KR) |
Correspondence
Address: |
MYERS BIGEL SIBLEY & SAJOVEC
PO BOX 37428
RALEIGH
NC
27627
US
|
Family ID: |
26634988 |
Appl. No.: |
10/924484 |
Filed: |
August 24, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10924484 |
Aug 24, 2004 |
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10227067 |
Aug 23, 2002 |
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6803176 |
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10227067 |
Aug 23, 2002 |
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09533770 |
Mar 23, 2000 |
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6485895 |
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Current U.S.
Class: |
430/270.1 |
Current CPC
Class: |
G03F 7/40 20130101 |
Class at
Publication: |
430/270.1 |
International
Class: |
G03C 001/76 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 21, 1999 |
KR |
99-14271 |
Nov 16, 1999 |
KR |
99-50903 |
Claims
What is claimed:
1. A resist composition comprising: at least one compound capable
of forming a photoresist pattern by a photolithography process; and
a thermal crosslinking agent capable of causing a partial
cross-linking reaction in the resist composition in response to a
temperature equal to or higher than the glass transition
temperature or the softening temperature of the at least one
compound and in the absence of UltraViolet (UV) radiation.
2. The resist composition of claim 1, wherein said at least one
compound is selected from the group consisting of a Novolak resin,
a diazonaphthoquinone compound, and mixtures thereof.
3. The resist composition of claim 1, wherein said resist
composition is a chemically amplified resist composition comprising
a photo acid generator.
4. The resist composition of claim 1, wherein said thermal
crosslinking agent is a vinylether derivative.
5. The resist composition of claim 4, wherein the vinylether
derivative is represented by the formula:
R--(--OCH.dbd.CH.sub.2).sub.x wherein x is an integer ranging from
2 to 4; and R is a C.sub.1 to C.sub.20 hydrocarbon or an oligomer
having a weight average molecular weight ranging from about 500 to
about 5000.
6. The resist composition of claim 1, wherein said thermal
crosslinking agent is present in an amount from about 1 to about 20
percent based on the weight of polymer present in said at least one
compound.
7. The resist composition of claim 1, wherein said thermal
crosslinking agent is selected from the group consisting of
1,4-butandiol divinylether, tri(ethyleneglycol)divinylether,
trimethyolpropane trivinyl ether, 1,4-cyclohexanedimethanol divinyl
ether, and mixtures thereof.
8. The resist composition of claim 1, wherein said thermal
crosslinking agent is a free radical initiator.
9. The resist composition of claim 8, wherein the free radical
initiator is present in an amount of from about 1 to about 15
percent based on the weight of polymer present in said at least one
compound.
10. The resist composition of claim 8, wherein the resist
composition comprises from about 3 to about 15 percent by weight of
said free radical initiator based on the weight of the solids in
the resist composition.
11. The resist composition of claim 8, wherein said free radical
initiator is selected from the group consisting of acyl peroxides,
alkyl peroxides, peresters, hydroperoxides, azo compounds, and
mixtures thereof.
12. The resist composition of claim 8, wherein said free radical
initiator is selected from the group consisting of benzoyl
peroxide, dicumyl peroxide, di-tert-butyl peroxide, cumyl
hydroperoxide, azobis (isobutyronitrile), and mixtures thereof.
13. The resist composition of claim 1, wherein said resist
composition further comprises an organic base.
14. The resist compound of claim 13, wherein the organic base is
present in an amount of from about 0.01 to about 2.0 percent by
weight based on the at least one compound.
15. The resist compound of claim 13, wherein the organic base is
one selected from the group consisting of N,N'-dimethylaniline,
N,N'-diethylaniline, triethylamine, triisobutylamine,
diethanolamine, triethanolamine, and mixtures thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/227,067, filed Aug. 23, 2002, now U.S. Pat. No. ______,
which itself is a continuation of U.S. application Ser. No.
09/533,770, filed Mar. 23, 2000, now U.S. Pat. No. 6,485,895, and
also claims the benefit of Korean Application Nos. 99-14271, filed
Apr. 21, 1999, and 99-50903, filed Nov. 16, 1999, the disclosures
of all of which are hereby incorporated herein by reference in
their entirety as if set forth fully herein.
FIELD OF THE INVENTION
[0002] The invention generally relates to methods for fabricating
semiconductor substrates and compositions of matter employed in
such methods.
BACKGROUND OF THE INVENTION
[0003] In a general process for forming patterns for semiconductor
memory devices, after a photoresist pattern is formed on a
predetermined target layer to be etched for forming patterns, the
target layer is typically etched to a desired pattern using the
photoresist pattern as an etching mask. Examples of target layers
include silicon layers, insulating layers, or conductive layers.
Because of the ever increasing integration of semiconductor
devices, it is important to develop lithography technology to form
contact holes in the semiconductor devices having smaller opening
sizes or finer patterns having narrower spaces. Stated differently,
it is believed important to develop design criteria for smaller
critical dimensions (CD) in the devices.
[0004] A photolithography technique employed for forming fine
contact holes uses E-beam lithography with an exposure tool of
shorter wavelength and a method that uses a half-tone phase shift
mask. In particular, the method employing the exposure tool of
shorter wavelength is believed to be disadvantageous in that it is
material-intensive and thus relatively expensive to implement.
Moreover, a method that utilizes the half-tone phase shift mask is
believed to possess limitations in mask manufacturing technology
and resolution. Accordingly, it may be difficult to obtain contact
holes smaller than 150 nm.
[0005] In an attempt to meet the demand for devices with smaller
feature sizes, efforts have focused on reducing the opening size or
space by applying heat to a photoresist pattern such that the
photoresist is able to flow. An example of this technique includes
coating a resist layer on a wafer patterned by a photolithography
process and then causing the photoresist pattern to flow by heating
the resist layer to a temperature that is higher than the glass
transition temperature or the softening temperature of the resist
layer to reduce the CD of the resultant resist pattern.
[0006] Notwithstanding any possible advantages, the above procedure
is potentially disadvantageous in that the flow rates in the upper
and middle parts of the photoresist pattern are often different.
This difference is believed to result in the photoresist pattern
having a bowed profile. The bowed profile is believed to be caused
by a swelling phenomenon occurring in the middle part of the
photoresist pattern. Due to the difficulty in controlling the flow
rate of the photoresist pattern by employing conventional resist
flow technology, it is often extremely difficult to reduce the CD
of the photoresist pattern while maintaining a vertical pattern
profile.
[0007] U.S. Pat. No. 5,096,802 proposes a photolithographic process
for producing a component with reduced feature sizes. The '802
patent proposes controlling the flow rate of a resist through hard
baking and deep-UV (DUV) exposure, resulting in the reduced feature
sizes. Potential problems may be associated with the '802 patent.
For example, the side walls of openings formed in the flowed resist
are typically tapered. Accordingly, a target layer underneath the
resist pattern is resultantly etched along the tapered side walls
during subsequent dry etching. Thus, the upper and lower parts of
the openings may have different critical dimensions. In general,
the degree of tapering at the side walls of the opening tends to
vary among the openings, thereby undesirably causing different
critical dimensions to a plurality of holes formed in the target
layer over the entire wafer surface. As such, it is typically
difficult to obtain a good sidewall profile in a flowed photoresist
pattern employing conventional technology.
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide methods
for forming fine patterns through thermal flowing of photoresist
patterns, in which distortion of the profile at the side walls of
openings or spaces is minimized, leading to a further reduction in
smaller feature size.
[0009] It is another object of the present invention to provide
compositions suitable for forming fine patterns which go beyond the
wavelength limit in a photolithography technology.
[0010] In one aspect, the invention provides methods for forming
fine patterns in semiconductor substrates. The method first
comprises coating a target layer to be etched on a semiconductor
substrate with resist compositions. The resist compositions
comprise compounds capable of forming a photoresist pattern by a
photolithography process, and crosslinking agents. The crosslinking
agents are those which are capable of causing partial crosslinking
reactions at temperatures equal to or higher than the glass
transition temperatures or the softening temperatures of the
compounds. The coating steps result in forming resist compound
layers comprising the compounds. Thereafter, lithography processes
are performed on the resist compound layers to form photoresist
patterns of at least one opening having a first width, wherein the
target layer is exposed through the first width. Next, the resist
compound layers having the photoresist patterns formed therein are
heated to temperatures equal to or higher than the glass transition
temperatures or the softening temperatures of the compounds, and
partial cross-linking reactions in the resist compositions occur.
Modified photoresist patterns result having at least one opening
having a second width which exposes the target layer, wherein the
second width is smaller than the first width. The methods of the
invention are believed to be desirable in that the flow rates of
the photoresist patterns may be controlled. Moreover, the methods
are potentially simpler relative to conventional methods.
[0011] In another aspect, the invention provides resist
compositions. The resist compositions comprise compounds capable of
forming photoresist patterns by photolithography processes, and
crosslinking agents. The crosslinking agents are capable of causing
partial cross-linking reactions in the resist compositions to form
resist compounds at temperatures equal to or higher than the glass
transition temperatures or the softening temperatures of the
compounds. The crosslinking agents are advantageous in that they
may be employed with a number of compounds without adversely
affecting the performance of the resist compositions.
[0012] In addition to the above, the invention is potentially
advantageous in that the distortion of the profile at the side
walls of contact holes is minimized, thus allowing for the
formation of vertical sidewall profiles. In addition, fine openings
which go beyond the wavelength limits in general photolithography
technologies can be formed in the photoresist patterns.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGS. 1A through 1D are sectional views illustrating the
sequence of steps in a method for forming a fine pattern according
to a preferred embodiment of the present invention; and
[0014] FIG. 2 is a graph illustrating the amount of flow of
photoresist pattern with respect to the temperature of a thermal
process, to evaluate the dependency on temperature of the resist
compound according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings and
examples, in which preferred embodiments of the invention are
shown. This invention may, however, be embodied in many different
forms and should not be construed as limited to the embodiments set
forth herein. Rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the invention to those skilled in the art. In the
drawings, the thickness of layers and regions are exaggerated for
clarity. Like numbers refer to like elements throughout. It will
also be understood that when a layer is referred to as being "on"
another layer or substrate, it can be directly on the other layer
or substrate, or intervening layers may also be present.
[0016] In one aspect, the invention relates to methods for forming
fine patterns in semiconductor substrates. The method first
comprises coating target layers to be etched on semiconductor
substrates with resist compositions (e.g., solutions). The resist
compositions comprise compounds capable of forming photoresist
patterns by photolithography processes and crosslinking agents. The
crosslinking agents are those which are capable of causing partial
crosslinking reactions in the resist compositions at temperatures
equal to or higher than the glass transition temperatures or the
softening temperatures of the compounds. The compositions are
described in greater detail herein.
[0017] The coating steps result in forming resist compound layers
comprising the resist compositions. Thereafter, lithography
processes are performed on the resist compound layers to form
photoresist patterns of at least one opening having a first width,
wherein the target layer is exposed through the first width.
Preferably, a plurality of openings are formed having the first
width. Next, the resist compound layers having the photoresist
patterns formed therein are heated to temperatures equal to or
higher than the glass transition temperatures or the softening
temperatures of the compounds wherein partial cross-linking
reactions in the resist compositions occur. Modified photoresist
patterns result having at least one opening of a second width which
exposes the target layer, wherein the second width is smaller than
the first width. Preferably, a plurality of openings having the
second width are formed.
[0018] In a preferred embodiment, the heating of the resist
compound layers to temperatures equal to or higher than the glass
transition temperatures or the softening temperatures of the
compounds causes the resist compound layers to flow with partial
cross-linking reactions occurring and the formation of at least one
opening of a second width resulting.
[0019] In various preferred embodiments, the steps of heating the
resist compound layers comprises heating the resist compound layers
having the photoresist patterns formed therein to first
temperatures which are equal to or higher than the glass transition
temperatures or the softening temperatures of the resist
compositions. Thereafter, the resist compound layers having the
photoresist patterns formed therein are cooled to room temperature.
The resist compound layers having the photoresist patterns formed
therein are then heated to second temperatures which are higher
than the first temperatures.
[0020] In various preferred embodiments, the methods of the
invention may further comprise cooling the resist compound layers
having the photoresist patterns formed therein; and heating the
resist compound layers having the photoresist patterns formed
therein to temperatures equal to or higher than the glass
transition temperatures or the softening temperatures of the
compounds. In these embodiments, the cooling and heating steps
occur subsequent to the step of heating the resist compound layers
having the photoresist patterns formed therein to second
temperatures.
[0021] In certain preferred embodiments, the step of heating the
resist compound layers having the photoresist patterns formed
therein to temperatures equal to or higher than the glass
transition temperatures or softening temperatures of the compounds
comprise heating the resist compound layers to temperatures that
exceed the glass transition temperatures or softening temperatures
by about 5.degree. C. to about 20.degree. C.
[0022] In various preferred embodiments, the step of heating the
resist compound layers having the photoresist patterns formed
therein to temperatures equal to or higher than the glass
transition temperatures or softening temperatures is carried out
from about 60 to about 180 seconds.
[0023] The methods of the invention may also comprise forming
target layers to be etched on semiconductor substrates.
[0024] In another aspect, the invention provides resist
compositions. The resist compositions comprise compounds capable of
forming photoresist patterns by photolithography processes, and
crosslinking agents capable of causing partial cross-linking
reactions in the compounds at temperatures equal to of higher than
the glass transition temperatures or the softening temperatures of
the at least one compounds to form resist compounds.
[0025] Various components may be employed as compounds capable of
forming photoresist patterns by photolithography processes. As an
example, the resist compositions may comprise compounds selected
from the groups consisting of Novolak resins, diazonaphthoquinone
(DNQ) compounds, and mixtures thereof. Most preferably, the
compounds that are employed are Novolak resins and
diazonaphthoquinone compounds in combination.
[0026] In certain embodiments, the resist compositions may be
present in the form of chemically amplified resist compositions
comprising photo acid generators (PAG).
[0027] A number of crosslinking agents may be used in the present
invention. In one embodiment, the crosslinking agent is a
vinylether derivative. An example of a vinylether derivative is
represented by the formula:
R--(--OCH.dbd.CH.sub.2).sub.x
[0028] wherein x is an integer ranging from 2 to 4; and R is a
C.sub.1 to C.sub.20 hydrocarbon or an oligomer having a weight
average molecular weight ranging from about 500 to about 5000.
Specific examples of vinyl ethers that can be employed as
crosslinking agents include, but are not limited to, 1,4-butandiol
divinyl ether, tri(ethyleneglycol)divinyl ether, trimethyolpropane
trivinyl ether, 1,4-cyclohexanedimethanol divinyl ether, and
mixtures thereof.
[0029] In other embodiments, the crosslinking agents may be in the
form of free radical initiators. In general, the free radical
initiators are preferably selected from those that are capable of
being decomposed at temperatures equal to or greater than the glass
transition temperatures or the softening temperatures of the at
least one compounds. Thus, free radicals are produced which effect
the partial crosslinking reactions.
[0030] Exemplary free radical initiators may include, but not be
limited to, acyl peroxides, alkyl peroxides, peresters,
hydroperoxides, and azo compounds. In another embodiment, the free
radical initiators are selected from the group consisting of
benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, cumyl
hydroperoxide, and azobis(isobutyronitrile)- . Other free radical
initiators may be employed if so desired.
[0031] Various amounts of the crosslinking agent may be employed.
Preferably, the crosslinking agent is present in an amount from
about 1 to about 20 percent based on the weight of polymer present
in said at least one compound. More preferably, the resist
compositions comprise from about 1 to about 15 percent by weight of
the free radical initiators based on the weight of the solids in
the resist compositions. Most preferably, the resist compositions
comprise from about 3 to about 15 percent by weight of the free
radical initiators based on the weight of the solids in the resist
compositions.
[0032] The resist compositions may comprise various other
materials. In one embodiment, the resist compositions comprise
organic bases. The organic bases may be present in various amounts.
Preferably, the organic bases are present in amounts of from about
0.01 to about 2.0 percent by weight based on the resist
compositions. Examples of organic bases that may be employed
include, but are not limited to, N,N'-dimethylaniline,
N,N'-diethylaniline, triethylamine, triisobutylamine,
diethanolamine, and triethanolamine.
[0033] The invention will now be described further with reference
to the drawings. It should be appreciated that the embodiments
referred to in the drawings are for illustrative purposes only, and
are not to be construed as limiting the invention.
[0034] FIG. 1A refers to a method for forming a fine pattern
according to a preferred embodiment of the present invention. As
shown, a target layer 20 is formed on a semiconductor substrate 10
and is etched to form a pattern having, for example, contact holes.
The target layer 20 may be in the form of various layers, such as,
for example, an insulation layer including a silicon layer, an
oxide layer or a nitride layer, and a conductive layer. In order to
form contact holes in the target layer 20, the target layer 20 is
preferably formed as an insulation layer made of an oxide.
[0035] Then, a resist composition comprising at least one compound
used in a general photolithography process and a crosslinking agent
that is capable of causing a partial crosslinking reaction in the
at least one compound by a thermal process higher than the glass
transition temperature or the softening temperature (hereinafter
the glass transition temperature or the softening temperature shall
be referred to as the "transition temperature" for convenience of
description), is coated on the target layer 20, resulting in a
resist compound layer 30.
[0036] The resist composition of the resist compound layer 30 may
by any resist composition for G-line, i-line, deep-UV, ArF, E-beams
or X-rays. Also, the resist composition may have a positive or
negative polarity.
[0037] In a preferred embodiment, the resist composition may
comprise a Novolak resin and a DNQ compound. The resist composition
may be in the form of a general chemically amplified resist
composition containing a photo acid generator (PAG).
[0038] The crosslinking agent of the resist compound layer 30 may
be added for easier control of the flow rate of the resist
composition in a photoresist pattern during thermal flowing of the
photoresist pattern.
[0039] The crosslinking agent preferably should be selected so as
to not affect the performance of the resist composition, which may
occur during a general photolithography process. Also, it may be
important to select an appropriate crosslinking agent in
consideration of sensitivity, transmittance or shelf life of the
resist compound that is eventually formed by mixing the
crosslinking agent with the at least one compound.
[0040] In embodiments wherein a free radical initiator is used as
the crosslinking agent, an organic base can be further added to the
resist composition which may result in a redox initiation system in
order to potentially facilitate the formation of free radicals by
the free radical initiator. Such a system is believed to encompass
an oxidation-reduction reaction between the free radical initiator
and the organic base in the resist composition. Thus, the
reactivity of the free radical initiator can be potentially
controlled by adding the organic base to the resist composition.
Examples of organic bases which can be used in the present
invention, include, but are not limited to, N,N'-dimethylaniline,
N,N'-diethylaniline, triethylamine, triisobutylamine,
diethanolamine, and triethanolamine. The organic base is preferably
present in an amount ranging from 0.01 to 2.0 percent by weight
based on the weight of the at least one compound capable of forming
a photoresist pattern by a photo lithography process.
[0041] Referring to FIG. 1B, soft baking, exposure, post-exposure
baking (PEB) and development are carried out on the resist compound
layer 30 according to a general photolithography process. A
photoresist pattern 30a results having a plurality of openings H1
present therein each exposing the target layer 30 through a width
D1. The width D1 of one opening H1 has a size which can be obtained
within the capability of conventional photolithography technology
limited by the wavelength, and is typically larger than that of a
fine pattern intended by the present invention.
[0042] The soft baking process may be performed under various
conditions. For example, the soft baking process may be employed at
from about 90.degree. C. to about 150.degree. C. for about 60 to
about 120 seconds. Moreover, during the exposure process G-line,
l-line, DUV, E-beams, or X-rays, may be used as an exposure tool,
depending on the type of photoresist solution employed. As an
example, the PEB process may be performed at a temperature of from
about 90.degree. C. to about 150.degree. C. for about 60 to about
120 seconds.
[0043] Referring to FIG. 1C, the photoresist pattern 30a is heated
at a temperature which is preferably at least 10.degree. C. higher
than the transition temperature of the at least one compound
capable of forming a photoresist pattern, such as, for example,
from about 120.degree. C. or 130.degree. C. to about 170.degree. C.
Preferably, the heating step is carried out for a duration of from
about 30 or 60 seconds to about 180 seconds, although other times
may be employed. As a result of the heating, the resist composition
of the photoresist pattern 30a starts to flow and simultaneously a
crosslinking reaction partially occurs in the flowing resist
composition due to the crosslinking agent that is activated at a
temperature higher than the transition temperature. In the
embodiment that employs free radical initiators as the crosslinking
agents, free radicals are produced in the photoresist pattern 30a
from the free radical initiators which are activated at a
temperature higher than the transition temperature. Because of the
presence of the free radicals, a partial cross-linking reaction
occurs in the flowing resist composition.
[0044] While the photoresist pattern 30a is heated to a temperature
higher than the transition temperature, a partial cross-linking
reaction and the thermal flow of the resist composition are
believed to simultaneously occur such that the overall flow rate of
the photoresist pattern 30a can be more easily controlled. Thus,
distortion of the profile of the photoresist pattern 30a at the
side walls may be minimized. The species and amount of the
crosslinking agent to be added, and the heating temperature and
heating duration may be determined by one skilled in the art in
order to potentially adjust the degree of cross-linking reaction
such as by, for example, free radicals. Stated differently, the
degree of crosslinking in the resist composition can be adjusted to
a desired level by appropriately selecting the species of the
crosslinking agent, and by appropriately selecting the heating
temperature and the heating duration.
[0045] As a result of heating the photoresist pattern 30a to a
temperature higher than the transition temperature of the at least
one compound for a predetermined duration, a modified photoresist
pattern 30b, having a plurality of reduced openings H2, each of
which exposes the target layer 20 and has a desired width D2
smaller than the width D1, is formed as shown in FIG. 1C.
[0046] The resultant structure having the modified photoresist
pattern 30b is then cooled to room temperature. The width D2 of the
reduced opening H2 can be as small as about 0.05 to about 0.2 .mu.m
which may exceed the wavelength limit of a general photolithography
process.
[0047] Heating the structure illustrated in FIG. 1C to a
temperature higher than the transition temperature is performed
only once in this embodiment, However, it should be appreciated by
one skilled in the art that this heating process can be repeated
many times as required. In this case, the heating temperature can
be increased gradually in each step. It is preferable, however,
that the temperature be cooled to room temperature after each
heating step.
[0048] Referring to FIG. 1D, the target layer 20 exposed through
the reduced openings H2 is dry etched using the modified
photoresist pattern 30b as an etching mask. Pattern 20a having
contact holes H3 exposing the semiconductor substrate 10 is thus
formed.
[0049] The invention is believed to be advantageous. As described
above, the methods of the invention allow for forming photoresist
patterns using the resist composition described herein. By heating
the temperature of the resist composition to a temperature higher
than the transition temperature of the resist composition, a
crosslinking reaction is effected simultaneously with the flow of
the resist composition (which is activated by virtue of being
exposed to the transition temperature) and the flow rate of the
resist composition in the photoresist pattern can be more easily
controlled. When openings in the photoresist pattern become
sufficiently small because of a thermal flow process, distortion of
the side walls of the resultant contact holes may be minimized.
Thus, a vertical side wall profile may result which is highly
desirable.
[0050] As emphasized herein, the present invention is not limited
to the embodiments described herein. As an example, the invention
may be applied to the formation of line end space patterns, in
addition to the formation of fine patterns having small feature
sizes of from about 0.05 to about 0.2 .mu.m which goes beyond the
wavelength limit in the conventional photolithography.
[0051] The examples are set forth to illustrate the invention and
are not meant as a limitation thereon.
EXAMPLE 1
[0052] The dependency of the resist composition containing at least
one compound capable of forming a photoresist pattern and a free
radical initiator on temperature was evaluated as follows.
[0053] First, 10 gms of SEPR-430 (manufactured by ShinEtsu Co. of
Tokyo, Japan) as a chemically amplified resist and 0.06 g of
benzoyl peroxide (BPO) as a free radical initiator were mixed to
obtain a resist composition. Then, a photoresist pattern having a
plurality of openings of a size of 280 nm (1:2 pitch) was formed on
a wafer using the resist compound by a general method.
[0054] A plurality of samples, i.e., wafers each having the
photoresist pattern, were prepared and heated to 155.degree. C.,
160.degree. C., 162.degree. C. and 164.degree. C., respectively,
for 120 seconds to induce thermal flow of the photoresist pattern.
The samples were then cooled at room temperature.
[0055] The opening size of each contact hole formed in each
resultant modified photoresist pattern was measured under 0.4, 0.2
and 0 depth of focus (DOF), and the amount of flow of the
photoresist pattern during the thermal process was calculated from
the results. The results are shown in FIG. 2.
[0056] FIG. 2 shows that when a photoresist pattern formed by the
method for forming a fine pattern according to the present
invention is caused to flow by application of heat, the amount of
flow of the photoresist pattern linearly increases as the
temperature of the thermal process increases. The minimal
distortion of the photoresist pattern in all the modified
photoresist patterns after thermal flow, resulting in contact holes
each having vertical sidewalls is not illustrated in this figure.
Also, it can be hypothesized that the higher the predetermined
temperature of the thermal process, the smaller the opening size of
the contact holes.
EXAMPLE 2
[0057] The effect of the content of the free radical initiator used
as a crosslinking agent in the resist composition according to the
present invention was evaluated as follows.
[0058] The DUV resist SEPR-430, commercially available from
ShinEtsu Co. was employed as a chemically amplified resist, and 0,
4, 6 or 8 wt % of benzoyl peroxide (BPO) as a free radical
initiator, were mixed to obtain a resist composition. Then, a
photoresist pattern having a plurality of openings each having an
opening size of 320 nm (1:2 pitch) was formed on each wafer using
the resist composition by employing a general method. For the
photoresist pattern, soft baking was carried out at 100.degree. C.
for 90 seconds and post-exposure baking (PEB) was performed at
115.degree. C. for 90 seconds.
[0059] A plurality of samples, that is, wafers each having the
photoresist pattern, were prepared and heated to 145.degree. C.,
150.degree. C., 155.degree. C., 160.degree. C. and 165.degree. C.,
respectively, for 120 seconds to induce thermal flow of the
photoresist pattern, and then cooled at room temperature.
[0060] The opening size of each contact hole formed in each
resultant modified photoresist pattern was measured, and the amount
of flow of the photoresist pattern during the thermal process was
calculated from the results. Table 1 below shows the results.
1TABLE 1 Temperature Resist of thermal ADI AFI .DELTA. Flow
compound process (.degree. C.) (nm) (nm) (nm) Profile Resist + 145
320 262 58 Tapered 0 wt % of BPO 150 320 214 106 Tapered 155 320 70
250 Tapered 160 320 0 Overflow Distorted (open failure) 165 320
(open Overflow Distorted failure) Resist + 145 320 320 0 vertical 4
wt % of BPO (no flow) 150 320 290 30 vertical 155 320 260 60
vertical 160 320 120 200 vertical 165 320 (open Overflow open
failure) failure Resist + 145 320 320 0 vertical 6 wt % of BPO (no
flow) 150 320 304 16 vertical 155 320 286 34 vertical 160 320 252
68 vertical 165 320 86 234 vertical Resist + 145 320 320 0 vertical
8 wt % of BPO (no flow) 150 320 320 0 vertical (no flow) 155 320
320 0 vertical (no flow) 160 320 320 0 vertical (no flow) 165 320
308 12 vertical
[0061] In Table 1, "ADI" (After Development Inspection) describes
the size of openings formed in a photoresist pattern after
development, "AFI" (After Flow Inspection) describes the size of
openings in the modified photoresist pattern obtained through
thermal flow, and ".DELTA. Flow" (the difference between the ADI
and AFI) indicates the amount of flow of the photoresist pattern.
Also, In the column of "Profile", the profile of the contact holes
at the side walls, formed in the modified photoresist pattern, are
described.
EXAMPLE 3
[0062] Table 2 shows the results of an experiment conducted in
order to investigate the effect content of the free radical
initiator contained in the resist composition. An i-line resist
ip3300, commercially available from Tokyo Ohka Kogyo Co. of Tokyo,
Japan, was employed and 0 wt % and 8 wt % of BPO based on the
weight of the resist, as a free radical initiator, were added to
the resist to prepare resist compositions.
[0063] Then, a photoresist pattern having a plurality of openings
of the size of 510 nm was formed on wafers using those compounds
formed by a general method. For the photoresist pattern, soft
baking was carried out at 110.degree. C. for 90 seconds and PEB was
performed at 110.degree. C. for 90 seconds.
[0064] A plurality of samples, that is, wafers each having the
photoresist pattern, were prepared and heated to 150.degree. C.,
155.degree. C., 157.degree. C. and 159.degree. C., respectively,
for 120 seconds to lead a thermal flow of the photoresist pattern,
and then cooled at room temperature.
[0065] The opening size of each contact hole formed in each
resultant modified photoresist pattern was measured, and the amount
of flow of the photoresist pattern during the thermal process was
calculated from the results. The results are shown in Table 2.
[0066] In Table 2, "ADI", "AFI", ".DELTA. Flow" and "Profile" have
the same meanings as set forth in Table 1. From the results of the
Examples 2 and 3, it can be seen that it may be possible to control
the opening size of the contact holes formed in the modified
photoresist pattern which is obtained through thermal flow using
the resist composition according to the present invention. Also, as
the content of the crosslinking agent (e.g., free radical
initiator) in the resist composition increases, the amount of flow
of the photoresist pattern may decrease, and relatively larger
contact holes can be formed. Therefore, by adjusting the content of
the crosslinking agent in the resist composition, contact holes
having a desired size can be obtained.
2TABLE 2 Temperature Resist of thermal ADI AFI .DELTA. Flow
compound process (.degree. C.) (nm) (nm) (nm) Profile Resist + 150
510 196 314 Tapered 0 wt % of BPO 155 510 10 500 Tapered 157 510 0
Overflow Distorted (open failure) 159 510 0 Overflow Distorted
(open failure) Resist + 150 510 425 85 Vertical 6 wt % of BPO 155
510 262 248 Vertical 157 510 190 320 Vertical 159 510 124 386
Vertical
[0067] Hereinafter, detailed embodiments for forming fine contact
holes in a semiconductor substrate by the method according to the
present invention will now be described.
EXAMPLE 4
[0068] 0.06 g of BPO was employed as a free radical initiator was
added to 10 gms of the i-resist solution ip-3300, commercially
available from Tokyo Ohka Kogyo Co. The mixture was completely
dissolved, resulting in a resist composition. The mixture was
filtered through a 0.2 .mu.m membrane filter. The resist
composition was coated on a silicon wafer treated with
hexamethyldisilazane (HMDS) to a thickness of about 0.7 .mu.m.
[0069] Soft backing was carried out on the wafer coated with the
resist composition at 100.degree. C. for 90 seconds, the resultant
structure was exposed using an i-line stepper having a numerical
aperture of 0.63, and post-exposure baking (PEB) was performed at
100.degree. C. for 90 seconds. Then, the resultant structure was
developed using 2.38 wt % of tetramethylammonium hydroxide (TMAH)
solution, resulting in a photoresist pattern having a plurality of
openings with an opening size of 0.35 .mu.m (1:2 pitch).
[0070] The wafer on which the photoresist pattern had been formed
was heated at 150.degree. C. for 120 seconds to induce thermal flow
of the photoresist pattern. The wafer was thereafter cooled to room
temperature, to form a modified photoresist pattern having a
plurality of contact holes with an opening size of 0.3 .mu.m.
EXAMPLE 5
[0071] 0.06 g of BPO as a free radical initiator and 2 mg of
N,N'-diethylaniline as an organic base were added to 10 gms of the
i-line resist solution ip-3300, commercially available from Tokyo
Ohka Kogyo Co. These compounds and completely dissolved, resulting
in a resist composition. The mixture was filtered through a 0.2
.mu.m membrane filter. The resist composition was then coated on a
silicon wafer treated with HMDS to a thickness of about 0.7
.mu.m.
[0072] Soft baking was carried out on the wafer coated with the
resist composition at 100.degree. C. for 90 seconds. The resultant
structure was then exposed using an i-line stepper having a
numerical aperture of 0.63, and PEB was performed at 100.degree. C.
for 90 seconds. Then, the resultant structure was developed using
2.38 wt % of TMAH solution, resulting in a photoresist pattern
having a plurality of openings having an opening size of 0.35 .mu.m
(1:2 pitch).
[0073] The wafer on which the photoresist pattern had been formed,
was heated at 130.degree. C. for 120 seconds to lead thermal flow
of the photoresist pattern (first heating step) and cooled to room
temperature. Then, the resultant structure was heated for 120
seconds at 145.degree. C. which is higher than the temperature in
the first heating step, (second heating step). The structure was
thereafter cooled to room temperature, resulting in a modified
photoresist pattern having a plurality of contact holes with an
opening size of 0.3 .mu.m.
EXAMPLE 6
[0074] 0.06 g of BPO was employed as a free radical initiator and
was added to 10 gms of a DUV resist solution comprising acetal
protected-polyhydroxystyrene resin, SEPR-430, commercially
available from ShinEtsu Chemical Co. The contents were completely
dissolved, and a resist composition resulted. The mixture was
filtered through a 0.2 .mu.m membrane filter. The resist
composition was coated on a silicon wafer and treated with HMDS to
a thickness of about 0.6 .mu.m.
[0075] A soft baking process was carried out on the wafer coated
with the resist composition at 100.degree. C. for 90 seconds. The
resultant structure was exposed using a KrF stepper having a
numerical aperture of 0.45, and PEB was performed at 115.degree. C.
for 90 seconds. Then, the resultant structure was developed using
2.38 weight percent of TMAH solution, resulting in a photoresist
pattern having a plurality of openings with an opening size of 0.30
.mu.m (1:2 pitch).
[0076] The wafer in which the photoresist pattern had been formed,
was heated to 158.degree. C. for 120 seconds to induce thermal flow
of the photoresist pattern. The wafer was then cooled to room
temperature, resulting in a modified photoresist pattern having a
plurality of contact holes with an opening size of 0.22 .mu.m.
EXAMPLE 7
[0077] 0.06 g of BPO was employed as a free radical initiator and 2
mg of N,N'-diethylaniline used as an organic base were added to 10
gms of the DUV resist solution, SEPR-430, commercially available
from ShinEtsu Co. The contents were completely dissolved, resulting
in a resist composition. The mixture was filtered through a 0.2
.mu.m membrane filter. The resist composition was coated on a
silicon wafer treated with HMDS to a thickness of about 0.6
.mu.m.
[0078] A photoresist pattern having a plurality of openings with an
opening size of 0.30 .mu.m (1:2 pitch) was formed on a wafer under
the same conditions as in Example 6. Then, in order to induce
thermal flow of the photoresist pattern, the wafer on which the
photoresist pattern had been formed, was heated to 140.degree. C.,
which is the glass transition temperature of the resist, for 120
seconds (first heating step) and cooled to room temperature. Then,
the resultant structure was heated to 160.degree. C. which is
higher than the temperature in the first heating step, for 120
seconds (second heating step). The structure was thereafter cooled
to room temperature, resulting in a modified photoresist pattern
having a plurality of contact holes with an opening size of 0.20
.mu.m.
EXAMPLE 8
[0079] 0.06 g of cumyl peroxide as a free radical initiator was
added to 10 gms of the DUV resist solution UV-III, commercially
available from Shipley Co. of Philadelphia, Pa. The contents were
completely dissolved, resulting in a resist composition. The
mixture was filtered through a 0.2 .mu.m membrane filter. The
resist composition was coated on a silicon wafer treated with HMDS
to a thickness of about 0.6 .mu.m.
[0080] Soft baking was carried out on the wafer coated with the
resist composition at 130.degree. C. for 90 seconds, and the
resultant structure was exposed using a KrF stepper having a
numerical aperture of 0.45. PEB was thereafter performed at
140.degree. C. for 90 seconds. Then, the resultant structure was
developed using 2.38 wt % of TMAH solution, resulting in a
photoresist pattern having a plurality of openings with an opening
size of 0.30 .mu.m (1:2 pitch).
[0081] Then, in order to control the thermal flow of the
photoresist pattern, the wafer on which the photoresist pattern had
been formed was heated to 142.degree. C., for 120 seconds (first
heating step). This temperature is close to the glass transition
temperature of the resist. The wafer was thereafter cooled to room
temperature. Then, the resultant structure was heated to
160.degree. C. which is higher than the temperature in the first
heating step, for 120 seconds (second heating step). The wafer was
thereafter cooled to room temperature, resulting in a modified
photoresist pattern having a plurality of contact holes with an
opening size of 0.20 .mu.m.
EXAMPLE 9
[0082] 0.06 g of tert-butyl peroxide as a free radical initiator
was added to 10 gms of the DUV resist solution UV-III, commercially
available from the Shipley Chemical Co. The contents were
completely dissolved resulting in a resist composition. The mixture
was filtered through a 0.2 .mu.m membrane filter. The resist
composition was coated on a silicon wafer treated with HMDS to a
thickness of about 0.6 .mu.m.
[0083] A photoresist pattern having a plurality of openings with an
opening size of 0.30 .mu.m (1:2 pitch) was formed on a wafer under
the same conditions as in Example 8. Then, in order to control the
thermal flow of the photoresist pattern, the wafer on which the
photoresist pattern had been formed was heated to 145.degree. C.
for 120 seconds (first heating step), which is close to the glass
transition temperature of the resist. The wafer was thereafter
cooled to room temperature. Then, the resultant structure was
heated to 160.degree. C. which was higher than the temperature in
the first heating step, for 120 seconds (second heating step). The
structure is thereafter cooled to room temperature. A modified
photoresist pattern having a plurality of contact holes with an
opening size of 0.20 .mu.m was formed.
EXAMPLE 10
[0084] 1.0 g of poly(methyl methacrylate.sub.30-t-butyl
methacrylate.sub.40-methacrylic acid.sub.30) (weight average
molecular weight=13,500) and 0.02 g of triphenylsulfonium nonaflate
as a photo acid generator were dissolved in propylene glycol
monomethyl ether acetate (PGMEA) to prepare a resist solution. 0.06
g of tert-butyl peroxide as a free radical initiator and 2 mg of
N,N'-diethylaniline as an organic base were then added to the
resist solution and completely dissolved therein, resulting in a
resist composition. The mixture was then filtered through a 0.2
.mu.m membrane filter. Then, the resist composition was coated on a
silicon wafer and treated with HMDS such that a thickness of about
0.5 .mu.m was achieved.
[0085] Soft baking was carried out on the wafer coated with the
resist composition at 130.degree. C. for 90 seconds. The resultant
structure was exposed using an ArF stepper having a numerical
aperture of 0.60, and PEB was performed at 140.degree. C. for 90
seconds. Then, the resultant structure was developed using 0.14
weight percent of TMAH solution. A photoresist pattern resulted
having a plurality of openings with an opening size of 0.30 .mu.m
(1:2 pitch). The wafer in which the photoresist pattern had been
formed was heated to 165.degree. C. for 120 seconds to induce
thermal flow of the photoresist pattern. The wafer was then cooled
to room temperature, resulting in a modified photoresist pattern
having a plurality of contact holes with an opening size of 0.20
.mu.m.
EXAMPLE 11
[0086] 0.06 g of BPO was employed as a free radical initiator was
added to 10 gms of the i-line resist solution ip-3300, commercially
available from Tokyo Ohka Kogyo Co. The mixture was completely
dissolved, resulting in a resist composition. The mixture was
filtered through a 0.2 .mu.m membrane filter. The resist
composition was coated on a silicon wafer treated with
hexamethyldisilazane (HMDS) to a thickness of about 0.7 .mu.m.
[0087] Soft baking was carried out on the wafer coated with the
resist composition at 100.degree. C. for 90 seconds, the resultant
structure was exposed using an i-line stepper having a numerical
aperture of 0.63, and PEB was performed at 100.degree. C. for 90
seconds. Then, the resultant structure was developed using 2.38 wt
% of tetramethylammonium hydroxide (TMAH) solution, resulting in a
photoresist pattern having a plurality of openings with an opening
size of 0.35 .mu.m (1:2 pitch).
[0088] The wafer on which the photoresist pattern had been formed
was heated at 150.degree. C. for 120 seconds to induce thermal flow
of the photoresist pattern. A modified photoresist pattern resulted
having a plurality of contact holes with an opening size of 0.3
.mu.m.
EXAMPLE 12
[0089] 0.06 g of BPO was employed as a free radical initiator and 2
mg of N,N'-diethylaniline used as an organic base were added to 10
gms of the DUV resist solution, SEPR-430, commercially available
from ShinEtsu Co. The contents were completely dissolved, resulting
in a resist composition. The mixture was filtered through a 0.2
.mu.m membrane filter. The resist composition was coated on a
silicon wafer treated with HMDS to a thickness of about 0.6
.mu.m.
[0090] A photoresist pattern having a plurality of openings with an
opening size of 0.30 .mu.m (1:2 pitch) was formed on a wafer under
the same conditions as in Example 6. Then, in order to induce
thermal flow of the photoresist pattern, the wafer on which the
photoresist pattern had been formed was heated to 160.degree. C.
for 120 seconds. The structure was thereafter cooled to room
temperature, resulting in a modified photoresist pattern having a
plurality of contact holes with an opening size of 0.20 .mu.m.
EXAMPLE 13
[0091] 0.06 g of cumyl peroxide as a free radical initiator was
added to 10 gms of the DUV resist solution UV-III, commercially
available from Shipley Co. of Philadelphia, Pa. The contents were
completely dissolved, resulting in a resist composition. The
mixture was filtered through a 0.2 .mu.m membrane filter. The
resist composition was coated on a silicon wafer treated with HMDS
to a thickness of about 0.6 .mu.m.
[0092] Soft baking was carried out on the wafer coated with the
resist composition at 130.degree. C. for 90 seconds, and the
resultant structure was exposed using a KrF stepper having a
numerical aperture of 0.45. PEB was thereafter performed at
140.degree. C. for 90 seconds. Then, the resultant structure was
developed using 2.38 wt % of TMAH solution, resulting in a
photoresist pattern having a plurality of openings with an opening
size of 0.30 .mu.m (1:2 pitch).
[0093] Then, in order to control the thermal flow of the
photoresist pattern, the wafer on which the photoresist pattern had
been formed was heated to 155.degree. C. for 120 seconds. The wafer
was thereafter cooled to room temperature, resulting in a modified
photoresist pattern having a plurality of contact holes with an
opening size of 0.20 .mu.m.
EXAMPLE 14
[0094] 0.06 g of tert-butyl peroxide as a free radical initiator
was added to 10 gms of the DUV resist solution UV-III, commercially
available from the Shipley Chemical Co. The contents were
completely dissolved resulting in a resist composition. The mixture
was filtered through a 0.2 .mu.m membrane filter. The resist
composition was coated on a silicon wafer treated with HMDS to a
thickness of about 0.6 .mu.m.
[0095] A photoresist pattern having a plurality of openings with an
opening size of 0.30 .mu.m (1:2 pitch) was formed on a wafer under
the same conditions as in Example 13. Then, in order to induce the
thermal flow of the photoresist pattern, the wafer on which the
photoresist pattern had been formed is heated to 158.degree. C. for
120 seconds. The structure is thereafter cooled to room
temperature. A modified photoresist pattern having a plurality of
contact holes with an opening size of 0.20 .mu.m was formed.
[0096] The resist composition according to the present invention
may be formed by mixing the at least one compound present in a
solution with a crosslinking agent, selected according to the type
of at least one compound contained in the resist composition (e.g.,
solution). The crosslinking agent preferably causes an appropriate
crosslinking reaction at a temperature allowing for thermal flow of
the photoresist pattern, without affecting performance of the
resist composition. Therefore, when contact holes are formed in a
semiconductor substrate using the resist composition by the method
according to the present invention, the flow rate of the resist
composition in the photoresist pattern can be more easily
controlled with minimal distortion of the vertical profile of the
photoresist pattern.
[0097] Therefore, even after the thermal flow occurs, the overall
flow rate of the photoresist pattern can be more uniformly
controlled, so that distortion of the profile of the contact holes
at the side walls can be minimized. A vertical side wall profile
may be thus maintained. By employing the method for forming a fine
pattern according to the present invention, it is possible to
obtain a photoresist pattern having fine openings which is beyond
the capability of the general photolithography technology limited
by the wavelength of the exposure light.
[0098] While this invention has been particularly shown and
described with reference to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
spirit and scope of the invention as defined by the appended
claims.
* * * * *