U.S. patent application number 09/893267 was filed with the patent office on 2003-01-09 for process of drying a cast polymeric film disposed on a workpiece.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Goldfarb, Dario L., McCullough, Kenneth John, Medeiros, David R., Moreau, Wayne M., Simons, John P., Taft, Charles J..
Application Number | 20030008238 09/893267 |
Document ID | / |
Family ID | 25401298 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030008238 |
Kind Code |
A1 |
Goldfarb, Dario L. ; et
al. |
January 9, 2003 |
PROCESS OF DRYING A CAST POLYMERIC FILM DISPOSED ON A WORKPIECE
Abstract
A process of drying a cast film polymeric disposed upon a
workpiece. In this process a cast polymeric film, which includes a
volatile organic compound therein, disposed on a workpiece, is
contacted with an extraction agent which may be liquid carbon
dioxide or supercritical carbon dioxide.
Inventors: |
Goldfarb, Dario L.; (Putnam
Valley, NY) ; McCullough, Kenneth John; (Fishkill,
NY) ; Medeiros, David R.; (Ossining, NY) ;
Moreau, Wayne M.; (Wappinger, NY) ; Simons, John
P.; (Wappingers Falls, NY) ; Taft, Charles J.;
(Wappingers Falls, NY) |
Correspondence
Address: |
Steven Fischman, Scully, Scott, Murphy & Presser
400 Garden City Plaza
Garden City
NY
11530
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
ARMONK
NY
|
Family ID: |
25401298 |
Appl. No.: |
09/893267 |
Filed: |
June 27, 2001 |
Current U.S.
Class: |
430/272.1 ;
34/415 |
Current CPC
Class: |
Y10S 430/136 20130101;
F26B 5/005 20130101; G03F 7/162 20130101; G03F 7/168 20130101; F26B
21/14 20130101 |
Class at
Publication: |
430/272.1 ;
34/415 |
International
Class: |
G03C 011/16; G03C
001/73; G03F 007/004; G03F 007/26; F26B 005/00 |
Claims
What is claimed is:
1. A process of drying a cast polymeric film comprising contacting
a polymeric film, which includes a volatile organic compound
therein, disposed upon a workpiece, with an extraction agent
selected from the group consisting of liquid carbon dioxide and
supercritical carbon dioxide.
2. A process in accordance with claim 1 wherein said polymeric film
is photoresist film.
3. A process in accordance with claim 2 wherein said workpiece is a
silicon wafer.
4. A process in accordance with claim 1 wherein said workpiece is a
silicon wafer.
5. A process in accordance with claim 1 wherein said polymeric film
is contacted with said extraction agent at a pressure in the range
of between about 100 psi and about 10,000 psi and a temperature in
the range of between about -53.degree. C. and about 70.degree.
C.
6. A process in accordance with claim 5 wherein said pressure is in
the range of between about 200 psi and about 5,000 psi and said
temperature is in the range of between about -20.degree. C. and
about 50.degree. C.
7. A process in accordance with claim 1 wherein said extraction
agent is selected from the group consisting of a liquid carbon
dioxide composition and a supercritical carbon dioxide
composition.
8. A process in accordance with claim 7 wherein said liquid carbon
dioxide composition or said supercritical carbon dioxide
composition includes an inert solvent.
9. A process in accordance with claim 8 wherein said inert solvent
is present in a concentration of up to about 10% by weight, based
on the total weight of said composition.
10. A process in accordance with claim 7 wherein said inert solvent
is an inert hydrocarbon. 11. A process in accordance with claim 10
wherein said hydrocarbon is selected from the group consisting of
cyclohexane and xylene.
Description
BACKGROUND OF THE DISCLOSURE
[0001] 1. Field of the Invention
[0002] The present invention is directed to a process of drying a
cast polymeric film disposed on a workpiece. More specifically, the
present invention is directed to a process of drying a cast
polymeric film disposed on a workpiece by contacting the film with
liquid or supercritical carbon dioxide.
[0003] 2. Background of the Prior Art
[0004] The casting of polymeric films by such methods as spin
coating, spraying, dip coating or roller coating is commonly
employed in many commercially important processing operations. A
common concern in these processes is the removal of the solvent
constituent of the polymeric composition to obtain a polymeric film
free of solvent.
[0005] A particularly important example of such processing involves
the application of polymeric films on semiconductor workpieces in
the fabrication of semiconductor devices. The most important of
these polymeric films are photoresist compositions, which are
disposed on workpieces by spin coating. Commonly, photoresist
compositions are disposed on semiconductor wafers. This spin
coating step is followed by baking, on a elevated temperature
surface such as a hot plate, to drive off the solvent. This
standard method of drying cast photoresists films on semiconductor
workpieces is discussed in W. Moreau, "Semiconductor Lithography,"
Chapter 7, Plenum Press, 1988. Unfortunately, hot plate drying of
photoresists surfaces removes most of the solvent but, as taught by
Ito et al., J. Photopolymer Sci., 1, 625 (1999), up to about 7% by
weight of the solvent may remain in the cast photoresist film. This
residual solvent, as taught by U.S. Pat. Nos. 5,492,793 6,043,003
and Asakawa et al., J. Vac. Sci. Technol. B, 13(3), 833-838
(May/June 1995), adversely affects photoresists, especially
chemically amplified photoresists. Moreover, some photoresists, as
taught by Kwong et al. Spie Proc 3999, 591 (2000), are heat
sensitive and decompose at baking temperatures of 100.degree. C.
Specifically, photoresists known as "fast" photoresists, which
contain acid amplifiers, are particularly susceptible to this
problem.
[0006] An alternative method of removing solvent contained in
photoresists, vacuum drying, although an improvement, does not
remove all the solvent in a photoresist composition. The
aforementioned Ito et al. reference indicates that up to 4% by
weight of the solvent remains in the cast film after even one
complete month of vacuum drying. The retention of even 4% solvent
in a photoresist film, as those skilled in the art are aware,
reduces lithographic resolution of the photoresist film.
[0007] Other polymeric films, which are applied in solution,
especially those that are sprayed upon surfaces, such as protective
coatings including enamels, varnishes, polyurethanes and lacquers,
have, in the past, required the presence of organic solvents to
reduce their viscosity. These organic solvents are usually volatile
organic compounds (VOCs). As such, the adverse environmental impact
of such materials have led to increasing governmental regulation of
their use. This has resulted in attempts to reduce the use of these
VOCs by the development of several alternative compositions. Thus,
such alternatives as high solids coating, water-based coatings,
powder coatings, non-aqueous dispersions and supercritical carbon
dioxide compositions have been developed. None of these
alternatives, however, provide the excellent results obtained by
spray coating of protective coatings. Thus, the complete
elimination of VOCs, consistent with the production of a high
performance coating, has, up to the present time, not been
obtained.
[0008] It is appreciated that the development of supercritical
carbon dioxide compositions, as described in U.S. Pat. No.
5,106,650, represent a significant advance in the art. However,
many high performance coatings employ amine/epoxy systems. Such
systems are not compatible with supercritical carbon dioxide. This
is so insofar as conventional amine active sites are highly
reactive with carbon dioxide and tend to form amine carbamates that
reversibly release carbon dioxide. This reaction causes undesirable
results insofar as the resultant film is characterized by the
presence of crystals, voids and the like.
[0009] It is this result that discourages spin coating of
photoresist-liquid carbon dioxide solutions of the type described
in U.S. Pat. No. 6,001,418. Therefore, although this positive tone
development is a significant advance in the art, it is not
employable when positive tone photoresists are utilized. Since most
photoresist employed in the manufacture of semiconductor devices
are positive photoresists, the invention of the '418 patent is not
commercializable.
[0010] U.S. Pat. No. 5,716,763 describes a method of baking a
photoresist coating onto a semiconductor mask blank which overcomes
problems identified in the prior art for performing this task. In
this method a semiconductor substrate is immersed in a heated
liquid, e.g. a silicone oil, for a time and at a temperature
sufficient to obtain a uniform temperature throughout the
substrate. Insofar as the heated liquid is chemically inert with
respect to the temperature sensitive photoresist, this teaching has
no relationship to the drying of a polymeric film.
[0011] The above remarks establishes the need in the art for a new
process of drying cast photoresist and other polymeric
VOC-containing films. Such a desired process would permit drying of
the photoresist or other polymeric film at temperatures far below
typical baking temperatures currently employed to remove VOCs.
BRIEF SUMMARY OF THE INVENTION
[0012] A new process has been developed for removing volatile
organic compounds from photoresist and other polymeric compositions
which are cast or sprayed onto a substrate. In this new process
environmental problems associated with the removal of VOCs and,
concurrently, the removal of residual amounts of these volatile
compounds, which produce nonuniform coatings, is provided.
[0013] In accordance with the present invention a process is
provided for drying photoresists and other polymeric coatings and
films that are cast upon workpieces. In this process, the
photoresist or other polymeric film, which includes a volatile
organic compound therein, disposed upon a workpiece, is contacted
with a liquid or supercritical carbon dioxide wherein volatile
organic compounds contained therein are extracted therefrom.
[0014] In further accordance with the present invention an
apparatus for drying a polymeric film composition disposed upon a
workpiece is set forth. In that apparatus means for immersing a
workpiece, upon which a polymeric film composition is disposed, in
liquid or supercritical carbon dioxide is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention may be better understood by reference
to the accompanying drawings of which:
[0016] FIG. 1 is a schematic diagram of an apparatus employed in
the present invention for drying polymeric films disposed upon a
workpiece.
DETAILED DESCRIPTION
[0017] The present invention is directed to a process of drying a
polymeric film composition which includes residual amounts of a
solvent. Such polymeric film compositions usually result from the
casting of a polymeric material upon a workpiece although the
invention is not limited to any particular method defining the
manner upon which the polymeric film is cast upon a workpiece. In
this process the polymeric film composition, disposed upon a
workpiece, is placed in a controlled chamber which is maintained at
a pressure of at least about 100 pounds per square inch (psi) and a
temperature of at least about -53.degree. C. Preferably, the
thermodynamic conditions in the controlled chamber are maintained
at a pressure in the range of between about 100 psi and about
10,000 psi and a temperature in the range of between about
-53.degree. C. and about 70.degree. C. More preferably, the
thermodynamic conditions in the chamber are maintained at a
pressure in the range of between about 200 psi and about 5,000 psi
and a temperature in the range of between about -20.degree. C. and
about 50.degree. C.
[0018] In the chamber, the polymeric film composition is contacted
with an extracting effective amount of an extraction agent selected
from the group consisting of liquid carbon dioxide and
supercritical carbon dioxide. The liquid or supercritical carbon
dioxide extraction agent is provided neat or in a composition which
includes up to 10% by weight, based on the total weight of the
composition, of an inert solvent.
[0019] In the preferred embodiment wherein a composition is
provided the inert solvent is preferably an inert hydrocarbon. In
the event that the hydrocarbon is aliphatic, it is preferred that
the hydrocarbon be a linear or cyclic alkane. A particularly
preferred aliphatic hydrocarbon, useful as the solvent is
cyclohexane. A particularly preferred aromatic hydrocarbon is
xylene.
[0020] The aforementioned process is practiced in an apparatus the
specific arrangement of which is depicted in FIG. 1. Therein, it is
seen that a process chamber in which drying occurs is denoted at
12. A workpiece upon which a polymeric film is disposed, is
depicted in FIG. 1 by reference numeral 16. The workpiece 16 is
specifically located in sample zone 14 of chamber 12. The process
chamber 12 is surrounded by a heater jacket 18 and may include a
stirring mechanism 20. Additionally, the process chamber 12
includes an inlet line 22, an outduct 24 and a thermocouple 26. The
inlet line 22 contains a high pressure pumping system 28 which is
in communication with a cylinder 30 for supplying supercritical
carbon dioxide to the process chamber 12. Thermocouple 26 is in
communication with a heater controller 32 which is utilized for
controlling and monitoring the temperature in the process chamber
12. The apparatus for conducting the process of the present
invention may also include a reservoir 34 for collecting and/or
purifying supercritical carbon dioxide that exits process chamber
12 through outduct 24. This material may then be recycled into
process chamber 12 through duct 35.
[0021] In the contact between the extraction agent and the
polymeric film, disposed on a workpiece, it is preferred, but not
essential, that the workpiece be disposed upon a turntable or other
rotating device to ensure that the extraction agent is distributed
uniformly over the polymeric film. This embodiment provides the
advantage of permitting polymeric film casting and solvent
extraction to occur in the same apparatus. As those skilled in the
art are aware, casting of polymeric films, such as photoresists,
typically occur by casting the polymeric composition on a rotating
workpiece, such as by being disposed on a turntable.
[0022] As stated above, the polymeric film is provided on a
workpiece. The workpiece may be a silicon wafer, a circuit board, a
chrome mask blank, a membrane mask or the like. Preferably, the
workpiece is a silicon wafer. The polymeric film composition is any
polymeric film which is formed from a solution of a polymer and a
solvent. In a preferred embodiment the polymeric film is a
photoresist material. More preferably, the photoresist polymer is a
positive photoresist, such as a diazoquione/novolak, a
polychloroacrylate/methylstyrene material or the like, which is
commonly employed in processing of semiconductor materials.
[0023] The following examples are given to illustrate the scope of
the present invention. Because these examples are given for
illustrative purposes only, the invention should not be deemed
limited thereto.
EXAMPLE 1
[0024] A first photoresist composition was spun cast upon a silicon
wafer. The first photoresist composition was KRS.RTM., a
ketal-protected polyhydroxystyrene chemically amplified photoresist
described in U.S. Pat. No. 6,043,003, which is incorporated herein
by reference. A second photoresist was also spun cast upon a
silicon wafer. The second photoresist was ZEP.RTM., a commercial
electron beam photoresist manufactured by Nippon Zeon. This
photoresist is based on polychloroacrylate and
poly-.alpha.-methylstyrene. In addition, a third spin cast film,
not a photoresist, SiLK.RTM., a poly(ethynylbenzene), manufactured
by Dow Corning, was similarly disposed upon a silicon wafer.
SiLK.RTM. is a dielectric insulating material usually disposed
between a substrate and a photoresist layer in the formation of
semiconductor devices.
[0025] Three identical samples of each of these three spin cast
films on silicon wafers were prepared. One of each of the three
devices was processed in accordance with the prior art method of
heating the cast film on a hot plate at a temperature of about
100.degree. C. to remove volatile organic solvents. Two samples of
each of the three film-coated silicon wafers were processed in
accordance with the present invention. In a first processing
scheme, in accordance with the present invention, the samples were
contacted with supercritical carbon dioxide at a temperature of
32.degree. C. and at a pressure of 2,000 psi. In a second
processing procedure, also in accordance with the present
invention, the supercritical carbon dioxide was applied at a
temperature of 70.degree. C. and a pressure of 5,000 psi.
[0026] The films of the nine thus processed workpieces were then
measured to determine their thicknesses. This measurement provides
a determination of the degree of solvent removal. The thinner the
film thickness, the greater the degree of solvent removal. However,
it is emphasized, that in the case of the dielectric insulating
material, SiLK.RTM., the product was thereupon cured at 300.degree.
C. in accordance with usual dielectric insulating layer formation
practice. Thus, the dielectric layer film thickness does not
conclusively establish the degree of solvent removal.
[0027] A second test was conducted which is determinative of
solvent concentration reduction in photoresist films. That test is
a measure of refractive index. The refractive index of the films of
the nine samples were measured at 248 nm. Those skilled in the art
are aware that the greater the solvent concentration, the lower is
the refractive index insofar as organic solvents have lower
refractive indeces than does photoresist polymers. Again, this
principle does not apply to the refractive index of SiLK.RTM.
which, as stated above, is subsequently cured at 300.degree. C.
driving off any residual organic solvent.
[0028] Finally, in a third test, the aforementioned samples were
tested to determine the absorptivity of the films at 248 nm.
Photoresists having low absorptivity are preferred since low
absorptivity is consistent with good lithographic performance.
[0029] The results of the test are summarized in the Table.
1TABLE Refractive Index @ Absorptivity @ Polymeric Film Solvent
Removal Film Thickness, .ANG. 248 nm 248 nm KRS .RTM. Photoresist
Hot Plate 8639 1.805 0.009 KRS .RTM. Photoresist 2000 psi @
32.degree. C. 8520 1.835 0.019 KRS .RTM. Photoresist 5000 psi @
70.degree. C. 7615 1.814 0.010 ZEP .RTM. Photoresist Hot Plate 2012
1.710 0.002 ZEP .RTM. Photoresist 2000 psi @ 32.degree. C. 1993
1.714 0.002 ZEP .RTM. Photoresist 5000 psi @ 70.degree. C. 1880
1.832 0.006 SiLK .RTM. Dielectric Hot Plate 5441 1.871 0.171 SiLK
.RTM. Dielectric 2000 psi @ 32.degree. C. 5439 1.863 0.179 SiLK
.RTM. Dielectric 5000 psi @ 70.degree. C. 5525 1.844 0.173
DISCUSSION OF RESULTS OF EXAMPLE 1
[0030] The film thickness and refractory index data of the
photoresist films establish that the degree of solvent removal was
greater when supercritical carbon dioxide was employed as the
extraction agent compared to solvent removal by the prior art
process of heating the cast films on a hot plate at temperatures as
high as 100.degree. C. Thus, improved photoresist characteristics
are obtained after processing of the photoresist layer in
accordance with the present invention.
[0031] The absorptivity of the photoresist films data in all three
solvent removal processes was substantially of the same order of
magnitude. As such, this data establishes that the process of the
present invention does not have any adverse effect upon the
chemical characteristics of the photoresist layer compared to the
processes employed in the prior art.
[0032] Turning to the data directed to the dielectric film, that
data establishes substantial identity in the characteristics of
films formed in accordance with the prior art method and the method
of the present invention.
[0033] In all cases, then, the present invention represents a
significant advance in the art insofar as the environmental
improvement of avoiding venting of harmful volatile organic
solvents into the atmosphere is provided without any detrimental
effect upon the physical properties of the cast photoresist or
other polymeric films. Furthermore, in view of the very high cost
of the ultra pure solvents employed in semiconductor fabrication,
the recovery of solvent, obtainable in the present invention,
involves a considerable economic advantage of the process of the
present invention over the processes of the prior art.
EXAMPLE 2
[0034] The KRS.RTM. photoresist film of Example 1 in which solvent
extraction took place at 2000 psi and 32.degree. C. was cured by
exposure to ultraviolet light and then developed in an alkaline
solution.
[0035] This successful processing of the KRS.RTM. further
emphasizes the benefits of the solvent extraction process of the
present invention. That is, the successful curing of the KRS.RTM.
photoresist film is indicative of the absence of any loss of
photoacid generator, an essential ingredient in the curing of the
photoresist film.
[0036] The above embodiments and examples are provided to
illustrate the scope and spirit of the present invention. These
embodiments and examples will make apparent, to those skilled in
the art, other embodiments and examples. Those other embodiments
and examples are within the contemplation of the present invention.
Therefore, the present invention could be limited by the appended
claims.
* * * * *