U.S. patent application number 14/260666 was filed with the patent office on 2014-10-30 for method of patterning a device.
The applicant listed for this patent is Orthogonal, Inc.. Invention is credited to Frank Xavier Byrne, John Andrew DeFranco, Diane Carol Freeman, Charles Warren Wright.
Application Number | 20140322656 14/260666 |
Document ID | / |
Family ID | 51789517 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140322656 |
Kind Code |
A1 |
Wright; Charles Warren ; et
al. |
October 30, 2014 |
METHOD OF PATTERNING A DEVICE
Abstract
A photoresist layer comprising a fluorinated photoresist
material is formed on a device substrate and exposed to patterned
radiation. The exposed photoresist layer is contacted with a
developing agent to remove a portion of the exposed photoresist
layer in accordance with the patterned light, thereby forming a
developed structure having a first pattern of photoresist covering
the substrate and a complementary second pattern of uncovered
substrate corresponding to the removed portion of photoresist, the
developing agent comprising a mixture of first and second
fluorinated solvents, wherein at least one of the first and second
solvents is a hydrofluoroether. The developed structure is treated
to form a treated structure. The treated structure is contacted
with a stripping agent to remove the first pattern of photoresist,
the stripping agent comprising at least the first or second solvent
in a concentration different from the developing agent.
Inventors: |
Wright; Charles Warren;
(Fairport, NY) ; Freeman; Diane Carol; (Pittsford,
NY) ; Byrne; Frank Xavier; (Webster, NY) ;
DeFranco; John Andrew; (Rochester, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Orthogonal, Inc. |
Rochester |
NY |
US |
|
|
Family ID: |
51789517 |
Appl. No.: |
14/260666 |
Filed: |
April 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61815465 |
Apr 24, 2013 |
|
|
|
Current U.S.
Class: |
430/325 ;
430/331 |
Current CPC
Class: |
G03F 7/325 20130101;
G03F 7/0046 20130101; G03F 7/038 20130101; G03F 7/0397 20130101;
G03F 7/426 20130101; G03F 7/422 20130101; G03F 7/20 20130101; G03F
7/40 20130101; G03F 7/0392 20130101 |
Class at
Publication: |
430/325 ;
430/331 |
International
Class: |
G03F 7/40 20060101
G03F007/40 |
Goverment Interests
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with Government support under SBIR
Phase II Grant No. 1058509 awarded by the National Science
Foundation (NSF). The government may have certain rights in the
invention.
Claims
1. A method of patterning a device, comprising: forming on a device
substrate a photoresist layer comprising a fluorinated photoresist
material; exposing the photoresist layer to patterned radiation to
form an exposed photoresist layer; contacting the exposed
photoresist layer with a developing agent to remove a portion of
the exposed photoresist layer in accordance with the patterned
radiation, thereby forming a developed structure having a first
pattern of photoresist covering the substrate and a complementary
second pattern of uncovered substrate corresponding to the removed
portion of photoresist, the developing agent comprising a mixture
of a first and second fluorinated solvents, wherein at least one of
the first and second solvents is a hydrofluoroether; treating the
developed structure to form a treated structure; and contacting the
treated structure with a stripping agent to remove the first
pattern of photoresist, the stripping agent comprising at least the
first or second solvent in concentrations different from the
developing agent.
2. The method of claim 1 wherein both the first and second solvents
are hydro fluoro ethers.
3. The method of claim 2 wherein the stripping agent comprises a
mixture of first and second solvents in a ratio different from the
developing agent.
4. The method of claim 2 wherein at least one of the first and
second solvents is a hydrofluoroether selected from the group
consisting of an isomeric mixture of methyl nonafluorobutyl ether
and methyl nonafluoroisobutyl ether, an isomeric mixture of ethyl
nonafluorobutyl ether and ethyl nonafluoroisobutyl ether,
3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl-hexane,
1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3,-hexafluoropropoxy)-pentane,
1-methoxyheptafluoropropane,
1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-trifluoromethyl-pentane,
1,3-(1,1,2,2-tetrafluoroethoxy)benzene,
1,2-(1,1,2,2-tetrafluoroethoxy)ethane,
1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoropentyl ether,
1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether,
1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and
1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane-propyl ether.
5. The method of claim 1 wherein the substrate comprises a support
and a layer of active organic material, and wherein the photoresist
layer is in contact with the layer of active organic material.
6. The method of claim 5 wherein the treating includes chemical or
physical etching of the active organic material in the second
pattern of uncovered substrate to form a patterned layer of active
organic material corresponding to the first pattern.
7. The method of claim 1 wherein the treating includes providing a
layer of active organic material over both the first pattern of
photoresist and the second pattern of uncovered substrate, and
wherein the stripping further removes active organic material
formed over the first pattern of photoresist, thereby forming a
patterned layer of active organic material corresponding to the
second pattern.
8. The method of claim 1 wherein the developing agent or the
stripping agent is obtained at least in part from a recycled
mixture of the first and second solvents produced by a recycling
apparatus from a waste stream including the developing and the
stripping agent.
9. The method of claim 8 wherein the developing agent or the
stripping agent is obtained by combining the recycled mixture with
a substantially pure source of the first or second agent.
10. The method of claim 8 wherein the recycled mixture is used
directly as the stripping agent.
11. The method of claim 1 wherein the stripping agent further
comprises a protic solvent in a concentration range of 0.001% to 3%
by volume.
12. The method of claim 1 wherein the photoresist layer is formed
by depositing a photoresist agent onto the substrate, the
photoresist agent comprising a coating solvent and the fluorinated
photoresist material, wherein the coating solvent includes the
first or second solvent, or a mixture thereof.
13. The method of claim 1 wherein the boiling points of the first
and second solvents differ by at least 25.degree. C.
14. The method of claim 13 wherein each of the first and second
solvents is selected from the group consisting of an isomeric
mixture of methyl nonafluorobutyl ether and methyl
nonafluoroisobutyl ether, an isomeric mixture of ethyl
nonafluorobutyl ether and ethyl nonafluoroisobutyl ether,
3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl-he-
xane,
1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3,-hexafluoropropoxy)-pentane,
1-methoxyheptafluoropropane,
1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-trifluoromethyl-pentane,
1,3-(1,1,2,2-tetrafluoroethoxy)benzene,
1,2-(1,1,2,2-tetrafluoroethoxy)ethane,
1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoropentyl ether,
1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether,
1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and
1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane-propyl ether.
15. The method of claim 13 wherein the developing agent comprises
the first solvent in a volume range of 75 to 99% and the second
solvent in a volume range of 1 to 25%.
16. The method of claim 13 wherein the stripping agent comprises
the second solvent in a volume range of 15 to 99% and the first
solvent in a volume range of 1 to 85%.
17. The method of claim 2 wherein the fluorinated photoresist
material has a fluorine content of 15 to 60% by weight.
18. The method of claim 17 wherein the fluorinated photoresist
material comprises a photopolymer including a first repeating unit
having a fluorinated alkyl group and a second repeating unit having
an acid-forming or alcohol-forming precursor group.
19. The method of claim 1 wherein before exposing the photoresist
layer to patterned radiation, photoresist material is removed from
an edge area of the device substrate using an edge bead removal
solvent comprising one or both of the first and second
solvents.
20. The method of claim 1 wherein the device includes an organic
thin film transistor, an organic solar cell, an organic light
emitting diode, a bioelectronic sensor or an organic
conductor-based touch sensor.
21. A photoresist system comprising: a) a developing agent
comprising a first solvent and a second solvent, wherein both
solvents are fluorinated solvents and at least one is a
hydrofluoroether; b) a photoresist coating composition comprising a
fluorinated photoresist material and a coating solvent, the coating
solvent comprising at least one of the first and second solvents;
and c) a stripping agent comprising at least one of the first and
second solvents in concentrations different from the developing
solution.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/815,465, filed on Apr. 24, 2013, the entire
disclosure of which is hereby incorporated herein by reference.
This application is also related to U.S. patent application Ser.
No. ______ entitled "Method of Patterning a Device," Attorney
Docket No. 16480.0012USU2, filed on even date herewith.
BACKGROUND
[0003] 1. Field of the Invention
[0004] The present invention relates to the use of fluorinated
solvents and solvent blends for processing fluorinated
photoresists. Such solvents and photoresists are particularly
useful for patterning organic electronic and biological
materials.
[0005] 2. Discussion of Related Art
[0006] Organic electronic devices offer significant performance and
price advantages relative to conventional inorganic-based devices.
As such, there has been much commercial interest in the use of
organic materials in electronic device fabrication. Specifically,
organic materials such as conductive polymers can be used to
manufacture devices that have reduced weight and drastically
greater mechanical flexibility compared to conventional electronic
devices based on metals and silicon. Further, devices based on
organic materials are likely to be significantly less damaging to
the environment than devices made with inorganic materials, since
organic materials do not require toxic metals and can ideally be
fabricated using relatively benign solvents and methods of
manufacture. Thus, in light of these superior weight and mechanical
properties, and particularly in light of the lowered environmental
impact in fabrication and additionally in disposal, electronic
devices based on organic materials are expected to be less
expensive than devices based on conventional inorganic
materials.
[0007] Fabrication of electronic devices, whether from organic or
inorganic materials, requires the creation on an industrial scale
of precisely defined patterns of the organic or inorganic active
materials in these devices, often at a microscopic level. Most
commonly, this is accomplished by "photolithography," in which a
light-sensitive "photoresist" film that has been deposited on a
substrate is exposed to patterned light. Although this can be done
in numerous ways, typically a microscopic pattern of light and
shadow created by shining a light through a photographic mask is
used to expose the photoresist film, thereby changing the chemical
properties of the portions of the photoresist that have been
exposed to light. In a "positive" photoresist, the portions of the
photoresist that are exposed to light become soluble in the
"developer" solution that is then applied to the exposed
photoresist, and the light-exposed portions of the photoresist are
washed away ("developed") by the developer solvent to leave a
pattern of unexposed photoresist and newly exposed underlying
substrate. A "negative" photoresist is treated as for a positive
photoresist; however, in a negative photoresist, it is the
unexposed rather than the exposed portions of the photoresist that
are washed away by the developing step.
[0008] In a standard process, the photoresist material is laying on
top of an active material layer that is to be patterned. Once the
development has taken place, the underlying layer is etched using
either a liquid etchant or a reactive ion plasma (RIE) with the
appropriate etch chemistry. In either case, the photoresist layer
blocks the etching of active material directly beneath it. Once the
etching is complete, the resist is typically stripped away, leaving
the pattern of active material on the substrate.
[0009] Alternatively, the photoresist can be used with a so-called
"liftoff" technique. In this case, the resist is processed on a
substrate before the active material layer is deposited. After the
photoresist pattern is formed, the active material is deposited on
both the substrate and the photoresist. In an additional "lift-off"
or "stripping" step, remaining photoresist along with an overlying
layer of active material is removed via the appropriate solvent to
leave the desired patterned active material.
[0010] Although the use of photoresists is routine in traditional
electronic devices based on inorganic materials, photolithography
has been difficult to achieve for devices using organic materials,
thereby hindering the development of devices based on these
materials. Specifically, organic materials are much less resistant
to the solvents that are used for conventional photolithography, as
well as to the intense light sources that are sometimes used in
these processes, with the result that conventional lithographic
solvents and processes tend to degrade organic electronics.
Although there have been various attempts to overcome these
problems, e.g., by ink jet printing or shadow mask deposition,
these alternative methods do not produce the same results as would
be obtained with successful photolithography. Specifically, neither
ink jet printing nor shadow mask deposition can achieve the fine
pattern resolutions that can be obtained by conventional
lithography, with ink-jet printing limited to resolutions of
approximately 10-20 .mu.m and shadow mask deposition to resolutions
of about 25-30 .mu.m.
[0011] US 2011/0159252 discloses a useful method for patterning
organic electronic materials by an "orthogonal" process that uses
fluorinated solvents and fluorinated photoresists. The fluorinated
solvents have very low interaction with organic electronic
materials. WO 2012/148884 discloses additional fluorinated material
sets for orthogonal processing.
[0012] Although these disclosures demonstrate good progress, many
of the more useful fluorinated solvents can be expensive. Further,
the different processing steps (coating, developing and stripping)
have very different solvent needs, thereby necessitating the use of
multiple fluorinated solvents. The coating solvent must solubilize
the photoresist material sufficiently to allow good film formation
on a substrate. The developer must discriminate between exposed
regions and unexposed regions, i.e., dissolve only one or the
other. The stripping solvent must remove the remaining photoresist
that the developer solvent left behind. At the same time, they all
must not harm the active material (e.g., an organic
semiconductor).
[0013] To improve manufacturing costs, fluorinated solvents can in
theory be recovered and recycled as long as the cost of recycling
is not too high. US 2010/0126934 (Nakazato) discloses a method of
purifying used fluorine-based solvent solutions using a series of
steps including washing, treatment with activated carbon and
alumina, and filtration. Distillation is mentioned, but it is noted
that sufficient purity is difficult to achieve with distiller sizes
typically used in a normal cleaning apparatus. Although the
recycling method of Nakazato may help purify the fluorine-based
solvents of other materials, it will not separate different
fluorinated solvents.
[0014] WO2009031731 (Lee) discloses a method for recycling main
solvents from conventional photoresist stripper waste. The method
uses a first distillation device to remove low boiling point
impurities from the photoresist stripper waste solution, a second
distillation device to remove high boiling point impurities, and a
third distillation device to recycle individual stripper solutions.
Lee discloses that it is essential to develop a recycling technique
which is capable of recycling stripper waste solutions as highly
pure, electronic-grade stripper solutions. There is no disclosure
in Lee about also recycling developing solutions or recycling
fluorinated solvents.
[0015] U.S. Pat. No. 5,994,597 (Bhatt) discloses a multi-step
process of recovering low vapor pressure solvent waste, e.g.,
benzyl alcohol, propylene carbonate, or gamma butyrolactone, from a
conventional photoresist line. Bhatt further teaches that, for
reuse as a developing agent or stripping agent, it is necessary to
recover a purified solvent, i.e., a solvent that is typically 99 or
greater weight percent pure. There is no disclosure in Bhatt
regarding fluorinated solvents.
[0016] U.S. Pat. No. 8,377,626 (Kim) discloses photoresist polymers
and processing methods. There is a brief mention that developers
may include conventional organic solvents such as ketones,
acetates, ethers, and alcohols, and that they may be used alone or
in a mixture thereof. There is no disclosure in Kim about
fluorinated solvents or recycling developer or stripping
solutions.
[0017] US20100151395 (Ishiduka) discloses the use of a
fluorine-substituted polymer as a protective overcoat on a
photoresist for immersion photolithography. Prior to development
with a conventional aqueous alkaline developer, the protective
overcoat is removed using a hydrofluoroether solvent or solvent
mixture. Ishiduka does not disclose using hydrofluoroether solvents
as developers nor recycling mixtures of developer and stripping
solvents.
[0018] In light of the above, there is a need to provide a more
cost-effective fluorinated solvent system for use with fluorinated
photoresists.
SUMMARY
[0019] In accordance with the present disclosure, a method of
patterning a device using a fluorinated photoresist comprises:
[0020] forming a photoresist layer on a device substrate, the
photoresist layer comprising a fluorinated photoresist
material;
[0021] exposing the photoresist layer to patterned radiation to
form an exposed photoresist layer;
[0022] contacting the exposed photoresist layer with a developing
solution to remove a portion of the exposed photoresist layer in
accordance with the patterned radiation, thereby forming a
developed structure having a first pattern of photoresist covering
the substrate and a complementary second pattern of uncovered
substrate corresponding to the removed portion of photoresist, the
developing solution comprising a mixture of first and second
fluorinated solvents, wherein at least one of the first and second
solvents is a hydrofluoroether;
[0023] treating the developed structure to form a treated
structure; and
[0024] contacting the treated structure with a stripping solution
to remove the first pattern of photoresist, the stripping solution
comprising at least the first or second solvent in a concentration
different from the developing solution.
[0025] In another aspect of the present disclosure, a photoresist
system comprises: a) a developing solution comprising a first
solvent and a second solvent, wherein both solvents are fluorinated
solvents and at least one is a hydrofluoroether; b) a photoresist
coating composition comprising a fluorinated photoresist material
and a coating solvent, the coating solvent comprising at least one
of the first and second solvents; and c) a stripping solution
comprising at least one of the first and second solvents in a
concentration different from the developing solution.
[0026] In an embodiment, using a mixture of first and second
solvents in the developing solution can improve development
performance. In an embodiment, using a stripping solution that
includes at least the first or second solvent of the developing
solution can simplify recycling of such solvents. In an embodiment,
using a mixture of first and second solvents in both the developing
solution and in the stripping solution (typically in different
ratios) can further improve recyclability of processing waste and
in some cases improve stripping performance. Enabling relatively
simple recycling of solvents from a photolithographic processing
waste stream can reduce manufacturing costs and the environmental
impact of the process.
BRIEF DESCRIPTION OF DRAWINGS
[0027] FIG. 1 is a flow chart depicting the steps in an embodiment
of the present invention;
[0028] FIG. 2A-2F is a series of cross-sectional views depicting
various stages in the formation of a patterned active organic
material structure according to an embodiment of the present
invention;
[0029] FIG. 3A-3D is a series of cross-sectional views depicting
various stages in the formation of a patterned active organic
material structure according to another embodiment of the present
invention; and
[0030] FIG. 4 is a representative plot of normalized thickness vs.
log (exposure) used to determine photoresist contrast.
DETAILED DESCRIPTION
[0031] It is to be understood that the attached drawings are for
purposes of illustrating the concepts of the invention and may not
be to scale.
[0032] A photoresist includes a light-sensitive material that can
be coated to produce a photo-patternable film. Photoresists can be
used to pattern devices, e.g., multilayer electronic devices,
optical devices, medical devices, biological devices and the like.
An embodiment of the present invention is directed to an improved
method of processing a fluorinated photoresist using mixtures of
fluorinated solvents in the developing solution, and selecting at
least one of the solvents from the developing solution for use in
the stripping solution. The solvents for the fluorinated
photoresist solution, the developing solution and stripping
solution are each chosen to have low interaction with other
material layers that are not intended to be dissolved or otherwise
damaged. Such solvents are collectively termed "orthogonal"
solvents. This can be tested by, for example, immersion of a device
comprising the material layer of interest into the solvent prior to
operation. The solvent is orthogonal if there is no serious
reduction in the functioning of the device.
[0033] Certain embodiments disclosed in the present disclosure are
particularly suited to the patterning of solvent-sensitive, active
organic materials. Examples of active organic materials include,
but are not limited to, organic electronic materials, such as
organic semiconductors, organic conductors, OLED (organic
light-emitting diode) materials and organic photovoltaic materials,
organic optical materials, medical materials and biological
materials. Many of these materials are easily damaged when
contacted with organic or aqueous solutions used in conventional
photolithographic processes. Active organic materials are often
coated to form a layer that may be patterned. For some active
organic materials, such coating can be done from a solution using
conventional methods. Alternatively, some active organic materials
are preferentially coated by vapor deposition, for example, by
sublimation from a heated organic material source at reduced
pressure. Solvent-sensitive, active organic materials can also
include composites of organics and inorganics. For example, the
composite may include inorganic semiconductor nanoparticles
(quantum dots). Such nanoparticles may have organic ligands or be
dispersed in an organic matrix.
[0034] Depending on the particular material set and solvation needs
of the process, the fluorinated solvent may be selected from a
broad range of materials such as chlorofluorocarbons (CFCs),
hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs),
perfluorocarbons (FCs), hydrofluoroethers (HFEs), perfluoroethers,
perfluoroamines, trifluoromethyl-substituted aromatic solvents,
fluoroketones and the like.
[0035] Particularly useful fluorinated solvents include those that
are perfluorinated or highly fluorinated liquids at room
temperature, which are immiscible with water and many (but not
necessarily all) organic solvents. Among those solvents,
hydrofluoroethers (HFEs) are well known to be highly
environmentally friendly, "green" solvents. HFEs, including
segregated HFEs, are preferred solvents because they are
non-flammable, have zero ozone-depletion potential, lower global
warming potential and show very low toxicity to humans.
[0036] Examples of readily available HFEs and isomeric mixtures of
HFEs include, but are not limited to, an isomeric mixture of methyl
nonafluorobutyl ether and methyl nonafluoroisobutyl ether
(HFE-7100), an isomeric mixture of ethyl nonafluorobutyl ether and
ethyl nonafluoroisobutyl ether (HFE-7200 aka Novec.TM. 7200),
3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl-hexane
(HFE-7500 aka Novec.TM. 7500),
1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3,-hexafluoropropoxy)-pentane
(HFE 7600 aka Novec.TM. 7600), 1-methoxyheptafluoropropane
(HFE-7000),
1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-trifluoromethylpentane
(HFE-7300 aka Novec.TM. 7300),
1,3-(1,1,2,2-tetrafluoroethoxy)benzene (HFE-978m),
1,2-(1,1,2,2-tetrafluoroethoxy)ethane (HFE-578E),
1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoropentyl ether
(HFE-6512), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether
(HFE-347E), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl
ether (HFE-458E), and
1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane-propyl ether
(TE6O-C3).
[0037] As discussed below, the developing solution comprises a
mixture of first and second fluorinated solvents and the stripping
solution comprises at least the first or second fluorinated
solvent, or optionally both. In a particularly useful embodiment,
at least one of the solvents is a hydrofluoroether. In a preferred
embodiment, both solvents are hydrofluoroethers. It should be noted
that, although either or both of the first and second solvents can
each be an isomeric mixture (e.g., HFE-7100, HFE-7200 or any
fluorinated solvent comprising multiple stereoisomers), the first
and second solvents are not isomeric to each other. If an isomeric
mixture is used as the first or second solvent, the isomeric
components preferably have the same or similar boiling points,
i.e., within a range of 10.degree. C. and more preferably within a
range of 5.degree. C. (as measured at atmospheric pressure). In
some embodiments, minor amounts of a non-fluorinated solvent may be
added to the developing solution or stripping solution. Such
non-fluorinated solvents include chlorinated solvents, alcohols and
other protic organic solvents, and substituted or unsubstituted
hydrocarbons and aromatic hydrocarbons, so long as they are
miscible with the fluorinated solvent in the amounts desired for
the developing and stripping solutions and maintain orthogonal
behavior with respect to active organic materials.
[0038] The fluorinated photoresist of the present disclosure is one
that includes a fluorinated photoresist material that is at least
partially fluorinated, i.e., it contains one or more fluorine
atoms. In an embodiment, the weight percentage of fluorine in the
fluorinated photoresist material is at least 15%, preferably in a
range of 30 to 60%, and more preferably in a range of 35 to 50%.
The fluorinated photoresist material should have sufficient
solubility or dispersability in a fluorinated solvent or mixture to
permit adequate coating and processing. In an embodiment, the
fluorinated photoresist material is a polymer or copolymer. The
fluorinated photoresist may be a chemically amplified resist. A
coatable fluorinated photoresist solution may include a fluorinated
photoresist material and a coating solvent, and may optionally
further include one or more additional components such as a
photo-acid generator, a stabilizer, a light sensitizer, a light
filter, an acid scavenger (quencher) or a coating aid. A
photoresist layer comprising the fluorinated photoresist material
should be sensitive to radiation, e.g., UV or visible light,
e-beam, X-ray and the like, so that the solubility properties of
the exposed areas are selectively altered to enable development of
an image. In a preferred embodiment, the radiation is UV or visible
light.
[0039] Examples of fluorinated photoresists include, but are not
limited to, materials disclosed in application nos. U.S. Ser. No.
12/994,353, PCT/US2011/034145, and PCT/US2012/034748, along with
U.S. provisional application Nos. 61/829,523, 61/829,536,
61/829,551, 61/829,556, 61/857,890 and 61/903,450, the entire
contents of which are incorporated by reference.
[0040] In an embodiment the fluorinated photoresist includes a
photopolymer comprising first repeating unit having a
fluorine-containing group and a second repeating unit having a
solubility-altering reactive group. In an embodiment, the
solubility-altering reactive group may be an alcohol-forming
precursor group or an acid-forming precursor group such as a
carboxylic or sulfonic acid-forming precursor group. The term
"repeating unit" is used broadly herein and simply means that there
is more than one unit on a polymer chain. The term is not intended
to convey that there is necessarily any particular order or
structure with respect to the other repeating units unless
specified otherwise. The photopolymer may optionally be blended
with one or more other polymers, preferably other
fluorine-containing polymers. The total fluorine content of the
blended polymers may suitably be in a weight range of 15 to 60%,
preferably 30 to 55%, relative to the total weight of the blended
polymers. The photopolymer may be produced, for example, by
co-polymerizing suitable monomers containing the desired repeating
units or by functionalizing preformed polymers to attach desired
repeating units.
[0041] In an embodiment, the fluorine containing group of the first
monomer or the first repeating unit is a fluorine-containing alkyl
or aryl group that may optionally be further substituted with
chemical moieties other than fluorine, e.g., chlorine, a cyano
group, or a substituted or unsubstituted alkyl, alkoxy, alkylthio,
aryl, aryloxy, amino, alkanoate, benzoate, alkyl ester, aryl ester,
alkanone, sulfonamide or monovalent heterocyclic group, or any
other substituent that a skilled worker would readily contemplate
that would not adversely affect the performance of the fluorinated
photopolymer. In a preferred embodiment, the fluorine-containing
group is an alkyl group having at least 5 fluorine atoms, or
alternatively, at least 10 fluorine atoms. In an embodiment, the
alkyl group is a hydrofluorocarbon or hydrofluoroether having at
least as many fluorine atoms as carbon atoms. In an embodiment the
fluorine-containing group is perfluorinated alkyl or a
1H,1H,2H,2H-perfluorinated alkyl having at least 4 carbon atoms,
for example, 1H,1H,2H,2H-perfluorooctyl (i.e., 2-perfluorohexyl
ethyl). Throughout this disclosure, unless otherwise specified, any
use of the term alkyl includes straight-chain, branched and cyclo
alkyls. In an embodiment, the first repeating unit does not contain
protic or charged substituents, such as hydroxy, carboxylic acid,
sulfonic acid, quaternized amine or the like.
[0042] In an embodiment, the solubility-altering reactive group of
the second repeating unit is an acid-forming precursor group. Upon
exposure to light, the acid-forming precursor group generates a
polymer-bound acid group, e.g., a carboxylic or sulfonic acid. This
can drastically change its solubility relative to the unexposed
regions thereby allowing development of an image with the
appropriate solvent. In an embodiment, the developing solution
includes a fluorinated solvent that selectively dissolves unexposed
areas.
[0043] One class of acid-forming precursor groups includes the
non-chemically amplified type (i.e., non-acid catalyzed). An
example of a second monomer with such a group is 2-nitrobenzyl
methacrylate. The non-chemically amplified precursor group may
directly absorb light to initiate de-protection of the acid-forming
groups. Alternatively, a sensitizing dye may be added to the
composition whereby the sensitizing dye absorbs light and forms an
excited state capable of directly sensitizing or otherwise
initiating the de-protection of acid-forming precursor groups. The
sensitizing dye may be added as a small molecule or it may be
attached or otherwise incorporated as part of the copolymer. Unlike
chemically amplified formulations that rely on generation of an
acid (see below), non-chemically amplified photopolymers may
sometimes be preferred when a photopolymer is used in contact with
an acid-sensitive or acid-containing material. Some active organic
materials can be sensitive to the presence of an acid or contain
some acid.
[0044] A second class of acid-forming precursor groups includes the
chemically amplified type. This typically requires addition of a
photo-acid generator (PAG) to the photopolymer composition, e.g.,
as a small molecule additive to the solution. The PAG may function
by directly absorbing radiation (e.g. UV light) to cause
decomposition of the PAG and release an acid. Alternatively, a
sensitizing dye may be added to the composition whereby the
sensitizing dye absorbs radiation and forms an excited state
capable of reacting with a PAG to generate an acid. The sensitizing
dye may be added as a small molecule, e.g., as disclosed in U.S.
provisional application No. 61/857,890, which is incorporated
herein by reference. The sensitizing dye may be attached to or
otherwise incorporated as part of the copolymer, e.g., as disclosed
in U.S. provisional application Nos. 61/829,523, 61/829,536,
61/829,551, and 61/829,556, which are incorporated herein by
reference. In an embodiment, the sensitizing dye (either small
molecule or attached) is fluorinated. In an embodiment, the
sensitizing dye may be provided in a range of 0.5 to 10% by weight
relative to the total copolymer weight. The photochemically
generated acid catalyzes the de-protection of acid-labile
protecting groups of the acid-forming precursor. In certain cases,
such de-protection may occur at room temperature, but commonly, an
exposed chemically amplified photoresist is heated for a short time
("post exposure bake") to more fully activate de-protection. In
some embodiments, chemically amplified photopolymers can be
particularly desirable since they enable the exposing step to be
performed through the application of relatively low energy UV light
exposure (e.g., less than 500 mJ/cm.sup.2 or in some embodiments
under 100 mJ/cm.sup.2). This is advantageous since some active
organic materials useful in applications to which the present
disclosure pertains may decompose in the presence of too much UV
light, and therefore, reduction of the energy during this step
permits the photopolymer to be exposed without causing significant
photolytic damage to underlying active organic layers. Also,
reduced light exposure times improve the manufacturing throughput
of the desired devices.
[0045] Examples of acid-forming precursor groups that yield a
carboxylic acid include, but are not limited to: A) esters capable
of forming, or rearranging to, a tertiary cation, e.g., t-butyl
ester, 2-methyl-2-adamantyl ester, 1-ethylcyclopentyl ester,
1-ethylcyclohexyl ester, and isobornyl ester; B) esters of lactone,
e.g., -butyrolactone-3-yl, -butyrolactone-2-yl, mavalonic lactone,
3-methyl-butyrolactone-3-yl, 3-tetrahydrofuranyl, and
3-oxocyclohexyl; C) acetal esters, e.g., 2-tetrahydropyranyl,
2-tetrahydrofuranyl, and 2,3-propylenecarbonate-1-yl; D)
beta-cyclic ketone esters, E) alpha-cyclic ether esters and F)
MEEMA (methoxy ethoxy ethyl methacrylate) and other esters which
are easily hydrolyzable because of anchimeric assistance. In an
embodiment, the second monomer comprises an acrylate-based
polymerizable group and a tertiary alkyl ester acid-forming
precursor group, e.g., t-butyl methacrylate ("TBMA") or
1-ethylcyclopentyl methacrylate ("ECPMA").
[0046] In an embodiment, the solubility-altering reactive group is
an hydroxyl-forming precursor group (also referred to herein as an
"alcohol-forming precursor group"). The hydroxyl-forming precursor
includes an acid-labile protecting group and the photopolymer
composition typically includes a PAG compound and operates as a
"chemically amplified" type of system. Upon exposure to light, the
PAG generates an acid (either directly or via a sensitizing dye as
described above), which in turn, catalyzes the de-protection of the
hydroxyl-forming precursor group, thereby forming a polymer-bound
alcohol (hydroxyl group). This significantly changes its solubility
relative to the unexposed regions thereby allowing development of
an image with the appropriate fluorinated solvent. In an
embodiment, the developing solution includes a fluorinated solvent
that selectively dissolves unexposed areas.
[0047] In an embodiment, the hydroxyl-forming precursor has a
structure according to formula
##STR00001##
wherein R.sub.5 is a carbon atom that forms part of the second
repeating unit (or second polymerizable monomer), and R.sub.10 is
an acid-labile protecting group. Non-limiting examples of useful
acid-labile protecting groups include those of formula (AL-1),
acetal groups of the formula (AL-2), tertiary alkyl groups of the
formula (AL-3) and silane groups of the formula (AL-4).
##STR00002##
##STR00003##
[0048] In formula (AL-1), R.sub.11 is a monovalent hydrocarbon
group, typically a straight, branched or cyclic alkyl group, of 1
to 20 carbon atoms that may optionally be substituted with groups
that a skilled worker would readily contemplate would not adversely
affect the performance of the precursor. In an embodiment, R.sub.11
may be a tertiary alkyl group. Some representative examples of
formula (AL-1) include:
##STR00004##
[0049] In formula (AL-2), R.sub.14 is a monovalent hydrocarbon
group, typically a straight, branched or cyclic alkyl group, of 1
to 20 carbon atoms that may optionally be substituted. R.sub.12 and
R.sub.13 are independently selected hydrogen or a monovalent
hydrocarbon group, typically a straight, branched or cyclic alkyl
group, of 1 to 20 carbon atoms that may optionally be substituted.
Some representative examples of formula (AL-2) include:
##STR00005##
[0050] In formula (AL-3), R.sub.15, R.sub.16, and R.sub.17
represent an independently selected a monovalent hydrocarbon group,
typically a straight, branched or cyclic alkyl group, of 1 to 20
carbon atoms that may optionally be substituted. Some
representative examples of formula (AL-3) include:
##STR00006##
[0051] In formula (AL-4), R.sub.18, R.sub.19 and R.sub.20 are
independently selected hydrocarbon groups, typically a straight,
branched or cyclic alkyl group, of 1 to 20 carbon atoms that may
optionally be substituted.
[0052] The descriptions of the above acid-labile protecting groups
for formulae (AL-2), (AL-3) and (AL-4) have been described in the
context of hydroxyl-forming precursors. These same acid-labile
protecting groups, when attached instead to a carboxylate group,
may also be used to make some of the acid-forming precursor groups
described earlier.
[0053] Many useful PAG compounds exist that may be added to a
photopolymer composition. In the presence of proper exposure and
optional sensitization, this photo-acid generator will liberate an
acid, which will react with the second monomer portion of the
fluorinated photopolymer material to transform it into a less
soluble form with respect to fluorinated solvents. The PAG should
have some solubility in the coating solvent. The amount of PAG
required depends upon the particular system, but generally, will be
in a range of about 0.1 to 6% by weight relative to the copolymer.
In an embodiment, the presence of a sensitizing dye may
substantially reduce the amount of PAG required relative to a
composition that does not include a sensitizing dye. In an
embodiment, the amount of PAG is in a range of 0.1 to 3% relative
to the copolymer. PAGS that are fluorinated or non-ionic or both
are particularly useful. Some useful examples of PAG compounds
include
2-[2,2,3,3,4,4,5,5-octafluoro-1-(nonafluorobutylsulfonyloxyimino)-pentyl]-
-fluorene (ONPF) and
2-[2,2,3,3,4,4,4-heptafluoro-1-(nonafluorobutylsulfonyloxyimino)-butyl]-f-
luorene (HNBF). Other non-ionic PAGS include: norbornene-based
non-ionic PAGs such as N-hydroxy-5-norbornene-2,3-dicarboximide
perfluorooctanesulfonate, N-hydroxy-5-norbornene-2,3-dicarboximide
perfluorobutanesulfonate, and
N-hydroxy-5-norbornene-2,3-dicarboximide trifluoromethanesulfonate;
and naphthalene-based non-ionic PAGs such as N-hydroxynaphthalimide
perfluorooctanesulfonate, N-hydroxynaphthalimide
perfluorobutanesulfonate and N-hydroxynaphthalimide
trifluoromethanesulfonate.
[0054] Some additional classes of PAGs include: triarylsulfonium
perfluoroalkanesulfonates, such as triphenylsulfonium
perfluorooctanesulfonate, triphenylsulfonium
perfluorobutanesulfonate and triphenylsulfonium
trifluoromethanesulfonate; triarylsulfonium hexafluorophosphates
(or hexafluoroantimonates), such as triphenylsulfonium
hexafluorophosphate and triphenylsulfonium hexafluoroantimonate;
triaryliodonium perfluoroalkanesulfonates, such as diphenyliodonium
perfluorooctanesulfonate, diphenyliodonium
perfluorobutanesulfonate, diphenyliodonium
trifluoromethanesulfonate, di-(4-tert-butyl)phenyliodonium,
perfluorooctanesulfonate, di-(4-tert-butyl)phenyliodonium
perfluorobutanesulfonate, and di-(4-tert-butyl)phenyliodonium
trifluoromethanesulfonate; and triaryliodonium hexafluorophosphates
(or hexafluoroantimonates) such as diphenyliodonium
hexafluorophosphate, diphenyliodonium hexafluoroantimonate,
di-(4-tert-butyl)phenyliodonium hexafluorophosphate, and
di-(4-tert-butyl)phenyliodonium hexafluoroantimonate. Suitable PAGs
are not limited to those specifically mentioned above. Combinations
of two or more PAGs may be used as well.
[0055] The fluorinated photopolymer composition may optionally
include additives such as stabilizers, coating aids, light
absorbers, acid scavengers ("quenchers") and the like.
[0056] The fluorinated photopolymer composition of the present
disclosure may be applied to a substrate (sometimes referred to
herein as a device substrate) using any method suitable for
depositing a photosensitive liquid material. For example, the
composition may be applied by spin coating, curtain coating, bead
coating, bar coating, spray coating, dip coating, gravure coating,
ink jet, flexography or the like. The composition may be applied to
form a uniform film or a patterned layer of unexposed photopolymer.
Alternatively, the photopolymer can be applied to the substrate by
transferring a preformed fluorinated photopolymer layer (optionally
patterned) from a carrier sheet, for example, by lamination
transfer using heat, pressure or both. In such an embodiment, the
substrate or the preformed photopolymer layer may optionally have
coated thereon an adhesion promoting layer.
[0057] In a useful (but non-limiting) embodiment this photoresist
can be a copolymer formed from a highly fluorinated
alkyl-containing monomer, such as a 1H,1H,2H,2H-perfluoroalkyl
methacrylate, and an acid precursor monomer, such as a tert-alkyl
methacrylate or a nitrobenzyl methacrylate.
[0058] Some specific, but non-limiting, examples include a random
copolymer of 1H,1H,2H,2H-perfluorooctyl methacrylate with
2-nitrobenzyl methacrylate (to form "FOMA-NBMA"), a random
copolymer of 1H,1H,2H,2H-perfluorooctyl methacrylate with
tert-butyl methacrylate (to form "FOMA-TBMA"), a random copolymer
of 1H,1H,2H,2H-perfluorodecyl methacrylate with 2-nitrobenzyl
methacrylate (to form "FDMA-NBMA"), a random copolymer of
1H,1H,2H,2H-perfluorodecyl methacrylate with tert-butyl
methacrylate (to form "FDMA-TBMA"), block copolymers of FOMA-NBMA,
FOMA-TBMA, FDMA-NBMA, FDMA-TBMA, derivatives thereof, structurally
similar compositions or other polymer photoresist or molecular
glass photoresist having sufficient content to permit the
photoresist to be dissolved in a fluorinated coating solvent. In
certain embodiments, the coating solvent may also need to solublize
a photo-acid generator.
[0059] A copolymer of FOMA and TBMA may be prepared as follows. A
solution of 110.10 g (0.7743 mol) of tert-butyl methacrylate,
(TBMA), 330.07 g (0.7636 mol) of 1H,1H,2H,2H-perfluorooctyl
methacrylate, ("FOMA"), 874.2 g of Novec.TM. 7600 and 5.51 g
(0.0335 mol) of azobisisobutyronitrile, ("AIBN") was stirred in a
jacketed reaction flask. The flask jacket was connected to a
programmable, constant temperature bath ("CTB") capable of heating
and maintaining a set jacket temperature. The solution was sparged
with nitrogen at a rate of 0.5 L/minute for 1 hour at ambient
temperature. A CTB program was initiated which heated the reaction
jacket to 68.degree. C., holds this temperature for 1 hour, heats
to 72.degree. C. and holds for 1 hour, and finally heats to
76.degree. C. and holds for 12 hours. When the heating program was
completed, the CTB was set to cool the reaction mixture to ambient
temperature. The clear, colorless polymer solution obtained was
diluted to a viscosity target by the addition of 3.714 kg of
Novec.TM. 7600, and a small sample was removed and dried under
vacuum for later characterization. In one embodiment, under yellow
lights, 22.0 g of CIBA/BASF CGI-1907 (aka "ONPF") photo-acid
generator ("PAG") (5% by weight of the original dry weight of TBMA)
was dissolved in the remaining photoresist solution. The solution
was filtered, and was then ready for use. Many other polymer
variations, e.g., having different ratios of monomers, different
types of monomers or additional monomers, can be prepared using a
similar method.
[0060] The FOMA component of the above resist is largely
responsible for the general solubility of the copolymer in
fluorinated solvents whereas the TBMA groups act as the solubility
"switch" as previously described. In certain embodiments, with
sufficient fluorine content in the photoresist, the resist can be
made both hydrophobic and oleophobic. That is, the resulting
material repels or resists both water and many organic solvents,
permitting these materials to serve as an in-process encapsulation
layers to protect the underlying organic materials from moisture
and damage from organic solvents.
[0061] As mentioned, the developing solution comprises a mixture of
first and second fluorinated solvents and the stripping solution
comprises at least the first or second fluorinated solvent, or
optionally both. In a particularly useful embodiment, at least one
of the solvents is a hydrofluoroether. In a preferred embodiment,
both solvents are hydrofluoroethers. A few non-limiting embodiments
are discussed below.
General Embodiment 1
[0062] In this embodiment, the first solvent is one that has a high
degree of discrimination between solubilizing exposed and unexposed
regions of the photoresist layer. Typically, the first solvent
dissolves the unexposed regions at a moderate rate, but dissolves
the exposed (switched) region at a much lower rate, preferably at
least 10.times. lower. This helps produce an image with reasonable
contrast and tolerable processing latitude, but an image may take
longer than desired to develop appropriately. The second solvent is
one that dissolves the unexposed regions at a rate greater than the
first solvent rate, and preferably, also dissolves the exposed
regions a rate higher than the first solvent rate. That is, the
second solvent is generally a stronger solvent than the first
solvent for both exposed and unexposed areas. Both should be
selected to have a low interaction with sensitive, active organic
materials if present during processing. Preferably the first and
second solvents are both hydrofluoroethers. In this embodiment, the
majority of the volume of the developing solution is typically from
the first solvent, but it has been unexpectedly found that a small
or moderate amount of the second solvent can significantly increase
development rate and improve cleanout of small features without
detrimental stripping action. Takt time is reduced and the
development of small features is improved. In an embodiment, the
developing solution includes the first solvent in a volume range of
75 to 99% and the second solvent in a volume range of 1 to 25%.
Alternatively, the developing solution comprises the first solvent
in a volume range of 90 to 98% and the second solvent in a volume
range of 2 to 10%. The volumes of first and second solvents do not
necessarily have to add up to 100%, as small amounts of additional
materials may be present in the developing solution. In an
embodiment, the first and second solvents comprise at least 97% of
the total volume of developing solution. In another embodiment, the
first and second solvents comprise at least 99% of the total volume
of developing solution. The ratio of solvents can be adjusted to
suit the preferred development time, which might depend upon the
available processing equipment. The ratio of solvents can also be
adjusted to suit the particular fluorinated photoresist system.
Although not limiting, useful development times are in a range from
15 sec to 150 sec, or alternatively, 30 sec to 120 sec. Longer
times can impact throughput and shorter times can be difficult to
control.
[0063] In the present General Embodiment 1, the stripping solution
typically includes at least the second solvent. Optionally, it may
further include the first solvent. In the case of the stripping
solution having both first and second solvents, it has been
surprisingly found that that the second solvent does not have to be
present in the majority, but it is usually at least 30% by volume
and may be in a volume range of 30 to 99%. The first solvent can be
in a range from 1 to 70%. In an embodiment, the stripping solution
includes the second solvent in a volume range of 40 to 97% and
first solvent is in a range from 3 to 60%. The volumes of first and
second solvents do not necessarily have to add up to 100%, as small
amounts of additional materials may be present in the stripping
solution. In an embodiment, the first and second solvents comprise
at least 90%, alternatively at least 97%, of the total volume of
the stripping solution, which may optionally further include up to
10% of a water-soluble, polar or protic solvent such as an alcohol,
e.g., IPA. If used, the amount of the protic solvent is preferably
in a volume range of 0.001 to 3%. Lower amounts of protic solvents
are generally more compatible with a wider array of active organic
materials. The ratio of solvents can be adjusted to suit the
preferred stripping time, which might depend upon the available
processing equipment. The ratio of solvents can also be adjusted to
suit the particular fluorinated photoresist system.
General Embodiment 2
[0064] Here, the first solvent is one that has a high degree of
discrimination between solubilizing exposed and unexposed regions
of photoresist layer. Typically, the first solvent dissolves the
unexposed regions at a moderate rate, but dissolves the exposed
(switched) region at a much lower rate, preferably at least
10.times. lower. This helps produce an image having reasonable
contrast and with good processing latitude, but an image may
sometimes take longer than desired to develop appropriately. The
second solvent in this embodiment is one that has higher
solubilizing power than the first solvent with respect to removing
the unexposed regions, but generally lacks sufficient solubilizing
power to dissolve the exposed photoresists alone. For example, the
first solvent, although it shows some development and good
discrimination, may be too slow to be practical on its own.
Conversely, the second solvent may be too fast to control, and
although it is not capable of stripping the exposed portion, it may
lead to some film delamination due to its high strength, making a
neat solution of the second solvent unsuitable as either a
developing or stripping solution.
[0065] It has been found that an appropriate mixture of the first
and second solvents can provide rapid development with good
contrast. The ratio of first and second solvents in this embodiment
depends upon the system, but each solvent is typically be in a
volume range of 5 to 95%. In this embodiment, the stripping
solution includes at least the first or second solvent and up to
20% by volume of a protic solvent (e.g. an alcohol such as IPA),
preferably in a range, 0.05 to 10%. Lower amounts of protic
solvents are generally more compatible with a wider array of active
organic materials. The stripping solution may optionally have the
same ratio of first and second solvents as used in the developing
solution, but the overall concentrations are different due to the
presence of the protic solvent. Preferably, the stripping solution
will have a higher ratio of second solvent to first solvent than
the developing solution.
General Embodiment 3
[0066] Here, the first solvent generally provides low solubilizing
strength with respect to both the exposed and unexposed regions of
the photoresist. The second solvent is one that can solubilize both
exposed and unexposed portions, but has a higher dissolution rate
for the unexposed portions. When sufficient second solvent is added
to the first solvent, the developing solution is capable of
selectively solubilizing unexposed regions, i.e., dissolving
unexposed regions at a rate that is at least 10 times higher than
solubilization of the exposed areas. In this embodiment, the volume
percentage of the second solvent is in a range from 20 to 80%,
preferably 25 to 60%. The stripping solution will include the
second solvent, optionally with a small amount of the first solvent
or protic solvent or both. The volume of the second solvent in the
stripping solution in this embodiment is at least 80%, preferably
at least 90%.
[0067] An advantage of certain embodiments of the present invention
is that by using mixed solvents for the developing solution and at
least one common solvent in the stripping solution, inexpensive
recycling methods can be used to recover and reuse the solvents.
This reduces both the manufacturing cost and environmental impact.
If the photoresist coating solution is part of the same waste
stream to be recycled, it is preferred that it also uses either the
first or second solvent or a combination thereof. This further
simplifies recycling.
[0068] In an embodiment, the first and second solvents are
fluorinated solvents, at least one of which is a hydrofluoroether,
and the waste stream from at least the developing and stripping
steps are collected and reused using a recycling apparatus. The
collected mixture of fluorinated solvents can be reconstituted,
e.g., by adding fresh solvent, to provide the correct mixture ratio
for use in either the developing or stripping solution. Preferably,
prior to reuse, the recycling apparatus separates the solvent
mixture from suspended and dissolved solids, e.g., by a flash
evaporation step under reduced pressure using a simple
roto-evaporating apparatus. Alternatively or in addition to flash
evaporation, filtration can be used. Preferably, prior to reuse,
the recycling apparatus washes the solvent mixture to remove water
soluble components such as protic solvents. Washing and filtering
methods disclosed in US 2010/0126934 (the contents of which is
incorporated by reference) can optionally be used.
[0069] In a further embodiment, the boiling points of the first and
second solvents differ by at least 25.degree. C. (measured at
atmospheric pressure) and a recycling apparatus is used to achieve
at least partial separation of the first and second solvents by
distillation. Prior to distillation, suspended and dissolved solids
can optionally be removed and the solvent mixture can optionally be
washed, as discussed above. Because solvent mixtures are being used
for at least the developing solution and optionally the stripping
solution, high purity solvent reclamation is not required and a
simple distillation column may be used to achieve reasonable levels
of solvent separation. Alternatively, a fractional distillation
column may be used, but an expensive system should not be required
because high purity (>99%) is not necessary. The simple,
low-cost recycling apparatus permits on-site recycling and
eliminates possible issues regarding shipping wastes from
manufacturing sites. The ability to use the mixed waste stream can
eliminate the need for multiple solvent recycling stations to
handle developing and stripping solutions separately.
[0070] At least two fractions are typically recovered by
distillation. One recycled solvent mixture is rich in the first
solvent and the other recycled solvent mixture is rich in the
second solvent. Depending on the needs of the developing and
stripping solutions, these may be used directly, or they can be
mixed with an appropriate amount of pure solvent to produce the
desired ratio. In an embodiment, a recycled solvent mixture is used
directly as the stripping solution without the addition of a pure
solvent.
[0071] Another use for the recycled solvent mixtures is in edge
bead removal. Edge bead removal (EBR) is a process whereby a
coating of photoresist is removed from an edge area of a substrate
where the thickness of the resist is usually larger than desired
and where no imaging is needed. This can be done, for example, by
directing focused jet or spray of edge bead removal solvent. In
embodiments wherein the first and second solvents that both have
reasonable solubilizing power for unexposed photoresist, the
recycled mixture should provide an inexpensive EBR solvent for
photoresists of the present disclosure.
[0072] Although not limited, the present invention can be used to
form devices having a layer of sensitive, active organic material
(see above). Such devices may include electronic devices such as
TFTs, touch screens, OLED lighting and displays, e-readers, LCD
displays, solar cells, sensors and bioelectronics devices. These
devices are typically multilayer structures having numerous other
layers such as dielectric layers, optical layers, conductors and a
support. Devices may include non-electronic devices such as
optical, medical, and biological devices having some patterned
active organic material, but that do not require an electrical
conductor or semiconductor to operate (e.g., lenses, color filter
arrays, down- or up-conversion filters, medical/biological test
strips and the like). The device substrate onto which the
fluorinated photoresist is provided may include a single layer of a
support material or may include a multilayer structure having a
support and numerous additional layers. The substrate surface is
not necessarily planar. The substrate and support are optionally
flexible. Support materials include, but are not limited to,
plastics, metals, glasses, ceramics, composites and fabrics.
[0073] A flow diagram for an embodiment of the present invention is
shown in FIG. 1, and includes the step 2 of forming a photoresist
layer on a substrate. This can be accomplished using methods
previously described.
[0074] In step 4, the photoresist layer is exposed to patterned
radiation, e.g. UV light, to form an exposed photoresist layer. The
term "radiation" refers to any radiation to which the photoresist
is sensitive and can form areas of differential developability due
to some chemical or physical change caused by the radiation
exposure. Non-limiting examples of radiation include UV, visible
and IR light, e-beams and X-rays. Commonly, the radiation is from
UV or visible light. Patterned radiation can be produced by many
methods, for example, by directing exposing light through a
photomask and onto the photoresist layer. Photomasks are widely
used in photolithography and often include a patterned layer of
chrome that blocks light. The photomask may be in direct contact or
in proximity. When using a proximity exposure, it is preferred that
the light has a high degree of collimation. Alternatively, the
patterned light can be produced by a projection exposure device. In
addition, the patterned light can be from a laser source that is
selectively directed to certain portions of the photoresist
layer.
[0075] In step 6, a developed structure is formed that includes a
first pattern of photoresist. This can be done by contacting the
exposed photoresist layer to a developing solution. As mentioned
above, the developing solution includes a mixture of first and
second fluorinated solvents, preferably wherein at least one of the
first and second solvents is a hydrofluoroether. During
development, a portion of the exposed photoresist layer is removed
in accordance with the patterned light. Depending on the nature of
the chemical or physical change caused by the patterned light, the
developing solution may dissolve the unexposed portion (negative
working resist) or it may dissolve the exposed portion (positive
working resist). Preferably, the developing solution dissolves the
unexposed portion. In either case, it leaves behind a developed
structure having a first pattern of photoresist that covers the
substrate and a complementary second pattern of uncovered substrate
corresponding to the removed portion of photoresist. By uncovered
substrate, it is meant that the surface of the substrate is
substantially exposed or revealed to a degree that it can be
subjected to further treatments--a small amount of residual
photoresist may be present in some embodiments. Contacting the
exposed photoresist layer can be accomplished by immersion into the
developing solution or by applying the developing solution in some
way, e.g., by spin coating or spray coating. The contacting can be
performed multiple times if necessary.
[0076] In step 8, a treated structure is formed by treating the
developed structure in some way. In an embodiment, the treating
includes a chemical or physical etch of the second pattern of
uncovered substrate. In this case, the first pattern of photoresist
acts as an etch barrier. In another embodiment, the treating
includes chemically modifying the surface of the second pattern of
uncovered substrate or the first pattern of photoresist. In another
embodiment, the treating includes doping the second pattern of
uncovered substrate, e.g., to modify its conductivity. In yet
another embodiment, the treating includes coating the developed
structure with, for example, an active organic material that is
deposited both on the surface of the first pattern of photoresist
and on the second pattern of uncovered substrate. In any of the
above embodiments, the substrate may optionally include an active
organic material layer such that the uncovered substrate is the
surface of that active organic material layer.
[0077] In step 10, the first pattern of photoresist is removed from
the treated structure using a stripping solution. As described
above, the stripping solution comprises at least the first or
second fluorinated solvent, or optionally both. In embodiments
wherein the surface of the first pattern of photoresist is covered
with another layer of material, e.g., an active organic material
layer, that portion is also removed. This is sometimes referred to
as a "lift off" process.
[0078] Turning now to FIG. 2, there is a series of cross-sectional
views depicting the formation of a patterned active organic
material structure at various stages according to an embodiment of
the present invention. In FIG. 2A, a substrate 20 includes a layer
of active organic material 24 provided on a support 22. In FIG. 2B,
a negative-type fluorinated photoresist layer 26 is formed on the
substrate 20 and in contact with the layer of active organic
material 24. Next, as shown in FIG. 2C, photoresist layer 26 is
exposed to patterned light by providing a photomask 30 between the
photoresist layer 26 and a source of collimated light 28. The
exposed photoresist layer 32 includes exposed areas 34 and
non-exposed areas 36. The structure is then developed in a
developing solution including first and second solvents. In this
embodiment the non-exposed areas 36 of the photoresist are
selectively dissolved to form a structure having a removed portion
of photoresist. As shown in FIG. 2D, developed structure 38 has a
first pattern of photoresist 40 covering the substrate, and a
complementary second pattern of uncovered substrate 42, in this
case the layer of active organic material 24, corresponding to the
removed portion of photoresist. Turning now to FIG. 2E, a treated
structure 44 is formed by subjecting the developed structure 38 to
a chemical or physical etch that selectively removes active organic
material from the second pattern of uncovered substrate, thereby
forming a patterned layer of active organic material 46
corresponding to the first pattern. By corresponding, it is meant
that the patterned layer of active organic material 46
substantially resembles that of the first pattern of photoresist
40, but the two patterns are not necessarily identical. For
example, the etching might also etch the sidewalls of the patterned
layer of active organic material, thereby making the dimensions
slightly smaller than the first pattern. Conversely, etching
kinetics or diffusion might be such that the dimensions of the
patterned layer of active organic material are slightly larger than
the first pattern. Further, the patterned layer of active organic
material might not have vertical sidewalls as shown. Rather than
rectangular, its cross section could resemble a trapezoid, an
inverted trapezoid (undercut), or some other shape, e.g., one
having curved sidewalls. Referring to FIG. 2F, treated structure 44
is contacted with a stripping solution that removes the first
pattern of photoresist 40, thereby forming patterned active organic
material structure 48 having the (now bare) patterned layer of
active organic material 46. Patterned active organic material
structure 48 may optionally be subjected to additional steps, if
necessary, to form a functional device such as an organic TFT
array, an OLED display, an e-reader, a solar cell, a bioelectronic
device or the like.
[0079] FIG. 3 shows a series of cross-sectional views depicting the
formation of a patterned active organic material structure at
various stages according to another embodiment of the present
invention. In FIG. 3A, a negative-type photoresist layer 126 is
formed on substrate 120. This structure is then exposed and
developed as described above to form developed structure 138, as
shown in FIG. 3B. Developed structure 138 has a first pattern of
photoresist 140 covering the substrate, and a complementary second
pattern of uncovered substrate 142 corresponding to a removed
portion of photoresist. Turning now to FIG. 3C, a treated structure
144 is formed by depositing a layer of active organic material 145
over both the first pattern of photoresist and the second pattern
of uncovered substrate. In FIG. 3D, the treated structure 144 is
then contacted with a stripping solution that removes the first
pattern of photoresist and the active organic material deposited
over the first pattern of photoresist, thereby forming patterned
active organic material structure 148 having a patterned layer of
active organic material 146 corresponding to the second pattern. By
corresponding, it is meant that the patterned layer of active
organic material 146 substantially resembles that of the second
pattern of uncovered substrate 142, but the two patterns are not
necessarily identical. Patterned active organic material structure
148 may optionally be subjected to additional steps, if necessary,
to form a functional device such as an organic TFT array, an OLED
display, an e-reader, a solar cell, a bioelectronic device or the
like.
EXAMPLES
[0080] In the examples below, most of the HFE solvents were
purchased from 3M under their "Novec.TM." brand. For convenience,
the solvents are simply referred to by their HFE number. HFE-6512
was purchased from Top Fluorochem Co, LTD.
Example 1
[0081] Approximately 1475 g (about 1 L) of combined waste solvents
from lithographic testing events was collected from a spin coating
bowl. The testing events used a fluorinated photoresist based on
FOMA-TBMA, the developing solution included HFE-7300
(b.p.=98.degree. C.) and the stripping solution included HFE-6512
(b.p.=133.degree. C.). The waste further included some amount of
IPA. The solvent fraction of the cloudy waste solution was removed
in vacuo using a rotary evaporator under full aspirator vacuum
(.about.28.5 in. Hg) with a bath temperature of 48-60.degree. C.
The distillation was stopped when condensate stopped collecting.
The pot residue included 37 g of viscous oil, primarily from
developed and stripped fluorinated photoresist. The amounts of the
IPA, Novec.TM. 7300 and HFE 6512 after the initial distillation
were measured by gas chromatography (GC). The results are shown in
Table 1 as "% area" under the GC trace, which approximately
corresponds to % volume. The distillate was then washed with
3.times.250 mL of distilled water and 1.times.250 mL of saturated
NaHCO.sub.3 solution. The aqueous fractions were the upper
fractions in all of these washes. The washed solution was then
dried by stirring over MgSO.sub.4, filtered and the solvent amounts
were again measured after drying, as shown in Table 1. The mixture
was then returned to the rotary evaporator. The bath temperature
was set to 40.degree. C. and approximately 500 mL of distillate was
collected. This first fraction of recycled solvent mixture was
analyzed as shown in Table 1. To make recycled developing solution,
50 mL of this distillate was added to 350 mL of fresh HFE-7300. GC
was used to verify the composition which matched the composition of
a developing solution prepared from all fresh solvents (Table 1).
This recycled developing solution was used in lithographic testing
and performed equivalently to developing solution prepared from
fresh solvents.
[0082] After the preparation of the developing solution, the
distillation was resumed with a bath temperature of 53.degree. C.
The distillation was continued until no more material remained in
the pot and the condensation rate had slowed to a stop. GC was run
on this second fraction of recycled solvent mixture (Table 1) and
the results were used to calculate the amount of HFE-7300 to add in
order to make a recycled stripping solution having 60% vol HFE-7300
and 40% vol HFE-6512. GC was used to verify the adjusted
composition after HFE-7300 was added, which matched the composition
of a stripping solution prepared from all fresh solvents (Table 1).
The recycled stripping solution was used in lithographic tests and
performed equivalently to stripper prepared with fresh
solvents.
TABLE-US-00001 TABLE 1 GC Analysis Result (% area) Sample
description IPA* HFE-7300 HFE 6512 Waste solvent solution after
initial 5.5 45.6 46.2 distillation Waste solvent solution after
water washes n.d. 46.4 50.6 First fraction of recycled solvent n.d.
72.4 25.6 mixture collected at 40.degree. C. Recycled developing
solution after adding n.d. 96.4 3.2 Novec .TM. 7300 Reference
developing solution made with n.d. 96.5 3.2 fresh solvents Second
fraction of recycled solvent n.d. 38.6 58.1 mixture collected at
53.degree. C. Recycled stripping solution after adding n.d. 54.8
42.7 Novec .TM. 7300 Reference stripping solution made with n.d.
57.3 42.4 fresh solvents *n.d. = none detected
Example 2
[0083] A silicon wafer was primed by vapor depositing HMDS. A
fluorinated photoresist solution was spin coated onto the silicon
wafer and then "soft baked" at 90.degree. C. for 60 seconds. The
photoresist layer was about 1.0 to 1.5 .mu.m thick. The photoresist
solution included a hydrofluoroether solvent (HFE-7600), a PAG
(CGI-1907), and a polymer comprising copolymer of FOMA, TBMA and
AMMA (9-anthrylmethyl methacrylate) as sensitizing dye, the polymer
having 42.5% by weight of fluorine relative to the polymer. The
photoresist was exposed through a reticle to patterned UV radiation
(365 nm) with doses ranging from 40 mJ/cm.sup.2 to 880 mJ/cm.sup.2,
followed by post-exposure baking at 90.degree. C. for 60 seconds.
The exposed photoresist was then developed to remove the unexposed
portion and to form a photoresist pattern on the substrate.
Developing solution composition and development times are shown in
Table 2. Two applications of developer (approximately 10 mL each)
were provided onto the photoresist layer, each forming a "puddle,"
and the dwell time of each application was half of the total
development time specified in Table 2. The wafer was spun dry at
the end of each dwell time. Table 2 shows that even a small amount
of a second solvent that is generally used in a stripping solution
can significantly reduce development time. Development time can be
easily tuned by adjusting the percentage of the second solvent.
TABLE-US-00002 TABLE 2 HFE-7300 (% vol) HFE-6512 (% vol)
Development Time (sec) 100 0 180 97 3 80 95 5 50 90 10 30
Example 3
[0084] An exposed photoresist on a silicon wafer was prepared as
described in Example 2. It was developed for a total of 90 sec
using two applications of developing solution, each at 45 sec. The
developing solution included a 97/3 volume ratio of HFE-7300 to
HFE-6512. After development the exposed photoresist was stripped by
applying about 10 mL of stripping solution onto the developed
photoresist to form a puddle. The time it took to remove (strip)
the photoresist images having the highest exposure (880
mJ/cm.sup.2) was monitored. The composition of the stripping
solutions and stripping times are shown in Table 3. As can be seen,
even a relatively large amount of a first solvent commonly used in
a developing solution does not seriously increase stripping time.
In general, faster stripping is better, but in some systems, it may
be advantageous to moderate the rate. Clearly, a wide range of
mixtures can effectively strip the photoresist, which makes for a
robust system.
TABLE-US-00003 TABLE 3 HFE-7300 (% vol) HFE-6512 (% vol) Stripping
Time (sec) 0 100 15 20 80 15 30 70 20 40 60 30 50 50 42
Example 4
[0085] A developed photoresist sample was prepared as described in
Example 3, except the photoresist was from a different synthesis
batch and the developing solution used a 97/3 volume ratio of
HFE-7300 to HFE-7600 (b.p.=131.degree. C.), rather than HFE-6512.
In this example, the stripping time was fixed at 120 sec using two
applications of 60 sec each, and the maximum stripping exposure
dose wherein stripping was complete was determined. The stripping
solution compositions and maximum stripping exposure doses are
shown in Table 4. Compared to Example 3, the developed photoresist
of this example is apparently more difficult to strip for reasons
not fully understood. Regardless, the important point is that the
presence of the HFE-7300 (common developer solvent) in combination
with either of the HFE-6512 or HFE-7600 stripping solvents did not
significantly reduce the maximum stripping exposure dose at a 25%
vol ratio. In the case of HFE-6512, addition of 25% HFE-7300
unexpectedly produces an even more effective stripping solution
than HFE-6512 alone, and HFE-7300 can be used at higher amounts as
well to good effect. In the case of HFE-7600, the presence of 50%
HFE-7300 reduced the maximum stripping exposure dose, but stripping
was far from shut down and it is clear that the stripping solution
can tolerate or even benefit from a wide range of solvent
mixtures.
TABLE-US-00004 TABLE 4 Maximum Stripping HFE-7300 HFE-6512 HFE-7600
Exposure Dose (% vol) (% vol) (% vol) removed (mJ/cm.sup.2) 0 100
n/a 530 25 75 n/a >880 50 50 n/a 859 0 n/a 100 558 25 n/a 75 551
50 n/a 50 243
[0086] It was also observed that a small amount of HFE-7300 (e.g.
3% by volume) in HFE-6512 improved the wetting behavior of the
stripping solution when applied to the developed photoresist
relative to neat HFE-6512. Poor wetting may in some cases increase
variability in stripping performance or require a larger volume of
stripping solution in order to properly cover the sample.
[0087] The contrast of a photoresist system is often an important
factor. Higher contrast is typically preferred, as it generally
results in straighter sidewalls for imaged areas and overall better
discrimination between imaging light and stray light for improved
feature resolution. It has been unexpectedly found that certain
mixed solvent developers not only speed up development rate, but
they also improve the contrast.
[0088] To study contrast, the following method was generally used.
A subject fluorinated photoresist was spin coated onto a silicon
wafer and soft-baked for 1 min at 90.degree. C. The film thickness
was generally in a range of about 1 to 1.5 um. An optical 22 step
tablet (.about.0.15 density units per step) was laid on top of the
wafer and the resist was exposed to 365 nm radiation using a 16 W
black light lamp. The maximum exposure dose was typically about 175
mJ/cm.sup.2. The wafer was post-exposure baked (PEB) for 1 min at
90.degree. C. to activate the switching reaction. The film
thickness was then immediately measured in 24 areas (steps). In
addition to the 22 areas of the step tablet, the maximum exposure
dose was measured just outside of the step tablet area (point 1) as
well as a minimum exposure dose area (covered by a metal disc) that
received no exposure (point 24).
[0089] Five minutes after the PEB, the wafer was contacted with
.about.10 mL of a developer solution using the "puddle" method and
spin-dried after the target time was reached. The time of each
puddle and number of puddles depended on the system. After each
puddle, the film thicknesses were measured in the same 24 areas.
Film thicknesses after each puddle were normalized to the starting
thickness and plotted versus log Exposure (log(E)) to create a set
of contrast curves. The contrast between each point was calculated
using equation 1:
Contrast=[normalized thickness]/[log(E)] (Eq. 1)
The highest calculated contrast (the "maximum contrast") for each
curve was determined. FIG. 4 shows an example graph of normalized
thickness vs. log(E)--for clarity, only the first 16 points are
shown. Other parameters can also be determined as desired such as
"0.5 speed point" (exposure dose at normalized density=0.5), "Emax
erosion" (normalized thickness loss of the maximum exposure point
1), "time to clear" (time it takes for the minimum exposure to be
fully removed), and "time to strip" (time it takes for maximum
exposure to be fully removed). For good line shapes, it is
desirable that the maximum contrast be at least 1.5, preferably at
least 1.9 and more preferably at least 2.1. As discussed earlier,
it is also desirable that the contrast be achieved in a processing
time in a range of about 15 to 150 sec. It has been unexpectedly
found that resist/developer systems of the present disclosure
having maximum contrasts higher than about 5 are prone to yield
film delamination in regions of moderate exposure. One can try and
address this by increasing exposure, but this sometimes results in
unwanted line broadening due to light scatter or flare. In
particular, image patterns having a variety of feature dimensions
and densities become more prone to delamination because small,
sparse features may receive significantly less exposure than
large/dense feature areas. Surprisingly, by controlling the maximum
contrast to a range of about 1.9 to about 5.0, preferably 2.1 to
4.3, the occurrences of delamination can be reduced and the system
becomes more robust to variations in exposure across the image. It
is particularly desirable if the maximum photopolymer contrast is
in the range of about 1.9 to about 5.0 for at least a 15 sec time
window within a development contact time period of 15 to 150
seconds. The larger this time window is, the more robust the
developer/photoresist system is to variations in the development
process.
Example 5
[0090] A fluorinated photoresist solution similar to those of
Examples 2-4 was spin coated onto the silicon wafer and then "soft
baked" at 90.degree. C. for 60 seconds. The photoresist layer was
about 1.4 .mu.m thick. The photoresist solution included a HFE-7600
as coating solvent, CGI 1907 as PAG (0.8% wt relative to polymer
wt), and a polymer comprising copolymer of FOMA, TBMA and AMMA, the
polymer having 42.5% by weight of fluorine relative to the polymer.
Contrast curves were measured as described above using HFE-7300 as
the developer. The process was then repeated for various mixtures
of HFE-7300 and HFE-6512, and various parameters were determined as
reported in Table 5. Note that maximum contrast values were only
reported if the low exposure regions had fully been removed and
when Emax erosion was less than 0.25. Larger erosion levels often
make the photoresist system impractical. In Table 5, at HFE-6512
concentrations of 25% or higher, the "time to clear" is reported as
"<30" sec. In these cases, 90 to 95% of the polymer in the low
exposure region was actually removed in the first 15 sec puddle.
For reasons not fully understood, it is often observed that the
first puddle, almost independent of puddle time, leaves a small
residue of 0.05 to 0.10 of normalized thickness. If shorter puddle
times were used, the time to clear would likely be much less than
30 sec. Also, in some cases, the "time to strip" entries are
estimates based on simple extrapolations from the available
data.
TABLE-US-00005 TABLE 5 Solvent Ratio Time to Time to HFE7300/ Clear
Max Contrast Emax Erosion Strip HFE6512 (sec) (time, sec) (time,
sec) (sec) 100/0 150 1.6 (150) n/a n/a 95/5 60 2.1 (60) n/a 2.0
(90) 0.02 (90) 90/10 30 2.4 (30) n/a 2.4 (60) 1.8 (90) 0.07 (90)
75/25 <30 1.7 (30) 0.16 (30) 180 0.30 (60) (estimate) 0.43 (90)
50/50 <30 n/a 0.36 (30) 60 25/75 <30 n/a 0.95 (30) 35
(estimate) 10/90 <30 n/a 0.95 (30) 35 (estimate) 0/100 <30
n/a 0.94 (30) 35 (estimate)
[0091] In Table 5, it is noted that the development rate of this
polymer in pure HFE-7300 is very slow. The first "puddle" that was
clear in the low exposure area was the puddle corresponding to 150
sec total development time. The contrast was only 1.6 at this time.
Perhaps higher contrast could eventually be achieved by extending
the development time, but such extended development time can be
prohibitive from a practical manufacturing standpoint. However,
when 5 or 10% HFE-6512 is added, much better contrasts are achieved
in a shorter amount of time. Further, there is a good development
time window for achieving these contrasts. At 25% HFE-6512, the
Emax is starting to show significant erosion and the mixture has
essentially become an effective, albeit slightly slow, stripping
solution. By 50% HFE-6512, the stripping rate is much faster. There
contrast curves for 75% HFE-6512 and 90% HFE-6512 were not
significantly different from 100% HFE-6512, showing that there is a
broad range of mixtures that are effective for stripping
(consistent with data from Table 4).
Example 6
[0092] The same fluorinated photoresist solution used in Example 5
was spin coated onto the silicon wafer and then "soft baked" at
90.degree. C. for 60 seconds. The photoresist layer was about 1.4
.mu.m thick. Contrast curves were measured as described above using
HFE-7500 (b.p.=128.degree. C.) as the developer. The process was
then repeated for various mixtures with HFE-7200 (b.p.=76.degree.
C.). Various parameters were determined and reported in Table
6.
TABLE-US-00006 TABLE 6 Solvent Ratio Time to Time to HFE7500/ Clear
Max Contrast Emax Erosion Strip HFE7200 (sec) (time, sec) (time,
sec) (sec) 100/0 150 1.2 (150) n/a n/a 90/10 90 1.4 (90) n/a n/a
2.4 (150) 80/20 60 1.8 (60) n/a n/a 2.1 (90) 2.6 (150) 20/80 15 2.2
(15) n/a 3.3 (30) 0.03 (30) 0/100 15 2.2 (15) n/a 2.0 (30) 5.8 (60)
0.03 (60) delamination of 51 mJ/cm.sup.2 step @ 60 sec 0/100 + 15
n/a 0.64 (15) 30 0.5% vol. IPA 20/80 + 15 n/a 0.30 (15) 60 0.5%
vol. IPA 0/100 + 15 1.7 (15) 0.08 (15) 60 0.1% vol. 3.7 (30) 0.10
(30) IPA
[0093] Referring to Table 6, it is observed that pure HFE-7500 is
similar to HFE-7300 in that it takes 150 sec to clear and the
contrast is low. Adding 10 or 20% of HFE-7200 to the developing
solution significantly reduces time to clear and improves contrast.
Going as far as 80% HFE-7200 produces a very short clear time and
slightly better contrasts. HFE-7200 is a much stronger developing
solvent than HFE-7500, and when used at 100% it produces a clear
time of 15 sec and reasonable contrasts at 2.2 and 2.0, but by 60
sec one of the steps has delaminated (based on debris pattern). Not
shown in the table, by 90 sec, more steps have delaminated. Thus,
the pure solvent is not as robust as some of the mixtures. It is
also noted that HFE-7200 alone is not an effective stripping agent
in this system. This example falls into the category of "General
Embodiment 2", and adding just 0.5% by volume of isopropyl alcohol
(IPA) makes it a very effective stripping solution. Similarly, 0.5%
IPA by volume added to the 20/80 HFE-7500/HFE-7200 blend is also
highly effective. Interestingly, adding only 0.1% by volume of IPA
to pure HFE-7200 can be made to produce a developing solution
having good contrast without delamination, but the development time
window is very short. By 30 sec, the only film left was in point 1
(Emax)--all the others had developed away. Shortly thereafter, this
step is also removed. Thus, the 0.1% IPA solution is also an
effective stripping solution. It appears that there may be an
induction period for stripping of Emax, but once it starts, it
strips very rapidly. Such as system is not expected to be robust as
a developing solution. Not shown, but a pure HFE-7500 with 0.5% IPA
is not an effective stripping solution. Thus, it is preferred that
the majority of the stripping solution volume comes from the higher
activity solvent.
Example 7
[0094] A fluorinated photoresist was spin coated onto the silicon
wafer and then "soft baked" at 90.degree. C. for 60 seconds. The
photoresist layer was about 1.4 .mu.m thick. The photoresist
solution included a HFE-6512 as coating solvent, CGI 1907 as PAG
(0.8% by wt relative to polymer wt), and a branched polymer
comprising copolymer of FOMA, TBMA, ECPMA, EGDMA (ethylene glycol
dimethylacrylate) and AMMA in mole ratios of 27.3, 30.4, 37.3, 3,
and 2, respectively. The polymer had 28.0% by weight of fluorine
relative to the polymer. Contrast curves were measured as described
above using HFE-7200 as the developer. The process was then
repeated for various mixtures of HFE-7200 and HFE-7600, and various
parameters were determined as reported in Table 7. Note that
maximum contrast values were only reported if the low exposures had
fully been removed and when Emax erosion was less than 0.25. In
Table 7, the pure HFE-7600 "time to clear" entry is "<30" sec.
In fact, 95% of the polymer in the low exposure region was actually
in the first 15 sec puddle. For reasons not fully understood, it is
often observed that the first puddle, almost independent of puddle
time, leaves a small residue of 0.05 to 0.10 of normalized
thickness. If shorter puddle times were used, the time to clear
would likely be much less than 30 sec. Interestingly, adding just
10% HFE-7200 eliminates this residual effect. Also, the "time to
strip" entries are estimates based on extrapolations from the
data.
TABLE-US-00007 TABLE 7 Solvent Ratio Time to Time to HFE7200/ Clear
Max Contrast Emax Erosion Strip HFE7600 (sec) (time, sec) (time,
sec) (sec) 100/0 30 1.2 (30) 0.05 (30) n/a 1.8 (60) 0.09 (60) 2.1
(90) 0.10 (90) 95/5 30 1.9 (30) 0.09 (30) n/a 2.1 (60) 0.11 (60)
2.5 (90) 0.13 (90) 90/10 15 1.3 (15) 0.05 (15) n/a 1.8 (30) 0.13
(30) 3.1 (60) 0.17 (60) 2.4 (90) 0.20 (90) 75/25 15 1.8 (15) 0.10
(15) n/a 1.8 (30) 0.20 (30) 0.27 (60) 0.35 (90) 10/90 15 2.0 (15)
0.21 (15) 105 0.27 (30) (estimate) 0.60 (60) 0.85 (90) 0/100 <30
n/a 0.11 (15) 110 0.34 (30) (estimate) 0.56 (60) 0.82 (90)
[0095] It is observed in Table 7 that adding 5 to 10% HFE-7600 to
the developing solution can improve contrast and reduce time to
clear, relative to pure HFE-7200. Increasing HFE-7600 to 25% or
higher results in increased Emax Erosion and the solution becomes a
more effect stripping solution than a developing solution. Note
that the 10/90 HFE-7200/HFE-7600 mixture is just as effective as
the pure HFE-7600 in stripping, and may be slightly advantaged in
that the mixture leaves less residual in the first 15 sec
puddle.
[0096] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations, combinations, and modifications can be
effected by a person of ordinary skill in the art within the spirit
and scope of the invention.
LIST OF REFERENCE NUMBERS USED IN THE DRAWINGS
[0097] 2 form photoresist layer on substrate step [0098] 4 form
exposed photoresist layer step [0099] 6 form developed structure
step [0100] 8 form treated structure step [0101] 10 remove first
pattern of photoresist step [0102] 20 substrate [0103] 22 support
[0104] 24 layer of active organic material [0105] 26 photoresist
layer [0106] 28 light [0107] 30 photomask [0108] 32 exposed
photoresist layer [0109] 34 exposed areas [0110] 36 non-exposed
areas [0111] 38 developed structure [0112] 40 first pattern of
photoresist [0113] 42 second pattern of uncovered substrate [0114]
44 treated structure [0115] 46 patterned layer of active organic
material [0116] 48 patterned active organic material structure
[0117] 120 substrate [0118] 126 photoresist layer [0119] 138
developed structure [0120] 140 first pattern of photoresist [0121]
142 second pattern of uncovered substrate [0122] 144 treated
structure [0123] 145 layer of active organic material [0124] 146
patterned layer of active organic material [0125] 148 patterned
active organic material structure
* * * * *