U.S. patent application number 11/098239 was filed with the patent office on 2005-10-20 for method of preparing a planar optical waveguide assembly.
Invention is credited to Gardner, Geoffrey Bruce, Schmidt, Randall Gene.
Application Number | 20050232557 11/098239 |
Document ID | / |
Family ID | 29734831 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050232557 |
Kind Code |
A1 |
Gardner, Geoffrey Bruce ; et
al. |
October 20, 2005 |
Method of preparing a planar optical waveguide assembly
Abstract
A method of preparing a planar optical waveguide assembly,
comprising the steps of: (i) applying a silicone composition to a
surface of a substrate to form a silicone film; (ii) exposing at
least one selected region of the silicone film to radiation having
a wavelength of from 150 to 800 nm to produce a partially exposed
film having at least one exposed region and at least one
non-exposed region; (iii) removing the non-exposed region of the
partially exposed film with a developing solvent to form a
patterned film; and (iv) heating the patterned film for an amount
of time sufficient to form at least one silicone core having a
refractive index of from 1.3 to 1.7 at 23.degree. C. for light
having a wavelength of 589 nm; wherein the substrate has a
refractive index less than the refractive index of the silicone
core.
Inventors: |
Gardner, Geoffrey Bruce;
(Sanford, MI) ; Schmidt, Randall Gene; (Midland,
MI) |
Correspondence
Address: |
DOW CORNING CORPORATION CO1232
2200 W. SALZBURG ROAD
P.O. BOX 994
MIDLAND
MI
48686-0994
US
|
Family ID: |
29734831 |
Appl. No.: |
11/098239 |
Filed: |
April 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11098239 |
Apr 4, 2005 |
|
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|
10178975 |
Jun 24, 2002 |
|
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6907176 |
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Current U.S.
Class: |
385/102 ;
430/311 |
Current CPC
Class: |
G02B 1/046 20130101;
G02B 2006/12069 20130101; G02B 6/138 20130101; G02B 1/046 20130101;
C08L 83/04 20130101 |
Class at
Publication: |
385/102 ;
430/311 |
International
Class: |
G02B 006/44 |
Claims
That which is claimed is:
1. A method of preparing a planar optical waveguide assembly,
comprising the steps of: (i) applying a silicone composition to a
surface of a substrate to form a silicone film, wherein the
silicone composition comprises: (A) an organopolysiloxane
containing an average of at least two silicon-bonded alkenyl groups
per molecule, (B) an organosilicon compound containing an average
of at least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and (C) a
catalytic amount of a photoactivated hydrosilylation catalyst; (ii)
exposing at least one selected region of the silicone film to
radiation having a wavelength of from 150 to 800 nm to produce a
partially exposed film having at least one exposed region and at
least one non-exposed region; (iii) removing the non-exposed region
of the partially exposed film with a developing solvent to form a
patterned film; and (iv) heating the patterned film for an amount
of time sufficient to form at least one silicone core having a
refractive index of from 1.3 to 1.7 at 23.degree. C. for light
having a wavelength of 589 nm; wherein the substrate has a
refractive index less than the refractive index of the silicone
core.
2. The method according to claim 1, wherein the organopolysiloxane
is an organopolysiloxane resin.
3. The method according to claim 2, wherein the organopolysiloxane
resin consists essentially of R.sup.2.sub.3SiO.sub.1/2 units and
R.sup.1SiO.sub.3/2 units, wherein the mole ratio of
R.sup.2.sub.3SiO.sub.1/2 units to R.sup.1SiO.sub.3/2 units is from
0.05 to 1.0, each R.sup.1 is independently selected from
hydrocarbyl, deuterium-substituted hydrocarbyl, and
halogen-substituted hydrocarbyl, all free of aliphatic
unsaturation, and R.sup.2 is R.sup.1 or alkenyl.
4. The method according to claim 3, wherein the organopolysiloxane
resin consists essentially of PhSiO.sub.3/2 units and
CH2=CH(CH.sub.3).sub.2SiO- .sub.1/2 units.
5. The method according to claim 1, wherein the photoactivated
hydrosilylation catalyst is a platinum(II) .beta.-diketonate.
6. The method according to claim 5, wherein the platinum (II)
.beta.-diketonate is platinum(II) bis(2,4-pentanedioate).
7. The method according to claim 1, wherein the substrate is
silicon or silicon dioxide.
8. The method according to claim 1, wherein the silicone core has a
thickness of from 1 to 100 .mu.m.
9. The method according to claim 1, further comprising (v) covering
the substrate and the silicone core with a curable polymer
composition to form a polymer film and (vi) curing the polymer film
to form a clad layer, wherein the clad layer has a refractive index
less than the refractive index of the silicone core.
10. The method according to claim 9, wherein the curable polymer
composition is a curable silicone composition.
11. The method according to claim 10, wherein the curable silicone
composition is the silicone composition in step (i).
12. The method according to claim 9, wherein the clad layer has a
thickness of from 5 to 200 .mu.m.
13. A method of preparing a planar optical waveguide assembly,
comprising the steps of: (i) applying a silicone composition to a
surface of a substrate to form a silicone film, wherein the
silicone composition comprises: (A) an organopolysiloxane
containing an average of at least two silicon-bonded alkenyl groups
per molecule, (B) an organosilicon compound containing an average
of at least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and (C) a
catalytic amount of a photoactivated hydrosilylation catalyst; (ii)
exposing at least one selected region of the silicone film to
radiation having a wavelength of from 150 to 800 nm to produce a
partially exposed film having at least one exposed region and at
least one non-exposed region; (iii) heating the partially exposed
film for an amount of time such that the exposed region is
substantially insoluble in a developing solvent and the non-exposed
region is soluble in the developing solvent; (iv) removing the
non-exposed region of the heated film with the developing solvent
to form a patterned film; and (v) heating the patterned film for an
amount of time sufficient to form at least one silicone core having
a refractive index of from 1.3 to 1.7 at 23.degree. C. for light
having a wavelength of 589 nm; wherein the substrate has a
refractive index less than the refractive index of the silicone
core.
14. The method according to claim 13, wherein the
organopolysiloxane is an organopolysiloxane resin.
15. The method according to claim 14, wherein the
organopolysiloxane resin consists essentially of
R.sup.2.sub.3SiO.sub.1/2 units and R.sup.1SiO.sub.3/2 units,
wherein the mole ratio of R.sup.2.sub.3SiO.sub.1/2 units to
R.sup.1SiO.sub.3/2 units is from 0.05 to 1.0, each R.sup.1 is
independently selected from hydrocarbyl, deuterium-substituted
hydrocarbyl, and halogen-substituted hydrocarbyl, all free of
aliphatic unsaturation, and R.sup.2 is R.sup.1 or alkenyl.
16. The method according to claim 15, wherein the
organopolysiloxane resin consists essentially of PhSiO.sub.3/2
units and CH2=CH(CH.sub.3).sub.2SiO- .sub.1/2 units.
17. The method according to claim 13, wherein the photoactivated
hydrosilylation catalyst is a platinum(II) .beta.-diketonate.
18. The method according to claim 17, wherein the platinum (II)
.beta.-diketonate is platinum(II) bis(2,4-pentanedioate).
19. The method according to claim 13, wherein the substrate is
silicon or silicon dioxide.
20. The method according to claim 13, wherein the partially exposed
film is heated at a temperature of from 50 to 250.degree. C. for
0.1 to 10 min.
21. The method according to claim 13, wherein the silicone core has
a thickness of from 1 to 100 .mu.m.
22. The method according to claim 13, further comprising further
comprising (vi) covering the substrate and the silicone core with a
curable polymer composition to form a polymer film and (vii) curing
the polymer film to form a clad layer, wherein the clad layer has a
refractive index less than the refractive index of the silicone
core.
23. The method according to claim 22, wherein the curable polymer
composition is a curable silicone composition.
24. The method according to claim 23, wherein the curable silicone
composition is the silicone composition in step (i).
25. The method according to claim 22, wherein the clad layer has a
thickness of from 5 to 200 .mu.m.
Description
[0001] This application is a divisional of application Ser. No.
10/178,975 filed Jun. 24, 2002.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of preparing a
planar optical waveguide assembly and more particularly to a method
of preparing a planar optical waveguide assembly containing at
least one silicone core.
BACKGROUND OF THE INVENTION
[0003] Methods of preparing planar optical waveguides containing a
silicone core are known in the art. For Example, U.S. Pat. No.
6,088,492 to Kaneko et al. discloses a method of producing an
optical waveguide using a siloxane-containing polymer, comprising
thermally polymerizing a solution for forming a siloxane-containing
polymer film, the solution being added with a metal alkoxide on a
substrate, to form an optical waveguide composed of the
siloxane-containing polymer film containing metal.
[0004] Methods of preparing planar optical waveguides containing a
silicone core are also disclosed in European Patent Application No.
EP 1 118 884 A1 to Nakamura et al.; Japanese Patent Application No.
200180643 A to Toyoda et al.; Japanese Patent Application No.
09124793 A to Hayashida et al.; and Japanese Patent Application No.
10148729 A to Tomaru et al.
[0005] Although the aforementioned references disclose methods of
preparing optical waveguides having a range of thermal and
environmental properties, there is a continued need for a method of
producing a planar optical waveguide assembly having superior
thermal stability and moisture resistance.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to a method of preparing a
planar optical waveguide assembly, comprising the steps of:
[0007] (i) applying a silicone composition to a surface of a
substrate to form a silicone film, wherein the silicone composition
comprises:
[0008] (A) an organopolysiloxane containing an average of at least
two silicon-bonded alkenyl groups per molecule,
[0009] (B) an organosilicon compound containing an average of at
least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and
[0010] (C) a catalytic amount of a photoactivated hydrosilylation
catalyst;
[0011] (ii) exposing at least one selected region of the silicone
film to radiation having a wavelength of from 150 to 800 nm to
produce a partially exposed film having at least one exposed region
and at least one non-exposed region;
[0012] (iii) removing the non-exposed region of the partially
exposed film with a developing solvent to form a patterned film;
and
[0013] (iv) heating the patterned film for an amount of time
sufficient to form at least one silicone core having a refractive
index of from 1.3 to 1.7 at 23.degree. C. for light having a
wavelength of 589 nm; wherein the substrate has a refractive index
less than the refractive index of the silicone core.
[0014] The present invention is further directed to a method of
preparing a planar optical waveguide assembly, comprising the steps
of:
[0015] (i) applying a silicone composition to a surface of a
substrate to form a silicone film, wherein the silicone composition
comprises:
[0016] (A) an organopolysiloxane containing an average of at least
two silicon-bonded alkenyl groups per molecule,
[0017] (B) an organosilicon compound containing an average of at
least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and
[0018] (C) a catalytic amount of a photoactivated hydrosilylation
catalyst;
[0019] (ii) exposing at least one selected region of the silicone
film to radiation having a wavelength of from 150 to 800 nm to
produce a partially exposed film having at least one exposed region
and at least one non-exposed region;
[0020] (iii) heating the partially exposed film for an amount of
time such that the exposed region is substantially insoluble in a
developing solvent and the non-exposed region is soluble in the
developing solvent;
[0021] (iv) removing the non-exposed region of the heated film with
the developing solvent to form a patterned film; and
[0022] (v) heating the patterned film for an amount of time
sufficient to form at least one silicone core having a refractive
index of from 1.3 to 1.7 at 23.degree. C. for light having a
wavelength of 589 nm; wherein the substrate has a refractive index
less than the refractive index of the silicone core.
[0023] The method of the present invention is scaleable to a high
throughput manufacturing process. Importantly, the method allows
simultaneous fabrication of multiple waveguides on a single
substrate. Additionally, the method employs conventional wafer
fabrication techniques (e.g., coating, exposing, developing,
curing) and equipment. Furthermore, the method uses a
photopatternable silicone composition, thereby eliminating
additional process steps, for example, applying a photoresist and
etching, associated with use of a non-photopatternable polymer
composition. Finally, the process of the instant invention has high
resolution, meaning that the process transfers images from a
photomask to the silicone film with good retention of critical
dimensions.
[0024] The planar optical waveguide assembly of the present
invention exhibits good thermal stability over a wide range of
temperatures and good environmental resistance, particularly
moisture resistance. Also, the waveguide assembly exhibits low
birefringence and low transmission loss.
[0025] The optical waveguide assembly of the present invention can
be used to fabricate components of optical integrated circuits,
such as attenuators, switches, splitters, routers, filters, and
gratings.
[0026] These and other features, aspects, and advantages of the
present invention will become better understood with reference to
the following description, appended claims, and accompanying
drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 shows a cross-sectional view of an embodiment of a
planar optical waveguide assembly prepared according to the method
of the present invention.
[0028] FIG. 2 shows a cross-sectional view of another second
embodiment of a planar optical waveguide assembly prepared
according to the method of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] As used herein, the term "planar optical waveguide assembly"
refers to a waveguide assembly containing at least one core having
a rectangular cross section. Also, as used herein, the "refractive
index" of a substance is defined as the ratio of the velocity of
light in a vacuum to the velocity of light in the substance at
23.degree. C. for light having a wavelength of 589 nm.
[0030] A first method of preparing a planar optical waveguide
assembly according to the present invention, comprises the steps
of:
[0031] (i) applying a silicone composition to a surface of a
substrate to form a silicone film, wherein the silicone composition
comprises:
[0032] (A) an organopolysiloxane containing an average of at least
two silicon-bonded alkenyl groups per molecule,
[0033] (B) an organosilicon compound containing an average of at
least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and
[0034] (C) a catalytic amount of a photoactivated hydrosilylation
catalyst;
[0035] (ii) exposing at least one selected region of the silicone
film to radiation having a wavelength of from 150 to 800 nm to
produce a partially exposed film having at least one exposed region
and at least one non-exposed region;
[0036] (iii) removing the non-exposed region of the partially
exposed film with a developing solvent to form a patterned film;
and
[0037] (iv) heating the patterned film for an amount of time
sufficient to form at least one silicone core having a refractive
index of from 1.3 to 1.7 at 23.degree. C. for light having a
wavelength of 589 nm; wherein the substrate has a refractive index
less than the refractive index of the silicone core.
[0038] A silicone composition is applied to a surface of a
substrate to form a silicone film, wherein the silicone composition
comprises (A) an organopolysiloxane containing an average of at
least two silicon-bonded alkenyl groups per molecule, (B) an
organosilicon compound containing an average of at least two
silicon-bonded hydrogen atoms per molecule in a concentration
sufficient to cure the composition, and (C) a catalytic amount of a
photoactivated hydrosilylation catalyst.
[0039] Component (A) is at least one organopolysiloxane containing
an average of at least two silicon-bonded alkenyl groups per
molecule. The organopolysiloxane can have a linear, branched, or
resinous structure. The organopolysiloxane can be a homopolymer or
a copolymer. The alkenyl groups typically have from 2 to about 10
carbon atoms, alternatively from 2 to 6 carbon atoms. Examples of
alkenyl groups include, but are not limited to, vinyl, allyl,
butenyl, and hexenyl. The alkenyl groups in the organopolysiloxane
can be located at terminal, pendant, or both terminal and pendant
positions. The remaining silicon-bonded organic groups in the
organopolysiloxane are independently selected from hydrocarbyl,
deuterium-substituted hydrocarbyl, and halogen-substituted
hydrocarbyl, all free of aliphatic unsaturation. As used herein,
the term "free of aliphatic unsaturation" means the groups do not
contain an aliphatic carbon-carbon double bond or carbon-carbon
triple bond. These monovalent groups typically have from 1 to about
20 carbon atoms, alternatively from 1 to 10 carbon atoms. Acyclic
monovalent groups containing at least 3 carbon atoms can have a
branched or unbranched structure.
[0040] Examples of hydrocarbyl groups include, but are not limited
to, alkyl, such as methyl, ethyl, propyl, 1-methylethyl, butyl,
1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl,
1-methylbutyl, 1-ethylpropyl, 2-methylbutyl, 3-methylbutyl,
1,2-dimethylpropyl, 2,2-dimethylpropyl, hexyl, heptyl, octyl,
nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl,
hexadecyl, heptadecyl, and octadecyl; cycloalkyl, such as
cyclopentyl, cyclohexyl, and methylcyclohexyl; aryl, such as phenyl
and naphthyl; alkaryl, such as tolyl and xylyl; and aralkyl, such
as benzyl and phenethyl. Examples of deuterium-substituted
hydrocarbyl groups include, but are not limited to, the hydrocarbyl
groups listed above wherein at least one deuterium atom replaces an
equal number of hydrogen atoms. Examples of halogen-substituted
hydrocarbyl groups include, but are not limited to,
3,3,3-trifluoropropyl, 3-chloropropyl, dichlorophenyl,
dibromophenyl, and 3,4,5,6-nonafluorohexyl.
[0041] The viscosity of the organopolysiloxane at 25.degree. C.,
which varies with molecular weight and structure, is typically from
0.001 to 100,000 Pa.s, alternatively from 0.01 to 10,000 Pa.s,
alternatively from 0.01 to 10,000 Pa.s.
[0042] Organopolysiloxanes useful in the silicone composition
include, but are not limited to, polydiorganosiloxanes and
organopolysiloxane resins. Examples of polydiorganosiloxanes
include those having the following formulae:
ViMe.sub.2SiO(Me.sub.2SiO).sub.aSiMe.sub.2Vi,
ViMe.sub.2SiO(Me.sub.2SiO).sub.0.25a(MePhSiO).sub.0.75aSiMe.sub.2Vi,
ViMe.sub.2SiO(Me.sub.2SiO).sub.0.95a(Ph.sub.2SiO).sub.0.05aSiMe.sub.2Vi,
ViMe.sub.2SiO(Me.sub.2SiO).sub.0.98a(MeViSiO).sub.0.02aSiMe.sub.2Vi,
Me.sub.3SiO(Me.sub.2SiO).sub.0.95a(MeViSiO).sub.0.05aSiMe.sub.3,
and PhMeViSiO(Me.sub.2SiO).sub.aSiPhMeVi, where Me, Vi, and Ph
denote methyl, vinyl, and phenyl respectively and a has a value
such that the viscosity of the polydiorganosiloxane is from 0.001
to 100,000 Pa.s at 25.degree. C.
[0043] Methods of preparing polydiorganosiloxanes suitable for use
in the silicone composition, such as hydrolysis and condensation of
the corresponding organohalosilanes or equilibration of cyclic
polydiorganosiloxanes, are well known in the art.
[0044] Examples of organopolysiloxane resins include an MQ resin
consisting essentially of R.sup.2.sub.3SiO.sub.1/2 units and
SiO.sub.4/2 units, wherein the mole ratio of
R.sup.2.sub.3SiO.sub.1/2 units to SiO.sub.4/2 units is from 0.5 to
1.1; an MDQ resin consisting essentially of
R.sup.2.sub.3SiO.sub.1/2 units, R.sup.2.sub.2SiO.sub.2/2 units, and
SiO.sub.4/2 units wherein the mole ratio of
R.sup.2.sub.3SiO.sub.1/2 units to SiO.sub.4/2 units is from 0.5 to
1.1 and the mole ratio of R.sup.2.sub.2SiO.sub.2/2units to
R.sup.2.sub.3SiO.sub.1/2 units and SiO.sub.4/2 units combined is
from 0.01 to 0.3; an MT resin consisting essentially of
R.sup.2.sub.3 SiO.sub.1/2 units and R.sup.1SiO.sub.3/2 units,
wherein the mole ratio of R.sup.2.sub.3SiO.sub.1/2 units to R.sup.1
SiO.sub.3/2 units is from 0.05 to 1.0; an MTQ resin consisting
essentially of R.sup.2.sub.3SiO.sub.1/2 units, R.sup.1SiO.sub.3/2
units, and SiO.sub.4/2 units, wherein the mole ratio of
R.sup.2.sub.3SiO.sub.1/2 units to R.sup.1SiO.sub.3/2 units is from
0.05 to 1.0 and the mole ratio of SiO.sub.4/2 units to
R.sup.2.sub.3SiO.sub.1/2 units and R.sup.1SiO.sub.3/2 units
combined is from 0.01 to 0.2; an MTD resin consisting essentially
of R.sup.2.sub.3SiO.sub.1/2 units, R.sup.1SiO.sub.3/2 units, and
R.sup.2.sub.2SiO.sub.2/2 units, wherein the mole ratio of
R.sup.2.sub.3SiO.sub.1/2 units to R.sup.1 SiO.sub.3/2 units is from
0.05 to 1.0 and the mole ratio of R.sup.2.sub.2SO.sub.2/2 units to
R.sup.2.sub.3SiO.sub.1/2 units and R.sup.1SiO.sub.3/2 units
combined is from 0.01 to 0.2; and a TD resin consisting essentially
of R.sup.1SiO.sub.3/2 units and R.sup.2SiO.sub.2/2 units, wherein
the mole ratio of R.sup.2SiO.sub.2/2 units to R.sup.1SiO.sub.3/2
units is from 0.02 to 1.0; wherein each R.sup.1 is independently
selected from hydrocarbyl, deuterium-substituted hydrocarbyl, and
halogen-substituted hydrocarbyl, all free of aliphatic
unsaturation, and R.sup.2 is R.sup.1 or alkenyl. The hydrocarbyl,
deuterium-substituted hydrocarbyl, and halogen-substituted
hydrocarbyl represented by R.sup.1 and R.sup.2, and the alkenyl
groups represented by R.sup.2 are as described an exemplified above
for the organopolysiloxane, component (A).
[0045] MQ resins can be prepared by methods well-known in the art.
For example, the resin can be prepared by treating a resin
copolymer produced by the silica hydrosol capping process of Daudt
et al. with at least an alkenyl-containing endblocking reagent. The
method of Daudt et al, is disclosed in U.S. Pat. No. 2,676,182,
which is hereby incorporated by reference to teach how to make
organopolysiloxane resins suitable for use in the present
invention.
[0046] Methods of preparing organopolysiloxane resins are well
known in the art; many of these resins are commercially available.
Organopolysiloxane resins are typically prepared by cohydrolyzing
the appropriate mixture of chlorosilane precursors in an organic
solvent, such as toluene. For example, a copolymer consisting
essentially of R.sup.2.sub.3SiO.sub.1/2 units and
R.sup.1SiO.sub.3/2 units, can be prepared by cohydrolyzing a
compound having the formula R.sup.2.sub.3SiCl and a compound having
the formula R.sup.1 SiCl.sub.3 in toluene, where R.sup.1 and
R.sup.2 are as defined above. The aqueous hydrochloric acid and
silicone hydrolyzate are separated and the hydrolyzate is washed
with water to remove residual acid and heated in the presence of a
mild condensation catalyst to "body" the resin to the requisite
viscosity. If desired, the resin can be further treated with a
condensation catalyst in an organic solvent to reduce the content
of silicon-bonded hydroxy groups. MDQ, MTQ, MTD, and TD resins can
be similarly prepared by cohydrolysis and condensation of
R.sup.2.sub.3SiCl, R.sup.2SiCl.sub.2, and SiCl.sub.4;
R.sup.2.sub.3SiCl, R.sup.1SiCl.sub.3, and SiCl.sub.4;
R.sup.2.sub.3SiCl, R.sup.1SiCl.sub.3, and R.sup.2SiCl.sub.2; and
R.sup.2SiCl.sub.2 and R.sup.1SiCl.sub.3; respectively, where
R.sup.1 and R.sup.2 are as defined above. Alternatively, silanes
containing hydrolysable groups other than chloro, such --Br, --I,
--OCH.sub.3, --OC(O)CH.sub.3, --N(CH.sub.3).sub.2, NHCOCH.sub.3,
and --SCH.sub.3, can be utilized as starting materials in the
cohydrolysis reaction. The properties of the resin products depend
on the types of silanes, the mole ratio of silanes, the degree of
condensation, and the processing conditions.
[0047] Component (A) can be a single organopolysiloxane or a
mixture comprising two or more organopolysiloxanes that differ in
at least one of the following properties: structure, viscosity,
average molecular weight, siloxane units, and sequence.
[0048] Component (B) is at least one organosilicon compound
containing an average of at least two silicon-bonded hydrogen atoms
per molecule. It is generally understood that crosslinking occurs
when the sum of the average number of alkenyl groups per molecule
in component (A) and the average number of silicon-bonded hydrogen
atoms per molecule in component (B) is greater than four. The
silicon-bonded hydrogen atoms in the organohydrogenpolysiloxane can
be located at terminal, pendant, or at both terminal and pendant
positions.
[0049] The organosilicon compound can be an organosilane or an
organohydrogensiloxane. The organosilane can be a monosilane,
disilane, trisilane, or polysilane. Similarly, the
organohydrogensiloxane can be a disiloxane, trisiloxane, or
polysiloxane. Preferably, the organosilicon compound is an
organohydrogensiloxane and more preferably, the organosilicon
compound is an organohydrogenpolysiloxane. The structure of the
organosilicon compound can be linear, branched, cyclic, or
resinous.
[0050] Examples of organosilanes include, but are not limited to,
monosilanes such as diphenylsilane and 2-chloroethylsilane;
disilanes such as 1,4-bis(dimethylsilyl)benzene,
bis[(p-dimethylsilyl)phenyl]ether, and 1,4-dimethyldisilylethane;
trisilanes such as 1,3,5-tris(dimethylsily- l)benzene and
1,3,5-trimethyl-1,3,5-trisilane; and polysilanes such as
poly(methylsilylene)phenylene and
poly(methylsilylene)methylene.
[0051] Examples of organohydrogensiloxanes include, but are not
limited to, disiloxanes such as 1,1,3,3-tetramethyldisiloxane and
1,1,3,3-tetraphenyldisiloxane; trisiloxanes such as
phenyltris(dimethylsiloxy)silane and
1,3,5-trimethylcyclotrisiloxane; and polysiloxanes such as a
trimethylsiloxy-terminated poly(methylhydrogensiloxane), a
trimethylsiloxy-terminated
poly(dimethylsiloxane/methylhydrogensiloxane), a
dimethylhydrogensiloxy-t- erminated poly(methylhydrogensiloxane),
and a resin consisting essentially of H(CH.sub.3).sub.2SiO.sub.1/2
units, (CH.sub.3).sub.3SiO.sub.1/2 units, and SiO.sub.4/2
units.
[0052] Component (B) can be a single organosilicon compound or a
mixture comprising two or more such compounds that differ in at
least one of the following properties: structure, average molecular
weight, viscosity, silane units, siloxane units, and sequence.
[0053] The concentration of component (B) in the silicone
composition of the present invention is sufficient to cure
(crosslink) the composition. The exact amount of component (B)
depends on the desired extent of cure, which generally increases as
the ratio of the number of moles of silicon-bonded hydrogen atoms
in component (B) to the number of moles of alkenyl groups in
component (A) increases. The concentration of component (B) is
typically sufficient to provide from 0.5 to 3 silicon-bonded
hydrogen atoms, alternatively from 0.7 to 1.2 silicon-bonded
hydrogen atoms, per alkenyl group in component (A).
[0054] Methods of preparing organosilicon compounds containing
silicon-bonded hydrogen atoms are well known in the art. For
example, organopolysilanes can be prepared by reaction of
chlorosilanes in a hydrocarbon solvent in the presence of sodium or
lithium metal (Wurtz reaction). Organopolysiloxanes can be prepared
by hydrolysis and condensation of organohalosilanes.
[0055] Component (C) is a photoactivated hydrosilylation catalyst.
The photoactivated hydrosilylation catalyst can be any
hydrosilylation catalyst capable of catalyzing the hydrosilylation
of component (A) with component (B) upon exposure to radiation
having a wavelength of from 150 to 800 nm and subsequent heating.
The platinum group metals include platinum, rhodium, ruthenium,
palladium, osmium and iridium. Preferably, the platinum group metal
is platinum, based on its high activity in hydrosilylation
reactions. The suitability of particular photoactivated
hydrosilylation catalyst for use in the silicone composition of the
present invention can be readily determined by routine
experimentation using the methods in the Examples section
below.
[0056] Examples of photoactivated hydrosilylation catalysts
include, but are not limited to, platinum(II) .beta.-diketonate
complexes such as platinum(II) bis(2,4-pentanedioate), platinum(II)
bis(2,4-hexanedioate), platinum(II) bis(2,4-heptanedioate),
platinum(II) bis(1-phenyl-1,3-butane- dioate, platinum(II)
bis(1,3-diphenyl-1,3-propanedioate), platinum(II)
bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedioate);
(.eta.-cyclopentadienyl)tr- ialkylplatinum complexes, such as
(Cp)trimethylplatinum, (Cp)ethyldimethylplatinum,
(Cp)triethylplatinum, (chloro-Cp)trimethylplat- inum, and
(trimethylsilyl-Cp)trimethylplatinum, where Cp represents
cyclopentadienyl; triazene oxide-transition metal complexes, such
as Pt[C.sub.6H.sub.5NNNOCH.sub.3].sub.4,
Pt[p-CN--C.sub.6H.sub.4NNNOC.sub.6H- .sub.11].sub.4,
Pt[p-H.sub.3COC.sub.6H.sub.4NNNOC.sub.6H.sub.11].sub.4,
Pt[p-CH.sub.3(CH.sub.2).sub.x--C.sub.6H.sub.4NNNOCH.sub.3].sub.4,
1,5-cyclooctadiene.Pt[p-CN--C.sub.6H.sub.4NNNOC.sub.6H.sub.11].sub.2,
1,5-cyclooctadiene.Pt[p-CH.sub.3O--C.sub.6H.sub.4NNNOCH.sub.3].sub.2,
[(C.sub.6H.sub.5).sub.3P].sub.3Rh[p-CN--C.sub.6H.sub.4NNNOC.sub.6H.sub.11-
], and
Pd[p-CH.sub.3(CH.sub.2).sub.x--C.sub.6H.sub.4NNNOCH.sub.3].sub.2,
where x is 1, 3, 5, 11, or 17;
(.eta.-diolefin)(.sigma.-aryl)platinum complexes, such as
(.eta..sup.4-1,5-cyclooctadienyl)diphenylplatinum,
.eta..sup.4-1,3,5,7-cyclooctatetraenyl)diphenylplatinum,
(.eta..sup.4-2,5-norboradienyl)diphenylplatinum,
(.eta..sup.4-1,5-cyclooc-
tadienyl)bis-(4-dimethylaminophenyl)platinum,
(.eta..sup.4-1,5-cyclooctadi- enyl)bis-(4-acetylphenyl)platinum,
and (.eta..sup.4-1,5-cyclooctadienyl)bi-
s-(4-trifluormethylphenyl)platinum. Preferably, the photoactivated
hydrosilylation catalyst is a Pt(II) .beta.-diketonate complex and
more preferably the catalyst is platinum(II)
bis(2,4-pentanedioate).
[0057] Component (C) can be a single photoactivated hydrosilylation
catalyst or a mixture comprising two or more such catalysts .
[0058] The concentration of component (C) is sufficient to catalyze
the addition reaction of components (A) and (B) upon exposure to
radiation and heat in the method described below. The concentration
of component (C) is typically sufficient to provide from 0.1 to
1000 ppm of platinum group metal, alternatively from 0.5 to 100 ppm
of platinum group metal, alternatively from 1 to 25 ppm of platinum
group metal, based on the combined weight of components (A), (B),
and (C). The rate of cure is very slow below 1 ppm of platinum
group metal. The use of more than 100 ppm of platinum group metal
results in no appreciable increase in cure rate, and is therefore
uneconomical.
[0059] Methods of preparing the preceding photoactivated
hydrosilylation catalysts are well known in the art. For example,
methods of preparing platinum(II) .beta.-diketonates are reported
by Guo et al. (Chemistry of Materials, 1998, 10, 531-536). Methods
of preparing (.eta.-cyclopentadienyl)trialkylplatinum complexes and
are disclosed in U.S. Pat. No. 4,510,094. Methods of preparing
triazene oxide-transition metal complexes are disclosed in U.S.
Pat. No. 5,496,961. And, methods of preparing
(.eta.-diolefin)(.sigma.-aryl)platinum complexes are taught in U.S.
Pat. No. 4,530,879.
[0060] Mixtures of the aforementioned components (A), (B), and (C)
may begin to cure at ambient temperature. To obtain a longer
working time or "pot life", the activity of the catalyst under
ambient conditions can be retarded or suppressed by the addition of
a suitable inhibitor to the silicone composition of the present
invention. A platinum catalyst inhibitor retards curing of the
present silicone composition at ambient temperature, but does not
prevent the composition from curing at elevated temperatures.
Suitable platinum catalyst inhibitors include various "ene-yne"
systems such as 3-methyl-3-penten-1-yne and
3,5-dimethyl-3-hexen-1-yne; acetylenic alcohols such as
3,5-dimethyl-1-hexyn-3-ol, 1-ethynyl-1-cyclohexanol, and
2-phenyl-3-butyn-2-ol; maleates and fumarates, such as the well
known dialkyl, dialkenyl, and dialkoxyalkyl fumarates and maleates;
and cyclovinylsiloxanes. Acetylenic alcohols constitute a preferred
class of inhibitors in the silicone composition of the present
invention.
[0061] The concentration of platinum catalyst inhibitor in the
present silicone composition is sufficient to retard curing of the
composition at ambient temperature without preventing or
excessively prolonging cure at elevated temperatures. This
concentration will vary widely depending on the particular
inhibitor used, the nature and concentration of the hydrosilylation
catalyst, and the nature of the organohydrogenpolysiloxan- e.
[0062] Inhibitor concentrations as low as one mole of inhibitor per
mole of platinum group metal will in some instances yield a
satisfactory storage stability and cure rate. In other instances,
inhibitor concentrations of up to 500 or more moles of inhibitor
per mole of platinum group metal may be required. The optimum
concentration for a particular inhibitor in a given silicone
composition can be readily determined by routine
experimentation.
[0063] The silicone composition can also comprise additional
ingredients, provided the ingredient does not adversely affect the
photopatteming or cure of the composition in the method of the
present invention. Examples of additional ingredients include, but
are not limited to, adhesion promoters, solvents, inorganic
fillers, photosensitizers, and surfactants.
[0064] The silicone composition can further comprise an appropriate
quantity of at least one organic solvent to lower the viscosity of
the composition and facilitate the preparation, handling, and
application of the composition. Examples of suitable solvents
include, but are not limited to, saturated hydrocarbons having from
1 to about 20 carbon atoms; aromatic hydrocarbons such as xylenes
and mesitylene; mineral spirits; halohydrocarbons; esters; ketones;
silicone fluids such as linear, branched, and cyclic
polydimethylsiloxanes; and mixtures of such solvents. The optimum
concentration of a particular solvent in the present silicone
composition can be readily determined by routine
experimentation.
[0065] The silicone composition can be a one-part composition
comprising components (A) through (C) in a single part or,
alternatively, a multi-part composition comprising components (A)
through (C) in two or more parts. In a multi-part composition,
components (A), (B), and (C) are typically not present in the same
part unless an inhibitor is also present. For example, a multi-part
silicone composition can comprise a first part containing a portion
of component (A) and a portion of component (B) and a second part
containing the remaining portion of component (A) and all of
component (C).
[0066] The one-part silicone composition is typically prepared by
combining components (A) through (C) and any optional ingredients
in the stated proportions at ambient temperature with or without
the aid of a solvent, which is described above. Although the order
of addition of the various components is not critical if the
silicone composition is to be used immediately, the hydrosilylation
catalyst is typically added last at a temperature below about
30.degree. C. to prevent premature curing of the composition. Also,
the multi-part silicone composition can be prepared by combining
the particular components designated for each part.
[0067] The substrate can be any material having a refractive index
less than the refractive index of the silicone core. The magnitude
of the difference in refractive index between the silicone core and
the substrate depends on several factors, including the thickness
of the core, wavelength of propagated light, and desired mode of
wave propagation (i.e., single mode or multimode). The difference
in refractive index between the silicone core and the substrate is
typically from 0.01 to 0.5, alternatively from 0.05 to 0.5,
alternatively form 0.1 to 0.3. For example, a waveguide containing
a silicone core having a thickness of 4 .mu.m and a refractive
index of 1.5, wherein the waveguide is capable of supporting the
first four modes of propagation at a wavelength of 590 nm, has a
difference in refractive index between the silicone core and the
substrate of about 0.1.
[0068] The substrate can be a rigid or flexible material. Examples
of substrates include, but are not limited to, a semiconductor
material such as silicon, silicon having a surface layer of silicon
dioxide, and gallium arsenide; quartz; fused quartz; aluminum
oxide; polyolefins such as polyethylene and polypropylene;
fluorocarbon polymers such as polytetrafluoroethylene and
polyvinylfluoride; polystyrene; polyamides such as Nylon;
polyimides; polyesters and acrylic polymers such as poly(methyl
methacrylate); epoxy resins; polycarbonates; polysulfones;
polyether sulfones; ceramics; and glass.
[0069] The silicone composition can be applied to the surface of
the substrate using any conventional method, such as spin coating,
dipping, spraying, brushing, or screen printing. The silicone
composition is typically applied by spin coating at a speed of from
200 to 5,000 rpm for 5 to 60 s. The spin speed, spin time, and
viscosity of the silicone composition can be adjusted so that the
silicone core produced in step (v) has the desired thickness.
[0070] When the silicone composition comprises a solvent, the
method can further comprise removing at least a portion of the
solvent from the silicone film. The solvent can be removed by
heating the silicone film at a temperature of from 50 to
150.degree. C. for 1 to 5 min, alternatively from 80 to 120.degree.
C. for 2 to 4 min.
[0071] At least one selected region of the silicone film is exposed
to radiation having a wavelength of from 150 to 800 nm,
alternatively from 250 to 450 nm, to produce a partially exposed
film having at least one exposed region and at least one
non-exposed region. The light source typically used is a medium
pressure mercury-arc lamp. The dose of radiation is typically from
0.1 to 5,000 mJ/cm.sup.2, alternatively from 250 to 1,300
mJ/cm.sup.2. The selected region of the silicone film is exposed to
radiation through a photomask having a pattern of images.
[0072] The non-exposed region of the partially exposed film is
removed with a developing solvent to form a patterned film. The
developing solvent is an organic solvent in which the non-exposed
region of the partially exposed film is at least partially soluble
and the exposed region is essentially insoluble. The developing
solvent typically has from 3 to 20 carbon atoms. Examples of
developing solvents include ketones, such as methyl isobutyl ketone
and methyl pentyl ketone; ethers, such as n-butyl ether and
polyethylene glycol monomethylether; esters, such as ethyl acetate
and y-butyrolactone; aliphatic hydrocarbons, such as nonane,
decalin, and dodecane; and aromatic hydrocarbons, such as
mesitylene, xylene, and toluene. The developing solvent can be
applied by any conventional method, including spraying, immersion,
and pooling. Preferably, the developing solvent is applied by
forming a pool of the solvent on a stationary substrate and then
spin-drying the substrate. The developing solvent is typically used
at a temperature of from room temperature to 100.degree. C.
However, the specific temperature will depend on the chemical
properties of the solvent, the boiling point of the solvent, the
desired rate of pattern formation, and the requisite resolution of
the photopatterning process.
[0073] The patterned film is then heated for an amount of time
sufficient to form at least one silicone core having a refractive
index of from to 1.3 to 1.7, alternatively from 1.4 to 1.7,
alternatively from 1.4 to 1.6, at 23.degree. C. for light having a
wavelength of 589 nm. The patterned film is typically heated for an
amount of time sufficient to achieve maximum crosslink density in
the silicone without oxidation or decomposition. The patterned film
is typically heated at a temperature of from 50 to 300.degree. C.
for 1 to 300 min, alternatively from 75 to 275.degree. C. for 10 to
120 min, alternatively from 200 to 250.degree. C. for 20 to 60 min.
The patterned film can be heated using conventional equipment such
as a hot plate or oven. The silicone core typically has a thickness
(height) of from 1 to 100 .mu.m, alternatively from 5 to 50 .mu.m,
alternatively from 8 to 20 .mu.m.
[0074] The first method can further comprise (v) covering the
substrate and the silicone core with a curable polymer composition
to form a polymer film and (vi) curing the polymer film to form a
clad layer, wherein the clad layer has a refractive index less than
the refractive index of the silicone core.
[0075] The curable polymer composition can be any polymer
composition that cures in step (vi) to form a clad layer having a
refractive index less than the refractive index of the silicone
core. The cure mechanism of the polymer composition is not limited.
The polymer composition can be cured, for example, by a
condensation or addition reaction. Examples of curable polymer
compositions include, but are not limited to, curable silicone
compositions, such as hydrosilylation-curable silicone
compositions, condensation-curable silicone compositions, and
peroxide-curable silicone compositions; curable polyolefin
compositions such as polyethylene and polypropylene compositions;
curable polyamide compositions; curable epoxy resin compositions;
curable amino resin compositions; curable polyurethane
compositions; curable polyimide compositions; curable polyester
compositions; and curable acrylic resin compositions.
[0076] In one embodiment of the method, the curable polymer
composition is the silicone composition of the present invention,
wherein the silicone composition cures to form a clad layer having
a refractive index less than the refractive index of the silicone
core. For example, the silicone core can be prepared using a
silicone composition comprising a vinyl-terminated
poly(methylphenylsiloxane) whereas the clad layer can be prepared
using a silicone composition containinig a vinyl-terminated
polydimethylsiloxane.
[0077] The curable polymer composition can be applied to the
silicone core and the substrate using any conventional method, such
as spin coating, dipping, spraying, brushing, or screen printing.
The curable polymer composition is typically applied by spin
coating at a speed of from 200 to 5000 rpm for 5 to 60 s. The spin
speed, spin time, and viscosity of the curable polymer composition
can be adjusted so that the cured clad layer produced in step (vii)
has the desired thickness.
[0078] The polymer film can be cured by a variety of means,
depending on the cure mechanism of the curable polymer composition,
including exposure to ambient or elevated temperature, irradiation,
and exposure to moisture.
[0079] The clad layer has a refractive index less than the
refractive index of the silicone core. The magnitude of the
difference in refractive index between the silicone core and the
clad layer is as described above for the difference in refractive
index between the silicone core and the substrate. Also, the clad
layer typically has a thickness of from 5 to 200 .mu.m,
alternatively from 15 to 50 .mu.m, alternatively from 20 to 35
.mu.m.
[0080] A second method of preparing a planar optical waveguide
assembly according to the present invention, comprises the steps
of:
[0081] (i) applying a silicone composition to a surface of a
substrate to form a silicone film, wherein the silicone composition
comprises:
[0082] (A) an organopolysiloxane containing an average of at least
two silicon-bonded alkenyl groups per molecule,
[0083] (B) an organosilicon compound containing an average of at
least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and
[0084] (C) a catalytic amount of a photoactivated hydrosilylation
catalyst;
[0085] (ii) exposing at least one selected region of the silicone
film to radiation having a wavelength of from 150 to 800 nm to
produce a partially exposed film having at least one exposed region
and at least one non-exposed region;
[0086] (iii) heating the partially exposed film for an amount of
time such that the exposed region is substantially insoluble in a
developing solvent and the non-exposed region is soluble in the
developing solvent;
[0087] (iv) removing the non-exposed region of the heated film with
the developing solvent to form a patterned film; and
[0088] (v) heating the patterned film for an amount of time
sufficient to form at least one silicone core having a refractive
index of from 1.3 to 1.7 at 23.degree. C. for light having a
wavelength of 589 nm; wherein the substrate has a refractive index
less than the refractive index of the silicone core.
[0089] Steps (i), (ii), and (v) of the second method are identical
to steps (i), (ii), and (iv), respectively, of the first
method.
[0090] The partially exposed film produced in step (ii) is heated
for an amount of time such that the region exposed to radiation
("exposed region") is substantially insoluble in a developing
solvent. The region that was not previously exposed to radiation
("non-exposed region") is soluble in the developing solvent. The
term "substantially insoluble" means that the exposed region of the
silicone film is not removed by dissolution in the developing
solvent to the extent that the underlying surface of the substrate
is exposed. The term "soluble" means that the unexposed region of
the silicone film is removed by dissolution in the developing
solvent, exposing the underlying surface of the substrate. The
partially exposed film is typically heated at a temperature of from
50 to 250.degree. C. for 0.1 to 10 min, alternatively from 100 to
200.degree. C. for 1 to 5 min, alternatively from 135 to
165.degree. C. for 2 to 4 min. The partially exposed film can be
heated using conventional equipment such as a hot plate or
oven.
[0091] The non-exposed region of the heated film produced in step
(iii) is removed with the developing solvent to form a patterned
film. The developing solvent, method of applying the developing
solvent, and temperature are as described in step (iii) of the
first method.
[0092] The second method can further comprise (vi) covering the
substrate and the silicone core with a curable polymer composition
to form a polymer film and (vii) curing the polymer film to form a
clad layer, wherein the clad layer has a refractive index less than
the refractive index of the silicone core. Steps (vi) and (vii) of
the second method are identical to steps (v) and (vi) of the first
method.
[0093] An embodiment of a planar optical waveguide assembly
prepared by either the first or second method of the present
invention is shown in FIG. 1. The optical waveguide assembly
comprises a substrate 10, a silicone core 20 covering a portion of
the substrate 10, wherein the silicone core 20 has a refractive
index of from 1.30 to 1.65 at 23.degree. C. for light having a
wavelength of 589 nm, and the substrate 10 has a refractive index
less than the refractive index of the silicone core 20.
[0094] Another embodiment of a planar optical waveguide assembly
prepared by either the first or second method of the present
invention is shown in FIG. 2. The optical waveguide assembly
comprises a substrate 10, a silicone core 20 covering a portion of
the substrate 10, wherein the silicone core 20 has a refractive
index of from 1.30 to 1.65 at 23.degree. C. for light having a
wavelength of 589 nm, and a clad layer 30 comprising a cured
polymer composition covering the substrate 10 and the silicone core
20, wherein the substrate 10 and the clad layer 30 each have a
refractive index less than the refractive index of the silicone
core 20.
[0095] The method of the present invention is scaleable to a high
throughput manufacturing process. Importantly, the method allows
simultaneous fabrication of multiple waveguides on a single
substrate. Additionally, the method employs conventional wafer
fabrication techniques (e.g., coating, exposing, developing,
curing) and equipment. Furthermore, the method uses a
photopatternable silicone composition, thereby eliminating
additional process steps, for example, applying a photoresist and
etching, associated with use of a non-photopatternable polymer
composition. Finally, the process of the instant invention has high
resolution, meaning that the process transfers images from a
photomask to the silicone film on a substrate with good retention
of critical dimensions.
[0096] The planar optical waveguide assembly of the present
invention exhibits good thermal stability over a wide range of
temperatures and good environmental resistance, particularly
moisture resistance. Also, the waveguide assembly exhibits low
birefringence and low transmission loss.
[0097] The optical waveguide assembly of the present invention can
be used to fabricate components of optical integrated circuits,
such as attenuators, switches, splitters, routers, filters, and
gratings.
EXAMPLES
[0098] The following examples are presented to further illustrate
the method of photopatterning the silicone composition of this
invention, but are not to be considered as limiting the invention,
which is delineated in the appended claims. Unless otherwise noted,
all parts and percentages reported in the examples are by weight.
The following methods and materials were employed in the
examples:
[0099] Irradiation of a silicone film was carried out using a OAI
7-inch medium pressure mercury projection lamp equipped with a
4-inch diameter interference filter centered at 365 nm (I-line) and
having a full width at half maximum (FWHM) of 10.+-.2 nm (Optics
Automation Instrumentation, Milpitas, Calif.). Radiation dose
(mJ/cm.sup.2) was measured using an International Light radiometer
calibrated against I-line radiation.
[0100] Thickness of a cured silicone film on a silicon wafer was
determined using a Tencor P-11 surface profilometer (KLA Tencor,
Milpitas, Calif.). Film thickness was measured at a step between
the coated and uncoated surfaces of the wafer. The reported value
for thickness, in microns, represents the average of three
measurements performed on different regions of the same wafer.
[0101] Film retention, expressed as percentage, was calculated
according to the equation:
Film retention (%)=t.sub.2/t.sub.1.times.100
[0102] where t.sub.2 is the thickness of a cured patterned silicone
film produced according to the method in the Examples below and
t.sub.1 is the thickness of a silicone film prepared using the same
method, except omitting the steps of UV exposure, post-exposure
heating, and developing (treatment with n-butyl ether). In the
latter case, a portion of the unpatterned cured silicone film was
removed to expose the wafer surface. Thickness measurements were
carried out as described above.
[0103] Resolution of the photopatterning process was determined by
measuring the size of a feature in the silicone film corresponding
to a 250-micron circular aperture (Examples 1-3) or a 40-micron
circular aperture (Examples 4-33) in the photomask. Measurements
were performed on a digitized photomicrograph of the via using
Image Pro Plus image analysis software (Silver Spring, Md.). The
reported value for resolution, expressed in units of microns,
represents the average of four measurements performed on different
features of the same wafer.
[0104] Resin A: an organopolysiloxane resin consisting essentially
of CH.sub.2.dbd.CH(CH.sub.3).sub.2SiO.sub.1/2 units,
(CH.sub.3).sub.3SiO.sub- .1/2 units, and SiO.sub.4/2 units, wherein
the mole ratio of CH.sub.2.dbd.CH(CH.sub.3).sub.2SiO.sub.1/2 units
and (CH.sub.3).sub.3SiO.sub.1/2 units combined to SiO.sub.4/2 units
is about 0.7, and the resin has a weight-average molecular weight
of about 22,000, a polydispersity of about 5, and contains about
5.5 mole percent (1.8% by weight) of vinyl groups.
[0105] Resin B: an organopolysiloxane resin consisting essentially
of PhSiO.sub.3/2 units and
CH.sub.2.dbd.CH(CH.sub.3).sub.2SiO.sub.1/2 units, wherein the mole
ratio of PhSiO.sub.3/2 units to CH.sub.2.dbd.CH(CH.sub.3-
).sub.2SiO.sub.1/2 units is about 3.0, and the resin has a
weight-average molecular weight of about 1600, has a polydispersity
of about 1.14, and contains about 5.2 wt % of vinyl groups.
[0106] Crosslinking Agent A: a mixture consisting of 88% of a
trimethylsiloxy-terminated
poly(dimethylsiloxane/methylhydrogensiloxane) having an average of
92 dimethylsiloxane units and 6 methylhydrogensiloxane units and
per molecule and containing about 0.08% of silicon-bonded hydrogen
atoms; 4% of dimethyl methylhydrogen cyclosiloxane; 4% of
octamethylcyclotetrasiloxane; 3% of decamethylcyclopentasiloxane;
and 1% of dimethylcyclosiloxanes (D.sub.6 or greater).
[0107] Crosslinking Agent B: an organohydrogenpolysiloxane resin
consisting essentially of PhSiO.sub.3/2 units and
H(CH.sub.3).sub.2SiO.su- b.1/2 units, wherein the mole ratio of
PhSiO.sub.3/2 units to H(CH.sub.3).sub.2SiO.sub.1/2 units is about
1.2, and the resin has a viscosity of about 0.35 Pa.s, has a
weight-average molecular weight of about 1250, and contains about
0.41 wt % of silicon-bonded hydrogen atoms.
[0108] Silicone Base: a mixture consisting of 61.32% of Resin A;
22.09% of a mixture consisting of 88% of a
trimethylsiloxy-terminated
poly(dimethylsiloxane/methylhydrogensiloxane) having an average of
100 dimethylsiloxane units and 9 methylhydrogensiloxane units per
molecule and containing about 0.11% of silicon-bonded hydrogen
atoms, 5% of dimethyl methylhydrogen cyclosiloxane, 3% of
octamethylcyclotetrasiloxane- , 2% of decamethylpentasiloxane, 1%
of methylhydrogen cyclosiloxanes, and 0.8% of
dimethylcyclosiloxanes (D.sub.6 or greater); 2.33% of a
trimethylsiloxy-terminated
poly(dimethylsiloxane/methylhydrogensiloxane) having an average of
3 dimethylsiloxane units and 5 methylhydrogensiloxane units per
molecule and containing about 0.8% of silicon-bonded hydrogen
atoms; and 14.27% of mesitylene. The Silicone Base was stored in a
sealed amber bottle.
[0109] The platinum(II) acetylacetonate used to prepare Catalysts
A-E was obtained from Strem Chemicals (Newburyport, Mass.). The
material was purified by sublimation at a temperature of
140.degree. C. and a pressure of 4 mmHg.
[0110] Catalyst A: a mixture consisting of 0.05% of platinum(II)
acetylacetonate in mesitylene.
[0111] Catalyst B: a mixture consisting of 0.10% of platinum(II)
acetylacetonate in mesitylene.
[0112] Catalyst C: a mixture consisting of 0.15% of platinum(II)
acetylacetonate in mesitylene.
[0113] Catalyst D: a mixture consisting of 0.20% of platinum(II)
acetylacetonate in mesitylene.
[0114] Catalyst E: a mixture consisting of 0.25% of platinum(II)
acetylacetonate in mesitylene.
[0115] Mesitylene: A.C.S. reagent grade.
Examples 1-3
[0116] Resin A (46.84 parts), 42.16 parts of Crosslinking Agent A,
and 10.12 parts of mesitylene were combined in an amber bottle.
Catalyst D (0.89 part) was added to the blend and mixing was
continued for 0.5 h at room temperature. The mixture was then
pressure-filtered (138 to 276 kPa nitrogen) through a stainless
steel canister containing 10-.mu.m and 5-.mu.m nylon membranes in
series. The silicone composition (filtrate) was stored prior to use
at -15.degree. C. in a closed polyethylene bottle wrapped in
aluminum foil.
[0117] In each of Examples 1-3, the silicone composition (about 2.5
g), which was at room temperature, was applied to a 100-mm silicon
wafer and spun out into a thin film (500 rpm for 10 s followed by
3000 rpm for 30 s). The coated wafer was heated on a hot plate at
110.degree. C. for 2 min to remove most of the solvent. The film
was then exposed to I-line radiation (365 nm) through a photomask
containing 250-.mu.m circular apertures and in near contact with
the film. The wafer was then heated on a hot plate under the
conditions of temperature and time specified in Table 1. The wafer
was allowed to cool to room temperature and mounted on a spin
coater. The coated surface of the wafer was flooded with nonane and
allowed to stand at room temperature for 2 min. The wafer was then
spun dry (500 rpm for 10 s followed by 3000 rpm for 30 s), placed
in an oven for 30 min at 250.degree. C., and allowed to cool to
room temperature. The film thickness, film retention, and
resolution values for each wafer are reported in Table 1.
1TABLE 1 Post. Film Film Ex- UV Bake Thick- Reten- am- Cata- Dose
Temp. Time ness tion Resolution ple lyst (mJ/cm.sup.2) (.degree.
C.) (s) (.mu.m) (%) (.mu.m) 1 D 1000 135 180 18.3 87 151 2 D 1000
144 265 16.8 80 168 3 D 1000 165 60 17.2 82 164
Examples 4-33
[0118] A silicone composition was prepared by combining the a
silicone base with the Catalyst specified in Table 2 according to
the following procedure: Silicone Base (99.15 parts) and 0.85 part
of Catalyst were combined in an amber bottle and mixed for 0.5 h at
room temperature. The mixture was then pressure-filtered (138 to
276 kPa nitrogen) through a stainless steel canister containing
10-.mu.m and 5-.mu.m nylon membranes in series. The silicone
composition (filtrate) was store prior to use at -15.degree. C. in
a closed polyethylene bottle wrapped in aluminum foil.
[0119] In each of Examples 4-33, a sample of the silicone
composition (about 2.5 g), which was at temperature, was applied to
a 100-mm silicon wafer and spun out into a thin film (500 rpm for
10 s followed by 3000 rpm for 30 s). The coated wafer was heated on
a hot plate at 110.degree. C. for 2 min to remove most of the
solvent. The film was then exposed to I-line radiation (365 nm)
through a photomask containing 40-.mu.m circular apertures and in
near contact with the film. The wafer was then heated on a hot
plate under the conditions of temperature and time specified in
Table 2. The wafer was allowed to cool to room temperature and
mounted on a spin coater. The coated surface of the wafer was
flooded with n-butyl ether and allowed to stand at room temperature
for 2 min. The wafer was then spun dry (500 rpm for 10 s followed
by 3000 rpm for 30 s), placed in an oven for 30 min at 250.degree.
C., and allowed to cool to room temperature. The film thickness,
film retention, and resolution values for each wafer are reported
in Table 2.
2TABLE 2 Post. Film Film Ex- UV Bake Thick- Reten- am- Cata- Dose
Temp. Time ness tion Resolution ple lyst (mJ/cm.sup.2) (.degree.
C.) (s) (.mu.m) (%) (.mu.m) 4 A 700 165 180 14.33 62 44.55 5 B 400
150 120 0.17 0.7 - 6 B 400 150 240 10.24 45 46.32 7 B 400 180 120
15.33 67 40.13 8 B 400 180 240 17.64 77 15.05 9 B 1000 150 120
12.19 53 52.15 10 B 1000 150 240 15.74 68 42.59 11 B 1000 180 120
18.25 79 25.26 12 B 1000 180 240 18.91 82 19.99 13 C 100 165 180
6.89 30 - 14 C 700 135 180 8.67 38 - 15 C 700 165 60 7.61 33 - 16 C
700 165 180 8.19 36 - 17 C 700 165 180 16.62 72 37.55 18 C 700 165
180 16.64 72 19.50 19 C 700 165 180 17.31 75 + 20 C 700 165 180
17.69 77 17.72 21 C 700 165 180 18.08 79 32.97 22 C 700 165 300
19.12 83 33.22 23 C 700 195 180 25.00 100 6.02 24 C 1300 165 180
18.43 80 27.78 25 D 400 150 120 12.12 53 47.59 26 D 400 150 240
16.02 70 39.89 27 D 400 180 120 19.10 83 32.99 28 D 400 180 240
25.00 100 8.43 29 D 1000 150 120 16.32 71 43.30 30 D 1000 150 240
18.82 82 23.53 31 D 1000 180 120 18.74 82 19.87 22 D 1000 180 240
25.00 100 5.66 33 E 700 165 180 19.07 83 21.79 - Denotes a value
not measurable due to poor image quality and + denotes a value not
measured.
Examples 34-38
[0120] Resin B (60.21 parts), 29.79 parts of Crosslinking Agent B,
and 9.00 parts of mesitylene were combined in an amber bottle.
Catalyst D (1.00 part) was added to the blend and mixing was
continued for 0.5 h at room temperature. The mixture was then
pressure-filtered (138 to 276 kPa nitrogen) through a stainless
steel canister containing 10-.mu.m and 5-.mu.m nylon membranes in
series. The silicone composition (filtrate) was stored prior to use
at -15.degree. C. in a closed polyethylene bottle wrapped in
aluminum foil.
[0121] In each of Examples 34-38, the silicone composition (about
2.5 g), which was at room temperature, was applied to a 100-mm
silicon wafer and spun out into a thin film. The wafers were spun
at 500 rpm for 10 s (Examples 34 and 36-38) or 25 s (Example 35),
followed by 1500 rpm fir 20 s. The coated wafer was heated on a hot
plate at 100.degree. C. for 2 min to remove most of the solvent.
The film was then exposed to I-line radiation (365 nm) through a
photomask containing 250-.mu.m circular apertures and in near
contact with the film. The wafer was then heated on a hot plate
under the conditions of temperature and time specified in Table 3.
The wafer was allowed to cool to room temperature and mounted on a
spin coater. The coated surface of the wafer was flooded with
n-butyl ether and allowed to stand at room temperature for 1 min
(Examples 34 and 35) or 0.1 min (Examples 36-38). The wafer was
then spun dry (200 rpm for 30 s followed by 3000 rpm for 30 s),
placed in an oven for 30 min at 200.degree. C., and allowed to cool
to room temperature. The film thickness, film retention, and
resolution values for each wafer are reported in Table 3.
3TABLE 3 Post. Film Film Ex- UV Bake Thick- Reten- am- Cata- Dose
Temp. Time ness tion Resolution ple lyst (mJ/cm.sup.2) (.degree.
C.) (s) (.mu.m) (%) (.mu.m) 34 D 981.5 130 30 7.6 88 500 35 D 981.5
130 60 10.8 - 500 36 D 981.5 130 15 7.3 85 250 37 D 226.5 130 30
7.2 84 500 38 D 981.5 130 30 7.9 92 500 + Denotes a value not
measured
* * * * *