U.S. patent application number 11/978391 was filed with the patent office on 2008-06-19 for epoxy removal process for microformed electroplated devices.
This patent application is currently assigned to MicroChem Corp.. Invention is credited to Donald W. Johnson, Harris R. Miller.
Application Number | 20080142478 11/978391 |
Document ID | / |
Family ID | 39364823 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080142478 |
Kind Code |
A1 |
Miller; Harris R. ; et
al. |
June 19, 2008 |
Epoxy removal process for microformed electroplated devices
Abstract
The present invention is directed to a method of removing
epoxy-based photoresist from a manufactured metallic microstructure
or deep etched via, comprising the steps of (1) providing a form
comprising an epoxy-based photoresist and a manufactured metallic
microstructure; (2) optionally exposing the form to a solvent,
aqueous alkali, or amine-based photoresist stripper; (3) exposing
the form to an alkali permanganate oxidizing solution to remove the
form from the manufactured metallic microstructure, the alkali
permanganate oxidizing solution comprising from about 4% to about
9% permanganate by weight, based on the total weight of the alkali
permanganate solution, and from about 3% to about 6% alkali by
weight, based on the total weight of the alkali permanganate
solution; and (4) exposing the manufactured metallic microstructure
to a neutralizing solution comprising from about 5% to about 10% by
weight of an acid and from about 1% to about 10% by weight of a
reducing agent, all weight percents being based on the total weight
of the neutralizing solution.
Inventors: |
Miller; Harris R.; (Sharon,
MA) ; Johnson; Donald W.; (Wayland, MA) |
Correspondence
Address: |
WIGGIN AND DANA LLP;ATTENTION: PATENT DOCKETING
ONE CENTURY TOWER, P.O. BOX 1832
NEW HAVEN
CT
06508-1832
US
|
Assignee: |
MicroChem Corp.
|
Family ID: |
39364823 |
Appl. No.: |
11/978391 |
Filed: |
October 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60855877 |
Nov 1, 2006 |
|
|
|
Current U.S.
Class: |
216/49 |
Current CPC
Class: |
B81C 99/0095 20130101;
G03F 7/423 20130101; G03F 7/425 20130101 |
Class at
Publication: |
216/49 |
International
Class: |
C23F 1/02 20060101
C23F001/02 |
Claims
1. A method of removing epoxy-based photoresist from a manufactured
metallic microstructure, comprising the steps of (1) providing a
form comprising an epoxy-based photoresist and a manufactured
metallic microstructure; (2) optionally exposing said form to a
solvent, aqueous alkali, or amine-based photoresist stripper; (3)
exposing said form to an alkali permanganate oxidizing solution to
remove said form from said manufactured metallic microstructure,
said alkali permanganate oxidizing solution comprising from about
4% to about 9% permanganate by weight, based on the total weight of
said alkali permanganate solution, and from about 3% to about 6%
alkali by weight, based on the total weight of said alkali
permanganate solution; and (4) exposing said manufactured metallic
microstructure to a neutralizing solution comprising from about 5%
to about 10% by weight of an acid and from about 1% to about 10% by
weight of a reducing agent, all weight percents being based on the
total weight of said neutralizing solution.
2. The method of claim 1, wherein said epoxy-based photoresist is a
crosslinked carboxylated epoxy cresol novolak photoresist.
3. The method of claim 1, wherein said alkali permanganate
oxidizing solution comprises about 5% permanganate by weight and
about 5% alkali by weight, all based on the total weight of said
alkali permanganate solution.
4. The method of claim 1, wherein said reducing agent is selected
from the group consisting of hydroxylamine sulfate, hydroxylamine
nitrate, hydroxylamine phosphate, and combinations thereof.
5. The method of claim 1, wherein said acid is selected from the
group consisting of sulfuric acid, sulfamic acid, methane sulfonic
acid, and combinations thereof.
6. The method of claim 1, wherein said solvent or amine-based
photoresist stripper is selected from the group consisting of NMP,
dimethylsulfoxide (DMSO), sulfolane, dimethylforamide (DMF),
dimethylacetamide (DMAC), diethylene glycol monobutyl ether,
propylene carbonate, and combinations thereof.
7. The method of claim 1, wherein said manufactured metallic
microstructure is a micromachined part.
8. The method of claim 1, wherein said manufactured metallic
microstructure is a metal bump.
9. A method of manufacturing a MEMS device, comprising the steps
of: (1) providing a form comprising an epoxy-based photoresist and
a manufactured MEMS device; (2) optionally exposing said form to a
solvent, aqueous alkali, or amine-based photoresist stripper; (3)
exposing said form to an alkali permanganate oxidizing solution to
remove said form from said manufactured MEMS device, said alkali
permanganate oxidizing solution comprising from about 4% to about
9% permanganate by weight, based on the total weight of said alkali
permanganate solution, and from about 3% to about 6% alkali by
weight, based on the total weight of said alkali permanganate
solution; and (4) exposing said manufactured MEMS device to a
neutralizing solution comprising from about 5% to about 10% by
weight of an acid and from about 1% to about 10% by weight of a
reducing agent, all weight percents being based on the total weight
of said neutralizing solution.
10. The method of claim 9, wherein said epoxy-based photoresist is
a crosslinked carboxylated epoxy cresol novolak photoresist.
11. The method of claim 9, wherein said alkali permanganate
oxidizing solution comprises about 5% permanganate by weight and
about 5% alkali by weight, all based on the total weight of said
alkali permanganate solution.
12. The method of claim 9, wherein said reducing agent is selected
from the group consisting of hydroxylamine sulfate, hydroxylamine
nitrate, hydroxylamine phosphate, and combinations thereof.
13. The method of claim 9, wherein said acid is selected from the
group consisting of sulfuric acid, sulfamic acid, methane sulfonic
acid, and combinations thereof.
14. The method of claim 9, wherein said solvent or amine-based
photoresist stripper is selected from the group consisting of NMP,
dimethylsulfoxide (DMSO), sulfolane, dimethylforamide (DMF),
dimethylacetamide (DMAC), diethylene glycol monobutyl ether,
propylene carbonate, and combinations thereof.
15. A method of removing crosslinked epoxy novolak photoresist from
a substrate, comprising the steps of: (1) providing a substrate
comprising a form made from crosslinked epoxy novolak photoresist;
(2) optionally exposing said substrate to a solvent, aqueous
alkali, or amine-based photoresist stripper; (3) exposing said
substrate to an alkali permanganate oxidizing solution to remove
said crosslinked epoxy novolak photoresist from said substrate,
said alkali permanganate oxidizing solution comprising from about
4% to about 9% permanganate by weight, based on the total weight of
said alkali permanganate solution, and from about 3% to about 6%
alkali by weight, based on the total weight of said alkali
permanganate solution; and (4) exposing said substrate to a
neutralizing solution comprising from about 5% to about 10% by
weight of an acid and from about 1% to about 10% by weight of a
reducing agent, all weight percents being based on the total weight
of said neutralizing solution.
16. The method of claim 15, wherein said alkali permanganate
oxidizing solution comprises about 5% permanganate by weight and
about 5% alkali by weight, all based on the total weight of said
alkali permanganate solution.
17. The method of claim 15, wherein said reducing agent is selected
from the group consisting of hydroxylamine sulfate, hydroxylamine
nitrate, hydroxylamine phosphate, and combinations thereof.
18. The method of claim 15, wherein said acid is selected from the
group consisting of sulfuric acid, sulfamic acid, methane sulfonic
acid, and combinations thereof.
19. The method of claim 15, wherein said solvent or amine-based
photoresist stripper is selected from the group consisting of NMP,
dimethylsulfoxide (DMSO), sulfolane, dimethylforamide (DMF),
dimethylacetamide (DMAC), diethylene glycol monobutyl ether,
propylene carbonate, and combinations thereof.
20. The method of claim 15, wherein said epoxy novolak photoresist
is SU-8.
21. A method of removing crosslinked epoxy-based photoresist,
comprising the steps of: (1) lithographically producing an etch
mask on a substrate with an epoxy-based photoresist; (2) exposing
said substrate to a DRIE plasma comprising alternating gases of
sulfur hexafluoride and octafluorocyclobutane; (3) exposing said
substrate to an alkali permanganate oxidizing solution to remove
said crosslinked epoxy novolak photoresist from said substrate,
said alkali permanganate oxidizing solution comprising from about
4% to about 9% permanganate by weight, based on the total weight of
said alkali permanganate solution, and from about 3% to about 6%
alkali by weight, based on the total weight of said alkali
permanganate solution; and (4) exposing said substrate to a
neutralizing solution comprising from about 5% to about 10% by
weight of an acid and from about 1% to about 10% by weight of a
reducing agent, all weight percents being based on the total weight
of said neutralizing solution.
22. The method of claim 21, wherein said alkali permanganate
oxidizing solution comprises about 5% permanganate by weight and
about 5% alkali by weight, all based on the total weight of said
alkali permanganate solution.
23. The method of claim 21, wherein said reducing agent is selected
from the group consisting of hydroxylamine sulfate, hydroxylamine
nitrate, hydroxylamine phosphate, and combinations thereof.
24. The method of claim 21, wherein said acid is selected from the
group consisting of sulfuric acid, sulfamic acid, methane sulfonic
acid, and combinations thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/855,877 filed Nov. 1, 2006.
BACKGROUND OF THE INVENTION 1. Field of the Invention
[0002] The present invention is directed to the production of
micromachines, microelectromechanical systems (MEMS) and more
particularly to methods for producing high aspect-ratio plated
microstructures and deep etched vias using an epoxy-based
photoresist and removing the photoresist with a permanganate-based
photoresist remover.
[0003] 2. Brief Description of the Art
[0004] A wide variety of MEMS devices are now being fabricated
using various types of UV sensitive photoresists. Epoxy-based
photoresists, in particular are capable of producing very high
aspect-ratio, micron-sized features with near perfect sidewalls.
Some commercial applications of these photoresist structures can be
found in ink-jet nozzles, micro-fluidic channels and bulk acoustic
wave filters for wireless transmission. Other MEMS devices use
these same epoxy-based photoresists as a microform or micro-mold to
produce a secondary metallic image by electrolytic or electroless
plating techniques. Once the metal micro-structure has been formed,
the epoxy photoresist is removed, leaving behind the final plated
metallic structure.
[0005] Removing the epoxy mold without harming the plated metal
structure can be difficult, because many of the properties that
make cured epoxy resins resistant to chemical attack from the
plating solution also make them resistant to their removal in
photoresist stripping chemistry. However, complete removal of the
epoxy mold is critical for producing many MEMS devices, such as
induction coils, harmonic micro-drives and fuel cell catalysts.
[0006] Advanced packaging and chip stacking techniques rely upon a
method of perforating the completed wafer with microscopic holes,
which pass completely through the substrate and are known as
through-hole-wafer-vias. The vias are commonly formed using a dry,
isotropic etching technique known as deep reactive ion etching
(DRIE). The wafer vias are isotropic, because of a process (a.k.a.
"Bosch") of alternating gases of sulfur hexafluoride and
octafluorocyclobutane. Alternating these two gases successively
deposits and removes polymer in the etched vias, which acts to
passivate the etched sidewall, which produces extremely high aspect
ratio etched structures under vacuum and a radio frequency (RF)
generated plasma. After the vias are completed, it is common to
fill them with plated metals, such as copper or polycrystalline
silicon.
[0007] Epoxy-based photoresists have been found to have very good
resistance to fluorine and chlorine plasmas, making them an ideal
photoresist for DRIE processing. However, removing the resist after
several hours of exposure to high temperature DRIE conditions can
be difficult or impossible.
[0008] Various methods for removing epoxy photoresists have been
reported, such as the use of hot molten salts, excimer lasers,
thermally stressing or cracking the resist, high pressure water
jets and even sand blasting. However, to date no satisfactory
method of removing or dissolving cross-linked epoxy resists from
micron-sized metallic structures has been demonstrated. It is
possible to modify the structure of the epoxy polymer and make it
more susceptible to common photoresist removers, such as N-methyl
pyrrolidine (NMP), as taught by U.S. Patent Application No.
2005/0147918 A1 and Japanese Patent No. JP 2007-109706. Such an
epoxy resin, known as BMR, is commercially available from Nippon
Kayaku Co. Ltd. Japan. It is also possible to remove the
photoresist using dry processing techniques, such as reactive ion
etching (RIE). However, RIE etch rates for photoresist stripping
rarely exceed 1-2 .mu.m per minute. This means that the dwell time
for stripping photoresist from a single wafer can be almost two
hours for a 100 .mu.m coating of photoresist, whether the plasma is
generated by RF or microwaves.
[0009] Because of the large number of wafers that can be
simultaneously batch processed and because of its relatively low
cost, wet chemical tank processing is the preferred method of
photoresist removal. One such process that has been widely accepted
in the preparation of printed circuit boards for through-hole
metallization is a process called desmear or etchback. See, for
example, U.S. Pat. Nos. 4,597,988; 4,515,829; 4,496,420; 4,601,783;
4,863,577; 5,498,311; 5,985,040; and 6,454,868. The printed circuit
board, which consists of a matrix of glass fibers embedded in epoxy
resin and interlaced with layers of copper metal, are commonly
perforated using a high-speed drill. During the process of drilling
the holes, the drill bit temperature exceeds the glass transition
temperature (Tg) of the epoxy resin and spreads excess, unwanted
epoxy into the drilled hole, making it difficult to plate the hole
with electrolytic or electroless copper plating solutions. This
thin layer of epoxy resin, which is "smeared" by the drill bit into
the printed circuit board hole can be removed by treatment with a
solution of alkali permanganate. This process, known as "desmear"
removes the cross-linked epoxy resin by reacting it with an aqueous
solution of alkali and permanganate to produce insoluble manganese
dioxide and alkali soluble carboxylic acids (See Scheme. 1). The
manganese dioxide precipitate is then removed by converting it to
aqueous, soluble manganese sulfate in a subsequent neutralizer
solution.
##STR00001##
[0010] Improved methods of removing cross-linked epoxy resists for
the production of MEMS and other micron-sized structures are needed
in the art. The present invention is believed to be an answer to
that need.
SUMMARY OF THE INVENTION
[0011] In one aspect, the present invention is directed to a method
of removing epoxy-based photoresist from a manufactured metallic
microstructure, comprising the steps of (1) providing a form
comprising an epoxy-based photoresist and a manufactured metallic
microstructure; (2) optionally exposing the form to a solvent,
aqueous alkali, or amine-based photoresist stripper; (3) exposing
the form to an alkali permanganate oxidizing solution to remove the
form from the manufactured metallic microstructure, the alkali
permanganate oxidizing solution comprising from about 4% to about
9% permanganate by weight, based on the total weight of the alkali
permanganate solution, and from about 3% to about 6% alkali by
weight, based on the total weight of the alkali permanganate
solution; and (4) exposing the manufactured metallic microstructure
to a neutralizing solution comprising from about 5% to about 10% by
weight of an acid and from about 1% to about 10% by weight of a
reducing agent, all weight percents being based on the total weight
of the neutralizing solution.
[0012] In another aspect, the present invention is directed to a
method of manufacturing a MEMS device, comprising the steps of: (1)
providing a form comprising an epoxy-based photoresist and a
manufactured MEMS device; (2) optionally exposing the form to a
solvent, aqueous alkali, or amine-based photoresist stripper; (3)
exposing the form to an alkali permanganate oxidizing solution to
remove the form from the manufactured MEMS device, the alkali
permanganate oxidizing solution comprising from about 4% to about
9% permanganate by weight, based on the total weight of the alkali
permanganate solution, and from about 3% to about 6% alkali by
weight, based on the total weight of the alkali permanganate
solution; and (4) exposing the manufactured MEMS device to a
neutralizing solution comprising from about 5% to about 10% by
weight of an acid and from about 1% to about 10% by weight of a
reducing agent, all weight percents being based on the total weight
of the neutralizing solution.
[0013] In another aspect, the present invention is directed to a
method of removing crosslinked epoxy novolak photoresist from a
substrate, comprising the steps of: (1) providing a substrate
comprising a form made from crosslinked epoxy novolak photoresist;
(2) optionally exposing the substrate to a solvent, aqueous alkali,
or amine-based photoresist stripper; (3) exposing the substrate to
an alkali permanganate oxidizing solution to remove the crosslinked
epoxy novolak photoresist from the substrate, the alkali
permanganate oxidizing solution comprising from about 4% to about
9% permanganate by weight, based on the total weight of the alkali
permanganate solution, and from about 3% to about 6% alkali by
weight, based on the total weight of the alkali permanganate
solution; and (4) exposing the substrate to a neutralizing solution
comprising from about 5% to about 10% by weight of an acid and from
about 1% to about 10% by weight of a reducing agent, all weight
percents being based on the total weight of the neutralizing
solution.
[0014] In another aspect, the present invention is directed to a
method of removing crosslinked epoxy-based photoresist, comprising
the steps of: (1) lithographically producing an etch mask on a
substrate with an epoxy-based photoresist; (2) exposing the
substrate to a DRIE plasma comprising alternating gases of sulfur
hexafluoride and octafluorocyclobutane; (3) exposing the substrate
to an alkali permanganate oxidizing solution to remove the
crosslinked epoxy novolak photoresist from the substrate, the
alkali permanganate oxidizing solution comprising from about 4% to
about 9% permanganate by weight, based on the total weight of the
alkali permanganate solution, and from about 3% to about 6% alkali
by weight, based on the total weight of the alkali permanganate
solution; and (4) exposing the substrate to a neutralizing solution
comprising from about 5% to about 10% by weight of an acid and from
about 1% to about 10% by weight of a reducing agent, all weight
percents being based on the total weight of the neutralizing
solution.
[0015] These and other aspects will become apparent upon reading
the following detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] This invention relates to a method for producing high
aspect-ratio, micron-sized structures in epoxy-based photoresists,
plating and forming micron-sized metal structures between, under
and/or around the micro-formed epoxy photoresist and removing said
epoxy photoresist without deforming the plated metal structures.
Such structures can be encountered in the fabrication of MEMS
devices or in computer flip-chip packaging structures known as
bumps.
[0017] There are several key differences which distinguish the use
of an alkali permanganate process for producing MEMS devices from
the preparation of printed circuit boards for plating. First, the
desmear printed circuit board process is rate controlled, which
means that time, temperature, pH and permanganate concentration all
must be tightly controlled to prevent too much epoxy from being
removed and exposing the many glass fibers that support the epoxy
polymer. Second, the desmear process for printed circuit boards is
performed prior to electrolytic or electroless plating.
[0018] The method of using alkali permanganate to remove
epoxy-based photoresists for MEMS applications and for
micro-machined parts is said to go to completion because all of the
resist is removed from the metal plated structure. Therefore, the
epoxy-based photoresist removal process stops when all of the
resist is reacted and it is therefore not necessary for critical
timing of the process step. In the event that the removal process
is incomplete and that some epoxy-based photoresist still remains,
the process steps can be repeated without adverse chemical
reactions. Since the entire epoxy mold is removed in the alkali
permanganate solution, a robust process can be obtained by
incorporating a small excess process time and without analytical
controls of the permanganate solution. Also, because the MEMS
device plating is completed before the epoxy-based photoresist is
removed, there are no issues with contaminating the plating
solution with permanganate residue.
[0019] As indicated above, the present invention is directed to a
method of removing epoxy-based photoresist from a manufactured
metallic microstructure or deep etched via, comprising the steps of
(1) providing a form comprising an epoxy-based photoresist and a
manufactured metallic microstructure; (2) optionally exposing the
form to a solvent, aqueous alkali, or amine-based photoresist
stripper; (3) exposing the form to an alkali permanganate oxidizing
solution to remove the form from the manufactured metallic
microstructure, the alkali permanganate oxidizing solution
comprising from about 4% to about 9% permanganate by weight, based
on the total weight of the alkali permanganate solution, and from
about 3% to about 6% alkali by weight, based on the total weight of
the alkali permanganate solution; and (4) exposing the manufactured
metallic microstructure to a neutralizing solution comprising from
about 5% to about 10% by weight of an acid and from about 1% to
about 10% by weight of a reducing agent, all weight percents being
based on the total weight of the neutralizing solution. Each of
these steps is discussed in greater detail below.
[0020] According to the invention, a form made from an epoxy-based
photoresist and a manufactured metallic microstructure may be any
microstructure commonly employed in microelectronics manufacturing,
such as a micromachined part, a microelectromechanical systems
(MEMS) device, a metal plated part, computer flip-chip packaging
structures, metallic bumps, and the like. Preferably, the metal
microstructure has a high aspect ratio, and more preferably an
aspect ratio of greater than two, where the aspect ratio is defined
as the ratio of the height to width of the structure. The form may
be made by any process or technique, such as lithography,
electroplating, combinations of these techniques, and the like.
[0021] A preferred epoxy-based photoresist used in the method of
the present invention is a carboxylated epoxy cresol novolak
photoresist known as KMPR.RTM., commercially available from
MicroChem Corp. U.S.A. and also by Kayaku MicroChem Corporation of
Japan. KMPR.RTM. photoresist is capable of producing near vertical,
high aspect-ratio micron-sized structures, which can be used for
either electrolytic or electroless plating.
[0022] The KMPR.RTM. photoresist plating form can be partially
removed from the plated metallic structures by optionally
pre-treating the form with a solvent, aqueous alkali, or amine
based photoresist stripper solution. Examples of solvents or amine
based strippers include N-methyl pyrrolidone (NMP),
dimethylsulfoxide (DMSO), sulfolane, dimethylforamide (DMF),
dimethylacetamide (DMAC), diethylene glycol monobutyl ether or
propylene carbonate, as well as combinations of these. Examples of
aqueous alkali include 20-45 wt % of aqueous sodium or potassium
hydroxide. Preferably, this pre-treatment step occurs at a solution
temperature of 60.degree. C.-80.degree. C.
[0023] Fully cross-linked KMPR.RTM. resist can be completely
removed from the ultra-high aspect ratio, micron-sized metal-plated
structures using an alkali permanganate oxidizing solution. The
permanganate component of the alkali permanganate oxidizing
solution is preferably selected from sodium or potassium
permanganate. The concentration of permanganate in the alkali
permanganate oxidizing solution is not critical, but is preferably
in the range of from about 4% by weight to about 9% by weight,
based on the total weight of the alkali permanganate solution. The
alkali component of the alkali permanganate oxidizing solution is
preferably selected from hydroxides such sodium hydroxide,
potassium hydroxide, magnesium hydroxide, and the like. Other
alkalis are known to those of skill in the art. The concentration
of alkali in the alkali permanganate oxidizing solution is also not
critical, but is preferably in the range of from about 3% by weight
to about 6% by weight, based on the total weight of the alkali
permanganate solution. One useful concentration is approximately 5%
by weight of permanganate and 5% by weight of alkali, based on the
total weight of the alkali permanganate oxidizing solution.
[0024] Conventional UV curable, epoxy-based photoresists, such as
SU-8, commercially available from MicroChem Corp. U.S.A, are so
highly cross-linked that hot N-methyl pyrrolidone (NMP) or other
organic solvents cannot remove it from the wafer surface. Only
strong acid-peroxide solutions are capable of removing SU-8
photoresist, but have the disadvantage of completely removing the
metallic structures from the wafer as well. Therefore, the
difficulty in removing cross-linked SU-8 can result in a wafer
that, if improperly imaged, can be rendered unusable.
[0025] Alkali permanganate solutions have also been shown to be
capable of removing thick coatings of cross-linked SU-8 photoresist
from bare silicon wafers. This occurs even after prolonged hard
baking of the patterned resist to temperatures as high as
150.degree. C. The alkali permanganate process allows SU-8
patterned wafers to be reworked or reprocessed. Therefore, the
fabrication cost of imaging with SU-8 photoresist can be reduced
and the commercial viability increased by the use of this
process.
[0026] Residual epoxy resist and manganese dioxide are removed from
the metal structures by neutralizing (reducing) the manganese
dioxide in a neutralizer solution that comprises (1) an acid, such
as sulfuric acid, sulfamic acid, methane sulfonic acid, and the
like, and (2) a mild reducing agent such as hydroxylamine sulfate,
hydroxylamine nitrate, hydroxylamine phosphate, and the like. The
concentration of acid is not critical, but is preferably in the
range of from about 5% by weight to about 10% by weight, based on
the total weight of the neutralizer solution. The concentration of
reducing agent is also not critical, but is preferably in the range
of from about 1% by weight to about 10% by weight, based on the
total weight of the neutralizer solution. The neutralizing solution
process acts quickly and can be processed at 20.degree.
C.-25.degree. C.
[0027] After the neutralizer step, the copper, nickel, gold,
tin-lead or lead-free tin-bismuth-silver plated micro-structures
remain intact, without distortion from any swelling or damage from
the removal of the KMPR.RTM. photoresist.
EXAMPLES
[0028] The following examples are intended to illustrate, but in no
way limit the scope of the present invention. All parts and
percentages are by weight, and temperatures are in degrees Celsius
unless explicitly stated otherwise.
Example 1
[0029] A copper MEMS structure was created by vacuum sputtering a
150 mm diameter silicon wafer with an adhesion layer of 200 .ANG.
titanium followed by 500 .ANG. of a copper metal seed layer. A
photoresist adhesion promoter containing hexamethyldisilazane
(HMDS) was spin coated for 30 seconds at 3000 rpm and then baked
for 2 minutes at 95.degree. C. A 50 .mu.m coating of KMPR.RTM. 1050
epoxy-based photoresist (generically known as a carboxylated epoxy
ortho cresol novolak photoresist and commercially available from
MicroChem Corp., Newton, Mass.) was spin-coated for 30 seconds at
3000 rpm on the copper coated silicon wafer and baked for 15
minutes at 100.degree. C. The edge bead was removed using a fine
stream of a dioxolane mixture (commercially available from
MicroChem Corp., Newton, Mass., as EBR PG) directed at the edge of
the wafer while spinning the wafer for 60 seconds at 600 rpm. The
coated wafer was then baked for 60 seconds at 65.degree. C.
[0030] The coated wafer was then exposed using an EVG 620 aligner
to 1100 mJ/cm.sup.2 of 350-436 nm filtered UV radiation. After
exposure, the wafer was post-exposure baked for 3 minutes at
100.degree. C. and then developed in 0.26N tetramethyl ammonium
hydroxide (commercially available from Rohm & Haas Electronic
Materials Co., Marlborough, Mass. as CD-26), rinsed in deionized
water and dried.
[0031] Once the imaged microform wafer was complete, it was cleaned
using oxygen plasma in a reactive ion etcher (RIE, available from
March Plasma Systems, Concord, Calif.). The wafers were plasma
treated for 2 minutes with 100 W of DC power, 10 sccm of oxygen at
a pressure of about 50 mTorr. The patterned and cleaned wafer was
then plated using a solution of copper sulfate and sulfuric acid
(commercially available from Technic, Inc., Cranston, R.I., as
Copper U Bath RTU), for 70 minutes at room temperature and a
current density of 100 mA.
[0032] The patterned photoresist microform was removed from the
plated copper structures and the copper seed layer by immersing the
wafers in a solution of NMP for 10 minutes at 70.degree. C.
followed by immersing the wafers in a solution of 5% w/w sodium
permanganate (NaMnO.sub.4) and 5% w/w sodium hydroxide (NaOH) for
10 minutes at 70.degree. C. Finally, the manganese dioxide was
neutralized and the photoresist completely removed by immersing the
wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of
methane sulfonic acid for 2 minutes at room temperature.
Example 2
[0033] A nickel MEMS structure was created by vacuum sputtering a
150 mm diameter silicon wafer with a seed layer of 500 .ANG. nickel
metal. A photoresist adhesion promoter containing
hexamethyldisilazane (HMDS) was spin coated for 30 seconds at 3000
rpm and then baked for 2 minutes at 95.degree. C. A 50 .mu.m
coating of KMPR.RTM. 1050 epoxy-based photoresist was then
spin-coated for 30 seconds at 3000 rpm on the nickel coated silicon
wafer and baked for 15 minutes at 100.degree. C. The edge bead was
removed using a fine stream of a dioxolane mixture directed at the
edge of the wafer while spinning the wafer for 60 seconds at 600
rpm. The coated wafer was then baked for 60 seconds at 65.degree.
C.
[0034] The coated wafer was then exposed using an EVG 620 aligner
to 1100 mJ/cm.sup.2 of 350-436 nm filtered UV radiation. After
exposure, the wafer was post-exposure baked for 3 minutes at
100.degree. C. and then developed in 0.26N tetramethyl ammonium
hydroxide, rinsed in deionized water and dried.
[0035] Once the imaged microform wafer was complete, the wafer was
cleaned using oxygen plasma in a reactive ion etcher (RIE). The
wafers were plasma treated for 2 minutes with 100 W of DC power, 10
sccm of oxygen at a pressure of about 50 mTorr. The patterned and
cleaned wafer was then plated using a solution of nickel sulfamate,
for 70 minutes at room temperature and a current density of 100
mA.
[0036] The patterned photoresist microform was removed from the
plated nickel structures and nickel seed layer by immersing the
wafers in a solution of NMP for 10 minutes at 70.degree. C.
followed by immersing the wafers in a solution of 5% w/w sodium
permanganate (NaMnO.sub.4) and 5% w/w sodium hydroxide (NaOH) for
10 minutes at 70.degree. C. Finally, the manganese dioxide was
neutralized and the photoresist completely removed by immersing the
wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of
methane sulfonic acid for 2 minutes at room temperature.
Example 3
[0037] A metal solder bump structure was created by vacuum
sputtering a 150 mm diameter silicon wafer with an adhesion layer
of 200 .ANG. titanium followed by another 500 .ANG. of a copper
metal seed layer. A photoresist adhesion promoter containing
hexamethyldisilazane (HMDS) was spin coated for 30 seconds at 3000
rpm and then baked for 2 minutes at 95.degree. C. A 50 .mu.m
coating of KMPR.RTM. 1050 epoxy-based photoresist was then
spin-coated for 30 seconds at 3000 rpm on the copper coated silicon
wafer and baked for 15 minutes at 100.degree. C. The edge bead was
removed using a fine stream of a dioxolane mixture directed at the
edge of the wafer while spinning the wafer for 60 seconds at 600
rpm. The coated wafer was then baked for 60 seconds at 65.degree.
C.
[0038] The coated wafer was then exposed using an EVG 620 aligner
to 1100 mJ/cm.sup.2 of 350-436 nm filtered UV radiation. After
exposure, the wafer was post-exposure baked for 3 minutes at
100.degree. C. and then developed in 0.26N tetramethyl ammonium
hydroxide, rinsed in deionized water and dried.
[0039] Once the imaged microform wafer was complete, the wafer was
cleaned using an oxygen plasma in a reactive ion etcher (RIE). The
wafers were plasma treated for 2 minutes with 100 W of DC power, 10
sccm of oxygen at a pressure of about 50 mTorr. The patterned and
cleaned wafer was then plated using a solution of stannous sulfate,
lead sulfate and sulfuric acid (commercially available from
Technic, Inc. as Techni NuSolder JM-6000 LS), for 70 minutes at
45.degree. C. and a current density of 100 mA.
[0040] The patterned photoresist microform was removed from the
plated tin-lead structures and copper seed layer by immersing the
wafers in a solution of NMP for 10 minutes at 70.degree. C.
followed by immersing the wafers in a solution of 5% w/w sodium
permanganate (NaMnO.sub.4) and 5% w/w sodium hydroxide (NaOH) for
10 minutes at 70.degree. C. Finally, the manganese dioxide was
neutralized and the KMPR.RTM. photoresist completely removed by
immersing the wafers in a solution of 5% w/w hydroxylamine sulfate
and 2% w/w of methane sulfonic acid for 2 minutes at room
temperature.
Example 4
[0041] Nickel air bridge and cantilever structures were created by
vacuum sputtering a 150 mm diameter silicon wafer with a seed layer
of 500 .ANG. nickel metal and a zero layer alignment mark. A
photoresist adhesion promoter containing hexamethyldisilazane
(HMDS) was spin coated for 30 seconds at 3000 rpm and then baked
for 2 minutes at 95.degree. C. A 50 .mu.m coating of KMPR.RTM. 1050
epoxy-based photoresist was then spin-coated for 30 seconds at 3000
rpm on the nickel coated silicon wafer and baked for 15 minutes at
100.degree. C. The edge bead was removed using a fine stream of a
dioxolane mixture directed at the edge of the wafer while spinning
the wafer for 60 seconds at 600 rpm. The coated wafer was then
baked for 60 seconds at 65.degree. C.
[0042] The KMPR.RTM. coated wafer was then exposed to 650
mJ/cm.sup.2 of 350-436 mn filtered UV radiation with a photo-mask
aligned to the zero layer using an EVG 620 aligner. After exposure,
the wafer was post-exposure baked for 3 minutes at 100.degree. C.
and then developed in 0.26N tetramethyl ammonium hydroxide, rinsed
in deionized water and dried.
[0043] The wafer was then cleaned using oxygen plasma in a reactive
ion etcher (RIE). The wafers were plasma treated for 2 minutes with
100 W of DC power, 10 sccm of oxygen at a pressure of about 50
mTorr. The patterned and cleaned wafer was then plated using a
solution of nickel sulfamate for 70 minutes at room temperature and
a current density of 100 mA. After plating, the wafer was rinsed in
deionized water, dried and plasma treated for another 2 minutes
with 100 W of DC power, 10 sccm of oxygen at a pressure of about 50
mTorr.
[0044] A second layer of KMPR.RTM. 1050 epoxy-based photoresist was
coated directly on top of the patterned and plated first layer of
KMPR.RTM. 1050 by spin coating for 30 seconds at 3000 rpm and
baking for 15 minutes at 100.degree. C. The edge bead was removed
using a fine stream of a dioxolane mixture directed at the edge of
the wafer while spinning the wafer for 60 seconds at 600 rpm. The
KMPR.RTM. coated wafer was then baked for 60 seconds at 65.degree.
C.
[0045] The KMPR.RTM. coated wafer was then exposed to 650
mJ/cm.sup.2 of 350-436 nm UV radiation and aligned to the same zero
layer with a different photo mask using an EVG 620 aligner. After
exposure, the wafer was post-exposure baked for 3 minutes at
100.degree. C. and then developed in 0.26N tetramethyl ammonium
hydroxide, rinsed and dried.
[0046] The wafer was then cleaned again using oxygen plasma for 2
minutes with 100 W of DC power, 10 sccm of oxygen at a pressure of
about 50 mTorr and plated again using a solution of nickel
sulfamate, for 70 minutes at room temperature and a current density
of 100 mA. After plating, the wafer was rinsed in deionized
water.
[0047] Once the imaged microform wafer was complete, the patterned
photoresist microform was removed from the plated nickel structures
and nickel seed layer by immersing the wafers in a solution of NMP
for 20 minutes at 70.degree. C. followed by immersing the wafers in
a solution of 5% w/w sodium permanganate (NaMnO.sub.4) and 5% w/w
sodium hydroxide (NaOH) for 20 minutes at 70.degree. C. Finally,
the manganese dioxide was neutralized and the photoresist
completely removed by immersing the wafers in a solution of 5% w/w
hydroxylamine sulfate and 2% w/w of sulfuric acid for 2 minutes at
room temperature.
Example 5
[0048] A gold metal bump structure was created by vacuum sputtering
a 150 mm diameter silicon wafer with an adhesion layer of 200 .ANG.
titanium followed by another 500 .ANG. of a gold metal seed layer.
A photoresist adhesion promoter containing hexamethyldisilizane
(HMDS) was spin coated for 30 seconds at 3000 rpm and then baked
for 2 minutes at 95.degree. C. A 50 .mu.m coating of KMPR.RTM. 1050
epoxy-based photoresist was then spin-coated for 30 seconds at 3000
rpm on the gold coated silicon wafer and baked for 15 minutes at
100.degree. C. The edge bead was removed using a fine stream of a
dioxolane mixture directed at the edge of the wafer while spinning
the wafer for 60 seconds at 600 rpm. The KMPR.RTM. coated wafer was
then baked for 60 seconds at 65.degree. C.
[0049] The KMPR.RTM. coated wafer was then exposed using an EVG 620
aligner to 1100 mJ/cm.sup.2 of 350-436 nm UV radiation. After
exposure, the wafer was post-exposure baked for 3 minutes at
100.degree. C. and then developed in 0.26N tetramethyl ammonium
hydroxide (commercially available from Rohm & Haas Electronic
Materials Co. as CD-26), rinsed in deionized water and dried.
[0050] Once the imaged KMPR.RTM. microform wafer was complete, the
wafer was cleaned using an oxygen plasma in a reactive ion etcher.
The wafers were plasma treated for 2 minutes with 100 W of DC
power, 10 sccm of oxygen at a pressure of about 50 mTorr. The
patterned and cleaned KMPR.RTM. wafer was then plated using a
non-cyanide solution of auric sulfate (commercially available from
Technic, Inc. as TechniGold 25 ES), for 70 minutes at 45.degree. C.
and a current density of 100 mA.
[0051] The patterned KMPR.RTM. photoresist microform was removed
from the plated gold structures and gold seed layer by immersing
the wafers in a solution of NMP for 10 minutes at 70.degree. C.
followed by immersing the wafers in a solution of 5% w/w sodium
permanganate (NaMnO.sub.4) and 5% w/w sodium hydroxide (NaOH) for
10 minutes at 70.degree. C. Finally, the manganese dioxide was
neutralized and the KMPR.RTM. photoresist completely removed by
immersing the wafers in a solution of 5% w/w hydroxylamine sulfate
and 2% w/w of sulfuric acid for 2 minutes at room temperature.
Example 6
[0052] A bare silicon wafer was stripped of cross-linked SU-8
photoresist (commercially available from MicroChem Corp.). A 50 um
coating of SU-8 was first prepared by spin-coating SU-8 2050 for 30
seconds at 3000 rpm on an untreated silicon wafer and baked for 15
minutes at 95.degree. C. The edge bead was removed using a fine
stream of a dioxolane mixture directed at the edge of the wafer
while spinning the wafer for 60 seconds at 600 rpm. The SU-8 coated
wafer was then baked for 60 seconds at 65.degree. C.
[0053] The SU-8 coated wafer was then exposed using an EVG 620
aligner to 500 mJ/cm.sup.2 of 350-436 nm filtered UV radiation.
After exposure, the wafer was post-exposure baked for 3 minutes at
95.degree. C. and then developed in 1-methoxy-2-propanol acetate
(commercially available from MicroChem Corp. as SU-8 developer),
rinsed with isopropanol and dried. Once the patterned SU-8 wafer
was complete, the wafer was hard baked for 30 minutes at
150.degree. C.
[0054] The patterned SU-8 wafer was placed in a solution of NMP for
10 minutes at 70.degree. C. followed by immersing the wafers in a
solution of 5% w/w sodium permanganate (NaMnO.sub.4) and 5% w/w
sodium hydroxide (NaOH) for 10 minutes at 70.degree. C. Finally,
the manganese dioxide was neutralized and the SU-8 photoresist was
completely removed by immersing the wafers in a solution of 5% w/w
hydroxylamine sulfate and 2% w/w of sulfuric acid for 2 minutes at
room temperature.
Example 7
[0055] The present invention may also be implemented in removal of
highly crosslinked epoxy-based photoresist, such as KMPR.RTM. or
SU-8 photoresist as described above, following exposure to fluorine
plasma in a deep reactive ion etch (DRIE) processing. Briefly, one
preferred embodiment of this aspect of the invention includes (1)
lithographically producing an etch mask with an epoxy-based
photoresist; (2) exposing the substrate to a DRIE plasma comprising
alternating gases of sulfur hexafluoride and octafluorocyclobutane;
(3) exposing the substrate to an alkaline oxidizing solution to
remove the crosslinked SU-8 photoresist from the substrate; and (4)
exposing the substrate to a reducing agent. The following example
provides details of this embodiment.
[0056] A 1000 .mu.m deep through-hole-wafer-via was created using a
10 .mu.m coating of KMPR.RTM. 1010 epoxy-based photoresist
(commercially available from MicroChem Corp.), which was
spin-coated for 30 seconds at 3000 rpm on a bare silicon wafer and
baked for 10 minutes at 100.degree. C. The edge bead was removed
using a fine stream of a dioxolane mixture directed at the edge of
the wafer while spinning the wafer for 60 seconds at 600 rpm. The
KMPR.RTM. coated wafer was then baked for 60 minutes at 65.degree.
C.
[0057] The KMPR.RTM. coated wafer was then exposed using an EVG 620
aligner to 500 mJ/cm.sup.2 of 350-436 nm filtered UV radiation.
After exposure, the wafer was post-exposure baked for 3 minutes at
100.degree. C. and then developed in 0.26N tetramethyl ammonium
hydroxide, rinsed in deionized water and dried. After drying, the
wafer was hard baked for 30 minutes at 150.degree. C.
[0058] After drying, the wafer was post-exposure baked for 3
minutes at 95.degree. C. and then developed in 1-methoxy-2-propanol
acetate, rinsed with isopropanol and dried. Once the patterned KMPR
wafer was complete, the wafer was hard baked for 30 minutes at
150.degree. C.
[0059] The KMPR.RTM. patterned and hard baked wafer was then etched
in a Surface Technology Systems (manufactured by STS plc, Newport,
UK) Multiplex ICP etcher for 8 hours using 600 W of coil power, 140
W of platen power, 140 sccm of sulfur hexafluoride and 95 sccm of
octafluorocyclobutane at a pressure of 31 mTorr. This resulted in a
1000 .mu.m deep silicon etch and which consumed only 16 .mu.m of
KMPR.RTM. photoresist.
[0060] The patterned KMPR.RTM. photoresist etch mask was removed
from the through-hole-wafer-via by immersing the wafers in a
solution of NMP for 10 minutes at 70.degree. C. followed by
immersing the wafers in a solution of 5% w/w sodium permanganate
(NaMnO.sub.4) and 5% w/w sodium hydroxide (NaOH) for 10 minutes at
70.degree. C. Finally, the manganese dioxide was neutralized and
the KMPR.RTM. photoresist completely removed by immersing the
wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of
sulfuric acid for 2 minutes at room temperature.
[0061] While the invention has been described above with reference
to specific embodiments thereof, it is apparent that many changes,
modifications, and variations can be made without departing from
the inventive concept disclosed herein. Accordingly, it is intended
to embrace all such changes, modifications, and variations that
fall within the spirit and broad scope of the appended claims. All
patent applications, patents, and other publications cited herein
are incorporated by reference in their entireties.
* * * * *