U.S. patent application number 10/669633 was filed with the patent office on 2004-08-12 for electroless copper plating of electronic device components.
Invention is credited to Grunwald, John.
Application Number | 20040154929 10/669633 |
Document ID | / |
Family ID | 29798374 |
Filed Date | 2004-08-12 |
United States Patent
Application |
20040154929 |
Kind Code |
A1 |
Grunwald, John |
August 12, 2004 |
Electroless copper plating of electronic device components
Abstract
A method and composition for improving the deposition plating
rate of electroless copper. The invention presents embodiments
comprising using elevated plating temperatures at the
substrate-solution interface. This is coupled with suitably
designed bath compositions, to preserve the electroless bath
stability, required to improve the deposition plating rate of
electroless copper. In one embodiment, the electroless bath
composition comprises suitable individual Cu.sup.++ and Cu.sup.+
complexing agent(s), or a combination of complexing agents,
surfactants, organic polymer additives, and the like, adapted and
suitably optimized. For example, potential organic additive types
or surfactants can be Polyoxes; Pluronics; Polyols; Polyglycols;
Carbowaxes; Hydroxy ethyl cellulose (HEC), carboxy acetylenic, or
fluocarbon acetylenic surfactants. The method and composition of
the present invention enable the production of electroless copper
coatings with improved adhesion to the substrate. This is achieved
by selecting activation systems that result in copper initiation at
moderate rates. An electroless copper composition assists, in that
it too, ensures slow initial copper reduction at the
substrate-solution interface.
Inventors: |
Grunwald, John; (Ramat Gan,
IL) |
Correspondence
Address: |
Edward Langer
c/o Shiboleth, Yisraeli, Roberts, Zisman & Co.
60th Floor
350 Fifth Avenue
New York
NY
10118
US
|
Family ID: |
29798374 |
Appl. No.: |
10/669633 |
Filed: |
September 25, 2003 |
Current U.S.
Class: |
205/291 |
Current CPC
Class: |
C23C 18/405
20130101 |
Class at
Publication: |
205/291 |
International
Class: |
C25D 003/38 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2002 |
IL |
153498 |
Claims
I claim:
1. A composition for electroless plating of copper on a substrate,
comprising copper ions, a complexing agent for Cu.sup.++ ions, a
complexing agent for Cu.sup.+ ions, a reducing agent capable of
reducing copper ions to metallic copper and hydroxide ions to a pH
of at least 10.
2. A composition for electroless plating of copper on a substrate,
comprising copper ions, a mixture of complexing agents for
Cu.sup.++ ions, a mixture of complexing agents for Cu.sup.+ ions, a
reducing agent capable of reducing copper ions to metallic copper
and hydroxide ions to a pH of at least 10.
3. A composition according to claim 1, wherein said agent that
forms a complex with Cu.sup.++ ions is selected from a group
consisting of EDTA, Quadrol and mixtures thereof.
4. A composition according to claim 1, wherein said agent that
forms a complex with Cu.sup.+ ions is selected from a group
consisting of derivatives of pyridine, alkali metal cyanides,
cyanates and heavy metal cyanide complexes.
5. A composition according to claim 4, comprising at least 10 ppm
of said agent that forms a complex with Cu.sup.+ ions.
6. A composition according to claim 4, comprising at least 20 ppm
of bipyridine.
7. A composition according to claim 1, further comprising at least
one surfactant.
8. An improved method for electroless plating of copper on a
substrate using an electroless composition according to claim
1.
9. An improved method for electroless plating of copper on a
substrate using an electroless composition according to claim
2.
10. A method according to claim 8, further comprising heating the
substrate to a temperature above the operating temperature of the
electroless plating bath.
11. A method according to claim 10, wherein at least part of the
surface of said substrate is non-metallic.
12. A method according to claim 8, wherein the substrate is
flat.
13. A method according to claim 9, wherein the substrate is
flat.
14. A method according to claim 8, wherein the substrate is made of
material selected from a group consisting of copper-clad polymer
and silicon material.
15. A method according to claim 14, wherein the substrate comprises
vias and trenches.
16. An article manufactured by the method of claim 8.
17. An article manufactured by the method of claim 9.
18. An article manufactured by the method of claim 10.
19. An article manufactured by the method of claim 11.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the manufacture of metal
components, such as lines, vias, and trenches, utilized in the
production of semiconductor devices and Printed Circuit Boards
(PCBs), and more particularly, to an improved method and
composition for applying electroless copper.
BACKGROUND OF THE INVENTION
[0002] US Pat. 2002/0011416 A1 (Landau), U.S. Pat. No. 6,319,831
(Tsai) and U.S. Pat. No. 6,180,523 (Lee) are indicative of the
prior art.
[0003] Copper has increasingly gained prominence as the preferred
metal in prior art interconnect technology, due to its low cost and
superior conductivity. Hence, the recent technological focus in the
semiconductor devices and Printed Circuit Boards production
industries on developing manufacturing techniques and compositions
to improve the current state-of-the art for applying electroless
copper plating.
[0004] Today, the reduction or deposition of copper metal from
solution, is performed either by electrolytic or electroless
plating. Currently, the industry favors electrolytic plating
(electroplating) over electroless plating. To understand this
preferrence, consider some of the salient advantages and
disadvantages of each process, as listed below:
[0005] Advantages of electroplating:
[0006] 1. Relatively low production cost per unit weight of plated
copper, since the reduction process of Cu.sup.++ to Cu.sup.o
(copper metal) is performed using low cost electrical current.
[0007] 2. Electrolytic reduction deposits high quality metal.
[0008] 3. Higher rate of deposition, typically 20-25 micron films
achievable in one hour or less, enabling higher throughput.
[0009] 4. Lower waste generation rate.
[0010] Disadvantages of electroplating:
[0011] 1. High capital investment and equipment maintenance
cost.
[0012] 2. Stringent process window.
[0013] 3. Limited deposit-application capability, resulting in a
lack of uniformity in the deposited copper film thickness.
Especially problematic, in view of the increasing trend towards
plating high aspect-ratio geometries, of vias, microvias, trenches
and other metal components.
[0014] Advantages of electroless plating:
[0015] 1. Low capital investment and control instrumentation
cost.
[0016] 2. Low equipment maintenance and installation cost.
[0017] 3. Excellent thickness uniformity of plated Cu film. This
feature is of special significance when plating high aspect-ratio
geometries.
[0018] Disadvantages of electroless plating:
[0019] 1. Lower rate of deposition, typically 20 hours or more, to
deposit a 20-25 micron film, resulting in low production
throughput.
[0020] 2. Higher plating cost per unit weight of plated copper, due
to the use of additional chemicals, as opposed to inexpensive
electrochemical reduction that uses electrical current.
[0021] 3. Inferior plate quality that can result in functional
device failure, as for example, when the components are subjected
to thermal stress.
[0022] 4. Low copper-to-substrate adhesion.
[0023] 5. Greater waste generation rate than in electroplating.
[0024] The most attractive feature of electroless plating is its
inherent deposited plate thickness uniformity. Its most problematic
attributes are its low rate of deposition and its inferior
functional plate quality. If the aforementioned problematic
attributes were minimized or eliminated, electroless plating would
most probably supplant electroplating as the preferred plating
process for the production of semiconductor devices and Printed
Circuit Boards.
SUMMARY OF THE INVENTION
[0025] Accordingly, it is a principal object of the present
invention to overcome the above-mentioned problems and provide an
improved method and composition for applying electroless copper,
that will enable electroless copper plating to become a preferred
alternative to electroplating, for the fabrication of electronic
devices.
[0026] The present invention provides a method and composition that
improve the deposition plating rate of electroless copper. To
achieve this, the invention presents embodiments comprising using
elevated plating temperatures, coupled with suitably designed bath
compositions, to preserve the electroless bath stability, required
to improve the deposition plating rate of electroless copper.
[0027] The present invention also provides a method and composition
that improves the quality of electroless copper coatings or films,
without lowering the rate of deposition, by combining elevated
interfacial substrate or solution temperatures with suitably
engineered solution chemistry. In one embodiment the electroless
bath composition comprises suitable individual Cu.sup.++ and
Cu.sup.+ complexing agent(s), or a combination of complexing
agents, surfactants, organic polymer additives, and the like, many
of which can be adapted from the prior art, and suitably optimized.
For example, potential organic additive types or surfactants can be
Polyoxes; Pluronics; Polyols; Polyglycols. Carbowaxes; Hydroxy
ethyl cellulose (HEC), carboxy acetylenic, or fluocarbon acetylenic
surfactants.
[0028] The method and composition of the present invention enable
the production of electroless copper coatings with improved
adhesion to the substrate. This is achieved by selecting activation
systems that result in copper initiation at moderate rates. An
electroless copper composition assists, in that it too, ensures
slow initial copper reduction at the substrate-solution
interface.
[0029] In some instances it may be beneficial to expose the surface
to be plated to an electroless copper composition especially
designed for slow "take-off" of the initial copper layer. This
composition may differ from the electroless copper composition,
designed to give the desired copper thickness.
[0030] In many instances it may be advisable to deposit an initial
film, immediately adjacent to the substrate-to be-plated, prior to
plating electroless copper. This initial film deposit helps achieve
improved adhesion, but more importantly, helps reduce copper
migration. Potential candidates for "non-copper" films are
electroless nickel, cobalt, gold, and alloys of copper or nickel.
U.S. Pat. No. 4,482,596 to Gulla, discloses one such method and
composition that plates electroless nickel or copper coatings.
Others can be found in the prior art literature.
[0031] The initial metal films can be very thin, often no more than
a few Angstroms thick, optimizable through routine
experimentation
[0032] The method of the invention affords electroless plating on
non-conducting substrates without the use of precious metal
sensitization. Examples of similar methods and compositions are
disclosed in Israeli pending applications # 150364, 150577 and
150940.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0033] The present invention provides a method and composition that
improve the deposition plating rate of electroless copper. The
invention presents embodiments comprising using elevated plating
temperatures at the substrate-solution interface. This is coupled
with suitably designed bath compositions, to preserve the
electroless bath stability, required to improve the deposition
plating rate of electroless copper. Elevated plating temperatures
can be attained by heating the electroless copper plating bath, by
heating the substrate to the desired temperature (exemplified to
some extent in US Pat. 2002/0086102), or by a combination of the
two approaches.
[0034] When choosing to heat the substrate, it is recommended to
dispense the electroless plating solution onto the substrate by
using spraying or splashing techniques. In the latter case, the
electroless plating solution should be stored in a storage vessel
and recirculated, as is done in well-known processes involving
photoresist developing solutions. A technique known as puddle
development is used. This embodiment offers several advantages,
some of which are listed below:
[0035] Avoiding excessively high temperature electroless baths that
may lead to their decomposition.
[0036] The wafer to be plated can be spun during deposition. This
is similar to techniques widely practiced in wafer lithography,
which result in interfacial solution movement, contributing to
improved adhesion and plate quality.
[0037] The wafer can be heated selectively using thermal laser
treatment, resulting in selective plating, as a potential means of
achieving a desired copper pattern.
[0038] Interfacial substrate-solution plating temperatures can be
well over the boiling temperature of the electroless
composition.
[0039] The above embodiment, wherein the substrate to be
metallized, i.e. the wafer, is kept "hot", via contact with a heat
source, or via radiant heat such as IR, thermal laser, microwave,
and induction current, during electroless plating, coupled with
"accommodating", tailor-made electroless copper chemistries, offers
new possibilities for process improvements to those skilled in the
art of electroless plating.
[0040] A preferred composition disclosed by the present invention
comprises the following:
[0041] A complexor or a combination of complexors, that afford
superior bath stability at elevated temperatures. They will not
form an overly "tight" or strong complex that would negatively
impact the rate of copper deposition. For example, EDTA strongly
complexes cupric copper, but it tends to diminish the rate of
deposition. On the other hand, Rochelle salt tends to give high
plating speeds, but fragile electroless solution stability. An
optional embodiment of this patent comprises therefore, a blend of
complexors, to balance bath stability and, rate considerations.
[0042] In choosing the desired complexor blend, one can be guided
by the stability constant of copper complexors listed in
appropriate handbooks.
[0043] High reducer or copper ratios, again to favor rate.
[0044] Stabilizers, monovalent copper (Cu+) complexors. Generally,
these are other than thio derivatives and the like, which tend to
result in stressed deposits, and can negatively impact Cu film
quality. Desirable additives will comprise derivatives of pyridine
(i.e. bipyridine), cyanides (i.e. alkali metal cyanides), cyanates,
heavy metal cyanide complexes (i.e. ferrocyanides), and the like,
many of which can found in the prior art literature and optimized
through trial-and error experimentation.
[0045] It was discovered that electroless copper compositions of
this invention can advantageously contain relatively high
concentrations of stabilizing additives, such as bipyridine,
significantly above levels or concentrations disclosed in the prior
art. The reason perhaps lies in combining elevated operating
temperatures with suitable electroless bath compositions, as
suggested in this invention.
[0046] The embodiment of the present invention that focuses on
improving plate quality will comprise:
[0047] Annealing of the as-plated deposit, to relieve stresses. In
choosing suitable annealing time or temperature conditions, one
needs to guard against "overheating", that may lead to degradation
of the workpiece, as for example, glass or epoxy laminates of PCBs.
In the case of silica wafers, "overheating" is not an issue. They
are known to undergo very high temperature processes without
causing major defects. Although the risk of copper migration
exists, the present invention minimizes it.
[0048] The capabilities of the present invention are further
illustrated in the following examples:
[0049] Notes:
[0050] 1. The sign (*) denotes, throughout this disclosure,
products supplied in Israel by MacDermid Israed Ltd. and used in
accordance to supplier's instructions.
[0051] 2. The sample was exposed to the above process steps by
immersion.
[0052] 3. Following each process step, the sample was rinsed with
water,
EXAMPLE 1
[0053] A 3".times.3" copper clad glass-epoxy pane, from which the
copper has been etched away, was processed according to the
following procedure:
[0054] a. Metex Conditioner 90*
[0055] b. Water rinse.
[0056] c. Metex G-3*
[0057] d. Mactivate 10*
[0058] e. Metex 9071*
[0059] f. Aqueous solution of Na.sub.3PO.sub.4, 5 min., RT.
[0060] g. Immerse for 2 hours, 70 deg.C, with intermittent work
agitation in the following electroless copper solution, hereinafter
referred to as "Micro-Via" composition.
1 Component Concentration CuSO.sub.4, 5 H.sub.2O 15 g/l EDTA 25 g/l
Quadrol 6 g/l Formaldehyde 37% 33 g/l NaOH 13 g/l Bipyridine 100
ppm NaCN 18 ppm Petro Ag 10 ppm
[0061] h. Water rinse
[0062] i. Dry
[0063] Upon examination, the sample displayed a pink copper
coating, with good adhesion (no apparent blisters or lifting of the
deposit). Coating thickness was measured to be 8 microns thick.
EXAMPLE 2
[0064] Same as EXAMPLE 1, except:
[0065] Prior to being immersed in the Micro-Via composition, the
sample was immersed for 5 min. in a working solution of 9072*, then
transferred without a water rinse to the Micro-Via composition.
[0066] After two hours in the Micro-Via, the sample was
water-rinsed and dried. The copper coating showed blistering or
lifting from the substrate. Coating thickness was about 8
microns.
EXAMPLE 3
[0067] Same process steps as in EXAMPLE 1, except:
[0068] The sample was made of double-sided copper-epoxy, containing
interconnecting holes.
[0069] Prior to step a, the sample was contacted with Metex
9221-S*, Metex 9275*, and Metex G-3*. Water rinsing following each
process step.
[0070] Plating time in the Micro-Via was approximately 6-7 hours,
with 2-ml formaldehyde added every 2 hours to one liter of
Micro-Via.
[0071] After rinsing with water and drying, copper thickness in the
holes was approximately 20 microns. After baking for approximately
24 hours in an air-circulating oven at approximately 150 deg C., no
lifting of the plate from the substrate was observed. It was then
exposed to the industry-accepted solder shock test. Metallurgical
examination of the holes showed reasonable copper plate integrity
and adhesion.
EXAMPLE 4
[0072] Same as EXAMPLE 1, except;
[0073] Formaldehyde was increased by 10 g/l.
[0074] 50 .mu.l sodium carbonate was added and dissolved
[0075] After plating for 1 hour, no lifting of the deposit was
observed, and thickness was determined as 3 microns.
EXAMPLE 5
[0076] Same as EXAMPLE 4, except:
[0077] Sodium carbonate was increased to 100 g/l.
[0078] After plating for one hour, thickness was measured at 4.5
micron, and the copper coating showed some lifting.
EXAMPLE 6
[0079] A Pyrex glass plate was processed as in EXAMPLE 1,
except:
[0080] After Mactivate 10* it was heated on a hot plate to a
temperature estimated at over 200 deg. C.
[0081] Then about 100 cc of Macudep 22* solution (made up with 20%
of Macudep* concentrate A, 20% concentrate B, and the balance DI
water) was dispensed onto it.
[0082] After about 5 sec., a copious pink-colored copper layer
covered the Pyrex plate.
[0083] Having described the invention with regard to certain
specific embodiments, it is to be understood that the description
is not meant as a limitation since further modifications may now
suggest themselves to those skilled in the art, and it is intended
to cover such modifications, as fall within the scope of the
appended claims, namely combining elevated substrate temperature
with suitably optimized electroless solution chemistry.
[0084] Also, while the invention has been described in terms of
electroless copper, it encompasses other electroless metal
depositions, such as electroless nickel, cobalt, alloys of nickel
or copper, and the like.
* * * * *