U.S. patent application number 10/289964 was filed with the patent office on 2004-05-13 for process for electrolytic copper plating.
This patent application is currently assigned to Shipley Company, L.L.C.. Invention is credited to Hayashi, Shinjiro, Kusaka, Masaru, Tsuchida, Hideki, Tsukagoshi, Satoru.
Application Number | 20040089557 10/289964 |
Document ID | / |
Family ID | 19155917 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040089557 |
Kind Code |
A1 |
Tsuchida, Hideki ; et
al. |
May 13, 2004 |
Process for electrolytic copper plating
Abstract
A process for electrolytic copper plating, that is suitable for
the formation of filled vias without compromising the brightness of
the deposit is provided. In this process, copper electroplating is
carried out in the presence of a transition metal oxide.
Inventors: |
Tsuchida, Hideki;
(Hasuda-shi, JP) ; Kusaka, Masaru;
(Kitaadachi-gun, JP) ; Hayashi, Shinjiro;
(Saitama-shi, JP) ; Tsukagoshi, Satoru;
(Kohnosu-shi, JP) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP
Dike, Bronstein, Roberts & Cushman, IP Group
P.O. Box 9169
Boston
MA
02209
US
|
Assignee: |
Shipley Company, L.L.C.
Marlborough
MA
|
Family ID: |
19155917 |
Appl. No.: |
10/289964 |
Filed: |
November 7, 2002 |
Current U.S.
Class: |
205/291 ; 205/91;
257/E21.175; 257/E21.585 |
Current CPC
Class: |
H01L 21/76877 20130101;
C25D 7/12 20130101; C25D 7/123 20130101; H05K 2201/09563 20130101;
C25D 3/38 20130101; H05K 3/423 20130101; H01L 21/2885 20130101 |
Class at
Publication: |
205/291 ;
205/091 |
International
Class: |
C25D 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2002 |
JP |
2001-341976 |
Claims
What is claimed:
1. A process for electrolytic copper plating comprising the steps
of contacting a substrate to be plated with an electrolytic copper
plating bath comprising a transition metal oxide and subjecting the
plating bath to sufficient current density to deposit a layer of
copper on the substrate.
2. The process according to claim 1 wherein the electrolytic copper
plating bath further comprises copper sulfate.
3. The process of claim 1 further comprising the step of
irradiating the electrolytic copper plating bath with ultraviolet
or visible light
4. The process of claim 1 wherein the electrolytic copper plating
bath further comprises a brightening agent having the structure
--X--S--Y, wherein X and Y are independently selected from
hydrogen, carbon, sulfur, nitrogen and oxygen, provided that X and
Y are the same only when they are carbon.
5. The process of claim 1 wherein the substrate is a printed wiring
board or a wafer.
6. The process of claim 1 wherein the substrate has one or more
through-holes or via holes.
7. A copper plating bath composition suitable for electrolytic
copper plating comprising a source of copper ions, an electrolyte,
water and a transition metal oxide.
8. The composition of claim 8 wherein the transition metal oxide is
titanium oxide.
9. The composition of claim 8 further comprising a brightening
agent having the structure --X--S--Y, wherein X and Y are
independently selected from hydrogen, carbon, sulfur, nitrogen and
oxygen, provided that X and Y are the same only when they are
carbon.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to a process for
electrolytic copper plating. In particular, the present invention
relates to an electrolytic copper plating process and bath
containing a transition metal oxide.
[0002] In recent years, improvements in the density and thinness of
printed wiring boards has been desired in response to improved
performance and decreased size of electronic devices such as
personal computers. A means that has been used in order to satisfy
these types of demands has been the use of multilayer printed
wiring boards (build-up printed wiring boards) that are
manufactured by forming a pattern on each layer, and then
laminating the next layer to the patterned layer.
[0003] With this type of build-up printed wiring board, methods
have been developed whereby the effective surface area of the
printed wiring boards is increased. This allows adequate electrical
connections to be made with MVHs (micro via holes) that are of
smaller diameter than possible with conventional plating of only
the inner wall surfaces of the MVHs. By such methods, referred to
as "via filling", all of the MVHs can be filled with a conductor,
thereby forming electrical connections between adjacent layers in
build-up printed wiring boards, and thereby decreasing the size and
increasing density of printed wiring boards.
[0004] Examples of via filling methods that have been disclosed
include methods wherein the MVHs are filled with conductive paste
using a printing method, methods wherein only the conductor layers
on the bottom surfaces of the MVHs are activated, followed by
selective electroless copper plating to perform filling, and
methods wherein electrolytic copper plating is carried out.
[0005] However, because conductive paste is a mixture of copper and
organic material, it has a lower conductivity relative to metallic
copper, and so providing sufficient electrical connections with
small-size MVHs is difficult with such pastes. This method is not
effective in decreasing the size and increasing the density of
printed wiring boards. In addition, filling methods that employ
printing processes require that a viscous paste be used in order to
fill holes that are small in diameter and do not pass through (i.e.
not through-holes). However, due to the viscosity of the paste, it
is difficult to completely fill these holes without a space or void
remaining. Methods that involve electroless copper plating are
superior to conductive paste methods in that the MVH packing
material is a metallic copper deposit that has high conductivity,
but the deposition rate of the copper metal is slow. These methods
thus have problems with productivity. When general high-speed
electroless copper plating baths have been employed, the deposition
rate for the plating films has been about 3 .mu.m/hr, but when such
baths are used in order to fill typical 100 .mu.m deep, 100 .mu.m
wide MVHs with copper, 30 hr or more is required. This is thus a
serious disadvantage in terms of productivity.
[0006] In contrast, electrolytic copper plating has a plated film
deposition rate of 10 to 50 .mu.m/hr, and thus can provide a
significant time decrease relative to electroless copper plating.
There has been the expectation that such methods would be applied
in electrolytic copper plating of MVHs. However, when copper is
deposited over all MVH surfaces, it is necessary for the deposition
rate near the bottoms of the MVHs to be more rapid than the
deposition rate at the MVH openings so that the MVH interiors can
be filled with copper without void formation. When the deposition
rate near the bottom of the holes is equivalent or slower relative
to the deposition rate at the openings, the MVHs will not be
filled, or the openings will be covered prior to complete filling
of the MVHs with copper. As a result, gaps or voids will remain in
the micro via holes, and these methods thus turn out to be
inappropriate for practical use.
[0007] In the past, electrolytic copper plating baths comprising
special compounds having sulfur atoms have been used in order to
accelerate deposition rates near the bottom surfaces of the MVHs.
In general, the electrolysis conditions have involved
direct-current electrolysis carried out using a soluble positive
electrode such as a phosphorus-containing copper electrode.
However, although good MVH filling performance is exhibited with
such methods immediately after production of the bath, the
electrolytic copper plating bath destabilizes over time. As a
result, clumps are formed when producing electrolytic copper
plating layers a certain period of time after production of the
bath, leading to degradation of external appearance, and problems
with uneven via filling. The inventors of the present invention
carried out research concerning these problems, and determined that
it is the decomposition products of the sulfur-containing compounds
that cause these problems, as described below. The present
invention is thus based on an oxidation reaction carried out via
titanium oxide, which is used as a method for decreasing amounts of
these decomposition products.
SUMMARY OF THE INVENTION
[0008] The present invention was developed in light of the above
state of affairs, and offers a process for electrolytic copper
plating that is appropriate for the formation of filled vias
without degradation in external appearance of the plated copper by
means of utilizing the photocatalytic capacity of a transition
metal oxide, such as titanium oxide. Thus, the present invention
offers a process for electrolytic copper plating, wherein plating
is carried out in the presence of titanium oxide.
[0009] The present invention offers a process for electrolytic
copper plating wherein plating is carried out in the presence of
titanium oxide using a plating solution including a compound having
the structure --X--S--Y--, wherein X and Y are each individually
selected from hydrogen, carbon, sulfur, nitrogen and oxygen atoms,
and X and Y can be the same only when they are carbon atoms.
[0010] In addition, in the present invention, the substrate that is
used for electrolytic copper plating is a typical printed wiring
board or wafer, and in particular, is a substrate material that has
through holes or via holes.
[0011] The present invention also offers a composite material
obtained by the plating method of the present invention.
BRIEF DESCRIPTION OF THE DRAWING
[0012] FIG. 1 is a schematic diagram of a via cross-section after
copper plating according to the present invention.
[0013] FIGS. 2A and 2B are schematic diagrams of via cross-sections
after copper plating according to conventional processes.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Any transition metal oxide may be used in the present
invention, provided it has photocatalytic capacity. Preferably, the
transition metal oxide is a titanium oxide. The preferred titanium
oxide is titanium dioxide. The titanium oxide may have a variety of
forms including, without limitation, rutile-form, anatase form or
amorphous form. The crystal grain diameter and particle size of the
transition metal oxide particles can be freely selected. In
particular, materials that manifest photocatalytic activity when
irradiated with ultraviolet lightor visible light are appropriate
for use in the present invention. As used herein, the term
"photocatalytic capacity" refers to the oxidative capacity of a
transition metal oxide, such as titanium oxide, which is manifested
by means of ultraviolet light or visible light.
[0015] Titanium oxide can be introduced in the form of a powder
into the copper electroplating solution, but it is preferable to
use the titanium oxide in the form of a molding, such as granules,
as a filter, as beads, or the titanium oxide can be supported by or
coated on an appropriate substrate material. Such substrate
material can be any desired material, and materials of various
shapes can be used, including sheets, spheres, rods, wires or mesh
moldings, as well as porous materials. Methods for manufacturing
the above moldings are well known, and include supporting or
coating methods, any of which may be used. A material produced by
forming a titanium dioxide layer on the surface of a plate or mesh
composed of titanium is preferably used.
[0016] The photocatalytic capacity of the titanium oxide is
typically manifested by irradiation with ultraviolet lightor
visible light. The ultraviolet light source can be sunlight or
artificial light. Examples of artificial light sources include,
without limitation, various types of ultraviolet lamps such as
low-pressure, medium-pressure and high-pressure ultraviolet lamps.
The ultraviolet light can be used as-is, or filtered prior to
irradiation. Visible light can be supplied to the plating bath in
sufficient quantity by irradiating the bath with ambient light or
artificial light.
[0017] The light source is situated so that a quantity of light
sufficient to manifest photocatalytic capacity impinges upon the
titanium oxide. The amount of ultraviolet or visible light
irradiation sufficient to manifest photocatalytic activity can be
readily determined by a person skilled in the art. The light source
can be situated outside the plating bath, but it is preferable for
the lamp to be situated inside the plating bath.
[0018] In the present electrolytic plating method, the plating
solution contains a compound having the structure --X--S--Y--. X
and Y are each individually selected from hydrogen, carbon,
nitrogen, sulfur and oxygen. In this specification, the above
compound will be referred to as a "sulfur-containing compound" for
purposes of abbreviation. Preferably, X and Y are each individually
selected from hydrogen, carbon, nitrogen and sulfur. More
preferably, X and Y are each individually selected from hydrogen,
carbon and sulfur. X and Y may be the same when they are carbon
atoms. X and Y may each be substituted
[0019] The above formula indicates that the S atom has an atomic
valence of 2. However, this does not mean that X and Y atoms have
atomic valences of 2. The X and Y denote atoms that can bond with
any other atoms depending on the atomic valence. For example, when
X is hydrogen, the compound has the structure: H--S--Y--.
[0020] In particular, the sulfur-containing compound has sulfonic
acid groups or alkali metal salts of sulfonic acidgroups. One or
more sulfonic acid groups or alkali metal salt groups can be
present in the molecule. More particularly, the sulfur-containing
compound has the structure --S--CH.sub.2O--R--SO.sub.3M . Event
more particularly, the sulfur-containing compound has the structure
--S--R--SO.sub.3M. In the above formulae, M denotes a hydrogen or
an alkali metal, and R denotes an alkyl group having 3 to 8
carbonatoms. It is additionally desirable for the sulfur-containing
compound to have one of the structures (1)-(8) indicated below.
M--SO.sub.3--(CH.sub.2).sub.a--S--(CH.sub.2).sub.b--SO.sub.3--M;
(1)
M--SO.sub.3--(CH.sub.2).sub.a--O--CH.sub.2--S--CH.sub.2--O--(CH.sub.2).sub-
.b--SO.sub.3--M; (2)
M--SO.sub.3--(CH.sub.2).sub.a--S--S--(CH.sub.2).sub.b--SO.sub.3--M;
(3)
M--SO.sub.3--(CH.sub.2).sub.a--O--CH.sub.2--S--S--CH.sub.2--O--(CH.sub.2).-
sub.b--SO.sub.3--M; (4)
M--SO.sub.3--(CH.sub.2).sub.a--S--C--(.dbd.S)--S--(CH.sub.2).sub.b--SO.sub-
.3--M; (5)
M--SO.sub.3--(CH.sub.2).sub.a--O--CH.sub.2--S--C(.dbd.S)--S--CH.sub.2--O---
(CH.sub.2).sub.b--SO.sub.3--M; (6)
[0021] In structures (1)-(6), a and b are integers of 3 to 8, and M
denotes hydrogen or an alkali metal.
A--S--(CH.sub.2).sub.a--SO.sub.3--M; and (7)
A--S--CH.sub.2--O--(CH.sub.2).sub.a--SO.sub.3--M (8)
[0022] In structures (7) and (8), a is an integer of 3 to 8; M is
hydrogen or an alkali metal; and A is hydrogen, C.sub.1-10 alkyl
group, aryl group, a chain-form or cyclic amine compound containing
1 to 6 nitrogen atoms, 1 to 20 carbon atoms and multiple hydrogen
atoms, or a heterocyclic compound containing 1 to 2 sulfur atoms, 1
to 6 nitrogen atoms, 1 to 20 carbon atoms and numerous hydrogen
atoms.
[0023] The sulfur-containing compound is generally used as a
brightening agent, but cases where the compound is used with other
objectives are within the scope of the present invention. A single
sulfur-containing compound or mixtures of sulfur-containing
compounds may be used.
[0024] When the sulfur-containing compound is a brightening agent,
it may be used in an amount of, for example, 0.1 to 100 mg/L, with
0.5 to 10 mg/L being preferred. When the sulfur-containing compound
is used with objectives other than those related to brightening
agents, the preferred range for the used amount thereof can be
selected appropriately by persons skilled in the art.
[0025] The inventors of the present invention et al. discovered
that degradation in the appearance of plated copper films and in
via filling capacity using electrolytic copper plating solutions is
caused by an increase in --X--S or --Y--S compound decomposition
product generated by breakdown of the aforementioned
sulfur-containing compound, --X--S--Y--. IFor example, when the
sulfur-containing compounds have the structure (1)
M--SO.sub.3--(CH.sub.2).sub.a--S--(CH.sub.2).sub.b--SO.sub.3--M,
the decomposition products M--SO.sub.3--(CH.sub.3).sub.a--S or
S--(CH.sub.2).sub.b--SO.sub.3--M can be envisioned, but these
products can also be represented as --X--S.sup.- and --Y--S.sup.-
respectively. In this specification, the decomposition products of
the sulfur-containing compounds are referred to as "--X--S" for
purposes of convenience.
[0026] In addition, the --X--S.sup.- compound contained in the
electrolytic copper plating bath can be a compound having a
structure wherein the other part of the molecule does not
decompose, or produced by cleavage of one of the X--S or S--Y bonds
of the sulfur-containing compound --X--S--Y--, or can be a compound
wherein said decomposition product maintains the X--S structure, or
the part bonded to the X also decomposes, or various mixtures of
these compounds.
[0027] The concentration of compound having the --X--S.sup.-
structure, which is the decomposition product of the
sulfur-containing compound, can be measured by any conventional
method. Suitable methods include, but are not limited to,
high-performance liquid chromatography. When high-performance
liquid chromatography is used, the plating bath can be subjected
directly to high-performance liquid chromatography, or when
contaminants are present that impede measurement, the contaminants
can be removed by a treatment, and said chromatographic analysis
can then be carried out.
[0028] When a single type of --X--S.sup.- compound is present, the
concentration of such compound should correspond to the
concentration of the compound having --X--S structures, and when a
mixture of compounds of the structure --X--S are present, the total
concentration of the various compounds corresponds to the
concentration of the compound having --X--S.sup.- structures.
[0029] In addition, the --X--S.sup.- compound in the electrolytic
plating bath ordinarily is present as a counter ion with respect to
a cation such as a metal ion or hydronium ion. Thus, in the present
invention, compounds with --X--S--H structures are also included
among the --X--S compounds when not specifically stated
otherwise.
[0030] While not intending to be bound by theory, the mechanism
whereby the compound having an --X--S.sup.- structure is produced
when, for example, a phosphorus-containing copper or other such
soluble anode is used, is thought to involve a reaction between the
sulfur-containing compound and the soluble anode during the
electrolysis stoppage period. It is thought that the S--X or S--Y
single bond of the sulfur-containing compound is cleaved to
generate a compound having the --X--S structure. In addition,
during electroplating, the sulfur-containing compound is thought to
accept electrons at the cathode, thus cleaving the S--X or S--Y
single bond and generating compound having the --X--S.sup.-
structure. Moreover, electrons released by the conversion of Cu to
Cu.sup.2+ at the soluble anode are thought to be taken up, with the
aforementioned sulfur-containing compound producing an --X--S
structure.
[0031] Again, while not intending to be bound by theory, the
detrimental influence of a compound having an --X--S.sup.-
structure on electrolytic plating is thought to result from bonding
between said compound and metal ions such as Cu.sup.+ or Cu.sup.2+
ions. When this compound is present, the deposited metal forms
clumps, and thus a metal layer with inferior adhesion and heat
resistance is produced. In addition, it is thought that these
compounds also degrade the appearance of the resulting deposit,
such as providing inferior brightness. When forming filled vias as
well, it is thought that the bonded compound formed from the
aforementioned decomposition product and metal ions causes
insufficient via filling by decreasing the metal deposition rate
near the bottoms of the vias to values that are equal to or less
than the metal deposition rates at the via openings. It is thought
that these compounds thus cause problems with filling of the vias
due to the presence of residual voids, depending on factors such as
via shape.
[0032] In the present invention, the concentration of compound
having an --X--S structure in the electrolytic plating bath is
preferably maintained at 2.0 .mu.mol/L or less, from the standpoint
of maintaining the brightness of the deposit. From the standpoint
of producing a bright deposit, 1.0 .mu.mol/L or below is
preferable. It is more preferable that the concentration of such
compound is 0.5 .mu.mol/L or less. From the standpoint of improving
via filling properties, it is desirable for the concentration of
compound having an --X--S.sup.- structure to be maintained at 0.15
.mu.mol/L or below, with 0.1 .mu.mol/L or below being
preferred.
[0033] A wide variety of electrolytic copper plating baths may be
used in the present invention. Examples of such baths include, but
are not limited to, copper sulfate plating baths, copper cyanide
plating baths, copper pyrophosphate plating baths and other such
solutions. Preferably, the electrolytic copper plating bath is a
copper sulfate plating bath. By way of example, a copper sulfate
plating solution is described below. Other compositions and
components of the plating bath can be used in ranges that would be
readily determined by persons skilled in the art, based on the
literature and descriptions regarding copper sulfate plating
solutions described below. Appropriate modifications in
composition, concentration and added amount of additives can be
made to the base copper electroplating bath composition, provided
that the objectives of the present invention can still be
attained.
[0034] Conventional copper sulfate plating solutions are aqueous
solutions having a base composition comprising sulfuric acid,
copper sulfate and a water-soluble source of chloride ions compound
in addition to the above-described sulfur-containing compound.
There are no particular restrictions on the base composition of
this plating bath The sulfuric acid concentration in the copper
sulfate plating solution is typically 30 to 400 g/L, with 170 to
210 g/L being preferred. While a sulfuric acid concentration of
less than 30 g/L may be used, it may be difficult to pass
electricity into the plating bath due to the decrease in
conductivity of the plating bath. If the concentration of sulfuric
acid is too high, precipitation of copper sulfate may occur.
[0035] The concentration of copper sulfate in copper sulfate
plating baths is typically 20 to 250 g/L, with 60 to 180 g/L being
preferred. While a copper sulfate concentration of less than 20
g/L' may be used, the supply of copper ions may be insufficient,
and it may not be possible to deposit an appropriate copper film.
While a concentration of copper sulfate of greater than 250 g/L may
be used, it may be difficult to dissolve in such a high
concentration
[0036] There are no particular restrictions on the water-soluble
source of chloride ions compound contained in the copper sulfate
plating bath, provided that the compound provides chloride ions to
the copper sulfate plating solution. Examples of said water-soluble
chloride ion source compound include, without limitation,
hydrochloric acid, sodium chloride, potassium chloride and ammonium
chloride. A single water-soluble chloride ion source compound can
be used, or mixtures of two or more types may be used. The
concentration of the water-soluble chloride ion source compound, in
terms of chloride ions, is typically 10 to 200 mg/L, with 30 to 80
mg/L being preferred. If the chloride ion concentration is too low,
such as less than 10 mg/L, it may be difficult for the brightening
agent, surfactant or other such compounds to act properly.
[0037] Surfactants can be used in the present electrolytic copper
plating solution. Any conventional surfactants used as additives in
electrolytic copper plating solutions may be used in the present
invention. Examples of preferred surfactants are those having
structures (9)-(13), but are not restricted to these.
HO--(CH.sub.2--CH.sub.2--O).sub.a--H (in the formula, a is an
integer of 5-500); (9)
HO--(CH.sub.2--CH(CH.sub.3)--O).sub.a--H (in the formula, a is an
integer of 5-200); (10)
HO--(CH.sub.2--CH.sub.2--O).sub.a--(CH.sub.2--CH(CH.sub.3)--O).sub.b--(CH.-
sub.2--CH.sub.2--O).sub.c--H (in the formula, a and c are integers,
a+c=5-250, and b is an integer of 1-100); (11)
--(NH.sub.2CH.sub.2CH.sub.2).sub.n-- (in the formula, n is 5-500);
and (12)
[0038] 1
[0039] (in the formula, a, b and c are integers of 5-200).
[0040] A single surfactant may be used in the present invention or
a mixture of surfactants may be used. The surfactant is typically
present in an amount of 0.05 to 10 g/L, with 0.1 to 5 g/L being
preferred. The surfactant concentration may be less than 0.05 g/L,
however, pinholes may be produced in the deposited copper film due
to insufficient wetting effects
[0041] Suitable substrates used in the present invention are any
that can withstand the conditions of the electrolytic copper
plating process. The substrate material may be of any material or
shape, provided that a copper layer can be electrodeposited
thereupon. Examples of suitable substrates include, but are not
limited to, resins, ceramics and metals. For example, printed
wiring boards are suitable substrate materials composed of resins,
and semiconductor wafers are suitable substrate materials composed
of ceramics. Examples of metals include silicon such as a silicon
wafer, but are not restricted to silicon. The present electrolytic
plating method is particularly superior regarding via hole filling.
Preferred substrate materials include substrate materials having
through holes and via holes. Printed wiring boards or wafers having
through holes and/or via holes are preferred.
[0042] Examples of reins that can be used in the substrate material
include high-density polyethylene, medium-density polyethylene,
branched low-density polyethylene, linear low-density polyethylene,
ultra-high molecular weight polyethylene and other polyethylene
resins, polypropylene resin, polybutadiene, polybutene resin,
polybutylene resin, polystyrene resin and other polyolefin resins;
polyvinyl chloride resin, polyvinylidene chloride resin,
polyvinylidene chloride-vinyl chloride copolymer resin,
polyethylene chloride, polypropylene chloride, tetrafluoroethylene
and other halogenated resins; AS resin; ABS resin; MBS resin;
polyvinyl alcohol resin; polymethyl acrylate and other polyacrylic
acid ester resin; polymethyl methacrylate and other polymethacrylic
acid ester resins; methyl methacrylate-styrene copolymer resin;
maleic anhydride-styrene copolymer resin; polyvinyl acetate resin;
cellulose propionate resin, cellulose acetate resin and other
cellulose resins; epoxy resin; polyimide resin; nylon and other
polyamide resins; polyamidoimide resin; polyarylate resin;
polyether imide resin; polyether ether ketone resin; polyethylene
oxide resin; PET resin and various other types of polyester resins;
polycarbonate resin; polysulfone resin; polyvinyl ether resin;
polyvinyl butyral resin; polyphenylene oxide and other
polyphenylene ether resins; polyphenylene sulfide resin;
polybutylene terephthalate resin; polymethyl pentene resin;
polyacetal resin; vinyl chloride-vinyl acetate copolymer;
ethylene-vinyl acetate copolymer; ethylene-vinyl chloride
copolymer; and other such resins; as well as copolymers and blends
thereof and other thermoplastic resins. Other examples include
epoxy resin; xylene resin; guanamine resin; diallylphthalate resin;
vinyl ester resin; phenol resin; unsaturated polyester resin; furan
resin; polyimide resin; polyurethane resin; maleic acid resin;
melamine resin; urea resin; and other thermosetting resins, and
mixtures thereof. Examples are not restricted to these substances.
Examples of preferred resins include epoxy resin, polyimide resin,
vinyl resin, phenol resin, nylon resin, polyphenylene ether resin,
polypropylene resin, fluorine-system resin and ABS resin, with
additionally desirable resins being epoxy resin, polyimide resin,
polyphenylene ether resin, fluorine-based resin and ABS resin, and
even more desirable resins being epoxy resin and polyimide resin.
The resin substrate material can be composed of an individual resin
or multiple resins, and the material can also be a composite formed
by the lamination or coating of resins on another substrate
material. The resin substrate materials that can be used in the
present invention are not restricted to resin moldings, as
composite materials can be used produced by inserting reinforcing
materials such as glass fiber strengthening members into resins.
Alternatively, a coating composed of resin can be formed on a
substrate material composed of various types of elements such as
ceramic, glass and silicon or other metals.
[0043] Examples of ceramics that can be used as substrate materials
include alumina (Al.sub.2O.sub.3), steatite (MgO.SiO.sub.2),
forsterite (2MgO.SiO.sub.2), mullite (3Al.sub.2O.sub.3.2SiO.sub.2),
magnesia (MgO), spinel (MgO.Al.sub.2O.sub.3), beryllia (BeO) and
other oxide-system ceramics or aluminum nitride, silicon carbide
and other non-oxide system ceramics. Other examples include,
without limitation, low-temperature ceramics.
[0044] Prior to copper electroplating, the substrate material that
is to be plated is subjected to a conductivization treatment
carried out on the areas to be plated. For example, when metallic
copper is used in order to fill the MVHs by means of the present
electroplating process, the internal surfaces of the MVHs are first
subjected to conductivization. The conductivization treatment used
in the present invention can be any conventional conductivization
method. Suitable examples of conductivization methods that can be
cited include, but are not restricted to, electroless copper
plating, direct plating, conductive microparticle adsorption
treatment, and various other methods.
[0045] In the electrolytic plating method of the present invention,
the plating temperature (solution temperature) is set appropriately
in accordance with the type of plating bath used. Typically, the
temperature is 10 to 40.degree. C., with 20 to 30.degree. C. being
preferred. While the temperature of the plating bath may be below
10.degree. C., the conductivity of the plating liquid will
decrease, and it will not be possible to increase the current
density during electrolysis. A reduction in plated coating growth
rate and productivity will result. If the plating temperature is
too high, the brightening agents may decompose.
[0046] In the electrolytic copper plating process of the present
invention, it is possible to use any type of current such as direct
current or PPR (pulse periodic reverse) current. Although the
positive electrode current density is to be set appropriately in
accordance with the type of plating bath used, the current density
is typically 0.1 to 10 A/dm.sup.2, with 1 to 3 A/dm.sup.2 being
preferred.
[0047] With the electrolytic plating method of the present
invention, any type of anode can be used such as soluble anodes or
insoluble anodes. A phosphorus-containing copper anode is an
example of a soluble anode. Examples of insoluble anodes include,
but are not restricted to, indium oxide, platinum-clad titanium,
platinum, graphite, ferrite, stainless steel or titanium coated
with lead dioxide or platinum group element oxide and other
materials.
[0048] In the plating method of the present invention, it is
preferable to pass air or oxygen through the plating solution in
order to increase the soluble oxygen concentration. While not
wishing to be bound by theory, it is thought that the soluble
oxygen in the plating solution functions as an oxidation agent,
thereby decreasing the amount of compound having the --X--S
structure in the plating solution. A method for increasing the
soluble oxygen concentration in the plating solution preferably
involves bubbling air or oxygen through the plating solution, but a
configuration may be used in which said bubbling is carried out in
conjunction with stirring of the plating solution. A configuration
also may be used in which bubbling is carried out separately from
stirring. Bubbling is carried out in order to increase the soluble
oxygen concentration in the plating solution, and can be carried
out during the electrolytic plating treatment, or during stoppage
of the plating treatment.
[0049] Stirring is not necessary with the present plating method,
but it is preferable for stirring to be carried out in order to
provide more uniform supply of additives and copper ions to the
surface of the material to be plated. The stirring method can be
air stirring or a jet flow. From the standpoint of increasing the
amount of soluble oxygen in the plating solution, it is desirable
to perform stirring using air, and even when stirring is carried
out using a jet flow, stirring by means of air can be employed in
conjunction. Replacement filtration or circulation filtration can
be carried out, and in particular, circulation filtration of the
plating liquid using a filter is preferred, because the temperature
of the plating liquid stabilized when this is done, and materials
such as waste and precipitate present in the plating liquid can be
removed.
[0050] The present electrolytic copper plating process provides
composite materials containing of a copper layer on a substrate
material. By carrying out the present plating process, it is
possible to achieve gap-less filling of vias, without clumping in
the resulting composite material copper layer.
[0051] The present invention is described below using working
examples, but these working examples do not limit the scope of the
present invention.
WORKING EXAMPLE
[0052] Experimental Methods
[0053] Process 1: 2 L of bath having the standard composition for
via filling indicated below was prepared, and to this was added 1
mg/L of MPS, thus preparing a bath with artificially compromised
via filling performance.
[0054] Process 2: 0.5 g/L of titanium oxide powder was added to the
above bath with compromised via filling performance, and the powder
was dispersed in the bath with a stirrer. The bath was then left
for 5 h while being irradiated with ultraviolet light.
[0055] Process 3: A plating treatment was carried out by PPR
electrolysis using the conditions described below.
[0056] Process 4: The filling condition was observed by a
cross-sectioning method.
Comparative Example 1
[0057] A plating treatment was carried out by PPR electrolysis
immediately after process 1 described in the Working Example.
Comparative Example 2
[0058] After process 1 described in the Working Example, the bath
was left for 5 h, and subsequently, a plating treatment was carried
out by PPR electrolysis.
[0059] Composition of the Bath for Process 1
1 CuSO.sub.4 .multidot. 5H.sub.2O 130 g/L H.sub.2SO.sub.4 190 g/L
Cl 60 mg/L SPS 4 mg/L Nonionic surfactant 250 mg/L MPS 1 mg/L Note:
SPS: Disodium bis(3-sulfopropyl)disulfide MPS: Sodium
3-mercapto-1-propanesulfonate (available from Tokyo Kasei) Titanium
oxide: Titanium (IV) oxide, anatase (available from Kanto Chemical;
Grade 1, 0.5 g/L)
[0060] Bath temperature: 23-37.degree. C.
[0061] Ultraviolet lamp: Pencil-type/output: 4 W
[0062] Body: Velight Co., Model No. PS-2000-20
[0063] Primary voltage: 120 V, 60 Hz
[0064] Lamp: Double Bore.RTM. lamp
[0065] PPR Electrolysis Conditions
[0066] Current density: 2 A/dm.sup.2
[0067] Forward:reverse current density (F:R C.D.): 1:1
[0068] Forward/reverse pulse time (F/R P.T.): 10/0.5 (ms)
[0069] Temperature: 20.degree. C.
[0070] Time: 60 min
[0071] Via size: Via diameter 120 .mu.m/depth 60 .mu.m
Results
[0072] When the above processes were carried out using an
evaluative substrate having 100 via holes, almost all of the 100
vias were well-filled in the Working Example. In Comparative
Examples 1 and 2, on the other hand, most of the vias were not
filled. A schematic diagram of the via cross-sections after
treatment is shown in FIG. 1 (Working Example) and in FIG. 2A
(Comparative Example 1) and 2B (Comparative Example 2). By means of
the present invention, good via filling capacity was obtained,
whereas filling was poor with Comparative Examples 1 and 2.
[0073] In the Working Example and in Comparative Example 2, the
copper deposit in the filled vias exhibited good brightness, but in
Comparative Example 1, a dull appearance was produced.
* * * * *