U.S. patent application number 10/342599 was filed with the patent office on 2003-12-04 for via filling method.
This patent application is currently assigned to Shipley Company, L.L.C.. Invention is credited to Kusaka, Masaru, Tsuchida, Hideki.
Application Number | 20030221967 10/342599 |
Document ID | / |
Family ID | 19191195 |
Filed Date | 2003-12-04 |
United States Patent
Application |
20030221967 |
Kind Code |
A1 |
Tsuchida, Hideki ; et
al. |
December 4, 2003 |
Via filling method
Abstract
A process for via filling is provided, wherein after flash
plating, a PPR current is applied for a cycle of 1 to 50 msec
positive electrolysis time and 0.2 to 5 msec reverse electrolysis
time until an F/R ratio representing the ratio of positive
electrolysis current density to reverse electrolysis current
density is at least 1/0.2 and less than 1/1.
Inventors: |
Tsuchida, Hideki;
(Hasuda-shi, JP) ; Kusaka, Masaru;
(Kitaadachi-gun, 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: |
19191195 |
Appl. No.: |
10/342599 |
Filed: |
January 15, 2003 |
Current U.S.
Class: |
205/103 ;
205/105; 205/123; 205/125 |
Current CPC
Class: |
H05K 3/421 20130101;
H05K 3/423 20130101; C25D 5/611 20200801; H05K 2203/1492 20130101;
H05K 2201/09563 20130101; C25D 5/18 20130101 |
Class at
Publication: |
205/103 ;
205/125; 205/123; 205/105 |
International
Class: |
C25D 005/02; C25D
005/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 15, 2002 |
JP |
2002-006183 |
Claims
What is claimed is:
1. A process for filling a via with a metal comprising the steps of
flash plating and then applying a PPR current for a cycle of 1 to
50 msec positive electrolysis time and 0.2 to 5 msec reverse
electrolysis time such that a F/R ratio representing a ratio of
positive electrolysis current density to reverse electrolysis
current density is from 1/0.2 to 1/1.
2. The process of claim 1, wherein the flash plating is performed
by direct-current electrolysis.
3. The process of claim 1, wherein the flash plating is performed
under conditions of applying a PPR current for a cycle of 1 to 50
msec positive electrolysis time and 0.2 to 5 msec reverse
electrolysis time until an F/R ratio is 1/1 to 1/10.
4. The process of claim 1, wherein the flash plating is performed
by pulse electrolysis.
5. The process of claim 1, wherein the PPR current is applied for a
cycle of 1 to 50 msec positive electrolysis time, 0.2 to 5 msec
reverse electrolysis time, and 0.1 to 20 msec rest time.
6. The process of claim 1, wherein the metal used for filling is
copper.
7. The process of claim 1, wherein the via filling is performed
using a metal plating bath containing a grain refiner.
8. The process of claim 1, wherein the via filling is performed
using a metal plating bath containing a surface active agent.
9. A printed circuit board containing a via filled by the process
of claim 1.
10. A wafer containing a via filled by the process of claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] This invention provides a novel via filling process. More
particularly, this invention provides a novel via filling process
that produces superior filling and superior flatness.
[0002] In recent years, there has been a strong demand for higher
density and thinner printed circuit boards in response to greater
high performance and miniaturization of electronic devices,
beginning with personal computers. One means responding to such
demands is to use a multilayer printed circuit board (build-up
printed circuit board) produced using the build-up method of
forming a pattern for each layer and laminating successive
layers.
[0003] A process for completely filling micro via holes (hereafter
sometimes called "MVH") with a conductor and electrically
connecting between adjacent layers of a build-up printed circuit
board has been developed for such build-up printed circuit boards
in recent years. This method, called via-filling, can increase the
effective surface area of the printed circuit board and obtain
adequate electrical connections even in MVH having a smaller
diameter compared to plating only the inner wall of MVH by prior
art methods, and is effective for miniaturizing and increasing the
density of printed circuit boards.
[0004] Processes published as via filling processes include the
process of filling MVH with a conductive paste by the printing
method, the method of selectively building up electroless plating
by activating only a conductive layer on the floor of MVH, and
methods using electroplating.
[0005] Being a mixture of organic substances, however, conductive
paste has low conductivity compared to pure metals, has difficulty
forming adequate electrical connections in small-diameter MVH, and
cannot be called an effective method for miniaturizing and
increasing the density of printed circuit boards. Moreover, filling
by the printing method requires packing a viscous paste into holes
that are impassable due to their small diameter, and has difficulty
filling holes completely without leaving voids due to the viscosity
of the paste. The method of using electroless plating is superior
to the conductive paste method on the point that the substance
filling MVH is a highly conductive metallic deposit, but has a slow
plating film deposition speed, which is a problem for productivity.
For example, the plating speed using a general-purpose high-speed
electroless copper plating bath is about 3 .mu.m/hr, but filling
blind via holes (hereafter sometimes called "BVH") that are
typically 100 .mu.m in diameter and 100 .mu.m deep by copper
plating using this bath takes 30 hours or longer, making this
extremely poor in productivity.
[0006] Because electroplating can substantially reduce time
compared to electroless plating, electroplating is expected to be
applied to MVH. When depositing a metal over the entire inner
surface of MVH, however, the plating speed near the floor inside
MVH must be faster than the plating speed at the opening in order
to fill MVH with metal without leaving voids. If the plating speed
near the floor is the same as or slower than the plating speed at
the opening, the MVH are not filled or the opening becomes clogged
before MVH are completely filled with metal plating, leaving voids
inside. In either case, the MVH are inadequate for practical
application. Therefore, filling conditions must be strictly
controlled to enable the optimum deposition of metal for filling
micro via holes.
[0007] Direct-current electrolysis is generally used as a condition
of electrolysis when using an electroless plating bath in prior art
to accelerate the plating speed near the floor inside MVH. The
method of using PR (periodic reverse) electrolysis alternating the
cathode and the anode is also known, but this has an extremely long
cycle of several seconds to several tens of seconds, and is not
able to satisfactorily control the plating speed of metal.
[0008] In addition, the filled surface is not flat, producing an
indented shape at the center of via. As a result, when filled to an
adequate height, the plating film thickens on the outside of the
via, which causes great inconvenience during later treatments and
is economically undesirable.
[0009] One method for improving via filling, disclosed by Japanese
Unexamined Patent Application No. 2000-68651, is the method of
applying electrolytic copper plating using a plating bath
containing a particular compound containing sulfur ions and a PPR
(pulse periodic reverse) current. However, although adsorption and
desorption of the particular compound containing sulfur ions to the
substrate is controlled by the invention disclosed in this patent
application, stricter control of plating conditions is required to
fill micro via holes having a high aspect ratio.
SUMMARY OF THE INVENTION
[0010] Reflecting on the situation outlined above, the purpose of
this invention is to offer a novel via filling process that
produces a surface having superior filling and flatness in a short
time.
[0011] This invention offers a via filling process wherein after
flash plating, a PPR current is applied for a cycle of 1 to 50 msec
positive electrolysis time and 0.2 to 5 msec reverse electrolysis
time until an F/R ratio representing the ratio of positive
electrolysis current density to reverse electrolysis current
density is from 1/0.2 to 1/1.
BRIEF DESCRIPTIONS OF THE INVENTION
[0012] FIGS. 1A-1E illustrate cross-sectional views of vias plated
according to the invention, not to scale.
[0013] FIGS. 2A-2E illustrate cross-sectional views of vias plated
according to comparative methods, not to scale.
DETAILED DESCRIPTION OF THE INVENTION
[0014] "Positive electrolysis time" means the time during which
electrolysis is applied using the plating object as a cathode, and
"reverse electrolysis time" means the time during which
electrolysis is applied using the plating object as an anode.
Positive electrolysis time and reverse electrolysis time can be
changed according to plating conditions such as the opening
diameter of the MVH to be filled, the aspect ratio, and the type of
metal used for filling. A wide range of both positive electrolysis
times and reverse electrolysis times may be used. Positive
electrolysis time is typically 1 to 50 msec, preferably 5 to 30
msec, and more preferably 10 to 20 msec. Reverse electrolysis time
is typically 0.2 to 5 msec, preferably 0.2 to 2 msec, and more
preferably 0.2 to 1 msec.
[0015] Less than 0.2 msec positive electrolysis time may not be
efficient because electrolysis stops before metal has started to
deposit properly. Greater than 50 msec positive electrolysis time
may increase the adsorption of grain refiner near the openings of
blind via holes when using the grain refiner described below, with
the result that the plating speed near the floor of blind via holes
may not be faster than the plating speed at the opening, and
satisfactory filling cannot be obtained.
[0016] Less than 0.2 msec reverse electrolysis time may lead to
adsorption of grain refiner near the openings of blind via holes
when using the grain refiner described below, with the result that
the plating speed near the floor of blind via holes may not be
faster than the plating speed at the opening, and satisfactory
filling may not be obtained. Greater than 5 msec reverse
electrolysis time is undesirable because the metallic film already
deposited dissolves, lengthening the time required to fill blind
via holes.
[0017] Typically, positive electrolysis is applied at a current
density of 0.1 to 20 A/dm.sup.2, and preferably 0.1 to 10
A/dm.sup.2. In general, reverse electrolysis is applied at a
current density of 0.1 to 200 A/dm.sup.2, and preferably 0.1 to 100
A/dm.sup.2.
[0018] In this specification, the ratio of current density during
positive electrolysis to current density during reverse
electrolysis is called the F/R ratio. That is, the level of reverse
electrolysis current density R when positive electrolysis current
density F is 1 is called the F/R ratio, and is lower when F/R=1/1
than when F/R=1/2. In this invention, the F/R ratio is preferably
in a range from 1/0.2 to 1/0.9, and more preferably a range from
1/0.4 to 1/0.6. Most typically, the F/R ratio is 1/0.5.
[0019] In this invention, a metallic layer is deposited on the
inner wall of via holes ahead of time as a pretreatment before
filling by PPR electrolysis, and the via filling method described
above is executed after assuring that this is conductive. Such
flash plating can be performed by any of direct-current
electrolysis, pulse electrolysis, or PPR electrolysis. That is,
this invention further offers the following three modes:
[0020] i) The method of executing the via filling process of this
invention after flash plating by direct-current electrolysis
[0021] ii) The method of executing the via filling process of this
invention after flash plating by pulse electrolysis
[0022] iii) The method of executing the via filling process of this
invention after flash plating by PPR electrolysis.
[0023] "Direct-current electrolysis" refers to electroplating using
a direct-current power source. Electrolysis conditions such as
current or time and plating solution compositions are well-known,
and can be determined as appropriate by persons skilled in the
art.
[0024] "Pulse electrolysis" refers to electroplating using a pulse
power source; that is, under the electrolysis condition of
alternating between positive electrolysis time and rest time in
pulses. Electrolysis conditions such as current or time and plating
solution compositions are well-known, and can be determined as
appropriate by persons skilled in the art.
[0025] PPR electrolysis for flash plating is typically performed by
applying a PPR current for a cycle of 1 to 50 msec positive
electrolysis time and 0.2 to 5 msec reverse electrolysis time until
the F/R ratio is in a range of 1/1 to 1/10.
[0026] Flash plating is performed by any of these methods until a
metal has been deposited over the entire inner wall of via holes
and adequate conductivity has been obtained. The thickness of the
metallic film after flash plating is completed is typically 0.5 to
5 micrometers.
[0027] When via holes have a high aspect ratio, the method using
PPR electrolysis is preferred because of its superior wrapping
ability. In addition, where direct-current electrolysis requires
two plating tanks because the plating solution composition used for
direct-current electrolysis is different from the plating solution
composition used for PPR electrolysis, PPR electrolysis uses only
one plating tank and all steps can be performed simply by varying
electrolysis conditions. Therefore, PPR electrolysis is more
convenient in terms of operation and more useful in terms of
economy. However, direct-current electrolysis and PPR electrolysis
also can be performed in the same plating tank depending on the
bath composition.
[0028] Preferably, a rest time is inserted in PPR electrolysis in
this invention. In this invention, "rest time" means the time
during which electrolysis is not applied. The rest time may be
inserted during the change from positive electrolysis to reverse
electrolysis or during the change from reverse electrolysis to
reverse electrolysis, and may be inserted during both times.
Preferably, however, the rest time is inserted during the change
from reverse electrolysis to positive electrolysis. It is
considered that inserting such a rest time produces a satisfactory
filling result by supplying metallic ions for plating inside the
via.
[0029] A wide range of rest times may be used. The rest time is
typically 0.1 to 20 msec, preferably 0.5 to 5 msec, and more
preferably 0.5 to 1 msec.
[0030] A rest time can be inserted in all PPR electrolysis; that
is, in both the PPR electrolysis used in the via filling method of
this invention and the PPR electrolysis used in flash plating.
[0031] In a particular embodiement, a PPR current can be applied in
this invention for a cycle of 1 to 50 msec positive electrolysis
time, 0.2 to 5 msec reverse electrolysis time, and 0.1 to 20 msec
rest time.
[0032] The process of this invention is useful for filling
depressions having a high aspect ratio, such as via holes, with
metal. The method of this invention can be used to fill holes
having an opening diameter of 100 micrometers or less and an aspect
ratio of 1 or greater, typically 3 or greater, and especially 5 or
greater.
[0033] This invention can be applied to all metals capable of being
electrodeposited, including copper, nickel, gold, silver,
palladium, tin, lead, platinum, chromium, zinc, cadmium, iron,
aluminum, and alloys of these such as solder.
[0034] This invention will be explained below for the case of
copper plating. However, this is no more than an example, and is
not meant to limit the scope of this invention in any way.
[0035] In addition, examples especially ideal for use in copper
sulfate plating are given as concrete examples of the grain
refiners and surface active agents described below, and the active
effects of such substances are explained. However, using compounds
presenting the same active effects when electroplating other metals
is well-known, and the same effects of this invention are also
obtained by systems containing such compounds.
[0036] When filling blind via holes by copper plating using the
method of this invention, the copper plating solution is typically
a copper sulfate plating solution, and preferably contains a grain
refiner. However, other copper salts may also be used to prepare
the copper plating solution.
[0037] Grain refiners are substances having a plus static charge in
the plating bath that are adsorbed to the surface of the plating
object during electrolysis and desorbed from the surface of the
plating object during reverse electrolysis. These substances have
an action aiding growth of the metallic film when adsorbed to the
surface of the plating object.
[0038] Typically, grain refiners are compounds having an
intramolecular --S--CH.sub.2O--R--SO.sub.3M structure or compounds
having an intramolecular --S--R--SO.sub.3M structure (where M is a
hydrogen or alkali metal atom, and R is an alkyl group containing 3
to 8 carbon atoms). Examples of even more typical grain refiners
are compounds having the following structures (1) to (6):
M-SO.sub.3--(CH.sub.2).sub.a--S--(CH.sub.2).sub.b--SO.sub.3--M;
(1)
(2)
M-SO.sub.3--(CH.sub.2).sub.a--O--CH.sub.2--S--CH.sub.2--O--CH.sub.2--S-
O.sub.3-M; (2)
(3)
M-SO.sub.3--(CH.sub.2).sub.a--S--SCH.sub.2--S--CH.sub.2--SO.sub.3-M;
(3)
(4)
M-SO.sub.3--(CH.sub.2).sub.a--O--CH.sub.2--S--S--CH.sub.2--(CH.sub.2).-
sub.b--SO.sub.3-M; (4)
(5)
M-SO.sub.3--(CH.sub.2).sub.a--S--C(.dbd.S)--S--(CH.sub.2).sub.b--SO.su-
b.3-M; (5)
(6)
M-SO.sub.3--(CH.sub.2).sub.a--OCH.sub.2--S--C(.dbd.S)--S--CH.sub.2--O--
-(CH.sub.2).sub.b--SO.sub.3-M; (6)
[0039] In the above Formulae (1) to (6), a and b=integers from 3 to
8, and M is hydrogen or an alkali metal.
[0040] Grain refiners are generally called brighteners and are used
to improve the appearance of the deposited metal film, but this
invention also includes grain refiners used for other purposes so
long as they offer a comparable active effect. Grain refiners may
be used alone or as a mixture of two or more types.
[0041] Grain refiners can be used in a range such as 0.1 to 100
mg/L, and preferably 0.5 to 10 mg/L. When grain refiners are used
for purposes other than to improve the appearance of plating film,
the ideal content range is a matter that can be determined as
appropriate by persons skilled in the art.
[0042] While not wishing to be bound in theory, when using a PPR
electrolysis method in which plating is performed while reversing
the direction of the current in an extremely short cycle such as
used in this invention, the grain refiner is adsorbed to the inner
surface of blind via holes in the plating object by electrolysis,
and during the short period reverse electrolysis, the grain refiner
is desorbed only near the openings of blind via holes where the
current tends to accumulate. Therefore, by repeatedly reversing the
direction of the current, a large amount of grain refiner is
adsorbed near the floors of blind via holes, and a small amount of
grain refiner is adsorbed near the openings. As a result, the grain
refiner has a stronger action aiding growth of the metal film near
the floors of blind via holes, the plating speed near the floors of
blind via holes becomes faster than the plating speed near
openings, and blind via holes can be filled with a metal deposit
without leaving voids.
[0043] The electrolytic copper plating solution used in this
invention typically contains a surface active agent acting as a
lubricant. The surface active agent can be any desired standard
surface active agent normally used as an additive in electrolytic
copper plating solutions. Preferably, the surface active agent is a
polyether containing at least five, and preferably at least twenty,
intramolecular ether oxygen atoms. Examples of this type of surface
active agent are compounds having the following structures (7) to
(9), but are not limited to these:
HO--(CH.sub.2--CH.sub.2--O).sub.a--H (where a=an integer from 5 to
500); (7)
HO--(CH.sub.2--CH(CH.sub.3) --O).sub.a--H (where a=an integer from
5 to 200); (8)
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.2O).sub.c--H (where a and c are integers, a+c=an
integer from 5 to 250, and b=an integer from 1 to 100). (9)
[0044] The surface active agent used in this invention may be used
alone or as a mixture of two or more types. Surface active agents
used in this invention can be used in a range of from 0.05 to 10
g/L, and preferably 0.1 to 5 g/L. Lower amounts of surface active
agent may be used but may cause many pin-holes in the deposit.
Greater amount of surface active agent may be used but such large
amount hardly provides any commensurate improvement in effect,
making it economically undesirable.
[0045] When using a copper sulfate plating solution, the copper
sulfate plating solution is an aqueous solution containing a basic
composition of sulfuric acid, copper sulfate, and a water-soluble
chlorine compound. Said plating solution can use any basic
composition without restrictions so long as it is used in standard
copper sulfate plating solutions. The concentration of sulfuric
acid in the copper sulfate plating solution is normally 30 to 400
g/L, and preferably 170 to 210 g/L. The concentration of copper
sulfate in the copper sulfate plating solution is normally 20 to
250 g/L, and preferably 60 to 180 g/L.
[0046] The water-soluble chloride compound contained in the copper
sulfate plating solution can be any compound without restrictions
so long as it is used in standard copper sulfate plating solutions.
Examples of said water-soluble chloride compound include
hydrochloric acid, sodium chloride, potassium chloride, and
ammonium chloride, but are not limited to these. The water-soluble
chloride compound may be used alone or as a mixture of two or more
types.
[0047] The concentration of said water-soluble chloride compound
contained in the copper sulfate plating solution, expressed as
concentration of chloride ions, is normally 10 to 200 mg/L, and
preferably 30 to 80 mg/L.
[0048] The substrate supplied to the via filling method of this
invention can be a substrate of any desired material and shape so
long as it can withstand the conditions of the via filling method
and a metal layer can be deposited on it by plating. Examples of
materials include resins, ceramics, and metals, but are not limited
to these. For example, this method is ideally used for printed
circuit board substrates or semiconductor wafers such as silicon
wafers. The substrate supplied to this invention is preferably a
substrate having through-holes and/or via holes, and more
preferably, a printed circuit board or wafer having through-holes
and/or via holes.
[0049] Examples of resins used as substrates include thermoplastic
resins, including polyethylene resins such as high-density
polyethylene, medium-density polyethylene, branching low-density
polyethylene, straight-chain low-density polyethylene, or super
high-molecular-weight polyethylene; polyolefin resins such as
polypropylene resin, polybutadiene, polybutene resin, polybutylene
resin, or polystyrene resin; halogenated resins such as polyvinyl
chloride resin, polyvinylidene chloride resin, polyvinylidene
chloride-polyvinyl chloride copolymer resin, chlorinated
polyethylene, chlorinated polypropylene, or tetrafluoroethylene; AS
resins; ABS resins; MBS resins; polyvinyl alcohol resins;
polyacrylic ester resins such as methyl polyacrylate;
polymethacrylic ester resins such as methyl polymethacrylate;
methyl methacrylate-styrene copolymer resin; maleic
anhydride-styrene copolymer resin; polyvinyl chloride resin;
cellulose resins such as cellulose propionate resin or cellulose
acetate resin; epoxy resins; polyimide resins; polyamide resins
such as Nylons; polyamide imide resins; polyallylate resins;
polyether imide resins; polyether ether ketone resins; polyethylene
oxide resins; polyester resins such as PET resin; polycarbonate
resins; polysulfone resins; polyvinyl ether resins; polyvinyl
butyral resins; polyphenylene ether resins such as polyphenylene
oxide; polyphenylene sulfide resins; polybutylene terephthalate
resins; polymethyl pentene resins; polyacetal resins; vinyl
chloride-vinyl acetate copolymers; ethylene-vinyl acetate
copolymers; ethylene-vinyl chloride copolymers; and copolymers and
blends of these; thermosetting resins, including epoxy resins;
xylene resins; guanamine resins, diallyl phthalate resins; vinyl
ester resins; phenolic resins, unsaturated polyester resins; furan
resins; polyimide resins; polyurethane resins, maleic acid resins;
melamine resins; and urea resins; and mixtures of these; but are
not limited to these. Preferred resins are epoxy resins, polyimide
resins, vinyl resins, phenolic resins, Nylon resins, polyphenylene
ether resins, polypropylene resins, fluorinated resins, and ABS
resins. More preferred resins are epoxy resins, polyimide resins,
polyphenylene ether resins, fluorinated resins, and ABS resins.
Even more preferred resins are epoxy resins and polyimide resins.
In addition, resins substrates may be comprised of a single resin
or several resins. The resin substrate may also may be a composite
having another resin coated or laminated on the substrate.
Moreover, resin substrates that can be used in this invention are
not limited to resin molded products, but may be resin composites
by way of reinforcing materials, such as materials reinforced by
fiberglass between resins, or resin films formed on substrates
comprised of other raw materials such as ceramics, glasses, or
metals.
[0050] Ceramics that can be used as resin materials include oxide
ceramics, beginning with alumina (Al.sub.2O.sub.3), steatite
(MgO.SiO.sub.2), forsterite (2MgO.SiO.sub.2), mullite
(3Al.sub.2O.sub.3.SiO.sub.2), magnesia (MgO), spinel
(MgO.Al.sub.2O.sub.3), and beryllia (BeO), non-oxide ceramics such
as aluminum nitride or silicon carbonate, and low-temperature
sintered ceramics, beginning with glass ceramics, but are not
limited to these.
[0051] The plating temperature (solution temperature) in the via
filling process of this invention is set as appropriate for the
type of plating bath, but is normally 11.degree. C. to 40.degree.
C., and preferably 20.degree. C. to 30.degree. C.
[0052] Any desired appropriate anode can be used in the via filling
process of this invention depending on the type of metal to be
plated. Either a soluble anode or an insoluble anode can be used.
For example, in the case of copper plating, a phosphated copper
anode can be used as a soluble anode, and an anode of a material
such as iridium oxide, platinum-clad titanium, platinum, graphite,
ferrite, titanium coated with zinc dioxide and a platinic element
oxide, or stainless steel can be used as an insoluble anode.
[0053] In the via filling process of this invention, preferably,
air or oxygen is passed through the plating solution to increase
the concentration of dissolved oxygen in the plating solution.
Although not wishing to become bogged down in theory, dissolved
oxygen in the plating solution is considered to decrease compounds
having the structure --X--S-- in said plating solution. A preferred
method for increasing the concentration of dissolved oxygen in the
plating solution is bubbling the plating solution with air or
oxygen. Said bubbling may be agitating the plating solution, or
bubbling unrelated to agitating. In addition, bubbling to increase
the concentration of dissolved oxygen in the plating solution may
be applied during electroplating treatment or when electroplating
treatment is suspended.
[0054] There is no objection to agitating in the via filling
process of this invention, and agitating is preferred to supply
metal ions and additives evenly to the surface to be plated. Air
agitation or a jet spray can be used for the agitation method. Air
agitation is preferred from the standpoint of increasing the
concentration of dissolved oxygen in the plating solution. Even
when agitation by a jet spray is used, preferably, agitating by air
is also used. Furthermore, open-change filtration or reflux
filtration can also be applied, and reflux filtration of the
plating solution by a filter device is especially preferred. Doing
this makes the temperature of the plating solution uniform, and can
also remove matter such as dirt or sediment in the plating
solution.
[0055] The via filling process of this invention produces filled
vias with no voids.
[0056] The case of copper plating was described above, but other
metals are plated in the same way as described above. In this case,
the method of this invention can be implemented using any desired
standard plating solution. The electroplating solution during this
can use any basic composition without restrictions so long as it is
used in standard electroplating. Moreover, the components of the
basic composition can be changed, concentrations can be changed, or
additives can be added as appropriate so long as the purposes of
this invention are achieved.
[0057] This invention will be explained in detail by the following
working examples, but such working examples are no more than
examples, and do not in any way limit the scope of this
invention.
EXAMPLE 1
[0058]
1 Plating Solution Composition CuSO.sub.4.5H.sub.2O 127.7 g/L
H.sub.2SO.sub.4 213.2 g/L Cl.sup.- 70 mg/L SPS 4 mg/L nonionic
surface active agent 250 mg/L Flash Plating Direct-Current
Electrolysis current density 2 A/dm.sup.2 temperature 20.degree. C.
time 11 min Filling Step current density 2 A/dm.sup.2 F/R ratio
1/0.5 positive electrolysis time 10 msec reverse electrolysis time
0.5 msec temperature 20.degree. C. time 45 minutes Note) SPS:
disodium bis(3-sulfopropyl)disulfide
COMPARATIVE EXAMPLE
[0059]
2 Filling Step current density 2 A/dm.sup.2 F/R ratio 1/0.5
positive electrolysis time 10 msec reverse electrolysis time 0.5
msec temperature 20.degree. C. time 56 minutes
[0060] The diameter of via was 120 micrometers, and the depth was
60 micrometers.
[0061] The results of Example 1 show that satisfactory filling was
obtained by the via filling method of this invention and that no
voids were present in the five vias evaluated by cross-sectional
analysis. These results are show in FIGS. 1A-1E. The results of the
Comparative Example show unsatisfactory filing of the vias, where 4
out of the 5 vias evaluated by cross-sectional analysis contained
voids. The comparative results are shown in FIGS. 2A-2E.
* * * * *