U.S. patent application number 10/943744 was filed with the patent office on 2006-03-16 for process for rendering metal corrosion-resistant in electrochemical metal deposition.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Co., Ltd.. Invention is credited to Ming-Wei Lin, Ming-Hsing Tsai.
Application Number | 20060054508 10/943744 |
Document ID | / |
Family ID | 36032731 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060054508 |
Kind Code |
A1 |
Lin; Ming-Wei ; et
al. |
March 16, 2006 |
Process for rendering metal corrosion-resistant in electrochemical
metal deposition
Abstract
A new and improved method for electroplating a metal onto a
substrate in such a manner as to render the metal essentially
corrosion-resistant during subsequent substrate processing such as
chemical mechanical polishing. The process involves incorporating
nitrogen into the metal as the metal is electroplated onto the
substrate. The process includes preparing the electroplating bath,
placing a leveler chemical containing nitrogen in the prepared
bath, circulating the leveler chemical throughout the bath and then
electroplating the metal on the substrate. In a preferred
embodiment, alkyl polyamide, alkyl amine, alkyl amine oxide or
thiourea with molecular weight ranging from 100.about.1,000,000 is
used as the leveler chemical.
Inventors: |
Lin; Ming-Wei; (Hsin-Chu,
TW) ; Tsai; Ming-Hsing; (Chu-pei city, TW) |
Correspondence
Address: |
TUNG & ASSOCIATES
Suite 120
838 W. Long Lake Road
Bloomfieled Hills
MI
48302
US
|
Assignee: |
Taiwan Semiconductor Manufacturing
Co., Ltd.
|
Family ID: |
36032731 |
Appl. No.: |
10/943744 |
Filed: |
September 16, 2004 |
Current U.S.
Class: |
205/266 ;
205/220; 205/291; 257/E21.175; 257/E21.583 |
Current CPC
Class: |
H01L 21/2885 20130101;
H01L 21/7684 20130101; C25D 3/38 20130101; C25D 3/02 20130101 |
Class at
Publication: |
205/266 ;
205/291; 205/220 |
International
Class: |
C25D 3/48 20060101
C25D003/48; C25D 3/38 20060101 C25D003/38; C25D 5/48 20060101
C25D005/48 |
Claims
1. A process for electroplating a substrate, comprising the steps
of: providing an electrolyte bath comprising a metal; mixing a
nitrogen-containing leveler chemical with said electrolyte bath;
electroplating said metal onto said substrate; and subjecting said
metal to chemical mechanical planarization.
2. The process of claim 1 wherein said leveler chemical comprises a
leveler chemical selected from the group consisting of alkyl
polyamide, alkyl amine, alkyl amine oxide and thiourea having a
molecular weight ranging from 100.about.1,000,000.
3. The process of claim 1 wherein said metal comprises copper.
4. The process of claim 3 wherein said leveler chemical comprises a
leveler chemical selected from the group consisting of alkyl
polyamide, alkyl amine, alkyl amine oxide and thiourea having a
molecular weight ranging from 100.about.1,000,000.
5. The process of claim 1 wherein said metal is a copper alloy.
6. The process of claim 5 wherein said leveler chemical comprises a
leveler chemical selected from the group consisting of alkyl
polyamide, alkyl amine, alkyl amine oxide and thiourea having a
molecular weight ranging from 100.about.1,000,000.
7. The process of claim 1 wherein said metal is a metal selected
from the group consisting of copper, aluminum, nickel, chromium,
zinc, tin, gold, silver, lead and cadmium.
8. The process of claim 7 wherein said leveler chemical comprises a
leveler chemical selected from the group consisting of alkyl
polyamide, alkyl amine, alkyl amine oxide and thiourea having a
molecular weight ranging from 100.about.1,000,000.
9. A process for providing a substantially corrosion-resistant
metal layer on a substrate, comprising the steps of: providing an
electrolyte bath comprising a metal; mixing a nitrogen-containing
leveler chemical with said electrolyte bath; and incorporating
nitrogen from said leveler chemical into said metal and providing
said metal on the substrate by electroplating said metal onto the
substrate.
10. The process of claim 9 wherein said leveler chemical comprises
a leveler chemical selected from the group consisting of alkyl
polyamide, alkyl amine, alkyl amine oxide and thiourea having a
molecular weight ranging from 100.about.1,000,000.
11. The process of claim 9 wherein said metal comprises copper.
12. The process of claim 11 wherein said leveler chemical comprises
a leveler chemical selected from the group consisting of alkyl
polyamide, alkyl amine, alkyl amine oxide and thiourea having a
molecular weight ranging from 100.about.1,000,000.
13. The process of claim 9 wherein said metal is a copper
alloy.
14. The process of claim 13 wherein said leveler chemical comprises
a leveler chemical selected from the group consisting of alkyl
polyamide, alkyl amine, alkyl amine oxide and thiourea, having a
molecular weight ranging from 100.about.1,000,000.
15. The process of claim 9 wherein said nitrogen is present in said
metal in a concentration of from about 10 ppm to about 1000
ppm.
16. The process of claim 15 wherein said metal is a metal selected
from the group consisting of copper, aluminum, nickel, chromium,
zinc, tin, gold, silver, lead and cadmium.
17. A process for providing a substantially corrosion-resistant
metal layer on a substrate, comprising the steps of: providing an
electrolyte bath comprising a metal; mixing a nitrogen-containing
leveler chemical with said electrolyte bath; and incorporating
nitrogen from said leveler chemical into said metal at a nitrogen
concentration of from about 10 ppm to about 1000 ppm and providing
said metal on the substrate by electroplating said metal onto the
substrate.
18. The process of claim 17 wherein said leveler chemical comprises
a leveler chemical selected from the group consisting of alkyl
polyamide, alkyl amine, alkyl amine oxide and thiourea having a
molecular weight ranging from 100.about.1,000,000.
19. The process of claim 17 wherein said metal is a copper
alloy.
20. The process of claim 17 wherein said metal is a metal selected
from the group consisting of copper, aluminum, nickel, chromium,
zinc, tin, gold, silver, lead and cadmium.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to electroplating systems used
in the deposition of metal layers on semiconductor wafer substrates
in the fabrication of semiconductor integrated circuits. More
particularly, the present invention relates to a process for
electroplating a corrosion-resistant metal such as copper on a
substrate in electrochemical metal deposition.
BACKGROUND OF THE INVENTION
[0002] In the fabrication of semiconductor integrated circuits,
metal conductor lines are used to interconnect the multiple
components in device circuits on a semiconductor wafer. A general
process used in the deposition of metal conductor line patterns on
semiconductor wafers includes deposition of a conducting layer on
the silicon wafer substrate; formation of a photoresist or other
mask such as titanium oxide or silicon oxide, in the form of the
desired metal conductor line pattern, using standard lithographic
techniques; subjecting the wafer substrate to a dry etching process
to remove the conducting layer from the areas not covered by the
mask, thereby leaving the metal layer in the form of the masked
conductor line pattern; and removing the mask layer typically using
reactive plasma and chlorine gas, thereby exposing the top surface
of the metal conductor lines. Typically, multiple alternating
layers of electrically conductive and insulative materials are
sequentially deposited on the wafer substrate, and conductive
layers at different levels on the wafer may be electrically
connected to each other by etching vias, or openings, in the
insulative layers and filling the vias using aluminum, tungsten or
other metal to establish electrical connection between the
conductive layers.
[0003] Deposition of conductive layers on the wafer substrate can
be carried out using any of a variety of techniques. These include
oxidation, LPCVD (low-pressure chemical vapor deposition), APCVD
(atmospheric-pressure chemical vapor deposition), and PECVD
(plasma-enhanced chemical vapor deposition). In general, chemical
vapor deposition involves reacting vapor-phase chemicals that
contain the required deposition constituents with each other to
form a nonvolatile film on the wafer substrate. Chemical vapor
deposition is the most widely-used method of depositing films on
wafer substrates in the fabrication of integrated circuits on the
substrates.
[0004] Due to the ever-decreasing size of semiconductor components
and the ever-increasing density of integrated circuits on a wafer,
the complexity of interconnecting the components in the circuits
requires that the fabrication processes used to define the metal
conductor line interconnect patterns be subjected to precise
dimensional control. Advances in lithography and masking techniques
and dry etching processes, such as RIE (Reactive Ion Etching) and
other plasma etching processes, allow production of conducting
patterns with widths and spacings in the submicron range.
Electrodeposition or electroplating of metals on wafer substrates
has recently been identified as a promising technique for
depositing conductive layers on the substrates in the manufacture
of integrated circuits and flat panel displays. Such
electrodeposition processes have been used to achieve deposition of
the copper or other metal layer with a smooth, level or uniform top
surface. Consequently, much effort is currently focused on the
design of electroplating hardware and chemistry to achieve
high-quality films or layers which are uniform across the entire
surface of the substrates and which are capable of filling or
conforming to very small device features. Copper has been found to
be particularly advantageous as an electroplating metal.
[0005] Electroplated copper provides several advantages over
electroplated aluminum when used in integrated circuit (IC)
applications. Copper is less electrically resistive than aluminum
and is thus capable of higher frequencies of operation.
Furthermore, copper is more resistant to electromigration (EM) than
is aluminum. This provides an overall enhancement in the
reliability of semiconductor devices because circuits which have
higher current densities and/or lower resistance to EM have a
tendency to develop voids or open circuits in their metallic
interconnects. These voids or open circuits may cause device
failure or burn-in.
[0006] FIG. 1 schematically illustrates a typical standard or
conventional electroplating system 10 for depositing copper onto a
semiconductor wafer 18. The electroplating system 10 includes a
standard electroplating cell having an adjustable current source
12, a bath container 14, a copper anode 16 and a cathode 18, which
cathode 18 is the semiconductor wafer that is to be electroplated
with copper. The anode 16 and semiconductor wafer/cathode 18 are
connected to the current source 12 by means of suitable wiring 38.
The bath container 14 holds a bath 20 typically of acid copper
sulfate (CuSO.sub.4) solution which may include an additive for
filling of submicron features and leveling the surface of the
copper electroplated on the wafer 18.
[0007] As illustrated in FIGS. 1 and 2, the electroplating system
10 typically further includes a pair of bypass filter conduits 24
which extend through the anode 16 and open to the upper, oxidizing
surface 22 of the anode 16 through respective sludge openings 26 at
opposite ends of the anode 16. The bypass filter conduits 24
connect to a bypass pump/filter 30 located outside the bath
container 14, and the bypass pump/filter 30 is further connected to
an electrolyte holding tank 34 through a tank inlet line 32. The
electrolyte holding tank 34 is, in turn, connected to the bath
container 14 through a tank outlet line 36. The electrolyte content
of the bath 20 can be increased, as needed, by adding electrolytes
to the electrolyte holding tank 34 and then circulating the bath 20
through the bypass filter conduits 24, the bypass pump/filter 30,
the tank inlet line 32, the electrolyte holding tank 34 and back
into the bath container 14 through the tank outlet line 36,
respectively.
[0008] In operation of the electroplating system 10, the current
source 12 applies a selected voltage potential typically at room
temperature between the anode 16 and the cathode/wafer 18. This
potential creates a electrical field around the anode 16 and the
cathode/wafer 18, which electrical field affects the distribution
of the copper ions in the bath 20. In a typical copper
electroplating application, a voltage potential may be applied s,
and a current flows between the anode 16 and the cathode/wafer 18.
Consequently, copper is oxidized typically at the oxidizing surface
22 of the anode 16 as electrons from the copper anode 16 and reduce
the ionic copper in the copper sulfate solution bath 20 to form a
copper electroplate (not illustrated) at the interface between the
cathode/wafer 18 and the copper sulfate bath 20.
[0009] The copper oxidation reaction which takes place at the
oxidizing surface 22 of the anode 16 is illustrated by the
following reaction formula (1): Cu---->Cu.sup.+++2e- (1)
[0010] The oxidized copper cation reaction product forms ionic
copper sulfate in solution with the sulfate anion in the bath 20:
Cu.sup.+++SO.sub.4.sup.------>Cu.sup.++SO.sub.4.sup.-- (2)
[0011] At the cathode/wafer 18, the electrons harvested from the
anode 16 flowed through the wiring 38 reduce copper cations in
solution in the copper sulfate bath 20 to electroplate the reduced
copper onto the cathode/wafer 18: Cu.sup.+++2e----->Cu (3)
[0012] As the anode 16 is consumed during the electroplating
process, small quantities of solid copper sulfate or "anode fines"
tend to precipitate at the interface between the copper sulfate
bath 20 and the oxidizing surface 22 of the anode 16 to form a
copper precipitate or sludge 28 on the oxidizing surface 22, as
illustrated in FIG. 2.
[0013] After the copper is electroplated onto the wafer 18, the
wafer 18 is frequently subjected to a CMP (chemical mechanical
polishing) process to smooth the surface of the electroplated
copper layer. Important components used in CMP processes include an
automated rotating polishing platen and a wafer holder, which both
exert a pressure on the wafer and rotate the wafer independently of
the platen. The polishing or removal of surface layers is
accomplished by a polishing slurry consisting mainly of colloidal
silica suspended in deionixed water or KOH solution. The slurry is
frequently fed by an automatic slurry feeding system in order to
ensure uniform wetting of the polishing pad and proper delivery and
recovery of the slurry. For a high-volume wafer fabrication
process, automated wafer loading/unloading and a cassette handler
are also included in a CMP apparatus.
[0014] As the name implies, a CMP process executes a microscopic
action of polishing by both chemical and mechanical means. While
the exact mechanism for material removal of an oxide layer is not
known, it is hypothesized that the surface layer of silicon oxide
is removed by a series of chemical reactions which involve the
formation of hydrogen bonds with the oxide surface of both the
wafer and the slurry particles in a hydrogenation reaction; the
formation of hydrogen bonds between the wafer and the slurry; the
formation of molecular bonds between the wafer and the slurry; and
finally, the breaking of the oxide bond with the wafer or the
slurry surface when the slurry particle moves away from the wafer
surface. It is generally recognized that the CMP polishing process
is not a mechanical abrasion process of slurry against a wafer
surface.
[0015] One of the problems which is inherent in the conventional
electroplating process is that the electroplated copper has a
tendency to corrode after it is subjected to chemical mechanical
polishing. The corrosion is manifested by small pits in the copper
and can adversely affect the yield of devices fabricated on the
wafer. Accordingly, a process is needed for rendering copper or
other metal corrosion-resistant as it is electroplated onto a wafer
substrate, to prevent corrosion of the metal during subsequent
chemical mechanical polishing or other processing.
[0016] An object of the present invention is to provide a new and
improved process for electroplating a metal on a substrate.
[0017] Another object of the present invention is to provide a new
and improved process for electroplating a corrosion-resistant metal
on a substrate.
[0018] Still another object of the present invention is to provide
a new and improved process for rendering an electroplating metal
corrosion-resistant by incorporating nitrogen into the metal.
[0019] Yet another object of the present invention is to provide a
new and improved process which is applicable to electroplating
copper or any of a variety of other metals on a substrate.
[0020] A still further object of the present invention is to
provide a new and improved process which is applicable to
preventing corrosion of an electroplated metal such as copper on a
substrate after chemical mechanical polishing of the metal.
[0021] Another object of the present invention is to provide a
process for electroplating a corrosion-resistant metal on a
substrate, including providing a nitrogen-containing leveler
chemical in an electroplating bath prior to electroplating the
metal on the substrate.
SUMMARY OF THE INVENTION
[0022] In accordance with these and other objects and advantages,
the present invention is generally directed to a new and improved
method for electroplating a metal onto a substrate in such a manner
as to render the metal essentially corrosion-resistant during
subsequent substrate processing such as chemical mechanical
polishing. The process involves incorporating nitrogen into the
metal as the metal is electroplated onto the substrate. The process
includes preparing the electroplating bath, placing a leveler
chemical containing nitrogen in the prepared bath, circulating the
leveler chemical throughout the bath and then electroplating the
metal on the substrate. In a preferred embodiment, alkyl polyamide,
alkyl amine, alkyl amine oxide or thiourea with molecular weight
ranging from 100.about.1,000,000 is used as the leveler
chemical.
[0023] The leveler chemical is typically circulated throughout the
bath. Typical concentrations of nitrogen incorporated into the
copper may range from about 0.1 ppm to about 1000 ppm. Due to the
amine and phenyl groups present in the leveler chemical, the copper
film deposited onto the substrate is resistant to corrosion
particularly during a chemical mechanical polishing process
following the electroplating process.
[0024] The process of the present invention may be used with any
electroplating bath formulation, such as copper, aluminum, nickel,
chromium, zinc, tin, gold, silver, lead and cadmium plating baths.
Plating baths containing mixtures of metals to be plated are also
contemplated by the present invention. It is preferred that the
plating bath be a copper or copper-alloy electroplating bath, and
more preferably, a copper electroplating bath.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The invention will now be described, by way of example, with
reference to the accompanying drawings, in which:
[0026] FIG. 1 is a schematic of a typical conventional
electroplating system suitable for implementation of the present
invention;
[0027] FIG. 2 is a side view of a typical conventional anode used
in an electroplating process;
[0028] FIG. 3 is a schematic of an electroplating system in
implementation of the present invention;
[0029] FIG. 4 is a cross-sectional view of a substrate with a
corrosion-resistant layer of metal electroplated thereon in
accordance with the process of the present invention; and
[0030] FIG. 5 is a flow diagram summarizing typical sequential
process steps in implementation of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] The present invention has particularly beneficial utility in
electroplating copper on a semiconductor wafer substrate in the
fabrication of integrated circuits on the substrate. However, the
invention is more generally applicable to electroplating copper or
other metals such as aluminum, nickel, chromium, zinc, tin, gold,
silver, lead and cadmium on substrates in a variety of mechanical
and industrial applications. The present invention is also
applicable to electroplating alloys of metals on substrates.
[0032] The process includes circulating a leveler chemical
containing amine and phenyl groups in an electroplating bath prior
to electroplating the metal on the substrate. Nitrogen from the
leveler chemical is incorporated into the metal as the metal is
electroplated onto the substrate, such that the electroplated metal
is substantially corrosion-resistant. The process is particularly
advantageous in preventing or substantially reducing or eliminating
corrosion of the metal during a subsequent chemical mechanical
polishing process.
[0033] According to a preferred embodiment, the nitrogen-containing
leveler chemical is alkyl polyamide, alkyl amine, alkyl amine oxide
or thiourea, with molecular weight ranging from
100.about.1,000,000. Briefly, after the electroplating bath is
prepared the leveler chemical is added to the bath at a
concentration of typically 0.1 ppm to 1000 ppm. Finally, as the
metal is electroplated onto the substrate, nitrogen from the
leveler chemical is incorporated into the metal to render the metal
substantially resistant to corrosion during subsequent processing.
The leveler chemical in the electroplating bath facilitates
incorporation of nitrogen into the electroplated metal in a
concentration of typically from about 0.1 ppm to about 1000
ppm.
[0034] The process of the invention may be used with any
electroplating bath formulation, such as copper, aluminum, nickel,
chromium, zinc, tin, gold, silver, lead and cadmium electroplating
baths. The present invention also contemplates the use of
electroplating baths containing mixtures of metals to be plated
onto a substrate. It is preferred that the electroplating bath be a
copper alloy electroplating bath, and more preferably, a copper
electroplating bath. Typical copper electroplating bath
formulations are well known to those skilled in the art and
include, but are not limited to, an electrolyte and one or more
sources of copper ions. Suitable electrolytes include, but are not
limited to, sulfuric acid, acetic acid, fluoroboric acid, methane
sulfonic acid, ethane sulfonic acid, trifluormethane sulfonic acid,
phenyl sulfonic acid, methyl sulfonic acid, p-toluenesulfonic acid,
hydrochloric acid, phosphoric acid and the like. The acids are
typically present in the bath in a concentration in the range of
from about 1 to about 300 g/L. The acids may further include a
source of halide ions such as chloride ions. Suitable sources of
copper ions include, but are not limited to, copper sulfate, copper
chloride, copper acetate, copper nitrate, copper fluoroborate,
copper methane sulfonate, copper phenyl sulfonate and copper
p-toluene sulfonate. Such copper ions sources are typically present
in a concentration in the range of from about 5 to about 300 g/L of
electroplating solution.
[0035] Referring to FIG. 3, a schematic of an electroplating system
40 which is suitable for implementation of the present invention is
shown. The electroplating system 40 typically includes a bath
container 44 in which a typically copper anode 46 and a cathode 48
are placed, the cathode 48 being the semiconductor wafer that is to
be electroplated with copper. An adjustable current source 42 is
connected to the anode 46 and to the semiconductor wafer/cathode 48
through suitable wiring 68. The bath container 44 holds an
electroplating bath 50 typically of acid copper sulfate
(CuSO.sub.4) solution, for example, which may include an additive
for filling of submicron features and leveling the surface of the
copper electroplated on the wafer 48, as is known by those skilled
in the art. A pair of bypass filter conduits 54 extends through the
anode 46 and each opens to the upper, oxidizing surface of the
anode 46. A bypass pump/filter 60 located outside the bath
container 44 is connected to the bypass filter conduits 54, and an
electrolyte holding tank 64 is connected to the bypass pump/filter
60 through a tank inlet line 62. A tank outlet line 66 in turn
connects the electrolyte holding tank 64 to the bath container 44.
The electrolyte content of the bath 50 can be increased, as needed,
by adding electrolytes to the electrolyte holding tank 64 and then
circulating the bath 50 through the bypass filter conduits 54, the
bypass pump/filter 60, the tank inlet line 62, the electrolyte
holding tank 64 and back into the bath container 44 through the
tank outlet line 66, respectively.
[0036] In accordance with the process of the present invention, the
electroplating metal bath 50, typically including CuSO.sub.4, is
first prepared in the bath container 44. As shown in FIG. 3, a
leveler chemical 70, preferably alkyl polyamide, alkyl amine, alkyl
amine oxide, thiourea, with molecular weight ranging from
100.about.1,000,000 is poured into the bath 50. In a preferred
embodiment, the leveler chemical 70 is present in the bath 50 in a
concentration of 0.1 ppm to 1000 ppm. This concentration of the
leveler chemical 70 in the electroplating bath 50 facilitates
incorporation of nitrogen into the electroplated metal in a
concentration of from about 0.1 ppm to about 1000 ppm. After the
desired concentration of the leveler chemical 70 is added to the
bath 50, the leveler chemical 70 is circulated from the bath
container 44 through the bypass filter conduits 54 and then through
the bypass pump/filter 60, the tank inlet line 62, the electrolyte
holding tank 64, the tank outlet line 66 and back into the bath
container 44, respectively.
[0037] Referring next to FIGS. 3 and 4, after the leveler chemical
70 is thoroughly mixed in the electroplating bath 50 typically in
the manner heretofore described, the electroplating system 40 is
operated typically in conventional fashion to electroplate the
metal from the metal electrolyte solution in the bath 50, onto the
substrate 48. Accordingly, the current source 42 applies a selected
voltage potential typically at room temperature between the anode
46 and the cathode/wafer 48. This potential creates a electrical
field around the anode 46 and the cathode/wafer 48, which
electrical field affects the distribution of the metal ions in the
bath 50. In a typical copper electroplating application, a voltage
potential of about 2 volts may be applied for about 2 minutes, and
a current of about 4.5 amps flows between the anode 46 and the
cathode/wafer 48. Consequently, the metal is oxidized typically at
the upper oxidizing surface of the anode 46 as electrons from the
metal anode 46 reduce the ionic metal in the electrolyte solution
bath 50 to form a substantially corrosion-resistant electroplated
metal layer 72, as shown in FIG. 4, at the interface between the
cathode/wafer 48 and the electrolyte bath 50. As a result of the
presence of the leveler chemical 70 in the electroplating bath 50,
nitrogen atoms are incorporated into the metal layer 72 typically
at a concentration of from about 0.1 to about 1000 ppm.
Accordingly, upon subsequent processing of the substrate 48, such
as during chemical mechanical polishing, the metal layer 72 resists
corrosion and the accompanying formation of pits therein which
otherwise would adversely affect the yield of devices fabricated on
the substrate 48.
[0038] Referring next to the flow diagram of FIG. 5, typical
process steps for carrying out the present invention are shown. In
process step S1, the metal electrolyte bath is prepared typically
using copper. Other metals which may be used include aluminum,
nickel, chromium, zinc, tin, gold, silver, lead and cadmium. In
process step S2, the leveler chemical is added to the prepared
electrolyte bath. In process step S3, the leveler chemical is
circulated in the electrolyte bath In process step S4, the metal in
the electrolyte bath is electroplated with nitrogen atoms from the
leveler chemical onto the substrate to form the
corrosion-resistant, nitrogen-enriched electroplated metal layer
thereon.
[0039] While the preferred embodiments of the invention have been
described above, it will be recognized and understood that various
modifications can be made in the invention and the appended claims
are intended to cover all such modifications which may fall within
the spirit and scope of the invention.
* * * * *