U.S. patent application number 10/495682 was filed with the patent office on 2005-01-06 for anodes for electroplating operations, and methods of forming materials over semiconductor substrates.
Invention is credited to Dean, Nancy F., Pinter, Michael R., Weiser, Martin W., White, Tamara L.
Application Number | 20050000821 10/495682 |
Document ID | / |
Family ID | 21743016 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050000821 |
Kind Code |
A1 |
White, Tamara L ; et
al. |
January 6, 2005 |
Anodes for electroplating operations, and methods of forming
materials over semiconductor substrates
Abstract
The invention includes anodes for electroplating, baths. The
anodes have a purity of at least 99.9%, and comprise one or more of
silver, gold, nickel, chromium, copper or various solder
compositions. The anodes can, for example, comprise at least
99.995% copper/phosphorus alloy, by weight; or at least 99.995%
nickel and sulfur, by weight. The invention also includes methods
of electroplating, materials over semiconductor substrates.
Inventors: |
White, Tamara L; (Spokane,
WA) ; Dean, Nancy F.; (Liberty Lake, WA) ;
Weiser, Martin W.; (Liberty Lake, WA) ; Pinter,
Michael R.; (Spokane, WA) |
Correspondence
Address: |
Honeywell
PO Box 2245
Morristown
NJ
07962-2245
US
|
Family ID: |
21743016 |
Appl. No.: |
10/495682 |
Filed: |
May 14, 2004 |
PCT Filed: |
November 16, 2001 |
PCT NO: |
PCT/US01/44055 |
Current U.S.
Class: |
205/157 ;
204/292; 257/E21.175; 257/E21.508 |
Current CPC
Class: |
H01L 2224/13099
20130101; H01L 2924/01028 20130101; H01L 2924/10253 20130101; H01L
2924/01022 20130101; H01L 2924/01051 20130101; H01L 2924/01047
20130101; H01L 2924/01078 20130101; H01L 24/05 20130101; H01L
2224/131 20130101; H01L 2924/01033 20130101; H01L 2924/01006
20130101; H01L 2924/01024 20130101; H01L 2924/01016 20130101; H01L
2924/01029 20130101; H01L 2924/01092 20130101; H01L 2924/01015
20130101; H01L 2224/1147 20130101; H01L 2924/014 20130101; C25D
7/123 20130101; H01L 2924/01079 20130101; H01L 24/12 20130101; H01L
21/2885 20130101; H01L 2924/19042 20130101; H01L 2224/11901
20130101; C25D 17/10 20130101; H01L 2924/01014 20130101; H01L
2924/01019 20130101; H01L 2924/01011 20130101; H01L 2924/01082
20130101; H01L 2924/3025 20130101; H01L 2224/0401 20130101; H01L
2924/01013 20130101; H01L 2924/0105 20130101; H01L 2924/10253
20130101; H01L 24/03 20130101; H01L 2924/01027 20130101; H01L
2924/14 20130101; H01L 2924/00 20130101; H01L 2924/014 20130101;
H01L 24/11 20130101; H01L 2924/00014 20130101; H01L 2224/05624
20130101; H01L 2224/131 20130101 |
Class at
Publication: |
205/157 ;
204/292 |
International
Class: |
C25D 007/12 |
Claims
1. An anode for an electroplating bath comprising a total number of
grains therein, and wherein at least 25% of the total number of
grains have a common crystallographic texture as one another, and
wherein the common crystallographic texture is (001).
2. The anode of claim 1 wherein at least 50% of the total number of
grains have the common crystallographic texture as one another.
3. The anode of claim 1 wherein at least 75% of the total number of
grains have the common crystallographic texture as one another.
4. The anode of claim 1 wherein at least 90% of the total number of
grains have the common crystallographic texture as one another.
5. The anode of claim 1 comprising an HCP metal.
6. The anode of claim 1 comprising cobalt.
7. An anode for an electroplating bath comprising an average grain
size of less than 100 micrometers.
8. The anode of claim 7 comprising an average grain size of less
than 50 micrometers.
9. The anode of claim 7 comprising an average grain size of less
than 10 micrometers.
10. The anode of claim 7 comprising an average grain size of less
than 1 micrometer.
11. The anode of claim 7 comprising predominantly one or more of
silver, gold, nickel, cobalt and chromium by weight.
12. An anode for an electroplating bath and having an alpha
particle emission rate of less than 0.1 counts/(cm.sup.2 hr).
13. The anode of claim 12 having an alpha particle emission rate of
less than 0.02 counts/(cm.sup.2 hr).
14. The anode of claim 12 having an alpha particle emission rate of
less than 0.002 counts/(cm.sup.2 hr).
15. The anode of claim 12 comprising less than 3 ppb total of
thorium and uranium.
16. The anode of claim 12 comprising less than 1 ppb total of
thorium and uranium.
17. The anode of claim 12 comprising less than 0.5 ppb total of
thorium and uranium.
18. The anode of claim 12 comprising one or more of bismuth,
silver, tin, lead, copper, nickel, chromium, and cobalt.
19. An anode for an electroplating bath, the anode comprising at
least 99.99% of silver, gold, nickel, chromium or cobalt, by
weight.
20. The anode of claim 19 comprising at least 99.99% silver.
21. The anode of claim 19 comprising at least 99.99% gold.
22. The anode of claim 19 comprising at least 99.99% chromium.
23. The anode of claim 19 comprising at least 99.99% cobalt.
24. The anode of claim 19 comprising at least 99.99% nickel.
25. The anode of claim 19 comprising less than 3 parts per billion
of uranium, and further comprising less than 3 parts per billion of
thorium.
26. The anode of claim 19 comprising an average grain size of less
than 100 micrometers.
27. The anode of claim 19 comprising an average grain size of less
than 50 micrometers.
28. The anode of claim 19 comprising an average grain size of less
than 10 micrometers.
29. The anode of claim 19 comprising an average grain size of less
than 1 micrometer.
30. The anode of claim 19 comprising at least 99.995% nickel, by
weight.
31. The anode of claim 30 comprising an average grain size of less
than 100 micrometers.
32. The anode of claim 30 comprising an average grain size of less
than 50 micrometers.
33. The anode of claim 30 comprising an average grain size of less
than 10 micrometers.
34. The anode of claim 30 comprising an average grain size of less
than 1 micrometer.
35. The anode of claim 30 comprising at least 99.9995% nickel.
36. An anode for an electroplating bath comprising at least 99.999%
copper, by weight.
37. The anode of claim 36 comprising at least 99.9995% copper.
38. The anode of claim 36 comprising an average grain size of less
than 100 micrometers.
39. The anode of claim 36 comprising an average grain size of less
than 50 micrometers.
40. The anode of claim 36 comprising an average grain size of less
than 10 micrometers.
41. The anode of claim 36 comprising an average grain size of less
than 1 micrometer.
42. The anode of claim 36 comprising less than 3 parts per billion
of uranium, and further comprising less than 3 parts per billion of
thorium.
43. An anode comprising at least 99.995%, by weight,
copper/phosphorous alloy, and comprising an average grain size of
less than 100 micrometers.
44. The anode of claim 43 wherein the phosphorus concentration is
from about 200 ppm to about 1000 ppm, by weight.
45. The anode of claim 43 comprising an average grain size of less
than 50 micrometers.
46. The anode of claim 43 comprising an average grain size of less
than 10 micrometers.
47. The anode of claim 43 comprising an average grain size of less
than 1 micrometer.
48. An anode for an electroplating bath comprising at least 99.995%
nickel and sulfur, by weight.
49. The anode of claim 48 comprising from about 0.01% sulfur to
about 5% sulfur, by weight.
50. The anode of claim 48 comprising an average grain size of less
than 100 micrometers.
51. The anode of claim 48 comprising an average grain size of less
than 50 micrometers.
52. The anode of claim 48 comprising an average grain size of less
than 10 micrometers.
53. The anode of claim 48 comprising an average grain size of less
than 1 micrometer.
54. An anode for an electroplating bath comprising a solder
composition having a purity of at least 99.999%, by weight; said
solder composition comprising one or more elements selected from
the group consisting of tin, antimony, lead, silver, copper and
bismuth.
55. The anode of claim 54 comprising an average grain size of less
than 30 micrometers.
56. The anode of claim 54 comprising an average grain size of less
than 10 micrometers.
57. The anode of claim 54 comprising an average grain size of less
than 5 micrometers.
58. The anode of claim 54 comprising an average grain size of less
than 1 micrometer.
59. The anode of claim 54 comprising at least 99.9995% solder.
60. The anode of claim 54 comprising less than 3 parts per billion
of uranium, and further comprising less than 3 parts per billion of
thorium.
61. The anode of claim 54 comprising at least 99.999% tin.
62. The anode of claim 54 wherein the solder composition comprises
tin and antimony.
63. The anode of claim 54 wherein the solder composition comprises
tin and lead.
64. The anode of claim 54 wherein the solder composition comprises
tin and silver.
65. The anode of claim 54 wherein the solder composition comprises
tin, silver and copper.
66. The anode of claim 54 wherein the solder composition comprises
silver and bismuth.
67. The anode of claim 54 wherein the solder composition comprises
tin and copper.
68. A method of forming materials over a semiconductor substrate,
comprising: providing a semiconductor substrate having a wiring
layer thereon; electrolytically depositing at least one of silver
and nickel over the wiring layer; any silver being deposited from
an anode that is at least 99.995% pure in silver; and any nickel
being deposited from an anode that is either at least 99.995% pure
in nickel, or at least 99.995% pure in nickel and sulfur, with the
sulfur being present to a concentration of from about 0.01% to
about 5%, by weight; and forming a solder over the at least one of
silver and nickel.
69. The method of claim 68 wherein the wiring layer comprises
copper, and is formed by electrolytic deposition utilizing an anode
that is either at least 99.999% copper, by weight, or at least
99.995% copper/phosphorous alloy, with the phosphorus concentration
being from about 200 ppm to about 1000 ppm, by weight.
70. The method of claim 68 wherein the solder is formed by
electrolytic deposition utilizing an anode that comprises a solder
composition having a purity of at least 99.999%, by weight; said
solder composition comprising one or more elements selected from
the group consisting of tin, antimony, lead, silver, copper and
bismuth.
71. The method of claim 68 wherein the electrolytic deposition
forms nickel over the wiring layer; the electrolytic deposition
occurs in a bath, and the bath is initially charged with metallic
materials that are either at least 99.995% pure in nickel, or at
least 99.995% pure in nickel and sulfur, with the sulfur being
present to a concentration of from about 0.01% to about 5%, by
weight.
72. The method of claim 68 wherein the electrolytic deposition
forms silver over the wiring layer; the electrolytic deposition
occurs in a bath, and the bath is initially charged with
particulates that are at least 99.995% pure in silver.
Description
TECHNICAL FIELD
[0001] The invention pertains to methodology for electroplating
materials over semiconductor substrates. In particular aspects, the
invention pertains to anodes for utilization in electroplating
operations. In other aspects, the invention pertains to metals
having a purity of at least 99.995%, and suitable for utilization
in charging the electrolyte of an electrolytic bath.
BACKGROUND OF THE INVENTION
[0002] Electroplating methods are utilized for numerous
applications in which it is desired to form a metal-containing
layer over a substrate. An exemplary prior art electroplating
apparatus 10 is described with reference to FIG. 1. Apparatus 10
comprise a vessel 12 which retains a liquid 14 (specifically, an
electrolyte solution) therein. Vessel 12 can comprise any suitable
material, including, for example, a metal having a non-corrosive
liner (not shown) extending along an interior surface of the vessel
to protect the metal from reacting with liquid 14. Alternatively,
vessel 12 can comprise a plastic or a glass. In some applications,
vessel 12 will be configured to enable temperature control of the
liquid 14 so that liquid 14 can be maintained at a desired
operating temperature during an electroplating process.
[0003] An anode 16 and a substrate 18 are provided within vessel
12. Anode 16 comprises a metal which is ultimately to be plated
along a conductive surface of substrate 18. In the shown
application, substrate 18 has a conductive surface 20. A power
source 22 is provided in electrical connection with anode 16 and
substrate 18, and generates a voltage differential between the
anode and the substrate. The voltage differential causes conductive
material to migrate from anode 16, through electrolytic solution
14, and to conductive surface 20. The conductive material forms a
layer 24 of plated conductive material across the surface 20 of
substrate 18.
[0004] The transfer of conductive material from anode 16 to
substrate 18 is actually a series of mass transfer events.
Specifically, conductive material is transferred from anode 16 into
electrolyte 14 in a first mass transfer, and subsequently passes
from electrolyte 14 to substrate 18 in a second mass transfer. If a
starting concentration of the conductive material of anode 16
within electrolyte 14 is low, a significant amount of material from
anode 16 can be transferred into electrolyte 14 to establish an
equilibrium between electrolyte 14 and anode 16 prior to effective
transfer of the anode material to substrate 18. Such can
effectively cause waste of a significant portion of anode 16, in
that such portion is utilized to establish an equilibrium rather
than being passed to substrate 18. A method of avoiding such waste
is to pre-charge electrolyte 14 with conductive material of the
type that will be transferred from anode 16. The pre-charging
causes electrolyte 14 to start with a concentration of the
conductive material that is close to the equilibrium concentration
that will be established during an electroplating operation. The
precharging can occur by providing particulates of the conductive
material of anode 16 within a suitable solvent (such as, for
example, an appropriate acid) to dissolve the particulates and form
a solution comprising the conductive material of anode 16. The
solution can subsequently be added to liquid 14 to form the
pre-charged electrolyte 14.
[0005] Electrolyte 14 can comprise any suitable conductive
solution. In particular applications, substrate 18 will comprise a
semiconductive wafer, such as, for example, a monocrystalline
silicon wafer. In such applications, it can be desired to avoid
utilization of sodium or potassium in electrolyte 14, as such can
influence a conductivity of the semiconductive material. In such
applications, suitable salts for inclusion in electrolyte 14 are,
for example, copper sulfate for copper baths, nickel sulfamate for
nickel baths and fluoroborate for lead/tin baths.
[0006] Another aspect of the prior art pertains to semiconductor
processing applications. A fragment of a semiconductor wafer
construction 50 is described with reference to FIG. 2. Construction
50 comprises a semiconductor substrate 52. To aid in interpretation
of the claims that follow, the terms "semiconductive substrate" and
"semiconductor substrate" are defined to mean any construction
comprising semiconductive material, including, but not limited to,
bulk semiconductive materials such as a semiconductive wafer
(either alone or in assemblies comprising other materials thereon),
and semiconductive material layers (either alone or in assemblies
comprising other materials). The term "substrate" refers to any
supporting structure, including, but not limited to, the
semiconductive substrates described above.
[0007] Substrate 52 can comprise, for example, a monocrystalline
silicon wafer having various insulative and conductive materials
formed thereover. Additionally, substrate 52 can comprise numerous
circuit components (not shown), which are together incorporated
into an integrated circuit.
[0008] A conductive material 54 is formed over substrate 52, and
can constitute a wiring layer in electrical connection with
circuitry (not shown) associated with substrate 52. Conductive
material 54 can comprise, for example, aluminum and/or copper.
[0009] An insulative material 56 is formed over conductive material
54. Insulative material 56 is patterned to have an opening 58
extending therethrough. Conductive materials 60 and 62 are formed
within the opening. Conductive material 60 can comprise, for
example, one or more of chromium, cobalt, nickel, copper, silver
and gold; and layer 62 can also comprise, for example, one or more
of chromium, nickel, copper, silver and gold. In particular
applications, layer 60 will comprise nickel and layer 62 will
comprise gold.
[0010] A solder bump 64 is formed over layer 62. Solder bump 64 can
comprise, for example, a tin-based solder or a lead-based solder,
with the term "based" being understood to denote a majority element
of solder. Solder bump 64 can ultimately be utilized for forming an
electrical connection to circuitry external of substrate 52, and
accordingly can be utilized together with layers 54, 60 and 62 to
form an interconnect between circuitry (not shown) associated with
substrate 52 and other circuitry (not shown) external of substrate
52.
[0011] Materials 54, 60, 62 and 64 can be formed by numerous
methods, including, for example, electroplating. Difficulties
occur, however, in forming materials 54, 60, 62 and 64 to have
desired purity and physical characteristics when utilizing
electroplating methods. It would therefore be desirable to develop
new methods for electroplating materials over semiconductor
substrates.
SUMMARY OF THE INVENTION
[0012] The invention includes anodes for electroplating baths. In
particular aspects, the anodes have a purity of at least 99.99%,
and comprise one or more of silver, gold, nickel, chromium, cobalt,
copper or various solder compositions. The anodes can, for example,
comprise at least 99.995% copper/phosphorus alloy, by weight; or at
least 99.995% nickel and sulfur, by weight. As another example, the
anodes can comprise at least 99.9995% copper, by weight; or at
least 99.999% of a solder composition, by weight.
[0013] The invention also encompasses methods of electroplating
materials over semiconductor substrates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Preferred embodiments of the invention are described below
with reference to the following accompanying drawings.
[0015] FIG. 1 is a diagrammatic, cross-sectional view of a prior
art electroplating apparatus.
[0016] FIG. 2 is a diagrammatic, cross-sectional, fragmentary view
of a prior art semiconductor wafer fragment.
[0017] FIG. 3 is a diagrammatic, isometric view of a billet at a
preliminary processing step of a method of the present invention
for forming an anode.
[0018] FIG. 4 is a view of a blank formed from the FIG. 3
billet.
[0019] FIG. 5 is an isometric view of another blank which can be
utilized in accordance with methodology of the present invention
for forming an anode.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Among the problems with prior art anodes (such as the anode
16 described with reference to FIG. 1) are that compositional and
physical properties of the anode materials are not tightly
controlled during formation of the anodes. The present invention
encompasses anode materials having improved compositional and
physical properties relative to prior art anode materials.
[0021] Among the compositional parameters that can be controlled by
methodology of the present invention are purity and homogeneity.
Specifically, methodology of the present invention can enable an
anode to be formed from one or more of silver, gold, nickel,
chromium, cobalt and copper to a purity of at least 99.99% by
weight (i.e., 4N purity, with the term "4N" understood to mean four
nines), and in particular aspects to a purity of at least 99.995%
(4N5), 99.999% (5N), 99.9999% (6N), or at least 99.99999% (7N).
[0022] Preferably, the anodes will comprise little to no
alpha-particle emitting materials, since alpha particles can be
severely detrimental to semiconductor constructions. Accordingly, a
preferred composition will have less than 3 ppb of uranium and less
than 3 ppb of thorium; and preferably will have less than 3 ppb
total of uranium and thorium; more preferably less than 1 ppb total
of uranium and thorium, and yet more preferably less than 0.5 ppb
total of uranium and thorium.
[0023] In further aspects, an anode material of the present
invention can comprise at least 99.995%, by weight, (4N5) of
copper/phosphorus alloy, with the phosphorus concentration
preferably being from about 200 ppm to about 1000 ppm, by weight;
such as, for example, from about 200 ppm to about 600 ppm, by
weight. The copper/phosphorus alloy can have a purity of 5N, 6N,
and even at least 7N. The copper/phosphorus alloy can alternatively
be referred to as phosphorus-doped copper. The incorporation of
phosphorus can aid in the development of a black oxide film on the
anode surface. This film can serve two important functions. First,
it can act as a filter by entrapping impurities in the film.
Second, the film can regulate the copper dissolution rate, and thus
maintain the copper in solution at a consistent and desired level.
Also, addition of phosphorus, and/or other alloy elements, can
promote grain refinement.
[0024] In another aspect, the anode can comprise at least 99.995%
(4N5) nickel and sulfur, by weight; and in particular aspects can
comprise 5N, 6N, or at least 7N purity of the nickel/sulfur
combination. The sulfur can be present to a concentration of from
about 0.01% to about 5%, by weight; and it can be preferred that
the sulfur is present to a concentration of from about 0.01% to
about 0.04%, by weight. The inclusion of sulfur can be advantageous
in that the sulfur can promote grain refinement. Additionally, the
sulfur can promote more uniform dissolution of the anode than would
occur in the absence of the sulfur. Additionally, addition of
sulfur can lower electrical resistance, which can enable lower
power consumption during a plating operation. Also, if layer 54 of
the FIG. 2 construction 50 comprises copper and layer 60 comprises
nickel, it can be advantageous to have sulfur incorporated within
material 60 during electrolytic deposition of the material 60 to
improve adhesion of nickel-containing material 60 to
copper-containing layer 54.
[0025] In other aspects of the invention, a composition of an anode
can correspond to a high-purity solder composition, such as, for
example, a solder composition having a purity of at least 99.99% by
weight (4N), with such composition including one or more elements
selected from the group consisting of tin, antimony, lead, silver,
copper and bismuth. In further aspects, the solder composition can
have a purity of at least 5N, 5N5, 6N, 6N5 or 7N. Exemplary solder
compositions comprise at least 5N purity of tin; tin/antimony;
tin/lead; tin/silver; tin/silver/copper; silver/bismuth; and
tin/copper.
[0026] Phosphorus can be included in solder alloys. If phosphorus
is included, it will preferably be provided to a concentration of
less than 1,000 ppm, such as, for example, a concentration of from
greater than 0 ppm to 500 ppm.
[0027] It can be preferred that the solder be lead-free in order to
reduce the amount of alpha-particle emitting materials in the
composition. Specifically, there are naturally occurring isotopes
of lead whose decay chain results in the emission of an alpha
particle. Furthermore, these lead isotopes cannot be removed from
the lead using conventional refining means. Suitable lead-free
compositions are tin/silver, tin/bismuth, tin/silver/copper,
bismuth/silver and tin/copper. The concentration of uranium in such
compositions is preferably less than 3 ppb, and the composition of
thorium is preferably also less than 3 ppb. In particular aspects,
a combined total of uranium and thorium is less than 3 ppb in a
solder-composition anode of the present invention. Further, a
preferred anode comprising a solder composition of the present
invention will preferably have an alpha count of less than or equal
to 0.001 counts/(cm.sup.2.hr), more preferably less than 0.02
counts/(cm.sup.2.hr), and even more preferably less than 0.002
counts/(cm.sup.2.hr). An advantage of eliminating alpha-particle
emitters from solder is that alpha particles can adversely impact
performance, primarily in the area known as soft errors. As line
widths decrease, it is possible for alpha particles to permanently
damage circuitry. Another advantage is that the elimination or
reduction of lead can lead to a cleaner waste stream from an
electrolytic deposition process.
[0028] An exemplary method of forming an anode composition
comprising at least 5N pure copper, silver and gold is vacuum
casting.
[0029] Exemplary methods of forming an anode composition comprising
at least 4N purity of one or more of nickel and chromium include
hot pressing and vacuum casting.
[0030] An exemplary method of forming a composition comprising
copper/phosphorus, having a purity of at least 5N, and a phosphorus
concentration of about 200 ppm to about 1000 ppm utilizes vacuum
casting and a master alloy. The purification of copper can be
accomplished by electrorefining.
[0031] An exemplary method of forming a nickel composition
comprising at least 4N5 purity of nickel and sulfur, with a sulfur
concentration of about 0.01% to about 5%, by weight, utilizes
vacuum casting and a master alloy. Another exemplary method is to
combine nickel and sulfur powders, and to then hot press the
combination to a near net shape corresponding approximately to a
desired final shape.
[0032] An exemplary method of forming an anode composition
comprising at least 5N purity of one or more of tin, antimony,
lead, silver, copper and bismuth; and suitable for electrolytic
deposition of a solder bump, comprises casting an alloy of the
desired materials.
[0033] Another compositional aspect of the various anode materials
of the present invention is the homogeneity of such materials. The
term "homogeneity" is utilized in reference to the materials to
indicate that the anode materials preferably have a uniform
composition throughout an entirety of an anode, and that inclusions
and precipitates are finely dispersed. Preferably, inclusions and
precipitates will be no more than 10 micrometers in average size.
In particular applications, an average length of all inclusions and
precipitates along a maximum dimension of the individual inclusions
and precipitates will be less than or equal to 10 micrometers, more
preferably less than 1 micrometer, and; yet more preferably an
average length of all inclusions and precipitates will be less than
or equal to one-tenth micrometer.
[0034] Among the physical characteristics that can be controlled
within an anode composition utilizing methodology of the present
invention are texture and grain size. Specifically, an average
grain size throughout an anode of the present invention will
preferably be less than 100 micrometers, more preferably less than
50 micrometers, even more preferably less than 10 micrometers, and
in particular embodiments less than 1 micrometer. The average grain
size can be determined by standard methods of the art. In
particular aspects of the invention, an average of the maximum
dimensions of the grains of an anode will be less than 100
micrometers, more preferably less than 50 micrometers, even more
preferably less than 10 micrometers, and in particular embodiments
less than 1 micrometer. For purposes of the interpreting this
disclosure and the claims that follow, an anode referred to as
having a stated average grain size is to be understood as having
such average grain throughout all of the grains of the anode unless
it is specifically stated that only a portion of the anode has the
stated average grain size.
[0035] The above-described preferred grain sizes can be relevant to
any of the anode compositions encompassed by the present invention,
including, for example, the compositions consisting essentially of,
or consisting of, one or more of copper, nickel, silver, gold,
chromium, cobalt, tin, antimony, lead and bismuth.
[0036] The term "texture" refers to the distribution of
crystallographic orientations, with a material having a relatively
random distribution of orientations being referred to as having a
weak texture, and a material having a relatively non-random
distribution being referred to as having a strong texture. Anodes
of the present invention can be microstructurally textured so that
the different grains of metal erode at the same rate. It is well
known that different crystallographic planes will erode at
different rates in most electrolytic cells, and advantage is taken
of this fact to etch metallographic samples so that the different
grains are visible during visual microscopic examination. In
embodiments in which the anode microstructure is textured so that
the grains all expose the same crystallographic face (or faces that
are very close to being the same), differential erosion of the
anode can be reduced, minimized, or even eliminated. Such can lead
to relatively uniform erosion of an anode. The uniform erosion can
lead to a more uniform plated film than would otherwise occur, as
well as a longer anode lifetime, and less particulate in the
plating bath. Accordingly, utilization of an appropriate texture in
anodes of the present invention can improve the uniformity of
dissolution of the anodes into a plating bath, which can ultimately
both extend the life of the anode and improve a uniformity of an
electroplated film formed from the anode. A uniform, and
substantially random texture can be desired for various anodes,
including an anode consisting essentially of copper,
copper/phosphorus, nickel, nickel alloy or nickel/sulfur;
consisting essentially of chromium or chromium alloy; consisting
essentially of silver or silver alloy; or consisting essentially of
a solder composition comprising one or more elements selected from
the group consisting of tin, antimony, lead, silver, copper and
bismuth.
[0037] In one aspect, an advantage of texture control in an anode
can be described by considering each grain within a metal object as
a crystal with its crystal lattice oriented in some particular way
relative to a reference plane. The reference plane can be, for
example, the erosion surface of the anode. Since each grain is
independent of the others, each grain lattice has its own
orientation relative to this plane. When grain orientation is not
random, but crystal planes tend to be aligned in some way relative
to a reference plane, the material is said to have a non-random
"texture". These textures are denoted using standard indices, which
define directions relative to crystallographic planes. For
instance, an anode made from a metal with cubic crystal structure,
such as copper, may have a <100>, a <110> or other
textures. Similarly, an anode made from a metal with hexagonal
crystal structure, such as cobalt, may have a <0002> texture.
The exact texture developed will depend on the metal type and the
work and heat treatment history of the anode. Miller indices,
denoted by the numeric indices enclosed in "( )", are also used to
describe families of planes or orientations in symmetric crystal
structures. Different textures can be produced in most metals by
altering their thermomechanical processing.
[0038] The effect of crystallographic orientation of a sputtering
target on sputtering deposition rate and film uniformity has been
described in an article by C. E. Wickersham, Jr., entitled
Crystallographic Target Effects in Magnetron Sputtering in the
J.Vac. Sci.Technol. A5(4), July/August 1987 publication of the
American Vacuum Society. In this article, the author indicates that
improvements in film uniformity may be achieved on a silicon wafer
by controlling the working process for making a target. Several
U.S. patents have issued which teach how to control the texture of
a sputtering target for optimal performance in many applications
(see, for example, U.S. Pat. Nos. 6,302,977, 6,238,494, 5,993,621,
5,809,393, 5,780,755, 5,087,297). The patents do not, however,
indicate that the control of texture would have any application
relative to the formation of anodes for use in electroplating
baths.
[0039] Crystallographic structure can influence the corrosion or
dissolution behavior of a material, as demonstrated by etching a
material for metallographic evaluation. Differently oriented grains
will "etch" or be eroded to different degrees. Therefore,
controlling the texture or uniformity of grain orientation of an
anode can be advantageous to uniform dissolution and hence uniform
film deposition. Control of the texture can be done in two
exemplary forms--control of dominant texture orientation, and
control of texture intensity.
[0040] The intensity of the texture, or relative fraction of grains
that share a common orientation, can be important for uniform
dissolution. If a random texture (low intensity for any specific
texture and a random orientation of grains) is present, then those
grains that are oriented favorably will erode faster, creating a
non-uniform surface. There can be a weak texture present, where one
orientation is preferred or more common than others, but a
significant fraction of the grains exhibit an orientation different
from this. Very strong textures, in which a high percentage of
grains have the same orientation, can therefore result in more
uniform erosion.
[0041] Specific desired textures for particular anodes can depend
upon the material and geometric features of the anode. For example,
for a flat surface, a texture which aligns the close packed planes
with the anode surface, may be advantageous. For cobalt, an HCP
metal, this would be the (001) planes, or a (001) texture. For FCC
metals such as copper, this would be a (111) texture, while for BCC
metals such as chromium, this would be a (110) texture. In
particular aspects, the invention includes anodes having at least
25% of the grains, at least 50% of the grains, at least 75% of the
grains, or at least 90% of the total number of grains with a
specific desired crystallographic texture. For HCP metals the
specific desired texture will typically be (001), for FCC metals
the specific desired texture will typically be (111), and for BCC
metals the specific desired texture will typically be (110).
[0042] Exemplary methods for forming desired grain sizes and
textures within anode compositions of the present invention are
described with reference to FIGS. 3-5.
[0043] Referring to FIG. 3, a billet 100 of an anode composition is
illustrated. Billet 100 can be formed by melting one of the
above-described anode compositions, pouring the composition into a
mold, and cooling the composition into a cylindrical shape. In
other words, the anode material can be cast into a cylindrical
shape. The cylindrical shape can be used directly as billet 100.
Alternatively, one or both of the ends of the cast cylindrical
shape can be cut to remove cavities or other defects that may be
associated with the ends prior to utilization of the cast material
as billet 100. Billet 100 has a width 105 and a length 110.
[0044] The material of the billet may be utilized in the as-cast
form. Alternatively, the material of billet 100 can be can be
thermomechanically processed into the desired shape of the billet
while imparting a desired grain size and texture to the material.
Also, a gradient freeze can be utilized during a casting process.
The gradient freeze can form a columnar microstructure within the
material of billet 100. Yet another method of forming billet 100 is
to subject the material of billet 100 to a long term thermal
treatment (such as a long term heating treatment) to form billet
100 as a single crystal.
[0045] Referring to FIG. 4, a blank 101 is illustrated. Blank 101
can be formed by subjecting billet 100 (FIG. 3) to various
thermomechanical processes, such as, for example, hot-forging,
rolling and/or cross-rolling. The thermomechanical processing has
increased the width of the billet to a new width 115, and decreased
the length to a new length 120. A ratio of change in length 120 to
length 110, divided by length 110, corresponds to a reduction ratio
of blank 101 relative to billet 100. Preferably such reduction
ratio will be from about 50% up to 90%. The thermomechanical
processing can reduce an average grain size of the anode material,
reduce particulate sizes, reduce inclusion sizes, and disperse
inclusions throughout the anode material. Additionally, the
thermomechanical processing can induce a desired texture. The
texture, grain size, particulate size and inclusion size can be
further influenced by subjecting the blank of FIG. 4 to thermal
processing, in addition to the mechanical processing techniques of
forging, rolling and cross-rolling.
[0046] If blank 101 is subjected to sufficient thermomechanical
processing, an average grain size within the blank can be reduced
to less than 100 microns. Additionally, a texture within the blank
can be transformed into a random texture; or in particular
applications to a strong texture oriented in a desired direction.
Suitable thermomechanical processes are described in U.S. Pat. Nos.
6,238,494; 6,113,761; 5,993,621; and 5,780,755, which are
incorporated herein by reference.
[0047] FIG. 5 illustrates another blank which can be utilized in
methodology of the present invention. Specifically, FIG. 5
illustrates a blank 150 having a substantially square shape. Blank
150 can be cut from the blank of FIG. 4, for example. Blank 150 can
be subjected to equal channel angular extrusion (ECAE) to randomize
the texture within the blank, and to reduce average grain size to
less than 100 microns, less than 50 microns, less than 10 microns,
and in particular applications to less than 1 micron. ECAE
methodology is described in, for example, U.S. Pat. Nos. 5,600,989
and 5,780,755, which are hereby incorporated by reference. Grain
size reduction and texture randomization can be accomplished by
utilizing a sufficient number of passes (preferably at least four,
and frequently at least six) through an ECAE apparatus, while
rotating the blank 150 between passes so that the blank has
different orientations from one pass to another.
[0048] The materials produced by the processing described with
reference to FIGS. 3-5 can be utilized as anodes in electrolytic
apparatusses, such as, for example, the prior art apparatus
described with reference to FIG. 1. Further, such materials can be
cut, pressed or rolled to produce powders, pellets, rolled strips
or other forms that can be readily dissolved in a suitable acid to
form a pre-charged electrolyte. The, pellets and powders can be
referred to as particulate forms of the material. The powder,
pellets or rolled strips can be referred to as metallic materials.
Any suitable acid can be utilized for dissolving the particulates
and/or metallic materials. An exemplary acid for dissolving the
metallic materials corresponding to solder-composition-containing
anodes is methyl-sulfonic acid, and an exemplary acid for
dissolving copper-composition-containing anodes is sulfuric
acid.
[0049] An anode material of the present invention can be
incorporated into an electrolytic deposition process for forming
one or more of the conductive layers shown in the semiconductor
construction 50 of FIG. 2. Specifically, the invention encompasses
a process wherein a semiconductor substrate is provided and a
wiring layer (such as the wiring layer 54 of FIG. 2) is formed over
the substrate. Such wiring layer can be formed by
sputter-deposition of a copper-seed layer, and subsequent
electrolytic deposition of copper over the seed layer. The copper
can be deposited from an anode formed in accordance with the
present invention, and accordingly having a purity of at least 4N5,
and a reduced number of inclusions and particulates. It can be
desired to avoid having inclusions and particulates in an anode, as
the inclusions and particulates can behave differently than
surrounding anode material during electrolytic deposition, and can
thus cause inhomogeneities in electrochemically deposited
materials. In particular embodiments, at least some of wiring layer
54 is electrolytically deposited from an anode consisting
essentially of copper; or copper and phosphorus.
[0050] After formation of wiring layer 54, the mask 56 is formed,
and subsequently under-bump material 60 is electrochemically
deposited on wiring layer 54. Material 60 can comprise at least one
of silver, nickel, chromium, cobalt and copper; and can be
electrochemically deposited from an anode that is at least 99.995%
pure in silver, from an anode that is at least 99.995% pure in
nickel, or from an anode that is at least 99.995% pure in one or
more of nickel, chromium, cobalt, copper and silver.
[0051] Numerous metals can be incorporated into under-bump
metallurgy utilizing methodology of the present invention. For
instance, chromium is often used as part of the under-bump
metallurgy between the circuit pad on the silicon die and the
solder that compromises the flip chip bumps. The chromium adheres
strongly to the circuit pad metal (often Al) and forms a diffusion
barrier between the remainder of the under-bump metallurgy and the
circuitry. The chromium utilized is typically a series of Cr/Cu
layers, and such are generally created by evaporation in prior art
methods. However, Cr and Cu can be plated in accordance with
methodology of the present invention to create the Cr/Cu
layers.
[0052] After formation of under-bump layer 60, the second
under-bump layer 62 can be formed on layer 60. In particular
embodiments, layer 60 will consist essentially of nickel, or
consist essentially of nickel and sulfur; and layer 62 will consist
essentially of silver. Layer 62 can accordingly be deposited from
an anode that is at least 4N5 pure in silver. Alternatively, layer
62 can comprise, consist essentially, of or consist of other metals
in addition to, or alternatively to, silver. For instance, layer 62
can be deposited from an anode that is at least 4N5 pure in one or
more of silver, chromium and copper.
[0053] Solder layer 64 is subsequently formed over layer 62. Layer
64 can be formed from an anode that is at least 4N pure in one or
more elements selected from the group consisting of tin, antimony,
lead, silver, copper and bismuth.
[0054] The construction 50 formed in accordance with methodology of
the present invention can be utilized in, for example, flip-chip
technologies or wafer scale packaging.
[0055] The processes described above are exemplary processes, and
it is to be understood that the invention encompasses other
embodiments in addition to those specifically described. For
instance, the invention encompasses an embodiment in which an anode
material is utilized for electrolytic deposition of a main
interconnect circuit. Specifically, the invention encompasses a
process wherein a semiconductor substrate is provided with trenches
and or vias etched therein. A continuous barrier layer is then
deposited by a PVD or CVD process. A conductive metal seed layer,
preferably Cu or Cu alloy, is then deposited by PVD, CVD, or
electroless deposition. The bulk of a semiconductor feature is then
formed via electrochemical deposition of copper. The copper can be
deposited from an anode formed in accordance with the present
invention, and accordingly have a purity of at least 4N5, and
having a reduced number inclusions and particulates.
[0056] Among the advantages of utilizing highly pure anode and
pre-charge materials of the present invention relative to prior art
materials, is that the materials of the present invention can
improve bath time life of an electrolytic bath; can improve anode
life; can improve deposited film composition, quality and
uniformity;; and can thus reduce costs associated with electrolytic
deposition methodologies.
[0057] The invention has been described with reference to several
exemplary processes. It is to be understood, however, that the
invention encompasses embodiments having numerous modifications and
variations relative to the above-described exemplary processes.
Several exemplary modifications and variations are described
next.
[0058] In one variation, a surface coating can be applied to
portions of the anode so that these portions are not eroded by the
electrolyte during plating. One method of applying such coating is
to flame spray the coating on a portion of the anode that is to be
protected. Flame spraying can enable a material which is brittle
and/or which has a much higher melting point than the anode
composition to be applied to an anode. The applied material can
then serve as a protective barrier. For example, a relatively inert
metal (such as, for example, Ti) or a ceramic (such as, for
example, alumina) could be flame sprayed on a Cu-comprising anode.
In other exemplary applications, other materials can be flame
sprayed on a wide range of anodes to produce a non-erodible surface
layer. Alternatively, another method of applying a protective
coating is to powder coat with a polyethylene coating.
[0059] In another variation, a compensation can be patterned into
an anode to compensate for an erosion profile. As anode dissolution
progresses over the useful lifetime of the anode, the surface of
the anode develops an erosion profile. The erosion profile is based
on a number of characteristics specific to anode, and to the set-up
and operation of the plating equipment. These include, but are not
limited to, the anode material, cell geometry, anode to cathode
ratio, plating chemistry, current density, shielding, and fluid
dynamics within the cell. Two factors will determine the useful
lifetime of an anode. As the erosion profile becomes more
pronounced, it will affect the uniformity of the thin film being
deposited across the wafer surface. The amount of non-uniformity
that a specific user can tolerate will limit anode life. The second
factor is burn-through of a the anode, in which the erosion
actually perforates the bottom side of the anode. An absence of
material in the surface of the anode can drastically impact thin
film uniformity. Once the erosion profile has been identified for a
specific process, a compensatory design can be developed which will
add material to the anode surface in direct relationship to the
rate in which those areas erode. This can have the beneficial
effect of extending anode life with acceptable deposition
characteristics versus just adding overall thickness, which would
only amplify the erosion profile at the end of the life cycle.
[0060] In another variation, "special" packaging of an anode can be
designed for shipping and handling of anodes. The special packaging
can reduce or eliminate the handling of the anodes during
installation of the anode into a plating reactor, which can reduce
introduction of impurities into a plating bath. The special
packaging can also reduce exposure of anodes to oxygen during
shipping to eliminate or reduce oxidation of high purity anode
materials during the shipping. For example, vacuum packaging of
anodes may be useful to reduce the amount of oxygen that a high
purity anode is exposed to during shipment, which can reduce
oxidation of the anode.
[0061] In another variation, a roughened texture can be imparted to
one or more surfaces of an anode. Doing so can increase the surface
area of a given part, which can improve the dissolution rate of
material from the anode. This may be particularly advantageous
during the initial or burn-in period of an anode, where it is
desired to quickly come to equilibrium in the bath. There are many
methods for imparting a roughened surface to an object. Some
textures, such as knurling, may be produced by machining the
object. Other rough surfaces may be produced by bead blasting a
surface, or impinging a surface with an abrasive media. Chemical
etching is another way of roughening a surface.
[0062] Bead blasting is generally very economical, but can have a
disadvantage of embedding pieces of the bead media into an anode
surface. This can be particularly problematic for soft materials,
such as solder anodes. One improved method of bead blasting is to
use dry ice as the blast media. The dry ice will sublime and hence
leave no residue on the anode. The anode will generally be suitable
for use after bead blasting with dry ice, and a cleaning associated
with utilization of either bead-blasting with conventional bead
media, or machining (in which case oils are typically required to
be cleaned from a surface of the machined part), can be
avoided.
[0063] In another variation, anodes can be cast so that they are
composed of one or a small number of grains that have a preferred
crystallographic texture. Such casting can eliminate high energy
grain boundaries which preferentially erode in an electrolyte
solution. The anode can be cast by pouring the metal of the anode
composition into a mold that has been heated to a temperature above
the melting point of the metal, and then cooling the metal slowly
from one side or end of the mold. Slow cooling can lead to
nucleation of a small number of grains, which then grow. The
cooling is normally done from the bottom side of the mold, which
results in a microstructure composed a small number of grains that
have approximately parallel sides (such grain microstructure is
often referred to as a columnar microstructure). The columnar
microstructure can virtually eliminate a cause of particulate
formation. Specifically, the columnar microstructure can virtually
eliminate a problem in which particulate formation occurs through
erosion of the grain boundaries around a small grain, followed by
the small grain breaking off and forming a particulate in an
electrolyte solution.
[0064] In another variation, anodes can be manufactured utilizing
different methods of manufacturing than casting and
thermomechanically processing. An exemplary method is to extrude
the shape of an anode material to a near net shape of a desired
anode, and to then cut the material to a desired thickness. This
process can be used for tubular parts, as well as solid parts.
[0065] In another variation, a protective coating can be applied
over a portion of the anode is to protect the entry point of the
electrode into the anode. This coating can be used to prevent
erosion of the anode were the anode and electrode connect. Such
corrosion can be particularly problematic as the electrolytic bath
is consuming the anode. If no protective coating were applied,
electrical contact could degrade as the anode erodes.
* * * * *