U.S. patent application number 10/778647 was filed with the patent office on 2004-12-23 for apparatus and method for highly controlled electrodeposition.
This patent application is currently assigned to Surfect Technologies, Inc.. Invention is credited to Griego, Thomas P., Sanchez, Fernando M..
Application Number | 20040256222 10/778647 |
Document ID | / |
Family ID | 32872767 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040256222 |
Kind Code |
A1 |
Griego, Thomas P. ; et
al. |
December 23, 2004 |
Apparatus and method for highly controlled electrodeposition
Abstract
An apparatus and method for highly controlled electrodeposition,
particularly useful for electroplating submicron structures.
Enhanced control of the process provides for a more uniform deposit
thickness over the entire substrate, and permits reliable plating
of submicron features. The apparatus includes a pressurized
electrochemical cell to improve plating efficiency and reduce
defects, vertical laminar flow of the electrolyte solution to
remove surface gases from the vertically arranged substrate, a
rotating wafer chuck to eliminate edge plating effects, and a
variable aperture to control the current distribution and ensure
deposit uniformity across the entire substrate. Also a dynamic
profile anode whose shape can be varied to optimize the current
distribution to the substrate. The anode is advantageously able to
use metallic ion sources and may be placed close to the cathode
thus minimizing contamination of the substrate.
Inventors: |
Griego, Thomas P.;
(Corrales, NM) ; Sanchez, Fernando M.;
(Albuquerque, NM) |
Correspondence
Address: |
PEACOCK MYERS AND ADAMS P C
P O BOX 26927
ALBUQUERQUE
NM
871256927
|
Assignee: |
Surfect Technologies, Inc.
Albuquerque
NM
|
Family ID: |
32872767 |
Appl. No.: |
10/778647 |
Filed: |
February 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10778647 |
Feb 12, 2004 |
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10728636 |
Dec 5, 2003 |
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60431315 |
Dec 5, 2002 |
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60447175 |
Feb 12, 2003 |
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60519813 |
Nov 12, 2003 |
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60447175 |
Feb 12, 2003 |
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60519813 |
Nov 12, 2003 |
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Current U.S.
Class: |
204/280 ;
204/199; 204/242; 205/143 |
Current CPC
Class: |
H01L 2924/014 20130101;
B22F 2998/00 20130101; C25D 15/02 20130101; B22F 2998/00 20130101;
H01F 41/16 20130101; H01L 2224/11334 20130101; H01F 41/26 20130101;
H01L 2924/01006 20130101; H01L 2924/01027 20130101; H01L 2924/01005
20130101; H01F 41/20 20130101; B23K 35/0244 20130101; B22F 2999/00
20130101; C25D 15/00 20130101; C25D 17/001 20130101; B22F 1/025
20130101; B22F 1/025 20130101; C25D 15/00 20130101; B22F 1/0088
20130101; B22F 2999/00 20130101 |
Class at
Publication: |
204/280 ;
204/242; 204/199; 205/143 |
International
Class: |
C25D 005/02; C25D
005/00; C25D 017/16 |
Claims
What is claimed is:
1. An apparatus for electrochemical deposition on a substrate, said
apparatus comprising: an anode; a cathode with a vertical mounting
surface; a pressurized cell to contain electrolytic solution; and
an aperture disposed between said anode and said cathode; wherein a
vertical flow of said electrolytic solution is substantially
laminar in a vicinity of said cathode.
2. The apparatus of claim 1 further comprising a reservoir.
3. The apparatus of claim 2 wherein the reservoir and cell comprise
a closed system.
4. The apparatus of claim 2 further comprising at least one
filter.
5. The apparatus of claim 4 wherein at least one of said at least
one filter is a submicron filter.
6. The apparatus of claim 1 wherein the substrate comprises a
semiconductor wafer.
7. The apparatus of claim 6 wherein the wafer is coated so that
only certain features on the wafer receive the deposition.
8. The apparatus of claim 7 wherein said features are submicron
features.
9. The apparatus of claim 1 wherein the cell is pressurized to at
least approximately one atmosphere above ambient pressure.
10. The apparatus of claim 9 wherein the cell is pressurized to at
least approximately two atmospheres above ambient pressure.
11. The apparatus of claim 1 wherein said cathode rotates about a
horizontal axis perpendicular to said mounting surface.
12. The apparatus of claim 1 wherein said cell has a geometry that
facilitates said laminar flow.
13. The apparatus of claim 12 wherein said cell comprises an
inverted triangular or conical shape in a vicinity of an
electrolyte inlet port.
14. The apparatus of claim 12 wherein said cell is of sufficient
height to ensure that said flow is laminar in a vicinity of said
cathode.
15. The apparatus of claim 1 wherein said aperture is electrically
insulating.
16. The apparatus of claim 1 wherein said aperture comprises an
opening.
17. The apparatus of claim 16 wherein said opening is circular.
18. The apparatus of claim 16 wherein a size of said opening is
variable.
19. The apparatus of claim 18 wherein the size of said opening may
be varied during operation of the cell.
20. The apparatus of claim 18 wherein said aperture comprises an
iris.
21. The apparatus of claim 20 wherein said iris comprises at least
three paddles.
22. The apparatus of claim 18 wherein the size of said opening is
larger than a size of the substrate.
23. The apparatus of claim 18 wherein said opening can be
completely closed.
24. The apparatus of claim 1 wherein said anode is situated less
than approximately 5 cm from said cathode.
25. The apparatus of claim 24 wherein said anode is situated less
than approximately 1 cm from said cathode.
26. The apparatus of claim 25 wherein said anode is situated less
than approximately 0.5 cm from said cathode.
27. The apparatus of claim 1 wherein a metal ion source is situated
behind said anode, thereby minimizing contamination from reaching
the substrate while said anode retains a constant surface
profile.
28. The apparatus of claim 1 wherein a surface profile of said
anode is controllably variable.
29. The apparatus of claim 28 wherein said surface profile can be
varied during operation of said cell.
30. The apparatus of claim 28 wherein said anode comprises parallel
hollow electrically conducting tubes.
31. The apparatus of claim 1 further comprising a magnet.
32. The apparatus of claim 31 wherein said magnet comprises an
electromagnet.
33. The apparatus of claim 31 wherein said magnet comprises at
least one permanent magnet.
34. The apparatus of claim 31 wherein said magnet provides for
codeposition of magnetic particles with electrochemical deposition
on the substrate.
35. The apparatus of claim 34 wherein a strength of said magnet is
adjusted to provide a desired concentration of magnetic particles
on the substrate.
36. An apparatus for performing multiple electrochemical
depositions on a substrate, said apparatus comprising: an anode
having a variable surface profile; a cathode with a vertical
mounting surface; a pressurized cell to contain electrolytic
solution; a closed system for circulation of the solution; and an
aperture with a variably sized opening disposed between said anode
and said cathode; wherein a vertical flow of said electrolytic
solution is substantially laminar in a vicinity of said
cathode.
37. The apparatus of claim 36 wherein the multiple depositions are
carried out without opening said cell between each deposition.
38. The apparatus of claim 36 wherein said surface profile of said
anode is controllably varied as desired for each deposition.
39. The apparatus of claim 36 wherein a size of said opening is
varied as desired for each deposition.
40. The apparatus of claim 36 further comprising a filter.
41. A method of electrolytically depositing a material on a
substrate, the method comprising the steps of: providing an
electrolytic cell; providing an anode; mounting the substrate on a
cathode so that a surface of the substrate is vertically disposed;
disposing an aperture between the anode and cathode; providing
laminar flow of electrolyte solution through a cell; pressurizing
the solution to a desired pressure; and providing an electric
potential difference between the cathode and the anode.
42. The method of claim 41 wherein the step of providing laminar
flow comprises filtering the solution.
43. The method of claim 41 further comprising the step of uniformly
plating submicron features on the substrate.
44. The method of claim 41 wherein the mounting step further
comprises rotating the substrate about a horizontal axis
perpendicular to the surface.
45. The method of claim 41 wherein the disposing step further
comprises varying a size of an opening of the aperture.
46. The method of claim 41 wherein the step of providing an anode
comprises situating the anode less than approximately 5 cm from the
cathode.
47. The method of claim 46 wherein the step of providing an anode
comprises situating the anode less than approximately 1 cm from the
cathode.
48. The method of claim 47 wherein the step of providing an anode
comprises situating the anode less than approximately 0.5 cm from
the cathode.
49. The method of claim 41 wherein the step of providing an anode
comprises situating the anode between a metallic ion source and the
cathode.
50. The method of claim 49 wherein the step of providing an anode
comprises minimizing contamination from reaching the cathode while
retaining a constant surface profile.
51. The method of claim 41 wherein the step of providing an anode
comprises controllably varying a surface profile of the anode.
52. The method of claim 41 wherein the mounting step further
comprises providing a magnetic field.
53. The method of claim 52 further comprising the step of using the
magnetic field to codeposit magnetic particles with the material on
the substrate.
54. The method of claim 53 further comprising varying the magnetic
field to adjust the composition of the magnetic particles on the
substrate.
55. A method of performing multiple electrolytic depositions on a
substrate, the method comprising the steps of: a. providing a
pressurized electrolytic cell; b. providing an aperture with a
variably sized opening; c. optimizing deposition parameters of the
cell including a pressure of the cell and a size of the opening for
a desired deposition; d. depositing a material on a substrate; and
e. repeating steps (a) through (d) without opening the cell.
56. An anode for use in an electrochemical process, said anode
comprising: a plurality of parallel hollow electrically conducting
tubes with sides in slideable contact with one another; and a clamp
circumferentially disposed around the plurality of tubes to prevent
motion of the tubes.
57. The anode of claim 56 wherein the tubes are cylindrical.
58. The anode of claim 56 wherein the tubes have a cross section
comprising a regular polygon.
59. The anode of claim 56 wherein a surface profile of the anode
comprises positions of ends of each of the tubes which face a
cathode.
60. The anode of claim 59 wherein the surface profile is adjustable
by sliding the tubes relative to one another.
61. The anode of claim 56 wherein a shape of the surface profile is
selected from the group consisting of flat, convex, hemispherical,
conical, domed, curved, and pyramidal.
62. The anode of claim 56 comprising an electrically conducting
material.
63. The anode of claim 56 comprising a soluble material.
64. The anode of claim 56 comprising an insoluble material.
65. The anode of claim 64 comprising a platinumized material.
66. The anode of claim 56 further comprising a receptacle for
placement of an electrochemical ionic source media.
67. The anode of claim 66 wherein the media is a metallic ion
source.
68. The anode of claim 66 wherein the receptacle is on a side of
the anode opposite the surface profile.
69. The anode of claim 68 wherein the anode minimizes contamination
from reaching a cathode while retaining a constant surface
profile.
70. The anode of claim 56 wherein the process is selected from the
group consisting of plating, electroplating, electrodeposition,
chemical and mechanical polishing (CMP), electropolishing, etching,
and electrolysis.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the filing of U.S.
Provisional Patent Application Ser. No. 60/431,315, entitled "Solid
Core Solder Particles for Printable Solder Paste", filed on Dec. 5,
2002, U.S. Provisional Patent Application Ser. No. 60/447,175,
entitled "Electrochemical Devices and Processes", filed on Feb. 12,
2003, and U.S. Provisional Patent Application Ser. No. 60/519,813,
entitled "Particle Coelectrodeposition", filed on Nov. 12, 2003.
This application also is a continuation-in-part of U.S. patent
application Ser. No. 10/728,636, entitled "Coated and Magnetic
Particles and Applications Thereof", filed Dec. 5, 2003. The
specifications of each application listed are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention (Technical Field)
[0003] The present invention relates to an apparatus and method for
electroplating substrates or other objects, particularly
semiconductor wafers. The present invention can also be used to
plate ceramic panels used in thin or thick film type packaging, as
well as anti-reflective coatings of lenses and other types of glass
substrates. The apparatus may also be used for microvia deposition,
wafer bumping, and flip chip bumping. The apparatus provides for a
much higher control of the deposition parameters, enabling fine
submicron features to be plated. The invention also relates to an
anode for electrochemical processes whose profile can be varied to
any desired shape. The anode may be used with metallic ion sources
without contaminating the substrate.
[0004] 2. Background Art
[0005] Note that the following discussion is given for more
complete background of the scientific principles and is not to be
construed as an admission that such concepts are prior art for
patentability determination purposes.
[0006] A traditional electroplating cell comprises a tank to hold
the chemical solution, one or two anodes that are either of a
soluble composition of the metal to be deposited or insoluble
platinumized anodes. The item to be plated is mounted horizontally
on the cathode, at a gap of approximately four inches from the
anode(s). A DC power supply, operating with either a constant,
switched or pulsed output, with an optional periodic polarity
reverse is most often utilized in current cells. Configurations of
this type do not provide sufficient control over the deposition
process to enable the uniform plating of submicron features on a
substrate. Nor can the operating geometries and other parameters of
the cell be easily varied to accommodate different types of plating
substrates or patterns, or to adjust the plating conditions to
ensure uniformity and quality of the deposit.
[0007] It is known in the art to enhance the deposit uniformity by
introducing an aperture to selectively mask off the edges of the
substrate. However, when plating submicron structures it is
critical that the size of the aperture be adjustable to more
precisely control the thickness uniformity, whether before or
during processing. In addition, an adjustable aperture enables the
cell to be used for multiple types of deposits, reducing the
capital equipment requirements of the user, and minimizing
contamination by avoiding transfer of the substrate from one cell
to another.
[0008] The use of shaped anodes to improve deposit uniformity and
efficiency are also known in the art. However, the optimal shape
depends on the particular electrochemical process and the
characteristics of the pattern on the substrate, among other
things. Thus there is a need for an anode with variable shape
capabilities.
[0009] Another drawback of the existing art is that in order to
place the anode close to the cathode, an insoluble anode must be
used with a metal salt solution, which is inferior to a metallic
ion source. Alternatively, a soluble metallic anode may be used,
but it cannot be placed close to the cathode because of potential
contamination. In addition, as the anode dissolves it changes
shape, reducing the very control of the deposit parameters that was
provided by choosing the initial shape of the anode. Accordingly,
there is a need for an insoluble anode that can use metallic ion
sources and that be placed close to the cathode.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
[0010] The present invention is of an apparatus for electrochemical
deposition on a substrate such as a wafer, the apparatus comprising
an anode, a cathode with a vertical mounting surface, a pressurized
cell to contain electrolytic solution, and an aperture disposed
between the anode and cathode; wherein a vertical flow of the
electrolytic solution is substantially laminar in a vicinity of the
cathode. The apparatus optionally comprises a reservoir, which
preferably forms a closed, filtered system with the cell. At least
one filter is preferably a submicron filter.
[0011] The wafer may optionally be coated so that only certain
features, such as submicron features, on the wafer receive the
deposition.
[0012] The cell is preferably pressurized to at least approximately
one atmosphere above ambient pressure, and optionally is
pressurized to at least approximately two atmospheres above ambient
pressure. The cathode preferably rotates about a horizontal axis
perpendicular to said mounting surface. The cell preferably has a
geometry that facilitates said laminar flow, for example comprising
an inverted triangular or conical shape in a vicinity of an
electrolyte inlet port. Additionally the cell is preferably of
sufficient height to ensure that said flow is laminar in a vicinity
of said cathode.
[0013] The aperture is preferably electrically insulating, and
preferably comprises a circular opening which is variable in size,
optionally during operation of the cell. The aperture preferably
comprises an iris with at least three paddles. The opening is
preferably continuously variable from a size larger than the size
of the substrate to completely closed.
[0014] The anode is preferably situated less than approximately 5
cm, more preferably less than approximately 1 cm, and most
preferably less than approximately 0.5 cm from the cathode. The
metal ion source is preferably situated behind the anode, thereby
minimizing contamination from reaching the substrate while the
anode retains a constant surface profile. The surface profile of
said anode is preferably controllably variable, and may be varied
during operation of the cell. The anode preferably comprises
parallel hollow electrically conducting tubes.
[0015] The apparatus may optionally comprise a magnet, such as an
electromagnet or at least one permanent magnet. The magnet
preferably provides for the codeposition of magnetic particles
along with the electrochemical deposition on the substrate. The
codeposition may occur before, during, and/or after the
electrochemical deposition. The strength of the magnet is
preferably adjusted to provide a desired concentration of magnetic
particles on the substrate.
[0016] The invention is further of an apparatus for performing
multiple electrochemical depositions on a substrate, the apparatus
comprising an anode having a variable surface profile, a cathode
with a vertical mounting surface, a pressurized cell to contain
electrolytic solution, a closed, optionally filtered system for
circulation of the solution, and an aperture with a variably sized
opening disposed between the anode and the cathode; wherein a
vertical flow of the electrolytic solution is substantially laminar
in the vicinity of the cathode. The multiple depositions are
preferably carried out without opening the cell between each
deposition, even though the surface profile of the anode and/or the
size of the opening are preferably controllably varied as desired
for each deposition.
[0017] The invention is also of a method of electrolytically
depositing a material on a substrate, the method comprising the
steps of providing an electrolytic cell, providing an anode,
mounting the substrate on a cathode so that a surface of the
substrate is vertically disposed, disposing an aperture between the
anode and cathode, providing laminar flow of electrolyte solution
through a cell, pressurizing the solution to a desired pressure,
and providing an electric potential difference between the cathode
and the anode. The solution is preferably filtered. Optionally,
submicron features on the substrate are uniformly plated. The
substrate is preferably rotated about a horizontal axis
perpendicular to the surface, and the aperture preferably has a
variable size opening.
[0018] The method preferably comprises situating the anode less
than approximately 5 cm, more preferably less than approximately 1
cm, and most preferably less than approximately 0.5 cm from the
cathode. The anode is preferably situated between a metallic ion
source and the cathode and preferably minimizes contamination from
reaching the cathode while retaining a constant surface profile.
The surface profile of the anode is preferably controllably varied
as desired. Optionally a magnetic field is provided to codeposit
magnetic particles with the material on the substrate. The magnetic
field is preferably varied to adjust the composition of the
magnetic particles on the substrate.
[0019] The invention is further of a method of performing multiple
electrolytic depositions on a substrate, the method comprising the
steps of providing a pressurized electrolytic cell, providing an
aperture with a variably sized opening, optimizing deposition
parameters of the cell including a pressure of the cell and a size
of the opening for a desired deposition, depositing a material on a
substrate; and repeating the above steps without opening the
cell.
[0020] The invention is also of an anode for use in an
electrochemical process, the anode comprising a plurality of
parallel hollow electrically conducting tubes with sides in
slideable contact with one another and a clamp circumferentially
disposed around the plurality of tubes to prevent motion of the
tubes. The tubes are preferably cylindrical or have a cross section
comprising a regular polygon. The surface profile of the anode
preferably comprises the positions of the ends of each of the tubes
which face the cathode. The anode's surface profile is preferably
adjustable by sliding the tubes relative to one another, and
preferably comprises a flat, convex, hemispherical, conical, domed,
curved, or pyramidal shape.
[0021] The anode preferably comprises an electrically conducting
material, which may be soluble, or preferably insoluble, for
example platinumized. The anode preferably comprises a receptacle
for placement of an electrochemical ionic source media, preferably
a metallic ion source, on the side of the anode opposite the
surface profile. The anode minimizes contamination from reaching
the cathode while retaining a constant surface profile. The anode
is preferably used in any of the following processes: plating,
electroplating, electrodeposition, chemical and mechanical
polishing (CMP), electropolishing, etching, or electrolysis.
[0022] Objects, advantages and novel features, and further scope of
applicability of the present invention will be set forth in part in
the detailed description to follow, taken in conjunction with the
accompanying drawings, and in part will become apparent to those
skilled in the art upon examination of the following, or may be
learned by practice of the invention. The objects and advantages of
the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The accompanying drawings, which are incorporated into and
form a part of the specification, illustrate several embodiments of
the present invention and, together with the description, serve to
explain the principles of the invention. The drawings are only for
the purpose of illustrating a preferred embodiment of the invention
and are not to be construed as limiting the invention. In the
drawings:
[0024] FIG. 1 is an exploded view of a preferred embodiment of the
electrodeposition apparatus of the invention;
[0025] FIG. 2 is an isometric view of the cell and reservoir;
[0026] FIG. 3 shows a cross section of the cell;
[0027] FIG. 4 depicts a close up of the cross section of the
plating area of the cell;
[0028] FIG. 5 shows the chuck in position for wafer loading or
unloading;
[0029] FIG. 6 shows the wafer in the loaded position;
[0030] FIG. 7 shows the chuck rotated to the vertical position;
[0031] FIG. 8 shows a cross section of the wafer chuck;
[0032] FIG. 9 is a detail of the rotating wafer mount;
[0033] FIG. 10 is an isometric view of the rear of the chuck,
showing the rotation mechanism;
[0034] FIG. 11 is a cutaway view of the cell depicting the iris
fully open;
[0035] FIG. 12 is a cutaway view of the cell depicting the iris
partially masking the substrate;
[0036] FIG. 13 is a cutaway view of the cell depicting the iris
fully closed;
[0037] FIG. 14 shows an isometric view of one embodiment the
dynamic profile anode assembly;
[0038] FIG. 15 shows an exploded view of the dynamic profile anode
assembly;
[0039] FIG. 16 shows a top view and cross section of the dynamic
profile anode assembly depicting a convex surface profile;
[0040] FIG. 17 depicts the dynamic profile anode and clamp showing
a convex surface profile;
[0041] FIG. 18 is an exploded view of FIG. 17;
[0042] FIG. 19 is a cross sectional view of a second embodiment of
the dynamic profile anode with a flat surface profile;
[0043] FIG. 20 is a cross sectional view of the dynamic profile
anode with a convex surface profile;
[0044] FIG. 21 is a cross sectional view of the dynamic profile
anode with a conical surface profile;
[0045] FIG. 22 is an isometric view of the dynamic profile anode
and anode diaphragm showing the conical surface profile;
[0046] FIG. 23 shows a cross section of the wafer chuck comprising
an electromagnet; and
[0047] FIG. 24 shows a schematic of the cell of the present
invention configured to provide co-deposition of magnetic
particles.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
BEST MODES FOR CARRYING OUT THE INVENTION
[0048] The present invention is of an apparatus and method for
highly controlled electrodeposition, particularly useful for
electroplating submicron structures. Enhanced control of the
process provides for a more uniform deposit thickness over the
entire substrate, and permits reliable plating of submicron
features, for example those on a semiconductor wafer. A primary
advantage of the invention is that the kinetics of the cell, which
are based on the geometries of the cell, can be changed quickly to
optimize plating on the substrate surface, for all deposits
including very thick film deposits and thin film deposits.
[0049] As used throughout the specification and claims, "substrate"
means any substrate, wafer, lens, panel, and the like, or any other
item which is to be attached to an electrode to be plated. Such
substrate may comprise any material such as a semiconductor,
including but not limited to silicon, gallium arsenide, sapphire,
glass, ceramic, metal alloy, polymer, or photoresist.
[0050] FIG. 1 depicts an exploded view of a preferred embodiment of
electrodeposit cell 10 of the present invention comprising bulkhead
24 and bulkhead door 26. Substrate chuck 12 is rotatable using
pivot assembly 14 and slides on guide rod 16 to seal against the
opening in bulkhead door 26. Aperture 18 is located between
bulkhead 24 and bulkhead door 26, and is operated using stepper
motor 20 which drives belt 22.
[0051] Referring to FIG. 2, reservoir 30 is where filter 34 and
pump 32 are preferably mounted, as well as instrumentation for
controlling the characteristics of the electroplating solution or
electrolyte that is introduced into the WAVE Cell, such as
temperature, pH, and concentrations of metal species and other
electrolyte components. This ensures that all electrolyte
characteristics are maintained at an optimal level. Any type of
brightener system may also be checked. All chemical maintenance is
preferably carried out in reservoir 30. Optionally, rather than
being a standalone unit, the reservoir may be integral with the
cell itself. The electrolyte solution is pumped into cell 10
through solution inlet 36. Pressure valve 38 regulates the pressure
in the cell, as more fully described below, and controls the
circulation of the electrolyte solution back to reservoir 30.
[0052] Unlike traditional electroplating devices, the entire
circulation path of the solution, and the process environment in
which the wafer is placed, is preferably enclosed, and more
preferably comprises at least one filter, including but not limited
to a submicron filter. Thus the electroplating environment is
equivalent to a clean room, without requiring the latter's expense,
and ensures a reliable and uncontaminated deposit process.
[0053] As shown in FIG. 3, connected to the cell's cathode will
preferably be the negative terminal 40 of a DC power supply,
operating with either a constant, switched or pulsed output, or
with optional periodic polarity reversal, and connected to anode
100 will preferably be the positive terminal 42 of the power
supply. FIG. 4 is an enlarged detail.
[0054] Chuck 12 is preferably comprised of articulating door 44
that can be opened and can interface with automation known in the
art for mounting and dismounting of the substrate, permitting
automated substrate loading and unloading. As shown in FIGS. 5 and
6, substrate 50 is mounted on chuck 12, which is preferably in the
horizontal position. Chuck 12 holds substrate 50 on a flat surface
and supplies the cathodic current to the surface of substrate 50
via at least one contact 52. Thus chuck 12, and more specifically
substrate 50, acts as the cathode in the present system, and the
terms are used interchangeably herein. Cell 10 of the present
invention is capable of handling substrates in a large size range,
such as wafers used in the semiconductor industry, including but
not limited to those from 75 mm to 300 mm in diameter. Optionally,
the edges of the substrate may be masked by a grip ring, preferably
comprised of both metallic and insulating materials, that will
supply current at the edge of the substrate while masking the edge
of the current contact itself so that unnecessary deposits don't
occur on the contact. FIG. 7 shows door 44 rotated into the
vertical position about pivot assembly 14 so it is ready to slide
along guide rods 16 and seal the opening in bulkhead door 26.
[0055] Chuck 12 is preferably rotatable, which provides advantages
in uniformity of deposit that are described more fully below.
Various views of the rotation mechanism are presented in FIGS.
8-10. Motor 58, optionally mounted on motor mount 66, is preferably
used to provide such rotation, connecting via gear 64 or other
rotation transfer means, such as a belt, to rotating shaft 62 that
protrudes through o-ring seals 60 in articulating door 44. A DC
current is preferably fed through shaft 62 via negative terminal
40, which will continuously supply cathodic current during the
process run. Once door 44 is closed, it can optionally be fastened
with bolts around the perimeter of the door and sealed by
compressive-type gasketing 46.
[0056] The electrolyte, or plating, solution is then circulated
into the cell, preferably entering from the base of the cell via
solution inlet 36. A process controller will preferably continue
the circulation of the electrolyte through the system until the
desired thickness has been deposited. Typical process steps for
operating the present cell preferably comprise a first rinsing,
pretreatment with an activating acid or cleaner, a second rinsing,
electroplating, and a final rinsing. Optionally, post-treatment
operations for sealing or for mask or photoresist removal may be
performed.
[0057] The pressure of the solution in cell 10 is regulated by
pressure valve 38 or other type of pressure regulator, which
preferably pressurizes the cell to one or two atmospheres above
open cell, or ambient, pressure. However, any pressure may be
utilitzed. For example, valve introduces back pressure into the
cell, which optionally is monitored and controlled by a pressure
gauge or other controller. The ability to pressurize the cell
provides control over pressure dependent characteristics of the
plating process, for example deposit kinetics, which results in
improved performance and an improved deposit.
[0058] Controlling the pressure in the cell also improves solution
exchange and ion supply on all surfaces of the wafer, including
deep filled vias and planer surface areas. In addition,
pressurization of the cell provides a high efficiency of deposition
at lower current densities. Existing electroplating systems are not
able to electroplate submicron structures in part because the mass
transfer of ions from the anode to the cathode has been
incompatible in terms of the scale of the pattern that is built up
on the surface of the wafers. According to the present invention,
using lower amperage densities, optionally combined with switching
the current on and off, enables finer control of the deposit
parameters. Thus submicron structures can be successfully
electroplated and nanoscale vias can be filled uniformly, making
electrolytic processes such as electroplating a viable alternative
to an angstrom scale process like sputtering or vapor
deposition.
[0059] Pressurizing the cell will also suppress the formation of
gases such as hydrogen at the deposition interface, (i.e. the
cathode, or substrate, surface). These gases cause undesirable
porosity or voids resulting in micropittings that typically occur
in a deposit on the surface of the cathode. Gases such as hydrogen
also may reduce the mechanical strength of the deposit; if hydrogen
is left in the boundary area, brittle deposits or highly stressed
deposits may be formed, resulting in tensile failure and possibly
the deposit peeling back from the substrate. The integrity of the
bond of the deposit, such as a metallic interconnect, to the
substrate or wafer is critical to assure the high reliability
necessary for electronic components.
[0060] For applications in the submicron range, particulates,
pores, and micropittings that would normally be acceptable in
traditional plating applications are not tolerable because of the
small size of the features to be plated as well as the required
thinness of the deposit. Thus the overall control of micropittings
is of paramount importance if semiconductor wafers are to be
electroplated. By using pressurization to minimize gas formation,
the integrity of the initial deposit on the surface of the wafer
(when the voltage or the potential is at its highest), which
creates the first boundary layer between the substrate and the
metal being deposited, will be greatly improved. This results in a
surface morphology of sufficient quality to successfully plate
submicron structures.
[0061] The vertical configuration of the preferred embodiment of
cell 10 also helps to reduce the presence of undesirable gas and
gas bubbles at the surface of substrate 50 due to the laminar flow
of electrolyte past the surface, which acts together with gravity
to remove the gas upward away from the interface area of the
substrate. The electrolyte optionally passes through baffles which
distribute the pressure within the solution and help create laminar
flow. Laminar flow formation is also preferably promoted by
utilizing a non-rectangular shape of cell 10 adjacent to solution
inlet 36, preferably a triangular or conical shape, as shown in
FIG. 1. The length of cell 10 is long enough to transform the
turbulent flow of the plating solution when introduced in the base
of the cell to a laminar flow as it passes the surface of the
wafer. The pressurization of the cell contributes to shortening the
overall length of the cell required to achieve the laminar
flow.
[0062] Laminar flow also enhances the plating solution by
continuously and uniformly supplying solution of the optimum
temperature and pH and ion species to the substrate. By sweeping
out gases and supplying a continuous, reliable supply of
electrolyte to the substrate, a more robust and uniform deposit is
achieved, allowing for a greater range of chemical compositions for
high-throw or low-throw baths to be utilized, giving the chemical
process engineer more latitude. If laminar flow is not present, a
defect or non-uniformity of the deposit's thickness or mechanical
properties may result.
[0063] The present invention also comprises further multiple means
to greatly enhance the uniformity of the thickness of the deposit
on substrate 50. The thickness can be kinetically controlled across
the entire substrate by rotation of substrate 50 as described
above, and by selective masking of the substrate's exposure to
anode 100, which techniques serve to provide a far more uniform
current density at all points on substrate 50.
[0064] In the present invention substrate 50 is preferably mounted
on rotating chuck 12 comprising the cathode. Thus the leading edge
of substrate 50 with respect to the directional flow of the plating
solution, which ordinarily will develop a thicker deposit than the
rest of the substrate, is continually changed, distributing the
mechanical forces on the substrate's edge as well as leveling out
the thickness of the plating at the edge, making it more consistent
with that at the center of the substrate.
[0065] Another cause of thickness nonuniformity in a traditional
electroplating cell, the "dog bone" effect, occurs because current
densities are higher at the edges of the cathode or substrate,
meaning that the deposit will have a greater thickness there. By
using an electrically insulating aperture, or masking device, the
center of the substrate, where current densities are the lowest,
receives preferentially higher exposure to the current, and the
edges of the substrate, where the amperage densities are highest,
is masked off from the current. The thickness of the deposit is
thus more uniform across the entire substrate. Although masking is
known in the art, only fixed apertures have been utilized.
[0066] The present invention comprises an adjustable aperture 18,
preferably comprising an iris mechanism, which enables variation of
the iris size from all the way open (exposing the whole wafer)
(FIG. 11), through partially masking substrate 50 (FIG. 12), to
completely closed (FIG. 13). The iris mechanism is preferably
computer controlled; the size of the iris may be adjusted, even
while deposition is proceeding, to provide precise control of the
deposition characteristics, including but not limited to the rate
of deposition, the deposition thickness, and the variance in
deposition thickness. Other variable aperture means may be utilized
instead.
[0067] A preferred embodiment of the iris mechanism aperture 18 of
the present invention comprises at least three paddles 54(a)-(c),
preferably connected via posts protruding through the cell via an
o-ring sealed port to belt 22 driven by stepper motor 20 that
articulates the paddles in unison so that they close down to a
desired aperture size, thereby reducing the open area of substrate
50 mounted on the cathode. Any type of motor or actuator may be
used instead of stepper motor 20. Optionally, more paddles 54 may
be used, making the opening in aperture 18 more circular.
[0068] The variable aperture also enhances the ability of the
present invention to plate submicron structures, such as wafer
interconnects. Because these structures give rise to highly
nonuniform current densities, successful plating requires extremely
precise plating parameter control. Along with pressurizing the
cell, varying the aperture size provides this control so that the
structures are uniformly plated regardless of the line width,
pitch, or density of the pattern.
[0069] Also, different wafer designs require different optimal
settings of the aperture size due to differences in the total
metallization area and distribution and density of features to be
plated. The variable size aperture allows the user to precisely
optimize the system for each wafer design. And an adjustable
aperture means that the user does not have to replace the aperture
for each separate wafer design.
[0070] The present invention is also of a dynamic profile anode 100
that may be used for plating, electroplating, electrodeposition,
chemical and mechanical polishing (CMP), electropolishing, etching,
electrolysis, or any other electrochemical process. Although shaped
anodes are known in the art, the present invention is of an anode
whose profile can be modified before or even during processing.
Examples of profiles include but are not limited to flat, convex,
domed, curved, hemispherical, conical, pyramidal, or any
combination thereof. The shape used will be determined through
experimentation and optimized for various types of wafer patterns.
For example, conical-type shapes concentrate the ionic current
toward the center of the substrate or cathode, thereby providing an
additional method of maximizing the uniformity of the deposit
thickness across the substrate.
[0071] FIG. 14 shows one embodiment of the anode assembly, with an
exploded view in FIG. 15 and a cross section in FIG. 16. The
assembly comprises anode 100, which is seated in anode diaphragm
110. Filter 120, preferably cloth or polypropylene, allows ions to
pass but prevents contamination from soluble metallic plating media
in basket 130 from reaching anode 100 and eventually the cathode.
Basket 130, which preferably comprises titanium or another
non-soluble metal, is connected via contact rods 140 to base
150.
[0072] FIGS. 17 and 18 detail the construction of anode 100. Anode
100 is comprised of tubes 102 which form a stack up which provides
the shape of the surface profile of anode 100, and clamp ring 104
which secures tubes 102 in place so it is dimensionally stable once
the desired surface profile is achieved. Contact bus plates 160
conduct electrical current to anode 100.
[0073] Another embodiment of dynamic profile anode 100 is shown in
FIGS. 19-22. FIG. 19 is a cross section view showing a flat surface
profile. Current is provided from positive terminal 42 through
o-ring seals 170 to basket 130, clamp ring 104 and tubes 102. FIG.
20 depicts a convex surface profile, while FIGS. 21 and 22 show a
cross section view and isometric view, respectively, of anode 100
with a conical surface profile. The surface profile may be changed
by removing clamp ring 104, adjusting tubes 102 until the desired
profile is achieved, and then engaging clamp ring 104 to hold tubes
102 in place.
[0074] Anode 100 is preferably removable or serviceable,
accommodating the use of either soluble or insoluble materials to
deposit onto the surface of the wafer. Anode 100 may optionally
comprise a soluble material which dissolves during processing.
Preferably, anode 100 may be platinumized, or be otherwise
insoluble. Unlike the prior art, the use of hollow tubes 102 allows
a metallic ion source, for example shot, chunks, rings, plates or
bars of a desired anode metal or alloy, which is preferable to a
metal salt solution, to be placed in basket 130 behind the anode.
But because anode 100 is itself insoluble, it retains the exact
desired shape throughout the deposition process. This combination
permits anode 100 to be placed very close to substrate 50. Typical
prior art systems require the distance between the anode and
cathode to be at least 10 cm. While allowing for any distance, the
anode design of the present invention permits anode 100 to be
situated at a distance from substrate 50 of less than 5 cm, more
preferably less than 1 cm, and most preferably less than 0.5 cm.
The ability to utilize such a short distance greatly improves the
control of the deposition, which enhances the uniformity of deposit
across substrate 50. In addition, a shorter path for the ions to
flow to the cathode means that contamination of substrate 50 with
other ions in solution, or ions from a metallic component in the
bath, is drastically reduced.
[0075] Anode 100 of the present invention thus provides for the use
of soluble metallic anodic materials but does not change its
surface profile due to the corrosion of the anodic material during
deposition, unlike anodes known in the art. However, if desired,
the user may controllably vary the surface profile of anode 100 in
order to obtain a shape that optimizes the deposition process. This
ability to modify the anode's shape as desired, while at the same
time retaining the desired shape (i.e. preventing corrosion) during
use of such soluble metallic materials, is novel.
[0076] In the present application the system preferably injects the
electroplating solution directly into the anode basket 130 in order
to help promote the convection of the electron flow carrying the
ion matter from the anode into the cell's process area. In
addition, it is preferable that the pressure at anode 100 is less
than the pressure at substrate 50, or cathode, so no
countercurrents develop which might disrupt laminar flow of the
electrolyte adjacent to the substrate 50.
[0077] In addition to the being operated as a single cell or a
dedicated cell for a specific chemical operation, the present
invention may be used as a multiple process cell. A first plating
solution is introduced into the cell and a first operation is
performed. The first plating solution may then be rapidly drained,
and a rinsing chemistry is preferably circulated throughout the
cell. The rinsing step may be repeated for a number of cycles to
achieve a desired level of purity of the rinsed wafer surface.
Subsequent chemical processes may then be performed to deposit
additional electroplated films or multiple compositions. For
example, a substrate may be plated with a nickel film over a copper
film and followed by a tin film. Or ceramic panels used in thick
film type packaging, which require multiple layer film formation,
can be produced. Because the system is preferably closed and
filtered, clean room conditions with little contamination can be
maintained throughout the entire multiple operation process. This
feature is also facilitated by the adjustable aperture and dynamic
profile anode, which allows the user to choose the optimal iris
size (or sizes) and anode profile for a particular process without
having to open the cell and replace the aperture.
[0078] Optionally the chuck may be magnetic, which allows for
magnetic particle codeposition. This process is more fully
described in U.S. Provisional patent application Ser. No.
60/519,813, entitled "Particle Coelectrodeposition", and U.S.
patent application Ser. No. 10/728,636, entitled "Coated and
Magnetic Particles and Applications Thereof". One example of such a
chuck is the back seal electrolytic vacuum chuck, disclosed in U.S.
Provisional patent application Attorney Docket No. 31248-5,
entitled "Pressurized Autocatalytic Vessel and Vacuum Chuck", filed
on Feb. 4, 2004. The specifications and claims of these references
are incorporated herein by reference. One embodiment of such a
chuck is shown in FIG. 23, which is identical to FIG. 8 except that
it includes electromagnet 70. The magnetic field may be provided by
an electromagnet as depicted, or alternatively a permanent magnet,
an array of magnets, or the like. The presence of the magnetic
field allows magnetic particles to be codeposited on substrate 50
in a highly controlled manner before, during, or after the
deposition of the electrolytic plating, providing numerous
chemical, material, and mechanical advantages to the deposited
structures.
[0079] FIG. 24 depicts a schematic and flow diagram of a preferred
embodiment of a codeposition tool and process. Pump 290 pumps
electrolyte stored in tank 264 to mixer 320, where it is mixed with
a slurry of magnetic particles in suspension which was pumped from
slurry tank 300 by slurry pump 310. The suspension-electrolyte
mixture enters cell 10 and proceeds upward in laminar flow to the
codeposition area comprising anode 100 and substrate 50. Substrate
50 preferably rotates via motor 58. Electromagnet 70 attracts
magnetic particles from the suspension-electrolyte so that they are
codeposited on substrate 50 along with the electrochemical
deposition. Controller 230 controls deposition parameters, such as
the electrode voltage via DC power supply 200 and the concentration
of magnetic particles in the suspension-electrolyte mixture via
slurry pump 310.
[0080] Waste suspension-electrolyte mixture exits cell 10 through
pressure valve 38. Magnetic separator 240 strips out excess
particles from the suspension-electrolyte mixture via an adjustable
magnetic field provided by DC separator power supply 242.
Nonmagnetic particles and sediments are filtered out using rotary
filter 250 and cartridge filter 260, although other types of
filters may be used. The filtered electrolyte is then recirculated
back into tank 264, where it is cooled via heat exchanger 270
controlled by temperature control 280. The electrolyte may thus be
recycled, providing substantial cost savings.
[0081] Although the invention has been described in detail with
particular reference to these preferred embodiments, other
embodiments can achieve the same results. Variations and
modifications of the present invention will be obvious to those
skilled in the art and it is intended to cover all such
modifications and equivalents. The entire disclosures of all
patents and publications cited above are hereby incorporated by
reference.
* * * * *