U.S. patent application number 10/731331 was filed with the patent office on 2005-06-09 for thrust pad assembly for ecp system.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Co., Ltd.. Invention is credited to Chen, Kei-Wei, Chuang, Ray, Lin, Shi-Chi, Liu, Chi-Wen, Tsao, Jung-Chih.
Application Number | 20050121329 10/731331 |
Document ID | / |
Family ID | 34634337 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050121329 |
Kind Code |
A1 |
Tsao, Jung-Chih ; et
al. |
June 9, 2005 |
Thrust pad assembly for ECP system
Abstract
A thrust pad assembly which is capable of reducing the quantity
of metal electroplated onto the edge region of a substrate to
eliminate or reduce the need for edge bevel cleaning or removal of
excess metal from the substrate after the electroplating process.
The thrust pad assembly includes an air platen through which air is
applied at variable pressures to the central and edge regions,
respectively, of a thrust pad. The thrust pad applies pressure to a
contact ring connected to an electroplating voltage source. The
contact ring applies relatively less pressure to the edge region
than to the central region of the substrate, thereby reducing the
ohmic contact.
Inventors: |
Tsao, Jung-Chih; (Taipei,
TW) ; Chen, Kei-Wei; (Yonghe City, TW) ; Liu,
Chi-Wen; (Hsinchu, TW) ; Lin, Shi-Chi;
(Hsinchu, TW) ; Chuang, Ray; (Taipei, TW) |
Correspondence
Address: |
TUNG & ASSOCIATES
Suite 120
838 W. Long Lake Road
Bloomfield Hills
MI
48302
US
|
Assignee: |
Taiwan Semiconductor Manufacturing
Co., Ltd.
|
Family ID: |
34634337 |
Appl. No.: |
10/731331 |
Filed: |
December 5, 2003 |
Current U.S.
Class: |
205/118 ;
257/E21.175 |
Current CPC
Class: |
C25D 17/001 20130101;
C25D 5/06 20130101; H01L 21/2885 20130101; C25D 17/14 20130101 |
Class at
Publication: |
205/118 |
International
Class: |
C25D 005/02 |
Claims
What is claimed is:
1. A thrust pad assembly for mounting a substrate in an
electroplating system, comprising: a contact ring for electrical
connection to the electroplating system and engaging the substrate;
and a variable pressure application system operably engaging said
contact ring for applying a central pressure to a center region of
the substrate through said contact ring and a peripheral pressure
less than said central pressure to an edge region of the substrate
through said contact ring.
2. The thrust pad assembly of claim 1 further comprising a thrust
pad engaged by said variable pressure application system and
engaging said contact ring for transmitting said central pressure
and said peripheral pressure to said contact ring.
3. The thrust pad assembly of claim 1 wherein said variable
pressure application system comprises a central air source for
applying said central pressure to the center region of the
substrate through said contact ring and a peripheral air source for
applying said peripheral pressure to the edge region of the
substrate through said contact ring.
4. The thrust pad assembly of claim 3 further comprising a thrust
pad engaged by said variable pressure application system and
engaging said contact ring for transmitting said central pressure
and said peripheral pressure to said contact ring.
5. The thrust pad assembly of claim 3 further comprising a platen
having a plurality of central air openings provided in pneumatic
communication with said central air source and a plurality of
peripheral air openings provided in pneumatic communication with
said peripheral air source for transmitting said central pressure
to the contact ring and the center region of the substrate and said
peripheral pressure to the contact ring and the edge region of the
substrate.
6. The thrust pad assembly of claim 5 further comprising a thrust
pad engaging said contact ring and engaged by said air platen for
transmitting said center pressure and said peripheral pressure to
said contact ring.
7. An electroplating system for electroplating a metal on a
substrate, comprising: a bath container for containing an
electrolyte bath; an anode for immersion in said electrolyte bath;
a current source for electrical connection to said anode; a contact
ring electrically connected to said current source for engaging the
substrate; and a variable pressure application system operably
engaging said contact ring for applying a central pressure to a
center region of the substrate through said contact ring and a
peripheral pressure less than said central pressure to an edge
region of the substrate through said contact ring.
8. The system of claim 7 further comprising a thrust pad engaged by
said variable pressure application system and engaging said contact
ring for transmitting said central pressure and said peripheral
pressure to said contact ring.
9. The system of claim 7 wherein said variable pressure application
system comprises a central air source for applying said central
pressure to the center region of the substrate through said contact
ring and a peripheral air source for applying said peripheral
pressure to the edge region of the substrate through said contact
ring.
10. The system of claim 9 further comprising a thrust pad engaged
by said variable pressure application system and engaging said
contact ring for transmitting said central pressure and said
peripheral pressure to said contact ring.
11. The system of claim 9 further comprising a platen having a
plurality of central air openings provided in pneumatic
communication with said central air source and a plurality of
peripheral air openings provided in pneumatic communication with
said peripheral air source for transmitting said central pressure
to the contact ring and the center region of the substrate and said
peripheral pressure to the contact ring and the edge region of the
substrate.
12. The system of claim 11 further comprising a thrust pad engaged
by said variable pressure application system and engaging said
contact ring for transmitting said central pressure and said
peripheral pressure to said contact ring.
13. A method of electroplating a metal on a substrate, comprising
the steps of: providing an electrically-conductive contact ring in
contact with a backside of the substrate; immersing said contact
ring and the substrate in an electrolyte bath; immersing an anode
in said electrolyte bath; applying a central pressure to a central
region on the substrate through said contact ring; applying a
peripheral pressure to an edge region on the substrate through said
contact ring, said peripheral pressure smaller in magnitude than
said central pressure; and applying a voltage potential to said
contact ring and said anode.
14. The method of claim 13 wherein said central pressure is greater
than about 14 psi and said peripheral pressure is less than about
14 psi.
15. The method of claim 13 wherein said anode comprises copper.
16. The method of claim 15 wherein said central pressure is greater
than about 14 psi and said peripheral pressure is less than about
14 psi.
17. The method of claim 13 further comprising the steps of
providing a thrust pad in contact with said contact ring and
providing a platen having a plurality of central air openings and a
plurality of peripheral air openings in contact with said thrust
pad, and wherein said applying a central pressure to a central
region on the substrate comprises the step of directing central air
pressure through said plurality of central air openings against
said thrust pad and wherein said applying a peripheral pressure to
an edge region on the substrate comprises the step of directing
peripheral air pressure through said plurality of peripheral air
openings against said thrust pad.
18. The method of claim 17 wherein said central air pressure is
greater than about 14 psi and said peripheral air pressure is less
than about 14 psi.
19. The method of claim 17 wherein said anode comprises copper.
20. The method of claim 19 wherein said central air pressure is
greater than about 14 psi and said peripheral air pressure is less
than about 14 psi.
21. The method of claim 13 wherein said applying a peripheral
pressure to an edge region on the substrate comprises applying a
peripheral pressure of from about 0 psi to about 14 psi to the edge
region on the substrate to form a metal layer having a thickness of
from about 100 angstroms to about 500 angstroms on the edge
region.
22. The method of claim 13 wherein said applying a central pressure
to a central region on the substrate comprises applying a central
pressure of greater than about 14 psi to the central region on the
substrate to form a metal layer having a thickness of greater than
about 7,000 angstroms to the central region.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to electrochemical plating
systems used in the deposition of metal layers on semiconductor
wafer substrates in the fabrication of semiconductor integrated
circuits. More particularly, the present invention relates to an
electrochemical plating system having a thrust pad assembly which
reduces the quantity of metal electroplated on the edge regions of
a cathode/wafer by the application of variable pressure to the
center and edge regions of the wafer.
BACKGROUND OF THE INVENTION
[0002] In the fabrication of semiconductor integrated circuits,
metal conductor lines are used to interconnect the multiple
components in device circuits on a semiconductor wafer. A general
process used in the deposition of metal conductor line patterns on
semiconductor wafers includes deposition of a conducting layer on
the silicon wafer substrate; formation of a photoresist or other
mask such as titanium oxide or silicon oxide, in the form of the
desired metal conductor line pattern, using standard lithographic
techniques; subjecting the wafer substrate to a dry etching process
to remove the conducting layer from the areas not covered by the
mask, thereby leaving the metal layer in the form of the masked
conductor line pattern; and removing the mask layer typically using
reactive plasma and chlorine gas, thereby exposing the top surface
of the metal conductor lines. Typically, multiple alternating
layers of electrically conductive and insulative materials are
sequentially deposited on the wafer substrate, and conductive
layers at different levels on the wafer may be electrically
connected to each other by etching vias, or openings, in the
insulative layers and filling the vias using aluminum, tungsten or
other metal to establish electrical connection between the
conductive layers.
[0003] Deposition of conductive layers on the wafer substrate can
be carried out using any of a variety of techniques. These include
oxidation, LPCVD (low-pressure chemical vapor deposition), APCVD
(atmospheric-pressure chemical vapor deposition), and PECVD
(plasma-enhanced chemical vapor deposition). In general, chemical
vapor deposition involves reacting vapor-phase chemicals that
contain the required deposition constituents with each other to
form a nonvolatile film on the wafer substrate. Chemical vapor
deposition is the most widely-used method of depositing films on
wafer substrates in the fabrication of integrated circuits on the
substrates.
[0004] Due to the ever-decreasing size of semiconductor components
and the ever-increasing density of integrated circuits on a wafer,
the complexity of interconnecting the components in the circuits
requires that the fabrication processes used to define the metal
conductor line interconnect patterns be subjected to precise
dimensional control. Advances in lithography and masking techniques
and dry etching processes, such as RIE (Reactive Ion Etching) and
other plasma etching processes, allow production of conducting
patterns with widths and spacings in the submicron range.
Electrodeposition or electroplating of metals on wafer substrates
has recently been identified as a promising technique for
depositing conductive layers on the substrates in the manufacture
of integrated circuits and flat panel displays. Such
electrodeposition processes have been used to achieve deposition of
the copper or other metal layer with a smooth, level or uniform top
surface. Consequently, much effort is currently focused on the
design of electroplating hardware and chemistry to achieve
high-quality films or layers which are uniform across the entire
surface of the substrates and which are capable of filling or
conforming to very small device features. Copper has been found to
be particularly advantageous as an electroplating metal.
[0005] Electroplated copper provides several advantages over
electroplated aluminum when used in integrated circuit (IC)
applications. Copper is less electrically resistive than aluminum
and is thus capable of higher frequencies of operation.
Furthermore, copper is more resistant to electromigration (EM) than
is aluminum. This provides an overall enhancement in the
reliability of semiconductor devices because circuits which have
higher current densities and/or lower resistance to EM have a
tendency to develop voids or open circuits in their metallic
interconnects. These voids or open circuits may cause device
failure or burn-in.
[0006] FIG. 1 schematically illustrates a typical standard or
conventional electroplating system 10 for depositing a metal such
as copper onto a semiconductor wafer 18. The electroplating system
10 includes a standard electroplating cell having an adjustable
current source 12, a bath container 14, a copper anode 16 and a
cathode 18, which cathode 18 is the semiconductor wafer that is to
be electroplated with copper. The anode 16 and the semiconductor
wafer/cathode 18 are connected to the current source 12 by means of
suitable wiring 38. The bath container 14 holds a bath 20 typically
of acid copper sulfate solution which may include an additive for
filling of submicron features and leveling the surface of the
copper electroplated on the wafer 18.
[0007] In operation of the electroplating system 10, the current
source 12 applies a selected voltage potential typically at room
temperature between the anode 16 and the cathode/wafer 18. This
potential creates a magnetic field around the anode 16 and the
cathode/wafer 18, which magnetic field affects the distribution of
the copper ions in the bath 20. In a typical copper electroplating
application, a voltage potential of about 2 volts may be applied
for about 2 minutes, and a current of about 4.5 amps flows between
the anode 16 and the cathode/wafer 18. Consequently, copper is
oxidized typically at the oxidizing surface 22 of the anode 16 as
electrons from the copper anode 16 and reduce the ionic copper in
the copper sulfate solution bath 20 to form a copper electroplate
(not illustrated) at the interface between the cathode/wafer 18 and
the copper sulfate bath 20.
[0008] The copper oxidation reaction which takes place at the
oxidizing surface 22 of the anode 16 is illustrated by the
following reaction formula (1):
Cu.fwdarw.Cu.sup.+++2e.sup.- (1)
[0009] The oxidized copper cation reaction product forms ionic
copper sulfate in solution with the sulfate anion in the bath
20:
Cu.sup.+++SO.sub.4.sup.--.fwdarw.Cu.sup.++SO.sub.4.sup.-- (2)
[0010] At the cathode/wafer 18, the electrons harvested from the
anode 16 flow through the wiring 38 and reduce copper cations in
solution in the copper sulfate bath 20 to electroplate the reduced
copper onto the patterned surface 19a of the cathode/wafer 18:
Cu.sup.+++2e.sup.-.fwdarw.Cu (3)
[0011] As the anode 16 is consumed during the electroplating
process, small quantities of solid copper sulfate or "anode fines"
tend to precipitate at the interface between the copper sulfate
bath 20 and the oxidizing surface 22 of the anode 16 to form a
copper precipitate or sludge on the oxidizing surface 22.
[0012] As shown in FIG. 2, during the electroplating process air
pressure 26 is applied against a thrust pad 24, which in turn
applies pressure through a contact ring (not shown) that is
disposed in electrical contact with the current source 12 and
presses against the backside 19 of the cathode/wafer 18. The
pressure exerted by the contact ring against the backside 19 of the
cathode/wafer 18 increases the ohmic contact between the contact
ring and the cathode/wafer 18, thus enhancing electroplating of the
copper or other metal on the patterned surface 19a of the
cathode/wafer 18. The air pressure 26 is typically the same
throughout all regions on the entire surface of the thrust pad 24.
Accordingly, substantially equal quantities of the electroplated
copper are applied to both the center region 18a and the edge
regions 18b of the cathode/wafer 18.
[0013] After the electroplating process, some excess electroplated
metal must typically be removed from the edge regions 18b of the
cathode/wafer 18 since excess metal in the edge regions 18b is
potentially a significant source of contaminant particles during
subsequent processing of the wafer 18. This excess metal removal
process is typically carried out using an edge bevel clean process
that is integrated into the electrochemical plating apparatus.
However, such edge bevel cleaning of wafers required after
electroplating is a common source of process flow bottlenecking and
hinders orderly and efficient flow of the electroplating process
sequence.
[0014] It has been found that the quantity of metal electroplated
onto the edge region of a substrate can be reduced by the
application of reduced-magnitude pressure to the edge region of the
substrate during electrochemical plating, thus reducing the ohmic
contact between the contact ring and the edge region of the
substrate. This eliminates the need for edge bevel cleaning of
substrates after electrochemical plating and facilitates efficient
and orderly flow of substrates and increases throughput of
electrochemically-plated substrates throughout a process flow
sequence during the fabrication of semiconductor integrated
circuits.
[0015] Accordingly, an object of the present invention is to
provide a new and improved thrust pad assembly which can be adapted
to an electrochemical plating system.
[0016] Another object of the present invention is to provide a new
and improved thrust pad which is capable of applying pressure of
reduced magnitude against the edge region of a substrate to reduce
or eliminate the deposition of excess quantities of a metal on the
edge region during electrochemical plating of the substrate.
[0017] Still another object of the present invention is to provide
a new and improved thrust pad assembly which generates zones of
variable pressure against a substrate in the electrochemical
plating of the substrate.
[0018] Yet another object of the present invention is to provide a
new and improved thrust pad assembly which is capable of reducing
or eliminating the need for edge bevel cleaning of substrates after
electrochemical plating.
[0019] A still further object of the present invention is to
provide a new and improved thrust pad assembly which significantly
increases throughput of substrates during electrochemical
plating.
[0020] Another object of the present invention is to provide a
novel method for electroplating a metal onto a substrate.
SUMMARY OF THE INVENTION
[0021] In accordance with these and other objects and advantages,
the present invention is generally directed to a new and improved
thrust pad assembly which is capable of reducing the quantity of
metal electroplated onto the edge region of a substrate to
eliminate or reduce the need for edge bevel cleaning or removal of
excess metal from the substrate after the electroplating process.
The thrust pad assembly typically includes an air platen through
which air is applied at variable pressures to the central and edge
regions, respectively, of a thrust pad. The thrust pad applies
pressure to a contact ring connected to an electroplating voltage
source. The contact ring applies relatively less pressure to the
edge region than to the central region of the substrate, thereby
reducing the ohmic contact between the contact ring and the edge
region of the substrate. Therefore, excess electroplating of the
metal onto the edge regions of the substrate is eliminated or
substantially reduced.
[0022] The present invention further includes a method of
electroplating a metal on a substrate. The method includes
providing a substrate, providing a contact ring in contact with the
substrate, providing the contact ring and the substrate in an
electrolyte bath, providing an anode in the electrolyte bath,
applying a voltage to the contact ring and the anode, applying a
central pressure to a central region on the substrate, and applying
a peripheral pressure which is less than the central pressure to an
edge region on the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention will now be described, by way of example, with
reference to the accompanying drawings, in which:
[0024] FIG. 1 is a schematic view of a typical conventional
electrochemical plating system for the electrochemical plating of a
metal layer onto a substrate;
[0025] FIG. 2 is a schematic view of a typical conventional thrust
pad assembly for an electrochemical plating system;
[0026] FIG. 3 is a cross-sectional, partially schematic, view of a
thrust pad assembly in accordance with the present invention;
[0027] FIG. 4 is a schematic view of an electrochemical plating
system in implementation of the thrust pad assembly of the present
invention;
[0028] FIG. 5 is a top view of an air platen element in an
illustrative embodiment of the thrust pad assembly of the present
invention; and
[0029] FIG. 6 is a graph illustrating the relationship between
plating thickness (on the Y-axis) and pressure (on the X-axis)
applied by the thrust pad assembly of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] The present invention has particularly beneficial utility in
the electroplating of copper or other metals onto a semiconductor
wafer substrate in the fabrication of integrated circuits on the
substrate. However, the invention is not so limited in application,
and while references may be made to such semiconductor wafer
substrate and integrated circuits, the invention may be more
generally applicable to electroplating metals on substrates in a
variety of industrial applications.
[0031] The present invention is generally directed to a new and
improved thrust pad assembly which is suitable for preventing
deposition of excess quantities of metal onto the edge or
peripheral region of a substrate as copper or other metal is
electroplated onto the substrate in the fabrication of
semiconductor integrated circuits on the substrate. The thrust pad
assembly eliminates the need for edge bevel cleaning or removal of
excess metal from the edge region of the substrate after the
electroplating process. The thrust pad assembly typically includes
an air platen through which air is applied at variable pressures to
the central and edge regions, respectively, of a thrust pad. The
thrust pad, in turn, transmits this variable pressure to a contact
ring which is electrically connected to the electroplating current
source. The thrust pad applies relatively less pressure to the edge
region than to the central region of the substrate, thus reducing
ohmic contact between the contact ring and the edge region of the
substrate. Electrical resistance between the anode and the edge
region of the substrate is reduced with respect to the electrical
resistance between the anode and the central region of the
substrate. This variable pressure application to the substrate, and
resulting disparity in electrical resistance, is used to control
the substrate plating shape such that excess electroplating of the
metal onto the edge region of the substrate is reduced or
eliminated while electroplating of the metal onto the central
region of the substrate remains optimal.
[0032] The present invention further contemplates a method of
electroplating a metal on a substrate. The method includes
providing a substrate, providing a contact ring in contact with the
substrate, immersing the contact ring and the substrate in an
electrolyte bath, immersing an anode in the electrolyte bath,
applying a voltage to the contact ring and the anode, applying a
central pressure to a central region on the substrate, and applying
a peripheral pressure which is less than the central pressure to an
edge region on the substrate.
[0033] Referring to FIGS. 3-5, an illustrative embodiment of the
thrust pad assembly of the present invention is generally indicated
by reference numeral 40. The thrust pad assembly 40 includes a
generally disk-shaped air platen 42 having a circular central
region 42a and an annular edge region 42b surrounding the central
region 42a, as shown in FIG. 5. In a typical embodiment, the
central region 42a represents typically from about 50% to about 80%
of the total surface area of the air platen 42, whereas the
encircling edge region 42b represents typically from about 20% to
about 50% of the total surface area of the air platen 42. Multiple
central air openings 44 extend through the central region 42a of
the air platen 42, and multiple peripheral air openings 46 extend
through the edge region 42b of the air platen 42. As shown in FIG.
3, the central air openings 44 are provided in pneumatic
communication with a central air source 76 of central air pressure
45, and the peripheral air openings 46 are provided in pneumatic
communication with a peripheral air source 77 of peripheral air
pressure 47.
[0034] As further shown in FIG. 3, an electrically-conductive
contact ring 50 extends downwardly from the bottom surface of the
air platen 42, and a thrust pad 48 is provided in the contact ring
50. The thrust pad 48 is typically a resilient material such as
rubber. As shown in FIG. 3, the central air openings 44 and the
peripheral air openings 46 of the air platen 42 communicate with
the upper surface 49 of the thrust pad 48. A wafer clamp 52 (shown
in phantom) removably secures a cathode/wafer 54 to the bottom
surface of the contact ring 50, typically in conventional
fashion.
[0035] Referring to FIG. 4, a schematic of an electroplating system
60 which is suitable for implementation of the present invention is
shown. The electroplating system 60 typically includes a bath
container 64 in which a typically copper anode 66 and the thrust
pad assembly 40 to which is mounted the cathode/wafer 54 are
placed, the cathode/wafer 54 being the semiconductor wafer that is
to be electroplated with the copper or other metal. A negative
terminal 62a of an adjustable current source 62 is connected to the
contact ring 50 of the thrust pad assembly 40 through wiring 67. A
positive terminal 62b of the adjustable current source 62 is
connected to the anode 66 through wiring 68. The bath container 64
holds an electroplating bath 70 typically of acid copper sulfate
(CuSO.sub.4) solution, for example, which may include an additive
for filling of submicron features and leveling the surface of the
copper electroplated on the wafer 54, as is known by those skilled
in the art. The electroplating system 60 may include additional
features such as a bypass pump/filter (not shown) connected to the
bath container 64 and an electrolyte holding tank (not shown)
connected to the the bypass pump/filter and to the bath container
64 to facilitate the addition of electrolytes to the bath 70 and
circulation of the bath 70, as needed.
[0036] Referring next to FIGS. 3 and 4, in application of the
thrust pad assembly 40, the thrust pad assembly 40 is initially
assembled in the bath container 64, with the clamp 52 (FIG. 3)
attaching the wafer 54 to the contact ring 50, and the anode 66 and
the thrust pad assembly 40 with the cathode/wafer 66 are immersed
in the electrolyte bath 70. The electroplating system 60 is
operated typically in conventional fashion to electroplate the
metal from the metal electrolyte solution in the bath 70, onto the
patterned surface 57a of the wafer 54. Accordingly, the current
source 62 applies a selected voltage potential, typically at room
temperature, between the anode 66 and the cathode/wafer 54. This
voltage potential creates a magnetic field around the anode 66 and
the cathode/wafer 54, which magnetic field affects the distribution
of the metal ions in the electrolyte bath 70. In a typical copper
electroplating application, a voltage potential of about 2 volts
may be applied for about 2 minutes, and a current of about 4.5 amps
flows between the anode 66 and the cathode/wafer 54. Consequently,
the metal is oxidized typically at the upper oxidizing surface of
the anode 66 as electrons from the metal anode 66 reduce the ionic
metal in the electrolyte solution bath 70 to form a substantially
corrosion-resistant electroplated metal layer 74 on the patterned
surface 57a of the wafer 54, as shown in FIG. 4, at the interface
between the cathode/wafer 54 and the electrolyte bath 70.
[0037] As the metal layer 74 is electroplated onto the wafer 54,
the contact ring 50 of the thrust pad assembly 40 applies pressure
of variable magnitude against the backside 57 of the wafer 54, as
follows. As shown in FIG. 3, central air pressure 45 is directed
from the central air source 76 through the respective central air
openings 44 of the air platen 42 and against the upper surface 49
of the thrust pad 48 at a pressure of typically greater than about
14 psi. Similarly, peripheral air pressure 47 is directed from the
peripheral air source 77 through the respective peripheral air
openings 46 of the air platen 42 and against the upper surface 49
of the thrust pad 48 at a pressure of typically less than about 14
psi. Accordingly, the central portion of the contact ring 50
applies a pressure of typically greater than about 14 psi to the
backside 57 of the wafer 54, whereas the peripheral portion of the
contact ring 50 applies a pressure of typically less than about 14
psi to the backside 57 of the wafer 54. Because the ohmic contact
between the contact ring 50 and the wafer 54 is directly
proportional to the pressure applied by the contact ring 50 against
the wafer backside 57, the electrical resistance between the anode
66 and the cathode/wafer 54 at the edge region 54b of the wafer 54
is correspondingly less than the electrical resistance between the
anode 66 and the cathode/wafer 54 at the center region 54a of the
wafer 54. Consequently, the electroplated metal 57a is
correspondingly thicker at the center region 54a than at the edge
region 54b of the wafer 54 for a given period of electroplating
time. Typically, the electroplating process is carried out for a
period of typically about 2 minutes to deposit an electroplated
metal 74 having a thickness of typically at least about 7,000
angstroms at the center region 54a and a thickness of typically
about 500-1000 angstroms at the edge region 54b of the wafer
54.
[0038] It will be appreciated by those skilled in the art that
because the thickness of the electroplated metal 74 at the edge
region 54b of the wafer 54 is attenuated with respect to the
thickness of the electroplated metal 74 at the center region 54a
throughout the electroplating process, electroplating of excessive
quantities of the metal layer 74 at the edge region 54b of the
wafer 54 is prevented. Accordingly, there is no need to subject the
wafer 54 to edge bevel clean methods which would otherwise be
needed to remove excess electroplated metal from the edge region
54b. This eliminates process bottlenecking at the electroplating
station and promotes an orderly and efficient flow of wafers
through the electroplating process.
[0039] Referring next to the graph of FIG. 6, wherein the
relationship of pressure applied against the backside of a wafer is
shown in relation to the thickness of metal electroplated onto the
wafer. As indicated by reference numeral 50, when a pressure of
from about 0 psi to about 13 psi is applied to the backside of the
wafer, the thickness of metal electropated onto the wafer is from
typically about 100 to about 500 angstroms. When a pressure of
greater than about 14 psi is applied to the backside of the wafer,
the thickness of metal electroplated onto the wafer is about 7,000
angstroms. As indicated by reference numeral 60, this thickness
gradually increases at pressures above about 23 psi.
[0040] While the preferred embodiments of the invention have been
described above, it will be recognized and understood that various
modifications can be made in the invention and the appended claims
are intended to cover all such modifications which may fall within
the spirit and scope of the invention.
* * * * *