U.S. patent application number 10/823840 was filed with the patent office on 2004-10-21 for electrical bias during wafer exit from electrolyte bath.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Lubomirsky, Dmitry, Yang, Michael.
Application Number | 20040206628 10/823840 |
Document ID | / |
Family ID | 33162392 |
Filed Date | 2004-10-21 |
United States Patent
Application |
20040206628 |
Kind Code |
A1 |
Lubomirsky, Dmitry ; et
al. |
October 21, 2004 |
Electrical bias during wafer exit from electrolyte bath
Abstract
Embodiments of the invention generally provide a method for
removing a substrate from a processing fluid contained in a
processing cell. The method includes tilting the substrate to a
tilt angle, rotating the substrate, vertically moving the substrate
upward out of the processing fluid, and applying an electrical
removal bias to the substrate during the vertical movement of the
substrate out of the processing fluid.
Inventors: |
Lubomirsky, Dmitry;
(Cupertino, CA) ; Yang, Michael; (Palo Alto,
CA) |
Correspondence
Address: |
PATENT COUNSEL
APPLIED MATERIALS, INC.
Legal Affairs Department
P.O. Box 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
33162392 |
Appl. No.: |
10/823840 |
Filed: |
April 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60463861 |
Apr 18, 2003 |
|
|
|
Current U.S.
Class: |
205/137 ;
205/157; 257/E21.175 |
Current CPC
Class: |
C25D 5/627 20200801;
C25D 7/123 20130101; H01L 21/2885 20130101; C25D 5/611 20200801;
C25D 21/00 20130101; C25D 21/12 20130101; C25D 17/001 20130101 |
Class at
Publication: |
205/137 ;
205/157 |
International
Class: |
C25D 005/00 |
Claims
What is claimed is:
1. A method for removing a substrate from a plating cell,
comprising: removing the substrate from a plating solution
contained in the plating cell; applying a plating bias to a plating
surface of the substrate during the removing step; and controlling
the plating bias to maintain a constant current density across an
immersed portion of the plating surface during the removing
step.
2. The method of claim 1, wherein controlling comprises using at
least one of a current control and a voltage control system to
maintain the constant current density.
3. The method of claim 2, wherein the constant current density is
between about 0.5 mA/cm.sup.3 and about 3 mA/cm.sup.3.
4. The method of claim 1, wherein removing further comprises
rotating the substrate during the removing.
5. The method of claim 4, wherein removing further comprises
tilting the substrate such that the plating surface is positioned
at an angle with respect to horizontal.
6. The method of claim 1, wherein the plating bias has a voltage of
between about 0.3 volts and about 5 volts.
7. The method of claim 1, wherein removing further comprises
rotating the substrate between about 5 rpm and about 60 rpm.
8. A method for removing a substrate from a plating solution,
comprising: moving the substrate out of the plating solution;
rotating the substrate during the moving; tilting the substrate to
a tilt angle during the removing; and applying a forward bias to
the substrate during the moving.
9. The method of claim 8, wherein tilting the substrate comprises
maintaining a constant tilt angle during the moving.
10. The method of claim 8, wherein tilting the substrate comprises
at least one of increasing or decreasing the tilt angle during the
moving.
11. The method of claim 8, further comprising controlling the
application of the forward bias to maintain a constant current
density across an immersed portion of the substrate during the
moving.
12. The method of claim 11, wherein controlling the forward bias
comprises using a current controller.
13. The method of claim 11, wherein controlling the forward bias
comprises using a time dependent controller.
14. The method of claim 8, wherein the forward bias generates a
current density on a surface of the substrate of between about 0.5
mA/cm.sup.3 and about 3 mA/cm.sup.3.
15. The method of claim 8, wherein the substrate is rotated between
about 10 rpm and about 100 rpm during the moving.
16. The method of claim 8, wherein the forward bias is configured
to generate a plating rate sufficient to overcome etching of a
layer deposited on the substrate.
17. A method for removing a substrate from a processing fluid
contained in a processing cell, comprising: tilting the substrate
to a tilt angle; rotating the substrate; moving the substrate
upward out of the processing fluid; and. applying an electrical
removal bias configured to generate a constant current density
across a substrate surface during the moving of the substrate out
of the processing fluid.
18. The method of claim 17, wherein the tilting, rotating, and the
upward movement are conducted simultaneously.
19. The method of claim 18, wherein the tilt angle is between about
5.degree. and about 30.degree..
20. The method of claim 18, wherein the substrate is rotated at
between about 20 rpm and about 60 rpm.
21. The method of claim 17, wherein the upward movement has a
duration of between about 0.5 seconds and 2 seconds.
22. The method of claim 18, applying the removal bias comprises
applying a constant current density across an immersed surface of
the substrate of between about 0.5 mA/cm.sup.3 and about 4
mA/cm.sup.3 to the surface of the substrate.
23. The method of claim 17, wherein applying the removal bias
comprises generating a constant current density of between about
1.5 mA/cm.sup.3 and about 3 mA/cm.sup.3 across an immersed surface
of the substrate.
24. The method of claim 17, wherein applying the removal bias
comprises applying a voltage of between about 0.4 volts and about 4
volts.
25. The method of claim 17, wherein applying the removal bias
further comprises maintaining a constant current density across an
immersed surface area of the substrate during the upward movement
of the substrate out of the processing fluid.
26. A method for removing a semiconductor substrate from an
electrochemical plating solution, comprising: tilting the substrate
to an angle with respect to horizontal; rotating the substrate at a
rotation rate of between about 20 rpm and about 60 rpm; vertically
moving the substrate out of the plating solution; and applying a
forward bias to an immersed surface of the substrate during the
vertically moving.
27. The method of claim 26, wherein the forward bias is adjusted
during the vertical moving to generate a constant current density
across an immersed surface area of the substrate.
28. The method of claim 26, wherein the tilting, rotating, moving,
and applying a forward bias are conducted simultaneously.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. provisional patent
application serial No. 60/463,861, filed Apr. 18, 2003, which is
herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the invention generally relate to a method
for withdrawing or removing a semiconductor substrate from a
processing fluid.
[0004] 2. Description of the Related Art
[0005] Metallization of sub-quarter micron sized features is a
foundational technology for present and future generations of
integrated circuit manufacturing processes. More particularly, in
devices such as ultra large scale integration-type devices, i.e.,
devices having integrated circuits with more than a million logic
gates, the multilevel interconnects that lie at the heart of these
devices are generally formed by filling high aspect ratio, i.e.,
greater than about 4:1, interconnect features with a conductive
material, such as copper. Conventionally, deposition techniques
such as chemical vapor deposition (CVD) and physical vapor
deposition (PVD) have been used to fill these interconnect
features. However, as the interconnect sizes decrease and aspect
ratios increase, void-free interconnect feature fill via
conventional metallization techniques becomes increasingly
difficult. Therefore, plating techniques, i.e., electrochemical
plating (ECP) and electroless plating, have emerged as promising
processes for void free filling of sub-quarter micron sized high
aspect ratio interconnect features in integrated circuit
manufacturing processes.
[0006] In an ECP process, for example, sub-quarter micron sized
high aspect ratio features formed into the surface of a substrate
(or a layer deposited thereon) may be efficiently filled with a
conductive material. ECP plating processes are generally two stage
processes, wherein a seed layer is first formed over the surface
features of the substrate (generally through PVD, CVD, or other
deposition process in a separate tool), and then the surface
features of the substrate are exposed to an electrolyte solution
(in the ECP tool), while an electrical bias is applied between the
seed layer and a copper anode positioned within the electrolyte
solution. The electrolyte solution generally contains a source of
metal that is be plated onto the surface of the substrate, and
therefore, the application of the electrical bias causes the metal
source to be plated onto the biased seed layer, thus depositing a
layer of the ions on the substrate surface that may fill the
features.
[0007] However, the decreasing size of features being filled by ECP
processes in semiconductor processing requires that the plating
process generate minimal defects in order to produce viable
devices. Research has shown that a primary cause of plating defects
is the presence of air bubbles on the surface of the substrate
being plated. Generally, air bubbles are formed on the surface of
the substrate during the process of immersing the substrate into
the plating solution. More particularly, as the substrate is
transitioned from the air into the plating solution, small bubbles
of air often adhere to the surface of the substrate. These air
bubbles prevent the electrolyte solution from contacting the
substrate surface at that particular location, and therefore,
prevent plating at that location, which in turn forms a defect in
the plated layer. Bubbles adhering to the substrate surface during
immersion may also dislodge and travel across the surface of the
substrate once its immersed in the plating solution, which may
generate multiple defects in multiple locations along the bubble
path. Therefore, it is desirable to immerse substrates into
electrolyte solutions using an immersion method that is configured
to minimize bubble formation. The immersion process also generally
includes applying a forward or plating bias to the substrate during
the immersion process. This bias is generally applied to counteract
etching of the seed layer on the substrate by the plating solution,
which is generally an acidic solution, as will be discussed
herein.
[0008] Further, once a substrate has been processed in an
electrochemical plating cell, the substrate is generally removed
from the cell for processing in other cells, such as bevel clean or
spin rinse dry cells, for example. However, there is an inherent
delay in time between the time when substrate processing is
completed and the time when the substrate is removed from the
plating solution, which is generally a low pH solution. During this
time period, which may be as little as 0.1 seconds or as much as
several seconds, the plating solution is able to react with and
possibly etch the layer that was just plated onto the substrate in
the plating cell. This reaction or etching of the plated layer has
been shown to detrimentally affect the surface characteristics of
the plated layer. More particularly, post processing etching of the
plated layer by the acidic solution has been shown to affect the
surface roughness and reflectivity of the plated layer. This is
important to plating processes, as the surface roughness and
reflectivity of a plated layer may have a substantial impact on the
effectiveness of subsequent processes, such as defect detection and
polishing processes.
[0009] Another challenge presented by conventional withdrawal
schemes is additive consumption. It is generally known in the art
that plating solution additives adsorb to the plated surface. As
such, when the substrate is removed from the plating solution after
a plating process has been completed, those additives that have
adsorbed onto the surface are inherently removed also. Thus,
withdrawal of the substrate substantially contributes to additive
consumption.
[0010] Therefore, there is a need for a method for removing or
withdrawing a substrate from an electrochemical plating solution,
wherein the method is configured to prevent etching of the plated
layer by the plating solution, and further, to minimize additive
consumption.
SUMMARY OF THE INVENTION
[0011] Embodiments of the invention generally provide a method for
immersing a substrate into a plating solution with minimal bubble
formation and a method for withdrawing the substrate from the
plating solution. The immersion method generally includes biasing
the substrate during the immersion process to prevent the plating
solution from etching the substrate surface, and in particular, the
thin seed layer formed thereon, prior to beginning the plating
process. The immersion method further includes tilting and/or
rotating the substrate during the immersion process to minimize
bubble formation and adherence to the substrate surface during the
immersion process. Once the substrate is immersed and a plating
process is completed, the method of the invention includes
withdrawing the substrate from the solution while applying a
removal bias to the substrate. The removal bias is a forward or
plating bias configured to prevent the plating solution from
etching the surface of the layer that was just plated onto the
substrate. As such, the removal bias is configured to prevent the
plating solution from etching the surface of the plated layer and
generating a roughened or less reflective surface that may be
detrimental to post plating processes.
[0012] Embodiments of the invention may further provide a method
for removing a substrate from a processing fluid contained in a
processing cell. The method includes tilting the substrate to a
tilt angle, rotating the substrate, vertically moving the substrate
upward out of the processing fluid, and applying an electrical
removal bias to the substrate during the vertical movement of the
substrate out of the processing fluid.
[0013] Embodiments of the invention may further provide a method
for removing a substrate from a plating cell. The method includes
vertically actuating the substrate to remove the substrate from a
plating solution contained in the plating cell, applying an
electrical removal bias to the substrate during the vertical
actuation of the substrate, and controlling the electrical removal
bias to maintain a constant current density across a plating
surface of the substrate during the vertical actuation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0015] FIG. 1 is a top plan view of one embodiment of an
electrochemical plating system of the invention.
[0016] FIG. 2 illustrates a partial perspective and sectional view
of an exemplary plating cell used in the plating system of the
invention.
[0017] FIG. 3 illustrates a sectional view of a plating cell and
head assembly during a substrate transfer process.
[0018] FIG. 4 illustrates a sectional view of a plating cell and
head assembly during a tilting process.
[0019] FIG. 5 illustrates a sectional view of a plating cell and
head assembly during an immersion process, i.e., during vertical
actuation.
[0020] FIG. 6 illustrates a sectional view of a plating cell and
head assembly during a tilting process after immersion.
[0021] FIG. 7 illustrates a sectional view of a plating cell and
head assembly during an immersion process wherein the head assembly
is positioning the substrate deeper in the plating solution.
[0022] FIG. 8 illustrates a sectional view of a plating cell and
head assembly positioned in a processing position.
[0023] FIG. 9 illustrates a view of the substrate area during
immersion.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Embodiments of the invention generally provide methods for
immersing and removing a substrate from an electrochemical plating
solution. The immersion method of the invention is configured to
minimize plating defects by minimizing bubble formation and
adhesion to the substrate surface during the immersion process. The
immersion method is further configured to minimize etching of a
seed layer formed on the surface of the substrate via application
of a loading bias to the substrate during the immersion process.
The withdrawal method of the invention is configured to prevent
etching of the surface of the plated layer via application of a
removal bias to the substrate during the time period between the
termination of the plating process and the time when the substrate
is removed from the plating cell or plating solution.
[0025] Immersion Mechanics
[0026] The immersion method of the invention generally includes
driving or actuating the substrate into the plating solution using
a combination of a tilt and swing immersion processes. More
particularly, the substrate may be tilted at an angle with respect
to horizontal, and then vertically actuated toward the plating
solution, while being rotated, which immerses the substrate and
maintains a constant angle between the substrate and the upper
surface of the plating solution. The combination of the tilt and
rotation causes bubbles to be dislodged from the substrate surface
and carried away from the substrate surface as a result of the
buoyancy of the bubbles. Further, the tilt angle of the substrate
may be adjusted during the immersion process, thus generating a
swing or pendulum type motion, which also urges bubbles attached to
the substrate surface to be dislodged therefrom.
[0027] FIG. 1 illustrates a top plan view of an ECP system 100 of
the invention. ECP system 100 includes a factory interface (FI)
130, which is also generally termed a substrate loading station.
Factory interface 130 includes a plurality of substrate loading
stations configured to interface with substrate containing
cassettes 134. A robot 132 is positioned in factory interface 130
and is configured to access substrates contained in the cassettes
134. Further, robot 132 also extends into a link tunnel 115 that
connects factory interface 130 to processing mainframe or platform
113. The position of robot 132 allows the robot to access substrate
cassettes 134 to retrieve substrates therefrom and then deliver the
substrates to one of the processing cells 114, 116 positioned on
the mainframe 113, or alternatively, to the annealing station 135.
Similarly, robot 132 may be used to retrieve substrates from the
processing cells 114, 116 or the annealing chamber 135 after a
substrate processing sequence is complete. In this situation robot
132 may deliver the substrate back to one of the cassettes 134 for
removal from system 100.
[0028] The anneal chamber 135 generally includes a two position
annealing chamber, wherein a cooling plate/position 136 and a
heating plate/position 137 are positioned adjacently with a
substrate transfer robot 140 positioned proximate thereto, e.g.,
between the two stations. The robot 140 is generally configured to
move substrates between the respective heating 137 and cooling
plates 136. Further, although the anneal chamber 135 is illustrated
as being positioned such that it is accessed from the link tunnel
115, embodiments of the invention are not limited to any particular
configuration or placement. As such, the anneal chamber may be
positioned in communication with the mainframe 113.
[0029] As mentioned above, ECP system 100 also includes a
processing mainframe 113 having a substrate transfer robot 120
centrally positioned thereon. Robot 120 generally includes one or
more arms/blades 122, 124 configured to support and transfer
substrates thereon. Additionally, the robot 120 and the
accompanying blades 122, 124 are generally configured to extend,
rotate, and vertically move so that the robot 120 may insert and
remove substrates to and from a plurality of processing cells 102,
104, 106, 108, 110, 112, 114, 116 positioned on the mainframe 113.
Similarly, factory interface robot 132 also includes the ability to
rotate, extend, and vertically move its substrate support blade,
while also allowing for linear travel along the robot track that
extends from the factory interface 130 to the mainframe 113.
Generally, process cells 102, 104, 106, 108, 110, 112, 114, 116 may
be any number of processing cells utilized in an electrochemical
plating platform. More particularly, the process cells may be
configured as electrochemical plating cells, rinsing cells, bevel
clean cells, spin rinse dry cells, substrate surface cleaning
cells, electroless plating cells, metrology inspection stations,
and/or other processing cells that may be beneficially used in
conjunction with a plating platform. Each of the respective
processing cells and robots are generally in communication with a
process controller 111, which may be a microprocessor-based control
system configured to receive inputs from both a user and/or various
sensors positioned on the system 100 and appropriately control the
operation of system 100 in accordance with the inputs.
[0030] In the exemplary plating system illustrated in FIG. 1, the
processing cells may be configured as follows. Processing cells 114
and 116 may be configured as an interface between the wet
processing stations on the mainframe 113 and the dry processing
regions in the link tunnel 115, annealing chamber 135, and the
factory interface 130. The processing cells located at the
interface locations may be spin rinse dry cells and/or substrate
cleaning cells. More particularly, each of cells 114 and 116 may
include both a spin rinse dry cell and a substrate cleaning cell in
a stacked configuration. Cells 102, 104, 110, and 112 may be
configured as plating cells, either electrochemical plating cells
or electroless plating cells, for example. Cells 106, 108 may be
configured as substrate bevel cleaning cells. Additional
configurations and implementations of an electrochemical processing
system are illustrated in commonly assigned U.S. patent application
Ser. No. 10/435,121 filed on Dec. 19, 2002 entitled
"Multi-Chemistry Electrochemical Processing System", which is
incorporated herein by reference in its entirety.
[0031] FIG. 2 illustrates a partial perspective and sectional view
of an exemplary plating cell 200 that may be implemented in
processing cells 102, 104, 110, and 112. The electrochemical
plating cell 200 generally includes an outer basin 201 and an inner
basin 202 positioned within outer basin 201. Inner basin 202 is
generally configured to contain a plating solution that is used to
plate a metal, e.g., copper, onto a substrate during an
electrochemical plating process. During the plating process, the
plating solution is generally continuously supplied to inner basin
202, and therefore, the plating solution continually overflows the
uppermost point (generally termed a "weir") of inner basin 202 and
is collected by outer basin 201 and drained therefrom for chemical
management and/or recirculation. Plating cell 200 is generally
positioned at a tilt angle, i.e., the frame portion 203 of plating
cell 200 is generally elevated on one side such that the components
of plating cell 200 are tilted between about 3.degree. and about
30.degree., or generally between about 4.degree. and about
10.degree. for optimal results. The frame member 203 of plating
cell 200 supports an annular base member 204 on an upper portion
thereof. Since frame member 203 is elevated on one side, the upper
surface of base member 204 is generally tilted from the horizontal
at an angle that corresponds to the angle of frame member 203
relative to a horizontal position. Base member 204 includes an
annular or disk shaped recess formed into a central portion
thereof, the annular recess being configured to receive a generally
disk shaped anode member 205. Base member 204 further includes a
plurality of fluid inlets/drains 209 extending from a lower surface
thereof. Each of the fluid inlets/drains 209 are generally
configured to individually supply or drain a fluid to or from
either the anode compartment or the cathode compartment of plating
cell 200, wherein the anode compartment generally includes the
volume in the cell below the membrane 208 and the cathode
compartment includes the volume in the cell above the membrane.
Anode member 205 generally includes a plurality of slots 207 formed
therethrough, wherein the slots 207 are generally positioned in
parallel orientation with each other across the surface of the
anode 205. The parallel orientation allows for dense fluids
generated at the anode surface during plating to flow downwardly
across the anode surface and into one of the slots 207. Plating
cell 200 further includes a membrane support assembly 206. Membrane
support assembly 206 is generally secured at an outer periphery
thereof to base member 204, and includes an interior region
configured to allow fluids to pass therethrough. A membrane 208 is
stretched across a lower surface of the support 206 and operates to
fluidly separate a catholyte chamber and anolyte chamber portions
of the plating cell. The membrane support assembly 206 may include
an o-ring type seal positioned near a perimeter of the membrane
208, wherein the seal is configured to prevent fluids from
traveling from one side of the membrane 208 secured on the membrane
support 206 to the other side of the membrane 208. A diffusion
plate 210, which is generally a porous ceramic disk member, is
configured to generate a substantially laminar flow or even flow of
fluid in the direction of the substrate being plated, and (not
shown) is positioned in the cell between membrane 208 and the
substrate being plated. The exemplary plating cell is further
illustrated in commonly assigned U.S. patent application Ser. No.
10/268,284, which was filed on Oct. 9, 2002 under the title
"Electrochemical Processing Cell", claiming priority to U.S.
Provisional Application Serial No. 60/398,345, which was filed on
Jul. 24, 2002, both of which are incorporated herein by reference
in their entireties.
[0032] As noted above, in order to minimize defects in plated
films, bubbles adhering to the substrate surface during the process
of immersing the substrate into the plating solution contained in a
plating cell should be minimized. Therefore, embodiments of the
invention provide a method for immersing a substrate into a
processing fluid that generates minimal bubbles. The immersion
method of the invention begins with the process of loading a
substrate into a head assembly 300, as illustrated in FIG. 3. The
head assembly 300 generally includes a contact ring 302 and a
thrust plate assembly 304 that are separated by a loading space
306. A more detailed description of the contact ring 302 and thrust
plate assembly 304 may be found in commonly assigned U.S. patent
application Ser. No. 10/278,527, which was filed on Oct. 22, 2002
under the title "Plating Uniformity Control By Contact Ring
Shaping", which is hereby incorporated by reference in its
entirety. A robot, such as robot 120 illustrated in FIG. 1, is used
to position a substrate on the contact ring 302 via access space
306. More particularly, robot 120 may be a vacuum-type robot
configured to engage a backside of the substrate with a reduced
pressure engaging device. The substrate may then be supported in a
face down (production surface facing down) orientation with the
vacuum engaging device attached to the backside or non-production
surface of the substrate. The robot may then extend into contact
ring 302 via access space 306, lower to position the substrate on
the contact pins/substrate support surface of contact ring 302,
disengage the vacuum engaging device, raise to a withdrawal height,
and then withdraw from the contact ring 302 leaving the substrate
positioned thereon.
[0033] Once the substrate is positioned on the contact ring 302,
thrust plate assembly 304 may be lowered into a processing
position. More particularly, FIG. 3 illustrates thrust plate 304 in
a substrate loading position, i.e., thrust plate 304 is vertically
positioned above the lower surface of contact ring 302 such that
the access space 306 is maximized. In this position, robot 120 has
the most amount of space available to loading the substrate onto
the contact ring 302. However, once the substrate is loaded, thrust
plate 304 may be actuated vertically, i.e., in the direction
indicated by arrow 410 in FIG. 4, to engage the backside of the
substrate positioned on the contact ring 302. The engagement of the
thrust plate 304 with the backside of the substrate positioned on
the contact ring 302 operates to mechanically bias the substrate
against the electrical contact pins positioned on contact ring 302,
while also securing the substrate to the contact ring 302 for
processing.
[0034] Once the substrate is secured to the contact ring 302 by the
thrust plate 304, the lower portion of the head assembly 300, i.e.,
the combination of the contact ring 302 and the thrust plate 304,
are pivoted to a tilt angle. The lower portion of the head assembly
is pivoted to the tilt angle via pivotal actuation of the head
assembly about a pivot point 408. The lower portion of head
assembly 300 is actuated about pivot point 408, which causes
pivotal movement of the lower portion of head assembly 300 in the
direction indicated by arrow 409 in FIG. 4. The lower portion of
head assembly 300 and the plating surface of the substrate
positioned on the contact ring 302 are tilted to the tilt angle as
a result of the movement of head assembly 300, wherein the tilt
angle is defined as the angle between horizontal and the plating
surface/production surface of the substrate secured to the contact
ring 302. The tilt angle is generally between about 3.degree. and
about 30.degree., and more particularly, between about 3.degree.
and about 10.degree..
[0035] Once the head assembly 300 is tilted, it may be actuated in
the Z-direction to begin the immersion process. More particularly,
head assembly 300 may be actuated in the direction indicated by
arrow 501, as illustrated in FIG. 5, to bring the substrate
positioned in the contact ring 302 toward the plating solution
contained within the plating cell 504 positioned below head
assembly 300. Plating cell 504, which is generally similar to
plating cell 200 illustrated in FIG. 2, is configured to contain a
plating solution therein. The plating solution is generally
contained within the inner weir of the plating cell 504 and
overflows the uppermost point 502 of the inner weir. Therefore, as
head assembly 300 is moved toward plating cell 504, the lower side
of contact ring 302, i.e., the side of contact ring 302 positioned
closest plating cell 504 as a result of the tilt angle, contacts
the plating solution as the head assembly 300 is actuated toward
cell 502. The process of actuating head assembly 300 toward cell
502 may further include imparting rotational movement to contact
ring 302. Thus, during the initial stages of the immersion process,
contact ring 302 is being actuated in a vertical or Z-direction,
while also being rotated about a vertical axis extending upward
through head assembly 300. Generally, the vertical axis about which
contact ring 302 is rotated is generally orthogonal to the
substrate surface. The process of immersing the substrate into the
plating solution while applying a bias to the substrate is
described in commonly assigned U.S. patent application Ser. No.
09/766,060, filed on Jan. 18, 2001 entitled "Reverse Voltage Bias
for Use in Electro-Chemical Plating System," which claims benefit
of U.S. Pat. No. 6,258,220, filed Apr. 8, 1999, both of which are
hereby incorporated by reference in their entirety.
[0036] As the substrate becomes immersed in the plating solution
contained within plating cell 504, the Z-motion of head assembly
300 is terminated and the tilt position of contact ring 302 is
returned to a substantially horizontal position, as illustrated in
FIG. 6. The termination of the vertical or the Z-direction movement
is calculated to maintain the substrate in the plating solution
contained in cell 504 when the tilt angle is removed. Further,
embodiments of the invention contemplate that the removal of the
tilt angle, i.e., the return of contact ring 302 to a horizontal
position, may be conducted simultaneously with the vertical
movement of contact ring 302 into the plating solution. As such,
embodiments of the invention contemplate that the substrate may
first contact the plating solution with the substrate being
positioned at a tilt angle, and then the tilt angle may be returned
to horizontal while the substrate continues to be immersed into the
plating solution. This process generates a unique movement that
includes both vertical actuation and tilt angle actuation, which
has been shown to reduce bubble formation and adherence to the
substrate surface during the immersion process. Further, the
vertical and pivotal actuation of the substrate during immersion
process may also include rotational movement of contact ring 302,
which has been shown to further minimize bubble formation and
adherence to the substrate surface during the immersion
process.
[0037] Once the substrate is completely immersed into the plating
solution contained within cell 504, head assembly 300 may be
further actuated in a vertical direction (downward) to further
immerse the substrate into the plating solution, i.e., to position
the substrate farther or deeper into the plating solution, as
illustrated in FIG. 7. This process may also include rotating the
substrate, which operates to dislodge any bubbles formed during the
immersion process from the substrate surface. Once the substrate is
positioned deeper within the plating solution, the head assembly
300 may again be pivoted about pivot point 408, so the substrate
surface may be positioned at the tilt angle, as illustrated in FIG.
8. Further, inasmuch head assembly 300 just actuated the substrate
downward into the plating solution in the previous step, the
tilting motion illustrated in FIG. 8 generally will not raise the
surface of the substrate out of the plating solution on the high
side of the tilted contact ring. More particularly, since pivot
point 408 is positioned in the middle of head assembly 300, when
the head assembly pivots the contact ring 302 about pivot point
408, one side, of the contact ring 302 is immersed further into the
plating solution, while the opposing side of the contact ring 302
is raised upward toward the surface of the plating solution as a
result of the pivotal motion. Thus, since the substrate is intended
to be maintained within the plating solution once immersed therein,
head assembly 300 must be actuated further into the plating
solution in order to move the contact ring 302 from the horizontal
position illustrated in FIG. 7 to the tilted position illustrated
in FIG. 8 without raising at least a portion of the substrate out
of the plating solution. This final tilting motion of head assembly
300 generally corresponds to positioning contact ring 302 in a
processing position, i.e., a position where the substrate supported
by contact ring 302 is generally parallel to an anode positioned in
a lower portion of the plating cell 502. Further, positioning
contact ring 302 in the processing position may include further
actuating head assembly 300 toward the anode positioned in the
lower portion of the plating cell, so that the plating surface of
the substrate may be positioned at a particular distance from the
anode for the plating process.
[0038] Additionally, the immersion process of the invention may
include an oscillation motion, i.e., tilting in opposing or
different directions, to further enhance the bubble removal
process. More particularly, head assembly 300 may be tilted back
and forth between a first tilt angle and a second tilt angle in an
oscillatory manner, i.e., in a manner where the substrate is tilted
between a first angle and a second angle several times, once the
substrate is immersed in the plating solution. This tilting motion
may be conducted in a quick manner, i.e., from about 2 tilts per
second up to about 20 tilts per second. The tilting motion may be
accompanied by rotation, which further facilitates dislodging
bubbles that are adhering to the substrate surface.
[0039] The immersion process of the invention may also include
vertical oscillation of the substrate in the plating solution. More
particularly, once the substrate is immersed in the plating
solution, the substrate may be actuated up and down. When the
substrate is raised upward in the plating solution, the volume of
solution below the substrate is increased, and therefore, a rapid
flow of solution to the area below the substrate is generated.
Similarly, when the substrate is lowered, the volume decreases and
an outward flow of solution is generated. As such, actuation of the
substrate vertically, i.e. repeated upward and downward motions,
causes reversing or oscillating fluid flows to occur at the
substrate surface. The addition of rotation to the oscillation
further increases the oscillating fluid flows across the substrate
surface. These oscillating fluid flows have been shown to improve
bubble removal, and therefore, decrease defects.
[0040] The immersion process of the invention may further include
oscillating the rotation of the substrate once it is immersed in
the plating solution. More particularly, the substrate is generally
rotated during both the immersion and plating processes. This
rotation generally increases fluid flow at the substrate surface
via circulation of the depleted plating solution that is generated
at the substrate surface. These rotation and fluid flow
characteristics may also be used during the immersion process to
facilitate bubble removal. More particularly, embodiments of the
invention contemplate that the substrate may be rotated at varying
rotation rates and in varying directions during and/or after the
substrate is immersed. For example, once the substrate is immersed
in the solution, the substrate may first be rotated in a clockwise
direction for a predetermined period of time before the rotation
direction is switched to counter clockwise for a predetermined
period of time. The rotation direction may be switched several
times, or only once, depending upon the application.
[0041] Additionally, embodiments of the invention may implement a
combination of the oscillation methods described above. For
example, an immersion process of the invention may include tilt
actuation, rotational actuation, and vertical actuation, or any
combination thereof.
[0042] Substrate Immersion Bias
[0043] FIG. 9 illustrates a diagram of a substrate surface as the
substrate surface is being immersed into electrolyte solution
without being rotated and with the substrate tilted from horizontal
to a tilt angle. In this embodiment, substrate 907 begins the
immersion as the edge of the substrate first contacts the
electrolyte solution at a first edge 908 of substrate 907. As the
vertical motion of the substrate support member or head assembly
continues, the area of the substrate immersed in the electrolyte
solution proportionally increases, as illustrated by the shaded
area 909. It is to be noted, however, that the shaded area 909 does
not represent the total immersed area. Rather, area 109 generally
represents the most recently immersed area, and therefore, the area
from the edge of the substrate to the line labeled j+1 would
represent the total immersed area of the substrate at time J+1.
Therefore, and in order for a power supply to provide a constant
current density across the surface of the substrate during the
immersion process, the time varying area of the substrate being
immersed may be calculated, or otherwise estimated or determined,
and used to determine a time varying current necessary to provide a
constant current density across the area of the substrate immersed
in the electrolyte solution. As such, embodiments of the present
invention supply current to the substrate as a function of the
immersion speed of the substrate, as the immersion speed of the
substrate, i.e., the vertical rate at which the substrate is
immersed into the plating solution, directly corresponds to the
change of the immersed area of the substrate during the immersion
process. Additionally, although the substrate is generally rotated
during the immersion process, the area calculation will be
unchanged in non-rotation embodiments, as the rotation of the
substrate does not increase or decrease the area of the substrate
being immersed in the plating solution per unit time.
[0044] The calculation of the time varying area of the substrate
immersed in the electrolyte solution generally includes
incrementally calculating the area of minute sections of the
immersed portion of the substrate and summing the sections together
to obtain the total area immersed for a particular time. The
calculation and application of current to the substrate during the
immersion process is illustrated in co-pending and commonly
assigned U.S. patent application Ser. No. 10/135,546, entitled
Apparatus and Method for Regulating the Electrical Power Applied to
a Substrate During Immersion, filed on Apr. 29, 2002, which is
hereby incorporated by reference in its entirety. Further, although
the referenced application is generally directed to controlling an
immersion bias, Applicants contemplate that the methodology may be
utilized to control a removal bias, as will be further discussed
herein.
[0045] In one embodiment of the invention, the current supplied to
the substrate is increased as the immersion surface area increases
in accordance with a time calculation. For example, the total time
for an immersion process can be determined through experimentation.
Thereafter, a correlation between the elapsed time in the immersion
process and the immersed surface area can be determined through
calculation. As such, with the correlation between the elapsed time
and immersion area determined, the current and supply to the
substrate can then be determined in accordance with the increase in
the immersion time, as the time is proportional to the immersion
area. Therefore, knowing the correlation between the immersion time
and the immersion surface area, processing recipes can be modified
to include a proportional change in the current supplied to the
substrate during the immersion process so that a uniform current
density across the immersed surface area can be maintained
throughout the immersion process.
[0046] In another embodiment of the invention, a sensor may be used
to determine the exact radial or tilting position of the substrate
during the immersion process. As such, the position is transmitted
to the controller, which may then calculate the immersed area in a
real-time manner. The calculated, immersed area may then be used to
determine the current to be supplied to the substrate in order to
maintain a uniform current density across the immersed substrate
area. The granularity/incremental section sampling of the
measurement process may be increased simply by taking more
measurements per unit time, and therefore, adjusting the current
supplied to the immersed surface area more per unit time. Although
the end result of the present embodiment is to provide a uniform
current density across the immersed surface area of the substrate,
the present embodiment also provides for a uniform current density
across the immersed area of the substrate during nonuniform
immersion processes. For example, if the immersion speed of the
substrate is not constant or is not repeatable between respective
immersion processes, the invention may be utilized to maintain a
uniform current density across the immersed area of the substrate
regardless of the immersion speed, as the current calculation is
independent of the elapsed immersion time. Therefore, the feedback
loop type system of the present embodiment may provide advantages
over other embodiments of the invention in specific configurations
wherein the elapsed time of the immersion process is not constant
across several substrate immersions.
[0047] In order for the immersion bias applied to the substrate to
be effective in reducing the erosion or etching of the seed layer
by the acidic plating solution, the voltage and current applied
between the substrate and anode must be sufficient to generate a
plating rate that will equal or overcome the erosion or etching
rate of the solution on the seed layer. Generally, the voltage will
be in the range of between about 0.7 volts and about 20 volts.
Similarly, the current applied to the substrate is generally
configured to generate a constant current density across the
surface of the substrate of between about 0.5 mA/cm.sup.2 and about
3 mA/cm.sup.2. The actual current and/or voltage applied to the
substrate may be monitored and/or varied in order to maintain a
constant current density across the surface of the substrate.
[0048] Substrate Withdrawal Mechanics and Bias
[0049] Plating processes involve applying an electrical bias to the
substrate via the contact ring 302. The plating bias is a forward
bias, i.e., the plating bias is configured such that the substrate
is electrically charged to be more negative than the anode 205 in
the plating cell, so that the positively charged metal ions in the
plating solution will plate on the negatively charged substrate. In
conventional plating systems, once the plating process is
completed, the electrical bias is terminated and the substrate is
removed from the plating cell. However, as noted above,
conventional plating systems and methods generally include time
delay between the termination of the plating bias and the removal
of the substrate from the plating solution. During this time delay,
the substrate is in contact with the plating solution, and since
plating solutions are often acidic in nature, the plating solution
can etch the surface of the plated layer during the time delay.
This etching causes the smooth surface of the plated layer to
roughen and decrease in reflectivity, which is not beneficial to
subsequent processing steps, such as defect inspection and CMP
processes.
[0050] Therefore, the method and apparatus of the present invention
is configured to apply a forward substrate removal bias (the
substrate is negative relative to the anode) to the substrate
during the delay time and the removal process. The removal bias is
configured to prevent etching of the surface of the plated layer,
and therefore, the removal bias is configured to preserve the
smooth surface of the plated layer. The removal bias is generally
applied to the substrate immediately after the plating bias is
terminated, i.e., the transition from the plating bias to the
removal bias may be seamless, such that the substrate is not
exposed to the plating solution without a forward bias applied
thereto. The removal bias is calculated to be sufficient to prevent
or counteract etching of the plated layer, however, the removal
bias may also configured to minimize deposition on the surface of
the plated layer. As such, the removal bias may be configured to be
just above the plating potential of the system, and the driving
current of the removal bias may be minimized, i.e., just enough
current to prevent etching while not causing significant deposition
on the smooth upper surface of the plated layer.
[0051] In similar fashion to the immersion bias control features of
the invention described above, embodiments of the invention are
also configured to control the current applied during the removal
or withdrawal bias. For example, controller 111 may be used to
control the current and/or voltage applied to the substrate during
the withdrawal process. The electrical current or voltage supplied
to the substrate during withdrawal may be controlled in order to
prevent additional deposition on areas of the substrate that remain
immersed in the plating solution longer than other areas of the
substrate, as deposition thickness in an electrochemical plating
process is generally a function of exposure time to the plating
solution. Further, the voltage or current may be controlled during
the substrate withdrawal process in order to prevent the current
density on the immersed portion of the substrate from increasing,
which will also generally cause an increased plating rate on the
portions of the substrate that remain immersed in the plating
solution.
[0052] Embodiments of the invention contemplate that either a
voltage control (control system where the voltage is monitored and
adjusted in order to control the electrical current or power
applied) or a current control system (control system where the
current itself is monitored and controlled) may be used to control
the removal bias. A current control system may be used to control
the removal bias by maintaining a constant current density across
the substrate surface during the entire substrate removal process.
More particularly, as noted above with regard to maintaining a
constant current density across the substrate surface during the
immersion process, as the substrate is removed from the plating
solution, the resistance of the electrical circuit supplying the
removal bias changes. The resistance change is a result of the
decreasing immersed conductive surface area of the substrate, which
results in an increase in the resistance of the circuit. Therefore,
as the resistance of the circuit increases and the immersed surface
area decreases, the current control system of the invention may
react to these changes to decrease the current supplied to the
substrate so that the current density across the surface of the
substrate remains constant through the withdrawal process.
[0053] The control system may control the current in a closed loop
manner, i.e., the current control system may be configured to
measure the resistance or other electrical parameter of the removal
bias circuit and control the current supplied thereto accordingly.
Alternatively, the current control system may be configured to
control the removal bias in response to a mechanical condition,
such as the position of the substrate or another measurable
mechanical parameter. For example, the position of the substrate,
i.e., the vertical position of the substrate relative to the
plating solution during the withdrawal process, may be correlated
with the immersed surface area of the substrate, and therefore, the
position of the substrate may also be used to control the
electrical removal bias applied to the substrate. Further still,
the electrical bias may be controlled in a time dependent manner,
i.e., the electrical removal bias may be adjusted per unit of time
that the substrate continues through a removal process, thus
essentially equating time or duration of the removal process with
the immersed surface area of the substrate.
[0054] During the substrate removal process, the substrate may be
rotated, tilted, pivoted, vertically actuated, horizontally
actuated, and/or vibrated with sonic or ultrasonic energy. For
example, during a removal process of the invention, a substrate may
be rotated in the plating solution while the removal bias is
initiated. The substrate may then be raised vertically out of the
solution to remove the substrate from the solution. During the
raising process the surface area of the substrate is incrementally
removed from the plating solution and the electrical bias supplied
thereto is controlled in accordance with the proportion of the
surface area removed from the solution (or remaining in the
solution), as noted above. The substrate may be held in a
horizontal position, i.e., in a position where the surface of the
substrate is generally parallel to the upper surface of the plating
solution contained in a weir-type plater.
[0055] Alternatively, the surface of the substrate may be tilted
from horizontal, i.e., the surface of the substrate may be
positioned such that a tilt angle is formed between the substrate
surface and the upper surface of the plating solution in a
weir-type plater. In this configuration, when the substrate is
vertically moved or raised out of the solution, the tilt angle
between the substrate surface and the upper surface of the plating
solution remains constant. However, embodiments of the invention
also contemplate that the tilt angle may be varied during the
removal process. For example, the tilt angle may be increased or
decreased during the substrate removal process, such that the
vertical movement of the substrate out of the solution does not
result in the tilt angle remaining constant, rather, the tilt angle
increases or decreases as the substrate is removed.
[0056] During the removal process, for example, the substrate may
be rotated between about 5 rpm and about 100 rpm, or more
particularly, between about 20 rpm and about 60 rpm. The tilt angle
of the substrate may be between about 30 and about 30.degree., or
more particularly, between about 5.degree. and about 20.degree..
The tilt angle may also be increased or decreased, as well as
pivoted or oscillated during the removal process. The electrical
bias applied to the substrate during the removal process may be
configured to generate an electrical current density across the
surface of the substrate of between about 0.5 mA/cm.sup.3 and about
5 mA/cm.sup.3, or more particularly, between about 0.5 mA/cm.sup.3
and about 1 mA/cm.sup.3, or more particularly, between about 1.0
mA/cm.sup.3 and about 3 mA/cm.sup.3. The voltage applied to the
substrate during removal may be between about 0.3 volts and about 5
or about 10 volts, for example, and more particularly, between
about 0.8 volts and about 5 volts.
[0057] In another embodiment of the invention, the method for
maintaining a uniform current density across the surface of the
substrate is utilized during the process of removing a substrate
from a plating cell. For example, once a plating process for a
substrate is complete, the substrate is removed from the plating
chamber by essentially reversing the steps of the immersion
process. In the reverse immersion process, it may be desirable to
maintain a constant current density across the immersed surface of
the substrate in order to avoid variances in uniformity, in similar
fashion to the constant current density maintained during the
immersion process. Therefore, in the reverse immersion process, the
current supplied to the substrate will generally be constant while
the entire surface area of the substrate is immersed in the plating
solution. However, once the surface of the substrate begins to be
removed from the plating solution, the current supplied thereto may
be decreased in proportion to the immersed area of the substrate.
This essentially operates to maintain a uniform current density
across the immersed area of the substrate throughout the process.
The process of controlling the current to the substrate during the
reverse immersion process is, for example, conducted to a feedback
loop type system or a time varying current control type system, as
discussed in the previous embodiments. Regardless of the type of
current control system implemented, the current supplied to the
substrate during the reverse immersion process will generally be
proportional to the surface area of the substrate remaining
immersed in the plating solution.
[0058] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *