U.S. patent application number 11/532258 was filed with the patent office on 2007-03-22 for method for stabilized polishing process.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Jie Diao, Renhe Jia, Laksh Karuppiah, Stan D. Tsai, You Wang.
Application Number | 20070062815 11/532258 |
Document ID | / |
Family ID | 37440549 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070062815 |
Kind Code |
A1 |
Jia; Renhe ; et al. |
March 22, 2007 |
METHOD FOR STABILIZED POLISHING PROCESS
Abstract
A method for electrochemically processing a substrate is
provided. In one embodiment, a method for electrochemically
processing a substrate includes processing a substrate using a
multi-step routine that includes a first processing period
performed using a varying voltage to achieve a target removal
current followed by a second processing period performed using a
constant voltage.
Inventors: |
Jia; Renhe; (Berkeley,
CA) ; Diao; Jie; (San Jose, CA) ; Tsai; Stan
D.; (Fremont, CA) ; Wang; You; (Cupertino,
CA) ; Karuppiah; Laksh; (San Jose, CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Assignee: |
APPLIED MATERIALS, INC.
|
Family ID: |
37440549 |
Appl. No.: |
11/532258 |
Filed: |
September 15, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60718851 |
Sep 19, 2005 |
|
|
|
Current U.S.
Class: |
205/48 |
Current CPC
Class: |
C25F 3/00 20130101; H01L
21/32125 20130101; C25F 3/02 20130101; C25D 5/18 20130101; B23H
5/08 20130101; C25F 7/00 20130101 |
Class at
Publication: |
205/048 |
International
Class: |
C25C 1/22 20060101
C25C001/22 |
Claims
1. A method for electroprocessing a substrate, comprising:
establishing an electrically-conductive path through an electrolyte
between an exposed layer of material on the substrate and an
electrode; electrochemically removing a first portion of the
exposed layer while adjusting voltage to achieve a target removal
current; and electrochemically removing a second portion of the
exposed layer with a constant voltage corresponding to the target
removal current.
2. The method of claim 1, further comprising: pressing the exposed
layer of material against a partially conductive surface of a
polishing pad.
3. The method of claim 2, wherein the pressing further comprises:
pressing the substrate against the polishing pad with a pressure of
less than 2 pounds per square inch.
4. The method of claim 1, wherein the target removal current is
determined before removing the first portion of the exposed
layer.
5. The method of claim 1, wherein the target removal current is
determined by an incoming thickness profile of the substrate using
historical data and/or an algorithm based on the incoming thickness
profile.
6. The method of claim 1, further comprising: adjusting a first
processing voltage across a first processing zone of the electrode
while removing the first portion; and adjusting a second processing
voltage across a second processing zone of the electrode while
removing the second portion.
7. The method of claim 1, further comprising: fixing the voltage to
provide the constant voltage corresponding to the target removal
current after the adjusted voltage has reached a near stabilized
state.
8. A method for processing a substrate in an electrochemical
mechanical planarizing system, comprising: processing a first
substrate on a polishing pad for a first processing period
performed to achieve a target removal current; and processing the
first substrate on the polishing pad for a second processing period
performed using a constant voltage based on the target removal
current.
9. The method of claim 8, wherein processing the first substrate
for the first processing period further comprises: adjusting a
processing voltage during the first processing period.
10. The method of claim 8, wherein processing the first substrate
for the first processing period further comprises: adjusting a
first processing voltage across a first processing zone during the
first processing period; and adjusting a second processing voltage
across a second processing zone during the first processing
period.
11. The method of claim 10, wherein adjusting the first and second
processing voltages further comprises: applying different voltages
to an outer portion of the first substrate relative to an inner
portion of the first substrate.
12. The method of claim 8, wherein processing the first substrate
for the first and second period includes establishing an
electrochemical circuit between an exposed layer of conductive
material on the first substrate in contact with the polishing pad,
and an electrode disposed in the polishing pad through an
electrolyte.
13. The method of claim 8, wherein processing the first substrate
for the first and second period includes establishing an
electrochemical circuit between an exposed layer of conductive
material on the first substrate and an electrode disposed in the
polishing pad in the presence of an electrolyte, wherein an upper
surface of the pad includes a partially conductive surface to bias
the exposed layer of conductive material.
14. The method of claim 8 further comprising: processing a second
substrate for a first processing period performed to achieve a
second target removal current; and processing the second substrate
for a second processing period performed using a second constant
voltage based on the second target removal current.
15. The method of claim 14, wherein the processing the second
substrate for the second processing period further comprises:
applying the second constant voltage greater than the first
constant voltage.
16. The method of claim 14 further comprising: conditioning a
processing surface of the polishing pad; and applying the second
constant voltage less than the first constant voltage.
17. The method of claim 8 further comprising: removing a conductive
material from the first substrate in a bulk processing step on a
processing tool; and processing the conductive material on the
first substrate for the first and second period on the processing
tool in-situ in a residual processing step.
18. The method of claim 17, wherein processing the conductive
material for the first and second periods further comprises:
processing the first substrate on a single polishing pad disposed
on the polishing tool.
19. The method of claim 17, wherein processing the conductive
material for the first and second periods further comprises:
processing the first substrate on two polishing pads disposed on
the polishing tool.
20. The method of claim 17, wherein processing the conductive
material for the first and second periods further comprises:
processing the first substrate on a fully conductive processing
pad.
21. The method of claim 20, wherein processing the first substrate
for the first and second period includes establishing an
electrochemical circuit between an exposed layer of conductive
material on the first substrate in contact with the polishing pad,
and an electrode disposed in the polishing pad through an
electrolyte.
22. The method of claim 8, wherein the second processing period is
much greater than the first processing period.
23. The method of claim 8, further comprising: fixing the voltage
to provide the constant voltage based on the target removal current
after the adjusted voltage has reached a near stabilized state.
24. The method of claim 8, further comprising: adjusting a first
processing voltage across a first processing zone of an electrode
disposed in the polishing pad while removing the first portion; and
adjusting a second processing voltage across a second processing
zone of the electrode while removing the second portion.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. provisional patent
application Ser. No. 60/718,851 (Attorney Docket No 010581 L),
filed Sep. 19, 2005, which application is incorporated by reference
in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention generally relate to a
method for electrochemical processing.
[0004] 2. Description of the Related Art
[0005] Electrochemical mechanical planarizing (ECMP) is a technique
used to remove conductive materials, such as copper and tungsten,
from a substrate surface by electrochemical dissolution while
concurrently polishing the substrate with reduced mechanical
abrasion compared to conventional planarization processes.
Electrochemical dissolution is performed by applying a bias between
a cathode and a substrate surface to remove conductive materials
from the substrate surface into a surrounding electrolyte.
Typically, the bias is applied to the substrate surface by a
conductive polishing pad on which the substrate is processed A
mechanical component of the polishing process is performed by
providing relative motion between the substrate and the conductive
polishing pad that enhances the removal of the conductive material
from the substrate. ECMP systems may generally be adapted for
deposition of conductive material on the substrate by reversing the
polarity of the bias.
[0006] Stability is a very important factor in determining a
successful ECMP process. For many ECMP processes, a fixed voltage
is applied to a substrate through a conductive pad surface as a
means to drive metal removal from the substrate. In this process,
any variation in electrical resistance or the mechanical
properties, either with time or with different process previously
done on the conductive surface, will lead to varied polishing rate
(as may be detected by monitoring current) with a certain applied
voltage. This variation, in turn, may lead to varied process time
for a certain amount of material removal, and thus process
instability.
[0007] Therefore, there is a need for an improved method and
apparatus for electrochemical processing of conductive
materials.
SUMMARY OF THE INVENTION
[0008] Embodiments of the invention generally provide a method for
processing a substrate in an electrochemical mechanical planarizing
system. In one embodiment, the method includes processing a
substrate using a routine that includes a first processing period
performed to achieve a target removal current followed by a second
processing period performed using a constant voltage based on the
target removal current.
[0009] In one embodiment, the first processing period includes
setting a specific current value (that may indicate a specific
removal rate) as the targeted removal current for the process, and
adjusting the voltage based on the measured current to achieve the
targeted removal current. If the measured current is lower than the
targeted removal current, the voltage is increased to get the
current closer to the target. Similarly, if the measured current is
higher than the target removal current, the voltage is decreased to
lower the current. This can be done through a closed loop feedback
system, so that the polishing tool can automatically adjust the
voltage, leading to the targeted removal rate. When the targeted
removal current is reached (stabilized), the voltage is measured
and set at the target voltage. So from this point forward in the
polishing routine, the polishing will be done with this constant
voltage.
[0010] This method is especially useful when removing residual
metal from the substrate. The first step (determining a voltage for
the target removal current) will determine a suitable voltage for
subsequent polishing. The second step includes fixing the voltage
once the target removal current is reached. Once voltage is fixed,
an endpoint may be determined by monitoring the current.
[0011] In another embodiment, a method for electroprocessing a
substrate is described. The method includes establishing an
electrically-conductive path through an electrolyte between an
exposed layer of material on the substrate and an electrode,
electrochemically removing a first portion of the exposed layer
while adjusting voltage to achieve a target removal current, and
electrochemically removing a second portion of the exposed layer
with a constant voltage corresponding to the target removal
current.
[0012] In another embodiment, a method for processing a substrate
in an electrochemical mechanical planarizing system is described.
The method includes processing a first substrate on a polishing pad
for a first processing period performed to achieve a target removal
current, and processing the first substrate on the polishing pad
for a second processing period performed using a constant voltage
based on the target removal current.
[0013] As a result, this process, with determining a voltage for a
target removal current and then fixing the voltage for that
specific removal current for the remaining metal residue polishing,
may minimize process variations due to changes in a full conductive
pad over time. Additionally, the method may minimize the variation
among different pads, meaning the rate of a certain full conductive
pad under a certain applied voltage might be different from that of
another pad, however this variation will be compensated with the
constant current plus the fixed voltage polishing.
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 plan view of an electrochemical mechanical
processing system;
[0016] FIG. 2 is a sectional view of one embodiment of a first
electrochemical mechanical planarizing (ECMP) station of the system
of FIG. 1;
[0017] FIG. 3 is a sectional view of another embodiment of an ECMP
station;
[0018] FIG. 4 is a flow diagram of one embodiment of a method for
electroprocessing conductive material;
[0019] FIG. 5 is a graph of process results for a conventional
electroprocess; and
[0020] FIG. 6 is a graph of current and voltage plots for an
exemplary electroprocess.
[0021] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is also contemplated that
elements and features of one embodiment may be beneficially
incorporated on other embodiments without further recitation.
DETAILED DESCRIPTION
[0022] Embodiments for a method for electroprocessing of conductive
materials and other materials from a substrate are provided.
Although the embodiments disclosed below focus primarily on
removing material from, e.g., planarizing, a substrate, it is
contemplated that the teachings disclosed herein may be used to
electroplate a substrate by reversing the polarity of an electrical
bias applied between the substrate and an electrode of the
system.
Apparatus
[0023] FIG. 1 is a plan view of one embodiment of a planarization
system 100 having an apparatus for electrochemically processing a
substrate. The exemplary system 100 generally comprises a factory
interface 102, a loading robot 104, and a planarizing module 106.
The loading robot 104 is disposed proximate the factory interface
102 and the planarizing module 106 to facilitate the transfer of
substrates 122 therebetween.
[0024] A controller 108 is provided to facilitate control and
integration of the modules of the system 100. The controller 108
comprises a central processing unit (CPU) 110, a memory 112, and
support circuits 114. The controller 108 is coupled to the various
components of the system 100 to facilitate control of, for example,
the planarizing, cleaning, or transfer processes of embodiments of
the present invention.
[0025] The factory interface 102 generally includes a cleaning
module 116 and one or more wafer cassettes 118. An interface robot
120 is employed to transfer substrates 122 between the wafer
cassettes 118, the cleaning module 116 and an input module 124. The
input module 124 is positioned to facilitate transfer of substrates
122 between the planarizing module 106 and the factory interface
102 by grippers, for example vacuum grippers or mechanical
clamps.
[0026] The planarizing module 106 includes at least a first
electrochemical mechanical planarizing (ECMP) station 128, disposed
in an environmentally controlled enclosure 188. Examples of
planarizing modules 106 that can be adapted to benefit from the
invention include MIRRA.RTM., MIRRA MESA.TM., REFLEXION.RTM.,
REFLEXION.RTM. LK, and REFLEXION.RTM. LK Ecmp.TM. Chemical
Mechanical Planarizing Systems, all available from Applied
Materials, Inc. of Santa Clara, Calif. Other planarizing modules,
including those that use processing pads, planarizing webs, or a
combination thereof, and those that move a substrate relative to a
planarizing surface in a rotational, linear or other planar motion
may also be adapted to benefit from the invention.
[0027] In the embodiment depicted in FIG. 1, the planarizing module
106 includes the first ECMP station 128, a second ECMP station 130
and a third ECMP station 132. Bulk removal of conductive material
disposed on the substrate 122 may be performed through an
electrochemical dissolution process at the first ECMP station 128.
After the bulk material removal at the first ECMP station 128, the
remaining conductive material is removed from the substrate at the
second ECMP station 130 through a multi-step electrochemical
mechanical process, wherein part of the multi-step process is
configured to remove residual conductive material. It is
contemplated that more than one ECMP station may be utilized to
perform the multi-step removal process after the bulk removal
process performed at a different station. Alternatively, each of
the first and second ECMP stations 128, 130 may be utilized to
perform both the bulk and multi-step conductive material removal on
a single station. It is also contemplated that all ECMP stations,
for example stations 128, 130, 132 may be configured to process the
conductive layer with a removal process having at least two
steps.
[0028] The exemplary planarizing module 106 also includes a
transfer station 136 and a carousel 134 disposed on an upper or
first side 138 of a machine base 140 In one embodiment, the
transfer station 136 includes an input buffer station 142, an
output buffer station 144, a transfer robot 146, and a load cup
assembly 148. The input buffer station 142 receives substrates from
the factory interface 102 by means of the loading robot 104. The
loading robot 104 is also utilized to return polished substrates
from the output buffer station 144 to the factory interface 102.
The transfer robot 146 is utilized to move substrates between the
buffer stations 142, 144 and the load cup assembly 148.
[0029] In one embodiment, the transfer robot 146 includes two
gripper assemblies, each having pneumatic gripper fingers that hold
the substrate by the substrate's edge. The transfer robot 146 may
simultaneously transfer a substrate to be processed from the input
buffer station 142 to the load cup assembly 148 while transferring
a processed substrate from the load cup assembly 148 to the output
buffer station 144. An example of a transfer station that may be
used to advantage is described in U.S. Pat. No. 6,156,124, filed
Oct. 6, 1999 and issued Dec. 5, 2000, which is herein incorporated
by reference in its entirety.
[0030] The carousel 134 is centrally disposed on the base 140. The
carousel 134 typically includes a plurality of arms 150, each
supporting a planarizing head assembly 152. Two of the arms 150
depicted in FIG. 1 are shown in phantom such that the transfer
station 136 and a planarizing surface 126 of the first ECMP station
128 may be seen. The carousel 134 is indexable such that the
planarizing head assemblies 152 may be moved between the
planarizing stations 128, 130, 132 and the transfer station 136. On
carousel that may be utilized to advantage is described in U.S.
Pat. No. 5,804,507, filed Oct. 27, 2005 and issued Sep. 8, 1998,
which is hereby incorporated by reference in its entirety.
[0031] A conditioning device 182 is disposed on the base 140
adjacent each of the planarizing stations 128, 130, 132. The
conditioning device 182 periodically conditions the planarizing
material disposed in the stations 128, 130, 132 to maintain uniform
planarizing results.
[0032] FIG. 2 depicts a sectional view of one of the planarizing
head assemblies 152 positioned over one embodiment of the first
ECMP station 128. The second and third ECMP stations 130, 132 may
be similarly configured. The planarizing head assembly 152
generally comprises a drive system 202 coupled to a planarizing
head 204. The drive system 202 generally provides at least
rotational motion to the planarizing head 204. The planarizing head
204 additionally may be actuated toward the first ECMP station 128
such that the substrate 122 retained in the planarizing head 204
may be disposed against the planarizing surface 126 of the first
ECMP station 128 during processing. The drive system 202 is coupled
to the controller 108 that provides a signal to the drive system
202 for controlling the rotational speed and direction of the
planarizing head 204.
[0033] In one embodiment, the planarizing head may be a TITAN
HEAD.TM. or TITAN PROFILER.TM. wafer carrier manufactured by
Applied Materials, Inc. Generally, the planarizing head 204
comprises a housing 214 and retaining ring 224 that defines a
center recess in which the substrate 122 is retained. The retaining
ring 224 circumscribes the substrate 122 disposed within the
planarizing head 204 to prevent the substrate from slipping out
from under the planarizing head 204 while processing. The retaining
ring 224 can be made of plastic materials such as PPS, PEEK, and
the like, or conductive materials such as stainless steel, copper,
gold, palladium, and the like, or some combination thereof. It is
further contemplated that a conductive retaining ring 224 may be
electrically biased to control the electric field during ECMP.
Conductive or biased retaining rings tend to slow the polishing
rate proximate the edge of the substrate. It is contemplated that
other planarizing heads may be utilized.
[0034] The first ECMP station 128 generally includes a platen
assembly 230 that is rotationally disposed on the base 140. The
platen assembly 230 is supported above the base 140 by a bearing
238 so that the platen assembly 230 may be rotated relative to the
base 140. An area of the base 140 circumscribed by the bearing 238
is open and provides a conduit for the electrical, mechanical,
pneumatic, control signals and connections communicating with the
platen assembly 230.
[0035] Conventional bearings, rotary unions and slip rings,
collectively referred to as rotary coupler 276, are provided such
that electrical, mechanical, fluid, pneumatic, control signals and
connections may be coupled between the base 140 and the rotating
platen assembly 230. The platen assembly 230 is typically coupled
to a motor 232 that provides the rotational motion to the platen
assembly 230. The motor 232 is coupled to the controller 108 that
provides a signal for controlling for the rotational speed and
direction of the platen assembly 230.
[0036] A top surface 260 of the platen assembly 230 supports a
processing pad assembly 222 thereon. The processing pad assembly
may be retained to the platen assembly 230 by magnetic attraction,
vacuum, clamps, adhesives and the like.
[0037] A plenum 206 is defined in the platen assembly 230 to
facilitate uniform distribution of electrolyte to the planarizing
surface 126 A plurality of passages, described in greater detail
below, are formed in the platen assembly 230 to allow electrolyte,
provided to the plenum 206 from an electrolyte source 248, to flow
uniformly though the platen assembly 230 and into contact with the
substrate 122 during processing. It is contemplated that different
electrolyte compositions may be provided during different stages of
processing.
[0038] The processing pad assembly 222 includes an electrode 292
and at least a planarizing portion 290. The electrode 292 is
typically comprised of a conductive material, such as stainless
steel, copper, aluminum, gold, silver and tungsten, among others.
The electrode 292 may be solid, impermeable to electrolyte,
permeable to electrolyte or perforated. At least one contact
assembly 250 extends above the processing pad assembly 222 and is
adapted to electrically couple the substrate being processing on
the processing pad assembly 222 to the power source 242. The
electrode 292 is also coupled to the power source 242 so that an
electrical potential may be established between the substrate and
electrode 292.
[0039] A meter 240 is provided to detect a metric indicative of the
electrochemical process. The meter 240 may be coupled or positioned
between the power source 242 and at least one of the electrode 292
or contact assembly 250. The meter 240 may also be integral to the
power source 242. In one embodiment, the meter 240 is configured to
provide the controller 108 with a metric indicative of processing,
such a charge, current and/or voltage. This metric may be utilized
by the controller 108 in a closed loop feedback system to adjust
the processing parameters in-situ or to facilitate endpoint or
other process stage detection.
[0040] A window 246 is provided through the pad assembly 222 and/or
platen assembly 230, and is configured to allow a sensor 254,
positioned below the pad assembly 222, to sense a metric indicative
of polishing performance. For example, the sensor 254 may be an
eddy current sensor or an interferometer, among other sensors. The
metric, provided by the sensor 254 to the controller 108, provides
information that may be utilized for processing profile adjustment
in-situ, endpoint detection or detection of another point in the
electrochemical process. In one embodiment, the sensor 254 an
interferometer capable of generating a collimated light beam, which
during processing, is directed at and impinges on a side of the
substrate 122 that is being polished. The interference between
reflected signals is indicative of the thickness of the conductive
layer of material being processed. One sensor that may be utilized
to advantage is described in U.S. Pat. No. 5,893,796, filed Aug.
16, 1996 and issued Apr. 13, 1999, which is hereby incorporated by
reference in its entirety.
[0041] Embodiments of the processing pad assembly 222 suitable for
removal of conductive material from the substrate 122 may generally
include a planarizing surface 126 that is substantially dielectric.
Other embodiments of the processing pad assembly 222 suitable for
removal of conductive material from the substrate 122 may generally
include a planarizing surface 126 that is substantially conductive.
At least one contact assembly 250 is provided to couple the
substrate to the power source 242 so that the substrate may be
biased relative to the electrode 292 during processing. Apertures
210, formed through the planarizing portion 290, allow the
electrolyte to establish a conductive path between the substrate
112 and electrode 292.
[0042] In one embodiment, the planarizing portion 290 of the
processing pad assembly 222 is a dielectric, such as polyurethane.
Examples of processing pad assemblies that may be adapted to
benefit from the invention are described in U.S. Pat. No.
6,991,528, filed Jun. 6, 2003 and issued Jan. 31, 2006, and United
States Patent Publication No. 2004/0020789, filed Jun. 6, 2003 and
published on Feb. 5, 2004, both of which are hereby incorporated by
reference in their entireties.
[0043] The at least one contact assembly 250 disposed in the
processing pad assembly of FIG. 2 may be coupled to the platen
assembly 230 and is adapted to bias a surface of the substrate 122.
The at least one contact assembly 250 is generally electrically
coupled to the power source 242 through the platen assembly 230 and
is movable to extend at least partially through a respective
aperture (not shown) formed in the processing pad assembly 222. One
contact assembly that may be adapted to benefit from the invention
is described in U.S. Pat. No. 6,884,153, filed May 23, 2003 and
issued Apr. 26, 2005, and is hereby incorporated by reference in
its entirety. Other examples of suitable contact assemblies are
described in U.S. Provisional Patent Application Ser. No.
60/516,680, filed Nov. 3, 2003, by Hu, et al, which is hereby
incorporated by reference in its entirety.
[0044] The at least one contact assembly 250 may comprise a rolling
ball contact although the contact assembly 250 may alternatively
comprise a structure or assembly having a conductive upper layer or
surface suitable for electrically biasing the substrate 122 during
processing. For example, the contact assembly 250 may include a pad
structure (not shown) having an upper layer made from a conductive
material or a conductive composite (i.e., the conductive elements
are dispersed integrally with or comprise the material comprising
the upper surface), such as a polymer matrix having conductive
particles dispersed therein, or a conductive coated fabric, among
others.
[0045] FIG. 3 is a sectional view of one embodiment of the second
ECMP station 130. The first and third ECMP stations 128, 132 may be
configured similarly. The second ECMP station 130 generally
includes a platen 302 that supports a fully conductive processing
pad assembly 304. The platen 302 may be configured similar to the
platen assembly 230 described above to deliver electrolyte through
the processing pad assembly 304, or the platen 302 may have a fluid
delivery arm 306 disposed adjacent thereto configured to supply
electrolyte to a planarizing surface of the processing pad assembly
304. The platen assembly 302 may include at least one of a meter
240 or sensor 254 (shown in FIG. 2) to facilitate endpoint
detection.
[0046] In one embodiment, the processing pad assembly 304 includes
interposed pad 312 sandwiched between a conductive pad 310 and an
electrode 314. The conductive pad 310 is substantially conductive
across its top processing surface 320 and is generally made from a
conductive material or a conductive composite (i.e., the conductive
elements are dispersed integrally with or comprise the material
comprising the planarizing surface), such as a polymer matrix
having conductive particles dispersed therein or a conductive
coated fabric, among others. The conductive elements or particles
may be conductive metals, such as copper, tin, gold, silver, or
combinations thereof.
[0047] The conductive pad 310, the interposed pad 312, and the
electrode 314 may be fabricated into a single, replaceable
assembly. The processing pad assembly 304 is generally permeable or
perforated to allow electrolyte to pass between the electrode 314
and top surface 320 of the conductive pad 310. In the embodiment
depicted in FIG. 3, the processing pad assembly 304 is perforated
by apertures 322 to allow electrolyte to flow therethrough. In one
embodiment, the conductive pad 310 is comprised of a conductive
material disposed on a polymer matrix disposed on a conductive
fiber, for example, tin particles in a polymer matrix disposed on a
woven copper coated polymer. The conductive pad 310 may also be
utilized for the contact assembly 250 in the embodiment of FIG.
2.
[0048] A conductive foil 316 may additionally be disposed between
the conductive pad 310 and the interposed pad 312. The foil 316 is
coupled to a power source 242 and provides uniform distribution of
voltage applied by the source 242 across the conductive pad 310. In
embodiments not including the conductive foil 316, the conductive
pad 310 may be coupled directly, for example, via a terminal
integral to the pad 310, to the power source 242. Additionally, the
pad assembly 304 may include an interposed pad 318, which, along
with the foil 316, provides mechanical strength to the overlying
conductive pad 310. Examples of suitable pad assemblies are
described in U.S. Pat. No. 6,991,528, and United States Patent
Publication No. 2004/0020789, both of which have been previously
incorporated by reference. Another suitable pad assembly is
described in U.S. patent application Ser. No. 11/327,527, filed
Jan. 5, 2006, entitled "Fully Conductive Pad for Electrochemical
Mechanical Processing," which is incorporated in reference in its
entirety.
[0049] In one embodiment, the pad assembly 304 depicted in FIG. 3
may include an electrode 314 that comprises a plurality of zones,
such as outer zone 315A, and inner zone 315B. The zones 315A, 315B
may be any shape or configuration, such as annular or concentric
circles as shown, or any other geometric shape. The zones 315A,
315B are insulated from each other in order to facilitate
independent voltage application to each zone. The independent
voltage application may facilitate enhanced removal of materials
from the substrate 122 by applying different voltages or biases to
the independent zones based on an incoming thickness profile of the
substrate and/or the amount of polishing time the substrate 122
spends over each zone. In this manner, the potential difference
between the substrate 122 and each zone 315A, 315B may be
different, for example between the center of the substrate relative
to the perimeter of the substrate, thus providing enhanced control
of removal of material from different regions of the substrate.
[0050] For example, the incoming thickness profile of the substrate
122 may include a greater thickness of conductive material on the
periphery of the substrate as compared to the center region of the
substrate. Due to the positioning and rotation of the head assembly
152 and/or the pad assembly 304, the periphery of the substrate 122
may spend more time over the outer zone 315A relative to the inner
zone 315B. In this example, the voltage or bias applied to the
outer zone 315A may be different than the voltage or bias applied
to the inner zone 315B in order to compensate for the difference in
material thicknesses in different regions of the substrate 122.
Although two zones 315A, 315B are shown, any number of
independently biasable zones may be used.
Multi-Step Polishing Method
[0051] FIG. 4 shows one embodiment of a method 400 for
electroprocessing conductive material, such as copper, tungsten,
tantalum, tantalum nitride, titanium, titanium nitride, and the
like, that may be practiced on the system 100 described above,
although the method 400 may also be practiced on other
electroprocessing systems. The method 400 is generally stored in
the memory 112 of the controller 108, typically as a software
routine. The software routine may also be stored and/or executed by
a second CPU (not shown) that is remotely located from the hardware
being controlled by the CPU 110.
[0052] Although the process is discussed as being implemented as a
software routine, some of the method steps that are disclosed
herein may be performed in hardware as well as by the software
controller. As such, the invention may be implemented in software
as executed upon a computer system, in hardware as an application
specific integrated circuit or other type of hardware
implementation, or a combination of software and hardware.
[0053] The method 400 begins at step 402 by electroprocessing the
substrate for a first processing period to achieve a target removal
current by measuring the current and adjusting the voltage. The
first processing step 402 is followed at step 404 by
electroprocessing the substrate (on the same pad) for a second
processing period using a constant voltage measured for the target
removal current.
[0054] In one embodiment, the first processing step 402 includes
setting a specific current value as the targeted removal current
for the process. The specific current value may indicate a specific
average removal rate that is determined, for example, by historical
data, and/or an algorithm. The specific current value may also be
determined by an algorithm based on an incoming thickness profile
of the substrate 122. Voltage is then increased or decreased based
on feed back from measurement of the current and/or the initial
voltage, which may be a closed-loop system. If the measured current
is lower than the targeted removal current, the voltage is
increased to get the current closer to the target. Similarly, if
the measured current is higher than the targeted removal current,
the voltage will be decreased to lower the current. This can be
done through the closed loop feedback system, so that the polishing
tool can automatically adjust the voltage, leading to the targeted
removal rate.
[0055] In one embodiment, the second processing step 404 includes
fixing an instantaneous voltage as soon as the targeted current is
reached. For example, when the target current has reached a
stabilized state, the voltage at the targeted current is locked in.
After the voltage is fixed in the polishing routine, the remainder
of polishing will be done with the fixed, constant voltage. The
method 400 may be repeated for each incoming wafer and eliminates
or minimizes pad variations over time. Additionally, the method 400
will substantially eliminate the variation among new, unused,
different pads, and/or variations between the same pad relative to
multiple substrates. For example, the average removal rate of a
certain full conductive pad under a certain applied voltage might
differ from that of another pad, and/or the same pad after a number
of substrates have been processed, however this pad variation will
be minimized or compensated by the method 400.
[0056] As an example, a new pad may include a surface to provide a
first removal rate of material from the substrate, either as-is, or
with a conditioning process to prepare the pad for polishing. The
pad may be pre-conditioned before a polishing process, conditioned
in-situ while polishing, or a combination of both. In any case, the
new pad may include a surface with a first removal rate. However,
after polishing multiple substrates, the pad surface may become
less efficient. Subsequent or concurrent conditioning processes may
enhance the pad surface, but the removal rate of the pad surface
may decrease. For example, the pad surface may exhibit a lower
removal rate due to accumulation of polishing by-products and/or
wear of the polishing surface. Pad properties, such as resistivity
may increase after a number of substrates have been processed due
to deterioration or other changes in the pad surface. This
deterioration may result in higher voltages to achieve the desired
current for subsequent polishing processes on subsequent
substrates. However, in some cases, an in-situ conditioning process
may enhance to surface of the pad resulting in lower polishing
voltages required to drive the same polishing current. In other
cases, the pad surface may not be changed significantly and the
higher voltage, relative to the voltage used for previous polishing
processes, may be needed to drive the desired current. In any case,
the method 400 may be configured to compensate for these variations
and enhance the polishing process for multiple substrates on the
same or different pads.
[0057] The method 400 may be used during polishing on the
planarizing module 106 of FIG. 1 with the polishing pads disposed
on the ECMP stations 128, 130, and 132. For example, the method 400
may be used to determine and set a constant voltage on the first
ECMP station 128, to perform bulk removal of conductive material,
and the method 400 may be repeated to determine and set a constant
voltage for residual material removal on the second ECMP station
130. Alternatively, the bulk and residual polishing processes may
be performed on a single station. Optionally, the bulk and residual
polishing process may be performed in a single application of the
method 400.
[0058] In one exemplary embodiment, the first step 402 includes
determining a corresponding voltage for obtaining a target removal
current under actual processing conditions. The second step 404
includes polishing with the determined voltage a certain amount of
time to reach an endpoint. In another example, the incoming
thickness profile of the substrate 122 may be determined prior to
polishing, and a specific current may be determined based on an
algorithm and/or data acquired from substrates having a similar
incoming thickness. For example, the substrate 122 may include an
incoming thickness of conductive material in a range between about
7000 Angstroms (.ANG.) to about 9000 .ANG., such as about 8000
.ANG.. The polishing process may commence with the historically
and/or algorithmically determined current for a first processing
period as the voltage is monitored. After the current has
stabilized, the voltage driving the stabilized current will be
fixed, and the voltage will remain constant throughout a second
processing period. The first and second processing periods of the
bulk removal process performed on the first ECMP station 128 may
include leaving about 1000 .ANG. to about 2000 .ANG. of conductive
material on the substrate 122 for subsequent removal on the second
ECMP station 130 in a residual removal process.
[0059] During the first processing period, the voltage is adjusted
to drive the targeted current and the rate of change of voltage
(.DELTA.V) or adjustment during this period may be very rapid.
However, as the polishing process continues, .DELTA.V may decrease
and reach a stabilized or near-stabilized state. A voltage fixing
point may be determined when .DELTA.V has reached a stabilized or
near stabilized state. At this fixing point, the voltage may be
stablized and the second processing period may continue until an
endpoint in the polishing process is determined.
[0060] The first and second processing periods, relative to time,
may be substantially the same amount of time, or have different
times. However, experiments have shown that the first processing
period to reach a fixed voltage is less than half of the time
needed for both the first and second processing periods. In one
embodiment, the second processing period may be typically much
greater than the first processing period.
[0061] The method 400 is especially useful when removing residual
material from the substrate, which may include residual conductive
material and barrier material. The first step 402, which includes
determining a corresponding voltage for the target removal current,
at the beginning of the method 400 will determine a suitable
voltage for subsequent polishing, and then the determined voltage
at step 404 will substantially provide this removal rate for a
certain amount of time. Step 404 is terminated at an endpoint, such
as an endpoint determined by current. The endpoint may also be
determined when the metal film breaks through or when residual
metal film has been cleared. The endpoint may be determined by
monitoring current passing between the substrate and counter
electrode, monitoring the potential difference between the
substrate and counter electrode, and monitoring charge removed from
the substrate, optical devices, among others. Examples of suitable
endpoint routines are described in United States Patent Publication
No. 2004/0182721, filed Mar. 18, 2003 and published on Sep. 23,
2004; U.S. Pat. No. 6,837,983, filed Jan. 22, 2002 and issued on
Jan. 1, 2003; United States Publication No. 2005/0061674, filed
Sep. 24, 2004 and published on Mar. 24, 2005; and United States
Publication No. 2006/0166500, filed Jan. 26, 2005 and published on
Jul. 27, 2006; all of which are incorporated by reference in their
entireties.
[0062] In another example, the method 400 may include moving the
substrate 122 retained in the planarizing head 204 over the
processing pad assembly 304 disposed in the second ECMP station
130. The planarizing head 204 is lowered toward the platen assembly
302 to place the substrate 122 in contact with the top surface of
the pad assembly 304. Although the pad assembly of FIG. 3 is
utilized in one embodiment, it is contemplated that other pad and
contact assemblies as described in FIG. 2 may alternatively be
utilized. In one embodiment, the substrate 122 is urged against the
pad assembly 304 with a force less than about 2 pounds per square
inch (psi). Electrolyte is supplied to the processing pad assembly
304 to establish a conductive path therethrough between the
substrate 122 and the electrode 314.
[0063] At a first clearance process step 402, a variable voltage is
provided from the power source 242 and runs between the top surface
of the pad assembly 304 and the electrode 314 until a target
removal current is achieved. In one embodiment, the voltage is
adjusted until the current achieves a target removal current in the
range of about 5 to about 4 amperes and passes through the
electrolyte filling the apertures 322 between the electrode 314 and
the substrate 122 to drive an electrochemical mechanical
planarizing process.
[0064] Once the voltage is stabilized at the target removal
current, a constant voltage is utilized at step 404 to conduct the
remainder of the electroprocess. An endpoint of the second step 404
is determined by detecting a metric indicative of endpoint, such as
current, voltage, charge, interferometry or other suitable endpoint
detection technique.
[0065] The method 400 may be used in the embodiment shown in FIG. 3
when the pad assembly includes an electrode with independently
biasable zones, such as outer zone 315A and inner zone 315B. For
example, the processing steps 402, 404 may be applied to the outer
zone 315A independent of the processing steps 402, 404 applied to
the inner zone 315B. In this example, the targeted removal current
for the outer zone 315A may be determined and the voltage may be
locked when the targeted current has reached a stabilized state for
the outer zone 315A, while a different targeted current for zone
315B results in the voltage driving and locked for the inner zone
315B being different. Moreover, the sequence in which the voltage
in each zone 315A, 315B is locked first, may vary.
[0066] FIG. 5 is a graph 500 of a conventional electroprocess that
utilizes constant voltage to drive electroprocessing of the
substrate. For comparison, FIG. 6 is a graph 600 of an exemplary
electroprocess that utilized the method of the present invention to
drive electroprocessing of the substrate with a first constant
current step followed by a constant voltage step. The results
illustrated in FIG. 5 show current (representative of the polishing
rate) dropping gradually over time, which is evidence of process
instability. The results illustrated FIG. 6 show a very stable
removal rate over time, which is evidence of the stability of the
process of the present invention.
[0067] Thus, the present invention provides an improved method for
electrochemically planarizing a substrate. The method
advantageously provides process repeatability and minimizes or
eliminates process variations due to changes in the electrical
characteristics of a conductive pad over time. Furthermore, the
method will substantially eliminate variation among different pads,
meaning that the rate of a certain full conductive pad under a
certain applied voltage might be different from that of another
pad, however this variation will be compensated with the constant
current plus the fixed voltage polishing.
[0068] It is contemplated that a method and apparatus as described
by the teachings herein, may be utilized to deposit materials onto
a substrate by reversing the polarity of the bias applied to the
electrode and the substrate.
[0069] 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.
* * * * *