U.S. patent application number 10/902241 was filed with the patent office on 2009-01-22 for method and system for controlled material removal by electrochemical polishing.
Invention is credited to Bulent M. Basol, George Xinsheng Guo, Cyprian E. Uzoh.
Application Number | 20090020437 10/902241 |
Document ID | / |
Family ID | 40263971 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090020437 |
Kind Code |
A1 |
Basol; Bulent M. ; et
al. |
January 22, 2009 |
Method and system for controlled material removal by
electrochemical polishing
Abstract
A method and apparatus for electropolishing a conductive layer
on a wafer is provided. The apparatus includes an electrode and a
conductive member having openings permitting an electropolishing
solution to flow through it. Surface of the conductive member
includes a surface profile. During the electropolishing process,
the surface of the conductive element is placed across from the
conductive layer and a potential difference is applied between the
conductive layer and the electrode. The process forms a conductive
layer profile of the conductive layer.
Inventors: |
Basol; Bulent M.; (Manhattan
Beach, CA) ; Uzoh; Cyprian E.; (San Jose, CA)
; Guo; George Xinsheng; (Palo Alto, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET, FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
40263971 |
Appl. No.: |
10/902241 |
Filed: |
July 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10302755 |
Nov 21, 2002 |
7204917 |
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10902241 |
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10152793 |
May 23, 2002 |
7378004 |
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10302755 |
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09511278 |
Feb 23, 2000 |
6413388 |
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10152793 |
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60491470 |
Jul 30, 2003 |
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Current U.S.
Class: |
205/668 ;
204/224R |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 2924/00 20130101; B24B 37/12 20130101; C25F 3/30 20130101;
B24B 37/046 20130101; C25F 7/00 20130101; H01L 21/32115 20130101;
H01L 23/53238 20130101; H01L 21/32125 20130101; H01L 2924/0002
20130101; H01L 21/2885 20130101; H01L 21/76838 20130101 |
Class at
Publication: |
205/668 ;
204/224.R |
International
Class: |
C25F 3/16 20060101
C25F003/16; C25D 17/00 20060101 C25D017/00 |
Claims
1. An apparatus for electropolishing a conductive layer on a
workpiece using a process solution, comprising: a carrier to hold
the workpiece; an electrode; and a conductive element placed
between the electrode and the conductive layer, the conductive
element having openings permitting process solution to flow through
the conductive element and the conductive element having a surface
placed across from the conductive layer, the surface of the
conductive element including a surface profile to control the
material removal profile of the conductive layer.
2. The apparatus of claim 1, wherein the surface profile is a
convex surface profile.
3. The apparatus of claim 1, wherein the surface profile is a
concave surface profile.
4. The apparatus of claim 1, wherein the surface profile is
flat.
5. The apparatus of claim 1 further comprising a power supply to
apply a potential difference between the electrode and the
conductive surface.
6. The apparatus of claim 1, wherein the surface of the conductive
element includes a pad to polish the conductive layer.
7. The apparatus of claim 1, wherein the carrier is configured to
vary the distance between the conductive layer and the surface of
the conductive layer.
8. The apparatus of claim 5, wherein the power supply is configured
to vary the potential difference between the conductive layer and
the electrode.
9. The apparatus of claim 5, wherein the power supply is configured
to apply a potential difference between the conductive element and
the electrode to electrochemically clean the conductive element at
process intervals.
10. The apparatus of claim 1, wherein the conductive layer is
copper.
11. A method of electropolishing a conductive layer on a wafer
using a process solution and an electrode, the method comprising:
placing a surface of a conductive element across from the
conductive layer, the surface of the conductive element having a
first surface profile; and applying a potential difference between
the conductive layer and the electrode; and forming a first
conductive layer profile of the conductive layer.
12. The method of claim 11, wherein the step of forming comprises
electropolishing the conductive layer according to a first material
removal profile.
13. The method of claim 11, wherein the step of placing comprises
placing a surface of another conductive element, the surface having
a second surface profile.
14. The method of claim 13 further comprising: applying a potential
difference between the conductive layer and the electrode; and
forming a second conductive layer profile of the conductive
layer.
15. The method of claim 14, wherein the step of forming comprises
electropolishing the conductive layer according to a second
material removal profile.
16. The method of claim 13 further comprising varying the potential
difference during the step of applying to vary material removal
rate from the conductive layer.
17. An apparatus for electropolishing a conductive layer on a
workpiece using a process solution, comprising: a carrier to hold
the workpiece; an electrode; and a conductive element placed
between the electrode and the conductive layer, the conductive
element having openings permitting process solution to flow through
the conductive element and the conductive element having a surface
placed across from the conductive layer; and wherein the conductive
element is comprised of movable sections to alter the profile of
the surface by moving the movable sections to control the material
removal profile of the conductive layer.
18. The apparatus of claim 17 further comprising a power supply to
apply a potential difference between the electrode and the
conductive surface.
19. The apparatus of claim 17, wherein the surface of the
conductive element includes a pad to polish the conductive
layer.
20. The apparatus of claim 17, wherein the carrier is configured to
vary the distance between the conductive layer and the surface of
the conductive element.
21. The apparatus of claim 18, wherein the power supply is
configured to vary the potential difference between the conductive
layer and the electrode.
22. The apparatus of claim 18, wherein the power supply is
configured to apply a potential difference between the conductive
element and the electrode to electrochemically clean the conductive
element at process intervals.
23. The apparatus of claim 17, wherein the conductive layer is
copper.
24. A method of electropolishing a conductive layer on a wafer
using a process solution and an electrode, the method comprising:
placing a surface of a conductive member across from the conductive
layer, the conductive element having openings permitting process
solution to flow through the conductive element and the conductive
element comprising movable sections; changing the profile of the
surface of the conductive member to a predetermined profile by
moving the movable sections; applying a potential difference
between the conductive layer and the electrode; and forming a
predetermined conductive layer profile of the conductive layer.
25. The method of claim 24, wherein the step of forming comprises
electropolishing the conductive layer according to a predetermined
material removal profile.
26. The method of claim 24, wherein the step of changing comprises
changing the profile of the surface of the conductive member to
another predetermined profile by moving the movable sections.
27. The method of claim 26 further comprising: applying a potential
difference between the conductive layer and the electrode; and
forming another predetermined conductive layer profile of the
conductive.
28. The method of claim 24, wherein the step of forming comprises
electropolishing the conductive layer according to another
predetermined material removal profile.
29. The method of claim 24 further comprising varying the potential
difference during the step of applying to vary material removal
rate from the conductive layer.
Description
RELATED APPLICATIONS
[0001] This application claims priority from Provisional
Application Ser. No. 60/491,470 filed Jul. 30, 2003 (NT-305 P).
This application is a continuation in part of U.S. patent
application Ser. No. 10/302,755 filed Nov. 21, 2002 (NT-205); and
U.S. patent application Ser. No. 10/152,793 filed May 23, 2002
(NT-102 D) which is a divisional application of U.S. patent
application Ser. No. 09/511,278 filed Feb. 23, 2000 (NT-102), now
U.S. Pat. No. 6,413,388, all incorporated herein by reference.
FIELD
[0002] The present invention relates to manufacture of
semiconductor integrated circuits and, more particularly to a
method for electrochemically or electrochemical-mechanically
polishing of conductive layers.
BACKGROUND
[0003] Conventional semiconductor devices generally include a
semiconductor substrate, usually a silicon substrate, and a
plurality of sequentially formed dielectric layers and conductive
paths or interconnects made of conductive materials. Interconnects
are usually formed by filling a conductive material in trenches
etched into the dielectric layers. In an integrated circuit,
multiple levels of interconnect networks laterally extend with
respect to the substrate surface. Interconnects formed in different
layers can be electrically connected using vias or contacts.
[0004] The filling of a conductive material into features such as
vias, trenches, pads or contacts, can be carried out by
electrodeposition or electroplating. In electrodeposition method, a
conductive material, such as copper is deposited over the substrate
surface including into such features. Then, a material removal
technique is employed to planarize and remove the excess metal from
the top surface, leaving conductors only in the features or
cavities. Conventionally, chemical mechanical polishing (CMP) and
electropolishing is employed to planarize and remove excess metal
layers deposited on semiconductor wafers.
[0005] Chemical mechanical polishing (CMP) process planarizes and
reduce the thickness of the copper layer to the level of the
barrier layer coating the top surface so that copper is only left
inside the etched features. CMP can further remove all of the
conductors from the top surface so that copper-filled features are
electrically isolated from one another. However, CMP process is a
costly and time-consuming process that reduces production
efficiency. Furthermore, although CMP can be used with the
conventional interlayer dielectrics, it may create problems with
porous low-k dielectrics because of the mechanical force applied on
the wafer surface during the CMP process. During the CMP step, the
porous low-k materials may be stressed and may delaminate or other
defects may form due to the low mechanical strength of such
materials.
[0006] Another material removal technique involves well-known
electropolishing processes. During an electropolishing process,
both the material to be removed and a conductive electrode remain
in an electropolishing solution. Typically, an anodic (positive)
voltage is applied to the material to be removed with respect to
the conductive electrode. With the applied voltage, the material is
electrochemically dissolved and removed from the wafer surface.
[0007] In interconnect manufacturing, electropolishing process can
be used to reduce the thickness of the overburden or excess copper
layers deposited on the semiconductor substrates, as exemplified in
FIG. 1. Copper 10 is electrodeposited on a dielectric layer 12 that
is previously formed on the semiconductor substrate 14. Features 16
as well as the surface 20 of the dielectric layer 14 are filled
with copper 10. Before the copper deposition, a barrier layer 22
such as Tantalum layer and a copper seed layer (not shown) are
coated in the features and the surface of the dielectric layer 12.
The conventional method for removal of the excess copper from the
surface 20 is CMP. As mentioned above, electropolishing can also be
used to reduce the thickness of this copper layer to an exemplary
level indicated by dashed line 24, or even eliminate all copper
from the surface as indicated by line 25. However, to be able to
achieve these results without removing any copper from the
features, the electropolishing process needs to be highly efficient
and uniform. In cases where the thickness of copper on the wafer
surface is not uniform but has a profile, the electropolishing
technique should provide capability to tune the removal rate
profile to match the initial copper thickness profile on the
wafer.
SUMMARY
[0008] Present invention provides an electrochemical or
electrochemical mechanical material removal system and an
electrochemical or electrochemical mechanical material removal
method employing a device made of a conductive material. The device
is positioned between an electrode of the system and a conductive
surface of a workpiece that is being electrochemically removed. The
device includes openings or pores, which allow a process solution,
such as an electroetching or electropolishing solution, to flow
through the device.
[0009] The solution contacts the electrode, the device and the
conductive surface when a material removal potential is applied
between the conductive surface (anode) and the electrode
(cathode).
[0010] In one aspect of the present invention, material removal
rate is controlled by adjusting the distance between the conductive
surface and a device surface that faces the conductive surface.
[0011] In another aspect of the present invention, material removal
profile from the conductive surface can be controlled with the
geometry or topography of the device surface.
[0012] A device surface, when placed substantially parallel to the
conductive surface, the electropolishing of the conductive surface
is efficient and produces a substantially uniform material removal
rate.
[0013] A device surface with a center high and edge low profile
causes a material removal rate which is higher near the center of
the conductive surface.
[0014] A device surface with an edge high and center low profile
causes a material removal rate which is lower near the center of
the conductive surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic illustration of a substrate having an
electroplated copper layer;
[0016] FIG. 2 is a schematic illustration of an embodiment of an
electropolishing system of the present invention;
[0017] FIG. 3 is a graph shoving a conventional electropolishing
removal profile and an electropolishing removal profile of the
present invention;
[0018] FIG. 4 is a schematic illustration of another embodiment of
an electropolishing system of the present invention;
[0019] FIG. 5A is a schematic illustration of an embodiment of a
conductive element of the present invention;
[0020] FIG. 5B is a graph shoving an electropolishing removal
profile obtained using the conductive element shown in FIG. 5A;
[0021] FIG. 6A is a schematic illustration of another embodiment of
a conductive element of the present invention;
[0022] FIG. 6B is a graph shoving an electropolishing removal
profile obtained using the conductive element shown in FIG. 6A;
[0023] FIG. 7A is a schematic plan view of an embodiment of a
conductive element of the present invention;
[0024] FIG. 7B is a schematic side view of an embodiment of the
conductive element of the present invention shown in FIG. 7A;
[0025] FIGS. 8A-8C are schematic illustrations of a conductive
element with movable sections;
[0026] FIGS. 9A-9B are schematic illustrations of embodiments of
various conductive elements; and
[0027] FIG. 10 is a schematic illustration of a switch system for
electrochemically cleaning the conductive element at process
intervals.
DETAILED DESCRIPTION
[0028] Present invention provides an electropolishing system and a
method using a conductive member positioned between an electrode
and a workpiece surface that is being electropolished. The
conductive member may be a perforated or porous plate, which allows
a process solution to flow through it. The electropolishing
solution contacts the electrode, the conductive member and the
workpiece surface while an electropolishing potential is applied
between the workpiece surface (anode) and the electrode (cathode).
Material removal rate may be controlled by adjusting the distance
between the conductive member surface and the workpiece surface as
well by the adjustment of the voltage applied between (or current
passing through) the workpiece surface and the electrode. In this
respect, as the conductive member surface gets closer to the
workpiece surface, the material removal rate is increased. Further,
material removal profile from the workpiece surface can be
controlled with the geometry or topography of the conductive member
surface that faces the workpiece surface. For example, if the
conductive member surface is flat and parallel to the workpiece
surface, the electropolishing of the workpiece surface produces a
substantially uniform removal rate. If the conductive member
surface has a center high and edge low profile, material removal
rate at the center of the workpiece surface is higher than the edge
of the workpiece. As a result, electropolishing process results in
a center low profile for the removal rate. Similarly, if the
conductive member has an edge high and center low profile, the
material etching or polishing rate at the center of the workpiece
surface will be lower than the edge of the workpiece. This, in
turn, results in a removal rate profile, which is edge low. Here,
the profile of the conductive member surface refers to three
dimensional shape of the surface or topography of the surface.
[0029] FIG. 2 shows an exemplary electropolishing system 100 to
perform process of the present invention. The system 100 comprises
a carrier 102 to hold a workpiece 104 or a wafer, an electrode 106
placed across the wafer 104 and a conductive member 108 positioned
between a front surface 110 of the wafer 104 and the electrode 106.
The conductive member 108 may be a conductive perforated plate and,
in this embodiment, is not connected to any power source. Since the
described process is an electrochemical removal or electropolishing
process, the electrode 106 becomes cathode of the system 100 while
the front surface 110 of the wafer 104 becomes the anode. In other
words, the front surface 110 may be defined as anodic compared to
the cathode electrode 106. The conductive member 108, although not
connected to any power source, is electrically more cathodic
compared to the front surface 110 of the wafer and more anodic
compared to the cathode electrode 106. Further, since the
conductive member 108 is between the front surface 110 and the
electrode 106, which is a cathode, its voltage is expected to be
positive but lower than the front surface voltage of the wafer 104.
The front surface 110 and the electrode 106 are connected to a
power supply 112 through electrical contacts (not shown). The
electrical contacts may be conductive brushes contacting the
perimeter of the wafer 104 while the wafer is moved or rotated.
Such electrical contacts are described in U.S. patent application
Ser. No. 10/282,930 entitled Method and System to Provide
Electrical Contacts for Electrotreating Processes filed Oct. 28,
2002, which is owned assignee of the present application.
Alternately, other contacting methods well known in the art may be
used. The wafer 104 may be a semiconductor wafer and the front
surface 110 may include a previously deposited copper layer to be
electropolished, such as exemplified in FIG. 1. The carrier 102 is
able to rotate and move wafer 104 vertically and laterally during
the process.
[0030] The conductive member 108 includes a first surface 114 and a
second surface 116 and a plurality of openings 118 extending
between the first and the second surfaces. The first surface 114
faces the front surface 110 of the wafer 104, and the second
surface 116 is placed across the electrode 106. In this embodiment,
the first surface 114 is flat and placed parallel to the front
surface 110 to facilitate uniform electropolishing of the front
surface. However, as will be described more fully below, the first
surface 114 of the conductive member 108 may have different
geometrical profiles to shape removal profile of the front surface
110 of the wafer 104. Preferably, a plurality of openings 118
extends between the first surface 114 and the second surface 116 of
the conductive member 108. A process solution 120 such as an
electropolishing solution flow through the openings 118.
[0031] Referring back to FIG. 2, the conductive member 108 divides
system 100 into two sections, namely a cathodic section 122 and an
anodic section 124. Openings 118 allow the electropolishing
solution 120 to flow between the cathodic section 122 and the
anodic section 124 of the system 100. In the cathodic section 122,
the electropolishing solution 120 is in contact with the cathode
electrode 106 and the conductive member 108, and in the anodic
section 124, the solution 120 is in contact with the front surface
110 (conductive surface) of the wafer 104 and the conductive member
108. Although FIG. 2 exemplifies the cathode electrode 106, the
conductive member 108 and the wafer 104 in a lateral configuration,
they can be aligned vertically or in upside down geometry and this
is within the scope of this invention.
[0032] The conductive member 108 is made of a conductive material,
such as a metal or metal alloy, or coated with a conductive
material. The conductive member 108 can also be a conductive porous
material or a mesh, instead of having openings 118 which are well
defined, as shown in FIG. 2. However, in any case the conductive
member should allow solution flow between the anodic section and
the cathodic section. The conductive member 108 is separated from
the front surface of the wafer 104 by a distance d.sub.1 and from
the electrode 106 by a distance d.sub.2. Preferably, the distance
d.sub.1 is smaller than the distance d.sub.2. The distance between
the front surface 110 of the wafer 104 and the electrode is
d.sub.3. In one exemplary embodiment d.sub.2 may be larger than 50
millimeters (mm) and d.sub.1 is smaller than 5 mm.
[0033] In one exemplary electropolishing process of the present
invention, the front surface of the wafer 104 is moved closer to
the first surface 114 of the conductive member 108 while the
electropolishing solution 120 is flowed through the conductive
member 108. As the wafer 104 is rotated or moved, or rotated and
moved in proximity of the first surface 114 of the conductive
member, a potential difference is applied between the front surface
and the electrode 106 to electropolish the copper of the front
surface 110. In this example, the distance d.sub.1 is 2-4 mm.
During electropolishing, the front surface 110 of the wafer 104 may
get very close to the first surface of the conductive member 108
but it never touches the conductive member.
[0034] In an alternative embodiment, the front surface 110 of the
wafer may be occasionally or continuously swept with a pad material
(not shown) during the electrochemical removal process. The
sweeping process may be used to planarize the front surface 110 as
it is electropolished. An example of use of pad material during
electrochemical mechanical processes can be found in U.S.
application Ser. No. 09/607,567 entitled Method and Apparatus for
Electrochemical Mechanical Deposition, filed Jun. 29, 2000, which
is owned by the assignee of the present application and which is
incorporated herein by reference. This process is sometimes
referred to as electrochemical mechanical etching (ECME) or
electrochemical mechanical polishing (ECMP). In one embodiment, the
pad material may be mounted on the first surface 114 of the
conductive member itself. The pad material may have openings to let
the process solution flow through or it may be made of a porous pad
material. The pad material may also be attached on the first
surface 114 of the conductive member 108 as pad pieces or strips.
It should be noted that in FIGS. 2 and 3 the electropolishing
solution 120 is shown to flow from the cathode electrode 106
towards the front surface 110 of the wafer 104. This is the
preferred process solution flow direction. However, the present
invention can be also performed by reversing the direction of the
process solution. Further, in one embodiment, the process solution
does not flow but forms a process solution pool in which
electropolishing is carried out. Furthermore, although not shown,
the electropolishing solution 120 may be re-circulated after
filtering and cleaning.
[0035] In FIG. 3, the curve 132 shows material removal profile
across the diameter of the wafer 104 when the electropolishing
process of the present embodiment is applied. Removal profile
depicted in curve 132 shows a flat removal profile with less than
2% non-uniformity. As shown in FIG. 3 for comparison reasons, when
the same electropolishing process is repeated after replacing the
conductive member 108 with a non-conductive member or by taking it
out of the process solution altogether, the removal profile
depicted with curve 134 is non-uniform and consequently
non-repeatable. It should be appreciated that when the
electrochemical removal process is applied to a large numbers of
wafers, copper removed from the wafer surface is mostly deposited
on the electrode surface. However, this copper may be porous or
powdery and as it deposits on the electrode it may change the shape
of the electrode and its surface conductance. Consequently, in
time, as more and more wafers are processed, electric field lines
between the electrode and the substrate are expected to change.
This causes changes in the material removal profiles. In other
words, the removal profile may not be repeatable for processing
large number of wafers. This is not acceptable in a semiconductor
IC production environment. Presence of the conductive element,
which is positioned very close to the front surface of the wafer,
assures uniform copper removal rate irrespective of the number of
wafers processed.
[0036] FIG. 4 shows another exemplary system to perform the
electropolishing process of the present invention. In system 200, a
conductive member 202 encloses a solution chamber 203 including a
cathode electrode 204 in a process solution 205. The process
solution 205 may be an electropolishing solution or electrolyte. It
should be noted that the cathode electrode 204 does not have to be
in the solution chamber 203. It may be placed at a different
location as long as there is fluid communication between it and the
solution chamber 203 through the process solution 205. A wafer
carrier 206 holds a conductive surface 208 of a workpiece 209 or
wafer close to an upper surface 210 of the conductive member 202.
Process solution 205 is delivered into the solution chamber 203
through a delivery port 214 and flowed through openings 216 of the
conductive member 202 towards the conductive surface 208 of the
wafer 204. During the process, wafer 209 is rotated and/or
laterally moved above the upper surface 210 of the conductive
member 202 while a potential difference is applied between the
conductive surface 208 and the cathode electrode 204 from a power
source 218. In this embodiment, sidewalls 220 of the solution
chamber 203 are made of a non-conductive, isolating material to
prevent electrical shorting between the cathode electrode 204 and
the conductive member 202. It should be noted that other components
such as filters, bubble reduction means, shaping plates, etc., may
be included in the solution chamber design of FIG. 4. For example,
a filter element may be attached to a lower surface 222 of the
conductive member 202 to reduce or eliminate particles that may
come to the front surface 208 of the wafer 209. Another filter
element may be placed over the cathode electrode 204 confining
particles generated on the electrode during the process to the
region close to the electrode.
[0037] As shown in FIGS. 5A and 6A, the conductive members can be
shaped depending on desired removal profile of the conductive
surface of the wafer. FIG. 5A shows a conductive member 300 with
center high design with openings 302 extending between a first
surface 304 and a second surface 306. The first surface 304 has a
convex shape. The conductive surface 310 of the wafer 312 faces the
first surface 304. For the purpose of clarity, in FIG. 5A, the
center high shape of the first surface 304 is exaggerated. In
practice, the height `h` of the convex surface may be in the range
of 0.5-3 mm or less. As shown in FIG. 5B with curve 315,
electropolishing process with the conductive member 300 yields a
center high material removal profile.
[0038] FIG. 6A shows another example of a conductive member 400
with edge high design with openings 402 extending between a first
surface 404 and a second surface 406. The first surface 404 has a
concave shape. The conductive surface 410 of the wafer 412 faces
the first surface 404. For the purpose of clarity, in FIG. 6A, the
center low shape of the first surface 404 is exaggerated. In
practice, depth `d` of the surface may be in the range of 0.5-3 mm
or less. As shown in FIG. 6B with curve 415, electropolishing
process with the conductive member 400 yields a center low and edge
high material removal profile. The second surfaces 306, 406 are
shown flat in FIGS. 5A and 6A. It should be understood that shapes
of these surfaces may be different. What is most effective in
determining removal profile is the shape of the first surfaces 304
and 404.
[0039] In another example, conductive member may have insulating or
high resistivity portions juxtaposed with the conductive portions.
Shape, geometry and the location of the insulating portions shape
the removal profile. One example of a conductive member 500 having
insulated regions 502, 504 and conductive region 505 is shown in
FIGS. 7A-7B. The conductive member 500 has a first surface 506 and
a second surface 508. Openings 510 extend between the first and the
second surfaces. The insulated regions 502, 504 of the conductive
member 500 may be made of an electrical insulation material or may
just be an electrically insulating film or layer partially coated
or attached on the first surface of the conductive member 500.
Insulated regions 502, 504 as well as the conductive region 505 may
not be co-planar but they may be formed as recesses or raised
regions. For example, the insulated regions 502, 504 may form the
recessed regions and the conductive region 505 may form the raised
region. As a front surface 512 of a wafer 514 is electropolished,
when a portion of the front surface 512 moves over the insulated
regions 502, 504, that portion is electropolished in a reduced rate
for that time duration. As shown in FIG. 7A in plan view and in
FIG. 7B in cross section, in this embodiment, as the wafer 514 is
rotated, edge region of the front surface 512 is partially exposed
to the insulated regions 502, 504 and material removal from the
edge region will be less than the center of the front surface 512
which is exposed to the conductive region 505 of the conductive
member 500. This electropolishing process yields a center high
removal profile similar to the one shown in FIG. 5B. During the
electropolishing process, electrical contact to the front surface
may be made along the edge of the wafer using conductive brush or
other type contacts. Such contacts are described in the above
mentioned U.S. application Ser. No. 10/282,930 which is
incorporated herein by reference.
[0040] FIGS. 8A-8C exemplifies a conductive member 600 having
movable sections 602, 604 and 606 and openings 608. By moving the
sections 602, 604 and 606 up and down with respect to one another,
various configurations of the conductive member 600 may be
obtained. Such configurations can be used to obtain different
material removal profiles that have been described above. For
example, conductive member configuration shown in FIG. 8A can be
used to obtain uniform material profiles. Conductive member
configuration shown in FIG. 8B can be used to obtain center
high-edge low material removal profile and the configuration in
FIG. 8C can be used to obtain center low-edge high material removal
profile.
[0041] Conductive members may have discontinuous surface profiles
including raised and recessed portions. Raised or recessed portions
may be aligned along certain profiles. FIG. 9A shows a conductive
member 700 having raised portions 702 and recessed portions 704
formed along a primary surface 705 of the conductive member 700.
Openings 706 may be formed through the raised portions 702 and
recessed portions 704. In this embodiment, a plurality of raised
portions 704 form a center high profile, which in turn enables
center high material removal profile during the electropolishing.
The surface to be electropolished must face the raised and recessed
portions, or primary surface 705 of the conductive member 700,
during the process. FIG. 9B shows another conductive member 800
having raised portions 802 and recessed portions 804 formed along a
primary surface 805 of the conductive member. Openings 806 are
formed through the portions 802 and 804. In this embodiment, raised
portions 804 have the same height, which enables uniform material
removal profile during the electropolishing. The surface to be
electropolished must face the raised and recessed portions, or
primary surface of the conductive member, during the process. The
recessed portions may be coated with an insulating material leaving
only the raised portions conductive and active during the
process.
[0042] FIG. 10 illustrates a method for cleaning a conductive
member 900. As described above, after a certain time of use or
process cycles, a conductive material accumulation may occur on the
conductive member 900 since the conductive member is more cathodic
compared to a conductive surface 902 of a wafer 904. Therefore,
conductive member needs to be cleaned with certain intervals. One
possible way of cleaning may be done by anodically polarizing the
conductive member 900 and dissolving the accumulated material at
certain intervals. FIG. 10 shows one embodiment of the cleaning
process. In this embodiment, when a switch 905 is connected
position "A", power source 906 applies a potential difference
between the conductive surface 902 and the cathode electrode 907.
In presence of electropolishing solution 908, this connection
results in electropolishing of the conductive surface 902. Most of
the removed material deposits on the cathode electrode 907.
However, depending on the distance between the surface 902 and the
top surface of the conductive member 900, some deposition can also
take place on the conductive member 900. This deposited conductive
material affects the electropolishing uniformity provided by the
conductive member 900 and needs to be cleaned at intervals.
Typically, larger distances would result in more deposition on the
conductive member. For cleaning the conductive member 900, the
switch 905 is turned to position "B" and a potential difference,
which may or may not be the same as the one applied when switch 905
was in "A" position, is applied between the conductive member 900
and the electrode 907 making the conductive member an anode. This
action cleans the accumulated material on the conductive member
900. After the cleaning, electropolishing process may continue on
other wafers by moving the switch 905 to position "A".
[0043] Although the present invention has been particularly
described with reference to the preferred embodiments, it should be
readily apparent to those of ordinary skill in the art that changes
and modifications in the form and details may be made without
departing from the spirit and scope of the invention.
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