U.S. patent application number 13/459075 was filed with the patent office on 2013-10-31 for methods and apparatus for active substrate precession during chemical mechanical polishing.
This patent application is currently assigned to Applied Materials, Inc.. The applicant listed for this patent is Hung Chen, Lakshmanan Karuppiah. Invention is credited to Hung Chen, Lakshmanan Karuppiah.
Application Number | 20130288577 13/459075 |
Document ID | / |
Family ID | 49477714 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130288577 |
Kind Code |
A1 |
Chen; Hung ; et al. |
October 31, 2013 |
METHODS AND APPARATUS FOR ACTIVE SUBSTRATE PRECESSION DURING
CHEMICAL MECHANICAL POLISHING
Abstract
In some aspects, a chemical mechanical polishing (CMP) apparatus
is provided that includes a polishing head having (a) a rotatable
spindle; (b) a membrane coupled to the rotatable spindle and
adapted to press a substrate against a polishing pad during
polishing of the substrate; and (c) a retaining ring rotatable
coupled to the spindle and adapted to surround a substrate being
pressed against a polishing pad during polishing and to limit
lateral movement of the substrate relative to the polishing head.
The CMP apparatus also includes a drive mechanism coupled to the
retaining ring and adapted to drive the retaining ring at a
different rate of rotation than the spindle during polishing.
Numerous other aspects are provided.
Inventors: |
Chen; Hung; (Sunnyvale,
CA) ; Karuppiah; Lakshmanan; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chen; Hung
Karuppiah; Lakshmanan |
Sunnyvale
San Jose |
CA
CA |
US
US |
|
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
49477714 |
Appl. No.: |
13/459075 |
Filed: |
April 27, 2012 |
Current U.S.
Class: |
451/59 ;
451/397 |
Current CPC
Class: |
B24B 47/10 20130101;
B24B 37/32 20130101 |
Class at
Publication: |
451/59 ;
451/397 |
International
Class: |
B24B 47/10 20060101
B24B047/10; B24B 1/00 20060101 B24B001/00; B24B 37/32 20120101
B24B037/32 |
Claims
1. A chemical mechanical polishing apparatus comprising: a
polishing head comprising: a rotatable spindle; a membrane coupled
to the rotatable spindle and adapted to press a substrate against a
polishing pad during polishing of the substrate; and a retaining
ring rotatable coupled to the spindle and adapted to surround a
substrate being pressed against a polishing pad during polishing
and to limit lateral movement of the substrate relative to the
polishing head; and a drive mechanism coupled to the retaining ring
and adapted to drive the retaining ring at a different rate of
rotation than the spindle during polishing.
2. The chemical mechanical polishing apparatus of claim 1 further
comprising a controller adapted to cause the drive mechanism to
rotate the retaining ring at a different rate of rotation than the
spindle during polishing.
3. The chemical mechanical polishing apparatus of claim 2 wherein
the controller is adapted to cause the drive mechanism to rotate
the retaining ring at about twice the rate of rotation of the
spindle during polishing.
4. The chemical mechanical polishing apparatus of claim 2 wherein
the controller is adapted to cause the drive mechanism to rotate
the retaining ring at about one-half the rate of rotation of the
spindle during polishing.
5. A method of polishing a substrate comprising: pressing the
substrate against a polishing pad using a polishing head having: a
rotatable spindle; a membrane coupled to the rotatable spindle and
adapted to press the substrate against the polishing pad during
polishing of the substrate; and a retaining ring coupled to the
spindle and adapted to surround the substrate being pressed against
the polishing pad during polishing and to limit lateral movement of
the substrate relative to the polishing head; rotating the spindle
and membrane of the polishing head at a first rotation rate during
polishing; and rotating the retaining ring of the polishing head at
a second rotation rate during polishing so as to cause the
substrate to rotate relative to the membrane of the polishing
head.
6. The method of claim 5 wherein the first rate is less than the
second rate.
7. The method of claim 5 wherein the first rate is greater than the
second rate.
8. A chemical mechanical polishing apparatus comprising: a
polishing head comprising: a rotatable spindle; a membrane coupled
to the rotatable spindle and adapted to press a substrate against a
polishing pad during polishing of the substrate; a retaining ring
rotatable coupled to the spindle and adapted to surround a
substrate being pressed against a polishing pad during polishing
and to limit lateral movement of the substrate relative to the
polishing head; and at least one rotation mechanism coupled to the
retaining ring, adapted to contact a substrate during polishing and
adapted to allow the substrate to rotate at a different rate than
the spindle during the during polishing.
9. The chemical mechanical polishing apparatus of claim 8 wherein
the at least one rotation mechanism comprises at least one roller
rotatably coupled to a trailing edge of the retaining ring.
10. The chemical mechanical polishing apparatus of claim 8 wherein
the retaining ring is stationary during polishing.
11. The chemical mechanical polishing apparatus of claim 8 wherein
the retaining ring comprises multiple retaining ring sections.
12. The chemical mechanical polishing apparatus of claim 8 wherein
the retaining ring has a different number of slurry grooves along a
leading edge of the retaining ring than along a trailing edge of
the retaining ring.
13. The chemical mechanical polishing apparatus of claim 8 wherein
the retaining ring has a different width along a leading edge of
the retaining ring than along a trailing edge of the retaining
ring.
14. A method of polishing a substrate comprising: pressing the
substrate against a polishing pad using a polishing head having: a
rotatable spindle; a membrane coupled to the rotatable spindle and
adapted to press the substrate against the polishing pad during
polishing of the substrate; a retaining ring coupled to the spindle
and adapted to surround the substrate being pressed against the
polishing pad during polishing and to limit lateral movement of the
substrate relative to the polishing head; and at least one rotation
mechanism coupled to the retaining ring, adapted to contact the
substrate during polishing and adapted to allow the substrate to
rotate at a different rate than the spindle during the during
polishing; rotating the spindle and membrane of the polishing head
at a first rotation rate during polishing; and rotating the at
least one rotation mechanism coupled to the retaining ring of the
polishing head at a second rotation rate during polishing so as to
cause the substrate to rotate relative to the membrane of the
polishing head.
15. The method of claim 14 wherein the at least one rotation
mechanism comprises at least one roller rotatably coupled to a
trailing edge of the retaining ring.
16. The method of claim 14 wherein the retaining ring is stationary
during polishing.
17. The method of claim 14 wherein the retaining ring comprises
multiple retaining ring sections.
18. The method of claim 14 wherein the retaining ring has a
different number of slurry grooves along a leading edge of the
retaining ring than along a trailing edge of the retaining
ring.
19. The method of claim 14 wherein the retaining ring has a
different width along a leading edge of the retaining ring than
along a trailing edge of the retaining ring.
20. The method of claim 14 further comprising applying a different
pressure along a leading edge of the retaining ring than along a
trailing edge of the retaining ring during polishing.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to semiconductor device
processing, and more particularly to active substrate precession
during chemical mechanical polishing.
BACKGROUND OF THE INVENTION
[0002] During semiconductor device manufacturing, numerous material
layers are deposited, patterned and etched to form electronic
circuitry and/or electrical connections on the substrate. In many
instances, a top surface of a substrate may be planarized between
processing steps. Such planarization typically is performed using
an etch-back step or chemical mechanical polishing (CMP).
[0003] During CMP, a substrate is placed face down on a polishing
pad and pressed against, and rotated relative to, the polishing pad
via a polishing head in the presence of a slurry. The slurry may
contain abrasive particles and/or chemicals that assist in material
removal from the substrate. Polishing is continued until enough
material is removed to form a planar surface on the substrate.
[0004] Maintaining uniformity across a substrate during CMP is
important to ensure uniform layer thicknesses for devices formed on
the substrate. However, maintaining thickness uniformity across the
entire surface of a substrate is difficult. This is particularly
true for larger diameter substrates. Therefore, a need exists for
methods and apparatus for improving uniformity during chemical
mechanical polishing, particularly for large substrate sizes.
SUMMARY OF THE INVENTION
[0005] In some aspects, a chemical mechanical polishing (CMP)
apparatus is provided that includes a polishing head having (a) a
rotatable spindle; (b) a membrane coupled to the rotatable spindle
and adapted to press a substrate against a polishing pad during
polishing of the substrate; and (c) a retaining ring rotatable
coupled to the spindle and adapted to surround a substrate being
pressed against a polishing pad during polishing and to limit
lateral movement of the substrate relative to the polishing head.
The CMP apparatus also includes a drive mechanism coupled to the
retaining ring and adapted to drive the retaining ring at a
different rate of rotation than the spindle during polishing.
[0006] In some aspects, a chemical mechanical polishing apparatus
is provided that includes a polishing head having (a) a rotatable
spindle; (b) a membrane coupled to the rotatable spindle and
adapted to press a substrate against a polishing pad during
polishing of the substrate; (c) a retaining ring coupled to the
spindle and adapted to surround a substrate being pressed against a
polishing pad during polishing and to limit lateral movement of the
substrate relative to the polishing head; and (d) at least one
rotation mechanism coupled to the retaining ring, adapted to
contact a substrate during polishing and adapted to allow the
substrate to rotate at a different rate than the spindle during the
during polishing.
[0007] In some aspects, a method of polishing a substrate is
provided that includes pressing the substrate against a polishing
pad using a polishing head having (a) a rotatable spindle; (b) a
membrane coupled to the rotatable spindle and adapted to press the
substrate against the polishing pad during polishing of the
substrate; and (c) a retaining ring rotatable coupled to the
spindle and adapted to surround the substrate being pressed against
the polishing pad during polishing and to limit lateral movement of
the substrate relative to the polishing head. The method includes
rotating the spindle and membrane of the polishing head at a first
rotation rate during polishing; and rotating the retaining ring of
the polishing head at a second rotation rate during polishing so as
to cause the substrate to rotate relative to the membrane of the
polishing head.
[0008] In some aspects, a method of polishing a substrate is
provided that includes pressing the substrate against a polishing
pad using a polishing head having (a) a rotatable spindle; (b) a
membrane coupled to the rotatable spindle and adapted to press the
substrate against the polishing pad during polishing of the
substrate; (c) a retaining ring coupled to the spindle and adapted
to surround the substrate being pressed against the polishing pad
during polishing and to limit lateral movement of the substrate
relative to the polishing head; and (d) at least one rotation
mechanism coupled to the retaining ring, adapted to contact the
substrate during polishing and adapted to allow the substrate to
rotate at a different rate than the spindle during the during
polishing. The method includes rotating the spindle and membrane of
the polishing head at a first rotation rate during polishing; and
rotating the at least one rotation mechanism coupled to the
retaining ring of the polishing head at a second rotation rate
during polishing so as to cause the substrate to rotate relative to
the membrane of the polishing head.
[0009] Numerous other aspects are provided. Other features and
aspects of the present invention will become more fully apparent
from the following detailed description, the appended claims and
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic diagram depicting a side view of an
example chemical-mechanical planarization system for polishing
substrates according to embodiments of the present invention.
[0011] FIGS. 2A-2B are top schematic views of a substrate and
retaining ring during polishing in accordance with embodiments of
the present invention.
[0012] FIG. 3 is a schematic side view of a first embodiment of an
example polishing system provided in accordance with the present
invention.
[0013] FIG. 4A is a schematic side view of a second embodiment of
an example polishing system provided in accordance with the present
invention.
[0014] FIGS. 4B-4E are schematic top views of example embodiments
of the polishing system of FIG. 4A in accordance with the present
invention.
DETAILED DESCRIPTION
[0015] The present invention provides methods and apparatus for
improving uniformity during chemical mechanical polishing of large
substrates (e.g., semiconductor wafers, glass substrates used for
liquid crystal displays (LCDs) or solar cells, or any other similar
underlying and/or supporting layer/structure).
[0016] As stated, during CMP a substrate is placed face down on a
polishing pad and pressed against, and rotated relative to, the
polishing pad via a polishing head. A slurry containing abrasive
particles and/or chemicals may be supplied to the polishing pad to
assist in material removal from the substrate as the substrate is
pressed against and rotated relative to the polishing pad. In this
manner, the top surface of the substrate may be planarized.
[0017] FIG. 1 illustrates a side view of an example
chemical-mechanical planarization (CMP) system 100 for polishing
substrates in accordance with the present invention. The system 100
includes a load cup assembly 102 for receiving a substrate (not
shown in FIG. 1) to be polished and for holding the substrate in
place for a polishing head 104 to pick up. The polishing head 104
is supported by an arm 106 that is operative to move the head 104
between the load cup assembly 102 and a polishing pad 108 on a
rotating platen 110. In operation, the polishing head 104 picks up
the substrate from the load cup assembly 102 and carries it to the
polishing pad 108. As the polishing pad 108 is rotated on the
platen 110, the head 104 rotates and pushes the substrate down
against the polishing pad 108. For example, an expandable membrane
(not shown) within the polishing head 104 may contact and press the
substrate against the polishing pad 108. Note that in the
embodiment shown, the diameter of the polishing pad 108 is more
than twice that of the substrate. Other platen, polishing pad
and/or substrate sizes may be used.
[0018] With reference to FIGS. 2A-2B, to maintain a substrate 202
in position under a polishing head 104, the polishing head 104
includes a retaining ring 204 that surrounds the substrate 202 and
limits its lateral movement during polishing. The substrate 202 has
a slightly smaller diameter D.sub.1 than a diameter D.sub.2 of the
retaining ring 204 (forming a gap 206 between the substrate 202 and
retaining ring 204 which is exaggerated in FIGS. 2A-2B). In some
embodiments, the gap 206 may be about 0.01 inches, although other
gap sizes may be used.
[0019] Rotation of the polishing pad 108 during polishing generates
a force that presses the substrate 202 against the retaining ring
204 as shown in FIG. 2B (causing the center of rotation of the
substrate 202 to no longer align with the center of rotation of the
polishing head 104/retaining ring 204). As mentioned, the polishing
head 104 is rotated during polishing, which causes the retaining
ring 204 to similarly rotate. This rotation of the retaining ring
204 causes rotation (precession) of the substrate 202 in a manner
similar to a gear wheel due to the misalignment of the centers of
rotation of the substrate 202 and retaining ring 204. (Note that
the membrane of the polishing head 104 used to press the substrate
202 against the polishing pad 108 typically has a low coefficient
of friction, allowing the substrate 202 to rotate relative to the
membrane of the polishing head 104 during polishing.)
[0020] Due to alignment and/or tolerances within the polishing head
104, the polishing head 104 may generate a non-concentric pressure
profile as it presses the substrate 202 against the polishing pad
108. Such a non-concentric pressure profile may produce a
non-concentric and/or asymmetrical polish profile on the substrate
202, and is thus undesirable. However, rotation (precession) of the
substrate 202 relative to the polishing head 104 during polishing,
as described above, may alleviate the affects of the non-concentric
pressure profile produced by the polishing head 104. For example,
for a 300 mm substrate, the mismatch between the diameter of the
substrate 202 and the retaining ring 204 is typically large enough
to allow the substrate 202 to precess about 180 degrees or more
relative to the polishing head 104 during polishing. This is
generally sufficient to reduce and/or mask any asymmetric polishing
profile that might otherwise result from a polishing head's
non-concentric pressure profile. However, any asymmetric polishing
profile is undesirable. Furthermore, for larger substrate sizes
such as 450 mm substrates, asymmetric polishing profiles may be
more pronounced. For example, the amount a substrate precesses
relative to the retaining ring 204 is proportional to the gap
between the substrate and retaining ring divided by the diameter of
the substrate:
amount of precession.about.(D.sub.2-D.sub.1)/D.sub.1=(gap
206)/D.sub.1
Accordingly, if the gap 206 remains relatively constant as
substrate size is increased, the amount the substrate 202 precesses
during polishing is reduced. This reduced precession may be
insufficient to mask the asymmetric polishing profile resulting
from a non-concentric polishing head pressure profile.
[0021] In accordance with embodiments of the present invention, a
polishing head/retaining ring configuration is employed that allows
active control over the amount a substrate precesses during
polishing. Such "active precession" allows a substrate to precess
sufficiently to reduce and/or minimize the asymmetric polishing
profile resulting from a non-concentric polishing head pressure
profile. This is beneficial to substrates of any size (e.g., 200
mm, 300 mm, 450 mm or other sized semiconductor wafers, or any
other substrate type or size).
[0022] FIG. 3 is a schematic side view of a first embodiment of an
example polishing system 300 provided in accordance with the
present invention. With reference to FIG. 3, the polishing system
300 includes polishing head 104 coupled to a controller 302. The
controller 302 may be a computer, a microcontroller, a programmable
logic controller or any other suitable controller.
[0023] Polishing head 104 includes a central spindle 304 rotatably
coupled to a retaining ring 204 via one or more bearing assemblies
306. A membrane 308 is coupled to the central spindle 304 and may
contact substrate 202, pressing substrate 202 against polishing pad
108. The membrane 308 is adapted to expand to press the substrate
202 against the polishing pad 108. For example, the membrane 308
may be a liquid or gas filled bladder. In some embodiments, the
portion of the membrane 308 that contacts the substrate 202 may be
a low friction material such as polytetrafluoroethylene (PTFE) or a
similar material.
[0024] Spindle 304 is coupled to a first drive mechanism 310 and
retaining ring 204 is coupled to a second drive mechanism 312 to
allow the spindle 304 and retaining ring 204 to be driven at
different rotation rates. In some embodiments, a single drive
mechanism may be used through suitable gearing and/or belts to
cause spindle 304 and retaining ring 204 to rotate at different
rates. Any suitable drive mechanisms may be used such as one or
more motors. Controller 302 may include computer program code for
directing rotation of spindle 304 and/or retaining ring 204 during
polishing as described further below.
[0025] Bearing assembly 306 keeps retaining ring 204 concentric
with membrane 308 and may comprise any suitable bearing assembly
such as ball bearings, roller bearings, slide bearings, track
bearings, non-contact bearings, or the like. The components of the
bearing assembly 306, such as the balls and races, may be formed of
a material compatible with the chemistry used during chemical
mechanical polishing within the polishing system 300 so as not to
degrade rapidly or generate particles that could contaminate a
substrate being polished. For instance, the bearing assembly 306
may be formed of a suitable polymer material. Alternatively or
additionally, the bearing assembly 306 may be shielded, sealed or
otherwise isolated from the polishing chemistry.
[0026] In operation, substrate 202 is placed on the polishing pad
108 and is pressed against the polishing pad 108 by polishing head
104 (via expansion of membrane 308). Retaining ring 204 surrounds
substrate 202 within the polishing head 104, and also contacts
polishing pad 108. Note that a suitable abrasive slurry (not shown)
may be applied to the polishing pad 108 before and/or during
polishing of the substrate 202.
[0027] Controller 302 causes drive 310 to rotate spindle 304 and
membrane 308 as indicated by arrow 314, and drive 312 to rotate
retaining ring 204 as indicated by arrow 316. Polishing pad 108 is
also rotated using the same or a different drive mechanism under
control of controller 302 or another controller (not shown). As
stated, rotation of polishing pad 108 causes substrate 202 to slide
into contact with retaining ring 204 as indicated by arrow 318.
[0028] In some embodiments, retaining ring 204 is rotated at a
faster rate than spindle 304. In other embodiments, retaining ring
204 is rotated at a slower rate than spindle 304. In either case,
retaining ring 204 and spindle 304 rotate at different rates so
that substrate 302 is actively precessed relative to membrane 308
(e.g., so that substrate 202 fully rotates beneath membrane 308
during polishing).
[0029] In one or more embodiments, spindle 304 may be rotated at a
rate of about 10 to about 150 rotations per minute (RPM), while
retaining ring 204 may be rotated at a rate of about 5 to about 300
RPM. For example, in some embodiments, retaining ring 204 may be
rotated at about one-half the rotation rate of spindle 304, while
in other embodiments, retaining ring 204 may be rotated at about
twice the rotation rate of spindle 304. Other rotation rates may be
used for the spindle 304 and/or retaining ring 204. Retaining ring
204 may be rotated during a portion of or the entire time spindle
304 is rotated, and/or may be maintained stationary one or more
times during polishing. Further, in some embodiments, retaining
ring 204 may switch direction of rotation during polishing.
[0030] Polishing of substrate 202 continues until a desired amount
of material is removed from the substrate 202. Because retaining
ring 204 rotates at a different rate than spindle 204, substrate
202 is actively precessed relative to membrane 308 and
non-concentric or otherwise asymmetric polishing head pressure
profile is averaged out during polishing (e.g., producing a more
uniform polish). This is beneficial to substrates of any size
(e.g., 200 mm, 300 mm, 450 mm or other sized semiconductor wafers,
or any other substrate type or size).
[0031] FIG. 4A is a schematic side view of a second embodiment of
an example polishing system 400 provided in accordance with the
present invention. The polishing system 400 of FIG. 4A is similar
to the polishing system 300 of FIG. 3. However, in the polishing
system 400 of FIG. 4A, the retaining ring 204 remains stationary
during polishing as indicated by coupling 402, and one or more
rollers 404 are employed to rotate substrate 202 relative to
membrane 308 during polishing. FIG. 4B is a schematic top view of
the polishing system 400 showing two rollers 404a and 404b. It will
be understood that other numbers of rollers may be used (e.g., 3,
4, 5, etc.).
[0032] Rollers 404a and 404b may be formed from any suitable
material such as polyphenylene sulfide (PPS), polyetheretherketone
(PEEK), polyethylene terephthalate (PET) or the like. Exemplary
diameters for the rollers 404a-b may range from about 0.5 to about
2 inches. In some embodiments, the rollers 404a-b may be spaced
apart by about 1 to 5 inches. Other materials, sizes and/or
spacings may be used for the rollers.
[0033] Controller 302 causes drive 310 to rotate spindle 304 and
membrane 308 as indicated by arrow 314, and drive 312 to rotate
rollers 404a and 404b as indicated by arrow 416. In some
embodiments a single drive mechanism may be used to rotate spindle
304, roller 404a and/or roller 404b through use of appropriate
belts, gears or the like; or a separate drive mechanism may be used
as shown in FIG. 4A. Polishing pad 108 is also rotated using the
same or a different drive mechanism under control of controller 302
or another controller (not shown). Rotation of polishing pad 108
causes substrate 202 to slide into contact with rollers 404a and
404b as indicated by arrow 418. This region may be referred to as
the trailing edge of the retaining ring 204, while the opposite
side may be referred to as the leading edge of the retaining ring
204.
[0034] In some embodiments, rollers 404a and 404b are rotated at a
faster rate than spindle 304. In other embodiments, rollers 404a
and 404b are rotated at a slower rate than spindle 304. In either
case, rollers 404a-b and spindle 304 rotate at different rates so
that substrate 302 is actively precessed relative to membrane 308
(e.g., so that substrate 202 fully rotates beneath membrane 308
during polishing).
[0035] In one or more embodiments, spindle 304 may be rotated at a
rate of about 10 to about 150 rotations per minute (RPM), while
rollers 404a-b may be rotated at a rate of about 30 to about 3600
RPM (depending on the diameter of the rollers). For example, in
some embodiments, rollers 404a-b may be rotated so that substrate
202 rotates at about one-half the rotation rate of spindle 304,
while in other embodiments, rollers 404a-b may be rotated so that
substrate 202 rotates at about twice the rotation rate of spindle
304. Other rotation rates may be used for the spindle 304 and/or
rollers 404a-b. Rollers 404a-b may be rotated during a portion of
or the entire time spindle 304 is rotated, and/or may be maintained
stationary one or more times during polishing. Further, in some
embodiments, rollers 404a-b may switch direction of rotation during
polishing.
[0036] Polishing of substrate 202 continues until a desired amount
of material is removed from the substrate 202. Because rollers
404a-b rotate at a different rate than spindle 204, substrate 202
is actively precessed relative to membrane 308 and any
non-concentric or otherwise asymmetric polishing head pressure
profile is averaged out during polishing (e.g., producing a more
uniform polish). This is beneficial to substrates of any size
(e.g., 200 mm, 300 mm, 450 mm or other sized semiconductor wafers,
or any other substrate type or size).
[0037] In general, retaining ring 204 may be formed from any
suitable material such as polyphenylene sulfide (PPS),
polyetheretherketone (PEEK), polyethylene terephthalate (PET) or
the like. In embodiments in which rollers 404 are employed, such as
in FIGS. 4A-4C, the retaining ring 204 may be modified to improve
substrate edge polish behavior. For example, features used to allow
entry of slurry into the polishing head 104 may be modified
depending on the application. In some embodiments, it may be
desirable to have slurry build up during polishing so additional
slurry grooves may be provided along the leading edge of the
retaining ring 204 relative to the trailing edge of the retaining
ring 204 (near rollers 404a-b). Likewise, in some embodiments it
may be desirable to have little slurry build up during polishing,
so more slurry grooves may be provided along the trailing edge of
the retaining ring 204 (near rollers 404a-b) than along the leading
edge of the retaining ring 204. Similarly, different forces may be
applied along the trailing edge of the retaining ring 204 relative
to the leading edge of the retaining ring 204 to better control pad
rebound during polishing. Similarly, the retaining ring 204 may
have different geometries (e.g., widths) along the trailing and
leading edges of the retaining ring 204.
[0038] While retaining ring 204 is shown as being a single ring
section, it will be understood that retaining ring 204 may comprise
multiple ring sections as illustrated by ring sections 204a and
204b in FIG. 4C. More than two ring sections may be used, as may
inner or outer ring sections. FIG. 4D illustrates a retaining ring
204 having larger and/or more slurry grooves 420a along a leading
edge of the retaining ring 204 than slurry grooves 420b along the
trailing edge of the retaining ring 204. Such an arrangement may be
reversed if desired. FIG. 4E illustrates a retaining ring 204 that
is wider along a leading edge of the retaining ring 204 than along
a trailing edge of the retaining ring 204. Such an arrangement may
be reversed if desired.
[0039] Accordingly, while the present invention has been disclosed
in connection with example embodiments thereof, it should be
understood that other embodiments may fall within the spirit and
scope of the invention, as defined by the following claims.
* * * * *