U.S. patent application number 12/840195 was filed with the patent office on 2012-01-26 for substrate holder to reduce substrate edge stress during chemical mechanical polishing.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Hung Chih Chen, Gautam Shashank Dandavate, Samuel Chu-Chiang Hsu, Denis M. Koosau.
Application Number | 20120021673 12/840195 |
Document ID | / |
Family ID | 45494017 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120021673 |
Kind Code |
A1 |
Chen; Hung Chih ; et
al. |
January 26, 2012 |
SUBSTRATE HOLDER TO REDUCE SUBSTRATE EDGE STRESS DURING CHEMICAL
MECHANICAL POLISHING
Abstract
Embodiments of the present invention generally relate to methods
for chemical mechanical polishing a substrate. The methods
generally include coupling a first substrate to be polished to a
dummy substrate, and removing a portion of the backside of the
first substrate to reduce the thickness of the first substrate. The
first substrate and the dummy substrate are positioned in a carrier
head assembly comprising an inflatable membrane and a support ring.
The first substrate is placed in contact with a polishing pad to
reduce the surface roughness of the backside of the first
substrate. The support ring restricts lateral movement of the
inflatable membrane to prevent the first substrate from contacting
an interior surface of the carrier head assembly. The support ring
is sized to allow vertical movement of the inflatable membrane
within the carrier head assembly.
Inventors: |
Chen; Hung Chih; (Sunnyvale,
CA) ; Hsu; Samuel Chu-Chiang; (Palo Alto, CA)
; Dandavate; Gautam Shashank; (Sunnyvale, CA) ;
Koosau; Denis M.; (Pleasanton, CA) |
Assignee: |
APPLIED MATERIALS, INC.
Santa Clara
CA
|
Family ID: |
45494017 |
Appl. No.: |
12/840195 |
Filed: |
July 20, 2010 |
Current U.S.
Class: |
451/28 |
Current CPC
Class: |
B24B 37/32 20130101 |
Class at
Publication: |
451/28 |
International
Class: |
B24B 7/20 20060101
B24B007/20; B24B 1/00 20060101 B24B001/00 |
Claims
1. A method, comprising: coupling a first substrate to a second
substrate, the first substrate having a first surface in contact
with the second substrate and the first surface opposite a second
surface; positioning the second substrate and the first substrate
in a carrier head assembly, the carrier head assembly comprising:
an inflatable membrane in contact with the second substrate; and a
support ring disposed circumferentially around the inflatable
membrane; and contacting the second surface of the first substrate
to a polishing pad to reduce the surface roughness of the second
surface of the first substrate.
2. The method of claim 1, wherein the support ring is sized to
restrict substantially all lateral movement of the inflatable
membrane, but allow the inflatable membrane to travel in a vertical
direction.
3. The method of claim 1, wherein the average distance between the
support ring and an interior surface of the carrier head assembly
is less than about ten-thousandths of an inch.
4. The method of claim 3, wherein the interior surface of the
carrier head assembly consists essentially of a planar surface.
5. The method of claim 4, wherein the first substrate is coupled to
the second substrate using an epoxy.
6. The method of claim 5, wherein the first substrate comprises a
through-silicon via, and a device feature formed on the first
surface.
7. The method of claim 6, further comprising removing a portion of
the second surface of the first substrate to decrease the thickness
of the first substrate prior to the contacting the second surface
of the first substrate to a polishing pad.
8. A method, comprising: coupling a first surface of a first
substrate to a second substrate; positioning the second substrate
and the first substrate in a carrier head assembly, the carrier
head assembly comprising: an inflatable membrane in contact with
the second substrate, the inflatable membrane comprising a textured
surface; and a support ring disposed circumferentially around the
inflatable membrane and the second substrate, the support ring
positioned to reduce lateral movement of the inflatable membrane
and the second substrate such that the first substrate does not
contact an interior surface of the carrier head assembly during
polishing; and contacting a second surface of the first substrate
to a polishing pad to reduce the surface roughness of the second
surface of the first substrate.
9. The method of claim 8, wherein there is substantially no lateral
movement of the inflatable membrane in the carrier head.
10. The method of claim 9, wherein the average distance between the
support ring and an interior surface of the carrier head assembly
is less that about ten-thousandths of an inch.
11. The method of claim 10, wherein the interior surface of the
carrier head assembly consists essentially of a planar surface.
12. The method of claim 11, further comprising removing a portion
of the second surface of the first substrate to decrease the
thickness of the first substrate prior to the contacting a second
surface of the first substrate to a polishing pad.
13. The method of claim 12, wherein first substrate is coupled to
the second substrate using an epoxy.
14. The method of claim 8, wherein the support ring contacts at
least about 25 percent of the sidewall of the second substrate.
15. The method of claim 14, wherein the support ring contacts at
least about 50 percent of the sidewall of the second substrate.
16. The method of claim 15, wherein the first substrate comprises a
through-silicon via, and a device feature formed on the first
surface.
17. A method, comprising: coupling a first surface of a first
substrate to a second substrate using an epoxy, the first surface
of the first substrate opposite a second surface, the first surface
having a device feature formed thereon; positioning the second
substrate and the first substrate in a carrier head assembly, the
carrier head assembly comprising: an inflatable membrane in contact
with the second substrate; and a support ring disposed
circumferentially around the inflatable membrane and the second
substrate, the support ring sized to restrict substantially all
lateral movement of the inflatable membrane, but allow the
inflatable membrane to travel in a vertical direction; and
contacting the first substrate to a polishing pad to reduce a
surface roughness of the second surface of the first substrate.
18. The method of claim 17, wherein the thickness of the first
substrate is about 100 microns.
19. The method of claim 18, wherein the support ring contacts at
least about 25 percent of the sidewall of the second substrate.
20. The method of claim 19, wherein the inflatable membrane
comprises a textured surface in contact with the second substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments of the present invention generally relate to a
method for chemical mechanical polishing (CMP) of a substrate and
an apparatus for practicing the method.
[0003] 2. Description of the Related Art
[0004] Vias have been used in semiconductor fabrication to provide
electrical coupling between one or more layers of conductive
material within a semiconductor device. More recently,
through-silicon vias (TSV) have arisen as an alternative method to
conventional wire bonding. Through-silicon vias allow for shorter
interconnects by forming an interconnect in the z-axis. The
interconnect is created through a substrate by forming a via
extending from a front surface to a back surface of the substrate.
After creating the interconnects in the z-axis, multiple substrates
can then be stacked on top of one another, and electrically coupled
through the vertically extending interconnect. TSV substrates may
provide a means for reducing the footprint of substrates in
semiconductor applications.
[0005] Therefore, there is a need in the art for methods and
apparatus for processing substrates useful in TSV applications.
SUMMARY OF THE INVENTION
[0006] Embodiments of the present invention generally relate to
methods for chemical mechanical polishing a substrate. The methods
generally include coupling a first substrate to be polished to a
dummy substrate, and removing a portion of the backside of the
first substrate to reduce the thickness of the first substrate. The
first substrate and the dummy substrate are positioned in a carrier
head assembly comprising an inflatable membrane and a support ring.
The first substrate is placed in contact with a polishing pad to
reduce the surface roughness of the backside of the first
substrate. The support ring restricts lateral movement of the
inflatable membrane to prevent the first substrate from contacting
an interior surface of the carrier head assembly. The support ring
is sized to allow vertical movement of the inflatable membrane
within the carrier head assembly.
[0007] In one embodiment, a method includes coupling a first
substrate to a second substrate. The first substrate has a first
surface in contact with the second substrate, and the first surface
is opposite a second surface. The second substrate and the first
substrate are positioned in a carrier head assembly. The carrier
head assembly comprises an inflatable membrane in contact with the
second substrate, and a support ring disposed circumferentially
around the inflatable membrane. The second surface of the first
substrate is contacted with a polishing pad to reduce the surface
roughness of the second surface of the first substrate.
[0008] In another embodiment, a method includes coupling a first
surface of a first substrate to a second substrate. The second
substrate and the first substrate are positioned in a carrier head
assembly. The carrier head assembly comprises an inflatable
membrane in contact with the second substrate, and a support ring
disposed circumferentially around the inflatable membrane and the
second substrate. The inflatable membrane comprises a textured
surface. The support ring is positioned to reduce lateral movement
of the inflatable membrane and the second substrate such that the
first substrate does not contact an interior surface of the carrier
head assembly during polishing. A second surface of the first
substrate is contacted with a polishing pad to reduce the surface
roughness of the second surface of the first substrate.
[0009] In another embodiment, a method includes coupling a first
surface of a first substrate to a second substrate using an epoxy.
The first surface of the first substrate is opposite a second
surface, and the first surface has a device feature formed thereon.
The second substrate and the first substrate are positioned in a
carrier head assembly. The carrier head assembly comprises an
inflatable membrane in contact with the second substrate, and a
support ring disposed circumferentially around the inflatable
membrane and the second substrate. The support ring is sized to
restrict substantially all lateral movement of the inflatable
membrane, but allow the inflatable membrane to travel in a vertical
direction. The first substrate is contacted with a polishing pad to
reduce a surface roughness of the second surface of the first
substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] 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.
[0011] FIG. 1 is a schematic sectional view of one embodiment of a
polishing station that includes a carrier head.
[0012] FIGS. 2A and 2B are schematic sectional views of carrier
head assemblies for use in substrate processing.
[0013] FIG. 3A is a schematic perspective view of one embodiment of
a membrane support structure for use in a polishing head
membrane.
[0014] FIGS. 3B and 3C are schematic views of textured surfaces of
membranes for use in a polishing head.
[0015] FIGS. 4A and 4B are schematic sectional views of carrier
head assemblies.
[0016] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
disclosed in one embodiment may be beneficially utilized on other
embodiments without specific recitation.
DETAILED DESCRIPTION
[0017] Embodiments of the present invention generally relate to
methods for chemical mechanical polishing a substrate. The methods
generally include coupling a first substrate to be polished to a
dummy substrate, and removing a portion of the backside of the
first substrate to reduce the thickness of the first substrate. The
first substrate and the dummy substrate are positioned in a carrier
head assembly comprising an inflatable membrane and a support ring.
The first substrate is placed in contact with a polishing pad to
reduce the surface roughness of the backside of the first
substrate. The support ring restricts lateral movement of the
inflatable membrane to prevent the first substrate from contacting
an interior surface of the carrier head assembly. The support ring
is sized to allow vertical movement of the inflatable membrane
within the carrier head assembly.
[0018] Embodiments of the present invention are beneficial for
processing substrates useful for through-silicon via applications.
Suitable apparatus for performing chemical mechanical polishing on
substrates are the REFLEXION LK.TM. and the REFLEXION GT CMP
systems available from Applied Materials, Inc. of Santa Clara,
Calif. It is contemplated that other commercially available
chemical mechanical polishing systems can advantageously utilize
embodiments disclosed herein.
[0019] FIG. 1 is a partial sectional view of one embodiment of a
polishing station 100 that includes a carrier head body 104. The
polishing station 100 includes the carrier head assembly 102 and a
platen assembly 120. A first substrate 110 and a second substrate
112 are disposed in the carrier head assembly 102 during polishing.
The carrier head assembly 102 generally retains a first substrate
110 against a polishing pad assembly 130 disposed on the platen
assembly 120. At least one of a carrier head assembly 102 or platen
assembly 120 is rotated or otherwise moved to provide relative
motion between the first substrate 110 and the polishing pad
assembly 130. In the embodiment depicted in FIG. 1, the carrier
head assembly 102 is coupled to an actuator or motor 150 that
provides at least rotational motion to the substrate 110 about axis
118. The motor 150 may also oscillate the carrier head assembly
102, such that the substrate 110 is moved laterally back and forth
across the surface 132 of the polishing pad assembly 130.
[0020] The polishing pad assembly 130 may comprise a conventional
material such as a foamed polymer disposed on the platen assembly
120 as a pad. In one embodiment, the conventional polishing
material is foamed polyurethane. In one embodiment, the pad is an
IC1010 polyurethane pad, available from Rodel Inc., of Newark, Del.
IC1010 polyurethane pads typically have a thickness of about 2.05
mm and a compressibility of about 2%. Other pads that can be used
include IC1000 pads with and without an additional compressible
bottom layer underneath the IC1000 pad, IC1010 pads with an
additional compressible bottom layer underneath the IC1010 pad, and
polishing pads available from other manufacturers. The compositions
described herein are placed on the pad to contribute to the
chemical mechanical polishing of a substrate.
[0021] In one embodiment, the carrier head assembly 102 includes a
carrier head body 104 defining a substrate receiving pocket. The
substrate receiving pocket allows a first substrate 110 and a
second substrate 112 to be disposed therein. A membrane 114 is
disposed in the substrate receiving pocket and may be evacuated to
chuck a second substrate 112 to the carrier head assembly 102, and
pressurized to control the downward force of a first substrate 110
when pressed against the polishing pad assembly 130. The membrane
114 is circumferentially encompassed by support ring 106. In one
embodiment, the carrier head may be a multi-zone carrier head. One
suitable carrier head assembly 102 is a TITAN HEAD.TM. carrier head
available from Applied Materials, Inc., located in Santa Clara,
Calif.
[0022] The platen assembly 120 is supported on a base 154 by
bearings 156 that facilitate rotation of the platen assembly 120
about axis 117. A motor 158 is coupled to the platen assembly 120
and rotates the platen assembly 120 such that the polishing pad
assembly 130 is moved relative to the carrier head assembly
102.
[0023] The combined slurry/rinse arm assembly or fluid delivery arm
assembly 140 is utilized to deliver slurry from a slurry supply 161
through tube 163 to a surface 132 of the polishing pad assembly
130. In an alternative embodiment, the rinse fluid and the
processing fluid may be provided to the polishing pad assembly 130
through separate delivery arm assemblies. In the embodiment
depicted in FIG. 1, the fluid delivery arm assembly 140 includes an
arm 142 extending from a stanchion 144. A motor 146 is provided to
control the rotation of the arm 142 about a center line of the
stanchion 144. An adjustment mechanism 147 may be provided to
control the elevation of a distal end 148 of the arm 142 relative
to the working surface of the polishing pad assembly 130. The
adjustment mechanism 147 may be an actuator coupled to at least one
of the arm 142 or the stanchion 144 for controlling the elevation
of the distal end 148 of the arm 142 relative to the platen
assembly 120.
[0024] The fluid delivery arm assembly 140 may include a plurality
of rinse outlet ports 160 arranged to uniformly deliver a spray
and/or stream of rinsing fluid to the surface of the polishing pad
assembly 130. The ports 160 are coupled by a tube 162 routed
through the fluid delivery arm assembly 140 to a rinsing fluid
supply 164. In one embodiment, the fluid delivery arm may have
between 12 and 15 ports. The rinsing fluid supply 164 provides a
rinsing fluid to the polishing pad assembly 130 before, during,
and/or after polishing the phase change alloy containing substrate
and/or after the substrate 110 is removed to clean the polishing
pad assembly 130. The polishing pad assembly 130 may also be
cleaned using fluid from the ports 160 after conditioning the pad
using a conditioning element, such as a diamond disk or brush (not
shown). The polishing station 100 can also include a pad
conditioner apparatus (not shown) to maintain the condition of the
polishing pad assembly 130 so that it will effectively polish the
first substrate 110. The pad conditioner may be coupled to arm 142,
or may be coupled to a separate arm (not shown).
[0025] The nozzle assembly 166 is disposed at the distal end of the
arm 142. The nozzle assembly 166 is coupled to the slurry supply
161 by a tube 168 routed through the fluid delivery arm assembly
140. Slurry supply 161 may generally supply any processing fluid.
The processing fluid supply may be a polishing slurry or polishing
abrasive. The nozzle assembly 166 includes a nozzle 170 that may be
selectively adjusted relative to the arm, such that the fluid
exiting the nozzle 170 may be selectively directed to a specific
area of the polishing pad assembly 130.
[0026] In one embodiment, the nozzle 170 is configured to generate
a spray of slurry. In another embodiment, the nozzle 170 is adapted
to provide a stream of slurry. In another embodiment, the nozzle
170 is configured to provide a stream and/or spray of slurry at a
rate between about 200 to about 500 ml/second to the polishing
surface.
[0027] In the embodiment depicted in FIG. 1, a first substrate 110
may be a substrate used in through-silicon via applications. The
first substrate 110 typically has a thickness of about 100 microns
or less. Because the substrate is thin and flexible, the first
substrate 110 is coupled to a second substrate 112 for support. The
second substrate may have a thickness of about two inches. If a
device feature is formed on a surface of the first substrate 110,
then first substrate 110 and second substrate 112 are coupled
together such that the device feature is positioned between the two
substrates, e.g., the surface of the first substrate 110 having the
device feature formed thereon is oriented towards the second
substrate 112. Orienting the substrate in this manner protects the
device feature formed on the first substrate 110 during subsequent
processes.
[0028] When coupling the first substrate 110 and the second
substrate 112, the two substrates may be fixedly coupled by epoxy,
or any other suitable material that does not have an adverse effect
on the substrates. The second substrate 112 is generally a glass
dummy substrate or a sacrificial substrate. After coupling the
first substrate 110 and the second substrate 112, but prior to
chemical mechanical polishing the first substrate 110, a portion of
the first substrate 110 may be removed. The thickness of the first
substrate 110 may be reduced using mechanical grinding, or etching.
The reduced thickness of the first substrate 110 allows for use in
TSV and stacked chip applications. Generally, the first substrate
has an initial thickness approximately equal to the second
substrate prior to the reduction in thickness. The process used for
reducing the thickness of the first substrate 110 typically leaves
a rough surface on the backside of the first substrate. To reduce
the surface roughness on the backside of the first substrate 110,
chemical mechanical polishing may be used. The reduced thickness of
the first substrate 110 leaves the substrate flexible and fragile.
Therefore, the first substrate 110 is coupled to a second substrate
112 as an additional means of support during grinding and polishing
of the first substrate 110.
[0029] FIG. 2A is a schematic sectional view of a polishing head
assembly for use in substrate processing. The polishing head
assembly has a carrier head body 204a defining a substrate
receiving pocket. The substrate receiving pocket is adapted to
contain a first substrate 210a and second substrate 212a during a
chemical mechanical polishing process.
[0030] A membrane 214a is disposed within the substrate receiving
pocket. The membrane 214a may be a flexible elastic membrane. In
one embodiment, the membrane 214a may be high strength silicone
rubber. A surface 213a of membrane 214a generally is textured to
increase the friction between the membrane 214a and a second
substrate 212a. The friction provided by the textured surface 213a
prevents the second substrate 212a, or the first substrate 210a
coupled thereto, from moving or sliding with respect to the
membrane 214a when placed in the substrate receiving pocket of the
carrier head body 204a. If the second substrate 212a moves or
slides with respect to membrane 214a, the first substrate 210a may
come into contact with the carrier head body 204a. As previously
mentioned, the first substrate 210a is thin and flexible, and can
break easily. If the first substrate 210a comes into contact with
the carrier head body 204a, the outer edge of the first substrate
210a is subjected to increased stress which may cause the substrate
to chip, crack, fracture or break.
[0031] A support ring 206a is disposed circumferentially around the
membrane 214a. The purpose of the support ring is to allow for
vertical movement of the membrane 214a, while restricting
horizontal movement of the membrane 214a within the carrier head
assembly 202a. Additionally, the support ring 206a provides lateral
support and stiffness to the membrane 214a, allowing the membrane
214a to retain its shape and not over-flex in the horizontal
direction. The membrane 214a is formed of a flexible material, and
may permit the first substrate 210a to come into contact with the
inner sidewall 208a of the carrier head body 204a during polishing
if sufficient support is not provided. For example, the first
substrate 210a may come into contact with the carrier head body
204a as a result of a rocking motion applied to the carrier head
assembly 202a.
[0032] The support ring 206a may be formed of an elastic material
and clamped to the membrane 214a. The distance between support ring
206a and the inner sidewall 208a of the carrier head body 204a is
preferably just enough to allow the membrane 214a to float in a
vertical direction, but have substantially no vertical movement.
For example, the distance between the support ring 206a and the
carrier head body 204a may be about ten-thousandths of an inch when
the membrane is centered in the carrier head assembly 202a. In
another embodiment, the support ring internal diameter is reduced,
and a membrane clamp is not used to secure the support ring 206a to
the membrane 214a. Therefore, when pressure is applied on the
membrane, the membrane expands and further reduces the gap between
the membrane 214a and the sidewall 208a. Furthermore, this
expansion also increases the rigidity or stiffness of the membrane,
allowing the first substrate 210a and the second substrate 212a to
stay substantially centered in the carrier head body 204a.
[0033] By having the support ring 206a substantially the same outer
diameter as the inner diameter of the carrier head body, the
movement of the membrane is restricted in the horizontal direction.
This restriction in the horizontal direction is useful for
protecting the first substrate 210a in instances where the first
substrate is adhered to the second substrate 212a off-center. For
example, if the first substrate 210a is coupled to the second
substrate 212a such that a portion of the first substrate 210a
extends past or protrudes beyond the outer diameter of the second
substrate 212a, it would be possible in some instances that the
first substrate 210a would contact the carrier head body 204a.
However, if the support ring 206a prohibits substantially all of
the horizontal movement of the membrane and the first and second
substrates frictionally held thereby, then there is less likelihood
that the first substrate 210a will contact the carrier head body
204a. A support ring of increased thickness, e.g., one having an
outside diameter substantially the same or slightly less than the
interior diameter of the carrier head body 204a, assists in
protecting the edges of the first substrate 210a. The combination
of increased support ring thickness to restrict lateral movement of
the membrane 214a, and the increased friction of surface 213a to
maintain the second substrate in the appropriate position reduces
the edge-stress applied to the first substrate 210a.
[0034] Additionally, the inner sidewall 208a of carrier head body
204a is substantially planar. For example, the inner sidewall 208a
of the carrier head body 204a may consist essentially of a
substantially planar surface. It is preferable to not have any
grooves to facilitate fluid flow, or any other deformations in the
sidewall 208a. When grooves are present, it may be possible that
the first substrate 210a or the second substrate 212a may contact
this groove. This may cause an unevenly worn spot to form where the
first or second substrate occasionally contacts the groove.
Additionally, if the first substrate 210a contacts the groove, it
may cause the first substrate to chip or crack. Since the membrane
214a is permitted to move in a vertical direction, it is possible
that the first substrate 210a could rub on the sidewall 208a until
the groove is contacted, damaging the first substrate 210a.
[0035] FIG. 2B is a schematic sectional view of carrier head
assembly for use in substrate processing. In the embodiment of FIG.
2B, a carrier head assembly 202b has a carrier head body 204b
defining a substrate receiving pocket. A membrane 214b is disposed
in the substrate receiving pocket. The membrane has a textured
surface 213b with a relatively high coefficient of friction. The
textured surface 214b is placed in contact with a second substrate
212b, which is coupled to a first substrate 210b. The textured
surface 213b of membrane 214b prevents the second substrate 212b
from moving relative to the membrane 214b once placed in contact
with the membrane 214b.
[0036] A support ring 206b is placed circumferentially around and
in contact with the membrane 214b and the second substrate 212b.
Although the support ring 206b in FIG. 2B is shown as extending
along most of the sidewall of the second substrate 212b, it is not
necessary for the support ring to be in contact with substantially
all of the sidewall of the second substrate 212b. For example, the
support ring 206b may be in contact with at least about 25 percent,
at least about 50 percent, or at least about 75 percent of the
sidewall of the second substrate 212b.
[0037] The support ring 206b may be clamped to the membrane 214b,
and allow for the second substrate to be inserted therein for
polishing. The extended support ring as shown in FIG. 2B is
additionally used to hold the second substrate in the appropriate
position with respect to the membrane 214b. For example, the
support ring 206b may hold the second substrate 212b in the center
of membrane 214b. Both the textured surface 213b and the support
ring 206b may be used to prevent the first substrate 210b from
contacting the inner sidewall 208b of the carrier head body
204b.
[0038] FIG. 3A is a schematic perspective view of one embodiment of
a membrane support structure for use in a polishing head membrane.
The membrane support structure comprises a plurality of concentric
circles 315a-d. A membrane (not shown) adapted to be inflated, for
example a bladder, may surround the concentric circles. The
concentric circles 315a-d provide additional rigidity to reduce
lateral movement of the membrane during chemical mechanical
polishing. The concentric circles 315a-d are typically formed from
the same material as the membrane, and may be coupled to an
interior surface of the membrane to reduce movement within the
membrane. Additionally, the concentric circles 315a-d may have
holes therethrough (not shown) for allowing spaces between the
concentric circles 315a-d to be pressurized to inflate and hold a
substrate against a polishing pad, or vacuum evacuated to chuck a
substrate to a carrier head. The concentric circles 315a-d aid in
preventing the membrane from deforming or skewing due to the
rocking motion applied during chemical mechanical polishing. If the
membrane skews, any substrates being polished may come into contact
with the sidewall of a polishing head, thereby damaging the
substrate.
[0039] FIGS. 3B and 3C are schematic views of textured surfaces of
membranes for use in a polishing head. In FIG. 3B, the texture is
provided by a set of grooves 316a-c that extend radially from near
the center of the surface of the membrane 314b. The grooves can be
radially symmetric, or they could form a cross-hatch pattern, or
they could be random. In the embodiment of FIG. 3B, three grooves
are shown. However, the number, size, and location of the grooves
may vary depending on the particular application. In the embodiment
of FIG. 3C, the texture is provided by bumps 319c that project from
a surface of membrane 314c. The bumps can form a pattern, or be
randomly formed on the surface of the membrane 314c. For example,
the bumps 319c may form concentric circles, a spiral, or may be
formed into regions. In the embodiment of FIG. 3C, the bumps
radiate from the center of the surface of membrane 314c in straight
lines. However, other variations are possible as long as bumps
provide sufficient texture. Additionally, the bumps 319c can have a
uniform concentration across the surface of membrane 314c, or the
bumps 319c can have regions of different concentration. The bumps
319c can have a uniform height, or the bumps can have different
heights.
[0040] FIG. 4A is a schematic sectional view of carrier head
assembly 400a. The membrane 414a disposed in carrier head body 404a
lacks both sufficient rigidity and interior concentric circles for
support. Therefore, the membrane 414a adopts a skewed shape in the
carrier head body 404a when the first substrate 410a is subjected
to a chemical mechanical polishing process. Because the membrane
414a skews, the first substrate 410a is permitted to come into
contact with the sidewall 408a of carrier head body 404a. This
contact increases the stress on the edge of the first substrate
410a leading to cracking, chipping, or breaking. It should be noted
that an appropriately sized support ring 406a could be used to
increase rigidity and reduce flexing of the membrane 414a.
[0041] Additionally, substrate 410a is permitted to come into
contact with the inner sidewall 408a of carrier head body 404a
because the second substrate 412a is permitted to move in relation
to membrane 414a. The second substrate 412a can slide or move in
relation to the membrane 414a when there is not sufficient friction
between the second substrate 412a or the membrane surface 415a.
Also, the membrane 414a has a wide range of lateral movement due to
the relatively small size of the support ring 406a, which allows
for a large gap between support ring 406a and the inner sidewall
408a of the carrier head body 404a. The wide range of horizontal
movement allows the first substrate 410a to contact the inner
sidewall 408a. This can be especially problematic in instances
where the first substrate 410a is off-centered from the second
substrate 410b, and/or where the second substrate 412a is
off-centered from the membrane 414a.
[0042] FIG. 4B is a schematic sectional view of carrier head
assembly 400b. The membrane 414b has sufficient rigidity such that
membrane 414b does not skew or horizontally flex during a chemical
mechanical polishing process. However, membrane 414b is still
permitted to move in a vertical direction, which may be influenced
or controlled by the amount of pressure in the membrane 414b. The
support ring 406b has sufficient thickness such that the first
substrate 410b and the second substrate 412b cannot contact the
inner sidewall 408b of the carrier head body 404b. Additionally,
the membrane surface 415b has sufficient texturing and a
sufficiently high coefficient of friction such that the second
substrate 412b does not move with respect to the membrane 414b
during polishing. The texturing of membrane surface 415b in
combination with the rigidity of membrane 414b and the support ring
406b prevent the first substrate from contacting the carrier head
body 404b.
[0043] Embodiments described herein provide methods and apparatus
for chemical mechanical polishing of thin, flexible, or fragile
substrates. By restricting the movement of the inflatable membrane
within the carrier head, fragile substrates are not permitted to
contact the carrier head, and are therefore not subjected to
increased edge stress which may break the substrates. Also, a
properly sized support ring assists in preventing the first
substrate from contacting the carrier head when the first substrate
is adhered to the second substrate off-center. Additionally, the
textured surface of the inflatable membrane assists in preventing
the second substrate in contact therewith from sliding off center
and contacting the carrier head. By reducing the contact between
the first substrate and the carrier head, the amount of damage or
stress subjected upon the first substrate can be reduced. This
results in a higher overall yield and higher quality substrates by
minimizing damage thereto.
[0044] 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.
* * * * *