U.S. patent application number 09/535575 was filed with the patent office on 2002-07-18 for carrier head with multi-part flexible membrane.
This patent application is currently assigned to zuniga. Invention is credited to Chen, Hung Chih, Tseng, Ming Kuie, Zuniga, Steven M..
Application Number | 20020094767 09/535575 |
Document ID | / |
Family ID | 24134818 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020094767 |
Kind Code |
A1 |
Zuniga, Steven M. ; et
al. |
July 18, 2002 |
CARRIER HEAD WITH MULTI-PART FLEXIBLE MEMBRANE
Abstract
A carrier head for a chemical mechanical polishing apparatus
includes a flexible membrane that applies a load to a substrate. A
central portion of the flexible membrane is formed of a first
material with a different rigidity than a second material that
forms the annular portion of the flexible membrane.
Inventors: |
Zuniga, Steven M.; (Soquel,
CA) ; Chen, Hung Chih; (San Jose, CA) ; Tseng,
Ming Kuie; (San Jose, CA) |
Correspondence
Address: |
Patent Counsel MS/2061
Legal Affairs Dept
Applied Materials inc
Box 450A
Santa Clara
CA
95052
US
|
Assignee: |
zuniga
|
Family ID: |
24134818 |
Appl. No.: |
09/535575 |
Filed: |
March 27, 2000 |
Current U.S.
Class: |
451/288 |
Current CPC
Class: |
F16J 3/02 20130101; B24B
37/30 20130101 |
Class at
Publication: |
451/288 |
International
Class: |
B24B 005/00 |
Claims
What is claimed is:
1. A carrier head for a chemical mechanical polishing apparatus,
comprising: a carrier structure; and a first flexible membrane
having a central portion positioned and an annular portion
surrounding the central portion, a volume between the first
flexible membrane and the carrier structure providing a first
pressurizable chamber, wherein the central portion of the first
flexible membrane is formed of a first material with a different
rigidity than a second material that forms the annular of the first
flexible membrane.
2. The carrier head of claim 1, wherein the first material is less
rigid than the second material.
3. The carrier head of claim 2, wherein the first and second
materials are elastomers.
4. The carrier head of claim 1, wherein a lower surface of the
central portion of the first flexible membrane provides a substrate
mounting surface.
5. The carrier head of claim 1, wherein the annular portion is a
perimeter portion of the first flexible membrane.
6. The carrier head of claim 5, wherein the perimeter portion is
secured to the carrier structure.
7. The carrier head of claim 6, wherein the perimeter portion is
secured between the carrier structure and a retaining ring.
8. The carrier head of claim 5, wherein the first flexible membrane
further includes an annular connector portion extending between the
central portion and the perimeter portion.
9. The carrier head of claim 8, wherein the connector portion is
formed of a third material that is more rigid than the first
material.
10. The carrier head of claim 9, wherein the third material is less
rigid than the second material.
11. The carrier head of claim 10, wherein the first and third
materials are elastomers and the second material is a
fiber-reinforced elastomer.
12. The carrier head of claim 8, wherein the connector portion is
formed of a third material that has a lower durometer than the
second material.
13. The carrier head of claim 1, further comprising a second
flexible membrane secured to the carrier structure and extending
below the first flexible membrane.
14. The carrier head of claim 13, wherein a lower surface of the
second flexible membrane provides a substrate mounting surface.
15. The carrier head of claim 1, wherein the annular portion has a
convolution.
16. A carrier head for a chemical mechanical polishing apparatus,
comprising: a carrier structure; and a first flexible membrane
having a perimeter portion secured to the carrier structure, a
central portion positioned to apply a pressure to a substrate, and
a connector portion extending between the central portion and the
perimeter portion, a volume between the first flexible membrane and
the carrier structure providing a first pressurizable chamber,
wherein the perimeter portion of the first flexible membrane is
formed of a first material, the connector portion is formed of a
second material that is more rigid than the first material, and the
central portion is formed of a third material that is more rigid
than the second material.
17. The carrier head of claim 16, wherein the first and second
materials are elastomers.
18. The carrier head of claim 17, wherein the third material is a
fiber-reinforced elastomer.
19. The carrier head of claim 16, further comprising an annular
flap joined to the connector portion, an edge of the flap secured
to the carrier structure.
20. The carrier head of claim 19, wherein the flap is formed of the
first material.
21. A flexible membrane for a carrier head, comprising: a central
portion formed of a first material; and a perimeter portion formed
of a second material having a different rigidity than the first
material.
22. The flexible membrane of claim 21, wherein the first material
is more rigid than the second material.
23. The flexible membrane of claim 21, wherein the central portion
applies a pressure to a substrate and the perimeter portion is
secured to a carrier structure.
24. A flexible membrane for a carrier head, comprising: a perimeter
portion; a central portion; and a connector portion extending
between the central portion and the perimeter portion, wherein the
perimeter portion of the flexible membrane is formed of a first
material, the connector portion is formed of a second material that
is more rigid than the first material, and the central portion is
formed of a third material that is more rigid than the second
material.
25. A carrier head for chemical mechanical polishing, comprising: a
carrier structure; a first flexible membrane connected to the
carrier structure, a first volume between the carrier structure and
the first flexible membrane providing a first chamber; and a second
flexible membrane connected to the carrier structure, the second
flexible membrane having a lower surface that provides a mounting
surface for a substrate, a second volume between the first flexible
membrane and the second flexible membrane providing a second
chamber, wherein at least one of a top surface of the second
flexible membrane and a bottom surface of the first flexible
membrane is textured to prevent adhesion between the first flexible
membrane and the flexible membranes when they contact.
Description
BACKGROUND
[0001] The present invention relates generally to chemical
mechanical polishing of substrates, and more particularly to a
carrier head for chemical mechanical polishing.
[0002] Integrated circuits are typically formed on substrates,
particularly silicon wafers, by the sequential deposition of
conductive, semiconductive or insulative layers. After each layer
is deposited, it is etched to create circuitry features. As a
series of layers are sequentially deposited and etched, the outer
or uppermost surface of the substrate, i.e., the exposed surface of
the substrate, becomes increasingly nonplanar. This nonplanar
surface can present problems in the photolithographic steps of the
integrated circuit fabrication process. Therefore, there is a need
to periodically planarize the substrate surface. In addition,
plaranization is needed when polishing back a filler layer, e.g.,
when filling trenches in a dielectric layer with metal.
[0003] Chemical mechanical polishing (CMP) is one accepted method
of planarization. This planarization method typically requires that
the substrate be mounted on a carrier or polishing head. The
exposed surface of the substrate is placed against a rotating
polishing pad. The polishing pad may be either a "standard" or a
fixed-abrasive pad. A standard polishing pad has a durable
roughened or soft surface, whereas a fixed-abrasive pad has
abrasive particles held in a containment media. The carrier head
provides a controllable load, i.e., pressure, on the substrate to
push it against the polishing pad. Some carrier heads include a
flexible membrane that provides a mounting surface for the
substrate, and a retaining ring to hold the substrate beneath the
mounting surface. Pressurization or evacuation of a chamber behind
the flexible membrane controls the load on the substrate. A
polishing slurry, including at least one chemically-active agent,
and abrasive particles if a standard pad is used, is supplied to
the surface of the polishing pad.
[0004] The effectiveness of a CMP process may be measured by its
polishing rate, and by the resulting finish (absence of small-scale
roughness) and flatness (absence of large-scale topography) of the
substrate surface. The polishing rate, finish and flatness are
determined by the pad and slurry combination, the relative speed
between the substrate and pad, and the force pressing the substrate
against the pad.
[0005] A reoccurring problem in CMP is the so-called "edge-effect",
i.e., the tendency of the substrate edge to be polished at a
different rate than the substrate center. The edge effect typically
results in non-uniform polishing at the substrate perimeter, e.g.,
the outermost three to fifteen millimeters of a 200 millimeter (mm)
wafer.
SUMMARY
[0006] In one aspect, the invention is directed to a carrier head
for a chemical mechanical polishing apparatus. The carrier head has
a carrier structure and a first flexible membrane. The first
flexible membrane has central portion and an annular portion
surrounding the central portion. A volume between the first
flexible membrane and the carrier structure provides a first
pressurizable chamber. The central portion of the first flexible
membrane is formed of a first material with a different rigidity
than a second material that forms the annular portion of the first
flexible membrane.
[0007] Implementations of the invention may include one or more of
the following features. The first material may be less rigid than
the second material. The first and second materials may be
elastomers. The annular portion may be a perimeter portion of the
first flexible membrane secured to the carrier structure. The
perimeter portion may be secured between the carrier structure and
a retaining ring. The first flexible membrane may include an
annular connector portion extending between the central portion and
the perimeter portion. The connector portion may be formed of a
third material that has is more rigid than the first material and
less rigid than the second material. The first and third materials
may be elastomers, and the second material may be a
fiber-reinforced elastomer. A second flexible membrane may be
secured to the carrier structure and may extend below the first
flexible membrane. A lower surface of the second flexible membrane
may provide a substrate mounting surface. The annular portion may
have a convolution.
[0008] In another aspect, the invention is directed to a carrier
head for a chemical mechanical polishing apparatus. The carrier
head has a carrier structure and a first flexible membrane. The
first flexible membrane has a perimeter portion secured to the
carrier structure, a central portion positioned to apply a pressure
to a substrate, and a connector portion extending between the
central portion and the perimeter portion. A volume between the
first flexible membrane and the carrier structure provides a first
pressurizable chamber. The perimeter portion of the first flexible
membrane is formed of a first material, the connector portion is
formed of a second material that is more rigid than the first
material, and the central portion is formed of a third material
that is more rigid than the second material.
[0009] Implementations of the invention may include one or more of
the following features. The first and second materials may be
elastomers, and the third material may be a fiber-reinforced
elastomer. An annular flap may be joined to the connector portion,
and an edge of the flap may be secured to the carrier structure.
The flap may be formed of the first material.
[0010] In another aspect, the invention is directed to a flexible
membrane for a carrier head. The flexible membrane has a central
portion formed of a first material and a perimeter portion formed
of a second material having a different rigidity than the first
material.
[0011] Implementations of the invention may include one or more of
the following features. The first material may be more rigid than
the second material. The central portion may apply a pressure to a
substrate, and the perimeter portion may be secured to a carrier
structure.
[0012] In another aspect, the invention is directed to a flexible
membrane for a carrier head that has a perimeter portion, a central
portion, and a connector portion extending between the central
portion and the perimeter portion. The perimeter portion of the
flexible membrane is formed of a first material, the connector
portion is formed of a second material that is more rigid than the
first material, and the central portion is formed of a third
material that is more rigid than the second material.
[0013] In another aspect, the invention is directed to a carrier
head for chemical mechanical polishing. The carrier head has a
carrier structure, a first flexible membrane connected to the
carrier structure, and a second flexible membrane connected to the
carrier structure. A first volume between the carrier structure and
the first flexible membrane provides a first chamber, and a second
volume between the first flexible membrane and the second flexible
membrane providing a second chamber. The second flexible membrane
has a lower surface that provides a mounting surface for a
substrate. At least one of a top surface of the second flexible
membrane and a bottom surface of the first flexible membrane is
textured to prevent adhesion between the first flexible membrane
and the flexible membranes when they contact.
[0014] Potential advantages of implementations of the invention may
include zero or more of the following. The distribution of pressure
at the substrate edge may be controlled. Both the pressure and the
loading area of the flexible membrane against the substrate may be
varied to compensate for non-uniform polishing. Non-uniform
polishing of the substrate is reduced, and the resulting flatness
and finish of the substrate are improved.
[0015] Other advantages and features of the invention will be
apparent from the following description, including the drawings and
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an exploded perspective view of a chemical
mechanical polishing apparatus.
[0017] FIG. 2 is a schematic cross-sectional view of a carrier head
according to the present invention.
[0018] FIG. 3 is an enlarged view from a carrier head with an edge
control assembly.
[0019] FIGS. 4A and 4B are schematic cross-sectional side views of
flexible membrane assemblies from the carrier head of FIG. 2.
[0020] FIGS. 5A and 5B are schematic views of the carrier head of
FIG. 2 illustrating the controllable loading area.
[0021] FIG. 6A and 6B are schematic diagrams illustrating the
pressure and force distribution in the carrier head of FIG. 2.
[0022] FIG. 7 is a schematic cross-sectional view of a carrier head
with a rigid membrane support ring in the substrate backing
assembly.
[0023] FIGS. 8A and 8B are schematic diagrams illustrating the
pressure and force distribution in the carrier head of FIG. 7.
[0024] Like reference numbers are designated in the various
drawings to indicate like elements.
DETAILED DESCRIPTION
[0025] Referring to FIG. 1, one or more substrates 10 will be
polished by a chemical mechanical polishing (CMP) apparatus 20. A
description of a similar CMP apparatus may be found in U.S. Pat.
No. 5,738,574, the entire disclosure of which is incorporated
herein by reference.
[0026] The CMP apparatus 20 includes a series of polishing stations
25 and a transfer station 27 for loading and unloading the
substrates. Each polishing station 25 includes a rotatable platen
30 on which is placed a polishing pad 32. Each polishing station 25
may further include an associated pad conditioner apparatus 40 to
maintain the abrasive condition of the polishing pad.
[0027] A slurry 50 containing a chemically active agent (e.g.,
deionized water for oxide polishing) and a chemically-active
catalyzer (e.g., potassium hydroxide for oxide polishing) may be
supplied to the surface of the polishing pad 32 by a combined
slurry/rinse arm 52. If the polishing pad 32 is a standard pad, the
slurry 50 may also include abrasive particles (e.g., silicon
dioxide for oxide polishing). Typically, sufficient slurry is
provided to cover and wet the entire polishing pad 32. The
slurry/rinse arm 52 includes several spray nozzles (not shown) to
provide a high pressure rinse of the polishing pad 32 at the end of
each polishing and conditioning cycle.
[0028] A rotatable multi-head carousel 60 is supported by a center
post 62 and rotated thereon about a carousel axis 64 by a carousel
motor assembly (not shown). The multi-head carousel 60 includes
four carrier head systems 70 mounted on a carousel support plate 66
at equal angular intervals about the carousel axis 64. Three of the
carrier head systems position substrates over the polishing
stations, and one of the carrier head systems receives a substrate
from and delivers the substrate to the transfer station. The
carousel motor may orbit the carrier head systems, and the
substrates attached thereto, about the carousel axis between the
polishing stations and the transfer station.
[0029] Each carrier head system 70 includes a polishing or carrier
head 100. Each carrier head 100 independently rotates about its own
axis, and independently laterally oscillates in a radial slot 72
formed in the carousel support plate 66. A carrier drive shaft 74
extends through the slot 72 to connect a carrier head rotation
motor 76 (shown by the removal of one-quarter of a carousel cover
68) to the carrier head 100. Each motor and drive shaft may be
supported on a slider (not shown) which can be linearly driven
along the slot by a radial drive motor to laterally oscillate the
carrier head 100.
[0030] During actual polishing, three of the carrier heads are
positioned at and above the three polishing stations. Each carrier
head 100 lowers a substrate into contact with the polishing pad 32.
The carrier head 100 holds the substrate in position against the
polishing pad and distributes a force across the back surface of
the substrate. The carrier head 100 also transfers torque from the
drive shaft 74 to the substrate.
[0031] Referring to FIG. 2, the carrier head 100 includes a housing
102, a base assembly 104, a gimbal mechanism 106 (which may be
considered part of the base assembly), a loading chamber 108, a
retaining ring 110, and a substrate backing assembly 112 which
includes three pressurizable chambers, such as a floating upper
chamber 154, a floating internal chamber 156, and an outer chamber
158. A description of a similar carrier head may be found in U.S.
patent application Ser. No. 09/470,820, filed Dec. 23, 1999, the
entire disclosure of which is incorporated herein by reference.
[0032] The housing 102 can be connected to the drive shaft 74 (see
FIG. 1) to rotate therewith during polishing about an axis of
rotation 107 which is substantially perpendicular to the surface of
the polishing pad. The housing 102 may be generally circular in
shape to correspond to the circular configuration of the substrate
to be polished. A vertical bore 120 may be formed through the
housing 102, and three additional passages (only two passages 122,
124 are illustrated in FIG. 2) may extend through the housing 102
for pneumatic control of the carrier head. O-rings 128 may be used
to form fluid-tight seals between the passages through the housing
and passages through the drive shaft.
[0033] The base assembly 104 is a vertically movable assembly
located beneath the housing 102. The base assembly 104 includes a
generally rigid annular body 130, an outer clamp ring 134, the
gimbal mechanism 106, and a lower clamp ring 132. A passage 136 may
extend through the body of the gimbal mechanism 106, the annular
body 130, and the lower clamp ring 132, to one of the chambers in
substrate backing assembly 112, e.g., the outer chamber 158. Two
fixtures 138 may provide attachment points to connect a flexible
tube between the housing 102 and the base assembly 104 to fluidly
couple passage 124 to passage 136 and the outer chamber 158. A
second passage (not shown) may extend through the annular body 130
to a second chamber in the substrate backing assembly 112, e.g.,
the floating upper chamber 154. Two fixtures (also not shown) may
provide attachment points to connect a flexible tube between the
housing 102 and the base assembly 104 to fluidly couple the
unillustrated passage in the housing to the second passage in the
annular body and the floating upper chamber 154.
[0034] The gimbal mechanism 106 permits the base assembly to pivot
with respect to the housing 102 so that the retaining ring 110 may
remain substantially parallel with the surface of the polishing
pad. The gimbal mechanism 106 includes a gimbal rod 140 which fits
into the vertical bore 120 and a flexure ring 142 which is secured
to the annular body 130. The gimbal rod 140 may slide vertically
the along the bore 120 to provide vertical motion of the base
assembly 104, but it prevents any lateral motion of the base
assembly 104 with respect to the housing 102 and reduces moment
generated by the lateral force of the substrate against the
retaining ring. The gimbal rod 140 may include a passage 144 that
extends the length of the gimbal rod to fluidly couple the bore 120
to a third chamber in the substrate backing assembly 112, e.g., the
internal chamber 156.
[0035] The loading chamber 108 is located between the housing 102
and the base assembly 104 to apply a load, i.e., a downward
pressure or weight, to the base assembly 104. The vertical position
of the base assembly 104 relative to the polishing pad 32 is also
controlled by the loading chamber 108. An inner edge of a generally
ring-shaped rolling diaphragm 146 may be clamped to the housing 102
by an inner clamp ring 148. An outer edge of the rolling diaphragm
146 may be clamped to the base assembly 104 by the outer clamp ring
134. Thus, the rolling diaphragm 146 seals the space between the
housing 102 and the base assembly 104 to define the loading chamber
108. A first pump (not shown) may be fluidly connected to the
loading chamber 108 by passage 122 to control the pressure in the
loading chamber 108 and the vertical position of the base assembly
104.
[0036] The retaining ring 110 may be a generally annular ring
secured at the outer edge of the base assembly 104, e.g., by bolts
114. When fluid is pumped into the loading chamber 108 and the base
assembly 104 is pushed downwardly, the retaining ring 110 is also
pushed downwardly to apply a load to the polishing pad 32. A bottom
surface 116 of the retaining ring 110 may be substantially flat, or
it may have a plurality of channels to facilitate transport of
slurry from outside the retaining ring to the substrate. An inner
surface 118 of the retaining ring 110 engages the substrate to
prevent it from escaping from beneath the carrier head.
[0037] Referring to FIGS. 2 and 3, the substrate backing assembly
112 includes an internal membrane 150, an external membrane 152, an
internal membrane support structure 160, a an upper membrane spacer
ring 162, a lower membrane spacer ring 164, and an edge control
ring 166. The volume between the base assembly 104 and the internal
membrane 150 forms the upper chamber 154 and the internal chamber
156, and the volume between the internal membrane 150 and the
external membrane 152 forms the outer chamber 158. The support
structure 160, the spacer rings 162 and 164, and the control ring
166 need not be secured to the rest of the carrier head, and may be
held in place by the internal and external flexible membranes.
[0038] Referring to FIG. 4A, the internal membrane 150 includes a
circular central portion 170 which will contact the external
membrane 152 in a controllable area, a relatively thick annular
portion 174 with an generally rectangular cross-section, an annular
inner flap 176 that extends from the corner of the thick portion
174, an annular outer flap 178 that extends from the outer rim of
the thick portion 174, and an annular connector portion 172 that
extends between the internal support structure 160 and the lower
spacer ring 164 to connect the thick portion 174 to the central
portion 170. The thick portion 174 can include an annular
protrusion 175 that extends radially outwardly at the top of the
thick portion. The inner flap 176 and the outer flap 178 can be
formed of a first elastomer, whereas the thick portion 174 and
connector portion 172 can be formed of a second elastomer that has
a higher durometer (i.e., is stiffer) than the first elastomer.
Thus, the sidewall portions 172, 174 of the inner membrane 150 are
stiffer than the inner and outer flaps 176, 178. The central
portion 170 of inner membrane 150 can be formed of a
fiber-reinforced elastomer which is even stiffer than the second
elastomer in the sidewall portions 172, 174. In particular, the
central portion 170 can be bendable but not particularly
stretchable. Alternatively, the central portion 170 can have about
the same rigidity as the sidewall portions 172, 174. The central
portion 170 can be thicker or thinner than the connector portion
172.
[0039] Returning to FIGS. 2 and 3, the rim of the inner flap 176 is
clamped between the flexure ring 142 and the annular body 130,
whereas the rim of outer flap 178 is clamped between the outer
clamp ring 134 and the lower clamp ring 132. The volume between the
base assembly 104 and the internal membrane 150 that is sealed by
the inner flap 176 provides the pressurizable floating internal
chamber 156. The annular volume between the base assembly 104 and
the internal membrane 150 that is sealed by the inner flap 176 and
the outer flap 178 defines the pressurizable floating upper chamber
154. A second pump (not shown) may be connected to the
unillustrated passage to direct fluid, e.g., a gas, such as air,
into or out of the floating upper chamber 154. A third pump (not
shown) may be connected to bore 120 to direct a fluid, e.g., a gas,
such as air, into or out of floating internal chamber 156. As
explained in greater detail below, the pressure in the chambers
154, 156, 158 will control a contact area of the internal membrane
150 against a top surface of the external membrane 152. Thus, the
second, third and fourth pumps control the area of the substrate
against which pressure is applied, i.e., the loading area, and the
third pump controls the downward force on the substrate in the
loading area.
[0040] Referring to FIGS. 3 and 4B, the external membrane 152
includes a central portion 180 that provides a mounting surface to
engage the substrate, and a lip portion 182 that extends back
inwardly over an outer edge portion 184 of the central portion 180,
a thick portion 186 located between the lower membrane spacer ring
164 and the edge control ring 166, and a perimeter portion 188 that
extends between upper the membrane spacer ring 162 and the lower
membrane spacer ring 164 to be secured to the base assembly. The
external membrane may be pre-molded into a serpentine shape. In
addition, the central portion 180 can be formed of an elastomer
that is stiffer than the elastomer that forms lip portion 182,
thick portion 186 and perimeter portion 188. The lip portion 182
and the outer edge portion 184 can operate to provide an
active-flap lip seal during chucking of the substrate, as discussed
in U.S. patent application Ser. No. 09/296,935, filed Apr. 22,
1999, the entirety of which in incorporated herein by
reference.
[0041] Returning to FIGS. 2 and 3, a rim of the external membrane
152 can be clamped between the lower clamp ring 132 and the
retaining ring 110. The sealed volume between the internal membrane
150 and the external membrane 152 defines the pressurizable outer
chamber 158. Thus, the outer chamber 158 can actually extend below
the internal chamber 156. A fourth pump (not shown) may be
connected to the passage 124 to direct a fluid, e.g., a gas, such
as air, into or out of the outer chamber 158. The fourth pump
controls the pressure in the outer chamber 158.
[0042] The internal membrane 150 can be formed of a flexible
material, such as an elastomer, elastomer coated fabric, or thermal
plastic elastomer (TPE), e.g., HYTREL.TM. available from DuPont of
Newark, Del., or a combination of these materials. The external
membrane 118 can be formed of a flexible and elastic material, such
as chloroprene or ethylene propylene rubber, or silicone. The
bottom surface of the central portion 170 of the internal membrane
150 or the top surface of the central portion 180 of the external
membrane 152 have small grooves to ensure that fluid can flow
between the internal and external membranes when they are in
contact. In addition or alternately, the bottom surface of the
central portion 170 of the internal membrane 150 or the top surface
of the central portion 180 of the external membrane 152 can have a
textured rough surface to prevent adhesion between the internal and
external membranes when they are in contact.
[0043] The internal support structure 160 can be a generally rigid
annular body located inside the floating internal chamber 156 to
maintain the desired shape of internal membrane 150. The support
structure 160 can have a wedge-shaped cross-section that is thicker
at the outer radius of the structure. The support structure 160 can
have a flat top surface to support the rectangular thick portion
174 of the internal membrane 150, and a sloped lower surface that
rests on the internal membrane 150 at its lowest point. The
connector portion 172 of the internal membrane 150 extends around
the lower outer corner of the internal support structure 160. The
support structure 160 maintains the proper spacing between the
thick portion 174 and the central portion 170 of the internal
membrane 150. Alternatively, the internal support structure may be
a disk-shaped body with a plurality of apertures therethrough.
[0044] The upper membrane spacer ring 162 is a generally rigid
annular body which can have an "L-shaped" cross-section located in
the external chamber 152. The upper membrane spacer ring 162 can be
located at the lower corner of the protrusion 175 in the inner
membrane 150 and can rest on the edge control ring 168. The two
prongs of the "L" of the upper membrane spacer ring 162 can be
formed by an inwardly extending flange 190 that extends between the
inner membrane 150 and the external membrane 152, and an upwardly
extending flange 192 that extends between the inner membrane 150
and the lower clamp ring 132. Thus, the lower flange 190 of the
upper membrane spacer ring 162 ensures proper spacing and prevents
adhesion between the upper and lower membranes 150, 152. A
plurality of grooves 194 can be formed in a lower surface of the
inwardly extending flange 190. The grooves 194 permit fluid to flow
between the external membrane 152 and the upper membrane spacer
ring 162 to ensure fluid communication between the two portions of
the outer chamber 158 on either side of the upper membrane spacer
ring 162.
[0045] The lower membrane spacer ring 164 is located inside the
outer chamber 158 below the upper membrane spacer ring 162. The
lower membrane spacer ring can be an annular body with a
spur-shaped cross-section positioned between the internal membrane
150 and the external membrane 152 to maintain the desired shape of
the external membrane 152 and to apply additional pressure to the
edge of the substrate. Specifically, the lower membrane spacer ring
164 may have a generally rigid ring-shaped portion 200 that extends
vertically from a base-piece 202. The ring-shaped portion extends
between the internal membrane 150 and the external membrane 152. A
compressible cushion 204 can be secured to an underside 206 of the
base-piece 202. In addition, a flexible annular flange 208 projects
outwardly at a downward angle from the outer rim of the base-piece
202 until it extends below the lower surface of the cushion 204.
The flange 208 projects between the lip portion 182 and the outer
edge portion 184 of the external membrane 152. The thick portion
186 of the external membrane 152 rests on the top surface of the
triangular base-piece 202.
[0046] The edge control ring 166 is a generally annular member
positioned between the retaining ring 110 and the external membrane
152. The edge control ring 166 includes a cylindrical portion 210
and a flange portion 212 which extends outwardly toward inner
surface 118 of retaining ring 110 to maintain the lateral position
of the external spacer ring. An overhang 214 formed in the
cylindrical portion 210 can fit over the thick portion 186 so that
the edge control ring 166 rests on the external membrane 152.
[0047] As discussed above, a controllable region of the central
portion 200 of the internal membrane 116 can contact and apply a
downward load to an upper surface of the external membrane 118. The
load is transferred through the external membrane to the substrate
in the loading area. In operation, fluid is pumped into or out of
the floating internal chamber 156 to control the downward pressure
of the internal membrane 150 against the external membrane 152 and
thus against the substrate, and fluid is pumped into or out of the
floating upper chamber 154 to control the contact area of the
internal membrane 150 against the external membrane 152.
[0048] Referring to FIGS. 5A and 5B, the contact area of the
internal membrane 150 against the external membrane 152, and thus
the loading area in which pressure is applied to the substrate 10,
may be controlled by varying the pressure in the floating upper
chamber 155. By pumping fluid out of the floating upper chamber
154, the thick rectangular portion 174 of the internal membrane 150
is drawn upwardly, thereby pulling the outer edge of the central
portion 170 away from the external membrane 152 and decreasing the
diameter of the loading area. Conversely, by pumping fluid into the
floating upper chamber 154, the thick portion 174 of the internal
membrane 150 is forced downwardly, thereby pushing the central
portion 170 of the internal membrane 150 into contact with the
external membrane 152 and increasing the diameter of the loading
area. In addition, if fluid is forced into the outer chamber 158,
the thick portion 174 of the internal membrane 150 is forced
upwardly, thereby decreasing the diameter of the loading area.
Thus, in the carrier head 100, the diameter of the loading area
will depend on the pressures in the upper, inner and outer
chambers.
[0049] As previously discussed, one reoccurring problem in CMP is
non-uniform polishing near the edge of the substrate. Referring to
FIGS. 3, 6A and 6B, the edge control ring 166 and the lower
membrane spacer ring 164 can be used to apply additional pressure
to multiple annular regions at the perimeter of the substrate. In
regular operation, the outer tip of the annular flange 208 of the
lower membrane spacer ring 164 rests on the top surface of the
external membrane 152 near the outermost edge of the central
portion 170. However, if the upper chamber 154 is sufficiently
pressurized, the rectangular portion 174 of the internal flexible
membrane 150 will be driven downwardly into contact with the upper
membrane spacer ring 162. This contact pressure is transmitted
through the upper membrane spacer ring 162, the edge control ring
166 and the thick portion 186 of the external membrane 152 to
create a downward pressure on the lower membrane spacer ring 164
(the load on the edge control ring 166 is shown by arrow A in FIG.
6B). At first, the increase in pressure in the upper chamber 155
merely increases the pressure applied by the flange 208 at the
outermost edge of the substrate. However, as the pressure in the
upper chamber 154 increases, the flexible flange 208 bends, and the
membrane spacer ring 164 is driven downwardly until the cushion 204
contacts the top surface of the external membrane 152. At this
point, the membrane support ring generates two separate annular
zones of increased pressure on the substrate. The first zone (shown
by arrow B) is created by the contact of the flange 208, and the
second zone (shown by arrow C) is created by the contact of the
cushion 204 on the external membrane. By properly selecting the
dimensions of the components, this multi-zone distribution of
pressure at the substrate edge can reduce polishing
non-uniformity.
[0050] Carrier head 100 may also be operated in a "standard"
operating mode, in which the floating chambers 156 and 158 are
vented or evacuated to lift away from the substrate, and the outer
chamber 158 is pressurized to apply a uniform pressure to the
entire backside of the substrate.
[0051] The operations of the carrier head 100 to load a substrate
into the carrier head at the transfer station 27, dechuck the
substrate from a polishing pad at the polishing station 25, and
unload the substrate from the carrier head at the transfer station
27, are summarized in the aforementioned Ser. No. 09/470,820.
[0052] Referring to FIG. 7, in another implementation of the
carrier head 100', the lower membrane spacer ring 164' is rigid and
does not have a flexible flange. Instead, the edge control ring
166' includes a projection 216 that can contact the outer surface
of the lip portion 184 of the external membrane 152. In addition,
the cushion 204' attached to the underside of the lower membrane
spacer ring 164' can extend radially outwardly beyond the lower
membrane spacer ring 164'.
[0053] Referring to FIGS. 7, 8A and 8B, in regular operation, the
cushion 204' of the lower membrane spacer ring 164' rests on the
top surface of the edge portion 182 of the external membrane 152.
If the floating upper chamber 154 is sufficiently pressurized, the
rectangular portion 174 of the internal membrane 150 will be driven
downwardly into contact with upper membrane spacer ring 162'. This
contact pressure is transmitted through the upper membrane spacer
ring 162 to create a downward pressure on the edge control ring
166' (shown by arrow A' in FIG. 8B), thereby causing the projection
216 to apply a downward pressure on the lip portion 182 of the
external membrane 152. Since the lip portion 182 is slightly rigid,
at first the load from edge control ring 166' presses the corner
183 of the lip portion 182 against the substrate, creating a first
region of increased pressure (indicated by arrow B') at the very
edge of the substrate. A further increase of the pressure in the
upper chamber 154 brings the edge control ring 166' into contact
with the thick portion 186 of the external membrane 152 and applies
a downward pressure to the lower membrane spacer ring 164'. This
generates an second region of increased downward pressure
(indicated by arrow C') on an annular second region of the
substrate interior to and separated from the first region.
Increasing the pressure in the upper chamber 154 still further
causes the lip portion 182 to deflect and contact the upper surface
of the outer edge portion 184. This generates a third region of
increased pressure (indicated by arrow D') on the substrate between
the first and second portions. By properly selecting the dimensions
of the components, this multi-zone distribution of pressure at the
substrate edge can reduce polishing non-uniformity.
[0054] The configurations of the various elements in the carrier
head, such as the flexible membranes, the spacer rings, the control
ring and the support structure are illustrative and not limiting. A
variety of configurations are possible for a carrier head that
implements the invention. For example, the floating upper chamber
can be either an annular or a solid volume. The upper and lower
chambers may be separated either by a flexible membrane, or by a
relatively rigid backing or support structure. The internal support
structure could be either ring-shaped or disk-shaped with apertures
therethrough. The carrier head could be constructed without a
loading chamber, and the base assembly and housing can be a single
structure.
[0055] The present invention has been described in terms of a
number of embodiments. The invention, however, is not limited to
the embodiments depicted and described. Rather, the scope of the
invention is defined by the appended claims.
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