U.S. patent application number 09/834205 was filed with the patent office on 2002-10-17 for carrier head for a chemical mechanical polishing apparatus.
Invention is credited to Crevasse, Annette Margaret, Easter, William Graham, Maze,, John Albert III, Miceli, Frank.
Application Number | 20020151260 09/834205 |
Document ID | / |
Family ID | 25266374 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020151260 |
Kind Code |
A1 |
Crevasse, Annette Margaret ;
et al. |
October 17, 2002 |
Carrier head for a chemical mechanical polishing apparatus
Abstract
A chemical mechanical polishing (CMP) device carrier head (54)
utilizing a pressure pack (58) for transferring a polishing force
(D) to a wafer (15) being polished. The pressure pack may include a
silicon gel material (60) encapsulated within a sealed urethane
casing (62). The pressure pack provides a desired fluid coupling in
the polishing force load path, allowing the carrier head to
function as a front side floating reference polishing apparatus.
The pressure pack may include a plurality of casings (70, 72)
defining a plurality of chambers (66, 68) in order to affect the
distribution of pressure across an abutting pressure plate (56,
65).
Inventors: |
Crevasse, Annette Margaret;
(Apopka, FL) ; Easter, William Graham; (Orlando,
FL) ; Maze,, John Albert III; (Clermont, FL) ;
Miceli, Frank; (Orlando, FL) |
Correspondence
Address: |
HOLLAND & KNIGHT LLP
PO BOX 1526
ORLANDO
FL
32802-1526
US
|
Family ID: |
25266374 |
Appl. No.: |
09/834205 |
Filed: |
April 12, 2001 |
Current U.S.
Class: |
451/288 |
Current CPC
Class: |
B24B 37/30 20130101;
B24B 41/061 20130101 |
Class at
Publication: |
451/288 |
International
Class: |
B24B 005/00 |
Claims
We claim as our invention:
1. A carrier head for a chemical mechanical polishing apparatus
comprising: a frame adapted for connection to a drive apparatus; a
pressure plate adapted for contact with a wafer; and a pressure
pack disposed between the frame and the pressure plate for
transferring a force there between.
2. The carrier head of claim 1, wherein the pressure pack comprises
a gelatinous material encapsulated within a sealed casing.
3. The carrier head of claim 1, wherein the pressure pack comprises
a fluid encapsulated within a sealed urethane casing.
4. The carrier head of claim 3, wherein the gelatinous material
comprises silicone.
5. The carrier head of claim 1, wherein the pressure pack comprises
a plurality of chambers.
6. The carrier head of claim 5, wherein a first chamber comprises
central portion of the pressure pack and a second chamber comprises
a perimeter portion of the pressure pack.
7. The carrier head of claim 5, wherein a first of the plurality of
chambers is filled with a fluid at a first pressure and a second of
the plurality of chambers is filled with a fluid at a second
pressure different than the first pressure.
8. The carrier head of claim 5, wherein a first of the plurality of
chambers is filled with a first material and a second of the
plurality of chambers is filled with a second material different
than the first material.
9. The carrier head of claim 8, wherein the viscosity of the first
material is different than the viscosity of the second
material.
10. The carrier head of claim 5, wherein the pressure plate
comprises a plurality of sections corresponding to the plurality of
chambers.
11. The carrier head of claim 5, wherein the pressure pack
comprises a first material forming a first casing and a second
material forming a second casing.
12. The carrier head of claim 1, wherein the pressure pack
comprises a fluid material encapsulated within a first sealed
casing, and a second sealed casing encapsulating the first
casing.
13. A wafer polishing apparatus comprising: a platen having a
polishing pad affixed to a surface thereof, a wafer carrier head
for holding a wafer to be polished and for abutting a surface of
the wafer against the polishing pad; a driving mechanism for
polishing the surface of the wafer by moving the wafer carrier head
with respect to the platen; wherein the wafer carrier head further
comprises: a pressure plate adapted for urging the surface of the
wafer against the polishing pad; a frame for applying a force
against the pressure plate; and a pressure pack disposed between
the frame and the pressure plate for transferring the force there
between.
14. The wafer polishing apparatus of claim 13, wherein the pressure
pack comprises a fluid encapsulated within a sealed urethane
casing.
15. The wafer polishing apparatus of claim 13, wherein the pressure
pack comprises a gelatinous material encapsulated within a sealed
casing.
16. The wafer polishing apparatus of claim 15, wherein the
gelatinous material comprises silicone.
17. The wafer polishing apparatus of claim 13, wherein the pressure
pack comprises a plurality of chambers.
18. The wafer polishing apparatus of claim 17, wherein a first
chamber comprises a central portion of the pressure pack and a
second chamber comprises a perimeter portion of the pressure
pack.
19. The wafer polishing apparatus of claim 17, wherein a first of
the plurality of chambers is filled with a fluid at a first
pressure and a second of the plurality of chambers is filled with a
fluid at a second pressure different than the first pressure.
20. The wafer polishing apparatus of claim 17, wherein a first of
the plurality of chambers is filled with a first material and a
second of the plurality of chambers is filled with a second
material different than the first material.
21. The wafer polishing apparatus of claim 20, wherein the
viscosity of the first material is different than the viscosity of
the second material.
22. The wafer polishing apparatus of claim 17, wherein the pressure
pack comprises a first material forming a first casing and a second
material forming a second casing.
23. The wafer polishing apparatus of claim 13, wherein the pressure
pack comprises a fluid material encapsulated within a first sealed
casing, and a second sealed casing encapsulating the first
casing.
24. A method of modifying a back side reference polishing apparatus
to function as a floating reference polishing device, the back side
polishing apparatus having a polishing pad affixed to a platen, a
wafer carrier for holding a wafer to be polished against the
polishing pad, a driving mechanism for polishing the wafer by
moving the wafer carrier with respect to the platen, the wafer
carrier further including a carrier head frame disposed against a
pressure plate for urging the wafer against the polishing pad, the
method comprising: removing the pressure plate; and replacing the
pressure plate with a replacement pressure plate and a pressure
pack, the pressure pack being disposed between the replacement
pressure plate and the carrier head frame for transferring a force
there between for urging the wafer against the polishing pad.
25. The method of claim 24, further comprising providing the
pressure pack to have a gelatinous material encapsulated within a
sealed casing.
26. The method of claim 24, further comprising providing the
pressure pack to have a plurality of chambers.
27. The method of claim 24, further comprising providing the
pressure pack to have a fluid material encapsulated within a
plurality of casings.
28. A chemical mechanical polishing apparatus adapted for applying
a polishing force to urge a substrate against a polishing pad,
wherein the improvement comprises a pressure pack disposed in a
load path of the polishing force.
29. The chemical mechanical polishing apparatus of claim 28,
wherein the pressure pack further comprises a gelatinous material
encapsulated within a sealed casing.
30. The chemical mechanical polishing apparatus of claim 28,
wherein the pressure pack further comprises a plurality of
chambers.
31. The chemical mechanical polishing apparatus of claim 28,
wherein the pressure pack comprises a fluid material encapsulated
within a plurality of casings.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to the field of substrate
polishing, and more specifically the field of polishing
semiconductor wafers, and in particular to an improved carrier for
a chemical mechanical polishing (CMP) apparatus.
[0002] It is well known in the field of integrated circuit
fabrication to polish a semiconductor wafer to achieve a planar
surface on one or both sides of the wafer. One method used to
polish such wafers is mechanical polishing, where a surface of the
wafer is scoured with an abrasive polishing pad. It is also known
to utilize a ID chemical slurry in conjunction with the abrasive
polishing pad to increase the material removal rate, and such a
process is commonly referred to as chemical mechanical polishing
(CMP). Many styles of CMP machines are commercially available from
manufactures including Applied Materials, Inc., Ebara, Strausbaugh,
LAM Research, and SpeedFam-IPEC International.
[0003] FIG. 1 illustrates a prior art chemical mechanical polishing
machine 10 including a polishing pad 12 disposed on a platen 14
being used to polish a semiconductor wafer 15 secured in a wafer
carrier 16. The carrier 16 includes a driving mechanism 18 for
rotating the wafer 15 about a central axis and for oscillating the
wafer 15 in a horizontal direction and lifting it in a vertical
direction. The CMP machine 10 also includes a driving mechanism 20
for rotating the platen about a central vertical axis. Various CMP
machine designs may include one or both such driving mechanisms 18,
20 for moving the wafer carrier 16 and wafer 15 with respect to the
platen 14 and polishing pad 12. A slurry delivery system 22
provides the chemical agent 24 used in the CMP process. As is known
in the art, CMP machine 10 may include a plurality of carriers 16
and an automatic control system for moving a plurality of
semiconductor wafers or other such substrates into and away from
the carriers for batch processing.
[0004] FIG. 2 is a partial cross-sectional view of one type of
wafer carrier head that may be used on a CMP machine. Wafer carrier
head 26 includes a carrier head frame 28 adapted for connection to
a drive apparatus 30. The drive apparatus 30 is operable to impart
rotation and horizontal movement while applying downward force D
during a wafer polishing operation. A wafer 15 is secured to the
carrier head 26 by a retaining ring 32, as is known in the art. A
pressure plate 34 is disposed between the frame 28 and the wafer 15
and is functional to transfer the downward force D to the wafer 15
to urge the surface to be polished against the polishing pad 12. It
is known that pressure plate 34 may be formed of a metal or metal
alloy and may be covered by a felt or polyurethane backing film
(not illustrated) to protect the wafer 15.
[0005] The prior art device of FIG. 2 firmly positions the wafer 15
against the pressure plate 34 during a polishing operation. This
type of design is sometimes referred to as back-side reference
polishing. The wafer surface that is being polished is urged toward
the polishing pad 12 in direct response to the movement of the
bottom side face 36 of the pressure plate 34. Such a system is
known to produce uneven material removal across the polished face
of wafer 15, since there is no mechanical flexibility provided to
accommodate problems such as a lack of parallelism between the
pressure plate bottom side face 36 and the top surface 38 of the
polishing pad 12.
[0006] In order to address the inflexibility of the carrier head 26
of FIG. 2, it is known to provide a floating or front-side
reference carrier head 40, as is illustrated in FIG. 3. In this
type of design, downward force D is transmitted to wafer 15 by a
flexible membrane 42 that is forced against the wafer 15 by a
pressurized fluid such as pressurized air 44 contained within a
volume 46 within wafer carrier head frame 28. A felt or urethane
film 43 may be disposed between the wafer 15 and the flexible
membrane 42. The pressurized air is provided and vented via a
delivery system 48 designed to be compatible with the driving
mechanism 30. A plate 50 having one or more holes 52 formed there
through is provided behind the flexible membrane 42. However, when
pressurized by pressurized air 44, flexible membrane 42 "floats"
away from the plate 50. This allows an even pressure to be applied
across the wafer in spite of minor mechanical misalignments and
results in a more consistent material removal rate across the
polished face of the wafer 15.
[0007] Although providing superior polishing performance, a front
side reference CMP machine may be more costly to manufacture due to
the necessity for incorporating a pressurized air delivery system
48 including associated electrical and pneumatic controls. Such
systems may also be more expensive to operate, since even a small
hole in the flexible membrane 42 will cause unacceptable polishing
performance and will necessitate a maintenance outage to replace
the membrane 42. Furthermore, while it would be desirable to
retrofit older back side reference 15 machines with floating head
capability, it is generally not practical to do so because of the
difficulty of routing an air supply system 48 through an existing
driving mechanism 30.
SUMMARY OF THE INVENTION
[0008] Thus there is a particular need for a chemical mechanical
polishing machine that offers the performance advantages of a front
side reference machine without the expense and maintenance
disadvantages of prior art machines. It is also desired to be able
to upgrade an existing back side reference CMP machine to provide
performance equivalent to a floating reference CMP machine.
[0009] Accordingly, an improved carrier head for a chemical
mechanical polishing apparatus is described herein as including: a
frame adapted for connection to a drive apparatus; a pressure plate
adapted for contact with a wafer; and a pressure pack disposed
between the frame and the pressure plate for transferring a force
there between. The pressure pack provides a desired degree of fluid
coupling between the frame and the wafer to ensure that an even
pressure is applied across the face of the wafer being polished.
The pressure pack may be formed as a gelatinous material
encapsulated within a sealed casing. The pressure pack may further
be formed of a plurality of chambers to provide a varied force
profile across the wafer surface, such as to provide a different
down force at the edge of the wafer than at the center of the wafer
in response to a single down force applied by the carrier driving
mechanism. In order to reduce the risk of damage resulting from a
leaking pressure pack, the pack may be formed to have a double
casing surrounding an interior fluid.
[0010] An improved wafer polishing apparatus is also described
herein as incorporating such an improved carrier head.
[0011] A method of modifying a back side reference polishing
apparatus to function as a floating reference polishing device is
also described herein. Such a back side polishing apparatus may
have a polishing pad affixed to a platen, a wafer carrier for
holding a wafer to be polished against the polishing pad, and a
driving mechanism for polishing the wafer by moving the wafer
carrier with respect to the platen, with the wafer carrier further
including a carrier head frame disposed against a pressure plate
for urging the wafer against the polishing pad. The method of
modifying such a device is described as including the steps of
removing the pressure plate; and replacing the pressure plate with
a replacement pressure plate and a pressure pack, the pressure pack
being disposed between the replacement pressure plate and the
carrier head frame for transferring a force there between for
urging the wafer against the polishing pad. The pressure pack
provides a desired degree of fluid coupling to ensure that an even
pressure is applied across the face of the wafer being polished
without the necessity for adding a pressurized air supply system to
the back side reference device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The features and advantages of the present invention will
become apparent from the following detailed description of the
invention when read with the accompanying drawings in which:
[0013] FIG. 1 illustrates a prior art polishing device.
[0014] FIG. 2 is a partial cross-sectional view of a prior art back
side reference wafer carrier head.
[0015] FIG. 3 is a partial cross-sectional view of a prior art
front side reference wafer carrier head.
[0016] FIG. 4 is a partial cross-sectional view of an improved
wafer carrier head incorporating a pressure pack for transmitting
force to a wafer being polished against a polishing pad.
[0017] FIG. 5 is a cross-sectional view of a multi-chamber pressure
pack.
DETAILED DESCRIPTION OF THE INVENTION
[0018] FIG. 4 illustrates an improved wafer carrier head 54 that
may be used in a chemical mechanical polishing machine such as the
machine 10 of FIG. 1. The carrier head 54 includes a frame 28
adapted to be moved relative to a platen 14 and polishing pad 12 by
a driving mechanism 30. The carrier head 54 includes a retaining
ring 32 and is adapted to position a semiconductor wafer 15 for
polishing against polishing pad 12. A force D is applied through
frame 28 to urge the wafer 15 against the polishing pad 12 during
the polishing operation. A pressure plate 56 is disposed between
the frame 28 and the wafer 15 for transmitting polishing force D
there between. As is known in the art, pressure plate 56 may be
fabricated from a hard substance, such as metal or ceramic, but may
include a covering of a softer substance, such as a felt pad or
polyurethane in order to protect wafer 15 from scratching. In one
embodiment, the hard material may be omitted and only a softer
substance may be used to transfer the force to the wafer. The
downward force D is transmitted to pressure plate 56 from the
carrier frame 28 through a pressure pack 58. Pressure pack 58
provides a desired degree of fluid coupling between the frame 28
and the wafer 15 to ensure that an even force is applied across
pressure plate 56 in spite of any slight misalignment between the
Gus abutting surfaces of the frame 28, pressure plate 56 and wafer
15. Adequate space is made available between frame 28 and pressure
plate 56 to permit the pressure plate 28 to more about freely to
accommodate the interactions between wafer 15 and pressure pack 58.
Pressure pack 58 includes a volume of fluid 60 encapsulated within
a sealed outer casing 62. The outer casing 62 may be a high quality
urethane and the fluid 60 may be water, silicone or other viscous
material. The flexible, fluid properties of pressure pack 58 allow
the pressure plate 56 to "float" relative to the frame 28, thus
ensuring that carrier 54 functions as a front side reference
polishing device.
[0019] A back side reference polishing apparatus such as wafer
carrier head 26 of FIG. 2 may be modified to function as a floating
reference polishing device by incorporating a pressure pack 58 into
an existing carrier frame 28. In order to provide space for
pressure pack 58, the prior art pressure plate 34 of carrier 26
must be removed. Pressure pack 58 and a replacement pressure plate
56 are then installed into the carrier head frame 28 in order to
provide the desired fluid coupling in the load path between driving
mechanism 30 and wafer 15. Depending upon the particular carrier
head being modified, other parts may have to be replaced or
modified in order to accommodate the pressure pack 58. Importantly,
however, there is no need to provide a supply of pressurized air
behind a membrane, as is described in the prior art carrier head 40
of FIG. 3. Fluid 60 is sealed within casing 62 and therefore is
available for repeated polishing operations without the need to be
replenished.
[0020] Contamination is a constant concern during semiconductor
fabrication processes. It is important that pressure pack 58 have a
low incidence of failure, and that in the event of a failure, the
spread of contaminants is minimized. Toward that end, it is
preferred that fluid 60 be a highly viscous material, such as a
gelatinous material, so that in the event of a failure of casing
62, the spread of the fluid 60 will be minimized for easier clean
up. It is also possible to manufacture pressure pack 58 from a
highly elastic solid material that does not have liquid properties,
such as a material having a consistency such as soft clay.
Furthermore, materials of construction for pressure pack 58 should
be selected to avoid any highly harmful or hard to clean
materials.
[0021] FIG. 5 illustrates another embodiment of a pressure pack 64
for use in a wafer polishing apparatus. Pressure pack 64 contains
two chambers, a first chamber 66 in a central portion of the
pressure pack 64, and a second chamber 68 forming a donut-shaped
volume around the perimeter of the pressure pack 64. One may
appreciate that any number of individual chambers may be provided.
The chambers 66, 68 of pressure pack 64 are defined by two separate
casings 70, 72 respectively. Advantageously, the fluid contained in
first chamber 68 is encapsulated by both casing 72 and casing 70,
so that a leak in either one of the casings will not result in
contamination of the associated machinery. Such a double casing
design may also be incorporated on a single chamber pressure pack.
An inner casing may be selected for its compatibility with an
encapsulated fluid and an outer casing may be selected for its
toughness or elasticity properties.
[0022] Advantageously, the physical properties of the two chambers
may be selected to be different so that the distribution of a force
across an abutting pressure plate may be made non-equal while still
maintaining a fluid coupling. Such a dual chamber pressure pack 64
may advantageously be used with a two-part pressure plate 65 having
corresponding center 67 and edge 69 portions. In order to achieve a
desired pressure loading on an abutting pressure plate, the fluid
pressure in the respective chambers 66, 68 may be different in a
relaxed state. For example, by filling fluid in chamber 66 to a
higher pressure than fluid in chamber 68, the pressure transferred
by the pressure pack 64 between abutting frame and pressure plate
members will be higher at the center portion of the pressure pack
64 than at the periphery portion of the pressure pack 64.
Similarly, the fluid material contained within the two chambers 66,
68 may be selected to be different to achieve a desired mechanical
effect. For example, the two fluids may have a different viscosity.
Furthermore, the material of casing 70 may be different than the
material of casing 72 in order to provide a desired mechanical
effect and/or to improve the compatibility with the encapsulated
fluids.
[0023] While the preferred embodiments of the present invention
have been shown and described herein, it will be obvious that such
embodiments are provided by way of example only. Numerous
variations, changes and substitutions will occur to those of skill
in the art without departing from the invention herein.
Accordingly, it is intended that the invention be limited only by
the spirit and scope of the appended claims.
* * * * *