U.S. patent application number 09/747844 was filed with the patent office on 2002-06-27 for piezoelectric platen design for improving performance in cmp applications.
Invention is credited to Boyd, John, Kistler, Rod, Owczarz, Alek.
Application Number | 20020081945 09/747844 |
Document ID | / |
Family ID | 25006879 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081945 |
Kind Code |
A1 |
Kistler, Rod ; et
al. |
June 27, 2002 |
Piezoelectric platen design for improving performance in CMP
applications
Abstract
An invention is disclosed for improved performance in a CMP
process using piezoelectric elements as a replacement for a platen
air bearing. In one embodiment, a platen for improving performance
in CMP applications is disclosed. The platen includes a plurality
of piezoelectric elements disposed above the platen. In operation,
the piezoelectric elements are used to exert force on the polishing
belt during a CMP process. In this manner, zonal control is
provided during the CMP process.
Inventors: |
Kistler, Rod; (Los Gatos,
CA) ; Boyd, John; (Atascadero, CA) ; Owczarz,
Alek; (San Jose, CA) |
Correspondence
Address: |
MARTINE & PENILLA, LLP
710 LAKEWAY DRIVE
SUITE 170
SUNNYVALE
CA
94085
US
|
Family ID: |
25006879 |
Appl. No.: |
09/747844 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
451/9 ;
451/41 |
Current CPC
Class: |
B24B 37/12 20130101;
B24B 21/04 20130101; B24B 49/16 20130101; B24D 9/08 20130101 |
Class at
Publication: |
451/9 ;
451/41 |
International
Class: |
B24B 049/00 |
Claims
What is claimed is:
1. A platen for improving performance in chemical mechanical
polishing (CMP) applications, comprising: a plurality of
piezoelectric elements disposed above the platen, wherein the
plurality of piezoelectric elements is capable of exerting force on
a polishing belt.
2. A platen as recited in claim 1, wherein an electric field is
used to activate the piezoelectric elements.
3. A platen as recited in claim 1, wherein the plurality of
piezoelectric elements comprises piezoelectric elements of varying
dimensions.
4. A platen as recited in claim 3, wherein piezoelectric elements
near an edge of the platen are smaller than piezoelectric elements
near the center of the platen.
5. A platen as recited in claim 1, wherein each piezoelectric
element of the plurality of piezoelectric elements can be
individually activated to exert force against the polishing
belt.
6. A platen as recited in claim 5, wherein each piezoelectric
element of the plurality of piezoelectric elements can be
individually activated to adjust force resistance against the
polishing belt.
7. A platen as recited in claim 1, wherein a sacrificial material
disposed above the platen is used to reduce wear on the platen.
8. A system for improving performance in chemical mechanical
polishing (CMP) applications, comprising: a wafer head capable of
carrying a wafer; a polishing belt disposed below the wafer head;
and a platen having a piezoelectric elements positioned below the
polishing belt, wherein the piezoelectric elements are capable of
exerting force on the polishing belt.
9. A system as recited in claim 8, wherein an electric field is
used to activate the piezoelectric elements.
10. A system as recited in claim 8, wherein the piezoelectric
elements are of varying dimensions.
11. A system as recited in claim 10, wherein piezoelectric elements
near an edge of the platen are smaller than piezoelectric elements
near the center of the platen.
12. A system as recited in claim 8, wherein each piezoelectric
element can be individually activated to exert force against the
polishing belt.
13. A system as recited in claim 12, wherein each piezoelectric
element can be individually activated to adjust force resistance
against the polishing belt.
14. A system as recited in claim 8, wherein the force exerted
against the polishing belt is transferred to the wafer to provide
zonal control during a CMP process.
15. A system as recited in claim 1, further comprising a
sacrificial material disposed above the platen, the sacrificial
material being used to reduce wear on the platen.
16. A system as recited in claim 15, wherein the sacrificial
material is slowly rolled across the platen during a CMP
process.
17. A method for improving performance in chemical mechanical
polishing (CMP) applications, comprising the operations of:
providing a platen having piezoelectric elements positioned below a
polishing belt disposed above the platen, wherein the piezoelectric
elements are capable of exerting force on the polishing belt.
applying a wafer to the polishing belt; and stabilizing the
polishing belt utilizing the platen, wherein the piezoelectric
elements apply specific forces to the polishing belt.
18. A method as recited in claim 17, further advancing a
sacrificial material across the platen.
19. A method as recited in claim 17, wherein the piezoelectric
elements are of varying dimensions.
20. A method as recited in claim 19, wherein piezoelectric elements
near an edge of the platen are smaller than piezoelectric elements
near the center of the platen.
21. A platen for improving performance in chemical mechanical
polishing (CMP) applications, comprising: a plurality of
piezoelectric elements disposed above the platen, wherein the
plurality of piezoelectric elements is capable of exerting force on
a polishing belt, wherein each piezoelectric element of the
plurality of piezoelectric elements can be individually activated
to exert force against the polishing belt, and wherein each
piezoelectric element of the plurality of piezoelectric elements
can be individually activated to adjust force resistance against
the polishing belt.
22. A platen as recited in claim 21, wherein the plurality of
piezoelectric elements comprises piezoelectric elements of varying
dimensions.
23. A platen as recited in claim 22, wherein piezoelectric elements
near an edge of the platen are smaller than piezoelectric elements
near the center of the platen.
24. A system for improving performance in chemical mechanical
polishing (CMP) applications, comprising: a wafer head capable of
carrying a wafer; a polishing belt disposed below the wafer head; a
platen having a piezoelectric elements positioned below the
polishing belt, wherein the piezoelectric elements are capable of
exerting force on the polishing belt, wherein each piezoelectric
element can be individually activated to exert force against the
polishing belt, and wherein each piezoelectric element can be
individually activated to adjust force resistance against the
polishing belt; and a sacrificial material disposed above the
platen, the sacrificial material being used to reduce wear on the
platen, wherein the sacrificial material is slowly rolled across
the platen during a CMP process.
25. A system as recited in claim 24, wherein the piezoelectric
elements are of varying dimensions.
26. A system as recited in claim 25, wherein piezoelectric elements
near an edge of the platen are smaller than piezoelectric elements
near the center of the platen.
27. A method for improving performance in chemical mechanical
polishing (CMP) applications, comprising the operations of:
providing a platen having piezoelectric elements of varying
dimensions positioned below a polishing belt disposed above the
platen, wherein the piezoelectric elements are capable of exerting
force on the polishing belt. applying a wafer to the polishing
belt; stabilizing the polishing belt utilizing the platen, wherein
the piezoelectric elements apply specific forces to the polishing
belt; and advancing a sacrificial material across the platen.
28. A method as recited in claim 27, wherein piezoelectric elements
near an edge of the platen are smaller than piezoelectric elements
near the center of the platen.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to the following applications:
(1) U.S. patent application Ser. No. ______ (Attorney Docket No.
LAM2P220A), filed Dec. 21, 2000, and entitled "Platen Design for
improving Edge Performance in CMP Applications"; and (2) U.S.
patent application Ser. No. ______ (Attorney Docket No. LAM2P220B),
filed Dec. 21, 2000, and entitled "Pressurized Membrane Platen
Design for Improving Performance in CMP Applications." Each of
these related application is incorporated herein be reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to chemical mechanical
polishing apparatuses, and more particularly to platen designs
using piezoelectric elements for improved performance in chemical
mechanical polishing applications.
[0004] 2. Description of the Related Art
[0005] In the fabrication of semiconductor devices, there is a need
to perform Chemical Mechanical Polishing (CMP) operations,
including polishing, buffing and wafer cleaning. Typically,
integrated circuit devices are in the form of multi-level
structures. At the substrate level, transistor devices having
diffusion regions are formed. In subsequent levels, interconnect
metallization lines are patterned and electrically connected to the
transistor devices to define the desired functional device.
Patterned conductive layers are insulated from other conductive
layers by dielectric materials, such as silicon dioxide. As more
metallization levels and associated dielectric layers are formed,
the need to planarize the dielectric material increases. Without
planarization, fabrication of additional metallization layers
becomes substantially more difficult due to the higher variations
in the surface topography. In other applications, metallization
line patterns are formed in the dielectric material, and then metal
CMP operations are performed to remove excess metallization.
[0006] In the prior art, CMP systems typically implement belt,
orbital, or brush stations in which belts, pads, or brushes are
used to scrub, buff, and polish one or both sides of a wafer.
Slurry is used to facilitate and enhance the CMP operation. Slurry
is most usually introduced onto a moving preparation surface, e.g.,
belt, pad, brush, and the like, and distributed over the
preparation surface as well as the surface of the semiconductor
wafer being buffed, polished, or otherwise prepared by the CMP
process. The distribution is generally accomplished by a
combination of the movement of the preparation surface, the
movement of the semiconductor wafer and the friction created
between the semiconductor wafer and the preparation surface.
[0007] FIG. 1 illustrates an exemplary prior art CMP system 10. The
CMP system 10 in FIG. 1 is a belt-type system, so designated
because the preparation surface is an endless belt 18 mounted on
two drums 24 which drive the belt 18 in a rotational motion as
indicated by belt rotation directional arrows 26. A wafer 12 is
mounted on a wafer head 14, which is rotated in direction 16. The
rotating wafer 12 is then applied against the rotating belt 18 with
a force F to accomplish a CMP process. Some CMP processes require
significant force F to be applied. A platen 22 is provided to
stabilize the belt 18 and to provide a solid surface onto which to
apply the wafer 12. Slurry 28 composing of an aqueous solution such
as NH.sub.4OH or DI containing dispersed abrasive particles is
introduced upstream of the wafer 12. The process of scrubbing,
buffing and polishing of the surface of the wafer is achieved by
using an endless polishing pad glued to belt 18. Typically, the
polishing pad is composed of porous or fibrous materials and lacks
fix abrasives.
[0008] FIG. 2 is a detailed view of a conventional wafer head and
platen configuration 30. The wafer head and platen configuration 30
includes the wafer head 14 and the platen 22 positioned below the
wafer head 14. The wafer head 14 includes a fixed retaining ring 32
that holds the wafer 12 in position below the wafer head 14.
Between the wafer head 14 and the platen 22 is the polishing pad
and belt 18. The polishing platen 22 is closely spaced from a
polishing pad or belt 18 with a very thin air space, referred to as
an "air bearing", being defined between the platen 22 and the
polishing pad 18. The air bearing between the platen 22 and the pad
18 has been conventionally used in an attempt to create a uniform
polishing of the surface.
[0009] To maintain the air bearing, air source holes generally are
formed in the platen 22 and are arranged in concentric ring
patterns from the center of the platen 22 to the outer edge of the
platen 22. Each ring establishes an air delivery zone where air
from an air source is directed through the holes during polishing,
thus establishing the air bearing. Air is exhausted past the platen
edge.
[0010] With multiple air delivery zones, the air distribution
profile of the air bearing can be varied radially as necessary to
achieve optimal polishing by vary the polishing rate in each zone.
Unfortunately, the distribution profiles of the zones are not
completely independent of each other. This complicates establishing
different distribution profiles for different zones.
[0011] Moreover, the air bearing is very sensitive to conditions.
For example, the pressure of the air bearing varies with the gap
between the pad 18 and the platen 22. Thus, if the pad 18 is pushed
toward the platen 22 in one area, the pressure of all areas of the
air bearing are affected, thus adding unwanted complexity to the
CMP process.
[0012] In view of the foregoing, there is a need for a method that
establishes greater independence of the air distribution profiles,
zone to zone, thereby facilitating establishing a polishing rate in
each zone independently of the other zones and, hence, improving
manufacturing flexibility and functionality.
SUMMARY OF THE INVENTION
[0013] Broadly speaking, the present invention fills these needs by
providing improved performance in a CMP process using piezoelectric
elements as a replacement for a platen air bearing. In one
embodiment, a platen for improving performance in CMP applications
is disclosed. The platen includes a plurality of piezoelectric
elements disposed above the platen. In operation, the piezoelectric
elements are used to exert force on the polishing belt during a CMP
process. In this manner, zonal control is provided during the CMP
process.
[0014] In another embodiment, a system for improving performance in
CMP applications is disclosed. The system includes a wafer head
capable of carrying a wafer, and a polishing belt positioned below
the wafer head. Further included in the system is a platen having
piezoelectric elements positioned below the polishing belt. The
piezoelectric elements are capable of exerting force on the
polishing belt.
[0015] A method for improving performance in CMP applications is
disclosed in yet another embodiment of the present invention.
Initially, a platen is provided having piezoelectric elements
positioned below a polishing belt, which is disposed above the
platen. The piezoelectric elements of the platen are capable of
exerting force on the polishing belt. A wafer is then applied to
the polishing belt, and the polishing belt is stabilized using the
platen, where the piezoelectric elements on the platen apply
specific forces to the polishing belt.
[0016] Advantageously, the piezoelectric elements of the
embodiments of the present invention improve performance during a
CMP process by providing increased zonal control to the pressurized
membrane. Further, unlike a conventional air bearing, the
piezoelectric elements of the embodiments of the present invention
greatly reduces the amount of air needed during the CMP
process.
[0017] Moreover, a CMP process using the piezoelectric elements of
the present invention is not as sensitive to conditions as
conventional CMP processes utilizing air bearings. Unlike air
bearings, the force exerted by the piezoelectric elements of the
present invention does not experience as great a variance as
experienced by air bearings when the gap between the polishing pad
and the platen varies. Thus, if the polishing pad is pushed toward
the platen in one area, the force exerted on the polishing belt by
other piezoelectric elements is not as affected as other areas
would be when utilizing an air bearing.
[0018] Other aspects and advantages of the invention will become
apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention, together with further advantages thereof, may
best be understood by reference to the following description taken
in conjunction with the accompanying drawings in which:
[0020] FIG. 1 illustrates an exemplary prior art CMP system;
[0021] FIG. 2 is a detailed view of a conventional wafer head and
platen configuration;
[0022] FIG. 3 is a diagram showing a platen configuration, in
accordance with an embodiment of the present invention;
[0023] FIG. 4 is a detailed diagram showing a platen configuration,
in accordance with an embodiment of the present invention;
[0024] FIG. 5 is a diagram showing a platen configuration having
varied annular bladders, in accordance with an embodiment of the
present invention;
[0025] FIG. 6A is a top view of an annular bladder configuration,
in accordance with an embodiment of the present invention;
[0026] FIG. 6B is a top view showing an annular bladder
configuration, in accordance with an embodiment of the present
invention;
[0027] FIG. 7 is a diagram showing a platen configuration, in
accordance with an embodiment of the present invention;
[0028] FIG. 8 is a top view of a piezoelectric element
configuration, in accordance with an embodiment of the present
invention; and
[0029] FIG. 9 is an illustration showing a CMP system, in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] An invention is disclosed for improved performance in a CMP
process using piezoelectric elements as replacement for a platen
air bearing. The present invention provides piezoelectric elements
atop a platen, which provide zonal control during the CMP process.
In the following description, numerous specific details are set
forth in order to provide a thorough understanding of the present
invention. It will be apparent, however, to one skilled in the art
that the present invention may be practiced without some or all of
these specific details. In other instances, well known process
steps have not been described in detail in order not to
unnecessarily obscure the present invention.
[0031] FIGS. 1-2 have been described in terms of the prior art.
FIG. 3 is a diagram showing a platen configuration 300, in
accordance with an embodiment of the present invention. Prior to
describing a platen configuration having piezoelectric elements,
another embodiment of the present invention, which utilizes annular
bladders will be described. The platen configuration having
piezoelectric elements will be described later with respect to
FIGS. 7-9.
[0032] The platen configuration 300 of FIG. 3 includes a wafer head
302 having a retaining ring 304 and a wafer 306 positioned below
the wafer head 302. The platen configuration 300 also includes a
platen 308 disposed below a polishing belt 310. The platen 308
includes a pressurized membrane 312 pressurized via annular
bladders 314.
[0033] During operation the platen 308 is placed against the
polishing pad or belt 310 that polishes the surface of the wafer
306. To promote polishing uniformity, each bladder 314 may be
individually pressurized via an air source. Advantageously, the
annular bladders 314 improve performance in the CMP process by
providing increased zonal control to the pressurized membrane 312.
Unlike a conventional air bearing, the pressurized membrane 312 of
the embodiments of the present invention greatly reduces the amount
of air needed during the CMP process.
[0034] Moreover, a CMP process using the pressurized membrane 312
of the present invention is not as sensitive to conditions as
conventional CMP processes utilizing air bearings. Unlike air
bearings, the pressure of the pressurized membrane 312 of the
present invention does not experience as great a variance as
experienced by air bearings when the gap between the polishing pad
310 and the platen 308 varies. Thus, if the polishing pad 310 is
pushed toward the platen 308 in one area, the pressure in other
areas of the pressurized membrane 312 are not as affected as other
areas would be when utilizing an air bearing.
[0035] FIG. 4 is a detailed diagram showing a platen configuration
400, in accordance with an embodiment of the present invention. The
platen configuration 400 shows a polishing belt 310 positioned
above a platen 308 having a pressurized membrane 312 pressurized by
annular bladders 314. As shown in FIG. 4, each annular bladder 314
comprises a thin tubular material 402. In one embodiment, the
tubular material 402 of each annular bladder 314 is pressurized via
air. However, it should be noted that the tubular material 402 can
be pressurized utilizing any other means capable of pressurizing an
annular bladder 314, such as a fluid, as will be apparent to those
skilled in the art.
[0036] The pressurized membrane 312 preferably comprises a smooth,
flexible material. Suitable materials include; polyurethane,
silicon, thin metals (e.g., stainless steel), peek, and Teflon. As
previously mentioned, the annular bladders 314 provide increased
zonal control during a CMP process. To further increase zonal
control, the size of the annular bladders 314 within the
pressurized membrane 312 can be varied, as described in greater
detail subsequently.
[0037] FIG. 5 is a diagram showing a platen configuration 500
having varied annular bladders, in accordance with an embodiment of
the present invention. The platen configuration 500 includes a
platen 308 having a pressurized membrane 312 pressurized via
annular bladders 314. As shown in FIG. 5, the platen configuration
500 includes annular bladders 314 having varying sizes.
[0038] More specifically, the annular bladders 314 decrease in size
as the annular bladders 314 approach the edge of the platen 308.
Generally, during a CMP process, more difficulty occurs within
about 10-15 mm of the wafer edge. For this reason, one embodiment
of the present invention increases resolution near the wafer edge
by decreasing the size of the annular bladders 314 near the edge of
the platen 308. Similarly, since the center of the wafer typically
requires less resolution, the central annular bladders 314 often
are larger than those at the edge of the platen 308.
[0039] FIG. 6A is a top view of an annular bladder configuration
600a in accordance with an embodiment of the present invention. The
annular bladder configuration 600a includes concentric annular
bladders 314a. In one embodiment, each concentric annular bladder
314a of the annular bladder configuration 600a forms a complete
circle about the center of the platen. In this manner each annular
bladder 314a can be individually pressurized to provide zonal
control during the CMP process. To further increase zonal control
during the CMP process, the length of each annular bladder can be
reduced, as discussed next with reference to FIG. 6B.
[0040] FIG. 6B is a top view showing an annular bladder
configuration 600b in accordance with an embodiment of the present
invention. The annular bladder configuration 600b includes
concentric annular bladders 314b. Unlike the embodiment of FIG. 6A,
each concentric annular bladder 314b of the annular bladder
configuration 600b does not form a complete circle about the center
of the platen. Each concentric annular bladder 314b of the annular
bladder configuration 600b varies in size depending on a particular
annular bladder's 314 proximity to the edge of the platen.
[0041] As mentioned above, during a CMP process, more difficulty
generally occurs within about 10-15 mm of the wafer edge. For this
reason, one embodiment of the present invention increases
resolution near the wafer edge by decreasing the size of the
annular bladders 314b near the edge of the platen. Similarly, since
the center of the wafer typically requires less resolution, the
central annular bladders 314b often are larger than those at the
edge of the platen.
[0042] Advantageously, embodiments of the present invention improve
performance in CMP applications by providing increased zonal
control via a membrane pressurized using internal annular bladders.
Other embodiments of the present invention also improve performance
in CMP applications by providing increased zonal control via
piezoelectric transducers.
[0043] Many polymers, ceramics, and molecules such as water are
permanently polarized, having some parts of the molecule positively
charged, while other parts of the molecule are negatively charged.
When an electric field is applied to these materials, these
polarized molecules align themselves with the electric field,
resulting in induced dipoles within the molecular or crystal
structure of the material. Furthermore, a permanently-polarized
material such as quartz (SiO.sub.2) or barium titanate
(BaTiO.sub.3) will produce an electric field when the material
changes dimensions as a result of an imposed mechanical force.
These materials are piezoelectric, and this phenomenon is known as
the piezoelectric effect. Conversely, an applied electric field can
cause a piezoelectric material to change dimensions. This
phenomenon is known as electrostriction, or the reverse
piezoelectric effect.
[0044] Hence, one embodiment of the present invention utilizes
piezoelectric materials to provide zonal control during a CMP
process. FIG. 7 is a diagram showing a platen configuration 700, in
accordance with an embodiment of the present invention. The platen
configuration 700 includes a wafer head 302 disposed above a wafer
306, and having a retaining ring 304. In addition, a platen 308 is
positioned below the polishing belt 310.
[0045] The platen 308 of the platen configuration 700 includes a
plurality of piezoelectric elements 702 disposed below the
polishing belt 310. During operation, the platen 308 is placed
against the polishing pad or belt 310 that polishes the surface of
the wafer 306. To promote polishing uniformity, each piezoelectric
element 702 may be individually activated to apply zonal force to
the polishing pad. Advantageously, the piezoelectric elements 702
improve performance in the CMP process by providing increased zonal
control to the polishing belt 310. Unlike a conventional air
bearing, the piezoelectric elements 702 of the embodiments of the
present invention greatly reduce the amount of air needed during
the CMP process.
[0046] Moreover, as with the pressurized membrane, a CMP process
using the piezoelectric elements 702 of the present invention is
not as sensitive to conditions as conventional CMP processes
utilizing air bearings. Unlike air bearings, the force exerted by
the piezoelectric elements 702 of the present invention does not
experience as great a variance as experienced by air bearings when
the gap between the polishing pad 310 and the platen 308 varies.
Thus, if the polishing pad 310 is pushed toward the platen 308 in
one area, the force exerted on the polishing belt 310 by other
piezoelectric elements 702 is not as affected as other areas would
be when utilizing an air bearing.
[0047] FIG. 8 is a top view of a piezoelectric element
configuration 800, in accordance with an embodiment of the present
invention. The piezoelectric element 702 configuration 800 includes
concentric piezoelectric elements 702. Similar to the annular
bladder configuration of FIG. 6A, in one embodiment of the present
invention, each concentric piezoelectric element 702 forms a
complete circle about the center of the platen. However, to further
increase zonal control during the CMP process, the length of each
piezoelectric element 702 can be reduced, as shown FIG. 8.
[0048] Unlike the embodiment of FIG. 6A, each concentric
piezoelectric element 702 of the piezoelectric element
configuration 800 does not form a complete circle about the center
of the platen. Each concentric piezoelectric element 702 of the
piezoelectric element configuration 800 varies in size depending on
a particular piezoelectric element's 702 proximity to the edge of
the platen.
[0049] As mentioned previously, during a CMP process, more
difficulty generally occurs within about 10-15 mm of the wafer
edge. For this reason, one embodiment of the present invention
increases resolution near the wafer edge by decreasing the size of
the piezoelectric elements 702 near the edge of the platen.
Similarly, since the center of the wafer typically requires less
resolution, the central piezoelectric elements 702 often are larger
than those at the edge of the platen.
[0050] Unlike an air bearing, the embodiments of the present
invention make physical contact with the polishing belt during the
CMP process. As result, wear on the platen may be increased do to
friction from the polishing belt. To provide additional protection
from wear to the platen, a sacrificial material can be positioned
between the platen and the polishing belt, as discussed next with
reference to FIG. 9.
[0051] FIG. 9 is an illustration showing a CMP system 900, in
accordance with an embodiment of the present invention. The CMP
system 900 in FIG. 9 is a belt-type system having an endless
polishing belt 310 mounted on two drums 910, which drive the
polishing belt 310 in a rotational motion as indicated by belt
rotation directional arrows 906. A wafer 306 is mounted on the
wafer head 302, which is rotated in direction 908. The rotating
wafer 306 is then applied against the rotating polishing belt 310
with a force F to accomplish a CMP process. Some CMP processes
require significant force F to be applied.
[0052] A platen 308, having piezoelectric elements 702, is provided
to stabilize the polishing belt 310 and to provide a solid surface
onto which to apply the wafer 306. Slurry 904 composing of an
aqueous solution such as NH.sub.4OH or DI containing dispersed
abrasive particles is introduced upstream of the wafer 306. The
process of scrubbing, buffing and polishing of the surface of the
wafer is achieved by using an endless polishing pad glued to the
polishing belt 310. Typically, the polishing pad is composed of
porous or fibrous materials and lacks fix abrasives.
[0053] Disposed between platen 308 and the polishing belt 310 is a
sacrificial material 914 fed roll-to-roll over the platen 308 via
rollers 916. During use, the sacrificial material 914 is fed slowly
over the platen 308 to provide protection from wear. In an
alternative embodiment, the sacrificial material 914 is indexed as
the CMP process progresses. In this manner, the sacrificial
material 914 is worn, rather than the material of the platen 308.
Hence, the piezoelectric elements 702 or the pressurized membrane
are protected from wear caused by the friction of the rotating
polishing belt 310.
[0054] Although the foregoing invention has been described in some
detail for purposes of clarity of understanding, it will be
apparent that certain changes and modifications may be practiced
within the scope of the appended claims. Accordingly, the present
embodiments are to be considered as illustrative and not
restrictive, and the invention is not to be limited to the details
given herein, but may be modified within the scope and equivalents
of the appended claims.
* * * * *