U.S. patent application number 09/850578 was filed with the patent office on 2002-11-07 for retainer ring and method for polishing a workpiece.
Invention is credited to Simon, Mark G..
Application Number | 20020164926 09/850578 |
Document ID | / |
Family ID | 25308535 |
Filed Date | 2002-11-07 |
United States Patent
Application |
20020164926 |
Kind Code |
A1 |
Simon, Mark G. |
November 7, 2002 |
Retainer ring and method for polishing a workpiece
Abstract
A chemical mechanical polishing (CMP) machine (20) includes a
workpiece carrier assembly (22) having a carrier base (24) with a
workpiece contacting side (26) for holding a first surface (30) of
a workpiece (32). A method utilizing the CMP machine (20) to polish
the workpiece (32) and achieve a minimal edge exclusion region (92)
entails adapting the carrier base (24) to reduce a first diameter
(53) of a workpiece contacting side (26) of the carrier base (24)
to a second diameter (84). The method further calls for providing a
retainer ring (68, 106) disposed concentrically on the carrier base
(24) for retaining the workpiece (32), and applying pressure on the
carrier base (24) to urge a second surface (34) of the workpiece
(36) against a polishing pad (36) of the CMP machine (20). In a
first embodiment, the retainer ring (68) includes a body portion
(70) and a holding lip (78) protruding radially inward from an
inner periphery (80) of the body portion (70) and overlying an
outer edge of the workpiece (32) to reduce the first diameter (53)
of the workpiece contacting side (26) to the second diameter (84).
In an alternative embodiment, the carrier base (24) is modified to
reduce the first diameter (53) of the workpiece contacting side to
the second diameter (84). Correspondingly, a width of the retainer
ring 106 is defined to include a value substantially equivalent to
one half of the difference between the first diameter (53) and the
second diameter (84).
Inventors: |
Simon, Mark G.; (Gilbert,
AZ) |
Correspondence
Address: |
Charlene R. Jacobsen
Suite 409
5727 North Seventh Street
Phoenix
AZ
85014
US
|
Family ID: |
25308535 |
Appl. No.: |
09/850578 |
Filed: |
May 7, 2001 |
Current U.S.
Class: |
451/28 ; 451/288;
451/398; 451/41; 451/59; 451/63 |
Current CPC
Class: |
B24B 37/32 20130101 |
Class at
Publication: |
451/28 ; 451/41;
451/59; 451/63; 451/398; 451/288 |
International
Class: |
B24B 001/00; B24B
007/19 |
Claims
What is claimed is:
1. A retainer ring for retaining a workpiece within a workpiece
carrier assembly of a polishing machine, said workpiece carrier
assembly including a carrier base for holding a first surface of
said workpiece and for abutting a second surface, opposite said
first surface, of said workpiece against a polishing pad of said
polishing machine, said retainer ring comprising: a body portion
configured to be disposed concentrically on an outer periphery of
said carrier base; and a holding lip for retaining said workpiece,
said holding lip protruding radially inward from an inner periphery
of said body portion.
2. A retainer ring as claimed in claim 1 wherein said body portion
is configured to be coupled to said carrier base.
3. A retainer ring as claimed in claim 1 wherein when said
workpiece is held in said carrier base, said holding lip is
configured to approach a perimeter of said workpiece to minimize a
gap between said holding lip and said perimeter.
4. A retainer ring as claimed in claim 1 wherein said holding lip
exhibits a width, said width protruding radially inward, and said
width being in a range of 0.005 and 0.012 inches.
5. A retainer ring as claimed in claim 4 wherein said width of said
holding lip is substantially 0.010 inches.
6. A retainer ring as claimed in claim 1 wherein said carrier base
includes a workpiece contacting side having a first diameter, and
said holding lip is configured to overlie an outer edge of said
workpiece contacting side of said carrier base to reduce said first
diameter of said workpiece contacting side to a second
diameter.
7. A retainer ring as claimed in claim 1 wherein said holding lip
exhibits a height configured to accommodate a thickness of said
workpiece.
8. A retainer ring as claimed in claim 1 wherein said retainer ring
is adapted to replace an existing retainer ring of said workpiece
carrier assembly.
9. A method for utilizing a polishing machine to polish a workpiece
to achieve a minimal edge exclusion region, said polishing machine
including a workpiece carrier assembly having a carrier base with a
workpiece contacting side for holding a first surface of said
workpiece, said workpiece contacting side exhibiting a first
diameter, and said method comprising: adapting said carrier base to
reduce said first diameter of said workpiece contacting side to a
second diameter; providing a retainer ring disposed concentrically
on an outer periphery of said carrier base for retaining said
workpiece when said workpiece is held by said carrier base; and
applying pressure on an upper side, opposite from said workpiece
contacting side, of said carrier base to urge a second surface of
said workpiece into sliding engagement with a polishing pad of said
polishing machine.
10. A method as claimed in claim 9 wherein said carrier base is an
existing carrier base exhibiting said first diameter, and said
adapting operation includes modifying said existing carrier base to
reduce said first diameter of said workpiece contacting side to
obtain said second diameter.
11. A method as claimed in claim 10 wherein said providing
operation comprises defining a width of said retainer ring to
include a value substantially equivalent to one half of a
difference between said first diameter and said second
diameter.
12. A method as claimed in claim 11 wherein said value is in a
range of 0.005 to 0.012 inches.
13. A method as claimed in claim 9 wherein said carrier base is an
existing carrier base exhibiting said first diameter, and said
providing operation includes: producing said retainer ring having a
body portion and a holding lip protruding radially inward from an
inner periphery of said body portion, said body portion being
configured to be disposed concentrically on said outer periphery of
said carrier base; and positioning said retaining ring such that
said holding lip overlies an outer edge of said workpiece
contacting side of said carrier base to reduce said first diameter
of said workpiece contacting side to obtain said second
diameter.
14. A method as claimed in claim 13 wherein said producing
operation includes establishing a width of said holding lip to be
substantially equivalent to one half of a difference between said
first diameter and said second diameter.
15. A method as claimed in claim 14 wherein said width of said
holding lip is in a range of 0.005 to 0.012 inches.
16. A workpiece carrier assembly retrofit kit for adapting a
workpiece carrier assembly of a polishing machine to polish a
workpiece having a minimal edge exclusion region, said workpiece
carrier assembly including an existing carrier base and an existing
retainer ring coupled to said existing carrier base, said existing
carrier base having a workpiece contacting side exhibiting a first
diameter, said existing retainer ring exhibiting a first width, and
said kit comprising: a carrier base configured to replace said
existing carrier base, said carrier base having a workpiece
contacting side exhibiting a second diameter, said second diameter
being less than said first diameter of said existing carrier base;
and a retaining ring configured to couple to said carrier base,
said retaining ring exhibiting a second width, said second width
being substantially equivalent to a sum of said first width and a
value substantially equivalent to one half of a difference between
said first diameter and said second diameter.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to the field of chemical
mechanical polishing machines. More specifically, the present
invention relates to a method and apparatus for polishing a
semiconductor wafer to obtain a minimal edge exclusion.
BACKGROUND OF THE INVENTION
[0002] The production of integrated circuits begins with the
creation of high quality semiconductor wafers. The semiconductor
wafers are typically polished prior to integrated circuit
fabrication so that a flat surface is available upon which the
circuit fabrication can take place. Additionally, during the
integrated circuit fabrication process, layers of, for example,
conductors and dielectrics, are built up on the wafer, on top of
which other such layers are to be created. Thus, it is typically
necessary to "re-flatten" the wafer surface during the actual
fabrication of the integrated circuit and not merely before it. The
act of re-flattening is referred to as planarization.
[0003] Chemical mechanical polishing (CMP) is a process for
improving the surface planarity of a semiconductor wafer and
involves the use of mechanical pad polishing systems usually with a
silica-based slurry. CMP generally includes attaching one side of
the wafer to a flat surface of a wafer carrier or chuck and
pressing the wafer against a flat polishing surface. The polishing
surface is moved under the wafer, and the wafer may also be rotated
about its vertical axis and oscillated back and forth to improve
polishing action. The polishing surface is generally a pad attached
to a rigid flat table which is rotated to provide movement and onto
which an abrasive and/or chemical slurry is pumped. The joint
functions of the pad, the slurry, and the relative movements of the
components produce a combined chemical and mechanical process at
the wafer surface which produces a highly flat surface on a wafer
where surface variations are kept to less than, for example, 0.5
.mu.m.
[0004] However, prior art CMP systems for planarizing semiconductor
wafers have a limitation related to polishing uniformity known as
"edge exclusion." Edge exclusion occurs when too much of the
exposed surface of the semiconductor wafer surface is polished.
This causes the edge or outer portion of the wafer to be unusable
for integrated circuit fabrication. Thus, the larger the edge
exclusion on the semiconductor wafer, the lower the number of
integrated circuits that a fabrication facility can produce per
wafer. For example, prior art CMP systems typically produce an edge
exclusion of approximately six millimeters wide on an eight inch
(i.e., 203.2 mm) diameter wafer. This six millimeter edge exclusion
represents an approximate eleven and a half percent reduction of
surface area of a wafer that may be used for integrated circuit
fabrication.
[0005] Given semiconductor processing costs, it is quite possible
that a single eight inch partially processed wafer is worth $10,000
or more in United States currency when planarization is performed.
Accordingly, the high cost of complex semiconductor wafers combined
with a highly competitive market has driven the need for a
reduction in the size of the edge exclusion in order to maximize
the number of integrated circuits that may be fabricated on a
single wafer.
[0006] In an attempt to respond to this need, original equipment
manufacturers (OEMs) are manufacturing CMP systems that now yield
an edge exclusion of approximately three millimeters. Thus, on an
eight inch wafer, this represents nearly a six and a half percent
increase in useable surface area over wafers polished using CMP
systems producing a six millimeter edge extension. These newly
designed CMP systems may cost in the range of two to three million
dollars. For those fabrication facilities that have significant
capital to invest, the purchase of a new CMP system may be
acceptable. However, for those fabrication facilities in which
financial resources may not be so readily available or for those
that already own a CMP system, the investment of a new CMP system
may be quite objectionable.
[0007] Other OEMs and second source manufacturers have attempted to
retrofit existing CMP systems in order to yield the desired three
millimeter edge exclusion. Such retrofits involve software and
hardware configuration changes that involve the replacement of, for
example, the wafer carrier assembly of a CMP system, the inclusion
of a variable pressurized retaining ring and corresponding software
processes, redesigned polishing pads, and so forth. Such
aftermarket parts are typically not part of an OEM's core business.
Hence, this creates problems for the OEMs in terms of investment of
time and effort in engineering and producing these aftermarket
products. Moreover, the development cost of new components and
software is typically passed to the consumer, i.e., the fabrication
facilities that purchase the retrofit components for their existing
CMP systems. While this investment may not be as great as
purchasing a new CMP system, these modifications to existing
equipment can still cost in the range of fifteen to seventy
thousand dollars when installed. Again, such costs may be
objectionable to some fabrication facilities.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is an advantage of the present invention
that an improved retainer ring for a wafer carrier assembly and a
method for polishing a workpiece utilizing an existing polishing
machine are provided.
[0009] It is another advantage of the present invention that it
limits edge exclusion compared to that which occurs on a
semiconductor wafer polished by known processes.
[0010] Yet another advantage of the present invention is that it
forms a simple modification to existing wafer carrier assemblies
and through the modification improves the CMP process for
semiconductor wafers.
[0011] The above and other advantages of the present invention are
carried out in one form by a retainer ring for retaining a
workpiece within a workpiece carrier assembly of a polishing
machine. The workpiece carrier assembly includes a carrier base for
holding a first surface of the workpiece and for abutting a second
surface, opposite the first surface, of the workpiece against a
polishing pad of the polishing machine. The retainer ring comprises
a body portion configured to be disposed concentrically on an outer
periphery of the carrier base and a holding lip for retaining the
workpiece, the holding lip protruding radially inward from an inner
periphery of the body portion.
[0012] The above and other advantages of the present invention are
carried out in another form by a method for utilizing a polishing
machine to polish a workpiece having a minimal edge exclusion
region. The polishing machine includes a workpiece carrier assembly
having a carrier base with a workpiece contacting side for holding
a first surface of the workpiece. The workpiece contacting side of
the carrier base exhibits a first diameter. The method calls for
adapting the carrier base to reduce the first diameter of the
workpiece contacting side to a second diameter and providing a
retainer ring disposed concentrically on an outer periphery of the
carrier base for retaining the workpiece when the workpiece is held
by the carrier base. The method further calls for applying pressure
on an upper side, opposite from the workpiece contacting side, of
the carrier base to urge a second surface of the workpiece into
sliding engagement with a polishing pad of the polishing
machine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] A more complete understanding of the present invention may
be derived by referring to the detailed description and claims when
considered in connection with the Figures, wherein like reference
numbers refer to similar items throughout the Figures, and:
[0014] FIG. 1 shows a partial block diagram of a chemical
mechanical polishing (CMP) machine that may use the preferred
embodiment of the present invention;
[0015] FIG. 2 shows a bottom view of a semiconductor wafer
surrounded by an existing retainer ring attached to a carrier base
of the CMP machine of FIG. 1;
[0016] FIG. 3 shows a perspective view of a retainer ring in
accordance with a preferred embodiment of the present
invention;
[0017] FIG. 4 shows a cross-sectional side view of a workpiece
carrier assembly of the CMP machine of FIG. 1 with the retainer
ring of FIG. 3;
[0018] FIG. 5 shows a semiconductor wafer polished in accordance
with a preferred embodiment of the present invention; and
[0019] FIG. 6 shows a cross-sectional side view of a workpiece
carrier assembly of the CMP machine of FIG. 1 with a carrier base
and a retainer ring in accordance with an alternative embodiment of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] FIG. 1 shows a partial block diagram of a chemical
mechanical polishing (CMP) machine 20 that may use the preferred
embodiment of the present invention. CMP machine 20 generally
includes a workpiece carrier assembly 22 having a carrier base 24
with a workpiece contacting side 26 and an upper side 28, opposite
from workpiece contacting side 26. Workpiece contacting side 26 is
configured to hold a first surface 30 of a workpiece, or
semiconductor wafer 32. Workpiece carrier assembly 22 picks up
semiconductor wafer 32 by a vacuum force and places a second
surface 34, opposite first surface 30, of wafer 32 in contact with
a polishing pad 36 supported by a platen 38. Slurry 40 is applied
to polishing pad 36.
[0021] Pressure, as represented by an arrow 42, is applied on upper
side 28 of carrier base 24 so that semiconductor wafer 32 contacts
polishing pad 36. Rotation of carrier assembly 22, as represented
by a second arrow 43, urges second surface 34 of semiconductor
wafer 32 in sliding engagement with polishing pad 36 so that
semiconductor wafer 32 is conditioned in the CMP process.
[0022] CMP machine 20 represents a conventional chemical mechanical
polishing system. Hence, those skilled in the art will recognize
that CMP machine 20 may include features such as a user interface,
input and output elements for supplying and receiving semiconductor
wafers, multiple workpiece carrier assemblies, necessary cabinets
and access panels for the mechanical and electrical components
within machine 20, and so forth (not shown) and will not be
discussed in detail herein. Software programs resident in computer
memory of CMP machine 20 function to control the downward pressure
on semiconductor wafer 32, the rotational speed of carrier assembly
22, the application of slurry 40 on polishing pad 36, and so
forth.
[0023] In addition, CMP machine 20 is shown using rotary motion to
rotate semiconductor wafer 32 relative to polishing pad 36 for
clarity of illustration. However, it should be understood to those
skilled in the art that CMP machine 20 may use a combination of
rotational and orbital motion, or rotational and linear motion.
That is, carrier assembly 22 may rotate in a circular path, while
polishing pad 36 rotates in an orbital path. Alternatively, carrier
assembly 22 may rotate in a circular path, while polishing pad 36
moves in a linear path.
[0024] FIG. 2 shows a bottom view of semiconductor wafer 32
surrounded by an existing retainer ring 44 attached to carrier base
24 of CMP machine 20 of FIG. 1. Retainer ring 44 was not shown in
FIG. 1 so that semiconductor wafer 32 would be viewable between
carrier base 24 and polishing pad 36. However, CMP machine 20
typically includes retainer ring 44 which functions to retain wafer
32 within a pocket of workpiece carrier assembly 22 (FIG. 1) formed
by workpiece contacting side 26 and an inner periphery 48 of
retainer ring 44.
[0025] FIG. 2 further shows semiconductor wafer 32 having an edge
exclusion region 50 about a perimeter 52 of wafer 32 that forms in
the conventional CMP process. Wafer 32 floats within the pocket
formed by workpiece contacting side 26 and inner periphery 48 of
retainer ring 44. Workpiece contacting side 26 exhibits a first
diameter 53, defined by inner periphery 48, that is greater than a
diameter 55 of wafer 32. Accordingly, when pressure 42 (FIG. 1) is
applied on upper side 28 (FIG. 1) of carrier base 24 (FIG. 1) so
that wafer 32 contacts polishing pad 36 (FIG. 1), polishing pad 36
may be forced into a gap 54 between inner periphery 48 of retainer
ring 44 and perimeter 52 of wafer 32. Consequently, excessive
polishing of semiconductor wafer 32 occurs about perimeter 52 to
form edge exclusion region 50.
[0026] Edge exclusion region 50 is defined by a width 57. Width 57
of edge exclusion region 50 significantly affects the ability to
include integrated circuits on semiconductor wafer 32. For example,
an integrated circuit pattern 56 is formed on second surface 34 of
semiconductor wafer 32. As can be seen, in integrated circuit
pattern 56, integrated circuits 58, 60, 62 and 64 cannot be used
because they fall, at least in part, within edge exclusion region
50. Thus, edge exclusion region 50 forms an area on second surface
34 of wafer 32 which excludes the acceptable fabrication of
integrated circuits. Width 57 of edge exclusion region 50 typically
ranges from 5 to 7 mm.
[0027] The present invention limits width 57 of edge exclusion
region 50 when polishing wafer 32 utilizing CMP machine 20 compared
to that which occurs on a semiconductor wafer polished by known
processes. In particular, width 57 of edge exclusion region 50 is
decreased from 5 to 7 mm on an eight inch (i.e. 203.2 mm) diameter
wafer to approximately 3 mm. Width 57 of edge exclusion region 50
is decreased by adapting carrier base 24 to reduce first diameter
53 of workpiece contacting side 24, thus decreasing gap 54 and
allowing less space in which wafer 32 may float and in which
polishing pad 36 may be forced.
[0028] Referring to FIGS. 3 and 4, FIG. 3 shows a perspective view
of a retainer ring 68 in accordance with a preferred embodiment of
the present invention. FIG. 4 shows a cross-sectional side view of
workpiece carrier assembly 22 of CMP machine 20 (FIG. 1) with
retainer ring 68. Retainer ring 68 is provided to replace existing
retainer ring 44 (FIG. 2) of workpiece carrier assembly 22 and
functions to retain wafer 32 within workpiece carrier assembly 22
of CMP machine 20 (FIG. 1).
[0029] Retainer ring 68 includes a body portion 70 configured to be
disposed concentrically on an outer periphery 72 of carrier base 24
of workpiece carrier assembly 22. Body portion 70 includes threaded
holes 74, and bolts 76 couple retainer ring 68 to carrier base
24.
[0030] Retainer ring 68 further includes a holding lip 78
protruding radially inward from an inner periphery 80 of body
portion 70. A width 79 of holding lip 78 is shown greatly
exaggerated in FIG. 4 for clarity of illustration. However,
retainer ring 68 is manufactured such that width 79 of holding lip
78 is in a range of 0.005 to 0.012 inches (0.127 to 0.3048 mm). For
example, for a CMP machine, such as CMP machine 20, configured to
polish semiconductor wafer 32 having diameter 55 (FIG. 2) of eight
inches (203.2 mm), holding lip 78 may protrude radially inward
substantially 0.010 inches (0.254 mm) from inner periphery 80.
[0031] When retainer ring 68 is coupled to carrier base 24,
retainer ring 68 is positioned such that holding lip 78 overlies an
outer edge 82 of workpiece contacting side 26 of carrier base 24 to
reduce first diameter 53 of workpiece contacting side 26 to a
second diameter 84. By way of example when width 79 of holding lip
78 is substantially 0.010 inches, second diameter 84 is reduced
substantially 0.020 inches from first diameter 53. Thus, when wafer
32 is held in workpiece carrier assembly 22, holding lip 78
approaches perimeter 52 of wafer 32 and a gap 86 formed between
wafer 32 and inner periphery 80 of body portion 70 is
minimized.
[0032] Holding lip 78 exhibits a height 88 configured to
accommodate the thickness of wafer 32. Thus, like retainer ring 44,
retainer ring 68 functions to retain wafer 32 within a pocket 90 of
workpiece carrier assembly 22 formed by workpiece contacting side
26 and holding lip 78 of retainer ring 68 when wafer 32 is held by
carrier base 24.
[0033] In a preferred embodiment, retainer ring 68 is readily
machined from polyphenyl sulfide (PPS). PPS may be unmodified or
modified with modifiers such as Teflon.RTM. PTFE
(Polytetrafluoroethylene), MoS (Molybdenum disulfide), graphite,
and so forth. PPS is rigid, hard, and resistant to corrosion.
Alternatively, retainer ring 68 may be fabricated from Delrin.RTM.
also characterized by strength, stiffness, hardness, and solvent
and fuel resistance. Retainer ring 68 is precision machined to
achieve tolerances of +/- one micron for holding lip 78.
[0034] FIG. 5 shows semiconductor wafer 32 polished in accordance
with a preferred embodiment of the present invention and having an
edge exclusion region 92. It has been discovered that the
replacement of existing retainer ring 44 (FIG. 2) with retainer
ring 68 in workpiece carrier assembly 22 results in edge exclusion
region 92 having a width 93 of approximately 3 mm being formed on
wafer 32 during the chemical mechanical polishing process utilizing
CMP machine 20. Edge exclusion region 92 with width 93 of 3 mm
represents a minimal edge exclusion currently achievable on newly
designed CMP machines and CMP machines with redesigned workpiece
carrier assemblies.
[0035] Width 93 of edge exclusion region 92 represents nearly a
fifty percent reduction of edge exclusion region 92 over edge
exclusion region 50 (FIG. 2) formed during a conventional CMP
process using retainer ring 44 (FIG. 2). This reduction of the edge
exclusion nets an approximate 6.4% increase in usable surface area
of semiconductor wafer 32 over edge exclusion region 50. As such,
an integrated circuit pattern 94, having the same surface area as
integrated circuit pattern 56 of FIG. 2, includes integrated
circuits 96, 98, 100, and 102. By minimizing edge exclusion region
92 on semiconductor wafer 32, the yield of integrated circuits from
wafer 32 increases.
[0036] Moreover, the replacement of retainer ring 44 with retainer
ring 68 on workpiece carrier assembly 22 is far less costly than
replacement of the entire workpiece carrier assembly on an existing
CMP machine, or purchase of an entirely new CMP machine. For
example, through its simple manufacture and retrofit onto the
existing carrier base 24 (FIG. 3), retainer ring 68 results in
significant savings for the consumer in terms of time and effort in
testing and qualifying replacement carrier assemblies or purchasing
a replacement CMP machine. Thus, retainer ring 68 may be one to
three hundredths of the cost of a replacement carrier assembly or
one thousandth of the cost of a replacement CMP machine.
[0037] FIG. 6 shows a cross-sectional side view of workpiece
carrier assembly 22 of the CMP machine of FIG. 1 with a carrier
base 104 and a retainer ring 106 in accordance with an alternative
embodiment of the present invention. Carrier base 104 may be a
replacement unit for carrier base 24 (FIG. 4). As such, carrier
base 104 and retainer ring 106 may form a retrofit kit that may be
used to upgrade an existing CMP machine to polish wafers to achieve
edge exclusion region 92 with width 93 (FIG. 5) of 3 mm rather than
edge exclusion region 50 (FIG. 2) with width 57 (FIG. 2) of 6 mm.
Alternatively, carrier base 104 may be adapted from carrier base 24
by precision machining the existing carrier base 24. In either
case, carrier base 104 has a workpiece contacting side 108
exhibiting second diameter 84 that is reduced from first diameter
53 (FIG. 2) by a value in a range of 0.010 to 0.024 inches (0.254
to 0.6096 mm).
[0038] Retainer ring 106 is provided to replace retainer ring 44
(FIG. 2). That is, retainer ring 106 is disposed concentrically on
an outer periphery 112 of carrier base 104 and serves to retain
semiconductor wafer 32 when wafer 32 is held by carrier base 104. A
width 114 of retainer ring 106 is defined to include a value
substantially equivalent to a one half of a difference between
first diameter 53 and second diameter 84. By way of example, when
second diameter 84 is reduced from diameter 53 by a total of 0.020
inches, width 114 is a sum of a width (not shown) of retainer ring
44 and 0.010 inches.
[0039] The reduction of second diameter 84 from first diameter 53,
and the corresponding increase of width 114 of retainer ring 106
relative to retainer ring 44, achieves a decrease in a gap 116
between retainer ring 106 and perimeter 52 of wafer 32 relative to
gap 54 (FIG. 2). As such, edge exclusion region 92 (FIG. 5) with
width 93 of 3 mm is produced.
[0040] The replacement of carrier base 24 with carrier base 104, or
alternatively, adaptation of carrier base 24 to produce carrier
base 104, and the replacement of retainer ring 44 with retainer
ring 106, achieves significant cost savings over the replacement of
workpiece carrier assembly 22 or the replacement of CMP machine
20.
[0041] In summary, the present invention teaches of an improved
retainer ring for a wafer carrier assembly and a method for
polishing a workpiece using an existing chemical mechanical
polishing machine. By decreasing the amount of gap between the
perimeter of a semiconductor wafer and a retainer ring, when the
wafer is positioned in a carrier base of a workpiece carrier, the
edge exclusion region is reduced by nearly fifty percent over that
which occurs on a semiconductor wafer polished by previously known
chemical mechanical polishing processes. In addition, the retainer
ring and the adaptation of the carrier base to reduce the diameter
of the workpiece contacting side of the carrier base form a simple
and cost effective modification to existing wafer carrier
assemblies and through the modification improves the CMP process
for semiconductor wafers.
[0042] Although the preferred embodiments of the invention have
been illustrated and described in detail, it will be readily
apparent to those skilled in the art that various modifications may
be made therein without departing from the spirit of the invention
or from the scope of the appended claims. For example, the
teachings of the present invention may be adapted to successfully
achieve minimal edge exclusion regions on workpieces of different
diameters and manufactured from a variety of materials. In
addition, the teachings of the present invention art not limited to
existing CMP machines but may be adapted for use with new CMP
machines to achieve minimal edge exclusion regions on
workpieces.
* * * * *