U.S. patent application number 12/970459 was filed with the patent office on 2011-06-23 for cmp retaining ring.
This patent application is currently assigned to ENTEGRIS, INC.. Invention is credited to John BURNS, Martin L. FORBES, Matthew A. FULLER, Jeffery J. KING, Mark V. SMITH.
Application Number | 20110151755 12/970459 |
Document ID | / |
Family ID | 37452770 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110151755 |
Kind Code |
A1 |
BURNS; John ; et
al. |
June 23, 2011 |
CMP RETAINING RING
Abstract
An improved chemical mechanical polishing retaining ring. A
representative embodiment comprises a base portion made from a
wear-resistant plastic material, and an upper portion, or backbone
portion, made from a stiffer and more wear resistant material. One
of the base or backbone portion is preferably overmolded onto the
other. The base portion can be generally defined by a flat
pad-contacting surface, an outer surface, and an inner surface. The
base portion can additionally include channels extending from the
outer surface to the inner surface to facilitate transfer of slurry
to and from the substrate to be polished during the process. One or
both of the base portion or backbone portion further includes a
plurality of circular ribs that serve to create additional bonding
surface with the overmolded material. The retaining ring may
additionally includes a plurality of bosses with threaded insert
holes by which the retaining ring is attached to a chemical
mechanical polishing system.
Inventors: |
BURNS; John; (Colorado
Springs, CO) ; FULLER; Matthew A.; (Colorado Springs,
CO) ; FORBES; Martin L.; (Divide, CO) ; KING;
Jeffery J.; (Colorado Springs, CO) ; SMITH; Mark
V.; (Colorado Springs, CO) |
Assignee: |
ENTEGRIS, INC.
Billerica
MA
|
Family ID: |
37452770 |
Appl. No.: |
12/970459 |
Filed: |
December 16, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12568497 |
Sep 28, 2009 |
7857683 |
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12970459 |
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11440461 |
May 24, 2006 |
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12568497 |
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60684151 |
May 24, 2005 |
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60765995 |
Feb 6, 2006 |
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Current U.S.
Class: |
451/286 |
Current CPC
Class: |
B24B 37/32 20130101;
Y10T 29/49826 20150115 |
Class at
Publication: |
451/286 |
International
Class: |
B24B 41/06 20060101
B24B041/06; B24B 37/04 20060101 B24B037/04 |
Claims
1. A retaining ring for use in a chemical mechanical polishing
operation, comprising: an annular backbone portion having one or
more circumferential and axially projecting backbone portion ribs
with one or more channels defined by the one or more ribs, the ribs
having an axial length greater than a corresponding width and the
backbone portion comprising a rigid polymer material; and a
wear-resistant polymer base portion having a flat bottom surface,
one or more circumferential and axially projecting base portion
ribs with one or more channels defined by the one or more ribs, the
ribs having an axial length greater than a corresponding width and
a plurality of grooves in the bottom surface extending between an
inner edge and an outer edge of the retaining ring, the grooves
adapted to facilitate transfer of slurry during the polishing
operation, wherein the backbone portion and the base portion are
bonded together by an overmolding process such that the backbone
portion ribs mate to the base portion channels and the base portion
ribs mate to the backbone portion channels such that they are
directly interlacing and conforming with each other, and wherein
the backbone portion ribs and the base portion ribs extend a
portion of an axial thickness of the bonded backbone portion and
base portion.
2. The retaining ring of claim 1, wherein the plurality of grooves
each include at least one divergent opening.
3. The retaining ring of claim 1, wherein the base portion
encapsulates the backbone portion.
4. The retaining ring of claim 1, wherein the base portion
comprises polyetheretherketone and the backbone portion comprises
polyetheretherketone blended with ceramic.
5. The retaining ring of claim 1, further comprising mounting
fixtures for securing the retaining ring to a polishing unit.
6. The retaining ring of claim 1, wherein the angle of the grooves
relative to a line tangent to the outer edge is at least 135
degrees.
7. The retaining ring of claim 1, wherein the grooves define a
plurality of pad contacting areas, the pad contact areas comprising
less than 92% of the area of the bottom surface.
8. The retaining ring of claim 1, wherein the backbone portion ribs
and base portion ribs are interlaced and the interlaced portion
extends at least 25% of the axial thickness of the retaining
ring.
9. The retaining ring of claim 1, wherein the annular backbone
portion has three axially projecting backbone portion ribs.
10. The retaining ring of claim 1, wherein the polymer base portion
has three axially projecting base portion ribs.
11. The retaining ring of claim 9, wherein the polymer base portion
has three axially projecting base portion ribs.
12. The retaining ring of claim 1, wherein one of more of the base
portion ribs has a flared cross-section.
Description
PRIORITY APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/568,497, filed Sep. 28, 2009, (U.S. Pat.
No. 7,857,683, issuing Dec. 28, 2010) which is a continuation of
U.S. patent application Ser. No. 11/440,461, filed May 24, 2006,
the disclosures of which are hereby incorporated by reference in
its entirety, which claims priority to U.S. Provisional Patent
Application No. 60/684,151, filed May 24, 2005, of the same title,
the disclosure of which is hereby incorporated by reference in its
entirety, and U.S. Provisional Patent Application No. 60/765,995,
filed Feb. 6, 2006, of the same title, the disclosure of which is
hereby incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a retaining ring for
holding semiconductor wafers in a chemical mechanical polishing
apparatus.
BACKGROUND OF THE INVENTION
[0003] Integrated circuits can be formed on semiconductor
substrates, particularly silicon wafers, by the sequential
deposition of conductive, semiconductive and insulative layers on
the wafer. Circuitry features can be etched on after each layer is
deposited. After a series of layers have been deposited and etched,
the uppermost surface of the substrate can become increasingly
non-planar. Non-planar surfaces can cause problems in the
photolithographic steps of the integrated circuit fabrication
process. As such, it is necessary to periodically planarize the
semiconductor substrate surface.
[0004] Damascene is a process in which interconnecting metal lines
are formed by isolating dielectrics. In damascening, an
interconnecting pattern is first lithographically defined in the
layer of dielectric, and then metal is deposited to fill in the
resulting trenches. Excess metal can be removed by
chemical-mechanical polishing (planarization). Chemical-mechanical
polishing (CMP), also called chemical-mechanical planarization,
refers to a method of removing layers of solid through
chemical-mechanical polishing carried out for the purpose of
surface planarization and definition of the metal interconnecting
pattern. Dual damascene is a modified version of the damascene
process that is used to form metal interconnecting geometry using a
CMP process instead of metal etching. In dual damascene, two
interlayer dielectric patterning steps and one CMP step create a
pattern that would otherwise require two patterning steps and two
metal CMP steps when using a conventional damascene process.
[0005] In a typical CMP operation, a rotating polishing pad, which
receives a chemically reactive slurry, is used to polish the
outermost surface of the substrate. The substrate is positioned
over the polishing pad and is held in place by a retaining ring.
Typically the substrate and retaining ring are mounted on a carrier
or polishing head. A controlled force is exerted on the substrate
by the carrier head to press the substrate against the polishing
pad. The movement of the polishing pad across the surface of the
substrate causes material to be chemically and mechanically removed
from the face of the substrate.
[0006] The machinery used to perform CMP is highly sophisticated,
with equipment costing millions of dollars. Nevertheless, there are
some components of the equipment that require frequent replacement
during the polishing operation that contribute significantly to the
high costs of CMP. One of these components is the retaining ring,
which serves to contain and position the wafer as it is being
planarized. As such, it is important to minimize the cost and time
to manufacture retaining rings, and to maximize the durability of
such rings as well as the ease with which they can be replaced.
SUMMARY OF THE INVENTION
[0007] One embodiment of the invention is a chemical mechanical
polishing retaining ring. The retaining ring can be comprised of a
base portion made from a wear-resistant plastic material, such as
polyetheretherketone (PEEK), and an upper portion, or backbone
portion, made from a stiffer and more wear resistant material, such
as a ceramic or a ceramic filled polymer. One of the base portion
or backbone is preferably overmolded onto the other. The base
portion can be generally defined by a flat pad-contacting surface,
an outer surface, an inner surface, an upper rim, and a recessed
portion. The base portion can additionally include channels
extending from the outer surface to the inner surface to facilitate
transfer of slurry to and from the substrate to be polished during
the process. Recessed portion further includes a plurality of
circular ribs that serve to create a bond with the overmolded
material. The recessed portion may additionally includes a
plurality of bosses with threaded insert holes by which the
retaining ring is attached to a CMP system. The ring shaped
backbone portion may comprise one or more mounting fixtures, an
inner edge, an outer edge, and a bonding surface that may include
one or more ribs, channels, or a combination of these.
[0008] In some embodiments the stiffer polymer material for the
backbone portion or upper portion, for example a ceramic filled
polymer material, can be over-molded onto an unfilled polymer
material for the base or lower portion. In other embodiments the
unfilled polymer material for the base portion or lower portion can
be overmolded onto the stiffer filled polymer material for the
backbone portion or upper portion.
[0009] In a further embodiment of the CMP retaining ring, the base
portion fully surrounds the backbone portion, such that the
backbone portion is fully encapsulated within the base portion. The
base portion can be generally defined by a flat pad-contacting
surface, an outer surface, an inner surface, and an upper rim. The
base portion can additionally include channels extending from the
outer surface to the inner surface to facilitate transfer of slurry
to and from the substrate to be polished during the process. The
base portion further includes a plurality of circular ribs that
serve to create a bond with the overmolded material. The retaining
ring may additionally include a plurality of bosses with threaded
insert holes by which the retaining ring is attached to a CMP
system. The ring shaped backbone portion may comprise one or more
mounting fixtures, an inner edge, an outer edge, and a bonding
surface that may include one or more ribs, channels, or a
combination of these, that serve to create a bond with the
overmolded base portion material. In such an embodiment, the base
portion is overmolded around the backbone portion such that the
backbone portion is fully encapsulated within the base portion.
[0010] An advantage of an embodiment of the invention is flexural
rigidity provided by the ceramic or ceramic-filled polymeric
material that comprises the backbone portion of the retaining ring.
This rigidity reduces or eliminates deformation caused by the
attachment of the retaining ring and reduces the compressibility of
the retaining ring. Deformation and compressibility of the ring can
lead to an uneven distribution of force across the ring, which
causes undesired changes in dimensions.
[0011] Another advantage of an embodiment of the present invention
is the wear resistance and elasticity of the base portion of the
retaining ring. Embodiments of the present invention provide a
durable yet flexible material that prevents chipping or cracking of
the substrate edge where it is supported by the ring while reducing
wear on the ring where it contacts the polishing pad.
[0012] Another advantage of an embodiment of the present invention
is increased bond strength between the overmolded base portion and
backbone portions. The circular ribs created in the bonding portion
of the base portion or backbone portion of the retaining ring allow
for a solid bond to be created when the other portion is overmolded
onto it. In embodiments utilizing injection molding, thinner ribs
and walls can be created which provide increased bonding and
strength.
[0013] Another advantage of an embodiment of the present invention
is ease of application of the polishing slurry during the polishing
process. The channels dispersed around the outside of the retaining
ring base portion facilitate the transport of slurry to and from
the substrate. The divergent openings to the channels on the inside
and outside of the ring and between adjacent pads or foil shaped
pads facilitates the transport of slurry to and from the
substrate.
[0014] Another advantage of an embodiment of the present invention
is decreased cost and maintenance. The retaining ring is durable
and has to be replaced less often due to its rigid upper portion
and wear resistant lower portion. The injection molding and
overmolding processes used to create the retaining ring are also
simple and inexpensive processes. In addition, by eliminating metal
from all or a part of the retaining ring in embodiments of the
invention, corrosion and metal particle contamination from abraded
particles can be significantly reduced or eliminated when the
retaining ring is exposed to acidic or other corrosive polishing
chemistries.
BRIEF DESCRIPTION OF THE FIGURES
[0015] FIG. 1 is a perspective view of a CMP retaining ring
according to an embodiment of the present invention.
[0016] FIG. 2 is a view of the base portion of a CMP retaining ring
according to an embodiment of the present invention.
[0017] FIG. 3 is a diagram of a CMP system employing a CMP
retaining ring according to an embodiment of the present
invention.
[0018] FIG. 4 is a view of the base portion of a CMP retaining ring
according to an embodiment of the present invention.
[0019] FIG. 5 is a view of the backbone portion of a CMP retaining
ring according to an embodiment of the present invention.
[0020] FIG. 6 is an exploded view of a CMP retaining ring according
to an embodiment of the present invention.
[0021] FIG. 7A is a cross sectional view of a CMP retaining ring
taken along the line 7A-7A in FIG. 1.
[0022] FIG. 7B is a cross sectional view of a CMP retaining ring
taken along the line 7B-7B in FIG. 1.
[0023] FIG. 8A is a perspective view of a CMP retaining ring
according to an embodiment of the present invention
[0024] FIG. 8B is a perspective view of a base portion of a CMP
retaining ring according to an embodiment of the present
invention.
[0025] FIG. 8C is a perspective view of a backbone portion of a CMP
retaining ring according to an embodiment of the present
invention.
[0026] FIG. 9A is a perspective view of a backbone portion of a CMP
retaining ring according to an embodiment of the present
invention.
[0027] FIG. 9B is a cross sectional view taken along the line 9B-9B
in FIG. 9A.
[0028] FIGS. 10A and 10B are cross sectional views taken along the
line 10-10 in FIG. 8A.
[0029] FIG. 11 is a perspective view of the bottom side of a CMP
retaining ring according to an embodiment of the present
invention.
[0030] FIG. 12 is a perspective view of a CMP retaining ring
according to an embodiment of the present invention.
[0031] FIG. 13 is a perspective view of a portion of the bottom of
a CMP retaining ring according to an embodiment of the present
invention.
[0032] FIG. 14 is a close-up view of a pad contacting area of a CMP
retaining ring according to an embodiment of the present
invention.
[0033] FIG. 15 is a cross sectional view taken along the line 15-15
in FIG. 13.
[0034] FIG. 16 is a perspective view of a portion of the bottom of
a CMP retaining ring according to an embodiment of the present
invention.
[0035] FIG. 17 is a perspective view of a portion of the bottom of
a CMP retaining ring according to an embodiment of the present
invention.
[0036] FIG. 18 is a cross sectional view of a CMP retaining ring
according to an embodiment of the present invention.
[0037] FIG. 19 is a perspective view of a CMP retaining ring
according to an embodiment of the present invention in a flexure
testing apparatus.
[0038] FIG. 20 is a graph displaying flexure testing results of a
CMP retaining ring according to an embodiment of the present
invention.
[0039] FIG. 21 is a perspective view of a portion of a fractured
CMP retaining ring according to an embodiment of the present
invention.
[0040] FIG. 22 is a table displaying pull-out testing results of a
CMP retaining ring according to an embodiment of the present
invention.
[0041] FIG. 23 is a cross sectional view of a CMP retaining ring
according to an embodiment of the present invention.
[0042] FIG. 24 is a cross sectional view of a CMP retaining ring
according to an embodiment of the present invention.
[0043] FIG. 25 is a perspective view of a portion of the bottom of
a CMP retaining ring according to an embodiment of the present
invention.
[0044] FIG. 26 is a perspective view of a portion of the bottom of
a CMP retaining ring according to an embodiment of the present
invention.
[0045] FIG. 27 is a perspective view of a portion of the bottom of
a CMP retaining ring according to an embodiment of the present
invention.
[0046] FIG. 28 is a cross sectional view of a CMP retaining ring
according to an embodiment of the present invention.
[0047] FIG. 29 is a cross sectional view of a CMP retaining ring
according to an embodiment of the present invention.
[0048] FIG. 30A is an overhead view of one embodiment of the base
portion of a CMP retaining ring according to an embodiment of the
present invention.
[0049] FIG. 30B is a cross section view of the base portion of a
CMP retaining ring taken along line 30B-30B in FIG. 30A.
[0050] FIG. 31 is an overhead view of one embodiment of the base
portion of a CMP retaining ring according to an embodiment of the
present invention.
[0051] FIG. 32 is a perspective view of the embodiment depicted in
FIG. 31.
DETAILED DESCRIPTION OF THE INVENTION
[0052] Referring to FIG. 1, there can be seen a CMP retaining ring
100 according to an embodiment of the present invention. Retaining
ring 100 comprises a lower or base portion 102 and an upper or
backbone portion 122.
[0053] Referring now to FIG. 2 and FIG. 4, a separated view of
lower base portion 102 according to an embodiment of the present
invention can be seen. Base portion 102 is generally defined by a
flat bottom surface 104, an outer surface 106, an inner surface
108, an upper rim 114, and a recessed portion 120. Recessed portion
120 further includes a plurality of circular ribs 110 and bosses
112 with threaded insert holes 118. Ribs 110 serve to create a
solid bond when upper backbone portion is overmolded onto base
portion and provide strength to the retaining ring by preventing
twisting or bending of the ring 100. Base portion 102 additionally
includes channels or grooves 116 extending from outer surface 106
to inner surface 108. Ribs 110 are axial with respect to retaining
ring 100, such that the ribs are substantially vertically oriented
when retaining ring 100 is in use. The use of overmolding, to
create a thermo-physical bond between multiple pieces, is disclosed
in U.S. Pat. No. 6,428,729, the disclosure of which is hereby
incorporated by reference.
[0054] Referring now to FIG. 3, there can be seen a chemical
mechanical polishing system 200 utilizing a CMP retaining ring 100
according to an embodiment of the present invention. In practice,
embodiments of the CMP retaining ring of the present invention, for
example retaining ring 100, can be affixed by mounting fixtures on
the ring to carrier head assembly 202 of a CMP system 200, with top
surface 124 of retaining ring 100 flush with carrier head assembly
202. In some embodiments the retaining ring 100 can be fastened by
inserting fastener inserts through threaded insert holes 118 and
into corresponding holes on carrier head assembly 202. Fastener
inserts can be inserted into retaining ring 100 during the
injection molding process, they can be ultrasonically welded
subsequent to the molding process, or they can be inserted
manually. Fastener inserts can be comprised of any suitable
material, including PEEK and stainless steel. A substrate 204 is
supported within retaining ring 100 and is brought into contact
with a polishing pad 206. Bottom surface 104 of retaining ring 104
contacts polishing pad 206. The polishing pad 206 operates to
polish the substrates 204 due to opposing rotational forces
imparted by axles 208a and 208b. Typically, a slurry, a chemically
reactive liquid, or combination of these is applied to the pad 206
and used to enhance the rate at which material is removed from the
substrate 204. Channels 116, with optionally divergent channel
openings on the inner 108 and outer 106 surfaces in base portion
102 of retaining ring 100, facilitate the transport of the slurry
or chemically reactive liquid to and from the outside of the
retaining ring 100 to the substrate 204. Channels or grooves 116
may be created during the molding process, or machined into bottom
surface 104 after the molding process.
[0055] Base portion 102 can be injection molded from a plastic,
preferably polyetheretherketone (PEEK) or blends with other
polymers that include PEEK or that may include other wear resistant
plastic materials and blends. PEEK is advantageous in that it can
support the wafer with little risk of chipping or cracking the
substrate edge, while still providing high wear and abrasion
resistance. Base portion 102 can also be comprised of PEEK that is
extruded or compression molded and then machined. One of skill in
the art will recognize that different polymers can be used to
increase or decrease the wear resistance of base portion 102.
[0056] In some embodiments, after base portion 102 is molded,
backbone portion 122 can be overmolded thereon. In other
embodiments, the backbone portion 122 can be molded first and the
base portion 102 is then overmolded onto the backbone portion 122.
In other embodiments, the backbone portion 122 or the base 102 can
be machined and the complementary base or backbone portion
overmolded onto the machined piece respectively.
[0057] FIG. 5 shows a view of what an overmolded upper portion or
backbone portion 122 would look like as a separate piece according
to an embodiment of the present invention. The circular ribbing 110
in base portion 102 helps create a solid bonding surface with
increased contact area between backbone portion 122 and base 102.
Backbone portion 122 can be comprised of a ceramic material or
other filler/additive. For example, the ceramic material may be
dispersed in a polymer like PEEK (an example of this is
STAT-PRO.RTM., a conductive ceramic PEEK from Entegris Inc.). The
ceramic material can then be used to tailor the structural
rigidity, shear resistance, thermal conductance, or other property
of the backbone portion 122. The backbone portion 122 structurally
enhances the ring's stiffness based on its modulus. The backbone
portion may have a flexural modular range that includes, but is not
limited to, 600,000 to 1,400,000 psi. The backbone portion 122
material can be filled into the recessed portions 120 of lower base
portion 102, so that it is coplanar with upper rim 114 and bosses
112. The rigidity that a ceramic material provides will help
provide solid equipment attachment and will reduce damage to the
ring from the shearing, rotational, and other forces imparted by
the carrier head to the ring 100.
[0058] FIG. 6 illustrates an exploded view of an embodiment of the
retaining ring 100 of the present invention. A ring base portion
102 is shown having one or more ribs 110 on a non-fluid contacting
side and optional holes 118 for inserts. Retaining ring 100 also
includes a backbone portion 122 that has mounting fixtures 126. The
mounting fixture 126 may for example include holes for inserts 128
which can be threaded or include mounting protuberances (not shown)
which can also be threaded for mounting the assembled device to a
tool. The holes 118, 126 for inserts 128 can optionally be molded
to include threads or other fasteners. In some embodiments, an
insert such as Heli-Coil.RTM. Standard and Screw-Lock Inserts or
other threaded or fastener insert may be used. The backbone portion
122 can have ribs 130 that mate with the ribs 110 on the base
portion 102. Alternatively, the backbone portion 122 can be molded
with ribs 130, and the ring base portion 102 overmolded onto the
backbone portion 122 to fill in the backbone portion rib channels
136. The base portion surface 104 that contacts a polishing pad can
include raised or recessed pad contacting structures termed pads or
foil shaped pads, described more fully below.
[0059] The retaining ring may use or comprise threaded inserts 128.
In other embodiments the retaining ring can comprise one or more
tapped threads formed directly into the ring without the use of
inserts. An over-molded retaining ring with two materials, for
example the backbone portion being the stiffer of the two, can
provide greater pull-out and torque-out strength than with just the
base portion material alone.
[0060] FIGS. 7A and 7B illustrate cross sections of an embodiment
of the invention. FIG. 7A shows a cross section taken at an insert
hole 126 while FIG. 7B shows a cross section between insert holes.
The backbone portion ribs 130 are shown interlocking or engaging
the ribs 110 of the base 102. In various embodiments the ribs 130
of the backbone portion 122 can be formed by molding, machining,
any combination of these, or other suitable process to make the
ribs. The base portion ribs 110, outer wall 106, and bottom pad
contacting surface 104 may be formed by molding or machining or any
combination of these. The base portion 102 can have a beveled edge,
for example a beveled outside edge 105 which can form part of the
base portion pad structures. An insert 128, which can be threaded,
is shown through a hole 126, cavity or recessed portion of the
backbone portion 122 and penetrating into a portion 118 of the base
portion 102. The base portion 102 and backbone portion 122 may be
held together by bonding of the base portion and backbone portion
materials during molding or by use of an adhesive, by the action of
a threaded bolt or screw in the inserts, or any combination of
these or other fixture mechanisms. As depicted in FIGS. 7A and 7B,
base 102 and backbone 122 are meshed, or interlaced, with one
another following the overmolding process.
[0061] FIGS. 8A-8C illustrate ribs 110, 130 which may be present in
various embodiments of the invention. The backbone portion 122 and
base portion ring 102 can have ribs that can mate and be bonded
together using an over-molding process. The 1.sup.st shot may be
coated or primed to increase the bond to the 2.sup.nd shot of
material.
[0062] FIGS. 9A and 9B illustrate a backbone portion 322 of a
retaining ring according to an embodiment of the present invention.
Backbone portion 322 may include ribs 330-333 of varying size and
shape. The ribs 330-333 of the backbone portion 322 can mate with
corresponding ribs on the base portion where machined base portion
and backbone portion rings are joined. The backbone portion ribs
can include rib channels 336, 337. Ribs may include one or more
voids 338 of varying size and shape along a given rib. There can be
one or more rows of ribs 330-333 or one or more rows of channels
336, 337 from the inner to the outer surface of the backbone
portion 322. The rib channels 336, 337 and rib voids 338 may be
filled with overmolded base portion material or mated with a
corresponding machined part and fastened together. The rib channel
and rib void size can be chosen depending upon the strength,
structural rigidity, and base portion bonding requirements for the
retaining ring. The high surface area of the ribs, rib channels,
and optional rib voids increase the bonding area with the base. The
ribs, channels, and rib voids promote stiffness in the retaining
ring. The top backbone portion surface 324 contacts the machine
tool carrier head assembly. The backbone portion stop 334 provides
a bonding surface for a portion of the base portion along the outer
diameter of the retaining ring.
[0063] The ribbed structure of the backbone portion adds structural
rigidity to the backbone portion in the completed retaining ring.
The ribs also provide for increased surface area for bonding the
base portion layer to the backbone portion. The ribs create proper
wall sections for injection molding that allow for a first shot of
material and an over-molded second shot of material. The size of
the ribs and troughs can be chosen to allow for the injection
molding. In some embodiments the ribs can have a height of about
2.5 cm or less from trough to top, preferably less than about 1 to
about 1.5 cm. In preferred embodiments there are at least two ribs
and preferably three ribs extending from each respective portion in
opposite axial directions, the respective ribs being in interlacing
engagement with sidewalls of the ribs preferably having parallel
faces. The interlacing portions of the ribs preferably extend at
least 25 percent of the axial thickness of the rib.
[0064] The backbone portion can comprise a moldable composite
thermoplastic material. One example of a useful material for the
backbone portion includes processable rigid rod polymers based on a
string of substituted and unsubstituted phenylene rings that
produce a highly rigid structure. Small amounts of these kinds of
resin can be used to reinforce other polymers used for the backbone
portion such as PEEK. Examples of rigid rod polymers that may be
used include but are not limited to Parmax SRP (from Mississippi
Polymer Technologies), Celazole.RTM. PBI (polybenzamidazole)
(CELAZOLE is a registered trademark of Celanese Advanced Materials,
Inc.), PEEK w/PBI fiber and PBO (polyphenylene benzobisoxazole).
The moldable composite may be a thermoplastic material that
contains a ceramic filler that provides structural rigidity to the
retaining ring which has one or more channels with divergent inlets
and outlets. The composite thermoplastic can optionally have good
thermal conductivity. Examples of such composite materials may
include those disclosed in U.S. Pat. No. 5,024,978 the contents of
which are incorporated herein by reference in their entirety into
the present disclosure. The composite thermoplastics can include
fiber-reinforced ceramic matrix composites. The inorganic or
ceramic reinforcing fibers can be dispersed with thermoplastic
solids that have been melted. These heated liquid dispersions can
be used in subsequent molding operations to form the backbone
portion ring. Inorganic or ceramic materials may include powdered
glasses, such as powdered aluminosilicate glasses or powdered
borosilicate glasses, powdered aluminosilicate glasses which are
thermally crystallizable to yield refractory glass-ceramic matrices
such as matrices comprising .beta.-spodumene, anorthite,
cordierite, or other phases, and crystalline materials useful for
composite manufacture such as but not limited to for example,
alumina, zirconia, silicon carbide, silicon nitride, combinations
of these and other materials. A variety of reinforcing particles
and or fibers including those selected from the group comprising
fibers of carbon, silicon carbide, glass, silicon nitride, alumina,
mullite or similar materials may also be used. In selecting
particles and or fibers for the filler, the physical form in which
the particle and or fibers may be chosen according to the
requirements of subsequent processing or the configuration or
properties desired in the composite preform or end product. Thus,
for example, the fibers may be provided in the form of a woven or
non-woven fiber fabric, fiber tows, i.e., fiber bundles or other
groups of fibers forming multi-fiber yarns, cords or twine can be
selected. Particle shapes may include but are not limited to
plate-like, spherical, oblong, irregularly shaped, or any
combination of these.
[0065] The backbone portion of the retaining ring is a material
that is mechanically stiffer than the wear resistant base portion
material. Some embodiments of the retaining ring may comprise a
metal containing backbone portion which can include a machined
metal backbone portion with ribs, a backbone portion made from
sintered powdered metal formed in the shape of a backbone portion
with or without ribs, a backbone portion made from an injection
molded metal. The geometry of a metal backbone portion can be
similar to plastic backbone portion. It can include ribs for
structure and to allow for even wall sections for the over-molding
of a second shot of polymer to form the base. The metal backbone
portion may also incorporate undercuts with respect to the second
shot for mechanical bonding.
[0066] One advantage of the all polymer retaining ring in
embodiments of the invention is that the polymers can be formulated
or treated so they have reduced amounts or are free of ionic
impurities for microelectronic manufacturing applications and can
be chosen and outgas very little, thwarting the trace contamination
from sodium, aluminum, iron, copper, lithium, and other inorganic
elements that commonly leach out of conventional ceramic retaining
rings. Polymers can also allow one single CMP ring material set for
the entire range of CMP processes (i.e. Oxide, Tungsten, Copper). A
single ring per wafer lowers overall consumables costs as one
material set can handle rings for an entire fab line. The polymer
material set can be chosen to be chemically compatible and handle a
wide array of chemistries including a broad pH range encountered in
CMP processing. The polymers can be chosen for their hydrolytic and
dimensional stability in liquid or aqueous slurry environments such
that substrate polishing rates and or polishing uniformity across
the substrate are maintained with in process tolerances.
[0067] FIGS. 10A and 10B detail an inverted cross section of a
molded retaining ring 300 according to an embodiment of the present
invention. FIG. 10A illustrates molded base portion flashing 340 on
the inside and outside diameters of the backbone portion 322 that
can be formed in a molding operation. The flashing thickness can be
adjusted. One or more surfaces of the ring may be finished by a
post molding machining operation to remove all or a portion of the
flashing, as shown in FIG. 10B. Post machining can remove the
flashing to a final surface and finish illustrated by the solid
line 342 in FIG. 10A. As illustrated by the tongue and groove
structure of the base portion and backbone portion in FIGS. 10A and
10B, a cross section of a retaining ring could be characterized by
one or more overlapping regions of base portion and backbone
portion material.
[0068] FIG. 10B details a cross section of the retaining device 300
that illustrates an embodiment with base portion flash removed from
the article in an optional post bonding or post molding process.
Following machining, surfaces that do not contact the pad can be
further optionally finished with about 600 grit or finer polishing
paper. For surfaces that contact the pad or substrate, polishing
paper of about 1500 grit or finer can be used. For less critical
substrates or pads, lower grit polishing or as machined surfaces
can be used.
[0069] FIG. 11 illustrates a perspective view of a retaining ring
300 having a pad contacting surface 304 of the ring base portion
302 with one or more raised pad contacting areas 315 with recessed
channels or grooves 316 between them. The grooves or channels 316
can have divergent inlet, divergent outlets, or any combination of
these. The channels 316 and raised pads 315 can be positioned or
formed circumferentially about the ring and permit fluid flow, for
example a polishing fluid or slurry, between the inner and outer
diameters of the ring when it contacts a polishing pad and is
rotated during use. While the description of the retaining ring,
base, and backbone portion have been described and illustrated with
ring shapes, other shapes may be possible provided that the more
generally retaining base portion can be mounted to a moving carrier
and has an inner surface perimeter that holds the substrate and
preferably corresponds to about the perimeter of the substrate. The
pads 315 with fluid channels 316 between them can have an outer
edge that essentially parallels the outer edge or circumference of
the ring 300 and the pads 315 can have an inner edge with one or
more surfaces that essentially parallel the inner edge of the ring
300. The pads 315 can be spaced apart from each other and form
variously shaped channels 316 as illustrated in FIG. 13, FIG. 14,
FIG. 16, FIG. 17, FIG. 25, FIG. 26, and FIG. 27. In some cases the
slurry grooves or channels may be curved or parallel between two
adjacent pads. In some embodiments, as shown in FIG. 17, the
channel or slurry groove may be tapered. The channels or slurry
grooves can have a divergent, widened, or funnel shaped channel on
the inner side, outer surface, or any combination of these. The
divergent channel surfaces improve the transfer of fluid between
the inner and outer ring surfaces and the retained substrate. Edges
of the pad structure can be beveled to reduce wear on the polishing
pad and retaining ring. The depth of the channels can be modified
(made deeper or more shallow) to accommodate or modify the flow of
fluid (polishing slurry or other liquid) into and out of the inner
ring area (where substrate is located). The channels can have one
or more divergent ends on the inner ring diameter surface, outer
ring diameter surface or both. The shape of the divergent channels
or grooves on the inner and outer sides of the ring can be
asymmetric in volume to modify fluid velocity in the region of the
ring and facilitate movement of fluid into or away from the
substrate. The shape of the divergent channels may be modified for
particular slurry composition, viscosity, particle size, and
rotation rate of the retaining ring to achieve a desired polishing
or material removal rate and or uniformity.
[0070] The ring shaped structure 300 or carrier assembly
illustrated in FIGS. 11 and 12 can be used to retain a substrate
for polishing or other surface treatment. In some embodiments, the
retaining ring 300 has a shape that permits mounting to a rotating
plate and retention of circularly shaped substrates. The retaining
ring has an inner surface 308 or diameter exposed to contact a
peripheral edge of a substrate to be polished; the substrate is
held against a polishing surface or pad. The retaining ring 300 can
comprise a ring shaped base portion 302 that contacts a polishing
pad. The ring shaped base portion 302 can be made of a material
that comprises a wear resistant material and that retains its shape
under the load of the tool. The ring shaped base portion 302 can
include a pad contacting surface side 304, an inner edge or surface
308, an outer edge or surface 306, and one or more ribs and/or rib
channels (shown in FIGS. 10A and 10B). The pad contacting surface
304 of the ring shaped base portion 302 can comprise one or more
channels or grooves 316 and one or more pads 315 between the inner
edge surface 308 and an outer edge surface 306 of the ring shaped
base portion 302.
[0071] The retaining ring 300 can further comprise a ring shaped
backbone portion 322. The ring shaped backbone portion 322 can be
made of a material that is different from the ring shaped base
portion 302. In some embodiments, the ring shaped backbone portion
322 comprises a stiffer and more wear resistant material than the
base, for example a ceramic thermoplastic composite. The ring
shaped backbone portion 322 can include one or more mounting
fixtures 326, an inner edge surface 323, an outer edge surface 325,
and one or more ribs and/or rib channels (shown in FIGS. 10A and
10B). The ring shaped base portion 302 and ring shaped backbone
portion 322 are joined along an interface that comprises bonding
surfaces between their corresponding ribs and channels as shown in
FIGS. 10A and 10B. These bonding surfaces can be joined by chemical
bonding, welding or fusion bonding, mechanical bonding, overmolding
one material onto the other, or any combination of these. The base
portion material and the backbone portion material can form
cohesive bonds along the surfaces of the ribs and rib channels
where they contact. The mounting fixtures can comprise structures
that couple the ring shaped backbone portion to a tool or rotating
platen.
[0072] The channels or grooves in the surface of the base portion
of the retaining ring can further include one or more divergent
openings which may be inlets, outlets or combination of these
between the inner and outer surfaces of the retaining ring. The
channel cross section can have a rectangular shape, a radius shape,
or other shapes. The shape of the cross section of the channel can
be chosen to reduce or eliminate low flow areas or dead volumes in
the channels, channels with a radius shape can provide a more
uniform slurry of liquid flow velocity along the channel or groove
surface. In some embodiments, the void volume of the divergent
openings in the base, for example where channel walls are not
parallel, can be greater than the channel void volume (where
channel walls are parallel). In some embodiments the base portion
material has higher wear resistance than the backbone portion. The
ring shaped base portion of the retaining ring can comprise a wear
resistant thermoplastic like PEEK or a co-polymer of PEEK. The ring
shaped backbone portion of the retaining ring can comprise a
ceramic filled thermoplastic material that is stiffer than the base
portion of the retaining ring. The ceramic material that may be
used as a backbone portion can have a higher density than the
material used for the base.
[0073] An embodiment of the structure of the retaining ring pads
315 or foils is illustrated in FIG. 14. The shape of the channels
316 formed between pads 315 is illustrated in FIG. 13. One
advantage of the present invention is that the channels 316 improve
the utilization of polishing slurry and reduce costs of polishing.
The channels 316 or grooves between the retaining ring pads 315
provide for fluid, liquid, or slurry flow which can be along a
groove formed by a leading edge of one pad structure and the bottom
inner edge of an adjacent pad structure. The divergent inlet on the
inner diameter of the ring of these channels can be shaped by the
bottom inner edge of one pad and the leading edge and leading
surface of the adjacent pad or foil. The divergent outlet on the
outer diameter of the ring can be formed by the bottom inner pad
edge and trailing edge of one pad with the leading edge and outer
edge of an adjacent pad. The channel shape promotes transfer of
fluid and slurry between the inner diameter of the ring (where the
substrate is held) and the outer diameter of the ring.
[0074] In FIG. 13, the shaped channel inlet 319 (opens to the inner
ring surface or edge) and shaped channel outlet 317 (opens to the
outer ring surface or edge) can be varied and, for example, the
void volume of the inlet 319 can be made large than the void volume
of the outlet 317. FIG. 15 shows a cross section along that
illustrates an optional bevel 305 on the outer pad surface. The
adjacent pads can be positioned relative to one another to form a
channel or groove. The channel walls may be parallel or
non-parallel. Inlet 319 and outlet 317 may be created during the
molding process, or machined into retaining ring 300 after the
molding process.
[0075] Referring now to FIG. 14, the one or more pads 315 or foils
that form channels along the ring can have an inner pad surface 344
that can have an edge or portion of its perimeter that is tangent,
parallel, or curvilinear with a portion of the inner ring surface.
A portion of the pad 315 can be offset from the inner ring surface.
The trailing 346 and leading 348 edges can optionally be rounded,
beveled, or otherwise formed with a radius. A rounded shape is
advantageous for fluid flow and reduces particle generation during
handling because it can prevent snags with gloves or polishing pad
irregularities. The leading surface 350 of the pad can form a
channel or groove with the inner pad surface of an adjacent pad. A
portion of the outer pad surface 352 and beveled trailing surface
354 can be tangent, parallel, or curvilinear with a portion of the
outer ring surface. The shape of the pad from the leading edge 348
to the outer pad surface 352 and trailing edge 346 can be chosen to
have a length that is greater than the length from the leading edge
348 to the trailing edge 346 along the inner pad surface 344.
[0076] FIG. 15 shows the beveled edge 305 of a pad structure 315
along the outer edge 306 of the ring along the base. A hole 318,
326, recess, or cavity which can be threaded or used for a mounting
insert or mounting protuberance is shown traversing the backbone
portion 322 and base portion 302. In some embodiments (not shown)
the hole may only traverse the base portion 302. FIG. 15 also
illustrates a step 307 formed between the divergent inlet recessed
into the base portion surface and the surface of the base portion
that contacts the pad 304. The size of this step can vary along the
pad structure or pad.
[0077] The depth of the channel or groove of the pad can be made to
handle the slurry flow requirements between the inside and outside
of the retaining ring during a polishing process. As shown in FIG.
18, the cross section of a slurry groove 316 in base portion 302
can include a smooth radius within the groove. In some embodiments
the groove has a rectangular cross section. In various embodiments
of the grooves, the deepest portion of the groove can be about 0.5
cm or less. In some embodiments the deepest portion of the channel
can be about 0.25 cm or less.
[0078] Testing has proven that the above embodiments provide a
rigid structure. As shown in FIGS. 19-21, a retaining ring 400
according to an embodiment of the present invention was flexure
tested with a flexure testing apparatus 460. Retaining ring 400 was
made from a molded Parmax (Mississippi Polymer Technology) backbone
portion 422 and overmolded with 450 g of PEEK base portion 402.
Flexure testing continued until the ring 400 fractured. Testing
results 462 are shown in FIG. 20. The results illustrate that a
lightweight retaining ring 400 with ribs and channels that are
overmolded provides a rigid structure. Even when fractured, as
shown in FIG. 21, the base portion 402 and backbone portion 422
remain cohesive along their bonding surfaces.
[0079] Further testing has demonstrated the substantial pull-out
strength of the backbone portion of embodiments of the present
invention. Mounting of the retaining ring to the CMP platen
rotating head was facilitated by multiple threaded bolts. The
ceramic filled PEEK allows multiple tapped threaded holes to be
produced around the perimeter to secure the retaining ring to the
head. Test samples used stainless steel socket head cap
screw--#8-32 that were threaded in 3 full turns into tapped #8-32
threads. The retaining ring backbone portion used a ceramic filled
PEEK. The results 500 from the test are shown in the Table in FIG.
22.
[0080] Referring now to FIGS. 23 and 24, a cross-section of a
further embodiment of the present invention is depicted. CMP
retaining ring 400 comprises a base portion 402 and a backbone
portion 422. Base portion 402 is generally defined by a flat bottom
surface 404, an outer surface 406, an inner surface 408, and an
upper surface 410. Base portion 402 can include a beveled edge, for
example beveled outside edge 405. Base portion may also include one
or more annular ribs 412. Backbone portion 422 may include one or
more annular ribs 430 adapted to mate with ribs 412 on base portion
402. In the present embodiment, backbone portion 422 is molded
first, and base portion 402 is overmolded onto backbone portion
422, such that backbone portion 422 is fully encapsulated within
base portion 402. Ribs 412 and ribs 430 provide additional bonding
surfaces for base portion 402 and backbone portion 422, increasing
the bond strength between base portion 402 and backbone portion
422.
[0081] Base portion 402 can be injection molded from a plastic,
preferably polyetheretherketone (PEEK) or blends with other
polymers that include PEEK or that may include other wear resistant
plastic materials and blends. PEEK is advantageous in that it can
support the wafer with little risk of chipping or cracking the
substrate edge, while still providing high wear and abrasion
resistance. Base portion 402 can also be comprised of PEEK that is
extruded or compression molded and then machined. One of skill in
the art will recognize that different polymers can be used to
increase or decrease the wear resistance of base portion 402.
[0082] Backbone portion 422 can be comprised of a ceramic material
or other filler/additive. For example, the ceramic material may be
dispersed in a polymer like PEEK (an example of this is
STAT-PRO.RTM., a conductive ceramic PEEK from Entegris Inc.). The
ceramic material can then be used to tailor the structural
rigidity, shear resistance, thermal conductance, or other property
of backbone portion 422. Backbone portion 122 structurally enhances
the stiffness of CMP ring 400 based on its modulus, wherein
backbone portion 422 may have a flexural modular range that
includes, but is not limited to, 600,000 to 1,400,000 psi. The
rigidity that a ceramic material provides will help provide solid
equipment attachment and will reduce damage to the ring from the
shearing, rotational, and other forces imparted by a carrier head
to CMP ring 400.
[0083] FIG. 24 depicts molded base portion flashing 440 on CMP ring
400. Base portion flashing 440 may be present on base portion 402
after the molding operation. One or more surfaces of ring 400 may
be finished by a post-molding machining process to remove all or a
portion of the flashing. Post-molding machining can remove the
flashing to a final surface and finish illustrated by the solid
line 442. Following machining, surfaces that do not contact the
polishing pad can be further optionally finished with about 600
grit or finer polishing paper. For surfaces that contact the pad or
substrate, polishing paper of about 1500 grit or finer can be used.
For less critical substrates or pads, lower grit polishing or as
machined surfaces can be used.
[0084] FIGS. 25-27 depict further embodiments of the structure of
retaining ring pads or foils 315 and channels or grooves 316.
Channels 316 may be straight, curved, or arcuate. CMP ring 300
includes a pad contacting surface 304, made up of a plurality of
foils 315. In a preferred embodiment, the pad contacting surface
304 is between 75% and 95% of the total area of ring 300. In a
further embodiment, the pad contacting surface 304 is less than 92%
of the total area of ring 300. In an alternate embodiment, the pad
contacting surface 304 is less than 90% of the total area of ring
300. In a further alternate embodiment, the pad contacting surface
304 is less than 88% of the total area of ring 300.
[0085] Channels 316 provide for slurry flow, and each channel 316
includes an inlet portion 319, an outlet portion 317, and a neck
portion 311. By varying the shape of foils 315, the shape of
channels 316, the shape of inlet 319 and outlet 317, or any
combination thereof, the slurry transfer characteristics can be
adjusted, thereby adjusting the polishing process. Numerous
parameters of channel 316 can be modified, such as the angle
.alpha., the width, the depth, the radii where channel 316 meets
outer surface 306 and inner surface 308, as well as the overall
number of channels 316 on ring 300. FIG. 26 depicts a CMP ring 300
having a channel 316 with larger radii in the area where channel
316 meets outer surface 306 and inner surface 308, as compared to
the radii of channel 316 depicted in FIG. 25. Angle .alpha. of
channel 316 in FIGS. 25 and 26 is 150 degrees.
[0086] FIG. 27 depicts a CMP ring 300 having a greater contact
surface 304 as compared to CMP ring 300 in FIGS. 25 and 26, while
maintaining the same ring dimensions. The radii where channel 316
meets outer surface 306 and inner surface 308 have been decreased
as compared to FIG. 25 to increase the area of contact surface 304.
The angle .alpha. of channel 316 is 144 degrees, however, the
numerical values of angle .alpha. presented herein are for
illustrative purposes only and should not be considered
limiting.
[0087] Angle .alpha. is measured relative to a line drawn tangent
across outer surface 306 at the point where channel 316 would
intersect with outer surface 306 if channel 316 did not include
outlet portion 317, as illustrated in FIGS. 25-27. The angle of the
channel can be taken with respect to a first reference at a side
wall of the channel where the side walls are parallel in the
central portion of the ring or said reference can be at the mid
line of the channel in the central portion of the ring
(intermediate the outer periphery and the inner periphery) where
the sidewalls of the channel are not parallel. For reference, angle
.alpha. is for counterclockwise rotation of ring 300 when pad
surface 304 is facing downward into a polishing pad. In a preferred
embodiment, angle .alpha. is at least 130 degrees.
[0088] The shape of the ribs and rib channels of the various
embodiments of the present invention may be varied to modify the
bonding between a base and a backbone. For example, the ribs and
rib channels may be annular and concentric with the retaining ring
profile when viewed from above, as depicted in FIGS. 2, 4-6, 8B,
8C, and 9A. The ribs and rib channels may be continuous around the
ring, or may be non-continuous, such as depicted in FIGS. 9A, 9B,
30A, 31, and 32. The ribs and rib channels may also be
non-concentric with the ring profile, having for example a spiral
shape when viewed from overhead. Further, the ribs may be
non-concentric such that they extend generally from one inner edge
of the ring to the other, for example the ribs may be orthogonal to
an edge, or meet an edge of the ring at an angle. The
non-concentric ribs may fully extend from one edge of the ring to
the other, or they may extend only partially between edges of the
ring, as depicted in FIG. 30B.
[0089] Additionally, the ribs may have a flared or tapered
cross-section to create mechanical coupling between the base and
the backbone, as depicted in FIGS. 28 and 29. For example, if a
backbone is first molded having one or more ribs with a flared
cross-sectional profile, when a base portion is overmolded onto the
backbone, the base will be interlocked with the backbone after the
molding process. Similarly, a base portion can be first molded
having one or more ribs with a flared cross-sectional profile, such
that when a backbone is overmolded onto the base portion, the
backbone and the base are interlocked.
[0090] Further, ribs may be provided with transverse passageways to
create mechanical interlocking between the base and the backbone,
as depicted in FIG. 32. For example, if a base portion 102 is first
molded having one or more ribs 110 including one or more transverse
passageways 127, when a backbone is overmolded onto base 102, the
material flows into passageways 127, creating a mechanical bond
between the backbone and base 102. Similarly, a backbone can be
first molded having one or more ribs including one or more
transverse passageways. When a base portion is overmolded onto the
backbone, the material fills in the passageways, thus creating a
mechanical bond between the base and backbone. In the case of
multiple ribs, the transverse passageways provide a link between
neighboring rib channels.
[0091] The embodiments above are intended to be illustrative and
not limiting. Additional embodiments are within the claims.
Although the present invention has been described with reference to
particular embodiments, workers skilled in the art will recognize
that changes may be made in form and detail without departing from
the spirit and scope of the invention.
* * * * *