U.S. patent application number 12/263908 was filed with the patent office on 2010-05-06 for monolithic linear polishing sheet.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Benjamin A. Bonner, Anand N. Iyer, Garlen C. Leung, Peter McReynolds, Gregory E. Menk, Gopalakrishna B. Prabhu, Erik S. Rondum.
Application Number | 20100112919 12/263908 |
Document ID | / |
Family ID | 42131991 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100112919 |
Kind Code |
A1 |
Bonner; Benjamin A. ; et
al. |
May 6, 2010 |
MONOLITHIC LINEAR POLISHING SHEET
Abstract
A chemical mechanical polishing article can be a single
contiguous layer having a polishing surface, the layer being an
elongated substantially rectangular sheet having a width and a
length at least four times greater than the width. Forming a
polishing article can include depositing a liquid precursor on a
moving belt, at least partially curing the liquid precursor while
on the moving belt to form a polishing layer, and detaching the
polishing layer from the belt.
Inventors: |
Bonner; Benjamin A.; (San
Jose, CA) ; Prabhu; Gopalakrishna B.; (San Jose,
CA) ; Rondum; Erik S.; (San Ramon, CA) ; Menk;
Gregory E.; (Pleasanton, CA) ; Iyer; Anand N.;
(Santa Clara, CA) ; McReynolds; Peter; (San Mateo,
CA) ; Leung; Garlen C.; (San Jose, CA) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
42131991 |
Appl. No.: |
12/263908 |
Filed: |
November 3, 2008 |
Current U.S.
Class: |
451/493 ;
451/527; 451/535; 451/537; 451/538; 451/539; 51/295; 51/297 |
Current CPC
Class: |
B24B 37/205 20130101;
B24D 11/003 20130101; B24B 21/004 20130101 |
Class at
Publication: |
451/493 ;
451/527; 451/537; 451/539; 451/535; 451/538; 51/297; 51/295 |
International
Class: |
B24D 11/00 20060101
B24D011/00 |
Claims
1. A chemical mechanical polishing article, consisting of: a single
contiguous layer having a polishing surface, the layer being an
elongated substantially rectangular sheet having a width and a
length at least four times greater than the width.
2. The article of claim 1, wherein the layer comprises
polyurethane.
3. The article of claim 2, wherein the layer comprises a porous
polyurethane.
4. The article of claim 1, wherein the layer has a thickness
between about 30 and 50 mils.
5. The article of claim 1, wherein the polishing surface includes a
plurality of grooves extending partially but not entirely through
the polishing pad.
6. The article of claim 5, wherein the grooves have a depth between
about 15 and 30 mils.
7. The article of claim 1, wherein at least a portion of the layer
is wound in a roll.
8. The article of claim 1, wherein the layer has a length between
about twenty and thirty feet.
9. The article of claim 1, wherein the layer has a width between
about two and four feet.
10. A chemical mechanical polishing article, consisting of: first
and second sheet portions, each sheet portion consisting of a
single contiguous layer having a polishing surface, each sheet
portion being an elongated substantially rectangular sheet having a
width and a length at least four times greater than the width; and
a window extending the length of and connecting the first and
second sheet portions.
11. A chemical mechanical polishing assembly, comprising: a feed
roller; a take-up roller; and a polishing sheet having a first end
wound around the feed roller and a second end wound around the
take-up roller, the polishing sheet consisting of single contiguous
layer having a polishing surface, the layer being an elongated
substantially rectangular sheet having a width and a length at
least four times greater than the width.
12. A method of forming a polishing article, comprising: depositing
a liquid precursor on a moving belt; at least partially curing the
liquid precursor while on the moving belt to form a polishing
layer; and detaching the polishing layer from the belt.
13. The method of claim 12, wherein depositing the liquid precursor
includes depositing the liquid precursor onto a carrier sheet
supported on the belt.
14. The method of claim 13, wherein the carrier sheet comprises a
thin polyethylene terephthalate polyester film.
15. The method of claim 13, further comprising removing the
polishing layer from the carrier sheet.
16. The method of claim 15, further comprising grinding top and
bottom surfaces of the polishing layer.
17. The method of claim 12, wherein at least partially curing the
liquid precursor includes heating.
18. The method of claim 12, further comprising fully curing the
polishing sheet after the polishing sheet is detached from the
belt.
19. The method of claim 12, further comprising compressing the
polishing sheet.
20. The method of claim 15, wherein compressing includes passing
the polishing sheet between pinch rollers.
21. The method of claim 12, further comprising forming grooves in
the polishing sheet.
22. The method of claim 12, further comprising trimming edges of
the polishing sheet.
Description
TECHNICAL FIELD
[0001] This disclosure relates to chemical mechanical
polishing.
BACKGROUND
[0002] An integrated circuit is typically formed on a substrate by
the sequential deposition of conductive, semiconductive or
insulative layers on a silicon wafer. One fabrication step involves
depositing a filler layer over a patterned stop layer, and
planarizing the filler layer until the stop layer is exposed. For
example, trenches or holes in an insulative layer may be filled
with a conductive layer. After planarization, the portions of the
conductive layer remaining between the raised pattern of the
insulative layer form vias, plugs and lines that provide conductive
paths between thin film circuits on the substrate. Planarization
can also be used to provide a planar surface for
photolithography.
[0003] Chemical mechanical polishing (CMP) is one accepted method
of planarization. This planarization method typically requires that
the substrate be mounted on a carrier or polishing head. The
carrier head places the exposed surface of the substrate against a
polishing pad and provides a controllable load, i.e., pressure, on
the substrate. A polishing liquid, such as an abrasive slurry, is
supplied to the surface of the polishing pad.
[0004] In one type of polishing system, the polishing pad is a
linear sheet that is incrementally advanced across a platen.
SUMMARY
[0005] In one aspect, a chemical mechanical polishing article is a
single contiguous layer having a polishing surface, the layer being
an elongated substantially rectangular sheet having a width and a
length at least four times greater than the width.
[0006] Implementations may include one or more of the following
features. The layer may be polyurethane, e.g., a porous
polyurethane. The layer may have a thickness between about 30 and
50 mils. The polishing surface may include a plurality of grooves
extending partially but not entirely through the polishing pad. The
grooves may have a depth between about 15 and 30 mils. At least a
portion of the layer may be wound in a roll. The layer may have a
length between about twenty and thirty feet, and a width between
about two and four feet.
[0007] In another aspect, a chemical mechanical polishing article
includes first and second sheet portions, and a window extending
the length of and connecting the first and second sheet portions.
Each sheet portion consists of a single contiguous layer having a
polishing surface, and each sheet portion is an elongated
substantially rectangular sheet having a width and a length at
least four times greater than the width.
[0008] In another aspect, a chemical mechanical polishing assembly
includes a feed roller, a take-up roller, and a polishing sheet
having a first end wound around the feed roller and a second end
wound around the take-up roller. The polishing sheet consists of
single contiguous layer having a polishing surface, the layer being
an elongated substantially rectangular sheet having a width and a
length at least four times greater than the width.
[0009] In another aspect, a method of forming a polishing article
includes depositing a liquid precursor on a moving belt, at least
partially curing the liquid precursor while on the moving belt to
form a polishing layer, and detaching the polishing layer from the
belt.
[0010] Implementations may include one or more of the following
features. The liquid precursor may be deposited onto a carrier
sheet, e.g., a polyethylene terephthalate polyester film, supported
on the belt. The polishing layer may be removed from the carrier
sheet. Top and bottom surfaces of the polishing layer may be
ground. At least partially curing the liquid precursor may include
heating. The polishing sheet may be fully cured after the polishing
sheet is detached from the belt. The polishing sheet may be
compressed, e.g., passed between pinch rollers. Grooves may be
formed in the polishing sheet. Edges of the polishing sheet may be
trimmed.
[0011] Advantages may include the following. The polishing layer
can be thicker without reducing the length of the sheet wrapped
around the feed roller, thus increasing pad life. Optical
transmission through a window in the polishing sheet can be
improved.
[0012] Other features and advantages will be apparent from the
following description, including the drawings and claims.
DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a schematic exploded perspective view of a
chemical mechanical polishing (CMP) apparatus.
[0014] FIG. 2 is a top plan view of the CMP apparatus of FIG.
1.
[0015] FIG. 3A is a top plan view, cut away, of the first polishing
station of the CMP apparatus of FIG. 1.
[0016] FIG. 3B is a schematic exploded perspective view of a
rectangular platen and a polishing cartridge.
[0017] FIG. 3C is a schematic perspective view of a polishing
cartridge attached to a rectangular platen.
[0018] FIG. 4 is a schematic perspective view, cut away of a linear
polishing sheet.
[0019] FIG. 5A is a schematic side view in cross-section of an
implementation of the polishing sheet.
[0020] FIG. 5B is a schematic side view in cross-section of another
implementation of the polishing sheet.
[0021] FIG. 5C is a schematic side view in cross-section of another
implementation of the polishing sheet.
[0022] FIG. 6 is a schematic side view of a feed roller of the
polishing cartridge.
[0023] FIG. 7 is a schematic perspective view, cut away, of another
implementation of the polishing sheet.
[0024] FIG. 8 is a schematic side view of a machine to manufacture
the polishing sheet of FIG. 7.
[0025] FIG. 9 is a schematic top view of an implementation of the
polishing sheet.
DETAILED DESCRIPTION
[0026] Referring to FIGS. 1 and 2, one or more substrates 10 will
be polished by a chemical mechanical polishing apparatus 20. A
description of a similar polishing apparatus may be found in U.S.
Pat. No. 6,244,935, the description of which is incorporated by
reference. Polishing apparatus 20 includes a machine base 22 with a
table top 23 that supports a series of polishing stations,
including a first polishing station 25a, a second polishing station
25b, and a final polishing station 25c, and a transfer station
27.
[0027] Each polishing station includes a rotatable platen. At least
one of the polishing stations, such as first station 25a, includes
a polishing cartridge 102 mounted to a rotatable, rectangular
platen 100. The polishing cartridge 102 includes a linearly
advanceable sheet or belt of polishing material. The remaining
polishing stations, e.g., second polishing station 25b and final
polishing station 25c, may include "standard" circular polishing
pads 32 and 34, respectively, each adhesively attached to a
circular platen 30. Each platen may be connected to a platen drive
motor that rotates the platen.
[0028] Each polishing station 25a, 25b and 25c also includes a
slurry delivery port, a pad rinse system (which can be a combined
slurry/rinse arm 52 that projects over the associated polishing
surface) and a pad conditioner apparatus 40.
[0029] A rotatable multi-head carousel 60 is supported above the
polishing stations by a center post 62 and is rotated about a
carousel axis 64 by a carousel motor assembly (not shown). Carousel
60 can include four carrier head systems mounted on a carousel
support plate 66 at equal angular intervals about carousel axis 64.
Three of the carrier head systems receive and hold substrates, and
polish them by pressing them against the polishing sheet of station
25a and the polishing pads of stations 25b and 25c. One of the
carrier head systems receives a substrate from and delivers a
substrate to transfer station 27.
[0030] Each carrier head system includes a carrier or carrier head
80. A carrier drive shaft 78 connects a carrier head rotation motor
76 (shown by the removal of one quarter of the carousel cover) to
carrier head 80 so that each carrier head can independently rotate
about its own axis. In addition, each carrier head 80 independently
laterally oscillates in a radial slot 72 formed in carousel support
plate 66.
[0031] Referring to FIGS. 3A, 3B, and 3C, polishing cartridge 102
is detachably secured to rectangular platen 100 at polishing
station 25a. Polishing cartridge 102 includes a feed roller 130, a
take-up roller 132, and a generally linear sheet 110 (which can be
considered to form a polishing belt or web) of a polishing pad
material. The polishing sheet (if completely unwound from the
rollers) has a length significantly greater than its width. An
unused or "fresh" portion 120 of the polishing sheet is wrapped
around feed roller 130, and a used portion 122 of the polishing
sheet is wrapped around take-up roller 132. A rectangular exposed
portion 124 of the polishing sheet that is used to polish
substrates extends between the used and unused portions 120, 122
over a top surface 140 of rectangular platen 100.
[0032] The rectangular platen 100 can be rotated (as shown by
phantom arrow "A" in FIG. 3A) to rotate the exposed portion of the
polishing sheet and thereby provide relative motion between the
substrate and the polishing sheet during polishing. Between
polishing operations, the polishing sheet can be advanced (as shown
by phantom arrow "B" in FIG. 3A) to expose an unused portion of the
polishing sheet. When the polishing material advances, polishing
sheet 110 unwraps from feed roller 130, moves across the top
surface of the rectangular platen, and is taken up by take-up
roller 132.
[0033] Referring to FIG. 4, polishing sheet 110 includes a
polishing layer with a polishing surface 112, and a leader 160 and
a trailer 162 that extend past the polishing layer (thus, polishing
surface 112 does not extend to the ends of the polishing sheet).
The leader and trailer can be formed of a material that is more
flexible, and optionally less compressible, than the polishing
layer. The leader 160 and trailer 162 can be attached to the feed
and take-up rollers 130 and 132 by tape or a pressure sensitive
adhesive on the back of the leader. A peelable liner may be placed
over the tape or adhesive and removed prior to attaching the
polishing sheet 110 to the rollers.
[0034] The polishing layer can be a porous polyurethane, and the
leader and trailer can be a thin tear-resistant material, e.g.,
polyethylene terephthalate. The polishing layer can be opaque,
whereas the leader and trailer can be transparent. The leader 160
and trailer 162 can be printed or embossed with information, such
as a part number, material type, lot number, or polishing layer
length.
[0035] Grooves can be formed in the polishing surface 112 running
across the width and transverse to the direction of travel of the
sheet The grooves can be about half the depth of the polishing
layer, e.g., 18-20 mils deep. The grooves can have a uniform width
and pitch, e.g., about one millimeter wide and spaced apart by
about two to three millimeters. Referring to FIG. 9, the grooves
128 can stop short of the edge of the polishing layer. Such a
groove configuration can improve resistance of the polishing pad to
tearing.
[0036] The backing layer 116 can be about five mils thick. The
polishing layer can be between about twenty to thirty feet long,
e.g., between twenty and twenty five feet long, and can be between
twenty and thirty inches wide, e.g., about twenty-eight inches
wide. The leader and trailer 160 and 162 have same width as the
polishing layer, and can be about six feet long.
[0037] Referring to FIG. 5A, in one implementation, the polishing
sheet includes a backing layer 116 and a polishing layer 114 formed
on the backing layer 116. In this implementation, the backing layer
116 can be a continuous sheet that spans the polishing layer 114.
In the transverse direction (perpendicular to the length and
direction of travel of the sheet), the wide edges 164 (along the
length of the sheet) of the polishing layer 114 and backing layer
116 can be aligned so that the polishing layer and backing layer
116 have the same width. In contrast, in the longitudinal direction
(parallel to the length and direction of travel of the sheet), the
backing layer 116 extends past the narrow edges 166 (edges across
the width of the sheet) of the polishing layer 114 to provide the
leader 160 and trailer 162. In the region of the leader 160 and
trailer 162, the top surface of the backing layer 116 can be the
outermost surface, i.e., there are no other layers on top of the
backing layer 116. As noted above, the leader 160 and trailer 162
can be printed or embossed with information, such as a part number,
material type, lot number, or polishing layer length.
[0038] The polishing layer 114 can be a porous polyurethane, and
the backing layer 116 can be a thin, flexible, generally
incompressible, fluid-impermeable sheet, e.g., polyethylene
terephthalate. The backing layer 116 can be transparent. The
polyurethane layer an be 35-40 mils thick. The polishing layer 114
can be laid down as a single continuous unbroken layer.
Alternatively, the polishing layer 114 can be tiled in adjacent
strips, e.g., two to four feet long.
[0039] The polishing layer 114 can be secured to the top surface of
the backing layer 116 by an adhesive 170, e.g., a
pressure-sensitive adhesive layer. For example, the polishing layer
114 and backing layer 116 can be fabricated separately and then
adhered together. Alternatively, the polishing layer 114 can adhere
to the backing layer 116 backing layer without an adhesive. For
example, a liquid polishing layer precursor can be dispensed onto
the backing layer 116 and cured so as to form a polishing layer 114
adhering to the backing layer 116.
[0040] Referring to FIG. 5B, in another implementation, the
polishing sheet includes a backing layer 116 and a polishing layer
114 formed on the backing layer 116, but the leader 160 and trailer
162 are separate pieces 172 bonded to the backing layer 116. In
this implementation, the backing layer 116 can be a continuous
sheet that spans and has coextensive edges with the polishing layer
114.
[0041] The polishing layer 114 can be a porous polyurethane. The
backing layer 116 can be either softer or less compressible than
the polishing layer and can be transparent or opaque. For example,
the backing layer can be a soft subpad such as a
urethane-impregnated fibrous mat, or a generally incompressible
layer such as polyethylene terephthalate. The separate pieces 172
can be thin, flexible, tear-resistant, generally incompressible,
fluid-impermeable sheets, e.g., polyethylene terephthalate.
[0042] As discussed above, the polishing layer 114 can be secured
to the backing layer with or without an adhesive. The leader and
trailer pieces 172 can be secured to the backing layer 116 with a
butt joint and a thin tape 174 on the underside of the polishing
sheet.
[0043] Referring to FIG. 5C, in another implementation, the
polishing sheet includes a polishing layer 114 without any backing
layer, and the leader 160 and trailer 162 are separate pieces
bonded to the polishing layer 114. The polishing layer 114 can be a
porous polyurethane. The tensile strength of the polishing layer
114 can be about 22 MPa (>3000 psi), which should exceed the
average stresses applied while vacuum chucking the web onto the
platen (.about.14 psi) or while advancing the web (.about.100
psi).
[0044] The separate pieces 172 can be thin, flexible,
tear-resistant, generally incompressible, fluid-impermeable sheets,
e.g., polyethylene terephthalate. The leader and trailer pieces 172
can be bonded to the polishing layer 114 by a thin tape 174 on the
underside of the polishing sheet.
[0045] In each of the above implementations, since the polishing
layer does not extend to the edges of the polishing sheet, the
polishing sheet can be fabricated using less polishing layer
material, and thus at lower cost in comparison to a polishing sheet
having the polishing layer across the entire length.
[0046] Referring to FIGS. 3B and 6, feed and take-up rollers 130
and 132 should be slightly longer than the width of polishing sheet
110. The rollers 130, 132 may be plastic or metal cylinders
slightly longer than the width of the polishing sheet and about 2''
in diameter. The opposing end faces 134 of feed roller 130 (only
the feed roller is shown in FIG. 6, but the take-up roller would be
constructed similarly) can each include a recess 136 which will
engage support and drive mechanisms on the platen. For example, one
end face can include keyed slot into which an alignment pin will
fit, and the other end face can include a keyed star pattern into
which a drive gear will fit. In addition, both ends of each roller
can include a circular flange 138 that projects above the surface
of the roller to hold the polishing sheet in place and prevents it
from sliding off either side of the roller.
[0047] Because the leader and trailer can be more flexible than the
polishing layer, they can be easier to manipulate and thus easier
to install on the rollers. In addition, because the leader and
trailer can be more flexible than the polishing layer, the leader
and trailer can be wound more tightly on the roller. This permits
the diameter of the roller to be decreased, thus either reducing
the volume required by the cartridge or permitting more polishing
material to be stored in the cartridge.
[0048] Referring to FIG. 7, in another implementation, the
polishing sheet is a single layer, specifically a polishing layer
114 with a polishing surface 112 but without any backing layer or
carrier film, and without a leader or trailer. The polishing layer
114 is a contiguous and monolithic layer; the entire length of the
polishing layer between the feed and take-up roller is an
uninterrupted seamless part, e.g., there is no adhesive connection
between separate pieces, and the entire polishing layer 114 is
generally of uniform composition. In some implementations, the
polishing layer is formed without heat-based molding of separate
pieces (such molding should generate regions of slightly different
consistency where the molding occurs, and the polishing layer 114
can be sufficiently homogeneous to lack such regions). The
polishing layer 114 has sufficient cohesive strength and mechanical
integrity to avoid tearing under the mechanical forces applied in
typical CMP process conditions. The polishing layer 114 can be a
porous polyurethane. The length of the polishing layer 114 can be
at least six times greater than the width. For example, the
polishing layer 114 can be about two to three feet wide, e.g., 2.5
feet wide, and thirty to forty feet long. Although illustrated in
FIG. 7 in a flat state, in use the end portions of the polishing
sheet 114 would be wound in a roll around take-up and feed rollers,
e.g., as shown in FIG. 3B. A ration of length to width of the
polishing sheet can be at least 4:1, e.g., 12:1.
[0049] The polishing layer 114 can be about 30 to 50 mils thick.
Because the backing layer and adhesive that would hold the backing
layer to the polishing layer are eliminated, the polishing layer
can be made thicker and yet the same length of polishing sheet can
be wound around a spindle without increasing the diameter of the
polishing magazine. Since the polishing layer 114 is thicker, the
number of substrates polished per unit length of the polishing
sheet can increase, and thus the pad life can increase. For
example, in comparison to a polishing sheet with a 40 mil thick
polishing layer, a 5 mil thick backing layer and a 5 mil thick
adhesive, a polishing sheet 50 mil thick polishing layer (but no
backing layer or adhesive) should have about a 20-33% increase in
capacity. Grooves extending partially but not entirely through the
polishing layer pad, e.g., having a depth between about 15 and 30
mils, e.g., about half the thickness of the polishing layer, can be
formed in the polishing surface 112 of the polishing layer 114.
[0050] Where a window stripe is formed in the polishing sheet, the
two portions on either side of the stripe can each be a single
contiguous layer. The sides of the window can be molded to the
sides of the polishing layer portions.
[0051] Referring to FIG. 8, a method of producing such a monolithic
polishing sheet is to deposit a liquid precursor 200 onto a moving
belt 210. The layer of liquid precursor on the belt 210 can be
subjected to a first curing process, e.g., the belt and layer can
pass through an oven 212 or other heat source, to at least
partially cure the precursor into a semi-solid sheet 202. The
semi-solid sheet 202 can then be detached from belt and pass
between pinch-rollers 214, 216 that compress the sheet to a desired
thickness. In addition, protrusions on one of the pinch rollers 216
can imprint grooves into the surface of the semi-solid sheet 202.
Then the sheet 202 can be subjected to a second curing process,
e.g., additional heat, such as from the second over 220 to be cured
to a final desired rigidity. Edges of the sheet 202 can be trimmed
to provide a polishing sheet of uniform width, and if necessary the
polishing sheet can be smoothed and/or thinned, e.g., with a
grinder or by passing between blades that will skive off top and
bottom portions of the sheet, to remove burrs or other defects. A
similar process can be used to produce the polishing layer 114 for
the implementation of FIG. 5C.
[0052] In some implementations, a polishing sheet can be formed by
casting the polyurethane precursor material on a carrier sheet
(e.g., with the carrier sheet on the moving belt or supported on
spaced-apart rollers so that the carrier sheet provides a moving
belt-like surface), and subjecting the precursor to the first
curing step. The carrier sheet can peeled off either before or
after the final cure step. Both sides of the polish sheet can then
be skived, ground and/or sanded to adjust pad thickness and remove
any cured crust layer.
[0053] Grooves can be formed on the cured polishing sheet using a
cutting tool such as a knife blade. If the grooves are formed by
imprinting with patterned rollers and a subsequent cure step, by
selecting an appropriate degree of compression, the grooves could
be formed with a smooth or non-porous surface layer in the grooves
(in contrast, the polishing surface itself can be porous, and
grooves formed in a porous pad with a knife have porous walls and
bottoms). If so, waste products or polishing debris can be less
likely to remain trapped in the grooves, thus reducing the
potential for defects, e.g., scratches.
[0054] Returning to FIGS. 3A, 3B and 3C, rectangular platen 100
includes a generally planar rectangular top surface 140 bounded by
a feed edge 142, a take-up edge 144, and two parallel lateral edges
146. A groove 150 (shown in phantom in FIGS. 3A and 3C) is formed
in top surface 140. The groove 150 can be a generally-rectangular
pattern that extends along edges 142, 144, 146 of top surface 140.
Alternatively, vacuum groove 150 can be circular and about 29'' in
diameter, and the polish area described by the motion of the head
and platen contained within area described by the dashed lines 150
in FIG. 3A.
[0055] A passage through platen 100 connects groove 150 to a vacuum
source. When passage is evacuated, exposed portion 124 of polishing
sheet 110 is vacuum-chucked to top surface 140 of platen 100. This
vacuum-chucking helps ensure that lateral forces caused by friction
between the substrate and the polishing sheet during polishing do
not force the polishing sheet off the platen. Optionally, a central
region 148 of top surface 140 can be free from grooves to prevent
potential deflection of the polishing sheet into the grooves from
interfering with the polishing uniformity.
[0056] An unillustrated compressible backing pad can be placed on
the top surface of the platen to cushion the impact of the
substrate against the polishing sheet. In addition, platen 100 may
include an unillustrated shim plate. Shim plates of differing
thickness may be attached to the platen to adjust the vertical
position of the top surface of the platen. The compressible backing
pad can be attached to the shim plate.
[0057] In some implementations, the rectangular platen 100 also
includes four retaining flanges 156 that hold feed and take-up
rollers 130 and 132 at feed and take-up edges 142 and 144,
respectively. Each retaining flange 156 includes a projection or
detent that can engage the corresponding feature on the end of the
rollers 130 or 132.
[0058] The rollers 130 and 132 can be positioned sufficiently below
top surface 140 so that the polishing sheet stays in contact with
the feed and take-up edges 142 and 144 of the platen when the
entire polishing sheet is wound around either roller. This assists
in the creation of a seal between the polishing sheet and the
rectangular platen when vacuum is applied to the passage to
vacuum-chuck the polishing sheet to the platen. Furthermore, feed
edge 142 and take-up edge 144 of the platen are rounded to prevent
abrasion of the underside of the polishing sheet as it moves across
the platen.
[0059] A transparent strip 118 can be formed along the length of
polishing sheet 110. The transparent strip may be positioned at the
center of the sheet, and may be about 0.6 inches wide. With respect
to FIGS. 5A and 5B, transparent strip 118 may be formed by removing
the upper layer 114 from this region of the transparent backing
layer 116. With respect to FIG. 5C, a transparent strip 118 may be
formed by molding a window into the polishing layer 114. The
transparent strip 118 can be aligned with an aperture or
transparent window 154 in rectangular platen 100 to provide optical
monitoring of the substrate surface for end point detection.
[0060] Referring again to FIGS. 3A, 3B and 3C, in operation,
exposed portion 124 of polishing sheet 110 is vacuum-chucked to
rectangular platen 100 by applying a vacuum to the passage. A
substrate is lowered into contact with polishing sheet 110 by
carrier head 80, and both platen 100 and carrier head 80 rotate to
polish the exposed surface of the substrate. After polishing, the
substrate is lifted off the polishing pad by the carrier head. The
vacuum on passage 152 is removed. The polishing sheet is advanced
to expose a fresh segment of the polishing sheet. The polishing
sheet is then vacuum-chucked to the rectangular platen, and a new
substrate is lowered into contact with the polishing sheet. Thus,
between each polishing operation, the polishing sheet may be
advanced incrementally. If the polishing station includes a
cleaning apparatus the polishing sheet may be washed between each
polishing operation.
[0061] The amount that the sheet may be advanced will depend on the
desired polishing uniformity and the properties of the polishing
sheet, but should be on the order of 0.05 to 1.0 inches, e.g., 0.4
inch, per polishing operation. Assuming that the exposed portion
124 of polishing sheet is 20 inches long and the polishing sheet
advances 0.4 inches after each polishing operation, the entire
exposed portion of the polishing sheet will be replaced after about
fifty polishing operations.
[0062] In another embodiment, a polishing sheet can be fabricated
with a polishing layer disposed on a carrier layer, e.g., a
polyethylene terephthalate polyester film, e.g. a Mylar sheet. In
some implementations, the polishing sheet can be formed by casting
the polyurethane precursor material on a carrier layer as discussed
above (e.g., with the carrier layer on the moving belt). However,
rather than removing the carrier layer, the polishing layer remains
on the carrier layer to form the final polishing sheet. In this
case, grinding and surface finishing operations to adjust the
polishing layer thickness or roughness would take place only on the
top surface. In some implementations, the initial carrier layer is
removed, grinding and surface finishing operations are performed,
and the polishing layer can then be attached to a new carrier layer
for the final polishing sheet
[0063] The invention is not limited to the embodiment depicted and
described. Rather, the scope of the invention is defined by the
appended claims.
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