U.S. patent application number 12/823872 was filed with the patent office on 2010-10-21 for polishing pad with projecting portion.
Invention is credited to Shou-Sung Chang, Alain Duboust, Wei Lu, Antoine P. Manens, Yongsik Moon, Siew Neo, Yan Wang.
Application Number | 20100267318 12/823872 |
Document ID | / |
Family ID | 36499154 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100267318 |
Kind Code |
A1 |
Duboust; Alain ; et
al. |
October 21, 2010 |
POLISHING PAD WITH PROJECTING PORTION
Abstract
A polishing pad include a polishing layer having a polishing
surface and a backing layer on a side of the polishing layer
opposite the polishing surface. An outer edge of the polishing
layer overhangs an outer edge of the backing layer.
Inventors: |
Duboust; Alain; (Sunnyvale,
CA) ; Chang; Shou-Sung; (Stanford, CA) ; Lu;
Wei; (Fremont, CA) ; Neo; Siew; (Santa Clara,
CA) ; Wang; Yan; (Sunnyvale, CA) ; Manens;
Antoine P.; (Sunnyvale, CA) ; Moon; Yongsik;
(Paramus, NJ) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
36499154 |
Appl. No.: |
12/823872 |
Filed: |
June 25, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11043361 |
Jan 26, 2005 |
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12823872 |
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10956617 |
Oct 1, 2004 |
7654885 |
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11043361 |
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60508321 |
Oct 3, 2003 |
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Current U.S.
Class: |
451/533 |
Current CPC
Class: |
B24B 37/26 20130101;
B24B 37/013 20130101; B24B 37/22 20130101; B24B 37/046 20130101;
B24B 37/205 20130101; B24D 11/02 20130101 |
Class at
Publication: |
451/533 |
International
Class: |
B24D 11/02 20060101
B24D011/02 |
Claims
1. A polishing pad, comprising: a polishing layer having a
polishing surface; and a backing layer on a side of the polishing
layer opposite the polishing surface, wherein an outer edge of the
polishing layer overhangs an outer edge of the backing layer.
2. The polishing pad of claim 1, wherein the polishing layer and
backing layer are substantially circular, and wherein a diameter of
the backing layer is less than a diameter of the polishing
layer.
3. The polishing pad of claim 1, wherein the backing layer is more
compressible than the polishing layer.
4. The polishing pad of claim 1, wherein the outer edge of the
polishing layer overhangs the outer edge of the backing layer by
about one-quarter inch.
5. The polishing pad of claim 1, wherein the polishing layer and
backing layer are secured by an adhesive.
6. The polishing pad of claim 1, wherein the polishing layer
comprises polyurethane with embedded hollow microspheres.
7. The polishing pad of claim 1, wherein the backing layer
comprises polyurethane impregnated polyester felt.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/043,361, filed on Jan. 26, 2005, which is a
continuation-in-part of U.S. patent application Ser. No.
10/956,617, filed on Oct. 1, 2004, which claims priority to U.S.
Provisional Application Ser. No. 60/508,321, filed on Oct. 3, 2003.
The entire disclosure of each of the above-referenced applications
is incorporated by reference.
BACKGROUND
[0002] This present invention relates to polishing pads used in
during chemical mechanical polishing.
[0003] 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 non-planar surface, and
planarizing the filler layer until the non-planar surface is
exposed. For example, a conductive filler layer can be deposited on
a patterned insulative layer to fill the trenches or holes in the
insulative layer. The filler layer is then polished until the
raised pattern of the insulative layer is exposed. 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. In addition, planarization is needed to planarize
the substrate surface for photolithography.
[0004] 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
exposed surface of the substrate is placed against the polishing
surface of a polishing pad, such as a rotating polishing disk or
linearly advancing belt. The carrier head provides a controllable
load on the substrate to push it against the polishing pad. A
polishing liquid, which can include abrasive particles, is supplied
to the surface of the polishing pad, and the relative motion
between the substrate and polishing pad results in planarization
and polishing.
[0005] Conventional polishing pads include "standard" pads and
fixed-abrasive pads. A typical standard pad has a polyurethane
polishing layer with a durable roughened surface, and can also
include a compressible backing layer. In contrast, a fixed-abrasive
pad has abrasive particles held in a containment media, and can be
supported on a generally incompressible backing layer.
[0006] One objective of a chemical mechanical polishing process is
to achieve topology uniformity across the substrate. Another object
is to achieve polishing uniformity. If different areas on the
substrate are polished at different rates, then it is possible for
some areas of the substrate to have too much material removed
("overpolishing") or too little material removed
("underpolishing"), which can result in non-uniform topography
across the substrate.
SUMMARY
[0007] In one aspect, the invention is directed to a polishing pad
with a polishing layer and a backing layer secured to the polishing
layer. The polishing layer has a polishing surface, a first
thickness, a first compressibility, a hardness between about 40 to
80 Shore D, and a thickness non-uniformity. The backing layer has a
second thickness and a second compressibility greater than the
first compressibility. The first thickness, first compressibility,
second thickness and second compressibility are such that the
polishing surface deflects, under an applied pressure of 1.5 psi or
less, more than the thickness non-uniformity of the polishing
layer.
[0008] Implementations of the invention can include one or more of
the following features. The second thickness may be greater than
the first thickness, or about the same as the first thickness. The
backing layer may have a hardness between about 1 and 10 Shore A.
The backing layer may have second thickness between about 30 and
200 mils, e.g., between about 30 and 90 mils. A plurality of
grooves may be formed in the polishing surface. A recess may be
formed in a bottom surface of the polishing layer, and an aperture
may be formed in the backing layer aligned with the recess. A
conductive sheet may be secured to the backing layer on a side
opposite the polishing layer. A plurality of holes may be formed
through the polishing layer and the backing layer to expose the
conductive sheet. A solid light-transmissive portion may be
positioned in the polishing layer. An aperture may be formed in the
backing layer aligned with the light-transmissive portion. A
light-transmissive adhesion layer may be on the side of the backing
layer opposite the polishing layer, and the adhesion layer may span
the aperture on the backing layer. A fluid-impermeable transparent
sheet may be between the backing layer and the polishing layer. An
outer edge of the polishing layer may overhang an outer edge of the
backing layer. The backing layer may have a product of the second
thickness and second compressibility of 2 mils or more, at an
applied pressure of 1.5 psi or less. The backing layer may include
a polyurethane, polyether or polysilicone foam.
[0009] In another aspect, the invention is directed to a polishing
pad with a polishing pad having a polishing surface, a solid
light-transmissive portion positioned in the polishing layer, a
backing layer on a side of the polishing layer opposite the
polishing surface, and a light-transmissive adhesion layer on the
side of the backing layer opposite the polishing layer. The backing
layer has an aperture aligned with the light-transmissive portion,
and the light-transmissive adhesion layer spans the aperture on the
backing layer.
[0010] Implementations of the invention can include one or more of
the following features. The adhesion layer may abut the backing
layer. The backing layer may be connected directly to the polishing
layer by an adhesive. A conductive layer may be on a side of the
adhesion layer opposite the backing layer, e.g., the conductive
layer may abut the adhesion layer. The backing layer may be more
compressible than the polishing layer. The adhesion layer may
include a double-sided adhesive tape. The adhesion layer may
include a polyethylene terephthalate film. The window may be
integrally molded in the polishing layer, or may be secured in an
aperture in the polishing layer by an adhesive. A fluid-impermeable
transparent sheet may be between the backing layer and the
polishing layer.
[0011] In another aspect, the invention is directed to a polishing
pad with a polishing layer having a polishing surface and a backing
layer on a side of the polishing layer opposite the polishing
surface. An outer edge of the polishing layer overhangs an outer
edge of the backing layer.
[0012] Implementations of the invention can include one or more of
the following features. The polishing layer and backing layer may
be substantially circular, and a diameter of the backing layer may
be less than a diameter of the polishing layer. The backing layer
may be more compressible than the polishing layer. The outer edge
of the polishing layer may overhang the outer edge of the backing
layer by about one-quarter inch. The polishing layer and backing
layer may be secured by an adhesive.
[0013] In another aspect, the invention is directed to a polishing
pad that has a polishing layer having a polishing surface, a solid
light-transmissive portion positioned in the polishing layer, a
backing layer on a side of the polishing layer opposite the
polishing surface, a fluid-impermeable transparent sheet between
the backing layer and the polishing layer, a light-transmissive
adhesion layer on the side of the backing layer opposite the
polishing layer, and a conductive layer on a side of the adhesion
layer opposite the backing layer. The backing layer has an aperture
aligned with the light-transmissive portion, and the transparent
sheet spans the solid light-transmissive portion.
[0014] In another aspect, the invention is directed to a substrate
processing apparatus. The apparatus can include a pad support, a
polishing pad according to one of the aspects discussed above, a
carrier head to hold a substrate in contact with the polishing pad,
a supply of processing fluid, and a motor connected to at least one
of the pad support and the carrier head to cause relative motion
between the processing pad and the substrate.
[0015] Implementations of the invention can include one or more of
the following features. The apparatus may include an electrode
positioned to contact the substrate, a cathode contacting the
processing fluid, and a power supply coupled between the electrode
and the cathode to create a bias.
[0016] In another aspect, the invention is directed to a method of
chemical mechanical processing. The method includes bringing a
substrate into contact with a polishing surface of a polishing
layer of a polishing pad according to one of the aspects discussed
above, supplying a polishing liquid to the polishing surface,
creating relative motion between the substrate and the polishing
surface, and applying a pressure to the substrate to press the
substrate against the polishing pad.
[0017] Implementations of the invention can include one or more of
the following features. The applied pressure may be 1.5 psi or
less, and the polishing surface may deflects more than a thickness
non-uniformity of the polishing layer under the applied pressure.
Supplying the polishing liquid may include supplying an
electrolyte, and the method may further include applying a bias
between a cathode exposed to the electrolyte and the substrate.
[0018] Any of the various implementations discussed above may also
be applicable to any of the various aspects of the invention.
[0019] Potential advantages of the invention may include one or
more of the following. Polishing uniformity across the substrate
may be improved, particularly at low pressures, e.g. below 1.5 or
1.0 psi or 0.8 psi, or even below 0.5 psi or 0.3 psi. Consequently,
materials, such as low-k dielectric materials, that require
low-pressure polishing to avoid irreversible damage, such as
delamination, can be polished with an acceptable degree of
uniformity. In addition, the polishing pad can provide good
mechanical contact to the substrate surface when the substrate is
polished at low down force and/or the substrate is not flat due to
internal stress induced by multiple levels of conductive and
dielectric layers. The likelihood of premature pad failure, such as
premature detachment of the pad from the platen in the region
around the window, can be reduced, thereby increasing polishing pad
lifetime. The likelihood of polishing liquid seeping into the
backing layer can be reduced.
[0020] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
DESCRIPTION OF DRAWINGS
[0021] FIG. 1A is a schematic cross-sectional side view
illustrating a conventional polishing pad.
[0022] FIG. 1B is a schematic cross-sectional side view
illustrating a substrate in contact with the polishing pad of FIG.
1A.
[0023] FIG. 2 is a schematic side view, partially cross-sectional,
of a chemical mechanical polishing station.
[0024] FIG. 3A is a schematic cross-sectional side view
illustrating the polishing pad of FIG. 2.
[0025] FIG. 3B is a schematic cross-sectional side view
illustrating a substrate in contact with the polishing pad of FIG.
3A.
[0026] FIG. 3C is a schematic cross-sectional side view
illustrating another implementation of the polishing pad in which
the covering layer and backing layer have about the same
thickness.
[0027] FIG. 3D is a schematic cross-sectional side view
illustrating another implementation of the polishing pad in which
an adhesive layer and a liner are attached to the backing
layer.
[0028] FIG. 3E is a schematic cross-sectional side view
illustrating another implementation of the polishing pad in which
the covering layer overhangs the backing layer.
[0029] FIG. 4 is a schematic cross-sectional side view illustrating
another implementation of the polishing pad in which a recess is
formed in the bottom surface of the covering layer.
[0030] FIG. 5 is a schematic cross-sectional side view illustrating
another implementation of the polishing pad including a transparent
sheet.
[0031] FIG. 6A is a schematic cross-sectional side view
illustrating another implementation of the polishing pad including
a window and an adhesive layer that spans the window.
[0032] FIG. 6B is a schematic cross-sectional side view
illustrating another implementation of the polishing pad including
a window, an adhesive layer that spans the window, and a
transparent sheet.
[0033] FIG. 7 is a schematic cross-sectional side view illustrating
another implementation of the polishing pad including a conductive
layer.
[0034] FIG. 8 is a schematic cross-sectional side view illustrating
another implementation of the polishing pad including a window and
a conductive layer.
[0035] FIG. 9 is a schematic cross-sectional side view illustrating
another implementation of the polishing pad including a window, a
transparent sheet, and a conductive layer.
[0036] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0037] As mentioned above, and referring to FIG. 1A, a conventional
polishing pad 60 can have a polyurethane covering layer 64 with a
durable rough polishing surface 66 and a compressible backing layer
62 with about the same thickness as the covering layer. In
addition, there may be small variations in the thickness of the
covering layer 64, e.g., on the order of a few mils, e.g., about
1-2 mil, across the polishing pad (for clarity, the variations are
significantly exaggerated in FIG. 1A).
[0038] For example, one polishing pad commercially available from
Rodel, Inc., has a covering layer formed of polyurethane with
embedded hollow microspheres (IC1000) and a backing layer formed of
polyurethane impregnated polyester felt (Suba IV). The covering
layer has a thickness of 50 or 80 mils and a hardness of 52-62 on
the Shore D scale, whereas the backing layer has a thickness of 50
mils and a hardness of about 61 on the Shore A scale.
[0039] Unfortunately, the conventional polishing pad can result in
unacceptable polishing uniformity at low pressures, e.g., below 1.5
psi or below 1.0 psi, and particularly at very low pressures, e.g.,
below 0.5 psi. Without being limited to any particular theory, it
may be that the dimensions and physical properties of the standard
polishing pad are such that, at low polishing pressures, the
backing layer remains rigid enough that the downward pressure of
the substrate 14 is not sufficient to completely "flatten out" the
covering layer. Consequently, as shown in FIG. 1B, any thickness
variation in the covering layer 64 results in pressure being
transmitted to the substrate in only the thick portions 66 of the
covering layer 64, thus causing the non-uniformity in the polishing
rate. In addition, a typical substrate is not perfectly flat due to
internal stresses, and the applied load may not be great enough to
conform the substrate against the polishing pad so as to create
uniform contact between the substrate and the polishing
surface.
[0040] In contrast to these conventional polishing pads, one
implementation of the polishing pad of the present invention has a
thinner covering layer and a thicker and more compressible backing
layer. Again without being limited to any particular theory, the
reduced thickness of the covering layer may make it easier to
deflect. In addition, the increased thickness and compressibility
of the backing layer may make the covering layer easier to deflect.
As a result, even at very low polishing pressures, the covering
layer can be conformed to the substrate (for example, if the
substrate is flat as shown then the covering layer will be
flattened out, whereas if the substrate is warped then the covering
layer will conform to have the same shape) so that thickness
variations in the covering layer need not adversely impact the
polishing uniformity, and so that good mechanical contact is
created between the substrate and the polishing surface so as to
provide a high polishing rate and a shorter polishing time.
[0041] Turning now to FIG. 2, one or more substrates 14 can be
polished at a polishing station 10 of a CMP apparatus. A
description of a suitable polishing apparatus can be found in U.S.
Pat. No. 5,738,574, the entire disclosure of which is incorporated
herein by reference.
[0042] The polishing station 10 includes a rotatable platen 16 on
which is placed a polishing pad 18. As described below, the
polishing pad 18 is a two-layer polishing pad with a soft backing
layer 20 and a hard durable outer layer 22 with a substantially
uniform composition. The durable outer covering layer 22 provides a
polishing surface 24. The polishing station can also include a pad
conditioner apparatus to maintain the condition of the surface of
the polishing pad so that it will effectively polish
substrates.
[0043] During a polishing step, a polishing fluid 30, e.g., a
slurry, can be supplied to the surface of polishing pad 18 by a
slurry supply port or combined slurry/rinse arm 32. Slurry 30 can
contain abrasive particles, a pH adjuster, or chemically active
components.
[0044] The substrate 14 is held against the polishing pad 18 by a
carrier head 34. The carrier head 34 is suspended from a support
structure, such as a carousel, and is connected by a carrier drive
shaft 36 to a carrier head rotation motor so that the carrier head
can rotate about an axis 38.
[0045] Referring to FIG. 3A, the covering layer 22 of the polishing
pad 18 is a relative durable and hard polishing material that is
inert in the polishing process, e.g., a cast polyurethane. For
example, the covering layer 22 can have a hardness of about 30 to
80, e.g., 40 to 80, e.g., 50 to 65, on the Shore D scale. The
polishing surface 24 of the covering layer 22 can have rough
surface texture, e.g., hollow microspheres can be embedded in the
polyurethane so that when the covering layer is skived from a cast
polyurethane block, the microspheres at the exposed surface are
ruptured to provide a pitted and rough surface texture.
[0046] The covering layer 22 is thin, e.g., less than 50 mils, such
as 40 mils or less, or 25 mils or less, or 20 mils or less, or 15
mils or less. In general, the covering layer 22 is as thin as
possible, subject to manufacturability. However, the conditioning
process tends to wear away the cover layer. Therefore, a thickness
of the covering layer can be selected to provide the polishing pad
with a useful lifetime, e.g., 3000 polishing and conditioning
cycles. For example, the covering layer can have a thickness of 5
to 10 mils. A thickness between about 5 and 20 mils should be
appropriate. There may be thickness non-uniformities across the pad
of about 1-3 mils, although larger non-uniformities are possible
(these non-uniformities refer to the global variations in thickness
across the polishing pad caused by the pad fabrication process,
rather than discrete thickness variations at a small scale (e.g.,
less than 100 mils), such as grooves, perforations, or surface
roughness).
[0047] Optionally, at least a portion of the polishing surface 24
can include a plurality of grooves 26 formed therein for carrying
slurry. The grooves may be of nearly any pattern, such as
concentric circles, straight lines, a cross-hatched, spirals, and
the like. The grooves 26 can extend through about 20-80%, e.g.,
25%, of the thickness of the covering layer 22. For example, in a
polishing pad having an covering layer 22 that is 20 mils thick,
the grooves 26 can have a depth D1 of about 5 mils.
[0048] The backing layer 20 is a compressible material that is
softer and more compressible than the covering layer 22. For
example, the backing layer can be an open-cell or a closed-cell
foam, such as polyurethane, polyether or polysilicone with voids,
so that under pressure the cells collapse and the backing layer
compresses. It is permissible for the material of the backing layer
20 to be laterally displaced under pressure from the substrate. The
backing layer 20 can have a hardness of 20 or less on the Shore A
scale, e.g., 12 or less, e.g., between 1 and 10 Shore A, e.g., 5 or
less.
[0049] As mentioned above, the backing layer 20 should be more
compressible than the covering layer 22. Compressibility may be
measured as a percentage thickness change at a given pressure. For
example, under a pressure of about 0.5 psi, the backing layer 20
can undergo about 3% compression. A suitable material for the
backing layer is PORON 4701-30 from Rogers Corporation, in Rogers,
Conn. (PORON is a trademark of Rogers Corporation).
[0050] In addition, the backing layer 20 is thick, e.g., 90 mils or
more. For example, the backing layer may be about 95 to 500 mils
thick, such as 95 to 200 mils, or 95 to 150 mils, or 95 to 125
mils. In particular, the backing layer 20 may be about 2 to 15
times as thick as the covering layer 22, e.g., 4.5 to 8 times as
thick (particularly for a 20 mil thick covering layer).
[0051] In general, the thickness of the backing layer 20 is
selected to ensure that, given the compressibility of the backing
layer 20 and the rigidity of the covering layer 22, the covering
layer will deflect at very low pressures, e.g., pressures of 0.5
psi or less, an amount at least equal to any non-uniformity in the
thickness of the covering layer, e.g., a few mils, e.g., about 2
mil (the non-uniformities are not shown in FIG. 3A). For example, a
100 mil thick backing layer should have a compression of at least
2% at 0.5 psi, whereas a 200 mil thick backing layer should have a
compression of at least 1% at 0.5 psi.
[0052] Moreover, the backing layer should be sufficiently
compressible that at the operating pressures of interest, e.g., at
1.5 psi to 0.1 psi, the polishing pad is below the maximum
compressibility of the polishing pad. The backing layer can have a
maximum compressibility greater than 10%, or greater than 20%. In
one implementation, the backing layer can have a compressibility of
25% at pressures of 3 to 8 psi, with a maximum compressibility that
is even higher.
[0053] The backing layer can have a compression force deflection
range of 1 to 10 psi (0.2 inches strain rate force at 25%
deflection).
[0054] In brief, at pressures of 1.5 psi or below (and possibly at
1.0 psi or below, 0.8 psi or below, or 0.5 psi or below, or 0.3 psi
or below), the backing layer can have a product of the
compressibility and thickness (CD) that is greater than the
non-uniformities in thickness of the cover layer. For example, at
pressures of 0.8 psi or below (and possibly at 0.5 psi or below),
the backing layer can have a product of the compressibility and
thickness (CD) of a few mils, e.g., 2 mils, or more (and possibly 3
mils or more).
[0055] Hydrostatic modulus K may be measured as applied pressure
(P) divided volumetric strain (.DELTA.V/V), i.e., K=PV/.DELTA.V.
Assuming that the backing layer undergoes pure compression (i.e.,
material is not displaced laterally under the applied pressure),
then the hydrostatic modulus K equals the applied pressure divided
by the compression (.DELTA.D/D). Thus, assuming that the backing
layer undergoes at least 2% pure compression at 0.5 psi, the
backing layer would have a compressibility modulus K of 25 or less.
On the other hand, if even lower pressures are to be use, e.g.,
pressures of 0.1 psi, then the backing layer 20 should have a
compressibility modulus of 5 or less. The backing layer may have a
compressibility modulus K of 50 psi or less per psi of applied
pressure in the range of 0.1 to 1.0 psi. Of course, if the material
of the backing layer does undergo lateral displacement under
compression, then the volumetric strain will be somewhat less than
the compression, so the hydrostatic modulus may be somewhat
higher.
[0056] Referring to FIG. 3B, and without being limited to any
particular theory, this configuration permits the downward force
from the substrate to "flatten out" the covering layer at low
pressures, even at pressures of 0.5 psi or less, such as 0.3 psi or
less, such as 0.1 psi, and thus substantially compensate for the
thickness non-uniformity of the polishing layer and for warp in the
substrate. For example, as illustrated, the variations in thickness
of the covering layer 22 are absorbed by the compression of the
backing layer 20 (for clarity, the variations are significantly
exaggerated in FIG. 3A), so that the polishing surface remains in
substantially uniform contact with the substantially planar
substrate across the substrate surface. As a result, a uniform
pressure can be applied to the substrate, thereby improving
polishing uniformity during low pressure polishing. Consequently,
materials, such as low-k dielectric materials, that require
low-pressure polishing to avoid damage, such as delamination, can
be polished with an acceptable degree of uniformity.
[0057] In one implementation, the covering layer 22 can be
manufactured, e.g., by a molding process, with grooves preformed in
the upper surface of the covering layer. In a molding process,
e.g., injection molding or compression molding, the pad material
cures or sets in a mold that has indentations that form the grooves
recess. Alternatively, the covering layer 22 can be manufactured by
a more conventional technique, e.g., by skiving a thin sheet of pad
material from a cast block. The grooves can then be formed by
machining or milling the top surface of the covering layer,
respectively.
[0058] Once the backing layer 20 and covering layer 22 have been
manufactured, they can be secured, e.g., with a thin adhesive layer
28, such as a pressure-sensitive adhesive.
[0059] Referring to FIG. 3C, in another implementation, the backing
layer is the same thickness or is thinner than the covering layer,
but is softer and more compressible than the covering layer. In
particular, the backing layer can be sufficiently compressible to
provide the same functionality as the polishing pad discussed with
reference to FIG. 3A. For example, the covering layer will deflect
at very low pressures an amount at least equal to any
non-uniformity in the thickness of the covering layer (the
non-uniformities are not shown in FIG. 3C). In brief, at pressures
of 1.5 psi or below (and possibly at 1.0 psi or below, or 0.8 psi
or below, or 0.5 psi or below, or 0.3 psi or below), the backing
layer can have a product of the compressibility and thickness (CD)
that is greater than the non-uniformities in thickness of the cover
layer, for example a few mils, e.g., about 2 mil. For example,
under a pressure of about 0.5 psi, the backing layer 20 can undergo
about 1% to 30% compression, e.g., 3% compression.
[0060] For example, the covering layer 22 can have a hardness of
about 30 to 80, e.g., 50 to 65, on the Shore D scale, and can have
a thickness between about 30 and 90 mils, e.g., 50 or 80 mils. The
backing layer can be an open-cell foam or a closed-cell foam, such
as polyurethane, polyether or polysilicone with voids. The backing
layer 20 can have a hardness of 20 or less on the Shore A scale,
e.g., 12 or less, e.g., between 1 and 10 Shore A, e.g., 5 or less,
and can have a thickness that is about the same or less than that
of the cover layer, e.g., 30 to 90 mils, e.g., 50 mils.
[0061] In use, the polishing pad 18 can be secured to the platen
with an adhesive layer. Referring to FIG. 3D, a polishing pad
otherwise constructed as described with respect to FIG. 3A or 3C
can be manufactured with an adhesive layer 50, e.g., a double-sided
adhesive tape, e.g., a Mylar sheet coated on both sides with
adhesive, covering the bottom of backing layer 20. In addition, a
non-adhesive liner 52 may be placed under the adhesive layer 50.
The liner 52 is removed prior to attaching the polishing pad 18 to
the platen. The adhesive layer 50 can provide additional structural
integrity to the polishing pad so that the pad can be removed from
the platen as a single unit without tearing the backing layer.
[0062] Referring to FIG. 3E, in another implementation, which can
otherwise be constructed as described with respect to FIG. 3A, 3C
or 3D, the backing layer 20 can have a diameter that is smaller
than the diameter of the covering layer 22. For example, the
backing layer 20 can have a diameter of 30.0 inches, and the
covering layer 22 can have a diameter of 30.5 inches. The outer
edge of the backing layer can be evenly recessed by a distance D2
of about 0.25 inches from the outer edge of the cover layer. Having
the outer edge of the cover layer 22 overhang the outer edge of the
backing layer 20 can help prevent polishing fluid, e.g., deionized
water, from entering the backing layer 20 due to capillary action
or the like, which could change the compressibility of the backing
layer 20 and impact the uniformity of the polishing process.
[0063] Referring to FIG. 4, in another implementation, which can
otherwise be constructed as described with respect to FIG. 3A, 3C,
3D or 3E, one or more recesses 70 can be formed in the bottom
surface 72 of the covering layer 22 to provide a thin section 74.
These recesses 70 can extend through 20 to 80%, e.g., 50%, of the
thickness of the covering layer 22. For example, in a polishing pad
having a covering layer 22 that is 20 mils thick, the recess 52 can
have a depth of about 10 mils, leaving the thin section 74 with a
thickness of about 10 mils. In addition, one or more apertures 76
can be formed in the backing layer 20 to permit sensor elements to
extend through the backing layer 20 and partially into the covering
layer 22.
[0064] In this implementation, the grooves 26 do not extend over
the thin section 74 in the covering layer 22. Thus, the polishing
surface 24 of the polishing pad includes portions with and without
grooves, and the indentation is located in one of the portions
without grooves. The grooves 26 can be sufficiently deep that they
extend to or past the plane defined by the inner surface of the
recess 70.
[0065] Referring to FIG. 5, in another implementation which can
otherwise be constructed as described with respect to FIG. 3A,
3C-3E or 4, a thin sheet 80 of fluid-impermeable, tear-resistant
material, e.g., polyethylene terephthalate, for example, Mylar, is
positioned between the backing layer 20 and the covering layer 22.
The sheet 80 may be secured to the cover layer 22 by an adhesive
layer 28, or the covering layer 22 can be deposited directly on the
sheet 80. The sheet 80 may be secured to the backing layer 20 by a
thin adhesive layer 88. The sheet 80 can be a transparent material,
and aligned portions 82 and 84 of the covering layer 22 and backing
layer 20, respectively, can be removed to provide an optical port
through the polishing pad.
[0066] Alternatively, a window could be formed in the polishing pad
without use of the transparent sheet. For example, a solid
transparent portion can be formed in the covering layer 22, and an
aperture can be formed in the backing layer 20 that is aligned with
the solid transparent portion. The transparent portion can be
formed by cutting an aperture in the covering layer 22 and securing
a transparent plug with an adhesive. Alternatively, the transparent
portion can be formed by placing an insert of transparent material
in a liquid pad material, curing the liquid pad material so that
the insert is integrally molded into the block of solidified pad,
and then skiving off the covering layer from the block.
[0067] In both these implementations, the adhesive layer 50 can be
removed from the region of the optical port or window.
[0068] In addition, instead of being removed from the region of the
optical port or window, the adhesive layer 50 can be substantially
transparent and can span the optical port. For example, referring
to FIG. 6A, the polishing pad 18 can include a solid transparent
portion 56 that is integrally molded into the covering layer or is
held by adhesive in an aperture in the covering layer. An aperture
58 is formed in the backing layer 20 aligned with the solid
transparent portion 56. Assuming that the transparent portion is
secured by adhesive, the edges of the transparent portion 56 can
project over and rest on a rim of the backing layer 20 around the
aperture 58 and be secured to the backing layer 20 by an adhesive
59, which can be part of the adhesive 28. On the other hand, if the
transparent 56 portion is integrally molded into the covering layer
22, then adhesive 59 is not needed and aperture 58 can be the same
size or a different size than the transparent portion. This
implementation can otherwise include the features described with
respect to any of FIGS. 3A, 3C-3E and 4.
[0069] The adhesive layer 50 spans the bottom surface of the
backing layer 20, including the aperture 58. The adhesive layer can
be a double-sided adhesive tape, such a thin, e.g., 2 mil thick,
polyethylene terephthalate sheet coated on both sides with
adhesive. To manufacture the polishing pad shown in FIG. 6A the
aperture can be formed in the backing layer 20 before the adhesive
layer 50 is applied to the bottom surface of the polishing pad. The
aperture can be formed in the backing layer 20 before or after the
backing layer 20 is secured to the covering layer 22.
[0070] A potential advantage of having the adhesive layer 50 span
the aperture 58 is reduced likelihood of failure of the window and
consequently increased lifetime of the polishing pad. Without being
limited to any particular theory, if the adhesive layer 50 does not
span the aperture 58, then adhesion of the polishing pad to the
platen around the window is reduced, such that cycling of pressure
during substrate loading and unloading from the pad can cause
failure of the attachment of the polishing pad to the platen around
the window, thus causing the portion of the pad around the window
to distort and create polishing nonuniformities. In contrast, the
adhesive layer 50 spanning the window reinforces adhesion to the
platen surface, thereby reducing the likelihood of pad failure.
[0071] Optionally, as shown in FIG. 6B, a thin sheet 80 of
fluid-impermeable, tear-resistant material, such as polyethylene
terephthalate, can be positioned between the backing layer 20 and
the covering layer 22 with the solid transparent portion 56. The
transparent portion 56 can be integrally molded in the cover layer
22, or can be a separate transparent element adhesively secured to
the fluid-impermeable sheet 80. The transparent portion 56 can be
adhesively secured to the fluid-impermeable sheet 80 by adhesive
59, which can be the same material as the adhesive layer 28 or a
different material. If the transparent portion 56 is integrally
molded in the cover layer, the adhesive 59 can optionally be
removed. In addition, the portion of the adhesive layer 88 above
the aperture 58 can be removed or can remain in place.
[0072] Referring to FIG. 7, in another implementation which can
otherwise be constructed as described with respect to any of FIGS.
3A-5, a conductive layer 90, e.g., a thin metal layer metal, such
as stainless steel, e.g., SST 410, is secured to the bottom surface
of the backing layer 22, e.g., with an adhesive layer 98. The metal
layer 90 may also be magnetic. A plurality of perforations 94
extend through both the cover layer 22 and the backing layer 20 to
expose the top surface 92 of the metal layer. In addition, one or
more holes 96 extend through the cover layer 22, backing layer 20
and metal layer 90, to permit electrodes secured to the platen to
project through the polishing pad and contact the substrate.
[0073] Referring to FIG. 8, if the polishing pad includes a
conductive layer 90 as described with reference to FIG. 7 and an
adhesive layer 50 spanning a window as described with reference to
FIG. 6A, then the conductive layer 90 can be positioned below the
adhesive layer 50. In addition, apertures can be formed in the
adhesive layer 50 in the perforations 94 to expose the top surface
92 of the metal layer. FIG. 8 illustrates an implementation in
which the transparent 56 portion is integrally molded into the
covering layer 22 and aperture 58 is the same dimensions as the
transparent portion.
[0074] Referring to FIG. 9, if the polishing pad includes a
conductive layer 90 as described with reference to FIG. 7, and an
adhesive layer 50 spanning a window and a transparent sheet as
described with reference to FIG. 6B, then the conductive layer 90
can be positioned below the adhesive layer 50. In addition,
apertures can be formed in the adhesive layers 50, 28 and 88 and
the transparent sheet 80 in the perforations 94 to expose the top
surface 92 of the metal layer.
[0075] The polishing pads of FIGS. 7-9 (which can also use the
various features described with respect to FIGS. 3A-6B in addition
or in alternative to the features illustrated) may be used for
electrochemical processing, such as electrochemical mechanical
polishing (ECMP) or simultaneous electrochemical deposition and
polishing, in addition to chemical mechanical polishing.
[0076] In electrochemical mechanical polishing, conductive
material, such as copper, is removed from the substrate surface by
electrochemical dissolution while the substrate surface is
concurrently polished. The substrate surface is placed in an
electrolyte (which also serves as the polishing fluid), and a bias
is applied between the substrate and a cathode that is in contact
with the electrolyte. The ECMP can be performed at low or very low
pressures, such as less than 1 psi, such 0.8 psi or less, or 0.5
psi or less, or 0.3 psi or less.
[0077] For example, referring to FIGS. 7-9, the metal sheet 90 can
be connected to a first electrode to serve as the cathode (the
holes 94 provide access for the electrolyte to the metal sheet 90),
and a second electrode can extend through the aperture 96 to
contact the substrate so that the substrate serve as an anode.
[0078] In electrochemical deposition, the bias voltage is reversed,
so that the substrate surface becomes the cathode, the electrode in
contact with the electrolyte becomes the anode, and conductive
material is electrodeposited onto the substrate. If this is
performed while the substrate is contacting a moving processing pad
at low pressure, then material will be preferrentially deposited
into any trenches in the dielectric layer.
[0079] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention.
[0080] For example, an adhesive layer can be applied to the bottom
surface of the polishing pad to secure the pad to the platen, and
the adhesive layer can be covered by a removable liner. In
implementations using the transparent sheet, the transparent sheet
need not span the entire polishing pad; the transparent sheet could
be just large enough to span each aperture to seal the window.
[0081] Either the polishing pad, or the carrier head, or both can
move to provide relative motion between the polishing surface and
the substrate. The polishing pad can be a circular (or some other
shape) pad secured to the platen, a tape extending between supply
and take-up rollers, or a continuous belt. The polishing pad can be
affixed on a platen, incrementally advanced over a platen between
polishing operations, or driven continuously over the platen during
polishing. The pad can be secured to the platen during polishing,
or there could be a fluid bearing between the platen and polishing
pad during polishing. In addition, although terms of vertical
positioning are used, it should be understood that the polishing
surface and substrate could be held upside down, in a vertical
orientation, or in some other orientation.
[0082] Accordingly, other embodiments are within the scope of the
following claims.
* * * * *