U.S. patent application number 10/721946 was filed with the patent office on 2004-06-03 for fixed abrasive polishing pad.
Invention is credited to Robinson, Karl M., Walker, Michael A..
Application Number | 20040106367 10/721946 |
Document ID | / |
Family ID | 25438237 |
Filed Date | 2004-06-03 |
United States Patent
Application |
20040106367 |
Kind Code |
A1 |
Walker, Michael A. ; et
al. |
June 3, 2004 |
Fixed abrasive polishing pad
Abstract
Apparatuses and methods are disclosed using a fixed abrasive
polishing pad to perform mechanical polishing of a surface. The
apparatus includes a polishing pad positioned opposing a wafer
support to provide for polishing of a surface of a wafer placed on
the support. The polishing pad includes a first member having a
first polishing surface formed from an abrasive first material that
is structurally degradable during polishing. The polishing pad also
includes a second member having a second polishing surface formed
from a second material that is less degradable and less abrasive
relative to said first material. The first and second polishing
surfaces define a polishing face that is brought into contact with
the surface to be polished. Preferably, a portion of the second
member can be removed from the polishing pad so that the first
polishing surface extends beyond the second polishing surface to
provide for a fixed amount of abrasion using the first member prior
to the second member contacting the surface and substantially
reducing or stopping the polishing process.
Inventors: |
Walker, Michael A.; (Boise,
ID) ; Robinson, Karl M.; (Boise, ID) |
Correspondence
Address: |
KIRKPATRICK & LOCKHART LLP
535 SMITHFIELD STREET
PITTSBURGH
PA
15222
US
|
Family ID: |
25438237 |
Appl. No.: |
10/721946 |
Filed: |
November 25, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10721946 |
Nov 25, 2003 |
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10352668 |
Jan 28, 2003 |
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6672951 |
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10352668 |
Jan 28, 2003 |
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09881421 |
Jun 14, 2001 |
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6527626 |
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09881421 |
Jun 14, 2001 |
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09593045 |
Jun 12, 2000 |
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6254460 |
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09593045 |
Jun 12, 2000 |
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09187307 |
Nov 4, 1998 |
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6409586 |
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09187307 |
Nov 4, 1998 |
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08917018 |
Aug 22, 1997 |
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5919082 |
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Current U.S.
Class: |
451/528 ;
451/2 |
Current CPC
Class: |
B24B 37/245 20130101;
B24B 37/205 20130101 |
Class at
Publication: |
451/528 ;
451/002 |
International
Class: |
B24C 003/00 |
Claims
What is claimed is:
1. A polishing pad comprising: a first member comprising a
structurally degradable abrasive first material; and, a second
member comprising a second material that is less degradable and
less abrasive than said first material.
2. The pad of claim 1, wherein said first member includes a portion
that extends beyond said second member.
3. The pad of claim 1, wherein: said first member includes a first
polishing surface; and, said second member includes a second
polishing surface that with said first polishing surface define a
polishing face.
4. The pad of claim 1, wherein: said first member includes a
plurality of first sections having first polishing surfaces; and,
said second member includes a plurality of second sections having
second polishing surfaces that with said first polishing surfaces
define a polishing face.
5. The pad of claim 4, wherein said plurality of first and second
sections are provided in an alternating arrangement.
6. The pad of claim 1, wherein: said second material is more
soluble in a solvent than said first material.
7. The pad of claim 6, wherein: said second material comprises an
acrylate polymer; and, said first material comprises a urethane
material containing discrete abrasive particles ranging from 15
nm-1000 nm is size and selected from the group consisting of
SiO.sub.2, CeO.sub.2, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, and
MnO.sub.2.
8. The pad of claim 1, wherein said first material comprises a
matrix material containing discrete particles that are more
abrasive than said matrix.
9. The pad of claim 8, wherein said discrete particles are selected
from the group consisting of SiO.sub.2, CeO.sub.2, Al.sub.2O.sub.3,
Ta.sub.2O.sub.5, and MnO.sub.2.
10. The pad of claim 8, wherein said matrix material is
substantially nonabrasive.
11. The pad of claim 8, wherein said matrix material is
abrasive.
12. The pad of claim 1, wherein said second material is
substantially nonabrasive.
13. The pad of claim 12, wherein said second material is
substantially nondegradable.
14. The pad of claim 1, wherein said second material is
substantially nondegradable.
15. The pad of claim 1, wherein said first member comprises a
chemically active material.
16. A polishing pad for use in performing chemical mechanical
polishing, comprising: a first member including a plurality of
first sections having first polishing surfaces and comprising a
first material further comprising an erodible, substantially
nonabrasive matrix material containing discrete particles of
abrasive material distributed therein; and, a second member
including a plurality of second sections having second polishing
surface and comprising a second material that is less erodible and
less abrasive than said first material, wherein said first and
second polishing surfaces define a polishing face and said second
member is removable to allow a portion of said first member
containing said first polishing surface to extend beyond said
second polishing surface.
17. The pad of claim 16, wherein said first and second members are
formed with said first polishing surface extending beyond said
second polishing surface.
18. The pad of claim 16, wherein said second material comprises a
soluble acrylate polymer.
19. The pad of claim 18, wherein said soluble acrylate polymer is
soluble in HCl/H.sub.2O solutions.
20. The pad of claim 18, wherein said soluble acrylate polymer is
soluble in a solvent selected from the group consisting of acetone
and isopropyl alcohol.
21. The pad of claim 18, wherein said soluble acrylate polymer
comprises polymethylmethacrylate.
22. The pad of claim 16, wherein said first material comprises a
material selected from the group consisting of urethanes and
polyphenyl oxide, and containing discrete abrasive particles
ranging from 15 nm-1000 nm in size and selected from the group
consisting of SiO.sub.2, CeO.sub.2, Al.sub.2O.sub.3,
Ta.sub.2O.sub.5, and MnO.sub.2.
23. An apparatus for performing mechanical polishing of a
semiconductor wafer surface, comprising: a polishing pad having a
polishing face, wherein said polishing pad further comprises, a
first member having a first polishing surface and comprising a
structurally degradable abrasive first material, and, a second
member having a second polishing surface and comprising a second
material that is less degradable and less abrasive than said first
material, wherein said first and second polishing surfaces define
said polishing face; a wafer support having a support surface, said
wafer support being disposed opposite to said pad, such that said
polishing face and said support surface are substantially parallel
and can be brought within close proximity; and, a motor connected
to provide relative motion between said polishing face and said
support surface.
24. The apparatus of claim 23, wherein said first member includes a
portion including said first polishing surface that extends beyond
said second polishing surface.
25 The apparatus of claim 23, wherein said motor includes, a
support motor to impart motion to said support, and, a platen motor
to impart motion to said pad.
26. The apparatus of claim 23, further comprising a source
positioned to dispense liquid from said liquid source between said
polishing face and said support surface.
27. The apparatus of claim 23, wherein said source is positioned to
dispense liquid through said pad.
28. A method of limiting mechanical abrasion of a surface during
polishing, said method comprising: providing a polishing pad
including a first member comprising a first material that is
abrasive to a wafer surface and structurally degradable during
polishing; incorporating a second member in the polishing pad
comprising a second material that is less degradable and less
abrasive than the first material to limit the amount of the first
member available to abrade the surface; and, polishing the wafer
surface with the first member.
29. The method of claim 28, further comprising removing a portion
of the second member to expose an amount of the first member
effective to polish the surface.
30. The method of claim 29, wherein: said incorporating further
comprises incorporating a second member comprising a material that
is more soluble in a solvent than the first material; and, said
removing further comprises removing a portion of the second member
using the solvent.
31. A method of performing mechanical polishing of a surface,
comprising: providing a polishing pad having a first member
comprising a first material that is abrasive to a surface and
structurally degradable during polishing that extends beyond a
second member comprising a second material that is less degradable
and less abrasive than the first material; and, polishing the
surface with the first member.
32. The method of claim 31, wherein said polishing further
comprises polishing the surface with the first member until the
second member contacts the surface.
33. The method of claim 31, further comprising providing liquid on
the surface during said polishing.
34. The method of claim 31, wherein said step of providing
comprises: providing a polishing pad having a first member
comprising an abrasive first material that is structurally
degradable during polishing, and a second member comprising a
second material that is less degradable and less abrasive than the
first material; and, removing a portion of the second member to
expose an amount of the first member effective to polish the
surface.
35. The method of claim 34, wherein said removing includes
chemically stripping the second member.
36. The method of claim 31, wherein said providing further
comprises providing an erodible, abrasive first material having a
matrix material containing discrete particles of abrasive material
distributed throughout and a less erodible.
37. The method of claim 36, wherein said providing a second
material further comprises providing a substantially nonerodible
second material.
38. The method of claim 37, wherein said providing a second
material further comprises providing a substantially nonabrasive
second material.
39. The method of claim 31, wherein said providing a second
material further comprises providing a substantially nonabrasive
second material.
40. A method of performing chemical mechanical polishing of a wafer
surface, comprising: providing a polishing pad having a first
member comprising a first material that is abrasive to a wafer
surface and erodible in polishing chemicals extending a
predetermined distance beyond a second member comprising a second
material that is substantially nonerodible in polishing chemicals
and substantially nonabrasive to a wafer surface; dispensing the
polishing chemicals onto the wafer surface; and, polishing the
wafer surface with the first member for a period of time sufficient
to erode the first member to be substantially flush with the second
member.
41. The method of claim 40, wherein said providing includes
providing a first member comprising polyurethane containing
discrete abrasive particles ranging from 15 nm-1000 nm in size and
selected from the group consisting of SiO.sub.2, CeO.sub.2,
Al.sub.2O.sub.3, Ta.sub.2O.sub.5, and MnO.sub.2 and a second member
comprising a soluble polyacrylate.
42. The method of claim 41, further comprising removing a portion
of the second member by exposing the polyacrylate material to a
HCl/H.sub.2O solution to expose an amount of the first member
effective to polish the surface.
43. A method of forming a polishing pad having a polishing face,
comprising: providing a polishing pad having a first member
comprising an abrasive first material that is structurally
degradable during polishing; and, incorporating a second member in
the polishing pad comprising a second material that is sufficiently
less degradable and less abrasive than the first material to limit
the amount of the first member available to abrade the surface.
44. The method of claim 43, further comprises removing a portion of
the second member to expose an amount of the first member effective
to polish the surface.
45. The method of claim 44, wherein: said incorporating further
comprises incorporating a second member comprising a material that
is more soluble in a solvent than the first material; and, said
removing further comprises removing a portion of the second member
using the solvent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
BACKGROUND OF THE INVENTION
[0003] The present invention generally relates to mechanical
polishing of a surface. More particularly, the present invention
relates to composite fixed abrasive polishing pads and methods of
use for mechanical polishing the surface on a semiconductor
substrate wafer.
[0004] Integrated circuits are typically constructed by depositing
layers of predetermined materials to form circuit components on a
wafer shaped semiconductor substrate. The formation of the circuit
components in each layer generally produces a rough, or nonplanar,
topography on the surface of the wafer. Nonplanar surfaces on the
wafer can result in defects in subsequent circuit layers formed on
the surface leading to flawed or improperly performing circuitry.
Therefore, nonplanar surfaces must be made smooth, or planarized,
to ensure a proper surface for the formation of subsequent layers
of the integrated circuit.
[0005] Planarization of the outermost surface of the wafer is
performed in two ways, locally over small regions of the wafers and
globally over the entire surface. For example, a layer of oxide is
typically deposited over the exposed circuit layer to provide an
insulating layer for the circuit and to locally planarize regions
by providing a continuous layer of material. A second layer of
material is then deposited on top of the insulating layer to
provide a surface that can be globally planarized without damaging
the underlying circuitry. The second layer is generally composed of
either an oxide or a polymer. Thick oxide layers can be deposited
using conventional deposition techniques. Spin coating is a
commonly used technique to form thick polymer layers on a
wafer.
[0006] While deposition and spin coating techniques are useful in
producing continuous uniform thickness layers, neither technique is
particularly effective at producing a globally planar surface when
applied to a nonplanar surface. As such, additional surface
preparation is generally required prior to forming additional
circuit layers on the wafer.
[0007] Other methods for globally planarizing the outermost surface
of the wafer include chemical etching, press planarization and
mechanical polishing, which includes chemical mechanical polishing,
or planarization, (CMP). In chemical etching, the second layer is
deposited over the preceding layers as described above and is
chemically etched back to planarize the surface. The chemical
etching technique is iterative in that following the etching step,
if the surface was not sufficiently smooth, a new layer of polymer
or oxide must be formed and subsequently etched back. This process
is time consuming, lacks predictably due to its iterative nature,
consumes significant amounts of oxides and/or polymers in the
process, and generates significant amounts of waste products.
[0008] In global press planarization, a planar force is applied to
press, or deform, the surface of the second layer to assume a
planar topography. The obvious limitation to this technique is that
a deformable material must be used to form the second layer.
[0009] Mechanical polishing of a surface is performed by
mechanically abrading the surface generally with a polishing pad.
Mechanical polishing can be performed either as a dry process (air
lubricant) or a wet process (liquid lubricant).
[0010] In mechanical polishing, the wafer must be polished for a
precise period of time to achieve a desired surface finish on the
layer. If the wafer is not polished for a sufficient length of
time, the desired finish will not be achieved. On the other hand,
if the wafer is polished for a period of time longer than
necessary, the continued polishing may begin to deteriorate the
surface finish. The ability to control the time required to polish
the surface of the wafer can greatly improve productivity by
allowing for the automation of the process, increasing the yield of
properly performing wafers, and reducing the number of quality
control inspections necessary to maintain the process.
[0011] The size and concentration of the particles used to abrade
the surface direct affect the resulting surface finish. If the
particulate concentration is too low or the particle size too
small, mechanical polishing will not proceed at a sufficient rate
to achieve the desired polishing effect in the time provided.
Conversely, if the particulate concentration is too high or the
particles are too large, then the particulates will undesirably
scratch the surface.
[0012] Polishing scratches are often a source of variability in the
performance of the finished integrated circuit. Performance
variability results from scratch induced problems, such as uneven
interconnect metallization across a planarized surface and
contamination effects due to the presence of voids formed or
particles trapped in a layer as a result of the scratches.
[0013] In addition, mechanical polishing techniques often
experience significant performance variations over time that
further complicate the automated processing of the wafers. The
degradation in performance is generally attributed to the changing
characteristics of the polishing pad during processing. Changes in
the polishing pad can result from particulates becoming lodged in
or hardening on the surface of the pad, pad wear, or aging of the
pad material.
[0014] Chemical mechanical polishing is a wet technique in which a
chemically reactive polishing slurry is used in conjunction with a
polishing pad to provide a synergistic combination of chemical
reactions and wet mechanical abrasion to planarize the surface of
the wafer. The polishing slurries used in the process are generally
composed of an aqueous basic solution, such as aqueous potassium
hydroxide (KOH), containing dispersed abrasive particles, such as
silica or alumina. The polishing pads are typically composed of
porous or fibrous materials, such as polyurethanes, that provide a
relatively compliant surface in comparison to the wafer.
[0015] The benefits of performing both a chemical and a mechanical
polishing of the surface are somewhat offset by the additional
undesirable variations in the surface quality that can occur in CMP
techniques. The additional variations generally result from
imbalances that occur in the chemical and mechanical polishing
rates. For example, if the chemical concentration is too low, the
desired chemical reactions may not proceed at an appreciable enough
rate to achieve the desired polishing effect. In contrast, if the
chemical concentration is too high, etching of the surface may
occur. Also, in CMP techniques, chemicals may become unevenly
distributed in the pad resulting in further variations in the
chemical polishing rate.
[0016] In addition, the chemicals that are needed to perform the
CMP process are relatively expensive and are generally not
recyclable. It is therefore desirable to minimize the amount of
chemicals used in the process to reduce both the front end costs of
purchasing and storing the chemicals and the back end costs of
waste disposal.
[0017] Efforts have been made in the prior art to decrease the
variability and increase the quality of the polish provided by CMP
techniques. For instance, U.S. Pat. No. 5,421,769 to Schultz et al.
discloses a noncircular polishing pad that attempts to compensate
for uneven polishing that occurs as a result of the edges of the
wafer traveling a greater distance across the polishing pad when a
spinning polishing motion is used. U.S. Pat. No. 5,441,598 to Yu et
al. discloses a polishing pad having a textured polishing surface
that attempts for provide a surface that will more evenly polish
wide and narrow depressions in the surface.
[0018] U.S. Pat. No. 5,287,663 to Pierce et al. discloses a
polishing pad having a rigid layer opposite the polishing surface
and a resilient layer adjacent to the rigid layer. The rigid layer
imparts stability to the pad to prevent the unintended
overpolishing, or dishing out, of material from between adjacent
hard underlying features, while the resilient layer serves to
redistribute any maldistribution of the polishing force. While the
apparatuses and methods may provide a more planar surface by
compensating for various features in the wafer, the inventions do
not directly address the problem of overpolishing the wafer
surface.
[0019] Other prior art efforts to minimize the uneven polishing of
the wafer have focused on including additional material in the
layers formed on the wafer to control overpolishing. U.S. Pat. Nos.
5,356,513 and 5,510,652 to Burke et al. and 5,516,729 to Dawson et
al. all disclose the inclusion in the layers of additional material
that is more or less susceptible to CMP than the material
comprising the operative portion of the circuit.
[0020] The additional material included in the layer, known as a
"polish stop", is used to prevent overpolishing of the wafer.
However, polish stops do not overcome the problem of overpolishing,
as discussed in the Dawson patent (col. 7, lines 18-59). Also, the
procedures must be performed iteratively to obtain global
planarization. The use of polish stops in the layer also increases
the complexity of the manufacturing process and adds materials that
are unnecessary to the end use of the circuit, both of which tend
to increase the likelihood of flawed or improperly performing
devices.
[0021] In view of these and other difficulties with prior art
mechanical polishing techniques, there is a need for mechanical
surface polishing methods and apparatuses that provide for a more
generally applicable and predictable polishing technique.
BRIEF SUMMARY OF THE INVENTION
[0022] The above difficulties are addressed by methods and
apparatuses in accordance with the present invention. The apparatus
includes a polishing pad having a polishing face. The polishing pad
includes a first member having a first polishing surface formed
from an abrasive first material that is structurally degradable
during polishing. The polishing pad also includes a second member
having a second polishing surface formed from a second material
that is less structurally degradable during polishing and less
abrasive to a surface being polished relative to said first
material.
[0023] The first and second polishing surfaces define a polishing
face that is brought into contact with a surface to be polished.
Preferably, a portion of the second member can be removed from the
polishing pad so that the first polishing surface extends beyond
the second polishing surface by a predetermined distance to provide
for fixed amount of abrasion using the first member prior to the
second member contacting the surface.
[0024] The apparatus further includes a wafer support having a
support surface that is disposed opposite to the polishing pad,
such that the polishing face and the support surface are in
substantially parallel planes and can be brought into close
proximity. Preferably, a motor is connected to provide relative
motion between the polishing face and the support surface. In wet
mechanical polishing techniques, a liquid or chemical source
containing the liquid lubricants or polishing chemicals is
positioned to dispense the liquid between the polishing face and
the support surface.
[0025] In a preferred embodiment, the second member is formed from
a second material that is substantially less structurally
degradable and substantially less abrasive, for example, at least
an order of magnitude, than the first member, and preferably
substantially nondegradable and substantially nonabrasive. The
first material includes a substantially nonabrasive matrix material
containing discrete particles of abrasive material. In addition,
the first and second members include a plurality of first and
second sections positioned in an alternating arrangement so that
the polishing face has alternating first and second polishing
surfaces.
[0026] In a preferred method of the invention, the second material
is removed from the polishing pad, such as by chemical stripping,
to expose a portion of the first member of the pad containing an
effective amount of abrasive material to perform the desired
polishing of the wafer surface.
[0027] The applicant has found that the overall quality of the
surface finish on the wafer can be increased and more tightly
controlled by providing a precise amount of abrasive material
effective to perform the polishing of the surface in a pad that
prevents overpolishing of the surface. In this manner, problems
associated with overpolishing and underpolishing of the surface can
be minimized, unlike the methods and apparatuses of the prior
art.
[0028] Accordingly, the apparatuses and methods of the present
invention provide for increased reliability and performance in the
mechanical polishing of surfaces, and specifically, chemical
mechanical polishing of semiconductor wafer surfaces. The above
advantages and others will become apparent from the following
detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Preferred embodiments of the present invention will be
described in greater detail with reference to the accompanying
drawings, wherein like members bear like reference numerals and
wherein:
[0030] FIG. 1 is a side view of an apparatus of the present
invention;
[0031] FIG. 2 is a top cross sectional view of an apparatus along
the line II-II of FIG. 1;
[0032] FIG. 3 is a cross section of a preferred embodiment of the
present invention prior to polishing the surface of a wafer;
[0033] FIG. 4 is a cross section of a preferred embodiment of the
present invention following the polishing the surface of a wafer;
and,
[0034] FIG. 5 is a cross section of an alternative preferred
embodiment of the present invention prior to polishing the surface
of a wafer.
DETAILED DESCRIPTION OF THE INVENTION
[0035] The operation of the apparatus 10 will be described
generally with reference to the drawings for the purpose of
illustrating present preferred embodiments of the invention only
and not for purposes of limiting the same. As shown in FIGS. 1 and
2, the apparatus 10 of the present invention includes a polishing
pad 20 for use in polishing a wafer 40.
[0036] The polishing pad 20 of the present invention includes at
least a first member 22 and a second member 24 having first and
second polishing surfaces, 26 and 28, respectively. The individual
first and second polishing surfaces, 26 and 28, respectively,
collectively define a polishing face 30 on the pad 20.
[0037] Preferably, as shown in FIGS. 2-5, a plurality of first and
second sections, 23 and 25, respectively, are included in the first
and second members, 22 and 24, respectively. The sections, 23 and
25, are arranged to provide alternating first and second polishing
surfaces, 26 and 28, respectively, on the polishing face 30.
[0038] The first and second sections, 23 and 25, respectively, may
be arranged in any geometrical shape, such as parallel rectangles
or concentric circles, so as to optimize the orientation of the
first and second members, 22 and 24, respectively, for a specific
polishing application. For example, the sections can be arranged to
minimize the differences in the amount of abrasive material
contacted from the inside to the outside of the wafer as discussed
in the Schultz patent. It will also be appreciated that additional
members may be added to the pad 20 to provide intermediate degrees
of polishing.
[0039] As shown in FIGS. 3 and 4, the first and second sections, 23
and 25, respectively, are discrete sections in the pad 20.
Alternatively, as shown in FIG. 5, either the first member 22 or
the second member 24 may be used as a matrix in which a plurality
of sections of the other member are inset to form the pad 20. Also,
the first and second members, 22 and 24, respectively, can be
comprised of a common matrix material.
[0040] The first member 22 is formed from an abrasive material that
is structurally degradable during the polishing of the wafer 40.
Structurally degradable is meant to include all forms of
degradation that result in a breakdown of the structure of the
material including, but not limited to, wear, erosion, chemical
dissolution, phase change and chemical breakdown of the
material.
[0041] In a preferred embodiment, the first member 22 includes
discrete particles of abrasive material 32 distributed throughout a
substantially less abrasive matrix, as shown in FIGS. 3-5.
Generally, oxide particles, such as SiO.sub.2, CeO.sub.2,
Al.sub.2O.sub.3, Ta.sub.2O.sub.5, and MnO.sub.2 are suitable for
use as abrasive materials. In this embodiment, an abrasive or
nonabrasive matrix material can also be used to form the first
member 22.
[0042] The abrasive material 32 can be randomly distributed
throughout the first member 22 or in any specific manner to achieve
a particular purpose. For instance, the abrasive material can be
loaded into the first member 22 such that larger particles will be
exposed first and used for an initial rough polish of the wafer 40.
The larger particles would then be followed by smaller particles
that would provide for a fine polish of the surface of the wafer
40. Alternatively, the first member 22 can be formed from a
material that is inherently abrasive, in addition to being
erodible, thereby eliminating the need for discrete abrasive
particles.
[0043] In a preferred embodiment, the second member 24 is formed
from a second material that is substantially structurally
nondegradable during polishing and substantially nonabrasive to
provide a precise endpoint to the polishing process. The
substantially nondegradable, nonabrasive characteristics of the
material used for the second member 24 provide the ability to
automate the polishing, because the second member does not
substantially abrade the wafer 40. In this manner, the pad can be
optimized for a set amount of abrasion relatively independent of
the polishing time. For example, once the desired amount of
abrasive has been worn from the first member 22, the second member
24 will contact the wafer 40 and substantially reduce or stop
further abrasion of the wafer 40. Therefore, the timing of the
process will not be as crucial to the overall quality of the
surface finish and performance of the integrated circuit.
[0044] The second member 24 can alternatively be a second material
that is less structurally degradable and/or less abrasive than the
first member 22. As such, the second member should not generally
degrade to an extent during polishing that additional abrasive
material in the first member 22 is exposed to the surface and
should generally produce less severe abrasions of the surface than
the first member 22. Preferably, the second material is
substantially less structurally degradable and substantially less
abrasive, for example, by at least an order of magnitude, than the
first member 22. A substantial difference in the degradability and
abrasiveness between the members, 22 and 24, is desirable to ensure
that the second member is sufficiently less degradable and abrasive
so as to limit the amount of the first member available to abrade
the surface, such as to an effective amount to perform the desired
polishing, and to provide flexibility in the use of the pad 20 from
a processing standpoint.
[0045] The embodiments including a less abrasive second member 24
may be useful to perform a final polish of the wafer 40, analogous
to the preceding discussion regarding the alignment of the
particles in the first member 22. The fine polishing of the wafer
40 may be desirable as a practical matter, because the first member
22 may not ideally degrade in all practical applications and a fine
polishing second member may provide for a more consistent surface
finish. Also, if the first member 22 and the second member 24 are
formed from a common matrix material, the first member 22 can be
made to be more abrasive than the second member 24 by inclusion of
abrasive material in the matrix or by selective chemical treatment
of the matrix material.
[0046] Suitable materials for use in the present invention are
described, for example, in U.S. Pat. No. 5,624,303 issued to
Robinson and U.S. patent application Ser. No. 08/743,861, which are
incorporated herein by reference.
[0047] In practice, a portion of the second member 24 is removed
from the pad 20 so that a portion of the first member 22 containing
the first polishing surface 26 extends beyond the second polishing
surface 28, as shown in FIG. 3. The amount of the second member 22
that is removed can be controller so that only an effective amount
of the first member 22 is exposed to provide the desired polishing
operation. The second member 24 can be removed either mechanically
or chemically, such as described in U.S. patent application Ser.
No. 08/743,861.
[0048] The polishing pad 20 can be employed in any number of
polishing apparatuses, one embodiment of which is shown in FIGS. 1
and 2 and described herein. The polishing pad 20 has an opposing
surface 34 that can be attached to a platen 36. The platen 36 can
be attached to a platen motor 38 to impart a polishing motion to
the platen 36 or the platen can be stationery. Commercially
available platens 36 and platen motors 38 can be used in the
present invention.
[0049] The wafer 40 has a device surface 42 that is to be polished
and a back surface 44 that is seated on a support surface 45 of a
wafer support 46. The wafer support 46 is brought into close
proximity with the polishing face 30. The device surface 42 of the
wafer 40 is positioned parallel to and brought into contact with
the polishing face 30 either directly or via the liquid lubricant
and/or the abrasive particles.
[0050] The wafer support 46 and the polishing pad 20 are placed in
relative motion to effect the polishing of the device surface 42.
The wafer support 46 can be moved in a polishing motion using a
motor 48 or can remain stationary with the polishing motion
provided by the polishing pad 20. One skilled in the art will
appreciate that the pad 20 and the wafer support 46 can be moved in
a variety of motions, such as rotational, translation or orbital,
to polish the wafer surface 42.
[0051] In wet mechanical polishing applications, a liquid dispense
line 50 is provided that has a source end 52 attached to a liquid,
or slurry, source 54 and a dispense end 56. The dispense end 56 is
positioned to dispense the liquid or slurry between the polishing
pad 20 and the wafer 40. The dispense end 56 can also be integral
with the polishing pad 20 and the liquid can be dispensed through
porous regions in the first and second members. The dispense line
50 can be constructed from polyethylene or other materials as is
known in the art. The liquid or slurry is transported from the
liquid source 54 through the dispense line 50 by conventional
means, such as a pump (not shown).
[0052] A liquid or slurry can be used with the pad 20 as a
lubricant for wet mechanical polishing of the surface and to flush
the polishing surface to prevent the buildup of particles during
the polishing process. A chemically active liquid lubricant can
also be selected that forms a reactive slurry in situ with the
particles that are released as the first member 22, in addition to
serving as a lubricant for the polishing pad 20.
[0053] The particular liquids or slurries used depend upon the
surface to be polished and the type of polishing pad used. For
example, deionized water can be used as a lubricant in wet
mechanical polishing or reactive slurries, such as aqueous
potassium hydroxide (KOH) containing SiO.sub.2 particles, can be
employed during chemical mechanical polishing of the surface.
[0054] The polishing pad 20 will be further described with respect
to chemical mechanical polishing as an exemplary implementation of
the present invention. The first member 22 is preferably comprised
of a material that is erodible or dissolves in the presence of
polishing chemicals used in the polishing technique.
[0055] Generally, the abrasive material 32 employed in the first
member 22 is unaffected by the polishing chemicals. However, an
abrasive material can be used that is either soluble or breaks down
in the polishing chemicals. In this way, the abrasive material will
remain abrasive for only a finite period of time and will not embed
in the pad 20 and affect the polishing characteristics of the pad.
Also, a chemically active first material can be selected for the
first member 22 that when solvated in the polishing chemicals can
vary that the polishing chemical strength with the amount of
polishing and the resultant degradation of the first member 22.
[0056] The second member 24 is preferably comprised of materials
that are substantially less erodible or soluble in the polishing
chemicals, for example, by at least an order of magnitude, in
addition to being substantially less abrasive to the surface that
is to be polished than the first member 22. Preferably, a material
used for the second member 24 that can be easily removed from the
pad 20, such as by chemical stripping or etching, to expose the
first polishing surface 26 and a portion of the first member 22
that contains an amount of abrasive material to perform the desired
amount of polishing.
[0057] The materials selected for the first and second members, 22
and 24, respectively, depend upon the composition of the wafer
surface to be polished and the polishing chemicals to be used. For
example, polyurethanes and polyphenyl oxides can be used to form
the first member 22, polyacrylates and polymethylmethacrylates can
be used to form the second member 24 and HCl/H.sub.2O solutions can
used as solvents, or stripping chemicals. As a further example,
polyimides and acetal resins can be used to form the first member
22, with urethanes and polyacrylates can be used to form the second
member, in conjunction with acetone or isopropyl alcohol
solvents.
[0058] The operation of the apparatus 10 will be described with
respect to the use of the pad 20 in a CMP process to polish the
surface of a silicon dioxide (SiO.sub.2) layer on a semiconductor
wafer. The first member 22 of the pad 20 is formed from
polyurethane and contains 15 nm-1,000 nm particles of silica
distributed throughout. The second member 24 is formed from an
acrylate polymer. Prior to polishing, the polishing pad has an
appearance similar to that shown in FIGS. 4 and 5.
[0059] A mild solution of hydrochloric acid (HCl) (<1 M) is used
to strip, or etch back, the second member 24. The HCl reacts with
the acrylate polymers to form water soluble polyacrylic acids that
are rinsed from the surface of the second member 24 using deionized
(DI) water. The acrylate polymer is stripped to expose the precise
amount of the first member 22 necessary to perform the desired
amount of polishing. The pad 20 at this time has an appearance
similar to that shown in FIG. 3.
[0060] The pad 20 is attached to the platen 36 and a wafer is
attached to the wafer support 46. The wafer support 46 is brought
sufficiently close to the polishing pad 20 to effect the polishing
operation by placing the wafer device surface 42 in contact with
the first member 22, either directly or via polishing chemicals or
the abrasive material 32. The polishing chemicals are dispensed
between the wafer device surface 42 and the first polishing surface
26 and the polishing pad 20. Relative motion, such as rotational,
translation or orbital, is provided between the device surface 42
and the first polishing surface 26. The polishing is performed for
a predetermined period of time corresponding to at least the time
required for the first member 22 to structurally degrade and become
flush with the second member 24.
[0061] When the first polishing face 26 becomes substantially flush
with the second polishing face 28, the contact of the second member
24 with the surface 42 will substantially reduce or prevent further
abrasion to the device surface 42 by the first member 22. The
polishing pad 20 will again have an appearance similar to that
shown in FIGS. 4 and 5. The polishing pad 20 can be reconditioned
to perform additional polishing be removing an another portion of
the second member 24 to further expose the first member 22 for use
in polishing additional surfaces or by other methods, such as those
described in the Robinson patent.
[0062] The polishing pad of the present invention can be used in
conjunction with the various modified pad designs described in the
background to provide additional features in the pad. One skilled
in the art can suitably modify the pad for use with various
polishing apparatuses known in the art.
[0063] The present invention provides the ability to control the
amount of abrasive material exposed to a surface during a
mechanical polishing operation. The control afforded by the present
invention allows for more automation and less monitoring of the
polishing process than was possible with the prior art. While the
subject invention provides these and other advantages over prior
art, it will be understood, however, that various changes in the
details, materials and arrangements of parts and steps which have
been herein described and illustrated in order to explain the
nature of the invention may be made by those skilled in the art
within the principle and scope of the invention as expressed in the
appended claims.
* * * * *