U.S. patent application number 11/846304 was filed with the patent office on 2009-03-05 for polishing pad and method of use.
Invention is credited to Rajeev Bajaj.
Application Number | 20090061744 11/846304 |
Document ID | / |
Family ID | 40408213 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090061744 |
Kind Code |
A1 |
Bajaj; Rajeev |
March 5, 2009 |
POLISHING PAD AND METHOD OF USE
Abstract
A polishing pad has one or more polishing elements made from a
hydrogel material having an intrinsic ability to absorb water. The
hydrogel material may or may not have micropores, but has a water
absorption capability of 4%-60% by weight, a wet tensile strength
greater than 1000 psi, a flexural modulus greater than 2000 psi,
and a wet Shore D hardness between 25-80, inclusive. The hydrogel
material may be made from one or a combination of the following
moieties: urethane, alkylene oxides, esters, ethers, acrylic acids,
acrylamides, amides, imides, vinylalcohols, vinylacetates,
acrylates, methacrylates, sulfones, urethanes, vinylchlorides,
etheretherketones, and/or carbonates.
Inventors: |
Bajaj; Rajeev; (Fremont,
CA) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL LLP
P.O. BOX 061080, WACKER DRIVE STATION, SEARS TOWER
CHICAGO
IL
60606-1080
US
|
Family ID: |
40408213 |
Appl. No.: |
11/846304 |
Filed: |
August 28, 2007 |
Current U.S.
Class: |
451/288 ;
451/41 |
Current CPC
Class: |
H01L 21/32125 20130101;
B24B 37/042 20130101; B24B 37/24 20130101 |
Class at
Publication: |
451/288 ;
451/41 |
International
Class: |
B24B 5/00 20060101
B24B005/00 |
Claims
1. A polishing pad comprising one or more polishing elements, said
polishing elements made from a hydrogel polymer having an intrinsic
ability to absorb water and having no micro-porosity, the hydrogel
material having a water absorption capability of 4%-60% by weight,
a wet tensile strength greater than 1000 psi, a flexural modulus
greater than 2000 psi, and a wet Shore D hardness between 25-80,
inclusive.
2. The polishing pad of claim 1, wherein the hydrogel material is
made from one or a combination of the following moieties: urethane,
alkylene oxides, esters, ethers, acrylic acids, acrylamides,
amides, imides, vinylalcohols, vinylacetates, acrylates,
methacrylates, sulfones, urethanes, vinylchlorides,
etheretherketones, and/or carbonates.
3. A method of polishing a wafer, comprising bringing a polishing
pad constructed from a material having an intrinsic ability to
absorb water in proximity to a semiconductor wafer in the presence
of a polishing composition disposed between the polishing pad and a
top layer disposed on the wafer, and rotating the wafer and the
polishing pad with respect to one another so as to effect removal
of some or all of the top layer disposed on the wafer.
4. The method of claim 3, further comprising soaking the polishing
pad in solution prior to commencing polishing operations.
5. The method of claim 4, wherein the solution comprises water.
6. The method of claim 4, wherein the solution comprises the
polishing composition.
7. The method of claim 4, wherein the soaking lasts for at least 10
minutes.
8. The method of claim 4, wherein the solution is an electrolyte
solution.
9. The method of claim 8, wherein the electrolyte solution is
copper sulfate.
10. The method of claim 9, wherein during the polishing operations,
the polishing pad is coupled to an electrical source.
11. The method of claim 10, wherein the electrical connection to
the pad is anodic.
12. The method of claim 10, wherein the electrical connection to
the pad is cathodic.
13. A polishing pad comprising one or more polishing elements, said
polishing elements made from a hydrogel material having a water
absorption capability of 4%-60% by weight, a microporosity of 1% to
20% by volume, micropores of 20-100 microns, a wet tensile strength
greater than 1000 psi, a flexural modulus greater than 2000 psi,
and a wet Shore D hardness between 25-80, inclusive.
14. The polishing pad of claim 13, wherein the hydrogel material is
made from one or a combination of the following moieties: urethane,
alkylene oxides, esters, ethers, acrylic acids, acrylamides,
amides, imides, vinylalcohols, vinylacetates, acrylates,
methacrylates, sulfones, urethanes, vinylchlorides,
etheretherketones, and/or carbonates.
15. A method of polishing a wafer, comprising soaking a polishing
pad having a polishing surface constructed from a material having
an intrinsic ability to absorb water in an electrolytic solution,
bringing the polishing surface of the polishing pad in proximity to
a semiconductor wafer in the presence of a polishing composition
disposed between the polishing pad and a top layer disposed on the
wafer, and rotating the wafer and the polishing pad with respect to
one another so as to effect removal of some or all of the top layer
disposed on the wafer.
16. The method of claim 15, wherein the electrolytic solution is
copper sulfate.
17. The method of claim 15, wherein the polishing surface is
attached to an electrical source during polishing operations.
18. The method of claim 17, wherein the electrical connection to
the polishing surface is anodic.
19. The method of claim 17, wherein the electrical connection to
the polishing surface is cathodic.
20. The method of claim 15 further comprising applying an anodic
current to the polishing surface while a cathodic bias is provided
by external means, and pressing the semiconductor wafer against the
polishing surface.
21. The method of claim 20, wherein the electrolytic solution is
copper sulfate.
22. The method of claim 20, wherein the top layer is copper.
23. The method of claim 15, further comprising applying an anodic
current to the polishing surface while an anodic bias is provided
by external means, and pressing the semiconductor wafer against the
polishing surface.
24. The method of claim 23, wherein the electrolytic solution is
copper sulfate.
25. The method of claim 23, wherein the top layer is copper.
26. A method, comprising manufacturing a polishing pad having a
polishing surface constructed from a material having an intrinsic
ability to absorb water using one of: injection molding, extrusion,
reaction injection molding or sintering.
27. The method of claim 26, further comprising forming surface
features on the polishing surface of the polishing pad during said
manufacturing.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of chemical
mechanical planarization (CMP) and, more specifically, to a CMP pad
for reduced defectivity.
BACKGROUND
[0002] In modern integrated circuit (IC) fabrication, layers of
material are applied to embedded structures formed on semiconductor
wafers. Chemical mechanical planarization (CMP) is an abrasive
process used to remove these layers and polish the surface of a
wafer. CMP may be performed on both oxides and metals and generally
involves the use of chemical slurries applied in conjunction with a
polishing pad that is in motion relative to the wafer (e.g., the
pad is often in rotational motion relative to the wafer). The
resulting smooth, flat surface is necessary to maintain the
photolithographic depth of focus, for subsequent wafer processing
steps and to ensure that the metal interconnects are not deformed
over contour steps. Damascene processing requires metal, such as
tungsten or copper, to be removed from the top surface of
dielectric to define interconnect structures, using CMP.
[0003] Polishing pads are typically made of urethanes, either in
cast form filled with micro-porous elements, or from non-woven felt
coated with polyurethanes. In use, the pad is rotated while
contacting the wafer, which is also rotating, thus effecting
polishing. Typically, two types of polishing pads are used: hard
polishing pads and soft polishing pads. Hard pads are typically
used for applications requiring planarization of micro-scale
features on the wafer surface, while soft pads are used for
applications where planarization is not required. For example, soft
pads may be used in a multi-step polishing process where wafers are
first polished with a hard pad to planarize the surface, followed
by polishing with a soft pad to create a smooth finish. Hard pads
typically create surface defects such as micro-scratches and are
not efficient at effecting the removal of slurry particles.
Therefore, a soft pad is used to polish the surface of the wafer to
smooth the micro-scratches as well as to enable more efficient
removal of particle defects.
SUMMARY OF INVENTION
[0004] An embodiment of the present invention provides a polishing
pad having one or more polishing elements (e.g., a single polishing
surface or multiple polishing surfaces or elements) made from a
hydrogel material having an intrinsic ability to absorb water. The
hydrogel material may have no micro-porosity, a water absorption
capability of 4%-60% by weight, a wet tensile strength greater than
1000 psi, a flexural modulus greater than 2000 psi, and a wet Shore
D hardness between 25-80, inclusive. In other embodiments, the
hydrogel material may have a water absorption capability of 4%-60%
by weight, a microporosity of 1% to 20% by volume, micropores of
20-100 microns, a wet tensile strength greater than 1000 psi, a
flexural modulus greater than 2000 psi, and a wet Shore D hardness
between 25-80, inclusive. In either instance, the hydrogel material
may be made from one or a combination of the following moieties:
urethane, alkylene oxides, esters, ethers, acrylic acids,
acrylamides, amides, imides, vinylalcohols, vinylacetates,
acrylates, methacrylates, sulfones, urethanes, vinylchlorides,
etheretherketones, and/or carbonates.
[0005] In accordance with an embodiment of the present invention,
polishing may be effected by bringing a polishing pad constructed
from a material having an intrinsic ability to absorb water in
proximity to a semiconductor wafer in the presence of a polishing
composition disposed between the polishing pad and a top layer
disposed on the wafer, and rotating the wafer and the polishing pad
with respect to one another so as to effect removal of some or all
of the top layer (e.g., copper) disposed on the wafer. The
polishing pad may be soaked in solution (e.g., water, the polishing
composition, an electrolytic solution such as copper sulfate, etc.)
prior to commencing polishing operations. In cases where an
electrolytic solution is used, the polishing pad may be coupled to
an electrical source during the polishing operations.
[0006] In some cases, an anodic current is applied to the polishing
pad (or to the polishing surface thereof) while a cathodic bias is
provided by external means, and the semiconductor wafer is pressed
against the polishing surface. In other cases, cathodic current is
applied to the polishing pad or surface while an anodic bias is
provided by external means, and the semiconductor wafer is pressed
against the polishing surface.
[0007] A polishing pad having a polishing surface constructed from
a material having an intrinsic ability to absorb water may be
manufactured using one of: injection molding, extrusion, reaction
injection molding or sintering. Surface features may be formed on
the polishing surface of the polishing pad during such
manufacturing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention is illustrated by way of example, and
not limitation, in the figures of the accompanying drawings, in
which:
[0009] FIG. 1A illustrates a conventional polishing pad of
conventional form which, in accordance with an embodiment of the
present invention, may include a polishing surface constructed from
a hydrogel material having an intrinsic ability to absorb
water.
[0010] FIG. 1B illustrates a polishing pad having a plurality of
polishing elements, one or more of which are constructed from a
hydrogel material having an intrinsic ability to absorb water in
accordance with a further embodiment of the present invention.
[0011] FIG. 2 illustrates a method of using a polishing pad
configured with a polishing surface made of a hydrogel material
having an intrinsic ability to absorb water in accordance with the
present invention.
DETAILED DESCRIPTION
[0012] Described herein are a polishing pad with reduced
defectivity, methods of using such a pad, and materials useful for
making CMP polishing pads with reduced defectivity. As indicated
above, CMP involves removing films from the surface of a wafer by
pressing a polishing pad against the wafer and rotating these
elements relative to one another in the presence of a polishing
composition (e.g., a slurry). During the polishing process, a
slurry layer forms between the wafer and the pad, thus forming a
hydrodynamic boundary layer. Maintaining a uniform fluid layer
between the pad and wafer during polishing is important. In cases
where the boundary layer is minimized or completely eliminated, the
pad may directly contact the wafer leading to a two-body
interaction causing higher defectivity. In contrast, a highly
lubricated interface will allow more uniform polishing, as well as
minimize defectivity. This is particularly important in the case of
copper CMP, where the film being polished is very soft and can be
easily scratched by direct, wafer-pad contact.
[0013] Conventional polishing pads are made of polymers, typically
urethane, having structures to provide means for distributing
slurry under the wafer during the polishing process. These
structures include voids or micro-pores, which are included by
adding hollow micro-elements as described in U.S. Pat. No.
5,578,362, or through introduction of bubbles formed during the
casting process. U.S. Pat. No. 6,896,593 describes the use of
supercritical CO.sub.2 to form pores during the molding
process.
[0014] Once the pad layer is formed, it maybe further machined on
the top surface by mechanical or laser means to add grooves. For
example, U.S. Pat. No. 5,489,233 describes the use of a solid
plastic sheet, with no intrinsic ability to absorb or transport
slurry, and a surface texture, or patter, with flow channels to
transport slurry across the wafer and enabling polishing. The
surface texture is mechanically produced upon the pad through
machining.
[0015] During polishing, a pad may be conditioned using a fine,
diamond-coated disk to create a micro-texture, which creates
micro-groove channels to further enhance slurry distribution under
a wafer. During wafer polishing processes the pad surface also
undergoes plastic deformation, which reduces slurry distribution,
leading to poor material removal and removal uniformity.
Conditioning processes remove the plastic deformation layer and
restore polish performance.
[0016] In conventional pads, the material itself does not have any
intrinsic ability to absorb significant water or polishing solution
and externally created structures such as micro-pores, grooves and
micro-grooves actively participate in slurry distribution. Slurry
distribution ability is important not only for material removal
uniformity but also for defectivity. In cases of poor slurry
distribution between the pad and the wafer there is a potential for
a slurry-poor region under the wafer to cause direct, pad-wafer
contact, leading to defectivity.
[0017] In one embodiment, the present invention provides a polymer
polishing pad with an intrinsic ability to absorb water or
polishing solution, and thereby provide a very low defectivity
polishing surface. The subject polishing pad may be made from a
hydrogel material having the ability to absorb water or polishing
solution in the range of 5-60 percent by weight. Water absorption
ability is controlled during material synthesis. A pad material
with the intrinsic ability to absorb water or polishing solution
will provide a lubricious surface during polish processes and
minimize the probability of direct, pad-wafer contact and, by
extension, eliminate or minimize defectivity and particularly
scratch defectivity. Methods of making hydrophilic urethane
formulations are described in U.S. Pat. Nos. 5,859,166; 5,763,682;
5,424,338; 5,334,691; 5,120,816; 5,118,779; and 4,008,189, each of
which is incorporated herein by reference.
[0018] Pad material properties play an important role in
defectivity caused on a wafer surface. A hard pad is typically
associated with higher defectivity, which is substantially scratch
defectivity, while softer pads typically are associated with lower
defectivity. One important aspect of soft pads is the ability of
the pad surface to conform locally to prevent a "hard contact"
between the wafer and the pad surface. Another aspect of local
surface conformality is the ability of the pad-wafer interface to
retain an aqueous interface. An aqueous interface provides
necessary lubricity between the wafer and the pad, thus minimizing
or eliminating the potential to cause scratches. A polymeric
material capable of absorbing water provides a very stable
polishing interface, thus minimizing potential for defectivity.
[0019] U.S. Pat. No. 5,763,682 states that many conventional
isocyanate-based foams are non-hydrophilic (i.e., relatively
hydrophobic). Typical urethane-based foams exhibit an aversion to
aqueous fluids, which results in such foams being unable to absorb
or pick up significant quantities of aqueous fluids. Accordingly,
typical polyurethane foams may be deemed inadequate for providing a
highly lubricated polishing interface.
[0020] As urethanes are made of reactions of isocyanate and a
polyol, the hydrophilic aspect of the final polymer chain can be
controlled through selection of polyol. U.S. Pat. Nos. 5,859,166;
5,763,682; 5,424,338; 5,334,691; 5,120,816; 5,118,779; and
4,008,189 describe methods to improve hydrophilicity of urethane
compositions. Hydrophilic polyurethanes can be made by adding
ethylene oxide units and alkylene oxide units to the polyol
molecule.
[0021] Total hydroxyl content of the polyol is also an important
factor in hydrophilicity of the polyurethane. It is known in this
particular art that in order to achieve satisfactory hydrophilic
properties in the foam, the polyhydric alcohol-alkylene oxide
adduct reactant that is used must contain a certain proportion of
ethylene oxide in the molecule. See U.S. Pat. No. 3,457,203,
incorporated herein by reference. Early hydrophilic polyurethane
foams were prepared from such adducts, which are products of
condensing a polyhydric alcohol with a mixture of ethylene oxide
and a higher alkylene oxide such as propylene oxide. However, when
wet, these compositions showed deterioration in mechanical
properties.
[0022] U.S. Pat. No. 4,008,189 describes compositions that can
minimize such deterioration in physical properties by using a
mixture of polyols comprised of three oxyalkylated polyether polyol
reactants. The first of these is characterized by a trihydroxy
alcohol nucleus, polyoxyethylene chain segments attached through
one end thereof to the nucleus, and polyoxypropylene chain segments
attached through one end thereof to the polyoxyethylene chain
segments. Such a polyol can be prepared by methods well known in
the art wherein a triol initiator is sequentially condensed, in the
presence of an alkaline catalyst such as KOH, first with ethylene
oxide and then with propylene oxide.
[0023] It is expected that such compositions would be particularly
suitable for polishing applications as they enable a highly
lubricated polishing interface. Moreover, it is expected a
cross-linked polymer network will provide the best properties,
though thermoplastic formulations can be used. Tecophilic.RTM.
Extrusion Molding formulations from Lubrizol Corp are one such
class of materials. These materials are tailored to absorb between
20% to 100% by weight of water. The degree of water absorption is
linked to a loss of mechanical properties, with the higher the
percentage by weight of water absorbed, the greater the loss in
mechanical strength. It would therefore be advantageous to use
formulations that absorb approximately 5-20 percent by weight of
water, though water absorption as high as 100 percent by weight
maybe used.
[0024] FIG. 1A illustrates a cross-sectional view of a conventional
polishing pad 100, such as the IC 1000 pad provided by Rohm and
Haas. Polishing pad 100 contains microelements 102 embedded in a
polymeric matrix 104, which may be polyurethane. The pad surface
contains grooves 106 for slurry transport during polish processes.
Such commercially available polishing pads may include multiple
surface modifications to affect slurry distribution across the
surface of the pad.
[0025] FIG. 1B shows a cross-sectional view of a polishing pad 108
made by SemiQuest, Inc. and described in U.S. patent application
Ser. No. 11/697,622, filed 6 Apr. 2007, assigned to the assignee of
the present invention and incorporated herein by reference. Pad 108
consists of polishing elements 110, which rest on a compressible
under-foam 112 disposed beneath a guide plate 114. Polishing action
is provided by the polishing elements, which are made of solid
polymer material, while slurry distribution is effected by open
spaces between the polishing elements. The open spaces are filled
with open cell foam.
[0026] In embodiments of the present invention, polishing surfaces
104 and/or 110 of either or both of the pads discussed above may be
made using hydrophilic polymer material. For example, these
polishing surfaces may be formed of a hydrogel material having the
ability to absorb water or polishing solution in the range of 4-60
percent by weight. The hydrogel material may be one or a
combination of following moieties: urethane, alkylene oxides,
esters, ethers, acrylic acids, acrylamides, amides, imides,
vinylalcohols, vinylacetates, acrylates, methacrylates, sulfones,
urethanes, vinylchlorides, etheretherketones, and/or carbonates. An
imide is a functional group consisting of two carboxylic acid
groups, or one dicarboxylic acid, bound to a primary amine or
ammonia, and is generally prepared directly from ammonia or the
primary amine, and the either the acid(s) or their acid
anhydrides.
[0027] In particular embodiments of the present invention, the
polishing surfaces of the pad may be made from hydrogel materials
that have no micro-porosity, have a wet tensile strength greater
than 1000 psi, a flexural modulus greater than 2000 psi, and/or a
wet Shore D hardness of between 25-80, inclusive. In other cases,
the hydrogel material may have a microporosity of approximately
1%-20% by volume, micropores of between approximately 20-100
microns, a wet tensile strength greater than 1000 psi, flexural
modulus greater than 2000 psi, and a wet Shore D hardness of
between 25-80, inclusive.
[0028] During polishing operations, a polishing pad constructed
from hydrogel material in accordance with the present invention is
brought into contact with a surface of a semiconductor wafer (e.g.,
a wafer having one or more thin films, oxides and/or metal layers
disposed thereon) in the presence of a polishing compound, and the
two are rotated with respect to one another so as to effect removal
of some or all of a top layer disposed over the surface of the
wafer substrate. FIG. 2 illustrates this arrangement. A polishing
pad 200 is affixed to a turntable 202 and brought in proximity with
a wafer 204 that is on a platen 206. A slurry or other polishing
compound 208 is introduced between the polishing pad and the wafer
and the pad and/or the wafer are rotated relative to one
another.
[0029] In some cases, the polishing pad may be soaked in water or
polishing solution prior to being used for polishing operations.
For example, the pad may be so soaked for a period of time (e.g.,
at least 10 minutes) to create a stable polishing surface prior to
processing the wafer.
[0030] Further, a polishing pad constructed in accordance with the
present invention may be soaked in electrolyte solution to create a
conductive matrix and surface. One example of such an electrolyte
solution is copper sulfate. Such a pad may be attached to an
external electrical source during polishing operations. Such
connections may be anodic and anodic or cathodic bias may be
applied by external means. A polishing pad saturated with
electrolyte solution (such as copper sulfate) in this fashion and
having anodic current applied to it, while a cathodic bias is
provided by external means, may be pressed against a semiconductor
wafer having a top conductive layer (such as copper) deposited
thereon so as to fill structures formed into the underlying film to
affect removal of the conductive layer. Alternatively, a polishing
pad constructed in accordance with the present invention and
saturated with electrolyte solution (such as copper sulfate) may
have an anodic current applied to it, while an anodic bias is
provided by external means. The pad may be pressed against a
semiconductor wafer with top conductive layer (such as copper)
deposited thereon so as to fill structures formed into the
underlying film to affect deposition of the conductive layer.
[0031] Polishing pads constructed from hydrogel material in
accordance with the present invention may be manufactured using
injection molding, extrusion, reaction injection molding or
sintering. Surface features may be formed on such pads during the
manufacturing process. Such features may aid in slurry distribution
during polishing operations.
[0032] Thus, polishing pads with reduced defectivity, methods of
making and using such pads, and materials useful for making same
have been described. Although discussed with reference to certain
illustrated embodiments, however, the present invention should not
be limited thereby and, instead, measured only in terms of the
claims, which follow.
* * * * *