U.S. patent application number 10/877553 was filed with the patent office on 2005-12-29 for article for polishin substrate surface.
Invention is credited to Basol, Bulent M., Guo, George Xinsheng.
Application Number | 20050287932 10/877553 |
Document ID | / |
Family ID | 35506545 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050287932 |
Kind Code |
A1 |
Basol, Bulent M. ; et
al. |
December 29, 2005 |
Article for polishin substrate surface
Abstract
An article for polishing a surface of a semiconductor workpiece
is provided. The article includes a polishing layer and a plurality
of protrusions repeating across the polishing layer. The
protrusions include abrasive particles and can be elastically
deformed while polishing the surface of the wafer.
Inventors: |
Basol, Bulent M.; (Manhattan
Beach, CA) ; Guo, George Xinsheng; (Palo Alto,
CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
35506545 |
Appl. No.: |
10/877553 |
Filed: |
June 25, 2004 |
Current U.S.
Class: |
451/41 ;
451/530 |
Current CPC
Class: |
B24B 37/245 20130101;
B24B 37/26 20130101 |
Class at
Publication: |
451/041 ;
451/530 |
International
Class: |
B24B 001/00 |
Claims
1. An article for polishing a surface of a semiconductor workpiece,
comprising: a polishing layer having a plurality of protrusions
repeating across the polishing layer, the protrusions including
abrasive particles and being capable of elastically deforming while
polishing the surface of the wafer, wherein the abrasive particles
are dispersed homogeneously across the polishing layer.
2. The article of claim 1, wherein the protrusions have a modulus
of elasticity in the range of 0.5 to 1.5 GPa.
3. The article of claim 1, wherein the protrusions have a yield
point at 5%-50% deformation.
4. The article of claim 1, wherein the polishing layer and the
protrusions are made of the same material.
5. A web including the article of claim 1.
6. A polishing pad including the article of claim 1.
7. The article of claim 1, wherein the plurality of protrusions
includes a majority protrusions and minority protrusions.
8. The article of claim 7, wherein the majority protrusions have a
predetermined height and minority protrusions are taller than the
predetermined height.
9. The article of claim 8, wherein during the polishing of the
surface, the minority protrusions are elastically deformed down to
the predetermined height of the majority protrusions.
10. A method of polishing a surface of a wafer during a process
using a polishing article having a surface including elastic
protrusions containing abrasive particles, comprising: establishing
relative motion between the polishing article and the wafer;
pressing the surface of the wafer on the protrusions such that ends
of the protrusions are elastically deformed, wherein the abrasive
particles are dispersed uniformly across the surface of the
polishing article; and polishing the surface of the wafer.
11. The method of claim 10, wherein the step of pressing includes
applying a pressure about 0.5 psi.
12. The method of claim 10, wherein the process is chemical
mechanical polishing.
13. The method of claim 10, wherein the process is electrochemical
mechanical polishing.
14. The method of claim 10, wherein the process is electrochemical
mechanical deposition.
Description
FIELD
[0001] The present invention generally relates to semiconductor
integrated circuit technology and, more particularly, to an
electrochemical polishing process and apparatus.
BACKGROUND
[0002] Conventional semiconductor devices generally include a
semiconductor substrate, usually a silicon substrate, and a
plurality of sequentially formed dielectric layers and conductive
paths or interconnects made of conductive materials. Interconnects
are usually formed by filling a conductive material in trenches
etched into the dielectric layers. In an integrated circuit,
multiple levels of interconnect networks laterally extend with
respect to the substrate surface. Interconnects formed in different
layers can be electrically connected using vias or contacts.
[0003] The filling of a conductive material into features such as
vias, trenches, pads or contacts, can be carried out by
electrodeposition or electroplating. In electrodeposition method, a
conductive material, such as copper is deposited over the substrate
surface including into such features. Then, a material removal
technique is employed to planarize and remove the excess metal from
the top surface, leaving conductors only in the features or
cavities. Currently, chemical mechanical polishing (CMP) and
electropolishing or electrochemical mechanical polishing (ECMP) are
employed to planarize and remove excess metal layers deposited on
semiconductor wafers.
[0004] Both CMP and ECMP processes involve placing the metal plated
surface of the wafer on a polishing pad and establishing a relative
motion between the surface and the polishing pad to planarize or
remove the metal layer while a polishing solution is supplied to
the polishing pad. For the case of electropolishing or
electrochemical mechanical polishing, an anodic potential is
applied to the metal plated surface of the wafer with respect to an
electrode that makes contact to the polishing solution, which also
wets the surface of the wafer. Both CMP and ECMP methods require
that the wafer be held by a wafer carrier which provides a
controllable load on the wafer surface to press it against the
polishing pad. Alternately, a force may be applied behind the
polishing pad pushing it onto the wafer surface. In general, among
other parameters, the type of the polishing pad used and the force
pressing the wafer against the polishing pad are important
parameters that determine the surface finish and flatness as well
as polishing rate of the polished metal layer. Other important
parameters are polishing solution or slurry, relative speed between
the polishing pad and the wafer, and the applied potential or
polishing current for the electropolishing case.
[0005] Copper removal processes such as CMP traditionally use
polymeric pad materials such as IC-1000.TM. pad supplied by Rodel.
The copper removal solution typically contains abrasive particles
to improve removal rate and surface quality. An alternative way of
chemical mechanical polishing of copper has been recently proposed
and it involves use of a fixed abrasive pad and an-abrasive free or
low-abrasive-content solution. This set of consumables offer better
dishing and erosion behavior on the wafer after the polishing
step.
[0006] Fixed abrasive polishing pads include a polishing surface
having three-dimensional abrasive protrusions. The polishing
surface including the abrasive protrusions are made of a high
modulus composite material, such as a material having a modulus of
elasticity E in the range of 3-6 GPa. The high modulus material is
comprised of hard abrasive particles disposed in a binder material.
Size of the abrasive particles may be in the 0.1-0.5 microns.
Mechanical polishing of a wafer surface is performed by contact
with the abrasive protrusions.
[0007] FIG. 1A illustrates an exemplary portion of a standard fixed
abrasive pad 10. A plurality of abrasive protrusions 12 are formed
on the surface of the fixed abrasive pad 10. The abrasive
protrusions 12 may be shaped as three-dimensional geometrical
shapes such as pyramids, cylinders, hemispheres, etc., and
distributed on the surface to form an array of abrasive protrusions
12. As described before, abrasive protrusions contain small
abrasive particles distributed in a binder material. During the
polishing operation, surface of the wafer first comes into contact
with upper ends 16 of the plurality of abrasive protrusions. In
terms of quality of the final surface finish, it is important that
the upper ends 16 of the abrasive protrusions 14 be in the same
contact plane P.sub.c, so that the upper ends of the abrasive
protrusions contact the wafer surface at the same time and polish
the wafer surface uniformly. The contact plane P.sub.c is an ideal
plane that all the upper ends 16 are expected to meet the wafer
surface at the same time, as the wafer surface is pushed onto the
fixed abrasive pad. As the same polishing pad is repeatedly used
for polishing, the abrasive protrusions begin to uniformly wear
against the conductive wafer surface and their height gets shorter.
FIG. 1B shows as a surface 18 of a wafer 20 is polished by the
abrasive protrusions 12, which are worn after a series of polishing
operations.
[0008] Although an ideal fixed abrasive pad has abrasive
protrusions with perfectly lined up upper ends, in practice fixed
abrasive pads often include some abrasive protrusions which are
taller than the majority of the abrasive protrusions. As
exemplified in FIG. 2A, upper end 16T of a tall abrasive protrusion
12T extends beyond the imaginary contact plane P.sub.c of upper
ends 16R of regular abrasive protrusions 12R that establish the
majority of the abrasive protrusions. Although, tall abrasive
protrusions are defects in the fixed abrasive pads, during a
chemical mechanical polishing process, their height is reduced down
to the height of the regular abrasive protrusions during polishing
of the first few wafers. As illustrated in FIG. 2B, as the surface
18 of the wafer 20 is forced against the abrasive protrusions 12T,
12R, with the downward pressure applied by a wafer carrier (not
shown), upper end 16T of the tall abrasive protrusion is eroded
down. During a CMP process, typically a process pressure of more
than 1 psi is necessary. With a force at this level, height of the
tall abrasive protrusions can be quickly reduced to the height of
the regular abrasive protrusions during the process of a wafer
without causing excessive scratching on the wafer surface.
Therefore, tall abrasive protrusions do not cause any visible
defects or scratches on the surface of the wafer during a CMP
process. However, the same is not true for an electropolishing
process using the same fixed abrasive pad at very low pressure
levels.
[0009] As exemplified in FIG. 2C, owing to the combined affect of
high modulus of the abrasive features and the low downward pressure
(<0.5 psi) applied to the wafer 20 during the electropolishing
or electrochemical mechanical polishing, the height of the tall
abrasive protrusion 12T cannot be quickly reduced. Doted line 21 in
the protrusion 12T shows where the tip of the protrusion is
supposed to be located. Even after processing a number of wafers,
the tall abrasive protrusions touch the surface 18 at specific
locations causing high local pressure application on the surface at
those locations and causing scratching. This is because such fixed
abrasive pads are manufactured to be utilized at relatively high
pressures commonly used in CMP processes. During electropolishing,
generally, a low downward pressure, such as a pressure of less than
0.5 psi is used. With a force at this level, the tall abrasive
protrusions may scratch as many as 20 to 50 wafers before their
height can be reduced to the height level of regular abrasive
protrusions. In addition, some of the high modulus materials used
in the standard fixed abrasive pads are fragile and brittle and may
break off upon impact instead of worn down uniformly. The pieces of
materials falling off may then cause further surface scratches
during a low force ECMP process.
[0010] To this end, there is need for high performance abrasive
polishing pads that can be safely used in the electropolishing
technology field.
SUMMARY
[0011] Present invention provides a high elasticity fixed abrasive
pad for polishing a surface of a semiconductor workpiece. The fixed
abrasive pad includes a polishing layer having a plurality of
protrusions repeating across the polishing layer. The protrusions
include abrasive particles and being capable of elastically
deforming while polishing the surface of the wafer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1A is a schematic side view of a prior art fixed
abrasive polishing pad;
[0013] FIG. 1B is a schematic side view of the prior art fixed
abrasive polishing pad in use while polishing a wafer;
[0014] FIGS. 2A-2B are schematic side views of a prior art fixed
abrasive polishing pad having a defective protrusion;
[0015] FIG. 3 is a schematic illustration of an electropolishing
system employing polishing article of the present invention;
[0016] FIG. 4 is a schematic side view of the fixed abrasive
polishing pad of the present invention;
[0017] FIGS. 5A-5B are schematic side views of a fixed abrasive pad
of the present invention with an exemplary tall protrusion and its
elastic deformation at the top; and
[0018] FIGS. 6A-6B are schematic side views of a fixed abrasive
protrusion and its elastic deformation and stretch.
DETAILED DESCRIPTION
[0019] The present invention provides a high elasticity fixed
abrasive pad for electrochemical mechanical polishing or
planarization of conductive surfaces. The high elasticity fixed
abrasive pad is a fault tolerant polishing pad so that any tall
abrasive protrusions on the high elasticity fixed abrasive pad of
the present invention elastically comply with the conductive
surface of the wafer that is pushed against the high elasticity
fixed abrasive pad. As the conductive surface is pressed against
the polishing surface including tall abrasive protrusions, upper
ends of the abrasive protrusions are bent and level with the
contact plane of the high elasticity fixed abrasive pad allowing
scratch-free processing even for the first wafer that is processed
with a new pad.
[0020] Reference will now be made to the drawings wherein like
numerals refer to like parts throughout. FIG. 3 shows an
electrochemical mechanical processing system (ECMPR) 100 using a
high elasticity fixed abrasive pad 102 having abrasive protrusions
104. The high elasticity fixed abrasive pad 102 of the present
invention will be referred to as the pad hereinafter. A wafer 106
having a surface 108 is held by a wafer carrier 110 which can
rotate and move the wafer laterally or vertically. The surface of
the wafer includes a conductive layer, preferably a copper layer,
to be electropolished by the system 100. A process solution 112,
such as an electropolishing solution, is delivered between the pad
and the surface of the wafer. The process solution can be delivered
onto the pad 102 from a supply line (not shown) or through openings
112 in the pad 102. Openings 112 may also allow electric field to
reach the surface 108 which is connected to a power supply 114. An
electrode 116 of the system 100 is also connected to the power
supply 114. The electrode, which is cathode for electropolishing,
may be placed in proximity of the pad or placed right under the pad
to support it. If the pad is directly mounted on the electrode, the
solution may be directly supplied to the top of the pad.
Alternately, the pad may be mounted on and supported by a porous
support plate through which the solution may flow to the pad and
flows through the openings of the pad to its top surface. The
support plate may be made of any material that has resistance to
the chemical environment of the system such as a hard polymer,
stainless steel, etc. The electropolishing pad may move with the
support plate, or a relative motion may be established between the
pad and the support plate using a moving mechanism. In the latter
case, the pad may be shaped as a belt pad.
[0021] There are several patents and patent applications describing
the electropolishing process carried out with the assistance of the
mechanical action provided by a pad or WSID. Details of such
processes are given in the following patents and patent
applications; U.S. Pat. No. 6,402,925; U.S. patent application Ser.
No. 10/238,665, entitled Method and apparatus for electroplating
and electropolishing, filed Sep. 20, 2002, U.S. patent application
Ser. No. 09/671,800 entitled, Method to minimize/eliminate metal
coating over the top surface of a patterned substrate and layer
structure made thereby, filed Sep. 28, 2000; U.S. patent
application Ser. No. 09/841,622 entitled Electroetching system and
method, filed Apr. 23, 2001; U.S. patent application Ser. No.
10/201,604 entitled, Multi-step electrodeposition process, filed
Jul. 22, 2002; U.S. application Ser. No. 10/238,665, entitled
Method and apparatus for electroplating and electropolishing, filed
Sep. 20, 2002 all commonly owned by the assignee of the present
invention and all incorporated herein by reference.
[0022] As shown in FIG. 4, the high elasticity fixed abrasive pad
of the present invention may include a multiplayer structure. In
this embodiment, an abrasive polishing layer 120 is attached on a
base layer 122. The abrasive polishing layer 120 includes the
abrasive protrusions 104. The polishing layer and hence the
abrasive protrusions are made of abrasive particles dispersed into
a binder matrix, and therefore material forming them is a composite
material. Exemplary, abrasive particles may be ceramic particles
such as ceria, alumina, zircon or the like. Particles may have a
particle size in the range of 50-500 nm. Exemplary, binder
materials may be polymeric materials such as polyester, acrylated
polyesters etc. An exemplary height and width for the pyramidal
shape protrusions may be 100-200 um and 100-500 um, respectively.
In this respect, upper ends 124 of the abrasive protrusions 104 are
ideally leveled across a contact plane P.sub.c, where the surface
of the wafer contacts and is polished uniformly by the abrasive
protrusions 104. The abrasive polishing layer comprises a composite
layer having abrasive particles dispersed in a binder matrix. As
opposed to high modulus fixed abrasive pads used for CMP, the
modulus of elasticity E of the abrasive polishing layer is very
low, in the range of 0.5-1.5 GPa. In this embodiment, abrasive
protrusions have triangular or pointed top shapes in side views.
The protrusions may have any three dimensional shape such as
pyramidal, cubic or the like, and this is within the scope of this
invention.
[0023] The fault tolerant nature of the high elasticity fixed
abrasive pad of the present invention may be seen in FIGS. 5A-5B.
FIG. 5A exemplifies an abrasive polishing layer 104 of the present
invention including tall abrasive protrusions 104T and regular
abrasive protrusions 104R. Upper ends 124R of the regular abrasive
protrusions 104R define the contact plane P.sub.c. The upper end
124T of the tall abrasive protrusion 104T extends beyond the
imaginary contact plane P.sub.c. As shown in FIG. 5B, as the
surface 108 of the wafer applies a pressure less that 0.5 psi onto
the abrasive polishing layer 120, upper ends 124T of the tall
abrasive protrusions 104T flexes and are moved into contact plane
of the regular abrasive protrusions 104R. As the polishing of the
surface continues the upper end of the tall abrasive protrusion
erodes gradually along with the upper ends 124R of the regular
abrasive protrusions 104R without causing any defects such as deep
scratches on the surface 108.
[0024] Additionally, the material of abrasive polishing layer
stretches upon impact of a moving wafer. Stretching occurs within
the plastic deformation limits of the material and thus it is
temporary. Protrusions recover back their original shape once the
impact of the wafer is over. As a result, the abrasive protrusions
would not break and fall off, which situation causes scratching as
is the case for brittle and hard abrasive protrusions. FIG. 6A
illustrates in side view an abrasive protrusion 200 having a
pyramidal shape without any impact that causes stretching. At this
state, a bottom width of the abrasive protrusion is A. FIG. 6B
shows the abrasive protrusion 200 as it is elastically deformed
with application of a force in the direction of arrow I. The arrow
I is represents the impact of wafer surface to the protrusion
during the process. Applied force moves the upper part of the
pyramid with respect to bottom with a distance D. In this respect,
maximum elastic deformation without changing the shape of the
abrasive protrusion may be between 5%-50%. In other words yield
point may be reached beyond 50% deformation.
[0025] Although various preferred embodiments and the best mode
have been described in detail above, those skilled in the art will
readily appreciate that many modifications of the exemplary
embodiment are possible without materially departing from the novel
teachings and advantages of this invention.
* * * * *