U.S. patent application number 09/795243 was filed with the patent office on 2001-11-08 for polishing pad surface on hollow posts.
Invention is credited to Golzarian, Reza, Koinkar, Vilas N..
Application Number | 20010039175 09/795243 |
Document ID | / |
Family ID | 26881303 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010039175 |
Kind Code |
A1 |
Golzarian, Reza ; et
al. |
November 8, 2001 |
Polishing pad surface on hollow posts
Abstract
A polishing pad comprising: a base from which extends multiple
posts having top surfaces that collectively provide a polishing
surface on the polishing pad, and each of the top surfaces being
recessed with an opening to provide a second cutting edge on the
post, and the opening providing a reservoir for polishing
fluid.
Inventors: |
Golzarian, Reza; (Santa
Clara, CA) ; Koinkar, Vilas N.; (Carlsbad,
CA) |
Correspondence
Address: |
Rodel Holdings, Inc.
Suite 1300
1105 North Market Street
Wilmington
DE
19899
US
|
Family ID: |
26881303 |
Appl. No.: |
09/795243 |
Filed: |
February 28, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60185619 |
Feb 29, 2000 |
|
|
|
Current U.S.
Class: |
451/526 ;
451/527; 451/529; 451/539 |
Current CPC
Class: |
B24B 37/26 20130101 |
Class at
Publication: |
451/526 ;
451/527; 451/529; 451/539 |
International
Class: |
B24D 011/00 |
Claims
What is claimed is:
1. A polishing pad comprising: a base from which multiple posts
extend, the posts having top surfaces that collectively provide a
polishing surface on the polishing pad, a leading first cutting
edge on each of the posts, and each of the top surfaces being
recessed to provide a second cutting edge on each of the posts.
2. A polishing pad as recited in claim 1 wherein each of the top
surfaces is recessed by an opening providing a reservoir for
polishing fluid. A polishing pad comprising: a base from which
extends multiple posts having top surfaces that collectively
provide a polishing surface on the polishing pad, and each of the
top surfaces being recessed to provide a reservoir for polishing
fluid.
3. The polishing pad of claim 1 wherein the post has an annular
cross-sectional shape.
4. The polishing pad of claim 1 wherein the top surface is inclined
with respect to the base surface.
5. A polishing pad comprising: a base from which extends multiple
posts having top surfaces that collectively provide a polishing
surface on the polishing pad, a leading first cutting edge on each
of the posts, and each of the top surfaces being recessed to
provide a second cutting edge on each of the posts.
6. A polishing pad as recited in claim 5 wherein, each of the top
surfaces is recessed to provide an opening providing a reservoir
for polishing fluid.
7. A polishing pad comprising: a base from which extends multiple
posts having top surfaces that collectively provide a polishing
surface on the polishing pad, and each of the top surfaces being
recessed to provide a reservoir for polishing fluid.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of provisional
application Ser. No. 60/185,619 filed Feb. 29, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a polishing pad for polishing a
semiconductor substrate, in which the pad has raised posts that
provide a polishing surface.
[0004] 2. Discussion of Related Art
[0005] Polishing of a semiconductor substrate is further known as,
polishing by chemical mechanical polishing or chemical mechanical
planarization, CMP. Such polishing by CMP removes a layer of metal
from an underlying barrier film of metal, and further removes the
barrier film from an underlying dielectric layer on the
semiconductor substrate, which leaves a smooth, planar polished
surface on the dielectric layer serving as a substrate on which
successive layers of material are fabricated, and further which
leaves electrical circuit interconnects of precise dimensions,
which interconnects are imbedded in trenches that are flush with
the polished surface.
[0006] A known polishing pad, includes multiple posts extending
upwardly from a base surface on the pad. Each of the posts has a
top surface, which top surfaces collectively provide a polishing
surface for the polishing pad. FIG. 1 discloses two of such posts 4
extending from a base surface 6 on a polishing pad. The posts 4 are
made from a polishing medium that includes abrasive particles in a
solid phase suspension medium. Such a pad having abrasive particles
is also known as a fixed abrasive pad. The posts 4 have top
surfaces 8 that collectively form the polishing surface on the
polishing pad. The polishing surface has a topography of peaks, as
provided by the projecting posts 4, and valleys formed by spaces
among the posts 4. The topography transports and distributes
polishing liquid or polishing fluid along the surface of a wafer
which is being polished. A disadvantage of the invention is that
the topography provides a single cutting edge on each post, which
limits the rate at which material is removed from the semiconductor
substrate by each post. A further disadvantage is that the
polishing topography of the known posts is inefficient to
distribute polishing fluid Otherwise, frictional forces between the
wafer and the polishing pad become excessively high. The topography
is periodically renewed by a process of conditioning wherein a
conditioning abrasive is passed across the topography by sweeping
motions, which trims away worn portions of the posts, and trims the
posts of uneven heights to a level, common height.
SUMMARY OF THE INVENTION
[0007] The invention provides a post with a second cutting edge
that serves to increase the polishing rate, which is the rate at
which material is being removed by each post. Further, the
invention provides a post that is recessed to provide an opening,
the opening providing a reservoir for polishing fluid. The opening
provides a second cutting edge on the post.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention will now be described by way of example with
reference to the accompanying drawings wherein:
[0009] FIG. 1 is an isometric view of part of a polishing pad
having posts;
[0010] FIG. 2 is an isometric view of part of a polishing pad and a
post according to the invention;
[0011] FIG. 3 is a cross section the post shown in FIG. 2;
[0012] FIG. 4 is an isometric view of another embodiment of part of
a polishing pad and a post; and
[0013] FIG. 5 is a section view of another embodiment of part of a
polishing pad and post.
DETAILED DESCRIPTION
[0014] A fixed abrasive polishing pad 1 comprises a polishing
medium including a plurality of finely divided abrasive particles
which are fixedly dispersed in a suspension medium. Suitable
materials for use as a suspension medium include, but are not
limited to, urethanes and acrylates, as disclosed in U.S. Pat. No.
5,250,085, hereby incorporated by reference herein. The abrasive
particles are small, hard particles which are capable of abrading
the surface of a semiconductor wafer. Suitable materials for the
abrasive particles include, but are not limited to, aluminum
oxides, silicon oxides, cerium oxides, carbides and industrial
diamonds.
[0015] The polishing medium of the fixed abrasive polishing pad 1
has an external surface which defines a plurality of posts 10, only
one of which is shown in FIGS. 2 and 3. Each of the posts 10 has a
top surface 12 which is at a height of approximately 40 microns
above a base surface 26 of the polishing pad. The top surface of
each post is approximately 200 microns across the largest
dimension. For example, each of the posts 10 has a cylindrical
outer wall 14 with a diameter of approximately 200 microns. The
posts 10 are spaced apart from one another by approximately 200
microns.
[0016] According to one embodiment of the invention, each post 10
has an opening 16 provided by a recess that extends through the top
surface 12 to a depth of approximately 30 microns below the top
surface as shown in FIG. 2. The opening 16 is bounded by a
cylindrical continuous inner wall 18. The cylindrical outer and
inner walls 14, 18, are one within the other, and define
therebetween a cross section of the post 10 around the recess and
the opening 16.
[0017] Although the outer and inner walls 14, 18 are preferably
cylindrical, it should be recognized that each of the outer and
inner walls may have some other shape such as square, triangular,
or other regular or irregular polygon shape.
[0018] The top surfaces 12 of the posts 10 define a polishing
surface for the fixed abrasive polishing pad 1. Diameter D1 of the
inner wall 18 and diameter D2 of the outer wall 14 can be selected
during manufacture, in conjunction with the population density of
the posts 10, to provide a desired surface area for the polishing
surface of the polishing pad. Preferably, the size and population
density of the posts is such that the top surfaces 12 have a
surface area which is between about 10 percent to 40 percent, more
preferably about 25 percent, of the available surface area of the
polishing pad 1.
[0019] During a polishing operation, a semiconductor wafer is urged
into contact with the polishing surface of the polishing pad 1 and
is swept by the polishing surface due to relative lateral motion
between the wafer and the polishing pad. Assuming relative motion
of the wafer in the direction of arrow 20 in FIG. 2, each post 10
has a first cutting edge 22 that is continuous along the top of its
exterior wall 14, which makes first contact with a portion of the
wafer as it sweeps over the post 10, or is moved relative to the
post 10. Each post 10 has a second cutting edge 24 that is
continuous along the top of the inner wall 13, which makes second
contact with a portion of the wafer that passes over the opening
16. The second cutting edge 24 is continuous along the edge of the
opening 16. No matter whether the motion of the pad 1 is rotating,
orbital or linear, the second cutting edge 24 increases the cutting
action or polishing activity of the pad 1.
[0020] As shown in FIG. 4, another embodiment of a post 30
according to the invention has an opening 32 in a top surface 34
providing a second cutting edge 24. The top surface 34 is inclined
at an angle .theta. with respect to a base surface 36 of the
polishing pad 1 from which each post 10 projects. The angle .theta.
is preferably within a range of 0.degree. to about 10.degree.. The
inclined top surfaces 34 of multiple posts 30 are preferably
inclined in the same direction.
[0021] FIG. 5 discloses an embodiment in which the opening 16 in
each recessed post 42 provides a reservoir for polishing fluid.
Flow of the polishing fluid to and from the reservoir is provided
by providing horizontal, fluid conveying channels 48, one shown, in
a bottom surface of a first layer 46 of the pad 1. The channels 48
are covered by a bottom layer 52 of the pad 1 that forms a subpad.
Holes 50, one shown, in the base surface 26 extend in the top layer
46, and communicate with respective channels 48. Each reservoir
opens into at least one of the respective channels 48, to enhance a
flow of polishing fluid to and from the reservoir, and along
corresponding channels 48, and along corresponding holes 50, which
replenishes the reservoir with polishing fluid, and which enhances
distribution of the polishing fluid over the polishing surface of
the post 42 during polishing.
[0022] According to another feature of the invention each opening
16, 32 provided by a corresponding recess serves as a reservoir for
polishing fluid that is dispensed during a polishing operation in a
known manner, for example, as described by U.S. Pat. No. 5,664,990.
The reservoirs distribute polishing fluid adjacent to the
corresponding second cutting edge 24. Polishing uniformity on a
wafer is controlled by selecting the openings 16, 32 to provide a
selected ratio of, or dimensional difference between, the
dimensions of the inner and outer walls, for example, as shown in
FIG. 3 by dimensions D1 and D2. Polishing uniformity is further
controlled by the population density of the posts 10, 30, 42. The
provision of a second cutting edge on each of the posts 10,30, 42
increases material removal, and enhances material removal uniformly
by all areas of the pad 1, while minimizing scratches and uneven
material removal. Furthermore, as the posts 10, 30, 42 wear down
during polishing, the structure will change from partially hollow
to solid, which is an indication to the user that the polishing pad
should be replaced.
[0023] Thus, the invention provides a post 10, 30, 42 with a second
cutting edge 24 that serves to increase the polishing rate, and
uniformity of material removal, as compared to a post 10, 30, 42
that has a single cutting edge 22.
[0024] Thus, the invention provides a corresponding post 10, 30, 42
that is recessed to provide an opening 16, 32 that, in turn,
provides a reservoir for polishing fluid. The opening 16, 32
further provides the second cutting edge 24.
[0025] In each embodiment of a post 10, 30, 42, the recess
providing a corresponding opening 16, 32 is made by a process of
machining, including, for example, but not limited to, boring,
punching, embossing or milling. Alternatively, the opening 16, 32
is made by the same process that makes the post 10, 30, 42,
including, for example, but not limited to, injection molding
fluent material, sintering powdered material in a binder, casting
fluent material, and brazing material onto the corresponding base
surface 26, 36. The invention in the embodiments described above
provides a fixed abrasive polishing pad 1 having partially hollow
posts 10, 30.
[0026] Embodiments of the invention having been described, other
embodiments and modifications of the invention are intended to be
covered by the spirit and scope of the appended claims.
* * * * *