U.S. patent application number 09/938056 was filed with the patent office on 2003-03-27 for multi-step polishing system and process of using same.
Invention is credited to Jew, Stephen, Li, Youlin J., Ramanujam, K.Y., Srivatsan, Sridharan.
Application Number | 20030060145 09/938056 |
Document ID | / |
Family ID | 25470790 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030060145 |
Kind Code |
A1 |
Li, Youlin J. ; et
al. |
March 27, 2003 |
Multi-step polishing system and process of using same
Abstract
A multi-step polishing system, and a process for polishing a
workpiece using the system. The system includes one or more
polishing stations. The workpiece is polished in the presence of an
oxidizer-free medium, and subsequently, the workpiece is polished
in the presence of an oxidizing medium. This polishing sequence
extends the life of the polishing pads and provides for a more
uniform polish.
Inventors: |
Li, Youlin J.; (Austin,
TX) ; Jew, Stephen; (Santa Clara, CA) ;
Srivatsan, Sridharan; (Sunnyvale, CA) ; Ramanujam,
K.Y.; (Fremont, CA) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60611
US
|
Family ID: |
25470790 |
Appl. No.: |
09/938056 |
Filed: |
August 23, 2001 |
Current U.S.
Class: |
451/66 |
Current CPC
Class: |
B24B 37/044 20130101;
C09G 1/02 20130101 |
Class at
Publication: |
451/66 |
International
Class: |
B24B 007/00 |
Claims
1. A wafer polishing process comprising: polishing a surface of a
wafer in the presence of an oxidizer-free medium; and,
subsequently, polishing the surface of the wafer in the presence of
an oxidizing medium.
2. The wafer polishing process of claim 1, wherein said
oxidizer-free medium comprises an oxidizer-free slurry, and said
oxidizing medium comprises an oxidizing slurry.
3. The wafer polishing process of claim 1, wherein said
oxidizer-free medium comprises an oxidizer-free fluid, and said
oxidizing medium comprises an oxidizing fluid.
4. The wafer polishing process of claim 1, wherein said polishing
in the presence of an oxidizer-free medium and said polishing in
the presence of an oxidizing medium both occur at a first polishing
station.
5. The wafer polishing process of claim 4, further comprising,
transferring said wafer from said first polishing station to a
second polishing station; and polishing said surface of said wafer
in the presence of an oxidizing medium at said second polishing
station.
6. The wafer polishing process of claim 1, wherein said polishing
in the presence of an oxidizer-free medium occurs at a first
polishing station and said polishing in the presence of an
oxidizing medium occurs at a second polishing station.
7. The wafer polishing process of claim 1, wherein said polishing
in the presence of an oxidizer-free medium and said polishing in
the presence of an oxidizing medium both comprise linear
chemical-mechanical polishing.
8. The wafer polishing process of claim 1, wherein said surface
comprises a copper-containing component.
9. The process of claim 8, wherein said oxidizing medium comprises
at least one oxidizer capable of oxidizing at least a portion of
said copper-containing component.
10. A wafer polishing process comprising: supplying an
oxidizer-free medium to a polishing portion of a polishing station;
polishing a surface of a wafer in the presence of said
oxidizer-free medium at said polishing station; discontinuing the
supply of said oxidizer-free medium to the polishing portion;
supplying an oxidizing medium to the polishing portion; and
polishing the surface of the wafer in the presence of said
oxidizing medium at said polishing portion.
11. The wafer polishing process of claim 10, wherein said surface
comprises a copper-containing component.
12. The wafer polishing process of claim 10, wherein said
oxidizer-free medium comprises an oxidizer-free slurry, and said
oxidizing medium comprises an oxidizing slurry.
13. The wafer polishing process of claim 10, wherein said
oxidizer-free medium comprises an oxidizer-free fluid, and said
oxidizing medium comprises an oxidizing fluid.
14. A wafer polishing process comprising: chemically-mechanically
polishing a copper-containing surface of a wafer in the presence of
an oxidizer-free slurry at a first polishing station; transferring
the wafer from said first polishing station to a second polishing
station; and chemically-mechanically polishing the
copper-containing surface of the wafer in the presence of an
oxidizing slurry at said second polishing station.
15. A wafer polishing system comprising: a first
chemical-mechanical polishing station having a polishing portion; a
source of an oxidizer-free medium in communication with said
polishing portion; and a source of an oxidizing medium in
communication with said polishing portion.
16. The wafer polishing system of claim 15, further comprising: a
second polishing station; and a transfer mechanism adapted to move
said wafer from said first polishing station to said second
polishing station.
17. A wafer polishing system comprising: a first polishing station
adapted to polish a surface of a wafer in the presence of an
oxidizer-free medium; a source of an oxidizer-free medium in
communication with said first polishing station; a second polishing
station adapted to polish said surface of said wafer in the
presence of an oxidizing medium; a source of an oxidizing slurry in
communication with said second polishing station; and a transfer
mechanism adapted to move a wafer from said first polishing station
to said second polishing station.
18. The wafer polishing system of claim 17, wherein said source of
oxidizing solution is also in communication with said first
polishing station.
19. The wafer polishing system of claim 17, further comprising: a
second source of an oxidizing medium in communication with said
first polishing station.
20. The wafer polishing station of claim 17, wherein said
oxidizer-free medium comprises an oxidizer-free slurry, and said
oxidizing medium comprises an oxidizing slurry.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the planarization
of semiconductor workpieces, and more particularly, to a multi-step
system and a process for polishing the workpieces using a
oxidizer-free medium at one or more polishing stations.
BACKGROUND
[0002] Many steps in the manufacture of semiconductor devices
produce a highly irregular surface on the front side of the wafer
which contains the semiconductor devices. In order to improve the
manufacturability of the devices on the wafer, many processing
steps require planarizing the wafer surface. For example, to
improve the uniformity of deposition of a metal interconnect layer,
the wafer is planarized prior to deposition to reduce the peaks and
valleys on the surface over which the metal is deposited.
[0003] In conventional planarization technology, a semiconductor
wafer is supported face down against a moving polishing pad. Two
types of polishing or planarizing apparatus are commonly used. In a
rotary planarizing apparatus, a wafer is secured on a chuck and is
brought into contact with a rotating polishing surface such as a
circular disk. The rotating polishing surface may include a fixed
abrasive for contacting and polishing the wafers, and/or a slurry
having abrasives may be placed in contact with the polishing
surface.
[0004] In a second type of planarization apparatus, utilizing
linear planarization technology, an endless belt travels over two
or more rollers. The wafer is placed against the linearly moving
polishing surface of the belt. The belt may have an abrasive
surface, and/or a slurry having abrasive particles may be placed in
contact with the polishing belt. An example of such a system is the
Teres.TM. CMP System manufactured by Lam Research Corporation,
Fremont, Calif., aspects of which are disclosed in U.S. Pat. Nos.
5,692,947, 5,762,536, and 5,871,390, and in commonly assigned
co-pending U.S. application Ser. No. 08/968,333, entitled "Method
and Apparatus for Polishing Semiconductor Wafers," filed Nov. 12,
1997.
[0005] Many metallic materials are used to form the components of
the semiconductor device. Because copper has high electrical
conductivity and low electromigration suspectibility, copper
metals, copper compounds, and copper metal-alloys are particularly
well suited for forming integrated circuits on semiconductor
wafers. As with any material used in semiconductor wafer
fabrication, one important factor in forming narrow and precise
components from a copper containing layer is the ability to begin
the processing steps with a copper substance layer made uniform
through the use of planarization.
[0006] One previous process for copper-containing surface
planarization utilized a multi-step, multi-slurry approach. In the
first step, large amounts of copper are removed in bulk, leaving a
thin, relatively planar copper layer for the second step. In the
second step, the copper is further planarized to leave a continuous
barrier layer with minimal topography. In both the first step and
the second step, an oxidizing slurry is used in conjunction with a
polishing pad in order to soften the copper by first oxidizing the
copper to copper oxide so that it can be more easily removed. In a
final step, a rotary buffer is used to completely remove the
barrier layer and leave clean, corrosion free copper and oxide
surfaces.
[0007] It is important to have a stable, repeatable process so that
a timed polish can be used. Bulk copper polishing removal rate
stability is affected by a phenomenon known as pad loading. In
standard oxide polishing, the removal rate stability is commonly
affected by the polishing pad groove integrity. The removal rate
stability tends to diminish as the grooves are worn down during the
act of polishing and conditioning. In copper oxide polishing,
however, the rate stability can deteriorate before the degradation
of the pad grooves. The pad tends to load with a residue that
reduces the ability of the pad to continue removing the copper
oxide uniformly from the surface of the wafer. Various in-situ
process changes, such as distilled water rinsing or chemical
rinsing have been somewhat effective to combat the residue
build-up, but are impractical in large-scale fabrication processes.
Furthermore, the frequent changing of a loaded pad is an
unattractive option not only because of the expense of the pad, but
also because of the down time to the fabrication equipment.
[0008] Accordingly, there is a need for an improved polishing
process that prevents the build-up of residue in the polishing pad,
thereby achieving a stable, repeatable planarization process.
SUMMARY
[0009] In one aspect of the invention, a wafer polishing process
includes polishing a surface of a wafer in the presence of an
oxidizer-free medium; and, subsequently, polishing the surface of
the wafer in the presence of an oxidizing medium.
[0010] Other aspects of the invention will be apparent to those
skilled in the art in view of the claims following the detailed
description below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a top schematic view of a system according to one
embodiment of the present invention.
[0012] FIG. 2 is a exploded perspective view of a portion of the
system of FIG. 1.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0013] The wafer polishing systems according to the present
invention include one or more polishing stations. At one of the
stations, a workpiece to be processed, such as a semiconductor
wafer, is polished in the presence of an oxidizer-free medium.
Then, subsequent to the oxidizer-free polishing, the wafer is
polished with an oxidizing medium. The oxidizing polishing may
occur at the same station or at a different station as the
oxidizer-free polishing. This sequence of polishing helps to
prevent the build-up of residues in the polishing pads, which not
only extends the life of the polishing pads, but also provides a
more stable, uniform, and repeatable polishing process.
[0014] Referring now to FIGS. 1 and 2, a wafer polishing system
according to one embodiment of the invention is shown generally at
10. The system 10 includes a first polishing station 20, a second
polishing station 30, and a third polishing station 40. In the
embodiment shown, the first polishing station 20 and the second
polishing station 30 are each linear chemical-mechanical polishers,
and the third polishing station 40 is a rotary chemical-mechanical
polisher, such as a rotary buffer. A transfer mechanism 50 is
adapted to move a workpiece, such as a wafer 60, successively from
one station to the next. The system 10 shown in FIG. 1 is modeled
generally on the Teres.TM. CMP System manufactured by Lam Research
Corporation, Fremont, Calif., aspects of which are disclosed in
U.S. Pat. Nos. 5,692,947, 5,762,536, and 5,871,390, and in commonly
assigned U.S. application Ser. No. 08/968,333, entitled "Method and
Apparatus for Polishing Semiconductor Wafers," filed Nov. 12, 1997,
all of which are incorporated by reference in their entireties.
Those skilled in the art will appreciate that other polishing
systems having one or more polishing stations may also be adapted
in accordance with the present invention. For example, rotary
polishing systems may be adapted in accordance with the present
invention.
[0015] As shown in FIG. 2, the first polishing station 20 includes
a workpiece holder 22, a polishing pad 24, and an inlet 26. The
workpiece holder 22 secures a workpiece, such as a wafer, in a
polishing portion 21 of the polishing station 20 defined generally
by an area adjacent both the polishing pad 24 and the workpiece
holder 22. The polishing station 20 is in communication via a
delivery system 70 with a source 62 of an oxidizer-free medium, and
with a source 64 of an oxidizing medium. The second polishing
station 30 includes a workpiece holder 32, a polishing pad 34, and
an inlet 36. The workpiece holder 32 secures a workpiece, such as a
wafer, in a polishing portion 31 of the polishing station 30
defined generally by an area adjacent both the polishing pad 34 and
the workpiece holder 32. The polishing station 30 is in
communication via a delivery system 70 with the source 62 of
oxidizer-free medium and the source 64 of an oxidizing medium. The
third polishing station 40 includes a workpiece holder 42 and a
rotary pad 44.
[0016] The delivery system 70 is adapted to deliver the
oxidizer-free medium and the oxidizing medium to the polishing
stations 20, 30. In a preferred delivery system shown in FIG. 2,
the delivery system 70 delivers either of the oxidizer or
oxidizer-free media to either of the inlets 26, 36. The media may
then be carried by the polishing pads 24, 34 to their respective
polishing portions 21, 31. The delivery system 70 includes lines
71, such as conventional piping, a shut-off valve 72 for source 62,
a shut-off valve 74 for source 64, and a pair of three-way valves
76, 78. By manipulating the valves 72, 74, 76, 78, either the
oxidizer-free medium or the oxidizing medium may be delivered to
either of the inlets 26, 36, of the polishing stations 20, 30.
Those skilled in the art will appreciate that other combinations of
medium sources and delivery systems may readily be used in
conjunction with the present invention. For example, each polishing
station may have its own separate pair of media sources. In another
example, each station may have separate inlets for the oxidizing
and oxidizer-free media, respectively.
[0017] In a process in accordance with the present invention, the
transfer mechanism 50 first places a workpiece, such as a wafer,
from a workpiece storage position 52 (FIG. 2) to a first position
54. As more thoroughly described in U.S. application Ser. No.
08/968,333, the transfer mechanism 50 and the workpiece holder 22
interact to position a surface of the workpiece in the polishing
portion 21 of the first polishing station 20. A oxidizer-free
medium is then supplied to the polishing portion 21 via the
delivery system 70 and the inlet 26. The surface of the workpiece
is then polished at the first polishing station 20 in the presence
of an oxidizer-free medium. Next, in one embodiment of the
invention, the supply of oxidizer-free medium is discontinued, and
an oxidizing medium is supplied to the polishing portion 21 via the
delivery system 70 and the inlet 26. The surface of the workpiece
is then polished in the presence of the oxidizing medium.
[0018] In an alternate embodiment, after the polishing in the
presence of an oxidizer free medium at the first polishing station
20, the transfer mechanism 50 transfers the workpiece to a second
polishing position, and the transfer mechanism 50 and the workpiece
holder 32 cooperate to position a surface of the workpiece in the
polishing portion 31 of the polishing station 30. The surface of
the workpiece is then polished at the second polishing station 30
in the presence of an oxidizing medium supplied from the source 38
via delivery system 70 and the inlet 36.
[0019] The transfer mechanism 50 then moves the workpiece to a
third position 58, and the workpiece holder 42 and the transfer
mechanism 50 cooperate to position a surface of the workpiece
adjacent a surface of the polishing pad 44. The surface of the
workpiece is then polished at the third polishing station 40.
[0020] Other system arrangements and sequences may also be useful
in the practice of the present invention. For example, a system may
have multiple polishing stations using an oxidizer-free medium
before the workpiece is transferred to a polishing station using an
oxidizing medium. In another example, an oxidizing medium may be
used at multiple polishing stations that are subsequent to at least
one polishing station which uses an oxidizer-free medium. In other
examples, the media are used at a polishing station having a rotary
polisher rather than a linear polisher. In all such embodiments
according to the present invention, a workpiece is polished on at
least one polishing station using an oxidizing-free medium before
it is polished at the first of the polishing stations that uses an
oxidizing medium.
[0021] In the preferred embodiment of the invention, the workpiece
is a semiconductor wafer, and the surface to be polished has a
metallic component. In an especially preferred embodiment of the
invention, the surface to be polished includes copper-containing
components, such as copper metals, copper compounds or copper metal
alloys. In other embodiments of the invention, the surface to be
polished is aluminum, tungsten, tungsten silicide, titanium
nitride, tantalum, or other materials capable of undergoing
oxidation and that are commonly used in semiconductors.
[0022] As used herein, the term "oxidizer-free medium" means a
medium that contains no components in a concentration sufficient to
substantially raise the oxidation state of the target surface
material to be polished. Conversely, the term "oxidizing medium"
means a medium than contains at least one component in a
concentration sufficient to substantially raise the oxidation state
of the target surface material to be polished. The classification
of a medium thus will be dependent upon the identity of the surface
being polished.
[0023] Oxidizing agents and oxidizing medium are well-known in the
semiconductor processing art. For example, common oxidizing agents
for copper containing surfaces include nitric acid, potassium
permanganate, hypochlorous acid, acetic acid, sulfuric acid, silver
nitrate, copper sulfate, and copper perchlorate. Common oxidizing
agents for tungsten surfaces include potassium ferricyanide,
potassium dichromate, potassium iodate, potassium bromate, vanadium
trioxide, cerium nitrate, and ferrous nitrate. Common oxidizing
agents generally include those that have peroxoy groups, such as
hydrogen peroxide, organic peroxides such as benzyl peroxide,
peracetic acid, di-t-butyl peroxide, monopersulfates,
dipersulfates, and sodium peroxide; and compounds containing
elements in their highest oxidation state, such periodic acid,
periodate salts, perbromic acid, perbromate salts, perchloric acid,
perchloric salts, perboric acid, and perborate salts and
permanganates; bromates, chlorates, chromates, iodates, iodic acid,
and cerium (IV) compounds, such as ammonium cerium nitrate.
[0024] Both the oxidizing media and the oxidizer-free media are
preferably slurries having abrasive particles. In an alternate
embodiment, the media are fluids without abrasive particles. In
this alternate embodiment, it is preferred to use polishing pads
that have fixed abrasives. Examples of suitable pads having fixed
abrasives are disclosed in U.S. application Ser. No. 09/540,810,
entitled "Fixed Abrasive Linear Polishing Belt and System," filed
on Mar. 31, 2000, which is incorporated herein by reference. In
other embodiments, the polishing may proceed without the use of any
abrasives.
[0025] Those skilled in the art will recognize abrasive components
useful with the present invention. Preferred abrasive components
include alumina, silica, ceria, and iron oxide. In the embodiments
where abrasive slurries are used, the slurries are preferably about
1 wt % to about 25 wt % abrasive material, more preferably about 2
to 15 wt % abrasive material, and more preferably about 5 wt %
abrasive material. Preferred abrasives will have a hardness of
about Mohs 5 to Mohs 6, and a particle size of about 0.01 microns
to about 0.5 microns, and more preferably, about 0.05 microns to
about 0.3 microns.
[0026] The media of the present invention may optionally contain a
film-forming agent. Common film-forming agents include
benzotriazole, urea, thiourea, and cyclic compounds, such as
imidazole, benzimidazole, benzothiazole and their derivatives. The
film-forming agent is preferably present at about 0.01 wt % to 1.0
wt % of the medium, and more preferably, at about 0.01 to 0.2 wt
%.
[0027] Numerous other additives may be included in both the
oxidizing and oxidizer-free media, including complexing or
chelating agents (such as glycine), surfactants (such as dodecyl
sulfate sodium salt, sodium lauryl sulfate, or dodecyl sulfate
ammonium sulfate), and complexing agents to disturb the passivation
layer (such as citric, lactic, tartaric, succinic, acetic, or
oxalic acids).
[0028] In a preferred embodiment of the invention, an oxidizer-free
slurry includes about 3 to about 25 wt %, and more particularly,
about 8 to about 15 wt % of an abrasive, such as alumina; about
0.5. to 2 wt %, and more particularly, about a 1 wt % of a
complexing or chelating agent, such as glycine; about 0.01 to about
1.0 wt %, and more particularly, about 0.05 wt % of a film-forming
agent, such as benzotriazole; and about 78 to about 96 wt %, and
more particularly, about 88 to about 92 wt % of a solvent, such as
water or an alcohol. In a particularly preferred embodiment of the
invention, the oxidizer-free medium is Cabot EPC 5001, sold by
Cabot Microelectronics of Aurora, Ill. In a preferred embodiment,
the oxidizing slurry has the same composition as the oxidizing-free
slurry, except that it also includes about 1 to about 10 wt %, and
more particularly, about 3 wt % of an oxidizing agent, such as
hydrogen peroxide.
[0029] Suitable polishing pads for use with the present invention
are those typically used in the art for chemical-mechanical
polishing. Suitable rotary pads include the Rodel Embossed Politex
sold by Rodel Corporation of Phoenix, Ariz. Suitable linear
polishing pads include IC-1000, also sold by Rodel, as well as
those disclosed in U.S. application Ser. No. 09/386,741, entitled
"Unsupported Chemical Mechanical Polishing Belt," filed Aug. 31,
1999, and in U.S. application Ser. No. 09/540,810, entitled "Fixed
Abrasive Linear Polishing Belt and System," filed on Mar. 31, 2000,
both of which are incorporated herein by reference. Suitable
addition rates for both the oxidizer-free and oxidizing media are
about 500 ml/min, and more preferably, about 50 to about 200
ml/min.
[0030] It should be readily understood by those persons skilled in
the art that the present invention is susceptible of a broad
utility and application. Many embodiments and adaptations of the
present invention other than those herein described, as well as
many variations, modifications and equivalent arrangements will be
apparent from or reasonably suggested by the present invention and
the foregoing description thereof, without departing from the
substance or scope of the present invention.
[0031] Accordingly, while the present invention has been described
herein in detail in relation to several embodiments, it is to be
understood that this disclosure is only illustrative and exemplary
of the present invention and is made merely for purposes of
providing a full and enabling disclosure of the invention. The
foregoing disclosure is not intended or to be construed to limit
the present invention or otherwise to exclude any such other
embodiments, adaptations, variations, modifications and equivalent
arrangements, the present invention being limited only by the
claims appended hereto and the equivalents thereof.
* * * * *