Abrading – Machine – Rotary tool
Reexamination Certificate
1997-10-01
2001-05-22
Hail, III, Joseph J. (Department: 3723)
Abrading
Machine
Rotary tool
C451S443000
Reexamination Certificate
active
06234883
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to conditioning of a polishing pad employed in chemical mechanical polishing (CMP). More particularly, the present invention relates to an apparatus and method for concurrent pad conditioning and wafer buffing in a CMP tool.
Chemical mechanical polishing (sometimes referred to as “CMP”) typically involves mounting a semiconductor wafer on a holder and rotating the wafer face against a polishing pad mounted on a platen, which in turn is rotating or moving linearly or orbitally. A slurry containing a chemical that chemically interacts with the facing wafer layer and an abrasive that physically removes that layer is flowed between the wafer and the polishing pad or on the pad near the wafer. In integrated circuit (IC) wafer fabrication, this technique is commonly applied to planarize various wafer layers such as dielectric layers, metallization layers, etc.
FIG. 1
shows some major components of a chemical mechanical polishing (CMP) apparatus. Examples of such apparatuses include the AvantGaard 676 or 776, commercially available from Integrated Processing Equipment Corporation (IPEC) of Phoenix, Arizona, and described in IPEC Bulletins #4500-104621 and #4500-104660 (1997), which are incorporated herein by reference for all purposes. CMP apparatus
100
includes a wafer carrier
128
that is fitted with an air chamber
126
(shown in phantom lines), which is designed to secure a wafer
124
by vacuum to wafer carrier
128
during wafer loading typically before CMP is to commence. During CMP, however, wafer
124
is bound by “wear rings” (not shown to simplify illustration) within wafer carrier
128
such that a wafer surface that is to be polished contacts a polishing pad
102
. During CMP, the polishing pad
102
orbits while the wafer
124
rotates.
A conventional polishing pad
102
for use with an apparatus such as illustrated in
FIG. 1
includes a plurality of slurry injection holes
120
, and adheres to a flexible pad backing
104
which includes a plurality of pad backing holes
118
aligned with the slurry injection holes
120
. A slurry mesh
106
, typically in the form of a screen-like structure, is positioned below the pad backing
104
. An air bladder
108
capable of inflating or deflating is disposed between a plumbing reservoir
110
and the slurry mesh
106
. The air bladder
108
pressurizes to apply the polishing force. A co-axial shaft
112
, through which a slurry inlet
114
(shown by phantom lines) is provided to deliver slurry through the plumbing reservoir
110
and the air bladder
108
to the slurry mesh
106
, is attached to the bottom of plumbing reservoir
110
. Slurry is delivered to the system by an external low pressure pump, and is distributed on the polishing pad surface by centripetal force, the polishing action, and slurry pressure distribution on the pad
102
. The polishing pad
102
may also be provided with grooves or perforations (not shown) for slurry distribution and improved pad-wafer contact.
Unfortunately after polishing on the same polishing pad over a period of time, the polishing pad suffers from “pad glazing.” As is well known in the art, pad glazing results when the particles eroded from the wafer surface along with the abrasives in the slurry tend to glaze or accumulate over the polishing pad. A glazed layer on the polishing pad typically forms atop eroded wafer and slurry particles that are embedded in the porosity or fibers of the polishing pad. Pad glazing is particularly pronounced during planarization of an oxide layer such as silicon dioxide layer (hereinafter referred to as “oxide CMP”). By way of example, during oxide CMP, eroded silicon dioxide particulate residue accumulates along with the abrasive particles from the slurry to form a glaze on the polishing pad. Pad glazing is undesirable because it reduces the polishing rate of the wafer surface and produces a non-uniformly polished wafer surface. The non-uniformity results because glazed layers are often unevenly distributed over a polishing pad surface.
One way of achieving and maintaining a high and stable polishing rate is by conditioning the polishing pad (the process of conditioning a polishing pad is hereinafter referred to as “pad conditioning”) on a regular basis, e.g., either every time after a wafer has been polished or simultaneously during wafer CMP. During pad conditioning, a conditioning arm or an abrasive disk is typically contacted with a polishing pad, which may be rotating or in an orbital state.
FIG. 2A
shows a top view of some significant components of a conditioning sub-assembly
200
, which may be integrated into a CMP apparatus such as the IPEC 676. Conditioning sub-assembly
200
includes a polishing pad
202
and a conditioning arm
204
that is disposed above polishing pad
202
and capable of pivoting about a pivoting point
206
. Conditioning arm
204
, as shown in
FIG. 2A
, is typically longer in length than a diameter of the polishing pad. For illustration purposes,
FIG. 2B
shows a bottom view of conditioning arm
204
of FIG.
2
A. The bottom surface of conditioning arm
204
includes a plurality of diamond abrasive particles
208
, which are substantially uniformly arranged on the conditioning arm such that if conditioning arm
204
contacts polishing pad
202
, abrasive particles
208
engage with a substantial portion of the polishing pad.
Before conditioning sub-assembly
200
of
FIG. 2A
begins conditioning of polishing pad
202
, conditioning arm
204
is lowered automatically to contact a polishing pad
202
, which may be rotating or in orbital state. A pneumatic cylinder (not shown to simplify illustration) may then apply a downward force on conditioning arm
204
such that abrasive particles
208
contact and engage with a substantial portion of polishing pad
202
. During pad conditioning, conditioning arm
204
pivots on pivoting end
206
and sweeps back and forth across polishing pad
202
like a “windshield wiper blade” from a first position
204
′ (shown by dashed lines) at one end of the polishing pad to a second position
204
&Dgr; (shown by dashed lines) at the other end of the polishing pad. This mechanical action of conditioning arm
204
allows abrasive particles
208
to break up and remove the glazed or accumulated particles coated on the polishing pad surface.
At the conclusion of some CMP procedures, a fine polishing, also referred to as buffing, is often performed on the wafer in order to produce the smoothest possible wafer surface. Buffing typically uses a relatively soft pad formed, for example, from polyurethane impregnated felt. An example is the Polytex™ pad available from Rodel Corp. of Newark, Del. Buffing also typically uses deionised water or may be assisted by a conventional oxide slurry.
Unfortunately, currently used pad conditioning and wafer buffing systems reduce the efficiency of CMP operations.
FIG. 3
is a simplified top view of a typical multi-station CMP apparatus, such as the IPEC 676 or 776, described previously. The CMP apparatus
300
has four polishing stations
302
,
304
,
306
and
308
, each with a polishing pad
310
and the other associated features described with reference to
FIG. 1
(not shown in this view to simplify illustration). As shown in
FIG. 3
, the apparatus
300
also includes two conditioning sub-assemblies
320
and
322
, such as described with reference to
FIGS. 2A and 2B
, each of which service two polishing stations. For example, as shown in FIG.
3
, conditioning sub-assembly
320
services polishing stations
302
and
304
. Each conditioning sub-assembly
320
includes a conditioning arm
324
that may be swung out above a polishing pad polishing pad
202
by pivoting about a pivoting point
326
.
With conventional CMP techniques, one of the four stations on the CMP apparatus is typically dedicated to buffing, or a separate buffing station must be provided in addition to the polishing stations. This reduces the number of polishing stations available on the apparatus, or requires
Berman Michael J.
Holland Karey L.
Beyer Weaver & Thomas LLP
Hail III Joseph J.
LSI Logic Corporation
Nguyen Dung Van
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