Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1997-07-23
2004-02-17
Rose, Robert A. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S446000, C451S060000
Reexamination Certificate
active
06692338
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to drainage of slurry from a polishing pad employed in chemical mechanical polishing. More particularly, the present invention relates to through-pad drainage of slurry from a chemical mechanical polishing pad.
Chemical mechanical polishing (sometimes referred to as “CMP”) typically involves mounting a semiconductor wafer faced down 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.
Slurry flow during chemical mechanical polishing of IC device silicon wafers can play an important role in uniformity of removal of material from the wafer surface. With exposure time to the wafer surface, the slurry's chemistry becomes neutralized and its abrasive particles are altered—being either agglomerated or broken apart. The slurry also becomes loaded with by-products, which are either in solution or suspended particles. All of these factors reduce the effectiveness of the slurry with exposure time.
On a rotary or a linear polisher, wafers move over the moving pad surface. Slurry is provided directly to the polishing pad surface from a source disposed above the pad. Therefore, the slurry is exposed to the edge of a wafer first, and the center of the wafer always sees “old” slurry. On an orbital polisher with through-the-pad slurry injection, the slurry flow is generally out toward the edges of the wafer, as governed by centripetal forces and slurry pressure distribution. Depending on injection hole distribution, the dwell time (the length of time the slurry spends on the pad's polishing surface) will vary. The edge of the wafer will see fresh slurry from nearby injection points plus “older” slurry injected near the wafer center. It should be noted that all by-products must flow past the wafer edge to exit the wafer-pad interface.
The quality and effectiveness of chemical mechanical planarization is a function of several factors including slurry application rate, distribution of slurry flow across the polishing pad, the dwell time of slurry on the polishing surface, and the slurry drain rate from the polishing surface. In conventional CMP, some of these parameters may be controlled with some degree of certainty. However, others such as the slurry flow across the pad and the slurry drain rate from the pad are not subject to any fine level of control.
FIG. 1A
shows some major components of a chemical mechanical polishing (CMP) apparatus such as an Avantgaard
676
, commercially available from Integrated Processing Equipment Corporation (IPEC) of Phoenix, Arizona. 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. 1A
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. In this configuration, a slurry flow path is defined by the slurry entering through slurry inlet
114
, spreading out through the slurry mesh
106
below the pad backing
104
, entering pad backing holes
118
and exiting through slurry injection holes
120
on the surface of polishing pad
102
. Slurry is distributed on the pad surface by centripetal force, the polishing action, and slurry pressure distribution on the pad
102
.
A CMP pad used in a slurry injection system is typically provided with grooves in its polishing surface for slurry distribution and improved pad-wafer contact. These grooves are of two types, either or both of which may be present on a conventional pad's polishing surface. The smaller of the two groove types, sometimes referred to as “microgrooves,” are typically about 10 mils wide and 10 mils deep. Microgrooves increase the pad roughness and thereby facilitate the polishing process by creating point contacts and providing space for a small amount of slurry at the wafer-pad surface interface during CMP. Larger or “macrogrooves” (also referred to as slurry distribution grooves) increase the amount of slurry that may be applied to the polishing pad surface per unit area, and thereby increase CMP efficiency. Conventional macrogrooves are typically about 50 mils deep by 50 mils wide.
FIG. 1B
shows a top view of a conventional polishing pad
102
, such as used with the slurry injection CMP apparatus shown in FIG.
1
. An example of such a pad is the IC
1000
, commercially available from Rodel Inc., Newark, Delaware. Polishing pads may be made of materials including, for example, urethane, polyurethane, felt, polymer and a filler material. Polishing pad
102
includes macrogrooves (slurry distribution grooves)
130
, which are shown in an X-Y configuration, and microgrooves
132
which oriented diagonally relative to macrogrooves
130
. At various intersections of grooves
130
in the X direction and grooves
130
in the Y direction, slurry injection holes
120
are provided.
FIG. 2A
shows some major components of an alternative chemical mechanical polishing apparatus
200
in which slurry is not injected through the pad to the polishing surface, but is instead applied directly to the polishing surface
212
by a conduit
206
positioned above the pad
220
. An example of such an apparatus is the Avantgaard
472
, commercially available from Integrated Processing Equipment Corporation (IPEC) of Phoenix, Arizona. CMP apparatus
200
includes a wafer carrier
202
, which is designed to secure a wafer
210
during CMP. The carrier
202
is connected to a shaft
204
which moves the carrier
202
towards or away from the polishing pad
220
and rotates and translates the carrier
202
and wafer
220
during polishing.
As shown in
FIG. 2B
, a conventional polishing pad
220
used in this type of CMP system is not typically provided with grooves in its polishing surface for slurry distribution. These pads
220
may have small “microgrooves”
222
, about 10 mils deep and 10 mils wide, to increase the pad roughness and thereby facilitate the polishing process by creating point contacts and providing space for a small amount of slurry at the wafer-pad surface interface during CMP. These pads
220
also do not have a pad backing, but instead are placed on a table or platen
208
. During polishing, the platen
208
rotates or orbits with the pad while the wafer
220
in the carrier
202
rotates and translates.
In both of the conventional CMP systems described above, slurry flow across the polishing surface of the pad is largely governed by centripetal f
LSI Logic Corporation
Rose Robert A.
Veseli Ralph
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