Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-06-26
2003-05-06
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S036000, C451S285000, C451S307000, C451S530000
Reexamination Certificate
active
06558236
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of Invention
The embodiments of the present invention generally relate to a method and apparatus polishing a substrate in a chemical mechanical polishing system.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to increase device density on a semiconductor workpiece, or substrate, such as a wafer. Chemical mechanical planarization systems generally utilize a polishing head to retain and press a substrate against a polishing material while providing motion therebetween. Some planarization systems utilize a polishing head that is moved over a stationary platen that supports the polishing material. Other systems utilize other motions, for example, providing a rotating platen. A polishing fluid is typically disposed between the substrate and the polishing material during polishing to provide chemical activity that assists in the removal of material from the substrate. Some polishing fluids also contain abrasives.
One type of polishing material that may be utilized for chemical mechanical polishing is known as fixed abrasive polishing material. Fixed abrasive polishing material generally comprises a plurality of abrasive particles suspended in a resin binder that is disposed in discrete elements on a backing sheet. As the abrasive particles are contained in the polishing material itself, systems utilizing fixed abrasive polishing materials generally utilize polishing fluids that do not contain abrasives. Examples of fix abrasive polishing material are disclosed in U.S. Pat. No. 5,692,950, by Rutherford et al. (issued Dec. 2, 1997) and U.S. Pat. No. 5,453,312, by Haas et al. (issued Sep. 26, 1995), both of which are hereby incorporated by reference in their entireties.
FIG. 1
generally depicts a schematic of a conventional chemical mechanical polishing apparatus
100
that utilizes a web
102
of polishing material to process a substrate
116
. The apparatus
100
generally includes at least one polishing station
106
. The polishing station
106
includes a polishing platen
108
and a polishing head
110
. The web
102
of polishing material is supported by the platen
108
below the polishing head
110
. Generally, the platen
108
has a top surface
112
that supports a polishing area
114
of the web
102
where processing occurs. The substrate
116
is retained by the polishing head
110
and pressed against the polishing area
114
while being moved relative thereto during processing.
The polishing area
114
of the web
102
is generally held against the platen
108
during processing typically by tensioning the web
102
between a supply roll
118
and a take-up roll
120
that are disposed on opposite sides of the platen
108
. The top surface
112
of the platen
108
may additionally contain a groove
122
that circumscribes the polishing area
114
. The groove
122
is coupled to a vacuum source
124
so that air and other fluids that may be present between the web
102
and the platen
108
are evacuated through the groove
122
, thus pulling the web
102
flush against the top surface
112
of the platen
108
.
Generally, the web
102
includes a plurality of abrasive elements
130
disposed on a flexible backing
132
. The abrasive elements
130
have a body
134
extending from the backing
132
and terminating in a working surface
136
that contacts the surface
128
of the substrate
116
.
During the processing operation, a polishing fluid
126
is disposed on the web
102
. The polishing fluid
126
generally provides chemical activity that assist in the removal of material from the surface
128
of the substrate
116
being polished. Optionally, the polishing fluid
126
may include abrasives to assist in the mechanical removal of material from the surface
128
of the substrate
116
. Typically, polishing fluids
126
generally have a viscosity in the range of about 0.01 to about 1.0 centipoises.
A factor in robust polishing systems and processes is controlling the cost of consumables such as the web
102
of polishing material. One factor that is detrimental to web life is deformation of the abrasive elements during polishing. Excessive deformation of the abrasive elements causes instability in substrate to substrate polishing performance (i.e., rate, uniformity, defects and the like) and ultimately results in a requirement for higher usage rates of web material per wafer processed.
During CMP processing, the substrate
116
is typically pressed against the abrasive elements
130
of the web
102
with a force of about 1.5 to about 8 psi during polishing. The relative motion between the platen
108
and the polishing head
110
results in the substrate
116
having a velocity of about 200 to about 1000 mm/sec in relation to the web
102
. The loading of the substrate
116
against the web
102
and shear forces created by the relative motion between the substrate
116
and web
102
result in the abrasive elements
130
being deformed. For comparison, an abrasive element
138
depicted in a non-deformed state is shown in phantom. The deformation of the abrasive elements
130
causes non-uniform wear of the elements
130
. Over successive polishing cycles, the deformation of the abrasive elements takes on a permanent deformation set. The formation of a permanent deformation set within the field of abrasive elements further aggravates the non-uniform wear of the web
102
and additionally may weaken the elements
130
to the point where some elements
130
may detach from the backing
132
, resulting in substrate scratching and web
102
failure. As such, deformed elements
130
substantially contribute to an undesirable rate of web consumption during polishing and poor polishing repeatability between substrates.
The effect of mechanical stresses causing undesirable deformation of the fixed abrasive elements is amplified by the effect of heat generated during the polishing process. Heat generated during the process of substrate polishing is partially absorbed by the web matrix material. The induction of heat into the web matrix material effectively reduces the relative modulus of the abrasive matrix features. In reducing the effective modulus of the fixed abrasive matrix features, the ability of the matrix material to withstand deformation under the applied mechanical stresses of the polish process is further reduced.
The polishing fluid
126
disposed within the process area of the web
102
generally provides little benefit in preventing deformation of the abrasive elements
130
. Typically, the polishing fluid
126
is generally applied to the web
102
from a central location and flows across the polishing area
114
of the web
102
. Due to the polishing fluids relatively low viscosity and wetting properties, as the polishing fluid
126
spreads across the web
102
, the polishing fluid
126
does not completely surround the entire abrasive elements
130
, particularly in the portion of the web
102
underneath the substrate
116
. Additionally, air pockets
140
may form or be trapped between some of the abrasive elements
130
that underlie the substrate
116
thus displacing the polishing fluid
126
from completely wetting out and surrounding the abrasive elements
130
.
In the absence of a more complete contact of the abrasive elements by the surrounding polishing fluid two important attributes to the polishing process are not realized. The limited interaction between the polishing fluid and the abrasive elements reduces the degree to which the process fluid can provide a heat sink and conduction path in reducing the latent heat build up within the abrasive elements. The ability to reduce the latent heat build up within the abrasive elements would limit the shear modulus loss that normally would be experience, reducing the level of deformation experienced, and in general provide improved process stability. Similarly, as the polishing fluid
126
does not completely surround the abrasive elements
130
,
Brett Declan Liam
Donohue Timothy James
Prabhu Gopalakrishna B.
Su Winston Y.
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