Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-08-31
2001-12-11
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S296000, C451S526000
Reexamination Certificate
active
06328632
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and apparatuses for planarizing microelectronic substrate assemblies and, more particularly, to polishing pads and planarizing machines for mechanical and/or chemical-mechanical planarization.
BACKGROUND OF THE INVENTION
Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) are used in the manufacturing of electronic devices for forming a flat surface on semiconductor wafers, field emission displays, and many other microelectronic substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly.
FIG. 1
schematically illustrates a rotary CMP machine
10
for planarizing a microelectronic substrate assembly
12
. The rotary machine
10
has a platen
20
, a wafer carrier assembly
30
above the platen
20
, and a polishing pad
40
between the platen
20
and the carrier assembly
30
. The carrier assembly
30
generally includes a head
32
to pick up, hold and release the substrate assembly
12
at the appropriate stages of the planarizing process. The carrier assembly
30
can also include a backing pad
34
to support the back side of the substrate assembly
12
. The head
32
may be a weighted, free-floating unit, or the carrier assembly
30
can further include an actuator
36
attached to the head
32
to impart axial and/or rotational motion (indicated by arrows C and D, respectively).
The polishing pad
40
can be a non-abrasive polymeric pad (e.g., polyurethane), or it may be a fixed-abrasive polishing pad in which abrasive particles are fixedly dispersed in a resin or another type of suspension medium. A planarizing fluid
44
covers the polishing pad
40
during planarization of the substrate assembly
12
. The planarizing fluid
44
may be a conventional CMP slurry with abrasive particles that etch and/or oxidize the surface of the substrate assembly
12
, or the planarizing fluid
44
may be a “clean” non-abrasive planarizing solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on non-abrasive polishing pads, and non-abrasive cleaning solutions without abrasive particles are used on fixed-abrasive polishing pads.
To planarize the substrate assembly
12
with the CMP machine
10
, the carrier assembly
30
presses the substrate assembly
12
face-downward against a planarizing surface
42
of the polishing pad
40
. At least one of the platen
20
or the head
32
moves relative to the other to move the substrate assembly
12
across the planarizing surface
42
in the presence of the planarizing solution
44
. As the face of the substrate assembly
12
moves across the planarizing surface
42
, the polishing pad
40
and/or the planarizing solution
44
continually remove material from the face of the substrate assembly
12
.
CMP processes should consistently and accurately produce a uniform, planar surface on substrate assemblies to enable circuit and device patterns to be formed with photolithography techniques. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the photo-patterns to within a tolerance of approximately 0.1 &mgr;m. Focusing photo-patterns to such small tolerances, however, is difficult when the planarized surfaces of substrate assemblies are not uniformly planar. Thus, to be effective, CMP processes should create highly uniform, planar surfaces on substrate assemblies.
One manufacturing concern of CMP processing is that the surface of the substrate assembly may not be uniformly planar because the rate at which material is removed from the substrate assembly (the “polishing rate”) may vary from one area to another. The polishing rate depends, in part, on the relative linear velocity between the surface of the wafer and the portion of the planarizing surface contacting the wafer. The linear velocity of the planarizing surface of a circular, rotating polishing pad varies across the planarizing surface of the pad in proportion to the radial distance from the center of the pad. Similarly, when the head rotates the wafer, the linear velocity also varies across the front face of the wafer in proportion to the radial distance from the center of the wafer. The variation of linear velocities across the face of the wafer and the planarizing surface of the polishing pad creates a relative velocity gradient in between the wafer and the polishing pad. In general, the relative velocity gradient between the wafer and the pad causes a higher polishing rate at the perimeter of the wafer than at the center of the wafer. Such a variance in the polishing rate produces a center-to-edge profile in which more material is removed from the perimeter of the wafer than the center.
Several devices and concepts have been developed to reduce the center-to-edge planarizing profile across wafers. U.S. Pat. No. 5,020,283 issued to Tuttle, which is herein incorporated by reference, discloses a nonabrasive polishing pad with voids in the surface of the pad. The area of the planarizing surface occupied by the voids increases with increasing radial distance to reduce the contact area between the wafer and the planarizing surface of the polishing pad towards the perimeter of the pad. Thus, at the periphery of the pad where the linear velocity of the pad is high, the voids are intended to reduce the polishing rate of the wafer compared to a planarizing surface without such voids.
U.S. patent application Ser. No. 08/834,524 filed by Hudson, which is herein incorporated by reference, discloses an abrasive polishing pad designed to reduce the center-to-edge planarizing profile across or substrate assembly. In one embodiment disclosed in Hudson, the abrasive polishing pad has a planarizing surface with a first planarizing region and a second planarizing region. The first planarizing region has a first abrasiveness and the second planarizing region has a second abrasiveness different than the first abrasiveness of the first region. Hudson discloses that the abrasiveness of the first and second regions can be controlled by using either different types, sizes or densities of abrasive particles fixedly suspended in a suspension medium. Additionally, this application discloses varying the contact
on-contact bearing surfaces on the pad between the first and second regions. The different abrasivity of the first and second planarizing regions are intended to compensate for variations in the relative velocity across the face of the wafer.
Another polishing pad developed to reduce the center-to-edge planarizing profile across a wafer is disclosed in U.S. Pat. No. 5,435,772 issued to Yu, which is also herein incorporated by reference. Yu discloses a circular polishing pad including a first region closer to the edge of the polishing pad and a second region adjacent to the first region toward the center of the polishing pad. The polishing pad disclosed in Yu is configured so that the second region is thicker or less compressible than the first region. Yu states that having a thicker or less compressible portion at the center of the pad and a thinner portion at the perimeter of the pad produces more uniform polishing results.
SUMMARY OF THE INVENTION
The present invention is directed toward polishing pads and planarizing machines in mechanical and/or chemical-mechanical planarization of semiconductor wafers, field emission displays or other microelectronic substrate assemblies. One polishing pad of the invention is a web-format pad for use with a web-format planarizing machine. The web-format polishing pad can include a body having a planarizing medium, an elongated first side edge, an elongated second side edge opposite the first side edge, and a length sufficient to extend across a planarizing zone. The planarizing medium can have an elongated interior region extending lengthwise along the body, an elongated first exterior side region extending lengthwise along the
Dorsey & Whitney LLP
Hail III Joseph J.
Micro)n Technology, Inc.
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