Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
2001-03-16
2002-04-02
Eley, Timothy V. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S296000
Reexamination Certificate
active
06364746
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and apparatuses for planarizing microelectronic substrate assemblies and, more particularly, to apparatuses and methods for endpointing mechanical and/or chemical-mechanical planarization of semiconductor wafers, field emission displays and other microelectronic substrate assemblies.
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
is a schematic isometric view of a web-format planarizing machine
10
for planarizing a microelectronic substrate assembly
12
. The planarizing machine
10
has a table
11
with a rigid panel or plate to provide a flat, solid support surface
13
for supporting a portion of a web-format planarizing pad
40
in a planarizing zone “A.” The planarizing machine
10
also has a pad advancing mechanism including a plurality of rollers to guide, position, and hold the web-format pad
40
over the support surface
13
. The pad advancing mechanism generally includes a supply roller
20
, first and second idler rollers
21
a
and
21
b
, first and second guide rollers
22
a
and
22
b
, and a take-up roller
23
. As explained below, a motor (not shown) drives the take-up roller
23
to advance the pad
40
across the support surface
13
along a travel axis T—T. The motor can also drive the supply roller
20
. The first idler roller
21
a
and the first guide roller
22
a
press an operative portion of the pad against the support surface
13
to hold the pad
40
stationary during operation.
The planarizing machine
10
also has a carrier assembly
30
to translate the substrate assembly
12
across the pad
40
. In one embodiment, the carrier assembly
30
has a head
32
to pick up, hold and release the substrate assembly
12
at appropriate stages of the planarizing process. The carrier assembly
30
also has a support gantry
34
and a drive assembly
35
that can move along the gantry
34
. The drive assembly
35
has an actuator
36
, a drive shaft
37
coupled to the actuator
36
, and an arm
38
projecting from the drive shaft
37
. The arm
38
carries the head
32
via another shaft
39
. The actuator
36
orbits the head
32
about an axis B—B to move the substrate assembly
12
across the pad
40
.
The polishing pad
40
may 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
50
flows from a plurality of nozzles
49
during planarization of the substrate assembly
12
. The planarizing fluid
50
may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the substrate assembly
12
, or the planarizing fluid
50
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 clean solutions without abrasive particles are used on fixed-abrasive polishing pads.
In the operation of the planarizing machine
10
, the pad
40
moves across the support surface
13
along the pad travel path T—T either during or between planarizing cycles to change the particular portion of the polishing pad
40
in the planarizing zone A. For example, the supply and take-up rollers
20
and
23
can drive the polishing pad
40
between planarizing cycles such that a point P moves incrementally across the support surface
13
to a number of intermediate locations I
1
, I
2
, etc. Alternatively, the rollers
20
and
23
may drive the polishing pad
40
between planarizing cycles such that the point P moves all the way across the support surface
13
to completely remove a used portion of the pad
40
from the planarizing zone A. The rollers may also continuously drive the polishing pad
40
at a slow rate during a planarizing cycle such that the point P moves continuously across the support surface
13
. Thus, the polishing pad
40
should be free to move axially over the length of the support surface
13
along the pad travel path T—T.
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.
In the highly competitive semiconductor industry, it is also desirable to maximize the throughput of CMP processing by producing a planar surface on a substrate assembly as quickly as possible. The throughput of CMP processing is a function of several factors, one of which is the ability to accurately stop CMP processing at a desired endpoint. In a typical CMP process, the desired endpoint is reached when the surface of the substrate assembly is planar and/or when enough material has been removed from the substrate assembly to form discrete components on the substrate assembly (e.g., shallow trench isolation areas, contacts, damascene lines, etc.). Accurately stopping CMP processing at a desired endpoint is important for maintaining a high throughput because the substrate assembly may need to be re-polished if it is “under-planarized,” or too much material can be removed from the substrate assembly if it is “over-polished.” For example, over-polishing can cause “dishing” in shallow-trench isolation structures or completely destroy a section of the substrate assembly. Thus, it is highly desirable to stop CMP processing at the desired endpoint.
One method for determining the endpoint of CMP processing is described in U.S. Pat. No. 5,036,015 issued to Sandhu (“Sandhu”), which is herein incorporated by reference. Sandhu discloses detecting the planar endpoint by sensing a change in friction between a wafer and the polishing medium. Such a change of friction may be produced by a different coefficient of friction at the wafer surface as one material (e.g., an oxide) is removed from the wafer to expose another material (e.g., a nitride). In addition to the different coefficients of friction caused by a change of material at the substrate surface, the friction between the wafer and the planarizing medium generally increases during CMP processing because more surface area of the substrate contacts the polishing pad as the substrate becomes more planar. Sandhu discloses detecting the change in friction by measuring the change in electrical current through the platen drive motor and/or the drive motor for the substrate holder.
Although Sandhu discloses a viable process for endpointing CMP processing, the change in electrical current through the platen and/or drive motor may not accurately indicate the endpoint of a substrate assembly. For example, the friction between the substrate assembly and the planarizing medium generally increases substantially linearly, and thus the change in the motor current at the endpoint may not be sufficient to provide a definite signal identifying that the endpoint has been reached. Moreover, friction losses and other power losses in the motors, gearboxes or other components may also change the current draw through the motors. The change in current through the drive motors, therefore, may not accurately reflect the drag force between the wafer and the polishing pad b
Eley Timothy V.
Micro)n Technology, Inc.
Nguyen Dung Van
LandOfFree
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