Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2000-08-31
2003-09-23
Rachuba, M. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S008000, C451S041000, C451S056000, C451S287000
Reexamination Certificate
active
06623329
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods and apparatuses for supporting microelectronic substrates during planarization.
BACKGROUND
Mechanical and chemical-mechanical planarization 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-device substrate assemblies. CMP processes generally remove material from a substrate or substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate.
FIG. 1
schematically illustrates an existing web-format-planarizing machine
10
for planarizing a substrate
60
. The planarizing machine
10
has a support table
14
with a sub-pad
16
at a workstation where an operative portion “A” of a planarizing pad
40
is positioned. The sub-pad
16
is generally a rigid plate to provide a flat, solid surface to which a particular section of the planarizing pad
40
may be secured during planarization.
The planarizing machine
10
also has a plurality of rollers to guide, position and hold the planarizing pad
40
over the sub-pad
16
. The rollers include a supply roller
20
, idler rollers
21
, guide rollers
22
, and a take-up roller
23
. The supply roller
20
carries an unused or pre-operative portion of the planarizing pad
40
, and the take-up roller
23
carries a used or post-operative portion of the planarizing pad
40
. Additionally, the left idler roller
21
and the upper guide roller
22
stretch the planarizing pad
40
over the sub-pad
16
to hold the planarizing pad
40
stationary during operation. A motor (not shown) drives at least one of the supply roller
20
and the take-up roller
23
to sequentially advance the planarizing pad
40
across the sub-pad
16
. Accordingly, clean pre-operative sections of the planarizing pad
40
may be quickly substituted for used sections to provide a consistent surface for planarizing and/or cleaning the substrate
60
.
The web-format-planarizing machine
10
also has a carrier assembly
30
that controls and protects the substrate
60
during planarization. The carrier assembly
30
generally has a substrate holder
50
to pick up, hold and release the substrate
60
at appropriate stages of the planarizing process. The substrate holder
50
engages a retainer ring
31
that surrounds the microelectronic substrate
60
and restricts lateral motion of the microelectronic substrate
60
relative to the substrate holder
50
. Several nozzles
33
attached to the substrate holder
50
dispense a planarizing solution
44
onto a planarizing surface
42
of the planarizing pad
40
. The carrier assembly
30
also generally has a support gantry
34
carrying a drive assembly
35
that can translate along the gantry
34
. The drive assembly
35
generally 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 substrate holder
50
via a terminal shaft
39
such that the drive assembly
35
orbits the substrate holder
50
about an axis B—B (as indicated by arrow “R
1
”). The terminal shaft
39
may also rotate the substrate holder
50
about its central axis C—C (as indicated by arrow “R
2
”).
The planarizing pad
40
and the planarizing solution
44
define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate
60
. The planarizing pad
40
used in the web-format planarizing machine
10
is typically a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution is a “clean solution” without abrasive particles. In other applications, the planarizing pad
40
may be a non-abrasive pad without abrasive particles. The planarizing solutions
44
used with the non-abrasive planarizing pads are typically CMP slurries with abrasive particles and chemicals.
To planarize the substrate
60
with the planarizing machine
10
, the carrier assembly
30
presses the substrate
60
against the planarizing surface
42
of the planarizing pad
40
in the presence of the planarizing solution
44
. The drive assembly
35
then orbits the substrate holder
50
about the axis B—B and optionally rotates the substrate holder
50
about the axis C—C to translate the substrate
60
across the planarizing surface
42
. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate
60
.
The CMP processes should consistently and accurately produce a uniformly planar surface on the substrate
60
to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects and other features, many substrates or substrate assemblies develop large “step heights” that create a highly topographic surface across the substrate assembly. Yet, as the density of integrated circuits increases, it is necessary to have a planar substrate surface at several intermediate stages during the fabrication of devices on a substrate assembly because non-uniform substrate surfaces significantly increase the difficulty of forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on non-uniform substrate surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface.
One problem with some conventional CMP techniques is that the carrier assembly
30
may not apply a uniform downward force on the substrate
60
. Accordingly, the planarized surface of the substrate
60
may develop non-uniformities that can adversely affect subsequent processing steps. One approach to address this problem is to rotate the substrate
60
and the substrate holder
50
as a unit about axis C—C, but a drawback with this approach is that it increases the mechanical complexity of the substrate holder
50
and the carrier assembly
30
. This approach particularly increases the mechanical complexity if the carrier assembly
30
includes fluid couplings between the arm
38
and the substrate holder
50
(for example, to supply the planarizing liquid
44
to the nozzles
33
).
Another problem with some conventional devices is that the retainer ring
31
can wipe the planarizing liquid
44
from the planarizing pad
40
as the substrate carrier
50
and the substrate
60
move across the planarizing pad
40
. Accordingly, the planarizing liquid
44
may not uniformly coat the lower surface of the substrate
60
, which can reduce the planarizing rate and/or the planarity of the substrate
60
. Still another problem is that the carrier assembly
30
can include a disposable film at the interface between the substrate holder
50
and the substrate
60
to grip the substrate
60
. The disposable film must be periodically replaced, which increases the time and expense required to maintain the apparatus
10
.
One approach for addressing some of the foregoing problems is to direct pressurized air against the rear surface of the substrate
60
during planarization. For example, U.S. Pat. No. 5,762,539 to Nakashiba et al. discloses a carrier apparatus that directs several jets of compressed air at different pressures toward the rear surface of the substrate to bias the substrate against the polishing pad while the carrier rotates relative to the polishing pad. One drawback with this approach is that the arrangement for supplying compressed air to the carrier may be complex and subject to leaks because it includes rotary couplings that direct the compressed air to the rotating carrier. A further disadvantage is that the compressed air can evaporate the planarizing liquid, reducing the effectiveness of the planarizing medium. When the planarizing liquid includes an abrasive slur
Perkins Coie LLP
Rachuba M.
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