Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2001-02-13
2004-06-29
Rachuba, M. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S041000, C451S056000, C451S443000, C451S444000
Reexamination Certificate
active
06755718
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus and method for conditioning and monitoring media used for chemical-mechanical planarization of microelectronic substrates.
BACKGROUND OF THE INVENTION
Chemical-mechanical planarization (“CMP”) processes remove material from the surface of a semiconductor wafer in the production of integrated circuits.
FIG. 1
schematically illustrates a CMP machine
10
having a platen
20
. The platen
20
supports a planarizing medium
21
that can include a polishing pad
27
having a planarizing surface
29
on which a planarizing liquid
28
is disposed. The polishing pad
27
may be a conventional polishing pad made from a continuous phase matrix material (e.g., polyurethane), or it may be a new generation fixed-abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. The planarizing liquid
28
may be a conventional CMP slurry with abrasive particles and chemicals that remove material from the wafer, or the planarizing liquid may be a planarizing solution without abrasive particles. In most CMP applications, conventional CMP slurries are used on conventional polishing pads, and planarizing solutions without abrasive particles are used on fixed abrasive polishing pads.
The CMP machine
10
also can include an underpad
25
attached to an upper surface
22
of the platen
20
and the lower surface of the polishing pad
27
. A drive assembly
26
rotates the platen
20
(as indicated by arrow A), or it reciprocates the platen
20
back and forth (as indicated by arrow B). Because the polishing pad
27
is attached to the underpad
25
, the polishing pad
27
moves with the platen
20
.
A wafer carrier
30
positioned adjacent the polishing pad
27
has a lower surface
32
to which a wafer
12
may be attached. Alternatively, the wafer
12
may be attached to a resilient pad
34
positioned between the wafer
12
and the lower surface
32
. The wafer carrier
30
may be a weighted, free-floating wafer carrier, or an actuator assembly
40
may be attached to the wafer carrier to impart axial and/or rotational motion (as indicated by arrows C and D, respectively).
To planarize the wafer
12
with the CMP machine
10
, the wafer carrier
30
presses the wafer
12
face-downward against the polishing pad
27
. While the face of the wafer
12
presses against the polishing pad
27
, at least one of the platen
20
or the wafer carrier
30
moves relative to the other to move the wafer
12
across the planarizing surface
29
. As the face of the wafer
12
moves across the planarizing surface
29
, material is continuously removed from the face of the wafer
12
.
One problem with CMP processing is that the throughput may drop, and the uniformity of the polished surface on the wafer may be inadequate, because waste particles from the wafer
12
accumulate on the planarizing surface
29
of the polishing pad
27
. The problem is particularly acute when planarizing doped silicon oxide layers because doping softens silicon oxide and makes it slightly viscous as it is planarized. As a result, accumulations of doped silicon oxide glaze the planarizing surface
29
of the polishing pad
27
with a coating that can substantially reduce the polishing rate over the glazed regions.
To restore the planarizing characteristics of the polishing pads, the polishing pads are typically conditioned by removing the accumulations of waste matter with an abrasive conditioning disk
50
. Conventional abrasive conditioning disks are generally embedded with diamond particles, and they are mounted to a separate actuator
55
on a CMP machine that can move the conditioning disk
50
rotationally, laterally, or axially, as indicated by arrows E, F, and G, respectively. Typical conditioning disks remove a thin layer of the pad material itself in addition to the waste matter to form a new, clean planarizing surface
29
on the polishing pad
27
. Some conditioning processes also include disposing a liquid solution on the polishing pad
27
that dissolves some of the waste matter as the abrasive disks abrade the polishing surface.
One problem with conventional conditioning methods is that the conditioning disk
50
can lose effectiveness by wearing down or by having the interstices between abrasive particles plugged with particulate matter removed from the polishing pad
27
. If the change in effectiveness is not detected, the polishing pad
27
may be insufficiently conditioned and subsequent planarizing operations may not remove a sufficient quantity of material from the wafer
12
. Another problem is that the conditioning disk
50
may condition the polishing pad
27
in a nonuniform manner, for example, because the build-up of deposits on the polishing pad may be non-uniform or because the relative velocity between the polishing pad and the conditioning disk changes as the conditioning disk moves radially across the planarizing surface
29
.
One approach to addressing the above problems is to measure a friction force at an interface with the polishing pad. U.S. Pat. No. 5,743,784 discloses detecting the roughness of a polishing pad with a floating head apparatus positioned away from the conditioning disk. One drawback with this method is that the friction force detected by the floating head may not accurately represent the friction force between the conditioning disk and the polishing pad. Furthermore, the separate floating head adds to the overall complexity of the CMP apparatus.
Another approach is to measure a contact force between a conditioning end effector and the polishing pad, as disclosed in U.S. Pat. No. 5,456,627. As discussed above, a drawback with this approach is that the contact force may not adequately represent the friction force between the polishing pad and the conditioner.
U.S. Pat. No. 5,036,015 discloses sensing a change in friction between the wafer and the polishing pad by measuring changes in current supplied to motors that rotate the wafer and/or the polishing pad to detect the endpoint of planarization. However, this method does not address the problem of detecting the condition of the conditioning disk.
SUMMARY OF THE INVENTION
The present invention is directed toward methods and apparatuses for conditioning and monitoring a planarizing medium used for planarizing a microelectronic substrate. In one aspect of the invention, the apparatus can include a conditioning body having a conditioning surface configured to engage a planarizing surface of the planarizing medium. In one embodiment (for example, when the planarizing medium includes a circular polishing pad, or an elongated polishing pad extending between a supply roller and a take-up roller) the conditioning body can have a circular planform shape. Alternatively, (for example, when the planarizing medium includes a high speed continuous loop polishing pad), the conditioning body can be elongated across a width of the polishing pad. At least one of the conditioning body and the planarizing medium is movable relative to the other to condition the planarizing surface.
The apparatus can further include a sensor coupled to the conditioning body to detect a frictional force imparted to the conditioning body by the planarizing medium when one of the conditioning body and the planarizing medium moves relative to the other. The sensor can be coupled to a support that supports the conditioning body relative to the planarizing medium. For example, the support can include two support members, one pivotable relative to the other, and the sensor can include a force sensor positioned between the two support members to detect a force applied by one support member to the other as the conditioning body engages the planarizing medium. Alternatively, the support can include a piston movably received in a cylinder and the sensor can include a pressure transducer within the cylinder or a pointer that detects motion of the piston relative to the cylinder.
In another aspect of the invention, the apparatus can include a feedback device that controls the relative velo
Dorsey & Whitney LLP
Micro)n Technology, Inc.
Rachuba M.
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