U.S. patent application number 09/741414 was filed with the patent office on 2001-12-13 for method and apparatus for detecting wafer slipouts.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Donohue, Timothy J..
Application Number | 20010051492 09/741414 |
Document ID | / |
Family ID | 26881472 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010051492 |
Kind Code |
A1 |
Donohue, Timothy J. |
December 13, 2001 |
Method and apparatus for detecting wafer slipouts
Abstract
A method and apparatus for detecting the disengagement of a
workpiece from a polishing head is provided. In one embodiment, the
apparatus generally includes a polishing head and a detector. The
polishing head has a fixed portion and a first portion. The
detector is adapted to provide a metric indicative of relative
motion between the fixed portion and the first portion.
Inventors: |
Donohue, Timothy J.; (Menlo
Park, CA) |
Correspondence
Address: |
Patent Counsel
APPLIED MATERIALS, INC.
P. O. Box 450-A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
26881472 |
Appl. No.: |
09/741414 |
Filed: |
December 19, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60185787 |
Feb 29, 2000 |
|
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|
Current U.S.
Class: |
451/8 ; 451/28;
451/9 |
Current CPC
Class: |
B24B 37/0053 20130101;
B24B 49/10 20130101; B24B 37/30 20130101 |
Class at
Publication: |
451/8 ; 451/9;
451/28 |
International
Class: |
B24B 049/00; B24B
001/00; B24B 007/10 |
Claims
What is claimed is:
1. Apparatus for detecting disengagement of a workpiece comprising:
a polishing head having a first portion and a second portion; and a
detector adapted to provide a metric indicative of relative motion
between the first portion and the second portion.
2. The apparatus of claim 1, wherein the detector is an
accelerometer, a limit switch, a proximity sensor, a Hall effect
sensor, an optical encoder or a reed switch.
3. The apparatus of claim 1, wherein the detector is a linear
voltage displacement transducer.
4. The apparatus of claim 3, wherein the transducer further
comprises: a sensor body; and a piston extending movably from the
sensor body and in contact with the first portion.
5. The apparatus of claim 1 further comprising: a column supporting
the polishing head; and a bracket coupling the detector to the
column.
6. The apparatus of claim 1, wherein the first portion comprises at
least a carrier plate, a cover or a retaining ring.
7. The apparatus of claim 1, wherein the first portion comprises a
cover having a surface adapted to interface with the detector.
8. The apparatus of claim 1, wherein the polishing head further
comprises a flexure coupling the second portion to the first
portion.
9. The apparatus of claim 8, wherein the flexure is coupled between
a retaining ring and the second portion.
10. The apparatus of claim 1, wherein the polishing head further
comprises a biasing device disposed between the first portion and
the second portion.
11. The apparatus of claim 1, wherein the metric is a change in
voltage.
12. The apparatus of claim 1, wherein the first portion moves in
response the workpiece moving across a polishing material.
13. Apparatus for detecting disengagement of a workpiece
comprising: a polishing material; a polishing head for retain the
workpiece against the polishing material during polishing; and a
detector adapted to provide a metric indicative of relative motion
between the polishing material and the polishing head.
14. The apparatus of claim 1, wherein the detector is a linear
voltage displacement transducer, an accelerometer, a limit switch,
a proximity sensor, a Hall effect sensor, an optical encoder or a
reed switch.
15. Apparatus for detecting disengagement of a workpiece
comprising: a polishing head having a first portion and a second
portion; and a means for detecting relative motion between the
first portion and the second portion.
16. The apparatus of claim 15, wherein the means for detecting is
an accelerometer, a limit switch, a proximity sensor, a Hall effect
sensor, an optical encoder, linear voltage displacement transducer
or a reed switch.
17. Apparatus for detecting disengagement of a workpiece
comprising: a platen; a polishing material disposed on the platen;
a polishing head supported above the polishing material, the
polishing head having a first portion and a second portion; and a
detector adapted to provide a metric indicative of motion between
the first portion and the second portion.
18. The apparatus of claim 17, wherein the platen is
stationary.
19. The apparatus of claim 17, wherein the platen rotates.
20. The apparatus of claim 17, wherein the polishing head moves
laterally relative to the platen during processing.
21. A method for detecting disengagement of a workpiece from a
polishing head comprising: pressing the workpiece retained in the
polishing head against a polishing material; providing relative
motion between the workpiece and the polishing material; and
detecting motion of the polishing head in a direction normal to the
polishing material.
22. The method of claim 21, wherein the step of detecting motion
further comprises the step of moving a first portion of the
polishing head relative to a second portion.
23. The method of claim 21, wherein the step of detecting motion
further comprises establishing a baseline or process window.
24. The method of claim 23, wherein the step of detecting motion
further comprises the step of detecting motion of the first portion
outside of the process window.
25. The method of claim 21, wherein the step of detecting motion
further comprises the step of moving a piston coupled to a
sensor.
26. The method of claim 25, wherein the sensor is a linear voltage
displacement transducer.
27. The method of claim 21, wherein the step of providing relative
motion between the workpiece and the polishing material further
comprises the step of polishing the workpiece.
Description
[0001] This application claims benefit of United States Provisional
Patent Application No. 60/185,787, filed Feb. 29, 2000, which is
hereby incorporated herein by reference in its entirety.
BACKGROUND OF THE DISCLOSURE
[0002] 1. Field of the Invention
[0003] Embodiments of the invention generally relate to a method
and apparatus for detecting wafer slipouts from a polishing
head.
[0004] 2. Background of the Invention
[0005] 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 typically include a polishing head and a
platen that supports a polishing material. The polishing head
generally includes a ring that circumscribes a substrate receiving
pocket in which the substrate is retained during processing.
Processing of the substrate is generally performed by providing
relative motion between the substrate and the polishing material in
the presence of a polishing fluid while pressing the substrate
against the polishing material.
[0006] During polishing, frictional forces between the substrate
and the polishing material causes the substrate to be forced
laterally against the ring of the polishing head. Occasionally, a
triggering event causes the retainment of the substrate within the
polishing head to become partially or completely lost. For example,
some of the pressure biasing the ring towards the polishing
material may be lost, thus diminishing the force capturing the
substrate between the polishing head and the polishing material. If
the pressure is sufficiently reduced, the lateral force of the
substrate against the ring may cause the ring to lift thus allowing
the substrate to escape from under the polishing head. Other
triggering events may include passing the substrate over a
polishing surface abnormality such as wrinkles in the polishing
material and run-out in the parallelism between the polishing head
and platen.
[0007] Once the wafer has slipped out from under the polishing
head, the substrate may be scratched or broken. Additionally, if
the slipout event is not timely detected, valuable production time
is lost while the damaged wafer waiting to be removed from the
polisher. Additionally, the non-retained wafer left in the
processing area may damage the tool or tool components such as
sensors or wiring.
[0008] Therefore, there is a need for a method and apparatus for
detecting wafer slipouts.
SUMMARY OF THE INVENTION
[0009] In one aspect of the invention, an apparatus for detecting
disengagement of a workpiece is provided. In one embodiment, the
apparatus includes a polishing head and a detector. The polishing
head has a first portion and a second portion. The detector is
adapted to provide a metric indicative of relative motion between
the first portion and the second portion.
[0010] In another aspect of the invention, a method for detecting
disengagement of a workpiece from a polishing head is provided. In
one embodiment, the method includes the steps of pressing the
workpiece retained in the polishing head against a polishing
material, providing relative motion between the workpiece and the
polishing material, and detecting motion of the polishing head in a
direction normal to the polishing material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0012] FIG. 1 depicts an illustrative polishing system having one
embodiment of a slipout detection mechanism;
[0013] FIG. 2 depicts one embodiment of a slipout detection
mechanism coupled to a polishing head; and
[0014] FIG. 3 depicts the polishing head of FIG. 2 having a
substrate in a slipout condition.
[0015] To facilitate an understanding, identical reference numerals
have been used, wherever possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION OF INVENTION
[0016] FIG. 1 is a perspective view of an exemplary chemical
mechanical polishing system 100 having one embodiment of a slipout
detection mechanism (slipout detector) 102 coupled thereto.
Although the slipout detector 102 is described in reference to one
embodiment of a chemical mechanical polishing system 100, the
slipout detector 102 may readily be adapted to other chemical
mechanical polishing systems that utilize a polishing head to
retain a substrate against a polishing surface.
[0017] Generally, the exemplary polishing system 100 includes a
polishing table (platen) 104, a drive system 106 and a polishing
head 108. The platen 104 generally has a polishing material 110
disposed on a top surface 112. The platen 104 may include a subpad
(not shown) disposed in the top surface 112 beneath the polishing
material 110 to maintain an effective modulus of the polishing
material 110, subpad and platen 104 stack at a predetermined value
that produces a desired polishing result. The platen 104 is
typically stationary. Alternatively, the platen 104 may move, for
example, rotating about a central axis.
[0018] The drive system 106 is coupled to a base 114 and supports
the polishing head 108 above the polishing material 110. Generally,
the drive system 106 provides x/y motion to the polishing head 108
so that a substrate 116 retained in the polishing head 108 is moved
in a programmed pattern while pressing the substrate 116 against
the polishing material 110.
[0019] The polishing head 108 may be actuated to move along an axis
normal to the polishing material 110 so that the substrate 116 may
contact or be moved clear of the polishing material 110. Examples
of polishing heads that may be utilized in accordance with the
invention are the DIAMOND HEAD.TM. wafer carrier and the TITAN
HEAD.TM. wafer carrier, both available from Applied Materials, Inc.
of Santa Clara, Calif.
[0020] To facilitate process control, a controller 118 comprising a
central processing unit (CPU) 120, support circuits 122 and memory
124, is coupled to the system 100. The CPU 120 may be one of any
form of computer processor that can be used in an industrial
setting for controlling various drives and pressures. The memory
124 is coupled to the CPU 120. The memory 124, or computer-readable
medium, may be one or more of readily available memory such as
random access memory (RAM), read only memory (ROM), floppy disk,
hard disk, or any other form of digital storage, local or remote.
The support circuits 122 are coupled to the CPU 120 for supporting
the processor in a conventional manner. These circuits include
cache, power supplies, clock circuits, input/output circuitry,
subsystems, and the like.
[0021] The slipout detector 102 is generally positioned above the
polishing head 108. The slipout detector 102 has a lead 126 that
couples the detector to the controller 118. The slipout detector
102 generally senses an indicia indicating movement of the
polishing head 108 in a direction normal to a plane defined by the
polishing material 110. As the polishing head 108 and substrate 116
are moved across the polishing material 110, the polishing head 108
generally experiences small movements in the normal direction.
These movements are generally due to non-uniformities present in
the polishing material 110, the top surface 112 of the base 114,
vibrations and the like. The slipout detector 102 generally
provides the controller 118 with a signal indicative of the
movement of the polishing head 108 over these irregularities. The
controller 118 utilized the signal to establish a baseline that is
indicative of the normal range of motion of the polishing head 108
across the polishing material 110 during normal processing. Once
this baseline is established, the controller 118 can detect when a
signal from the slipout detector 102 falls outside of a process
window established using the baseline, such as the substrate 116
slipping out from under the polishing head 108.
[0022] FIG. 2 depicts one embodiment of the polishing head 108
interfaced with an embodiment of the slipout detector 102.
Generally, the polishing head 108 is disposed between a movable
stage 202 of the drive system 106 and the platen 104. The polishing
head 108 is coupled to a lower end 210 of the column 204 that
extends between the stage 202 toward the polishing material 110.
The column 204 generally includes an actuator 206 that facilitates
movement of the polishing head 108 along the axis normal to the
polishing material 110. In one embodiment, the column 204 is
coupled to a pair of linear actuators such as a ball screws that
provides controllable motion of the column 204 and polishing head
108 normal to the polishing material 110. Alternatively, other
types of actuators may be utilized, such as solenoids, lead screws,
pneumatic cylinders, hydraulic cylinders and the like.
[0023] In one embodiment, the polishing head 108 includes a first
portion 250 and a second portion 252 that are movable relative each
other. Generally, the first portion 250 includes a retaining ring
216 and a cover 222. The second portion 252 typically includes a
housing 212, a carrier plate 214, a biasing device 218 and a gimbal
248. The housing 212 has a center portion 224 and an extending lip
226 that defines a space 228 therebetween. The center portion 224
of the housing 212 is coupled to the lower end 210 of the column
204. A first side 230 of the carrier plate 214 is disposed adjacent
to the lip 226 of the housing 212. A second side 232 of the carrier
plate 212 typically applies pressure to the substrate 116 during
processing (i.e., presses the substrate 116 against the polishing
material 110).
[0024] The gimbal 220 is coupled between the carrier plate 214 and
the lip 226 of the housing 212. The gimbal 220 allows the carrier
plate 214 to pivot relative the housing 212, thus allowing the
carrier plate 214 and substrate 116 to follow the contours of the
polishing material 110. Thus, as the drive system 106 moves the
polishing head 108 across the surface of the polishing material
110, the gimbal 220 allows the carrier plate 214 and substrate 116
to maintain a substantially parallel alignment with the surface of
the polishing material 110. In one embodiment, the gimbal 220
comprises a metallic flexure.
[0025] The carrier plate 214 additionally includes a flexure 248
extending from the perimeter of the carrier plate 214 to the
retaining ring 216. The flexure 248 allows the retaining ring 216
to move relative the housing 212, thus allowing the first portion
250 of the polishing head 108 to move normally relative to the
second portion 252 and the polishing material 110 during
polishing.
[0026] The retaining ring 216 is disposed at the carrier plate's
perimeter to prevent the substrate 116 from slipping out from under
the polishing head 108 during processing. Generally, the retaining
ring 216 is comprised of a polymeric material 110 that is typically
placed in contact with the polishing material 110 during
processing.
[0027] The cover 222 is coupled to the retaining ring 216. The
cover 222 generally has a central opening 234 that allows the
housing 212 to extend therethrough. The cover 222 additionally
includes an upper surface 236 that is generally parallel to the
carrier plate 214.
[0028] Disposed between the carrier plate 214 and the housing 212
is the biasing device 218. The biasing device 218 generally
provides a controllable force that urges the carrier plate 214 away
from the housing 212 so that the substrate 116 is pressed against
the polishing material 110. In one embodiment, the biasing device
218 is inflatable bellows. Alternatively, the biasing device 218
may comprise other force generating mechanisms such as a linear
actuator, for example, a pneumatic cylinder or lead screw.
[0029] The slipout detector 102 generally detects motion of the
polishing head 108 relative to the platen 104. In one embodiment,
the slipout detector 102 is coupled to the second portion 252 of
the polishing head 108. As the second portion 252 is held at a
predetermined distance from the polishing material 110 during
polishing, other portions of the system 100 that are also held at a
fixed distance from the polishing material 110 may equally provide
a reference point to determine the relative normal motion of the
first portion 250. As such, the slipout detector 102 may
alternatively be support from portions of the system 100 that fixed
in distance to the polishing material 110 during processing.
Optionally, the slipout detector 102 may be coupled to the first
portion 250 of the polishing head 108 to reference the change in
position of other portions of the system 100 relative thereto.
[0030] In one embodiment, the slipout detector 102 is coupled to
the column 204 supporting the polishing head 108. Typically, the
slipout detector 102 is coupled to the column 204 by a bracket 240.
The bracket 240 generally comprises an aluminum or polymer clamp
that holds the slipout detector 102 in a position offset to a
center line of the polishing head 108 and above the first portion
250 of the polishing head 108.
[0031] The slipout detector 102 provides a signal to the controller
118 in response to changes in a metric indicative of the motion of
the polishing head 108. In one embodiment, the slipout detector 102
comprises a linear voltage displacement transducer (LVDT). The
transducer generally includes a sensor body 242 having a piston 244
extending therefrom. The sensor body 242 generally is held by the
bracket 240 and orientated over the housing 212 such that the
piston 244 is in contact with the upper surface 236 of the cover
222 when the polishing head 108 is lowered to a position where the
substrate 116 is in contact with the polishing material 110. Thus,
when the system 100 is processing the substrate 116, a process
window indicative of the normal distance between the cover 222 and
the sensor body 242 may be complied by the controller 116 as the
substrate 116 is processed.
[0032] For example, as the piston 244 moves in relation to the
sensor body 242, the signal provided by the detector 102 is
indicative of the distance between the cover 222 (or other first
portion 250 of the polishing head 108) and the sensor body 242. As
the first portion 250 of the polishing head 108 moves in relation
to the sensor body 242, the baseline (i.e., the minimum maximum
range of normal relative motion) between the cover 222 and the
detector 102 may be determined by the controller 118, which is used
to establishing the process window. For simplicity of illustration,
the process window is depicted as DP. Alternatively, the process
window may be set as a predetermined value.
[0033] Thus, in the event that the substrate 116 becomes disengaged
from the polishing head 108 as depicted in FIG. 3, the first
portion 250 of the polishing head 108 is moved away from the
polishing material 110 as the wafer substrate 116 slides between
the retaining ring 216 and the polishing material 110. As the first
portion 250 of the polishing head 108 is forced upward, the piston
244 is correspondingly moved further into the detector 102 such as
the distance between the sensor body 242 and the cover 222 is now
D.sub.S.
[0034] The controller 118 receives the signal from the detector 102
indicating that the distance D.sub.S lies beyond the process window
D.sub.Pe. The controller 118 then indicates that the substrate 116
has become disengaged from the polishing head 108. The system 100
may then be shut down to remove the substrate 116 or other actions
may be alternatively taken.
[0035] As the slipout detector 102 provides a metric indicative of
the motion of the first portion 250 of the polishing head 108, it
is contemplated that other sensing means may be utilized in place
of the LVDT transducer. For example, other sensing means that may
be utilized as slipout detectors include accelerometers, limit
switches, proximity sensor, optical encoders, Hall effect sensors,
reed switches and like sensors.
[0036] Although the teachings of the present invention that have
been shown and described in detail herein, those skilled in the art
can readily device other varied embodiments that still incorporate
these teachings and do not depart from the scope and spirit of the
invention.
* * * * *