U.S. patent application number 09/954529 was filed with the patent office on 2003-03-27 for sensor for in-situ pad wear during cmp.
Invention is credited to Benvegnu, Dominic J., Kaushal, Tony S..
Application Number | 20030060127 09/954529 |
Document ID | / |
Family ID | 25495561 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030060127 |
Kind Code |
A1 |
Kaushal, Tony S. ; et
al. |
March 27, 2003 |
Sensor for in-situ pad wear during CMP
Abstract
Wear of a CMP polishing pad is detected in-situ by monitoring a
change in the height of an identification mark positioned on a
rotatable spindle supporting a wafer in contact with the chemical
mechanical polishing pad. As the pad experiences wear, its
thickness decreases and the relative height of the identification
mark declines. This change in height can be detected by optical
interrogation of the identification mark, and then calibrated to
reveal a precise amount of pad wear. Alternatively, changes in
thickness of the polishing pad can be correlated to a drop in
dielectric properties of the pad as monitored by an electrical
sensor measuring capacitance. Apparatuses for sensing pad wear in
accordance with the present invention can also be utilized to
evaluate the quality of new polishing pads, to indicate the optimum
time for replacing worn polishing pads, and to identify the point
at which a worn polishing pad begins to damage a wafer being
polished.
Inventors: |
Kaushal, Tony S.;
(Cupertino, CA) ; Benvegnu, Dominic J.; (La Honda,
CA) |
Correspondence
Address: |
APPLIED MATERIALS, INC.
2881 SCOTT BLVD. M/S 2061
SANTA CLARA
CA
95050
US
|
Family ID: |
25495561 |
Appl. No.: |
09/954529 |
Filed: |
September 10, 2001 |
Current U.S.
Class: |
451/8 |
Current CPC
Class: |
G05B 2219/45232
20130101; B24B 49/12 20130101; B24B 37/20 20130101; B24B 49/10
20130101; G05B 2219/37559 20130101 |
Class at
Publication: |
451/8 |
International
Class: |
B24B 049/00 |
Claims
What is claimed is:
1. A method for detecting wear of a chemical mechanical polishing
pad comprising: detecting in-situ a change in thickness of a
chemical mechanical polishing pad by sensing a change in position
of a spindle supporting a head and a wafer into contact with the
chemical mechanical polishing pad; and correlating the change in
pad thickness with an amount of pad wear.
2. The method of claim 1 wherein the change in position is detected
by monitoring a change in an intensity of light reflected from a
visual identification mark positioned on the spindle.
3. The method of claim 1 further comprising correlating the amount
of pad wear with a rate of pad wear of polishing pads of known
quality in order to identify a quality of the polishing pad.
4. A method for detecting wear of a chemical mechanical polishing
pad comprising: detecting in-situ a change in thickness of a
chemical mechanical polishing pad by sensing an increase in
capacitance resulting from application of a potential difference
across the worn polishing pad; and correlating the change in pad
thickness with an amount of pad wear.
5. The method of claim 4 further comprising correlating the amount
of pad wear with a rate of pad wear of polishing pads of known
quality in order to identify a quality of the polishing pad.
6. A method of determining in situ a quality of a chemical
mechanical polishing pad material, the method comprising: applying
a compression force to a spindle supporting a wafer into contact
with the polishing pad; detecting a distance of displacement of the
spindle toward the polishing pad in response to the compression
force; and correlating the displacement distance with displacement
distances of prior polishing pads of known quality.
7. The method of claim 6 wherein the displacement distance is
sensed from a change in a height of a visual identification mark
located on the spindle.
8. The method of claim 7 wherein the displacement distance is
sensed from a change in intensity of light from a light source that
is reflected from the visual identification mark.
9. The method of claim 6 wherein the displacement distance is
detected from an increase in a capacitance resulting from
application of a potential difference across the polishing pad.
10. An apparatus for detecting pad wear in-situ comprising: a
platen supporting a chemical mechanical polishing pad; a head
supporting a wafer into contact with the chemical mechanical
polishing pad; a spindle in contact with the head; a visual
identification mark positioned on the spindle; a light source
configured to illuminate the visual identification mark; and a
detector configured to receive light reflected from the visual
identification mark, such that a reduction in thickness of the pad
causes a change in position of the visual identification mark that
may be correlated with an amount of pad wear.
11. An apparatus for detecting wear of a chemical mechanical
polishing pad in-situ comprising: a platen supporting a chemical
mechanical polishing pad in contact with a wafer; a power supply
having a first terminal in electrical communication with the platen
and the second terminal in electrical communication with the wafer;
and a detector configured to sense a change in capacitance between
the first and second terminals, such that a reduction in thickness
of the pad causes a change in capacitance that may be correlated
with an amount of pad wear.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to Chemical
Mechanical Polishing (CMP). In particular, it relates to
apparatuses and methods enabling in-situ measurement of pad wear
during CMP processes.
[0002] Polishing of semiconductor wafers by CMP during fabrication
of integrated circuits is an accepted practice in the semiconductor
industry. Typically, a wafer to be polished is secured to a head
supported by a spindle, and then placed into contact with a
polishing pad in combination with an abrasive slurry. Over time,
continued frictional contact between the wafer and the polishing
pad alters the character of the surface of the polishing pad. This
in turn affects the quality of the wafer polishing resulting from
the frictional contact.
[0003] The surface of the polishing pad is typically regenerated
through periodic contact with a separate conditioning disk
containing diamond abrasive. The resulting fresh surface of the
polishing pad produced by contact with the conditioning pad is
important to ensure the effectiveness and consistency of
polishing.
[0004] The material forming the polishing pad is relatively soft
and may be abraded or worn away through repeated contact with the
conditioning disk and the wafer. Conventionally, the issue of wear
of polishing pads has been addressed by replacing the polishing
pads at regular intervals, for example after approximately every
1000 wafers polished.
[0005] However, this conventional periodic replacement approach is
based upon only a generalized estimate of pad wear. In reality, pad
wear is dependent upon a host of variables, including the quality
of the pad, wafer-to-wafer variation in operational parameters of a
CMP process, and tool-to-tool variation in operational parameters
of a CMP process. Over-frequent replacement of CMP polishing pads
wastes pad material and increases the consumables cost of the CMP
process. Conversely, under-frequent replacement of CMP polishing
pads may result in uneven polishing and the loss of wafers in
production.
[0006] Therefore, methods and structures permitting direct
measurement of the wear of polishing pads in a CMP device are
desirable.
SUMMARY OF THE INVENTION
[0007] Embodiments of the present invention provide structures and
methods permitting in-situ measurement of wear of CMP polishing
pads. Structures and methods for detecting pad wear may utilize
sensors that monitor physical changes in pad thickness. One
approach utilizes an optical sensor detecting a change in the
relative height of a mark positioned on a rotatable spindle
supporting the wafer in contact with the polishing pad. As the pad
experiences wear and exhibits reduced thickness, the relative
height of the spindle mark will drop. This change in height can be
calibrated to a given amount of pad wear. In an alternative
embodiment in accordance with the present invention, changes in
polishing pad thickness can be correlated to a drop in dielectric
properties of the pad as detected by an electrical sensor.
Apparatuses and methods for sensing wear in CMP polishing pads
according to embodiments of the present invention can also be
utilized to evaluate the quality of new polishing pads, or to
indicate the optimum time for replacement of polishing pads.
[0008] An embodiment of a method for detecting wear of a chemical
mechanical polishing pad in accordance with the present invention
comprises detecting in-situ a change in thickness of a chemical
mechanical polishing pad by sensing a change in a position of a
spindle supporting the wafer in contact with the chemical
mechanical polishing pad. This change in pad thickness is then
correlated with an amount of pad wear.
[0009] An alternative embodiment of a method for detecting wear of
a chemical mechanical polishing pad in accordance with the present
invention comprises detecting in-situ a change in thickness of a
chemical mechanical polishing pad by sensing an increase in
capacitance resulting from application of a potential difference
across the worn polishing pad. This change in pad thickness is then
correlated with an amount of pad wear.
[0010] An embodiment of a method of determining the quality of a
chemical mechanical polishing pad in-situ in accordance with the
present invention comprises applying a compression force to spindle
supporting the wafer in contact with the polishing pad, detecting a
distance of displacement of the spindle toward the polishing pad,
and correlating the distance of movement with compression distances
of prior polishing pads of known quality.
[0011] An embodiment of an apparatus for detecting in-situ wear of
a CMP polishing pad comprises a spindle supporting a head and a
wafer in contact with a chemical mechanical polishing pad. A visual
identification mark positioned on the spindle. A light source is
configured to illuminate the visual identification mark. A detector
is configured to receive light reflected from the visual
identification mark, such that a reduction in thickness of the pad
causes a change in position of the visual identification mark that
may be correlated with an amount of pad wear.
[0012] An alternative embodiment of an apparatus for detecting wear
of a chemical mechanical polishing pad in-situ comprises a platen
supporting a chemical mechanical polishing pad in contact with a
wafer. A power source has a first terminal in electrical
communication with the platen and the second terminal in electrical
communication with the wafer. A detector is configured to sense a
change in capacitance between the first and second terminals, such
that a reduction in thickness of the pad causes a change in
capacitance that may be correlated with an amount of pad wear.
[0013] These and other embodiments of the present invention, as
well as its features and some potential advantages are described in
more detail in conjunction with the text below and attached
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 shows a cross-sectional view of a chemical mechanical
polishing apparatus.
[0015] FIG. 2 shows a cross-sectional view of an apparatus for
detecting pad wear in accordance with one embodiment of the present
invention.
[0016] FIG. 3 plots polyurethane pad wear versus time.
[0017] FIG. 4 plots compression distance versus applied compression
force for normal and defective CMP pads.
[0018] FIG. 5 shows a cross-sectional view of an apparatus for
detecting pad wear in accordance with an alternative embodiment of
the present invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0019] FIG. 1 is a side view of a chemical mechanical polishing
apparatus. CMP apparatus 100 includes chemical mechanical polishing
pad 104 of thickness Y supported by platen 102. Platen 102 and
polishing pad 104 are in contact with and rotatable about axle 106.
Chemical mechanical polishing slurry 108 is dispensed from vessel
110 to the surface of pad 104.
[0020] Rotatable carousel 118 supports first spindle 116 and second
spindle 120. Head 114 supports wafer 112 in contact with pad 104,
and is secured to and rotatable about first spindle 116. Pad
conditioning disk 124 is secured to and rotatable about second
spindle 120. Conditioning disk 124 typically features a diamond
abrasive useful in regenerating chemical mechanical polishing pad
104 after use.
[0021] Specifically, contact between polishing pad 104 and
conditioning disk 124 roughens the surface of polishing pad 104
from a worn state following a prior polishing operation, and
readies polishing pad 104 for a subsequent polishing operation. A
180.degree. rotation of carousel 118 enables continuous operation
of CMP device 100, by allowing polishing pad 104 to be exposed to
conditioning disk 124 while second polishing pad 130 is in turn
utilized to polish the next wafer secured to head 114.
[0022] FIG. 2 shows a simplified side view of an apparatus for
detecting pad wear in accordance with one embodiment of the present
invention. Wear detection apparatus 200 includes head 202
supporting wafer 206 that is to be polished. Polishing pad 204
having an initial thickness Y is supported by platen 203. Rotatable
spindle 207 biases head 202 and wafer 206 into contact with
chemical mechanical polishing pad 204 with a loading force F of
between approximately 2-4 psi.
[0023] Spindle 207 bears identification mark 208 located at a fixed
position. Initially, identification mark 208 is positioned at
height h.
[0024] Wear detection apparatus 200 further includes optical
interrogation device 210 (such as a laser or other light source)
that is directed at visual identification mark 208. Initially, mark
208 lies at height h and light from source 210 is reflected back to
optical detector 212. However, as polishing pad 204 experiences
wear, it is reduced in thickness. Accordingly, spindle 207 drops
and the height of identification mark 208 is reduced. Because the
path of light from optical interrogation device 210 remains fixed,
light from device 210 is no longer fully reflected by mark 208. The
decrease in intensity of reflected light sensed at detector 212 can
be calibrated at controller 213 to a drop in the height of the mark
and hence a change in thickness of the polishing pad attributable
to pad wear. In making this pad wear determination, controller 213
can take into account the change in mark position attributable to
reduced thickness of the wafer due to wafer polishing.
[0025] FIG. 3 plots pad wear versus time of a polyurethane
polishing pad tested against a diamond conditioning disk of a CMP
apparatus. The pad was maintained in contact with the conditioning
disk at a constant pressure of approximately 0.5 psi. Voltage
levels on the y-axis indicate the intensity of light received by
the optical detector.
[0026] FIG. 3 reveals a steady decline in pad thickness resulting
from continuous abrasion of the polishing pad by the conditioning
disk. FIG. 3 illustrates that wear of a CMP polishing pad can be
constantly monitored in-situ. This quantification of pad wear
enables determination of the optimum time for pad replacement for
each individual pad. This analysis further enables monitoring of
the quality of pads received from vendors, as poor quality pads
will wear at an excessive rate.
[0027] The apparatus of FIG. 2 may allow polishing pad quality to
be determined even before the pad is exposed to polishing
conditions. Specifically, the compressibility of a polishing
pad--its shape change in response to an applied force--may reveal
the quality of the pad material. Compressibility of a CMP polishing
pad may be measured by detecting the change in height of a visual
identification mark on a spindle in response to a loading force of
known magnitude applied to the axle to bias the head and wafer
against the polishing pad.
[0028] Accordingly, FIG. 4, plots displacement distance D (in
.mu.m) versus applied compression force F (in Newtons), for normal
and defective CMP pads. FIG. 4 shows that a defective pad exhibits
a substantially larger displacement distance in response to the
same applied compression force. Again, displacement distance can be
measured through optical interrogation of an identification mark
positioned on an axle supporting a polishing pad.
[0029] While the invention has been described so far in connection
with determination of pad wear through an optical sensor directed
to an axle supporting the pad, the invention is not limited to this
particular embodiment. Other sensor types could be employed to
measure pad wear in-situ, and the resulting method or apparatus
would fall within the scope of the present invention.
[0030] For example, FIG. 5 shows an alternative embodiment in
accordance with the present invention, wherein thickness Y of
polishing pad 504 may be determined by applying a potential
difference across pad 504 and measuring its resulting dielectric
property.
[0031] Specifically, one terminal of power supply 502 is connected
to head 505 supporting wafer 506, and the other terminal of power
supply 502 is connected to platen 508 supporting polishing pad 504.
As a result of this configuration, capacitor structure 512 is
created having as plates wafer 506 and platen 508, and having as a
dielectric chemical mechanical polishing pad 504. As pad 504
experiences wear, its thickness decreases. The distance Y
separating wafer 506 and platen 508 correspondingly decreases. The
correlation between pad thickness and capacitance can be calibrated
to reveal an amount of pad wear.
[0032] Only certain embodiments of the present invention are shown
and described in the instant disclosure. One should understand that
the present invention is capable of use in various other
combinations and environments and is capable of changes and
modification within the scope of the inventive concept expressed
herein. For example, while the invention has been discussed above
in connection with identifying pad wear for identifying pad
replacement and the level of pad quality, one should understand
that the present invention could be employed for other purposes,
such as identifying the point at which a worn pad may begin to
damage the wafer being polished.
[0033] Given the above detailed description of the present
invention and the variety of embodiments described therein, these
equivalents and alternatives along with the understood obvious
changes and modifications are intended to be included within the
scope of the present invention.
* * * * *