U.S. patent application number 13/397845 was filed with the patent office on 2013-08-22 for cmp groove depth and conditioning disk monitoring.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Co., Ltd.. The applicant listed for this patent is Soon Kang Huang, Bo-I Lee, Chin-Hsiang Lin, Jiann Lih Wu, Chi-Ming Yang. Invention is credited to Soon Kang Huang, Bo-I Lee, Chin-Hsiang Lin, Jiann Lih Wu, Chi-Ming Yang.
Application Number | 20130217306 13/397845 |
Document ID | / |
Family ID | 48982623 |
Filed Date | 2013-08-22 |
United States Patent
Application |
20130217306 |
Kind Code |
A1 |
Wu; Jiann Lih ; et
al. |
August 22, 2013 |
CMP Groove Depth and Conditioning Disk Monitoring
Abstract
Some embodiments relate to a chemical mechanical polishing (CMP)
system. The CMP system includes a polishing pad having a polishing
surface, and a wafer carrier to retain a wafer proximate to the
polishing surface during polishing. A motor assembly rotates the
polishing pad and concurrently rotates the wafer during polishing
of the wafer. A conditioning disk has a conditioning surface that
is in frictional engagement with the polishing surface during
polishing. A torque measurement element measures a torque exerted
by the motor assembly during polishing. A condition surface
analyzer determines a surface condition of the conditioning surface
or the polishing surface based on the measured torque. Other
systems and methods are also disclosed.
Inventors: |
Wu; Jiann Lih; (Hsin-Chu
City, TW) ; Lee; Bo-I; (Sindian City, TW) ;
Huang; Soon Kang; (Hsin Chu, TW) ; Yang;
Chi-Ming; (Hsinchu City, TW) ; Lin; Chin-Hsiang;
(Hsinchu, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wu; Jiann Lih
Lee; Bo-I
Huang; Soon Kang
Yang; Chi-Ming
Lin; Chin-Hsiang |
Hsin-Chu City
Sindian City
Hsin Chu
Hsinchu City
Hsinchu |
|
TW
TW
TW
TW
TW |
|
|
Assignee: |
Taiwan Semiconductor Manufacturing
Co., Ltd.
Hsin-Chu
TW
|
Family ID: |
48982623 |
Appl. No.: |
13/397845 |
Filed: |
February 16, 2012 |
Current U.S.
Class: |
451/9 |
Current CPC
Class: |
B24B 37/005 20130101;
B24B 49/16 20130101; B24B 49/18 20130101 |
Class at
Publication: |
451/9 |
International
Class: |
B24B 49/16 20060101
B24B049/16; B24B 49/18 20060101 B24B049/18 |
Claims
1. A chemical mechanical polishing (CMP) system, comprising: a
polishing pad having a polishing surface; a wafer carrier to retain
a wafer proximate to the polishing surface during polishing; a
motor assembly to rotate the polishing pad about a polishing pad
axis and concurrently rotate the wafer about a wafer axis during
polishing of the wafer; a conditioning disk having a conditioning
surface, wherein the conditioning surface is in frictional
engagement with the polishing surface during polishing; a torque
measurement element to measure a torque exerted by the motor
assembly during polishing; and a condition surface analyzer to
determine a surface condition of the conditioning surface or the
polishing surface based on the measured torque.
2. The CMP system of claim 1, further comprising: a feedback path
to adjust a CMP process parameter in real-time during polishing of
the wafer based on the surface condition determined by the
condition surface analyzer.
3. The CMP system of claim 1, wherein the polishing pad includes a
plurality of grooves in the polishing surface, the CMP system
further comprising: a depth measurement element to measure groove
depths of the respective grooves during polishing of the wafer.
4. The CMP system of claim 3, wherein the depth measurement element
comprises an acoustic transducer to measure the groove depths while
a liquid is present on the polishing surface.
5. The CMP system of claim 3, wherein the depth measurement element
is arranged on a scan arm to diametrically traverse over the
polishing pad to measure the groove depths of the respective
grooves.
6. The CMP system of claim 1, wherein the motor assembly rotates
the polishing pad about a platen axis at a first angular velocity
and rotates the wafer about a wafer carrier axis at an second
angular velocity.
7. The CMP system of claim 6, further comprising: a feedback path
to adjust the first angular velocity or the second angular velocity
based on the surface condition determined by the condition surface
analyzer.
8. The CMP system of claim 1, wherein the conditioning surface has
a hardness that is greater than a hardness of the polishing
surface.
9. The CMP system of claim 8, wherein the conditioning surface is a
diamond encrusted surface.
10. The CMP system of claim 2, further comprising: a slurry
dispenser to dispense an abrasive slurry onto the polishing
surface; wherein the feedback path is configured to adjust a slurry
composition or slurry temperature based on the surface condition
determined by the condition surface analyzer.
11. The CMP system of claim 2, wherein wafer carrier includes a
plurality of concentric and variable down-force elements adapted to
apply respective down-forces with respect to the polishing pad to
concentric wafer regions; wherein the feedback path is configured
to adjust the respective down-forces based on the surface condition
determined by the condition surface analyzer.
12. A chemical mechanical polishing (CMP) system for polishing a
wafer, comprising: a platen arranged to rotate about a platen axis;
a polishing pad arranged over the platen and arranged to rotate
about the platen axis coincidentally with the platen, the polishing
pad including a polishing surface having one or more grooves
disposed therein; a depth measurement element to measure groove
depths of respective grooves in real-time during polishing of the
wafer; and a feedback path to adjust a CMP parameter in real-time
based on the respective measured groove depths.
13. The CMP system of claim 12, wherein the depth measurement
element comprises an acoustic transducer to measure the groove
depths while a liquid is present on the polishing surface.
14. The CMP system of claim 13, wherein the liquid comprises slurry
or deionized water.
15. The CMP system of claim 12, wherein the depth measurement
element is arranged on a scan arm to diametrically traverse over
the polishing pad to measure the groove depths of the respective
grooves.
16. A method of chemical mechanical polishing (CMP), comprising:
setting a set of CMP process parameters to be used for planarizing
one or more wafers; providing an abrasive slurry on a polishing
surface of a CMP station; placing a conditioning surface in
frictional engagement with the polishing surface to condition the
polishing surface; placing a to-be-polished wafer surface proximate
to the conditioned polishing surface; polishing the to-be-polished
wafer surface while employing the set of CMP process parameters;
and during polishing of the wafer, measuring a surface condition of
the polishing surface or conditioning surface.
17. The method of claim 16, further comprising: adjusting a CMP
process parameter during polishing based on the measured surface
condition.
18. The method of claim 16, wherein the surface condition is
measured by measuring a torque of a motor assembly used to move the
polishing surface or wafer.
19. The method of claim 16, wherein polishing surface includes a
number of grooves, and wherein the surface condition is measured by
measuring depths of the respective grooves during polishing.
20. The method of claim 19, wherein the depths of the respective
grooves are measured using an acoustic transducer.
Description
BACKGROUND
[0001] Over the last four decades, the density of integrated
circuits has increased by a relation known as Moore's law. Stated
simply, Moore's law says that the number of transistors on
integrated circuits (ICs) doubles approximately every 18 months.
Thus, as long as the semiconductor industry can continue to uphold
this simple "law," ICs double in speed and power approximately
every 18 months. In large part, this remarkable increase in the
speed and power of ICs has ushered in the dawn of today's
information age.
[0002] Unlike laws of nature, which hold true regardless of
mankind's activities, Moore's law only holds true only so long as
innovators overcome the technological challenges associated with
it. One of the advances that innovators have made in recent decades
is to use chemical mechanical polishing (CMP) to planarize layers
used to build up ICs, thereby helping to provide more precisely
structured device features on the ICs.
[0003] To limit imperfections in planarization, improved
planarization processes are described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 shows a block diagram of a CMP system in accordance
with some embodiments.
[0005] FIG. 2 is a top view of a CMP system having a polish pad
that includes a series of concentric grooves, and a groove depth
measurement element traversing over the polish pad.
[0006] FIG. 3 is a cross sectional side view of FIG. 2's CMP
system.
[0007] FIG. 4 shows a block diagram of another CMP system in
accordance with some embodiments.
[0008] FIG. 5 is a flow diagram illustrating a method of performing
a planarization process in accordance with some embodiments.
DETAILED DESCRIPTION
[0009] The present disclosure will now be described with reference
to the drawings wherein like reference numerals are used to refer
to like elements throughout, and wherein the illustrated structures
are not necessarily drawn to scale. It will be appreciated that
this detailed description and the corresponding figures do not
limit the scope of the present disclosure in any way, and that the
detailed description and figures merely provide a few examples to
illustrate some ways in which the inventive concepts can manifest
themselves.
[0010] Conventional CMP techniques lack real-time feedback to
adequately account for changes in the surface condition of
polishing pads and/or conditioning disks. For example, an overly
worn conditioning disk can cause wafers to be planarized more
slowly and/or less uniformly, relative to a new conditioning disk.
Thus, it is imperative to be able to monitor the surface condition
of polishing pads and/or conditioning disks so they can be changed
at an optimum time that strikes a good balance between maximizing
the useful lifetime of the pad/disk, maximizing wafer throughput,
and maximizing wafer surface uniformity.
[0011] FIG. 1 shows a block diagram of a CMP system 100 in
accordance with some embodiments of the present disclosure. The CMP
system 100 includes platen 102, polishing pad 104, slurry arm 106,
wafer carrier 108, and conditioning disk 110. In some embodiments,
this CMP system can process wafers that are 450 mm in diameter,
however it is also applicable to other wafer sizes.
[0012] Prior to wafer planarization, slurry arm 106 dispenses
slurry 111, which contains abrasive slurry particles, onto
polishing surface 112 of polishing pad 104 before wafer
planarization occurs. Motor assembly 114, under control of CMP
controller 116, then rotates the platen 102 and polishing pad 104
(e.g., via platen spindle 118) about a polishing pad axis 120--as
shown by first angular velocity arrow 122. As polishing pad 104
rotates, conditioning disk 110, which can be pivoted via scan arm
124 and rotated about disk axis 142, traverses over polishing pad
104 such that conditioning surface 126 of conditioning disk 110 is
in frictional engagement with polishing surface 112 of polishing
pad 104. In this configuration, conditioning disk 110 scratches or
"roughs up" polishing surface 112 continuously during polishing to
help ensure consistent and uniform planarization. Motor assembly
114 also concurrently rotates a wafer housed within wafer carrier
108 about wafer axis 128 (e.g., via wafer carrier spindle 130)--as
shown by second angular velocity arrow 132. While this
dual-rotation 122, 132 occurs, the wafer is "pressed" into slurry
111 and polishing surface 112 with a down-force applied by wafer
carrier 108. The combination of abrasive slurry 111, dual rotation
(122, 132), and down-force planarizes the lower surface of the
wafer until an endpoint for the CMP operation is reached.
[0013] To remedy shortcomings of conventional CMP systems, CMP
system 100 includes a surface condition analyzer 136 to determine
surface condition(s) of polishing pad 104 and/or conditioning disk
110 in real-time during polishing. In some cases, a feedback path
138 provides for real-time adjustment of CMP process parameters 140
based on the measured surface condition(s). In this way, the
disclosed CMP techniques facilitate consistent and uniform
planarization of wafers. Also, because the real-time measurement
limits downtime for the CMP system 100 in that wafers can be
continuously processed and polishing pads 104 and conditioning
disks 110 are replaced at precisely the time they are spent, these
techniques can also significantly improve manufacturing throughput
while at the same time maximizing the useful lifetime of polishing
pads 104 and conditioning disks 110.
[0014] To determine a surface condition of polishing pad 104, the
polishing pad 104 includes a number of grooves (e.g., 134a, 134b)
in the polishing surface 112. As the polishing pad 104 becomes more
worn, the polishing surface 112 is worn down, thereby reducing the
depth of the grooves. In this way, the groove depths correspond to
the condition of the polishing pad 104. To take advantage of this
behavior, a depth measurement element 142, such as an acoustic
transducer, measures the groove depths of the respective grooves in
real-time during polishing of the wafer. The depth measurement
element 142 can be arranged on a scan arm (not shown) to
diametrically scan over the polishing surface 112 during polishing
to measure these groove depths. The surface condition analyzer 136
can compare the respective measured groove depths to a
predetermined groove depth threshold, and the CMP controller 116
can notify a CMP operator when the polishing pad 104 has reached
the end of its useful life based on the measured groove depths.
[0015] To determine a surface condition of conditioning disk 110,
CMP system 100 includes a torque measurement element 144 to measure
a torque exerted by the motor assembly 114 during polishing. A
surface condition analyzer 136 then determines the condition of
conditioning surface 126 (and possibly the polishing surface 112 to
some extent) based on the measured torque. In making this
determination, the surface condition analyzer 136 makes use of the
fact that measured torque is proportional to the amount of friction
between the engagement and conditioning surfaces 126, 112. Because
the amount of friction measured is set by the conditioning
surface's ability to "rough up" the polishing surface 112, the
measured torque corresponds generally to the overall condition of
the conditioning surface 126. For example, assuming equal slurry
compositions, temperatures, angular velocities, etc.; more measured
torque generally corresponds to more friction between the
conditioning surface 126 and polishing surface 112, which generally
corresponds to a less worn (e.g., newer) conditioning surface 126.
Conversely, a lower torque generally corresponds to smoother (e.g.,
older) conditioning surface 126.
[0016] Based on the measured condition of conditioning surface 126,
the CMP controller 116 can make real-time changes to CMP process
parameters during polishing in some embodiments. For example, as
the conditioning surface 126 becomes more worn (as indicated by
less friction and less measured torque), the CMP controller 116 can
apply more down-force to the conditioning disk 110 (and/or more
up-force from the platen 102) so there is greater frictional
engagement between the conditioning surface 126 and polishing
surface 112. The CMP controller 116 can also apply more down-force
to the wafer via the wafer carrier 108, can increase the platen's
angular velocity 122, can increase the wafer's angular velocity
132, can alter the composition of slurry 111, and/or can increase
the temperature of the slurry 111 to increase the polish rate to
offset the change in conditioning surface 126. Other changes to CMP
process parameters 140 could also be made.
[0017] In addition, in some embodiments, the surface condition
analyzer 136 can compare the measured torque to some predetermined
torque threshold for a given set of CMP process parameters 140,
wherein the predetermined torque threshold corresponds to a torque
at which the conditioning disk 110 is to deemed "spent". For
example, for a given slurry composition, temperature, angular
velocities, etc.; if the torque falls below some predetermined
torque threshold (indicating conditioning surface 126 is too worn),
the conditioning disk 110 is deemed spent. Thus, the CMP controller
116 can notify a CMP operator that it is time to replace the
conditioning disk 110.
[0018] FIGS. 2-3 illustrate a more detailed view of one example of
how groove depths can be measured for a polishing pad 200. FIG. 2's
polishing pad 200 includes a number of grooves 202a, 202b, which
have lower surfaces 204a, 204b that are recessed relative to
polishing surface 206. Although only two grooves are shown, it will
be appreciated that any number of grooves ranging from one to
hundreds or thousands of grooves can be included on the polishing
pad 200, depending on the relative sizes of polishing pad and
respective groove widths. A depth measurement element 208, such as
an acoustic transducer, measures groove depths of the respective
grooves in real-time during wafer polishing. The depth measurement
element 208 can be arranged on a scan arm (not shown) to
diametrically scan over the polishing pad 200 during polishing--as
shown by arrow 210.
[0019] In embodiments where depth measurement element 208 is an
acoustic transducer, the acoustic transducer transmits an acoustic
pulse or wave 214 and subsequently measures a reflected acoustic
pulse or wave 216 which is based on the transmitted acoustic pulse
or wave. Often, this measurement is carried out while a liquid 212,
such as deionized water or slurry for example, is present on the
polishing pad 200 to help limit attenuation of the propagating
acoustic pulse or wave. To measured the groove depth, the acoustic
transducer can analyze a time between transmission of the pulse or
wave 214 and reception of the reflected pulse or wave 216; or can
measure a phase difference between the transmitted pulse or wave
214 and received pulse or wave 216. Thus, to measure a first
polishing pad thickness t1, the acoustic transducer will measure a
first distance dl based on the time or phase difference between the
transmitted and reflected waves or pulses. As the acoustic
transducer continues its scan, it will see a change in the time or
phase difference as it starts to pass over groove. In particular,
it will see a longer time delay between transmitted and reflected
pulses or waves or a corresponding change in phase difference,
which is indicative of a second distance d1. By taking the
difference between d1 and d2, the acoustic transducer can determine
the corresponding groove depth.
[0020] If a measured groove depth is less than some predetermined
groove depth, it can indicate the polishing pad is spent. Hence, in
such an instance, a CMP controller can notify a CMP operator so the
CMP operator can replace the polishing pad 200 with a new polishing
pad. Further, in some embodiments it is possible that the polishing
ability of the polishing pad 200 changes as the pad wears. Because
of this, monitoring the groove depth in real-time allows the CMP
system to account for changes in the polishing characteristics of
the polishing pad 200 as it wears. For example, as the polishing
surface becomes more worn (as indicated by diminished groove
depths), the CMP controller 116 can apply more down-force to the
wafer via the wafer carrier 108, can increase the platen's angular
velocity 122, can increase the wafer's angular velocity 132, can
alter the composition of slurry 111, and/or can increase the
temperature of the slurry 111 to increase the polish rate or
otherwise change the CMP parameters to offset the change in
polishing surface.
[0021] FIG. 4 show a cross-sectional side view of another CMP
station 400 in accordance with some embodiments. CMP station 400
comprises platen 402, polishing pad 404 supported by platen 402,
wafer carrier 406 to hold wafer 408 proximate to polishing pad 404
during polishing, and conditioning disk 422 having conditioning
surface 424. Wafer carrier 406 includes an annular retaining ring
410, inside of which a pocket 412 houses wafer 408. A plurality of
concentric, variable-pressure elements (PE) 414a-414c are included
on wafer carrier 406. The variable pressure elements 414, which are
proximate to pocket 412, exert independent amounts of suction or
pressure onto corresponding concentric regions on the back-side of
the wafer 408a. Corresponding concentric surfaces on the front of
the wafer 408b may be called "to-be-polished" wafer surfaces.
[0022] In some CMP processes, wafer 408 is held inside pocket 412
with upward suction applied to wafer's backside by variable
pressure elements 414 so as to keep the wafer 408 raised above the
lower face of retaining ring 410. Platen 402 is then rotated about
platen axis 418, which correspondingly rotates polishing pad 404.
Abrasive slurry 420 in then dispensed onto the polishing pad 404,
and conditioning disk 422 is lowered onto polishing pad 404. A
platen motor (not shown) then begins rotating wafer carrier 406
around platen axis 418. Meanwhile, wafer carrier 406 is lowered,
retaining ring 410 is pressed onto polishing pad 404, with wafer
408 recessed just long enough for wafer carrier 406 to reach
polishing speed. When wafer carrier 406 reaches wafer polishing
speed, wafer 408 is lowered facedown inside pocket 412 to contact
the surface of polishing pad 404 and/or abrasive slurry 420, so
that the wafer 408 is substantially flush with and constrained
outwardly by retaining ring 410. Retaining ring 410 and wafer 408
continue to spin relative to polishing pad 404, which is rotating
along with platen 402. This dual rotation, in the presence of the
downforce applied to wafer 408 and the abrasive slurry 420, cause
the wafer 408 to be gradually planarized. During this planarization
process, the surface condition of conditioning disk 422 and/or
polishing pad 404 can be monitored in real-time, and CMP parameters
can be adjusted based on the measured surface condition(s).
[0023] After CMP, wafer carrier 406 and wafer 408 are lifted, and
polishing pad 404 is generally subjected to a high-pressure spray
of deionized water to remove slurry residue and other particulate
matter from the pad 404. Other particulate matter may include wafer
residue, CMP slurry, oxides, organic contaminants, mobile ions and
metallic impurities. Wafer 408 is then subjected to a post-CMP
cleaning process.
[0024] FIG. 5 illustrates another method of planarization in
accordance with some embodiments of the present disclosure. While
this method and other methods disclosed herein may be illustrated
and/or described as a series of acts or events, it will be
appreciated that the illustrated ordering of such acts or events
are not to be interpreted in a limiting sense. For example, some
acts may occur in different orders and/or concurrently with other
acts or events apart from those illustrated and/or described
herein. In addition, not all illustrated acts may be required to
implement one or more aspects or embodiments of the disclosure
herein. Further, one or more of the acts depicted herein may be
carried out in one or more separate acts and/or phases.
[0025] As FIG. 5 shows, method 500 starts at 502 when CMP process
parameters are set for a CMP system. CMP process parameters can
include, but are not limited to: a polish time for which wafers are
to be polished, a down-force to be applied to a to-be-polished
wafer surface relative to a polishing pad, a down-force to be
applied to the conditioning surface, an angular velocity of the
polish pad or wafer, a slurry composition or a slurry temperature.
A wafer typically includes a number of electrical connections and
electrical isolation regions that are established using alternating
layers of conductors and insulators.
[0026] In step 504, the method provides an abrasive slurry on a
polishing surface of the CMP system.
[0027] In 506, the method places a conditioning surface in
frictional engagement with the polishing surface to condition the
polishing surface. The conditioning surface typically has a
hardness that is greater than that of the polishing surface. For
example, in many embodiments the conditioning surface is a diamond
encrusted surface.
[0028] In 508, the method places a to-be-polished wafer surface
proximate to the conditioned polishing surface.
[0029] In 510, the method polishes the to-be-polished wafer surface
while using the CMP process parameters.
[0030] In 512, during polishing of the wafer, the method measures a
surface condition of the polishing surface and/or conditioning
surface.
[0031] In 514, the method adjusts one or more CMP process
parameters during polishing based on the measured surface
condition.
[0032] Thus, it will be appreciated that some embodiments relate to
a CMP system. The CMP system includes a polishing pad having a
polishing surface, and a wafer carrier to retain a wafer proximate
to the polishing surface during polishing. A motor assembly rotates
the polishing pad about a polishing pad axis and concurrently
rotates the wafer about a wafer axis during polishing of the wafer.
A conditioning disk has a conditioning surface that is in
frictional engagement with the polishing surface during polishing.
A torque measurement element measures a torque exerted by the motor
assembly during polishing. A condition surface analyzer determines
a surface condition of the conditioning surface or the polishing
surface based on the measured torque.
[0033] Other embodiments relate to a CMP system for polishing a
wafer. This CMP system includes a platen arranged to rotate about a
platen axis, and a polishing pad arranged over the platen. The
polishing pad is arranged to rotate about the platen axis
coincidentally with the platen, and includes a polishing surface
having one or more grooves disposed therein. A depth measurement
element measures groove depths of the respective grooves in
real-time during polishing of the wafer. A feedback path adjusts a
CMP process parameter in real-time based on the respective measured
groove depths.
[0034] Another method relates to chemical mechanical polishing
(CMP). In this method, a set of CMP process parameters are set.
These CMP parameters are to be used to planarize one or more
wafers. The method provides an abrasive slurry on a polishing
surface of a CMP station. The method places a conditioning surface
in frictional engagement with the polishing surface to condition
the polishing surface. A to-be-polished wafer surface is placed
proximate to the conditioned polishing surface. The to-be-polished
wafer surface is then polished while employing the set of CMP
process parameters. During polishing of the wafer, the method
measures a surface condition of the polishing surface or
conditioning surface. A CMP process parameter can be adjusted
during polishing based on the measured surface condition.
[0035] Although the disclosure has been shown and described with
respect to a certain aspect or various aspects, equivalent
alterations and modifications will occur to others skilled in the
art upon the reading and understanding of this specification and
the annexed drawings. In particular regard to the various functions
performed by the above described components (assemblies, devices,
circuits, etc.), the terms (including a reference to a "means")
used to describe such components are intended to correspond, unless
otherwise indicated, to any component which performs the specified
function of the described component (i.e., that is functionally
equivalent), even though not structurally equivalent to the
disclosed structure which performs the function in the herein
illustrated exemplary embodiments of the disclosure. In addition,
while a particular feature of the disclosure may have been
disclosed with respect to only one of several aspects of the
disclosure, such feature may be combined with one or more other
features of the other aspects as may be desired and advantageous
for any given or particular application. Furthermore, to the extent
that the terms "including", "includes", "having", "has", "with", or
variants thereof are used in either the detailed description and
the claims, such terms are intended to be inclusive in a manner
similar to the term "comprising".
* * * * *