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Int. J. Nano Technology (IJNT)
1
A comprehensive review of end point detection in
chemical mechanical polishing for deep-submicron
integrated circuits manufacturing
H. Hocheng and Y. -L. Huang
Department of Power Mechanical Engineering,
National Tsing-Hua University, Hsinchu, Taiwan, R.O.C.
E-mail: [email protected]
Abstract: As the number of metal levels and the wafer size increase, the
need for global planarity across the wafer becomes more crucial. Chemical
mechanical planarization (CMP) is considered the key technique to achieve
this goal. Accurate in situ end point detection and monitoring method can
reduce the product variance, improve the yield and throughput. During
CMP process, the wafer is brought downward against the polishing pad
completely. The monitoring of the wafer polishing in such a con®guration
becomes a dif®cult task. Many methods have been proposed in the past
years, including the optical, electrical, acoustical/vibrational, thermal,
frictional, chemical/electrochemical methods and others, which are
critically reviewed in this study. The mainstream of the industrial
application and the future trend are investigated.
Keywords: chemical mechanical planarization, chemical mechanical
polishing, CMP, end point detection, monitoring, semiconductor.
Reference to this paper should be made as follows: Hocheng, H. and
Huang, Y.-L. (2002) `A comprehensive review of end point detection in
chemical mechanical polishing for deep-submicron integrated circuits
manufacturing', Int. J. Nano Technology, Vol. X, No. Y, pp. 1±18.
Biographical notes: Professor H. Hocheng earned his Diplom-Ing. from
Technische Hochschule at Aachen and PhD from University of California
at Berkeley. He has been faculty at National Tsing Hua University since
1989. He was awarded Outstanding Research from National Science
Council. His research interest lies in the area of innovative processing of
materials.
Mr. Y.L. Huang earned his Bachelor's degree of Engineering from
National Chiao-Tung University in 1995. He has been since then working
on his doctorate theses at National Tsing-Hua University. His current
research interest is the end point detection for CMP process.
1 Introduction
With the shrinking device scale and higher performance requirement of integrated
circuits (IC), the utilization of the advanced photolithographic and anisotropic
etching techniques are essential. The increasing number of interconnection layers
requires highly planarized surface on every layer to ensure that the accumulated
roughness of the layers are less than the depth of focus of the lithography stepper.
Copyright # 2002 Inderscience Enterprises Ltd.
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H. Hocheng and Y.-L. Huang
Figure 1
Schematic diagram of CMP machine.
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The innovative solution to improve the surface planarity was introduced, known as
chemical mechanical planarization (CMP) technique. CMP has become a key
process for the Cu interconnects, low-k materials and dual damascene process.
During a CMP process, the wafer is held by a rotating carrier that brings the
wafer against a rotating circular pad or a linearly moving belt with an applied
downward force, as shown in Figure 1. The slurry made of abrasive particles
suspended in a chemically etching liquid is dispensed on the pad to achieve the
removal of the surface layer. As more wafers are polished, the pad starts to degrade
and affects its planarizing ability. In order to ensure the wafers are properly
planarized and to control the constant yield of CMP, the on-line monitoring and end
point detection techniques are needed. This study presents a review of the existing
monitoring and end point detection methods shown in the journals, conference
proceedings, patents and industrial reports.
2
De®nition of end point
Monitoring for CMP processes can be divided into two categories, in situ quality
monitoring and end point detection. The former is to detect the abnormal wafer
conditions, such as the surface scratches and wafer slipping, and the abnormal
conditions of the applied consumables, namely pad and slurry, during CMP. The
end point detection is to determine when to stop a CMP process. For oxide CMP, the
end point is reached when the wafer surface is ¯at enough for the following
lithography process, and the thickness of the dielectric layer enough to insulate the
metal lines, as shown in Figure 2(a). For metal CMP, the fully removal of the extra
metal on the wafer surface without overpolishing the metal lines inside the vias or
contacts that might cause dishing and erosion de®nes the end point, as shown in
Figure 2(b). End point detection is considered a vital step in the volume production
of high value-added semiconductor manufacturing.
Currently, CMP processes are operated based on empirical open-loop designs,
without monitoring and feedback to determine the end point of the process. Since
the wafer surface is in full engagement with the polishing pad and rotated by the
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A comprehensive review of end point detection in chemical mechanical polishing
3
Figure 2 Schematic diagram of CMP end point for (a) Oxide CMP process; (b) Metal CMP process.
carrier, in situ detection of the end point of a CMP process is dif®cult to perform.
The production line often takes two hours per shift for off-line product evaluation,
thus reducing the CMP equipment capacity by 50% [1]. Therefore an accurate,
robust and easy-to-use monitoring technique is required.
3 End point detection methods
Numerous approaches have been proposed for in situ monitoring and end point
detection. In the past three years, T. Bibby and K. Holland [1], D.L. Hetherington
and D.J. Stein [2, 3], and H. Hocheng, H.Y. Tsai and Y.-L. Huang [4] have reviewed
the proposed approaches. In this study, Tables 1, 2, 3, 4, 5, and 6 summarize the US
patents using optical, electrical, acoustical/vibrational, thermal, frictional, and
chemical/electrochemical methods, respectively. Table 7 summarizes a variety of
miscellaneous patents that cannot ®t into the above categories.
3.1
Optical methods
Optical method is one of the most practically used methods in monitoring CMP
processes. Many researches have devoted into this area [5±18]. These researches
mainly focused on the various arrangement of the optical measuring module and the
processing algorithms of the detected signal.
The optical measuring module can be installed inside the platen [Table 1,
5,433,651, 5,609,511, 5,838,447, 5,893,796, 5,964,643, 5,985,679, 6,045,439,
6,071,177, 6,074,517, 6,106,662, 6,111,634, 6,146,248, 6,159,073, 6,171,181,
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H. Hocheng and Y.-L. Huang
Table 1 Optical monitoring for CMP.
US patent no.
Date
5,081,796
5,413,941
5,427,878
5,433,651
5,461,007
5,483,568
5,499,733
5,605,760
5,609,511
5,658,183
5,663,797
5,667,424
5,672,091
5,691,253
5,695,660
5,708,506
5,724,144
5,730,642
5,733,171
5,777,739
5,801,066
5,823,853
5,838,447
5,838,448
5,872,633
5,891,352
5,893,796
5,899,792
5,910,846
5,934,974
5,936,733
5,949,927
5,961,369
5,964,643
5,985,679
5,993,289
6,024,628
6,028,669
6,045,439
6,071,177
Jan. 21, 1992
May 9, 1995
Jun. 27, 1995
Jul. 18, 1995
Oct. 24, 1995
Jan. 9, 1996
Mar. 19, 1996
Feb. 25, 1997
Mar. 11, 1997
Aug. 19, 1997
Sep. 2, 1997
Sep. 16, 1997
Sep. 30, 1997
Nov. 25, 1997
Dec. 9, 1997
Jan. 13, 1998
Mar. 3, 1998
Mar. 24, 1998
Mar. 31, 1998
Jun. 7, 1998
Sep. 1, 1998
Oct. 20, 1998
Nov. 17, 1998
Nov. 17, 1998
Feb. 16, 1999
Apr. 6, 1999
Apr. 13, 1999
May 4, 1999
Jun. 8, 1999
Aug. 10, 1999
Aug. 10, 1999
Sep. 7, 1999
Oct. 5, 1999
Oct. 12, 1999
Nov. 16, 1999
Nov. 30, 1999
Feb. 15, 2000
Feb. 22, 2000
Apr. 4, 2000
Jun. 6, 2000
6,074,517
6,075,606
6,077,452
6,106,662
6,110,752
6,111,634
6,114,706
6,117,780
6,146,242
6,146,248
6,159,073
6,172,756
6,190,234
Jun. 13, 2000
Jun. 13, 2000
Jun. 20, 2000
Aug. 22, 2000
Aug. 29, 2000
Aug. 29, 2000
Sep. 5, 2000
Sep. 12, 2000
Nov. 14, 2000
Nov. 14, 2000
Dec. 12, 2000
Jan. 9, 2001
Feb. 20, 2001
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Assignee
End point detection
Micron Technology Inc.
Micron Technology Inc.
Digital Equipment Corp.
IBM
Motorola
Kabushiki Kaisha Toshiba
Luxtron
Rodel
Hitachi
Micron Technology
Micron Technology
Chartered Semiconductor
Ebara
Motorola
Luxtron
Applied Materials
IBM, Toshiba
Micron Technology
Speedfam
Micron Technology
Micron Technology
Speedfam
Ebara
Nikon
Speedfam
Luxtron
Applied Materials
Nikon
Micron Technology
Aplex Group
Micron Technology
Wallace T.Y. Tang
Speedfam-IPEC
Applied Materials
LSI Logic
Speedfam-IPEC
United Microelectronics Corp.
Luxtron
Applied Materials
Taiwan Semiconductor
Manufacturing Co. Ltd.
LSI Logic
Trung T. Doan
Luxtron
Speedfam-IPEC
Luxtron
Lam Research
Micron Technology
Mosel Vitelle
Strasbaugh
Lam Research
Applied Materials
Filmetrics
Applied Materials
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*
*
*
*
*
*
*
*
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5
Table 1 continued.
US patent no.
6,214,734
6,271,047
6,280,289
6,285,035
6,287,171
6,301,006
6,309,276
6,309,555
Date
Apr. 10, 2001
Aug. 7, 2001
Aug. 28, 2001
Sep. 4, 2001
Sep. 11, 2001
Oct. 9, 2001
Oct. 30, 2001
Oct. 30, 2001
Assignee
End point detection
VLSI Technology
Nikon
Applied Materials
LSI Logic
Speedfam-IPEC
Micron Technology
Applied Materials
United Microelectronics Corp.
Note: *also for quality monitoring.
Table 2 Electrical monitoring for CMP.
US patent no.
4,793,895
5,081,421
5,132,617
5,213,655
5,242,524
5,265,378
5,321,304
5,337,015
5,486,129
5,559,428
5,644,221
5,685,766
5,731,697
5,738,562
5,762,536
5,865,665
5,868,896
6,020,264
6,129,613
6,143,123
6,185,865
6,254,454
Date
Assignee
End point detection
Dec. 27, 1988
Jan. 14, 1992
Jul. 21, 1992
May 25, 1993
Sep. 7, 1993
Nov. 30, 1993
Jun. 14, 1994
Aug. 9, 1994
Jan. 23, 1996
Sep. 24, 1996
Jul. 1, 1997
Nov. 11, 1997
Mar. 24, 1998
Apr. 14, 1998
Jun. 9, 1998
Feb. 2, 1999
Feb. 9, 1999
Feb. 1, 2000
Oct. 10, 2000
Nov. 7, 2000
Feb. 13, 2001
Jul. 3, 2001
IBM
AT&T Bell Laboratories
IBM
IBM
IBM
LSI Logic
LSI Logic
IBM
Micron Technology
IBM
IBM
Speedfam
IBM
Micron Technology
Lam Research
William Yueh
Micron Technology
IBM
Philips Elec. North America
Micron Technology
Lam Research
Agere Systems
Table 3 Acoustical/vibration monitoring for CMP.
US patent no.
5,222,329
5,240,552
5,245,794
5,399,234
5,439,551
5,876,265
5,904,609
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Date
Assignee
Jun. 29, 1993
Aug. 31, 1993
Sep. 21, 1993
Mar. 21, 1995
Aug. 8, 1995
Mar. 2, 1999
May 18,1999
Micron Technology
Micron Technology
Advanced Micro Devices
Motorola
Micron Technology
Fujitsu
Fujitsu
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Table 4 Thermal monitoring for CMP.
US patent no.
Date
Assignee
End point detection
5,196,353
5,597,442
Mar. 23, 1993
Jan. 28, 1997
5,643,050
Jul. 1, 1997
5,647,952
Jul. 15, 1997
5,722,875
5,834,377
Mar. 3, 1998
Nov. 10, 1998
5,891,352
6,007,408
6,077,452
6,077,783
6,110,752
6,150,271
Apr. 6, 1999
Dec. 28, 1999
Jun. 20, 2000
Jun. 20, 2000
Aug. 29, 2000
Nov. 21, 2000
Micron Technology
Taiwan Semiconductor
Manufacturing Co. Ltd.
Industrial Technology Research
Institute
Industrial Technology Research
Institute
Tokyo Electron, IPEC-Planar
Industrial Technology Research
Institute
Luxtron
Micron Technology
Luxtron
LSI Logic
Luxtron
Lucent Technology
Table 5 Frictional monitoring for CMP.
US patent no.
5,036,015
5,069,002
5,308,438
5,562,529
5,595,526
5,624,300
5,639,388
5,643,046
5,667,629
5,743,784
5,830,041
5,846,882
6,046,111
6,268,224
6,293,845
Date
Assignee
End point detection
Jul. 30, 1991
Dec. 3, 1991
May 3, 1994
Oct. 8, 1996
Jan. 21, 1997
Apr. 29, 1997
Jun. 17, 1997
Jul. 1, 1997
Sep. 16, 1997
Apr. 28, 1998
Nov. 3, 1998
Dec. 8, 1998
Apr. 4, 2000
Jul. 31, 2001
Sep. 25, 2001
Micron Technology
Micron Technology
IBM
Fujitsu
Intel
Fujitsu
Ebara
Kabushiki Kaisha Toshiba
Chartered Semiconductor
Applied Materials
Ebara
Applied Materials
Micron Technology
LSI Logic
Mitsubishi Materials
*
Note: *also for quality monitoring.
6,190,234, 6,280,289, 6,285,035], at the periphery of the platen [Table 1, 5,081,796,
5,413,941, 5,672,091], or inside the carrier [Table 1, 5,695,660, 5,891,352, 5,949,927,
6,028,669, 6,077,452, 6,110,752, 6,172,756, 6,287,171], as shown in Figure 3. In the
®rst case, the measuring light is directed to the wafer surface through windows
opened on the pad and in the platen. Hence the measurement is performed every
time the window passes beneath the wafer. In the second case, the wafer has to move
partly outside the pad for measurement. This gives the opportunities to clean the
wafer surfaces with water or compressed air before or during measurement, which
also gives a constant interface for the measuring light. In the third case, the
measuring module inside the carrier directs the measuring light through the wafer
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Table 6 Chemical/electrochemical monitoring for CMP.
US patent no.
5,637,185
5,733,176
5,836,805
5,876,266
5,911,619
6,071,818
6,080,670
6,117,779
6,121,147
6,126,848
6,206,769
6,214,732
6,251,784
6,258,205
6,258,231
6,261,851
6,293,847
6,325,706
Date
Assignee
End point detection
Jun. 10, 1997
Mar. 31, 1998
Nov. 17, 1998
Mar. 2, 1999
Jun. 15, 1999
Jun. 6, 2000
Jun. 27, 2000
Sep. 12, 2000
Sep. 19, 2000
Oct. 3, 2000
Mar. 27, 2001
Apr. 10, 2001
Jun. 26, 2001
Jul. 10, 2001
Jul. 10, 2001
Jul. 17, 2001
Sep. 25, 2001
Dec. 4, 2001
Rensselaer
Micron Technology
Lucent Technology
IBM
IBM
LSI Logic
LSI Logic
LSI Logic
LSI Logic
IBM
Micron Technology
Lucent Technology
IBM
LSI Logic
Agere Systems
IBM
Agere Systems
Lam Research
*
Note: *also for quality monitoring.
Table 7 Miscellaneous monitoring for CMP.
US patent no.
Date
Assignee
End point
detection
5,234,868
5,492,594
5,609,718
5,618,447
5,637,031
5,643,048
5,655,951
5,659,492
5,700,180
5,705,435
5,720,845
5,736,427
5,834,375
5,834,645
5,851,135
6,113,466
Aug. 10, 1993
Feb. 20, 1996
Mar. 11, 1997
Apr. 8, 1997
Jun. 10, 1997
Jul. 1, 1997
Aug. 12, 1997
Aug. 19, 1997
Dec. 23, 1997
Jan. 6, 1998
Feb. 24, 1998
Apr. 7, 1998
Nov. 10, 1998
Nov. 10, 1998
Dec. 22, 1998
Sep. 5, 2000
6,113,479
6,117,777
6,120,347
6,150,260
6,159,786
Sep. 5, 2000
Sep. 12, 2000
Sep. 19, 2000
Nov. 21, 2000
Dec. 12, 2000
6,160,314
6,276,987
Dec. 12, 2000
Aug. 21, 2001
IBM
IBM
Micron Technology
Micron Technology
Industrial Technology Research Institute
Micron Technology
Micron Technology
IBM
Micron Technology
Industrial Technology Research Institute
Keh-Shium Liu
Micron Technology
Industrial Technology Research Institute
Speedfam
Micron Technology
Taiwan Semiconductor Manufacturing
Co. Ltd.
Obsidian
Chartered Semiconductor
Micron Technology
Chartered Semiconductor
Taiwan Semiconductor Manufacturing
Co. Ltd.
United Microelectronics Corp.
IBM
Note: *also for quality monitoring.
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Figure 3 Optical methods to monitor CMP: (a) Inside the platen [US patent 6,280,289]; (b) At the
periphery of the platen [US patent 5,081,796] and (c) Inside the carrier [US patent 5,695,660.]
substrate to the wafer surface. This technique can eliminate the possible interruption
of the slurry or the cleaning water.
The applied signal processing algorithms vary with different CMP processes. For
the oxide CMP processes, the changing oxide ®lm thickness can be measured by the
changes in wavelength of the re¯ected lights. While in metal CMP processes, the
removal of a re¯ective surface tells the end point. The comparison of the spectra is
also used for the analysis of signal [13].
The optical technique is the most intuitive method to monitor CMP processes.
But for a patterned wafer, the scattering and diffraction effects due to the existence
of the metal lines often interfere the measurement. Besides, the optical methods
measure only one point on wafer surface to represent the condition across the whole
wafer, which can lead to wrong judgements.
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Figure 4 An electrical method to monitor CMP [US patent 5,337,015].
3.2
Electrical methods
Methods in this section measure the changes of electrical properties or use
the sensors for certain signals to detect the process end point. Most of the references
in this area are found in patents. Many of the methods use the embedded electrodes
in the pad or on the carrier to measure the variations in the electrical conductivity,
capacity, impedance, or resistance during CMP processes, as shown in Figure 4.
These methods require a modi®ed carrier and platen to accommodate the electrodes
and a complex wiring route, which seriously limit the acceptance in the practical
applications.
Displacement sensors, such as LVDT (line variable displacement transducer),
measure the small position difference of the carrier to estimate the ®lm thickness
of the wafer held by the carrier [Table 2, 5,868,896]. Pressure sensors were also used
to detect the pressure variance of the carrier [Table 2, 6,143,123, 6,129,613] or in
the bearing ¯uid [Table 2, 6,186,865]. The pressure sensor generates a signal in response
to the measured pressure that corresponds to a planarizing parameter of the wafer.
3.3
Acoustic/vibrational methods
CMP processes are often used to remove the surplus metal layers from wafer surface.
Different acoustic waves and vibrations are sent out while polishing different
materials. The acoustic signal can be detected either by acoustic sensors attached to
the equipment or by a microphone located near the wafer being polished, as shown
in Figure 5. Vibrations are detected by commercial accelerometers. The frequency
spectrum and the signal magnitude are obtained from the acquired signals for further
analysis [19±26].
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H. Hocheng and Y.-L. Huang
Figure 5
An acoustical method to monitor CMP [US patent 5,222,329].
Page 10 of 18
Using acoustic methods to monitor CMP processes can ®lter low-frequency
background noise easily, especially when measuring the acoustic emission (AE)
signal to detect the end point and to monitor the abnormal conditions [4, 22±24]. The
inherent high frequency feature of AE signal keeps the acquired signal away from
low-frequency noise. However, it requires that the sensors be placed as close to the
acoustic source, i.e. the polished wafer, as possible, which makes the proper sensor
placement a challenge.
3.4
Thermal methods
Thermal methods measure the thermal properties of the pad or the wafer during
CMP, as shown in Figure 6. Since the temperature does affect chemical reactions,
many CMP equipments have already installed a platen temperature controller or a
pad temperature-measuring module. Thus many investigators have tried to use the
thermal principles to detect the end point of metal CMP [26±38]. Some researches
used an infra-red camera to take the full 2-dimensional thermal images instead of the
temperature of one point on the pad [26, 27]. The information of the temperature and
the thermal emissivity of the pad can be extracted from the acquired thermal images,
which can be used to evaluate the polishing end point as well as the pad life [27, 28].
The temperature distribution was also found closely related to the kinematic
nonuniformity of the wafer [28].
The advantage of this technique is that it can perform the measurement at a
distance from the pad without attaching sensors with the entangled wires. However,
the usage of thermal methods is limited for metal CMP. This is due to the low
sensitivity of the change of the temperature distribution correlated to the uniformity
variation of the oxide layer on the wafer.
3.5
Frictional methods
The frictional methods measure the change of the torque, the motor current [32, 33,
34, 38], or the motor voltage applied to the carrier or the platen [13, 36]. This is also a
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A comprehensive review of end point detection in chemical mechanical polishing
Figure 6 A thermal method to monitor CMP [US patent 5,722,875].
Figure 7 A frictional method to monitor CMP [US patent 5,639,388].
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Figure 8
A chemical method to monitor CMP [US patent 6,261,851].
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widely used method to detect the end point of metal CMP processes. The hardness of
the oxide layer differs from that of the metal layer, and so is the coef®cient of friction
of the two layers engaged with the pad. Thus when the upper metal layer is removed
and the pad starts to polish the underlying oxide layer, the electric motor has to
change the power to drive the carrier or the platen. The power variation is used to
monitor the end point of removal of the metal layer. However, the acquired signal
often contains considerable unwanted noise and needs to be ®ltered, or even the
change is too weak to judge, that limits its applications.
3.6
Chemical/electrochemical methods
Recently, some researches have used chemical and electrochemical methods for
monitoring, especially reported in the US patents. The proposed methods mainly
measure the particle size [39, 40], the presence of certain vapour [Table 6, 6,293,847,
6,261,851, 6,080,670], the electrochemical potential [Table 6, 6,258,231, 6,214,732],
zeta potential, conductivity [Table 6, 5,836,805, 6,251,784], or pH level of the slurry
or the wafer to detect the end point. For example, during metal CMP, the
conductivity of the waste slurry or the current that passes through the waste slurry
rises gradually as a function of time, levels off, and then decreases [Table 6,
5,836,805]. When the current, which will never decrease to zero, reaches
approximately zero, the end point is reached. The disadvantage of this method is
the electrodes have to contact the rotating wafer or the slurry to measure the data.
The response time of the method is also a concern.
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3.7
13
Miscellaneous methods
There are methods cannot be categorized into the previous sections [41±46]. Most of
these techniques involve the process parameters operation. For example, the US
patent 5, 705, 435 monitors the end point by the ratio of the removal rates of the
dielectric layers with and without pattern layer beneath. Others use a spacer of
known thickness to stop polishing at the desired polishing depth, or use a self-stop
layer [45]. These methods can be achieved without extra equipment or performing
data analysis, but they also require inserting a stop layer with lower removal rate and
thus increasing the complexity of the whole semiconductor process. A comprehensive database of the removal rates of different materials under different operating
parameters is also required.
4 Analysis of monitoring techniques
4.1
Mainstream of industrial applications
Based on the survey shown in the previous sections, one can conclude that the major
efforts of end point detection were devoted to the application of optical principles.
Actually most of the related US patents apply optical methods to monitor CMP
processes. Figure 9 shows a comparison of the commercial CMP equipment vendors
with their number of ®led patents of different methods. It shows that all vendors
have patents in the area of optical methods, and these techniques are used on their
own CMP equipments. It is the industrial point of view that the optical methods are
the most practical to monitor CMP processes. On the other hand, many vendors
have investigated the frictional and thermal methods. While the optical methods
provide data of only one point of the wafer, the frictional and thermal methods give
information across the whole wafer. Therefore most commercialized CMP machines
now apply the optical technique to monitor the end point, whereas at the same time
provide the data of pad temperature and motor current for process monitoring.
Figure 9 Comparison of patented methods among major CMP vendors.
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H. Hocheng and Y.-L. Huang
Figure 10 Comparison of patented amount among different categories.
4.2
Future trend
4.2.1 Versatile development
Recently, researches that investigated the acoustical/vibrational and chemical/
electrochemical techniques are gradually increasing, as shown in Figure 10. The use
of acoustical/vibrational methods can prevent the interference of low-frequency
noise, while a successful ®ltering and signal processing plus the robust mountings of
the sensors are the prerequisites.
4.2.2 Fusion of multiple sensors
Since each monitoring method possesses its advantages and disadvantages, a multisensor system compensating the individual drawbacks is desired as a solution.
Several CMP equipments now are installed with optical as well as thermal/frictional
sensors. A good diagnostic approach to the analysis of the acquired multiple data is
required in the future.
4.2.3 Beyond metal CMP
Most of the current methods are used for metal CMP. There is no plausible method
to detect the end point for oxide CMP due to the limited changes in wafer surface
during the process. A practical method to monitor the oxide CMP is desired, which
can be also applied to the mass LCD production.
5
Conclusions
An extensive review of the existing end point detection techniques for CMP is
provided in this paper. Based on the applied sensors, these techniques can be
categorized into optical, electrical, acoustical/vibrational, thermal, frictional,
chemical/electrochemical methods and others. The mainstream of current industrial
practice is the optical applications, while recently the acoustical/vibrational and the
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A comprehensive review of end point detection in chemical mechanical polishing
15
chemical/electrochemical methods have been explored widely. Many vendors now
provide secondary monitoring setup other than the optical devices on their CMP
equipment. In the future, the fusion of multiple sensors with sophisticated diagnostic
approach will be pursued. The monitoring technique beyond the metal CMP for
broader applications such as LCD production is desired.
6 Acknowledgement
The current research is supported by National Science Council under contract
NSC90±2212-E007±064.
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