U.S. patent application number 10/101605 was filed with the patent office on 2002-09-26 for method and apparatus for measuring properties of a polishing pad.
Invention is credited to Choi, Bong, Kim, Tae-Jin, Song, Ju-Hun.
Application Number | 20020137434 10/101605 |
Document ID | / |
Family ID | 19707253 |
Filed Date | 2002-09-26 |
United States Patent
Application |
20020137434 |
Kind Code |
A1 |
Choi, Bong ; et al. |
September 26, 2002 |
Method and apparatus for measuring properties of a polishing
pad
Abstract
A comprehensive measurement of properties of a polishing pad of
a CMP apparatus is used to create a database by which the CMP
apparatus can be maintained and the polishing process can be
precisely controlled. The measuring apparatus includes a measuring
table and a control section. The measuring table has a flat top
surface on which the polishing pad is placed, a camera, a sensor
for sensing the relative location of the top surface of the
polishing pad, a bracket to which the camera and the sensor are
fixed, and an X-Y drive for moving the bracket in X- and
Y-directions orthogonal to each other. The control section controls
the operation of the camera, the sensor and the X-Y drive, and
processes signals from the camera and sensor, so that a profile of
the surface of the polishing pad can be discerned and an image of
the surface of the polishing pad can be produced. The control
section also assigns values to the sensed data and displays the
values of the measured data, graphs and a surface image of the
polishing pad. The measuring apparatus can also measure the
hardness of the polishing pad and the transmittance through a
transparent window of the polishing pad.
Inventors: |
Choi, Bong; (Suwon-si,
KR) ; Song, Ju-Hun; (Suwon-si, KR) ; Kim,
Tae-Jin; (Yongin-si, KR) |
Correspondence
Address: |
VOLENTINE FRANCOS, P.L.L.C.
Suite 150
12200 Sunrise Valley Drive
Reston
VA
20191
US
|
Family ID: |
19707253 |
Appl. No.: |
10/101605 |
Filed: |
March 21, 2002 |
Current U.S.
Class: |
451/28 |
Current CPC
Class: |
B24B 49/12 20130101;
B24B 37/20 20130101; B24B 37/24 20130101 |
Class at
Publication: |
451/28 |
International
Class: |
B24B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2001 |
KR |
2001-14932 |
Claims
What is claimed is:
1. Apparatus for measuring properties of a polishing pad,
comprising: an upper plate having a flat top surface on which the
polishing pad is to be placed; a camera operative to produce
signals representative of an image of a surface portion of the
polishing pad; a sensor operative to generate signals
representative of a relative location of a surface portion of the
polishing pad; a bracket fixing said camera and said sensor in
place above the top surface of said upper plate, whereby the camera
is positioned to produce signals representative of an image of a
top surface portion of the polishing pad and the sensor is
positioned to generate signals representative of the relative
location of a top surface portion of the polishing pad when the
polishing pad is disposed on said upper plate; X-axis and Y-axis
linear drive mechanisms to which said bracket is connected, said
linear drive mechanisms being operable to move said bracket, and
the camera and sensor fixed in place by the bracket, in X- and
Y-directions extending orthogonal to each other in a plane above
the top surface of said upper plate, whereby the top surface of the
polishing pad can be scanned by said camera and said sensor when
the polishing pad is disposed on the top surface of said upper
plate; and a control system operatively connected to said camera so
as to control the operation of said camera and receive the signals
produced by said camera, operatively connected to said sensor so as
to control the operation of said sensor and receive signals
generated by said sensor, and operatively connected to said X-axis
and Y-axis linear drive mechanisms so as to control the movement of
said camera and said sensor in said X- and Y-directions, and said
control system including a processor configured to process said
signals to produce data by which an image of and the profile of the
top surface of a polishing pad disposed on the top surface of said
upper plate can be discerned.
2. Apparatus for measuring properties of a polishing pad as claimed
in claim 1, wherein said upper plate has a plurality of vacuum
holes extending through a central portion of the top surface
thereof.
3. Apparatus for measuring properties of a polishing pad as claimed
in claim 1, wherein said sensor is a non-contacting laser
sensor.
4. Apparatus for measuring properties of a polishing pad as claimed
in claim 1, and further comprising a hardness-measuring sensor
operative to measure hardness of a polishing pad, said
hardness-measuring sensor being supported by said X-axis and Y-axis
linear drive mechanisms.
5. Apparatus for measuring properties of a polishing pad as claimed
in claim 1, and further comprising a transmittance sensor operative
to measure transmittance.
6. Apparatus for measuring properties of a polishing pad as claimed
in claim 5, wherein said transmittance sensor includes a
light-receiving element that is disposed coplanar with the top
surface of said upper plate, and a light-emitting element that is
disposed above the light-receiving element as spaced therefrom,
whereby a polishing pad is insertable between the light-receiving
element and the light-emitting element.
7. Apparatus for measuring properties of a polishing pad as claimed
in claim 1, wherein said X-axis and Y-axis linear drive mechanisms
comprise a Y-axis carrier extending along a first side of said
upper plate, a Y-axis guide rail extending parallel to said Y-axis
carrier along a second side of the top surface of said upper plate,
a Y-axis slider supported by said Y-axis carrier so as to be
movable longitudinally therealong, a Y-axis guide rail slider
supported by said Y-axis guide rail so as to be movable
longitudinally therealong, an X-axis carrier disposed above the top
surface of said upper plate and having opposite ends respectively
mounted to said Y-axis slider and said Y-axis guide rail slider;
and an X-axis slider supported by said X-axis carrier so as to be
movable longitudinally therealong between the opposite ends
thereof, said bracket being fixed to said X-axis slider so as to
move therewith.
8. Apparatus for measuring properties of a polishing pad as claimed
in claim 7, wherein said X-axis and Y-axis linear drive mechanisms
include a respective feed screw associated with each of said X-axis
carrier and said Y-axis carrier.
9. Apparatus for measuring properties of a polishing pad as claimed
in claim 1, wherein said control system includes a display
comprising a screen, said processor and said display being
operative to produce on said screen numeric displays pertaining to
a polishing pad disposed on the top surface of said upper plate, a
graph of the profile of the top surface of the polishing pad, and
an image of the top surface of the polishing pad
10. A method of measuring properties of a polishing pad of a
chemical and mechanical polishing apparatus, comprising the steps
of: placing the polishing pad on a table top; fixing the polishing
pad to the table top using suction; scanning a surface the
polishing pad, fixed to the table top, in X- and Y-axis directions
orthogonal to each other, and using data derived from said scanning
to locate the center of the polishing pad; once the center of the
polishing pad is located, measuring the hardness of the polishing
pad at the center of the polishing pad, and displaying a value of
the hardness on a screen; moving a sensor, aimed at the polishing
pad fixed to the table top, in the direction of the Y-axis, and
using signals from the sensor to discern a profile of the top
surface of the polishing pad; displaying the profile of the
polishing pad on the screen; scanning the surface of the polishing
pad, fixed to the table top, with a camera to thereby take pictures
of the surface of the polishing pad; and displaying the pictures on
the screen as an image of the surface of the polishing pad.
11. A method of measuring properties of a polishing pad of a
chemical and mechanical polishing apparatus as claimed in claim 10,
and further comprising the steps of: positioning a transparent
window of the polishing pad adjacent a transmittance sensor for
measuring transmittance; measuring transmittance through the
transparent window using the transmittance sensor; and displaying a
value of the transmittance on the screen.
12. A method of measuring properties of a polishing pad of a
chemical and mechanical polishing apparatus as claimed in claim 11,
wherein the step of displaying the value of the transmittance on
the screen comprises the substeps of: calculating an error between
the measured value and a standard value of the transmittance; and
displaying the measured value, the standard value and the error of
the transmittance on the screen.
13. A method of measuring properties of a polishing pad of a
chemical and mechanical polishing apparatus as claimed in claim 10,
wherein the step of displaying the value of the hardness of the
polishing pad on the screen comprises the steps of: calculating an
error between the measured value and a standard value of the
hardness of the polishing pad; and displaying the measured value,
the standard value and the error of the hardness on the screen.
14. A method of measuring properties of a polishing pad of a
chemical and mechanical polishing apparatus, comprising the steps
of: placing a polishing pad, having a transparent window, on a flat
surface of a measuring table before the polishing pad is installed
in a chemical and mechanical polishing apparatus; with the
polishing pad disposed on the flat surface, scanning the polishing
pad with a sensor and using signals derived from the sensor to
discern the surface profile of the polishing pad, measuring the
hardness of the polishing pad, and measuring a transmittance
through the transparent window of the polishing pad; subsequently
installing the polishing pad in the chemical and mechanical
polishing apparatus, and polishing a wafer using the polishing pad;
subsequently removing the polishing pad from the chemical and
mechanical polishing apparatus and placing the used polishing pad
back on the flat surface of the measuring table; with the used
polishing pad disposed back on the flat surface, scanning the used
polishing pad with the sensor and using signals derived from the
sensor to discern the surface profile of the used polishing pad,
measuring the hardness of the used polishing pad, and measuring the
transmittance through the transparent window of the used polishing
pad; and filing values of the surface profile, hardness and
transmittance of the polishing pad, before and after the polishing
pad has been used to polish the wafer, in a database.
15. A method of measuring properties of a polishing pad of a
chemical and mechanical polishing apparatus, as claimed in claim
14, and further comprising using the database to create a schedule
for the replacing of polishing pads in the chemical and mechanical
polishing apparatus.
16. A method of measuring properties of a polishing pad of a
chemical and mechanical polishing apparatus, as claimed in claim
14, and further comprising using the database to establish
operating parameters of the chemical and mechanical polishing
apparatus.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method and apparatus for
measuring various properties of a polishing pad. More specifically,
the present invention relates to a method and apparatus for
measuring various properties of a polishing pad used to carry out
the chemical and mechanical polishing of semiconductor wafers.
[0003] 2. Description of the Related Art
[0004] Recently, as the need arises for more highly integrated
semiconductor devices, a multi-layered structure has been used to
yield a higher number of semiconductor chips per wafer. The
multi-layered structure has been realized through the use of a
conductive wiring pattern electrically connecting a plurality of
layers on a semiconductor wafer. A planarization process is
required to form such a multi-layered structure.
[0005] Chemical mechanical polishing (hereinafter referred as CMP)
is a known planarization technique for forming the above-mentioned
multi-layered structure. In CMP, the wafer is polished by the
motion of a polishing pad relative to the wafer while the wafer is
under pressure and a polishing solution or a slurry is provided
between the wafer and the polishing pad.
[0006] The polishing pad carries out two major functions. That is,
the polishing pad simultaneously causes the wafer to mechanically
abrade and facilitates a chemical reaction between the slurry and
the wafer. To this end, the polishing pad causes the polishing
solution or slurry to flow smoothly by means of many small pores
and grooves open at the surface of the polishing pad. Also, the
polishing pad removes reactants from the surface of the wafer by
means of its foam cell walls. The small pores have diameters of
about 30.about.70 .mu.m so that the slurry deposited on the surface
of the wafer can be stored temporarily in the pores. Hence, the
Material-Removal-Rate (hereinafter referred to as MRR), namely the
rate of polishing as a function of the pressure between the wafer
and the polishing pad, can be kept constant during the polishing
process. Also, a Within-Wafer-Non-Uniformity (hereinafter referred
to as WIWNU) of the MRR is kept to a minimum.
[0007] However, during the CMP process, an elastic deformation
occurs in the polishing pad due to a stress concentration resulting
from a difference in density or size of device patterns on the
wafer. Generally, the larger the stress concentration, the higher
the MRR is. The uniformity of the MRR is also influenced by the
hardness of the polishing pad. Generally, though, a hard polishing
pad has a good local planarizing characteristic for inner portions
of a chip, but generates a defect on a surface of the chip.
[0008] The polishing pads used in CMP apparatus are generally
classified into two types, namely a non-woven fabric type and a
foamed cross-linked polymer type. The non-woven fabric type of
polishing pad is manufactured by impregnating or coating a
non-woven fabric (e.g., polyester felt) with a cross-linked polymer
(e.g., polyurethane resin). On the other hand, the foamed
cross-linked polymer type of polishing pad is manufactured, for the
most part, by coating a non-woven fabric pad with foamed
polyurethane.
[0009] Both types of polishing pads provide a great number of pores
open over the entire surface of the polishing pad. As mentioned
earlier, the pores temporarily store the polishing solution and
provide the polishing solution for the surface of the wafer. Such
polishing pads of a CMP apparatus are mainly used for polishing a
glass substrate or a mono-crystalline silicon wafer. In addition,
new polishing pads are continually being developed to provide
better performance during the CMP process. For example, the IC-1000
(manufactured by Rodel Inc. U.S.A) has been recently used in CMP
apparatus without producing scratches on the surface of the wafer
and offers the same performance as the IC-60 (also manufactured by
Rodel Inc. U.S.A.).
[0010] Now, again, the performance of a polishing pad is basically
decided by the hardness, surface state and compressibility of the
polishing pad as these characteristics relate to the material being
polished.
[0011] As concerns hardness, if the hardness of the polishing pad
is not uniform over the entire polishing pad, the magnitude of a
load applied to the polishing pad varies at different portions of
the polishing pad. Thus, the thickness of the polishing pad becomes
non-uniform during the polishing process. Consequently, the wafer
is not planarized correctly. Hence, polishing pads should have a
hardness tailored to the particular polishing operation.
[0012] A polishing pad for polishing an insulating film should have
a hard and rough surface to remove a reactant of the insulation
film produced as the result of the chemical etching of the film by
means of the slurry. In the case of polishing a metal such as
aluminum, a ductile polishing pad is preferably used because the
aluminum is prone to being damaged and contaminated due to its own
ductility. When such a ductile polishing pad is used for polishing
process, the RMM is about 3,000 .ANG./min and the selectivity of
aluminum with respect to an oxide is about 40:1. On the other hand,
a hard polishing pad is advantageous when polishing a hard metal
such as tungsten. In the case of polishing tungsten, the RMM is
about 2,000 .ANG./min and the selectivity with respect to an oxide
is about 20:1. When polishing copper, a polishing pad having a
medium hardness should be used. In this case, the RMM is about
4,000 .ANG./min and the selectivity thereof with respect to an
oxide is about 100:1
[0013] Generally, the lower the density of the polishing pad is,
the higher the MRR is. Also, the larger the compressibility is, the
higher the MRR is.
[0014] As concerns compressibility, the extent to which a polishing
pad will deform under compression has a direct effect on the
evenness of the wafer and uniformity of a residual thin film of the
wafer. With this in mind, a hard polishing pad, i.e., having a
small compressive deformability, should be used when polishing a
stepped surface of a wafer. For instance, an IC-1000 polishing pad,
manufactured by Rodel Inc. U.S.A., is usually used in this case.
Also, a second generation IC-series pad, namely the IC-1400
polishing pad, offers an extended lifetime and improvement in the
uniformity of the surface of a wafer. The IC-1400 polishing pad has
a structure of two layers--a surface layer and a lower layer. The
surface layer is formed using the IC-1000 polishing pad, and the
lower layer is made of an independent foamed material serving as a
buffer layer to improve water permeability and a slight change of a
compressive characteristic of the polishing pad, thereby increasing
the uniformity of the surface of the wafer. Furthermore, a surface
of the second generation polishing pad has concentric grooves
formed therein.
[0015] The Q-2000 polishing pad (also a trade name of Rodel Inc.
U.S.A.) has been developed for the purpose of decreasing a
dependency of the polishing pad on the conditioner to improve a
local planarity of the wafer. This pad, too, has a structure
consisting of two layers. The surface layer thereof comprises a
foamed polymer sheet having a high degree of hardness, and in which
grooves are formed to ensure a smooth and uniform flow of the
slurry.
[0016] As described above, the polishing pads are designed and
selected for use based on the type and surface characteristics of
the material to be polished. Because the polishing pads play a very
important role in the CMP process, a strict management of the
maintenance and deployment of the polishing pads is required in
fabricating semiconductor devices.
[0017] To this end, the polishing pads are periodically replaced
according to product specifications provided by the manufacturer.
The product specifications are conservative in their approach to
preventing a polishing pad from damaging a wafer. The reliance on
the product specifications to manage the replacement of the
polishing pads increases the manufacturing cost of the
semiconductor devices because the polishing pad is sometimes
replaced even if the used polishing pad is still functional.
Furthermore, the end user of a CMP apparatus generally buys the
polishing pad with the CMP apparatus from the manufacturer, and
operates the CMP apparatus according to specifications provided by
the manufacturer. Then, after the useful life of the polishing pad
has expired, the end user mounts a new polishing pad to the
apparatus. However, because the characteristics of the replacement
polishing pad may differ slightly from the characteristics
described in the specifications, operating the CMP apparatus
according to the specifications usually results in a processing
error. That is, a wafer can be damaged by a polishing pad even when
the replacing of the polishing pads are being scheduled according
to the product specifications of the manufacturer.
[0018] Meanwhile, the polishing pad has a transparent window by
which the polishing of the wafer can be monitored. Accordingly,
when to end the CMP process can be determined by monitoring the
surface state of the wafer through the transparent window.
[0019] Now, when foreign material becomes lodged in the pores of
the polishing pad, such foreign material may microscopically
scratch the surface of the wafer. Furthermore, the gaps between
adjacent pores and/or the depths of the pores are altered and made
irregular by the foreign material. Hence, the condition of the
slurry is changed by these changes in the gaps and/or depths of the
pores which, in turn, leads to changes in the efficacy of the CMP
process. Another problem that sometimes occurs is that the light
transmittance through the transparent window of the polishing pad
changes. When this occurs, the end point of the polishing process
cannot be detected accurately. Thus, the wafer may be polished
excessively or insufficiently.
[0020] As described above, the planarization of the wafer is
influenced during the CMP process by various properties of the
polishing pad; these properties include the surface profile,
hardness, distribution and uniformity of the pores, and the degree
of transparency of the window. Accordingly, such properties of the
polishing pad need to be measured precisely if a wafer is to be
sufficiently and uniformly polished.
[0021] U.S. Pat. No. 5,934,974, issued to Tzeng Huey-Ming,
discloses a technique of measuring the degree of wear of a
polishing pad by using a non-contact laser sensor. According to the
patent, a device is mounted on a CMP apparatus to measure the
thickness of the polishing pad during the polishing process without
interrupting the process. Although the device can be easily adapted
for use with a belt type of CMP apparatus, it is difficult to
incorporate the device into a rotary type of CMP apparatus.
[0022] U.S. Pat. No. 5,974,679, issued to Birang, et al, discloses
a technique of measuring a surface profile of the polishing pad by
bringing a sensor into contact with a surface of the polishing pad.
In this system, the sensor is part of a measuring apparatus mounted
on a rotary plate of the CMP apparatus for measuring the thickness
of the polishing pad. According to the Birang et al. patent, the
measuring apparatus can measure the surface profile of the
polishing pad only when the CMP apparatus stops because, as
mentioned above, the measuring apparatus is mounted on the rotary
plate of the CMP apparatus.
[0023] Japanese Patent Laid-open Publication No. 8-61949 discloses
a technique of measuring the profile of a polishing pad by using a
laser sensor and simultaneously measuring the profile of the rotary
plate using an excess current sensor.
[0024] In all of the conventional techniques described above, a
measuring device mounted on the CMP apparatus itself is used to
scan the polishing pad in the radial direction to detect a profile
of the polishing pad in one direction.
[0025] However, a typical CMP apparatus does not have enough space
to accommodate such measuring devices. Also, the mounting structure
for the measuring devices complicates the overall structure of the
CMP apparatus. Furthermore, the conventional measuring devices can
only measure the surface profile or thickness of the polishing pad.
That is, the conventional measuring devices can not conduct a
comprehensive measurement of the properties of the polishing
pad.
SUMMARY OF THE INVENTION
[0026] Accordingly, an object of present invention is to overcome
the aforementioned problems and limitations of the prior art.
[0027] More specifically, an object of the present invention is to
provide a method of and apparatus for measuring and discerning
properties of a polishing pad, such as the profile, surface state,
hardness and transmittance through the transparent window thereof,
before and/or after the polishing pad is used in a CMP
apparatus.
[0028] A further object of the present invention is to provide a
method of and apparatus for measuring and discerning properties of
a polishing pad to produce data by which the CMP process can be
maintained and managed efficiently.
[0029] A still further object of the present invention is to
provide a method of and apparatus for discerning the wear of a used
polishing pad to provide data useful for estimating the optimal
operating parameters of the CMP apparatus.
[0030] The apparatus for measuring properties of a polishing pad
according to the present invention includes a measuring table and a
control section. The measuring table has a flat table top on which
the polishing pad is placed. A camera for taking a picture of the
top surface of the polishing pad, and a proximity sensor for
measuring profile of the top surface of the polishing pad, are
fixed to a bracket. Drive means move the bracket along the
directions of X and Y axes in a plane above the polishing pad. The
control section includes a control system for controlling the
movement of the camera and the sensor along directions of the X and
Y axes, as well as the operation of the camera and the sensor.
Accordingly, the profile of the surface of the polishing pad can be
discerned, and an image of the surface of the polishing pad can be
produced. The control system also includes a display having a
screen on which measured values, graphs and images can all be
displayed
[0031] The table top is an upper plate that is precision-made to
have a high degree of surface flatness so that it will affect the
measurements of the surface profile of the polishing pad as little
as possible. On the other hand, the upper plate has a plurality of
holes formed at a central portion thereof. A vacuum pump
communicates with the holes to produce suction by which the
polishing pad is fixed to the upper plate. Therefore, vibrations
and the like will not disturb the polishing pad when the polishing
pad is being measured.
[0032] The sensor for sensing the profile of the polishing pad is
preferably a non-contacting laser sensor.
[0033] The apparatus for measuring properties of the polishing pad
may further include a hardness-measuring sensor for measuring the
hardness of the polishing pad and a transmittance sensor for
measuring the transmittance through a transparent window in the
polishing pad. These sensors may also be mounted by the bracket to
the drive means. Preferably, however, the transmittance sensor is
fixed to the upper plate so as to overhang the edge of the upper
plate.
[0034] The transmittance sensor may comprise a light-receiving
element that is disposed coplanar with the top surface of the upper
plate, and a light-emitting element that is disposed a
predetermined distance above the light-receiving element so that
the polishing pad may be inserted between the light-receiving
element and the light-emitting element.
[0035] The drive means includes a Y-axis linear drive mechanism and
an X-axis linear drive mechanism. The Y-axis linear drive mechanism
comprises a Y-axis carrier extending along a first side of the
upper plate, a Y-axis guide rail extending parallel to the Y-axis
carrier along a second side of the top surface of the upper plate,
a Y-axis slider supported by the Y-axis carrier so as to be movable
longitudinally therealong, and a Y-axis guide rail slider supported
by the Y-axis guide rail so as to be movable longitudinally
therealong. The X-axis linear drive mechanism comprises an X-axis
carrier disposed above the top surface of the upper plate and
having opposite ends respectively mounted to the Y-axis slider and
the Y-axis guide rail slider; and an X-axis slider supported by the
X-axis carrier so as to be movable longitudinally therealong. The
bracket to which the sensors are mounted is fixed to the X-axis
slider so as to move therewith.
[0036] A respective feed screw or linear motor is connected each of
the X-axis slider and Y-axis slider for moving the same along the
X-axis and Y-axis carriers.
[0037] In a method of measuring properties of a polishing pad of a
CMP apparatus according to the present invention, the polishing pad
is placed on the table top and fixed thereto using a vacuum. The
polishing pad is then scanned in the directions of the X and Y axes
to locate the center of the polishing pad. Once the center of the
polishing pad is located, the hardness thereof is measured and a
value of the hardness is displayed on the screen. Next, a profile
of the polishing pad is discerned by moving the proximity sensor
over the polishing pad in the direction of the Y axis, and the
profile is displayed in the form of a graph on the screen. In
addition, the surface of the polishing pad is scanned with the
camera while pictures of the surface of the polishing pad are
taken. These pictures are then used to display an image of the
surface of the polishing pad on the screen.
[0038] In addition, the transparent window of the polishing pad may
be aligned with the transmittance sensor so that the transmittance
through the transparent window is measured. Likewise, the measured
value of the transmittance through the transparent window is
displayed on the screen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The above and other objects and advantages of the present
invention will become more apparent from the following detailed
description thereof made in conjunction with the accompanying
drawings, of which:
[0040] FIG. 1 is a schematic diagram of a rotary CMP apparatus;
[0041] FIG. 2 is a plan view of a polishing pad of the rotary CMP
apparatus shown in FIG. 1;
[0042] FIG. 3 is a perspective view of measuring apparatus for
measuring properties of a polishing pad according to the present
invention;
[0043] FIG. 4 is a perspective view of a measuring table of the
measuring apparatus according to the present invention;
[0044] FIG. 5 is a perspective view of a sensor array fixed to an
X-axis slider of the measuring table;
[0045] FIG. 6 is a perspective view of a transmittance sensor of
the measuring table for measuring the transmittance of a
transparent window of the polishing pad;
[0046] FIG. 7 is a block diagram of a control section of the
measuring apparatus according to the present invention;
[0047] FIG. 8 is a flowchart of the overall operation of the
measuring apparatus according to the present invention;
[0048] FIGS. 9 and 10 are flowchart of a subroutine in which the
measuring apparatus detects a center of the polishing pad according
to the present invention;
[0049] FIGS. 11 to 14 are front views of a display screen of the
control section of the measuring apparatus according to the present
invention; and
[0050] FIG. 15 is a graph illustrating a surface profile of the
polishing pad measured by means of a laser sensor according to the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0051] Hereinafter, the present invention will be described in
detail with reference to the accompanying drawings.
[0052] Referring to FIG. 1, a CMP apparatus includes a rotary
platen 10 and a polishing pad 12 attached to the top surface of the
rotary platen 10. As the polishing process progresses, the pores of
the polishing pad are clogged with residual material generated by
the polishing process. If left unchecked, the essential function of
the pores, e.g., of storing polishing slurry, would be degraded. To
counteract this problem, a conditioner head 14 is supported at the
periphery of the polishing pad 12 in contact with the polishing pad
12. The conditioner head 14 comprises a nickel plate having diamond
particles electro-deposited on a surface thereof. The conditioner
head 14 thus produces fine cuts in the surface of the polishing pad
12 to expose new pores that can then store the slurry.
[0053] A rotary head 16 is supported at the periphery of the
polishing pad 12, symmetrically to the conditioner head 14 with
respect to the center of the polishing pad. The rotary head 16
produces a vacuum by which a wafer 18 is adhered to the bottom
surface thereof. The rotary head 16 moves the wafer 18 adhered
thereto downward to press the wafer 18 against the polishing pad
12. The rotary head 16 also rotates eccentrically relative to the
polishing pad 12 so that the wafer 18 makes contact with the
polishing pad 12 over an area wider than that of just the wafer 18.
The slurry constituting a polishing solution is supplied through a
nozzle 20 situated above the polishing pad 12.
[0054] In addition, the polishing pad 12 and the wafer 18 are
rotated in directions opposite to each other while the polishing
solution is supplied between the polishing pad 12 and the wafer 18
so as to polish the wafer 18.
[0055] The pores that are formed in a surface of the polishing pad
12 have diameters of about 30.about.70 .mu.m so as to be capable of
accommodating the slurry, of rendering the MRR (Material Removal
Rate) constant and of minimizing the WIWNU (Within Wafer
Non-Uniformity).
[0056] FIG. 2 is a plan view of the polishing pad 12. The polishing
pad 12 is in the form of a disc and has a transparent window 12a at
a location where the wafer is brought into contact with the rotary
head 16. The polishing pad 12 also has a plurality of concentric
circular grooves 12b. Laser light is transmitted to the surface of
the wafer 18 through the transparent window 12a, and is then
reflected by the wafer 18. The reflected light is transmitted back
through the window 12a and is then received in a light sensor (as
illustrated back in FIG. 1). The concentric grooves 12b provide
space for storing and supplying the slurry. Accordingly, the shape
and a distribution of the grooves 12b as well as those of the pores
are very important factors affecting the polishing characteristics
of the polishing pad 12. In particular, these factors dictate the
uniformity of contact between the slurry and the surface of the
wafer 18.
[0057] FIG. 3 shows a measuring apparatus for measuring and
discerning properties of the polishing pad 12, namely, the surface
profile, surface state, hardness and transmittance of a transparent
window thereof. As will be described in further detail later on,
the properties of the polishing pad, 12 before and after use in the
CMP apparatus, can be filed in a database. The measuring apparatus
of the present invention basically includes a measuring table 100
and a control section 200.
[0058] The control section 200 is in the form of a cabinet. A
monitor 202 is disposed at the top of the control section 200 and a
first tray 204 for supporting a keyboard 208 and a second tray 206
for supporting a mouse 210 are mounted at an intermediate portion
of the control section 200. A disc driver 212 for driving a data
disc on which data is recorded, for example, a floppy disc, an
optical disc or the like, is located at the center of a lower
portion of the control section 200. The control section 200 also
includes a computer processor, an interface circuit board and a
power supply.
[0059] The measuring table 100 basically comprises an XY-carrier
110 to which a plurality of sensors are mounted, an additional
transmittance sensor 120, and a vacuum pump 130 disposed at the
bottom of the measuring table 100. Referring also now to FIG. 4,
the XY-carrier 110 is installed on an upper plate 102 of the
measuring table 100. The transmittance sensor 120 is fixed to the
front of the upper plate 102. The upper plate 102 of the measuring
table 100 is made by a precision machine-process so as to possess a
high degree of surface flatness. A pad-accommodating section on
which the polishing pad 12 is placed is formed at the center of the
top surface of the upper plate 102, and a plurality of vacuum holes
104 are formed in the pad-accommodating section. The vacuum pump
130 is connected to the plurality of vacuum holes 104 to produce a
vacuum by which the polishing pad 12 is adhered to the upper plate
102 of the measuring table.
[0060] The XY-carrier 110 comprises X-axis and Y-axis linear drive
mechanisms. The Y-axis linear drive mechanism includes a Y-axis
carrier 111, a Y-axis slider 112, a Y-axis guide rail 114, and a
Y-axis guide rail slider 115. The X-axis linear drive mechanism
includes an X-axis carrier 116 and an X-axis slider 117. The Y-axis
carrier 111 extends along the left edge of the upper plate 102 of
the measuring table 100 (in the direction of a Y axis). The Y-axis
guide rail 114 extends along the right edge of the upper plate 102
of the measuring table parallel to the Y-axis carrier 111. The
Y-axis carrier 111 carries the Y-axis slider 112 in the direction
of the Y axis. The Y-axis guide slider 115 is guided for movement
along the Y-axis guide rail in the direction of the Y axis.
[0061] One end of the X-axis carrier 116 is fixed to the Y-axis
slider 112 and the other end of the X-axis carrier is fixed to the
Y-axis guide slider 115. As a result, the X-axis carrier 116 can
traverse the measuring table 100.
[0062] In addition, the X-axis linear drive mechanism and the
Y-axis linear drive mechanism comprise feed screws 116b and 111b
that are rotated by stepper motors 116a and 111a, respectively
(briefly refer to FIG. 7). The X-axis slider 117 and the Y-axis
slider 112 are threaded to the feed screws 116b and 111b,
respectively, so as to move in the direction of the axis X and the
Y axis when the feed screws 116b and 11b are rotated by the stepper
motors 116a and 111a. Alternatively, the X-axis linear drive
mechanism and the Y-axis linear drive mechanism may comprise the
stators of linear motors, and the X-axis slider 117 and the Y-axis
slider 112 may respectively be integrated with the respective
movers of the linear motors. In any case, the X-axis carrier 116 is
moved in the direction of the Y axis, and the X-axis slider 117 is
moved in the direction of the X axis. In this way, the X-axis
slider 117 can be scanned across the pad-accommodating portion of
the upper plate 102 in an XY-plane defined by the X and Y axes of
the measuring table 100.
[0063] Referring to FIG. 5, a bracket 118 is mounted to the X-axis
slider 117, and a camera 140, a laser sensor 150 and a
hardness-measuring sensor 160 are fixed to the X-axis slider 117 by
bracket 118.
[0064] Referring to FIG. 6, the transmittance sensor 120 for
measuring the transmittance through the transparent window 12a of
the polishing pad 12 includes a light-receiving element 122 and a
light-emitting element 124. The light-receiving element 122 is
mounted to one end of a first holding arm 121, the other end of
which is fixed to the top portion of the measuring table 100. The
light-emitting element 124 is attached to an end portion of a
second holding arm 123 disposed above and in parallel with the
first holding arm 121 as spaced a predetermined distance therefrom.
The first and second holding arms 121 and 123 have lengths that are
sufficient to extend from an edge of the polishing pad 12 to the
center of the transparent window 12a of the polishing pad 12. The
light-receiving element 122 and the light-emitting element 124 are
positioned such that an extension of the top surface of the upper
plate 102 of the measuring table 100 lies between the
light-receiving sensor 122 and the light-emitting sensor 124. In
particular, the light-receiving sensor 122 lies coplanar with the
top surface of the upper plate 102.
[0065] Accordingly, when the transmittance through the transparent
window 12a is to be measured, the polishing pad can be supported on
the top surface of the upper plate 102 with the transparent window
12a disposed in the path of light transmitted to the
light-receiving element 122 from the light-emitting element 124
(FIG. 7).
[0066] The camera 140 is, for example, a CCD (charge coupled
device) camera having a high resolution and a high magnification.
Such a camera is suitable for observing the surface of the
polishing pad 12 using the naked eye. The camera 140 can also
search for foreign matter in the grooves or the pores of the
polishing pad 12.
[0067] The laser sensor 150 is a common sensor widely used for
measuring the interference of laser light. More specifically, the
laser sensor 150 directs a laser onto the surface of the polishing
pad 12 and detects the interference pattern of light reflected by
the surface of the polishing pad 12. Hence, the relative position
of the surface of the polishing pad can be detected, whereby the
surface profile of the polishing pad 12 can be discerned.
[0068] The hardness-measuring sensor 160 is a common sensor widely
used for measuring hardness.
[0069] Referring now especially to FIG. 7, the control section 200
comprises a control system that may include a personal computer,
the sensors and camera connected to the personal computer through
an interface board. In this case, each of the sensors and the
camera can communicate with the interface board through an RS232
serial bus or a USB (universal serial bus).
[0070] Specifically, the control section 200 includes a
microcomputer 218, a memory 216 including a DRAM, a SRAM and an
EPROM, a keyboard 208, a mouse 210, a hard disc driver 216, a
floppy disc driver 212, a CD-ROM driver 214 and a monitor 202. The
microcomputer 218 is connected through a system bus to a
hardness-measuring sensor interface 220, a laser sensor interface
222, a camera interface 224, a motor operating portion 226 and a
transmittance sensor interface 228.
[0071] As shown in FIG. 7, the profile, the surface state and the
hardness of the polishing pad 12 are measured while the polishing
pad 12 is adhered by a vacuum to a central portion (position A in
FIG. 7) of the upper plate 102 of the measuring table 100. On the
other hand, the transmittance through the transparent window 12a is
measured while the polishing pad 12 is positioned on the measuring
table 100 with the transmittance sensor 120 aligned with the
transparent window 12a (position B in FIG. 7).
[0072] The operation of the measuring apparatus will now be
described in more detail with reference to FIGS. 8-14.
[0073] Referring to FIG. 8, at first, the control system of the
control section 200 is initialized (step S1). In this step, the
motors 111a, 116a are first initialized and then the sensors
120,140, 150 and 160 are initialized using the initialization
screen shown in FIG. 11. Referring to FIG. 11, when the motors are
initialized, the current X-axis and Y-axis positions of the motors
are input, and "X-axis motor homing", "Y-axis motor homing", "motor
initialization" and "manual motor movement" actions are performed.
Also, when a sensor is initialized, a current sensor reading is
input and then a "sensor initialization" action is performed.
[0074] Furthermore, the environment is set up by inputting
reference values before the properties of the polishing pad are
measured. In order to set up the environment, a pad data reference
value, a hardness reference value and a transmittance reference
value of the polishing pad are inputted using the environment setup
screen shown in FIG. 12, and then a "setup reference value" action
is performed.
[0075] When the system initialization is completed, a project start
screen is displayed on the monitor 202, as shown in FIG. 13 (step
S2). The project start screen includes an image display window for
displaying images taken by the CCD camera 140, a data display
window for displaying the pad data and a graph display window for
displaying a graph of the surface profile of the pad.
[0076] The image display window includes an image display region, a
"CCD" button for selecting the CCD camera, a "previous" button for
selecting a previous image, a "delete" button for deleting a
current image and a "next" button for selecting a next image.
[0077] The data display window has a display portion for displaying
information pertaining to the polishing pad such as its serial
number, pad data, reference value of the hardness, measured value
of the hardness, error of the hardness, reference value of the
transmittance through the window, measured value of the
transmittance and error of the transmittance. Furthermore, the data
display window has a key pad portion including various buttons such
as a "serial number" button, a "reading pad" button, a "measuring
hardness" button, a "measuring transmittance" button, a
"transmittance reference value" button, a "hardness reference
value" button, a "save" button, a "preview" button and a "print"
button.
[0078] Each measuring mode can be selected using the project start
screen (steps S3-S6).
[0079] Firstly, when the "measuring transmittance" button is
pressed after the transparent window 12a of the polishing pad 12 is
aligned with the transmittance sensor 120 (step S3), the
transmittance sensor 120 measures the transmittance through the
transparent window 12a (step S7). A transmittance signal generated
by the transmittance sensor is transferred through the
transmittance sensor interface 228 to the microcomputer 218. The
transmittance signal is converted into the measured value by the
microcomputer 218 and compared with the transmittance reference
value to calculate the error of the transmittance. Then, the error
and the measured value of the transmittance are displayed on the
screen of the data display window.
[0080] Next, the polishing pad 12 is placed at the center of the
measuring table 100, and then is fixed to the measuring table 100
using the vacuum produced by vacuum pump 130. After the polishing
pad 12 is fixed to the measuring table 100, the XY-carrier 110 is
moved in the directions of the X and Y axes to scan the surface of
the pad 12 with the camera 140 and the sensors 150,160 in a plane
defined by the X and Y axes. At this time, signals produced by the
camera 140 and the sensors 150, 160 are processed to discern the
surface profile and state of the polishing pad 12 and to measure
the hardness of the polishing pad 12 (S8-S10). In particular, when
the hardness mode is selected (step S4), the hardness of the
polishing pad 12 is measured (step S8). When the pad-reading mode
is selected (step S5), the surface profile of the polishing pad 12
is read (step S9). When the CCD mode is selected (step S6), a
picture of the polishing pad 12 is taken (step S10).
[0081] Referring to FIG. 9, the microcomputer 218 performs the
homing of the X-axis motor 116a and the Y-axis 111 a motor to
search out the center of the polishing pad 12 placed on the
measuring table 100. To detect the position of the center of the
polishing pad 12, the X-axis motor 116a is operated to move the
X-axis slider 117 along the X-axis carrier 116 to a center point
along the axis X (step S12). When the movement to is completed
(step S13), the Y-axis motor 111a is operated to move the X-axis
carrier 117 along the Y-axis carrier 111 to the point where the
axis Y starts on the polishing pad 12 (step S14). The point where
the axis Y starts is checked (step S15) and then, the Y-axis motor
111a accurately moves the X-axis carrier 116 in the direction of
the Y axis (step S16). The starting point of the axis Y is detected
during the accurate movement of the X-axis carrier 117 in step S16
(step S17).
[0082] Referring to FIG. 10, once the starting point of the axis Y
is detected (step S17 in FIG. 9), the Y-axis motor 111a is operated
to accurately move the X-axis carrier 117 along the Y-axis carrier
111 to a point where the Y axis ends on the polishing pad 12 (step
S18). The end point is checked (step S19), and then the Y-axis
motor 111a accurately moves the X-axis carrier 116 in the direction
of the Y axis (step S20). The end point along the Y axis is
detected during the accurate movement of the X-axis carrier 116 in
step S20 (step S21). When the end point along the Y axis is
detected at step S21, a center point along the Y axis is calculated
based on the starting point and the ending point along the Y axis.
Then the X-axis carrier 116 is moved along the Y-axis carrier 111
to the center point along the Y axis (step S22). When the movement
of the X-axis carrier 116 to the center point along the Y axis is
completed (step S23), the center of the polishing pad 12 has been
found.
[0083] When the movement of the X-axis slider 117 to the center of
polishing pad 12 is completed, the "measuring hardness" button is
clicked (step S4) so that the hardness-measuring sensor 160
measures the hardness of the polishing pad 12 at its central
portion (step S8). A hardness signal generated by the
hardness-measuring sensor 160 is transferred through the
hardness-measuring sensor interface 220 to the microcomputer 118.
The hardness signal is converted into a measured value by means of
the microcomputer 218 and compared with the reference value of the
hardness to calculate the error of the hardness. Then, the error
and the measured value of the hardness are displayed on the screen
of the data display window.
[0084] When the "reading pad" button is pressed on the project
start screen (step S5), the laser sensor 150 measures the surface
profile of the polishing pad 12 (step S9). The laser sensor 150
measures the surface profile of the polishing pad while accurately
moving from the center of the polishing pad 12 to the outer
peripheral edge of the polishing pad. Accordingly, a profile signal
generated by the laser sensor 150 is transferred to the
microcomputer 118. The microcomputer 118 converts the profile
signal into digital data and displays the digital data as a graph
on the project start screen shown in FIG. 13.
[0085] FIG. 15 is an exemplary graph of a surface profile of the
polishing pad measured by the laser sensor 150 according to the
present invention. A plurality of peaks 300 regularly arranged at a
low portion of the graph in FIG. 15 correspond to the grooves
formed in the surface of the polishing pad. According to the
present invention, the measuring of the profile of the polishing
pad serves as a two-dimensional examination by which the distance
between adjacent grooves and the depths of the grooves can be
determined. Accordingly, a polishing pad whose grooves have an
irregular depth and spacing can be detected, thereby insuring that
the only polishing pads that are used are those that will supply
the slurry uniformly over the surface of the wafer.
[0086] When the "CCD" button is clicked on the project start screen
(step S6), a surface image of the polishing pad is displayed (step
S10). Therefore, an operator can observe an enlarged image of the
surface of the polishing pad as scanned by the laser sensor 150,
can capture important ones of these images and can save the images
in a database.
[0087] The measured data of the polishing pad according to the
above-mentioned procedure and screen images of the polishing pad
are filed in the database according to the serial number of the
polishing pad and are thus saved on the hard drive. As shown in
FIG. 14, the measured data and screen images of the polishing pad
filed in the database can be searched on the basis of measured data
or serial number of the polishing pad.
[0088] As described above, the measuring apparatus according to the
present invention can measure the profile, the hardness, the
transmittance of the transparent window and the surface state of
the polishing pad, wherein the properties of each polishing pad can
be exactly observed. Accordingly, when the polishing pad is mounted
in the CMP apparatus, the polishing process can be set up based on
the actual characteristics of the polishing pad. As a result, the
polishing process can be carried out under conditions that minimize
the number of polishing defects in the wafer.
[0089] Furthermore, the presence of foreign matter in the pores and
grooves of the polishing pad is easily discerned from the displayed
image of the surface of the polishing pad. Therefore, measures can
be taken to prevent micro-scratches from being produced in the
wafer. In addition, the measured hardness of the polishing pad can
be used to ensure that the polishing pad is suitable for the
particular material layer of the wafer to be polished.
[0090] Also, because the transmittance through the transparent
window of the polishing pad can be measured, an excessive or
insufficient polishing of the wafer can be prevented.
[0091] Furthermore, operating characteristics of the CMP apparatus
can be estimated from the wear exhibited by its polishing pad as
discerned using the present invention. Therefore, a schedule for
replacing the polishing pads can be accurately determined.
Moreover, using such information, the CMP apparatus can be set-up
to optimize the efficacy of the polishing pads and prolong the
useful life thereof. Accordingly, the present invention contributes
to reducing the manufacturing cost of the semiconductor
devices.
[0092] Finally, although the present invention has been described
in connection with the preferred embodiments thereof, the present
invention is not so limited. Rather, various changes and
modifications can be made to the preferred embodiments by one
skilled in the art within the spirit and scope of the present
invention as hereinafter claimed.
* * * * *