U.S. patent application number 13/562441 was filed with the patent office on 2013-03-14 for polishing monitoring method, polishing end point detection method, and polishing apparatus.
The applicant listed for this patent is Taro TAKAHASHI. Invention is credited to Taro TAKAHASHI.
Application Number | 20130065493 13/562441 |
Document ID | / |
Family ID | 47830267 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130065493 |
Kind Code |
A1 |
TAKAHASHI; Taro |
March 14, 2013 |
POLISHING MONITORING METHOD, POLISHING END POINT DETECTION METHOD,
AND POLISHING APPARATUS
Abstract
A method of monitoring a thickness of a conductive film on a
substrate during polishing of the substrate with use of an eddy
current sensor is provided. This method includes: polishing the
conductive film by pressing the substrate against a polishing
surface on the rotating polishing table; obtaining output signal of
the eddy current sensor during polishing; calculating an amount of
output adjustment of the eddy current sensor using the output
signal obtained when the substrate is not present above the eddy
current sensor; with use of the amount of output adjustment,
correcting the output signal obtained when the substrate is present
above the eddy current sensor; and monitoring the thickness of the
conductive film based on the corrected output signal.
Inventors: |
TAKAHASHI; Taro; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAKAHASHI; Taro |
Tokyo |
|
JP |
|
|
Family ID: |
47830267 |
Appl. No.: |
13/562441 |
Filed: |
July 31, 2012 |
Current U.S.
Class: |
451/59 ; 451/259;
451/28 |
Current CPC
Class: |
H01L 22/14 20130101;
B24B 37/013 20130101; H01L 22/26 20130101; B24B 49/105
20130101 |
Class at
Publication: |
451/59 ; 451/28;
451/259 |
International
Class: |
B24B 37/013 20120101
B24B037/013; B24B 7/00 20060101 B24B007/00; B24B 49/10 20060101
B24B049/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2011 |
JP |
2011-173792 |
Nov 21, 2011 |
JP |
2011-253801 |
Claims
1. A method of monitoring a thickness of a conductive film on a
substrate during polishing of the substrate with use of an eddy
current sensor provided in a polishing table, said method
comprising: polishing the conductive film by pressing the substrate
against a polishing surface on the rotating polishing table;
obtaining output signal of the eddy current sensor during
polishing; calculating an amount of output adjustment of the eddy
current sensor using the output signal obtained when the substrate
is not present above the eddy current sensor; with use of the
amount of output adjustment, correcting the output signal obtained
when the substrate is present above the eddy current sensor; and
monitoring the thickness of the conductive film based on the
corrected output signal.
2. The method according to claim 1, wherein: a resistance component
and reactance component of impedance of electric circuit including
a coil of the eddy current sensor are defined as coordinates on a
coordinate system; the coordinates are rotated and moved such that
a distance between an origin of the coordinate system and a point
specified by the coordinates is reduced in accordance with a
decrease in the thickness of the conductive film; and the output
signal of the eddy current sensor is represented by the rotated and
moved coordinates.
3. The method according to claim 2, wherein said correcting of the
output signal is performed by moving the origin of the coordinate
system.
4. The method according to claim 3, wherein said monitoring the
thickness of the conductive film based on the corrected output
signal comprises monitoring the thickness of the conductive film
based on the distance between the moved origin of the coordinate
system and the point specified by the coordinates of the
impedance.
5. The method according to claim 1; further comprising: obtaining
resistance components and reactance components of impedance of
electric circuit including a coil of the eddy current sensor at
each of different thicknesses of the conductive film under
conditions of various distances between a coil end of the eddy
current sensor and the conductive film; plotting the resistance
components and the reactance components onto rectangular coordinate
axes; drawing preliminary measurement linear lines each connecting
points specified by coordinates consisting of the resistance
components and the reactance components at each thickness of the
conductive film; and determining in advance a reference point at
which the preliminary measurement linear lines intersect with each
other.
6. The method according to claim 5, wherein said correcting of the
output signal is performed by moving the reference point that has
been determined in advance.
7. The method according to claim 6, wherein said monitoring the
thickness of the conductive film based on the corrected output
signal comprises monitoring the thickness of the conductive film
based on an angle of a line connecting the moved reference point to
a point specified by coordinates of the impedance.
8. The method according to claim 1, wherein said correcting of the
output signal is performed by using an average of the output signal
obtained when the substrate is not present above the eddy current
sensor while the polishing table makes N revolutions.
9. The method according to claim 1, wherein said calculating of the
amount of output adjustment comprises calculating the amount of
output adjustment of the eddy current sensor using only output
signal obtained from a region where a top ring for holding the
substrate is not present on or above the polishing surface, among
the output signal obtained when the substrate is not present above
the eddy current sensor.
10. The method according to claim 9, wherein said calculating of
the amount of output adjustment comprises calculating the amount of
output adjustment of the eddy current sensor using only output
signal obtained from a region where a dresser for dressing the
polishing surface and an atomizer for cleaning the polishing
surface are not present on or above the polishing surface, among
the output signal obtained when the substrate is not present above
the eddy current sensor.
11. A method of monitoring a thickness of a conductive film on a
substrate during polishing of the substrate with use of an eddy
current sensor provided in a polishing table, said method
comprising: polishing the conductive film by pressing the substrate
against a polishing surface on the rotating polishing table;
obtaining resistance components and reactance components of
impedance of electric circuit including a coil of the eddy current
sensor at each of different thicknesses of the conductive film
under conditions of various distances between a coil end of the
eddy current sensor and the conductive film; plotting the
resistance components and the reactance components onto rectangular
coordinate axes; drawing preliminary measurement linear lines each
connecting points specified by coordinates consisting of the
resistance components and the reactance components at each
thickness of the conductive film; determining a reference point at
which the preliminary measurement linear lines intersect with each
other; correcting the reference point using output signal of the
eddy current sensor obtained during polishing, before polishing, or
after polishing; and monitoring the thickness of the conductive
film based on an angle of a line connecting the corrected reference
point to a point specified by coordinates of the impedance.
12. A polishing apparatus, comprising: a rotatable polishing table
having a polishing surface; a top ring configured to press a
substrate against the polishing surface to polish a conductive film
on the substrate; an eddy current sensor arranged in said polishing
table; and a monitoring device for monitoring a thickness of the
conductive film based on output signal of said eddy current sensor,
wherein said monitoring device is configured to obtain the output
signal of said eddy current sensor during polishing, calculate an
amount of output adjustment of said eddy current sensor using the
output signal obtained when the substrate is not present above said
eddy current sensor, with use of the amount of output adjustment,
correct the output signal obtained when the substrate is present
above said eddy current sensor, and monitor the thickness of the
conductive film based on the corrected output signal.
13. The polishing apparatus according to claim 12, wherein: a
resistance component and reactance component of impedance of
electric circuit including a coil of said eddy current sensor are
defined as coordinates on a coordinate system; the coordinates are
rotated and moved such that a distance between an origin of the
coordinate system and a point specified by the coordinates is
reduced in accordance with a decrease in the thickness of the
conductive film; and the output signal of said eddy current sensor
is represented by the rotated and moved coordinates.
14. The polishing apparatus according to claim 13, wherein said
monitoring device is configured to correct the output signal by
moving the origin of the coordinate system.
15. The polishing apparatus according to claim 14, wherein said
monitoring device is configured to monitor the thickness of the
conductive film based on the distance between the moved origin of
the coordinate system and the point specified by the coordinates of
the impedance.
16. The polishing apparatus according to claim 12, wherein said
monitoring device is configured to: obtain resistance components
and reactance components of impedance of electric circuit including
a coil of the eddy current sensor at each of different thicknesses
of the conductive film under conditions of various distances
between a coil end of the eddy current sensor and the conductive
film; plot the resistance components and the reactance components
onto rectangular coordinate axes; draw preliminary measurement
linear lines each connecting points specified by coordinates
consisting of the resistance components and the reactance
components at each thickness of the conductive film; and determine
in advance a reference point at which the preliminary measurement
linear lines intersect with each other.
17. The polishing apparatus according to claim 16, wherein said
monitoring device is configured to correct the output signal by
moving the reference point that has been determined in advance.
18. The polishing apparatus according to claim 17, wherein said
monitoring device is configured to monitor the thickness of the
conductive film based on an angle of a line connecting the moved
reference point to a point specified by coordinates of the
impedance.
19. The polishing apparatus according to claim 12, wherein said
monitoring device is configured to correct the output signal by
using an average of the output signal obtained when the substrate
is not present above the eddy current sensor while the polishing
table makes N revolutions.
20. The polishing apparatus according to claim 12, wherein said
monitoring device is configured to calculate the amount of output
adjustment of the eddy current sensor using only output signal
obtained from a region where a top ring for holding the substrate
is not present on or above the polishing surface, among the output
signal obtained when the substrate is not present above the eddy
current sensor.
21. The polishing apparatus according to claim 20, wherein said
monitoring device is configured to calculate the amount of output
adjustment of the eddy current sensor using only output signal
obtained from a region where a dresser for dressing the polishing
surface and an atomizer for cleaning the polishing surface are not
present on or above the polishing surface, among the output signal
obtained when the substrate is not present above the eddy current
sensor.
22. A method of detecting a polishing end point, said method
comprising: rotating a top ring and a polishing table while the top
ring is pressing a substrate against a polishing pad on the
polishing table to polish a film of the substrate; during polishing
of the substrate, sweeping an eddy current sensor across a surface
of the substrate; obtaining resistance component X and inductive
reactance component Y of impedance of the eddy current sensor;
plotting coordinates X and Y, which consist of the resistance
component X and the inductive reactance component Y, onto a XY
coordinate system on which a plurality of impedance areas are
defined in advance, the plurality of impedance areas including a
reference impedance area and at least one offset impedance area;
calculating a plurality of film thickness index values in the
plurality of impedance areas, respectively, using plural pairs of
coordinates X and Y which belong respectively to the plurality of
impedance areas; and determining polishing end points of the
substrate in the plurality of impedance areas, respectively, using
the plurality of film thickness index values.
23. The method according to claim 22, wherein said plurality of
impedance areas are obtained by: polishing a substrate identical to
the substrate to be polished; obtaining the resistance component X
and the inductive reactance component Y during polishing of the
identical substrate; plotting coordinates X and Y, which consist of
the resistance component X and the inductive reactance component Y
obtained, onto the XY coordinate system to form an initial
impedance area; and dividing the initial impedance area along its
longitudinal direction.
24. The method according to claim 22, wherein said reference
impedance area is obtained by: polishing a substrate identical to
the substrate to be polished; obtaining the resistance component X
and the inductive reactance component Y in a center of the
identical substrate; and plotting coordinates X and Y, which
consist of the resistance component X and the inductive reactance
component Y obtained, onto the XY coordinate system.
25. The method according to claim 22, wherein said offset impedance
area has the same width as that of the reference impedance
area.
26. The method according to claim 22, wherein the film thickness
index value is represented by a distance between a point specified
by the coordinates X and Y and an origin of the XY coordinate
system.
27. The method according to claim 22, further comprising:
translating the offset impedance area until the offset impedance
area overlaps the reference impedance area.
28. The method according to claim 22, wherein the film thickness
index value is represented by an angle between a linear line
connecting a point specified by the coordinates X and Y to a
predetermined reference point and a predetermined reference line
extending through the reference point.
29. The method according to claim 28, further comprising:
multiplying the angle obtained in the offset impedance area by a
coefficient such that the angle obtained in the offset impedance
area is equal to the angle obtained in the reference impedance
area.
30. A method of detecting a polishing end point, said method
comprising: rotating a top ring and a polishing table while the top
ring is pressing a substrate against a polishing pad on the
polishing table to polish a film on the substrate; obtaining output
signal of an eddy current sensor provided in the polishing table
while sweeping the eddy current sensor across a surface of the
substrate; obtaining output signal of the eddy current sensor while
sweeping the eddy current sensor across the surface of the
substrate in the same path as that when the previous output signal
is obtained; calculating a film thickness index value from the
output signal of the eddy current sensor; and determining a
polishing end point of the substrate from a change in the film
thickness index value.
31. The method according to claim 30, wherein the number of
revolutions of the polishing table required for the eddy current
sensor to describe the same path is calculated from a ratio of a
rotational speed of the top ring to a rotational speed of the
polishing table.
32. The method according to claim 31, wherein a time required for
the polishing table to make one revolution is measured, and the
rotational speed of the polishing table is calculated from the
measured time.
33. The method according to claim 31, wherein a time required for
the top ring to make one revolution is measured, and the rotational
speed of the top ring is calculated from the measured time.
34. The method according to claim 30, further comprising: sorting
the output signal of the eddy current sensor in accordance with a
plurality of zones defined in advance on the surface of the
substrate, wherein said calculating of the film thickness index
value comprises calculating film thickness index values for the
respective zones on the substrate from the sorted output
signal.
35. A method of detecting a polishing end point, said method
comprising: rotating a top ring and a polishing table while the top
ring is pressing a substrate against a polishing pad on the
polishing table to polish a film on the substrate; during polishing
of the substrate, sweeping an eddy current sensor across a surface
of the substrate, said eddy current sensor being provided in the
polishing table; obtaining output signal of the eddy current
sensor; producing a film thickness profile from the output signal
of the eddy current sensor; judging whether a salient portion
appearing in the film thickness profile is due to the film
remaining on the substrate or due to metal lying under the film
based on a change in position of the salient portion appearing in
the film thickness profile; and determining a polishing end point
of the substrate based on a size of the salient portion that
appears due to the film remaining on the substrate.
36. A polishing apparatus, comprising: a rotatable polishing table
for supporting a polishing pad; a top ring configured to press a
substrate against the polishing pad on said rotating polishing
table while rotating the substrate; an eddy current sensor arranged
in said polishing table so as to sweep a surface of the substrate;
and a monitoring device for monitoring a film thickness of the
substrate from output signal of said eddy current sensor, wherein
said monitoring device is configured to obtain resistance component
X and inductive reactance component Y of impedance of said eddy
current sensor, plot coordinates X and Y, which consist of the
resistance component X and the inductive reactance component Y,
onto a XY coordinate system on which a plurality of impedance areas
are defined in advance, the plurality of impedance areas including
a reference impedance area and at least one offset impedance area,
calculate a plurality of film thickness index values in the
plurality of impedance areas, respectively, using plural pairs of
coordinates X and Y which belong respectively to the plurality of
impedance areas, and determine polishing end points of the
substrate in the plurality of impedance areas, respectively, using
the plurality of film thickness index values.
37. A polishing apparatus, comprising: a rotatable polishing table
for supporting a polishing pad; a top ring configured to press a
substrate against the polishing pad on said rotating polishing
table while rotating the substrate; an eddy current sensor arranged
in said polishing table so as to sweep a surface of the substrate;
and a monitoring device for monitoring a film thickness of the
substrate from output signal of said eddy current sensor, wherein
said monitoring device is configured to obtain output signal of
said eddy current sensor while said eddy current sensor is sweeping
the surface of the substrate, obtain output signal of said eddy
current sensor while said eddy current sensor is sweeping the
surface of the substrate in the same path as that when the previous
output signal is obtained, calculate a film thickness index value
from the output signal of said eddy current sensor, and determine a
polishing end point of the substrate from a change in the film
thickness index value.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This document claims priorities to Japanese Application
Number 2011-173792, filed Aug. 9, 2011 and Japanese Application
Number 2011-253801, filed Nov. 21, 2011, the entire contents of
which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a polishing monitoring
method and a polishing apparatus for monitoring a change in
thickness of a conductive film formed on a surface of a substrate,
such as a semiconductor wafer, during polishing.
[0004] The present invention also relates to a polishing end point
detection method used in a polishing apparatus for polishing an
object (a substrate), such as a semiconductor wafer, and more
particularly to a polishing end point detection method using an
eddy current sensor. The present invention further relates to a
polishing apparatus capable of performing such a polishing end
point detection method.
[0005] 2. Description of the Related Art
[0006] With a recent trend toward higher integration and higher
density in semiconductor devices, circuit interconnects become
finer and finer and the number of levels in multilayer interconnect
is increasing. In the process of achieving the multilayer
interconnect structure with finer interconnects, film coverage (or
step coverage) of step geometry is lowered through thin film
formation as the number of interconnect levels increases, because
surface steps grow while following surface irregularities on a
lower layer. Therefore, in order to fabricate the multilayer
interconnect structure, it is necessary to improve the step
coverage and planarize the surface in an appropriate process. It is
also necessary to planarize surfaces of semiconductor device so
that irregularity steps formed thereon fall within a depth of focus
in optical lithography. This is because finer optical lithography
entails shallower depth of focus.
[0007] Accordingly, the planarization of the semiconductor device
surfaces is becoming more important in fabrication process of the
semiconductor devices. Chemical mechanical polishing (CMP) is the
most important planarization technique. This chemical mechanical
polishing is a process of polishing a substrate, such as a
semiconductor wafer, with use of a polishing apparatus by placing
the substrate in sliding contact with a polishing pad while
supplying a polishing liquid containing abrasive grains, such as
ceria (CeO.sub.2), onto the polishing pad.
[0008] The polishing apparatus that performs the above-described
CMP process has a polishing table having the polishing pad, and a
substrate holder for holding the semiconductor wafer (substrate).
The substrate holder is often called a top ring or polishing head.
When polishing the substrate, the top ring presses a surface of the
substrate against the polishing pad while a polishing liquid supply
unit supplies the polishing liquid onto the polishing pad. The top
ring and the polishing table are rotated independently to provide
relative movement between the substrate and the polishing pad to
thereby polish a film that forms the surface of the substrate.
[0009] This polishing apparatus is widely used in polishing of a
conductive film, such as a barrier film or a metal film, formed on
the surface of the semiconductor wafer (substrate). A polishing end
point and a change in polishing conditions during polishing are
determined based on a thickness of the conductive film. Therefore,
the polishing apparatus typically has a film thickness detector for
detecting the thickness of the conductive film during polishing. An
eddy current sensor is typically used as the film thickness
detector.
[0010] The eddy current sensor is provided in the polishing table.
During polishing of the substrate, the eddy current sensor induces
eddy current in the conductive film on the substrate while sweeping
under the substrate as the polishing table rotates, and detects the
thickness of the conductive film from a change in impedance due to
a magnetic field of the induced eddy current.
[0011] FIG. 39 is a diagram showing a relationship between signal
value of the eddy current sensor and polishing time (t) from when
polishing of the semiconductor wafer (substrate) is started until
the conductive film on the semiconductor wafer is cleared
(removed). Immediately after polishing of the semiconductor wafer
is started, the conductive film is still thick. As a result, the
eddy current sensor outputs high signal as shown in FIG. 39. As the
polishing process proceeds, the signal value of the eddy current
sensor is lowered with the decrease in the thickness of the
conductive film. When the conductive film is cleared (removed), the
signal value of the eddy current sensor becomes constant.
Therefore, it is possible to judge the polishing end point by
detecting such a point of time (i.e., a singular point) when the
signal value becomes constant.
[0012] However, a change in operating environment, such as ambient
temperature of the eddy current sensor or permeation of the liquid
into the polishing pad, or a change in the eddy current sensor
itself with time may cause drift (i.e., translation) of the output
signal value of the eddy current sensor. Such drift results in
upward translation of a graph itself as indicated by a movement
from a solid line to a dotted line depicted in FIG. 39. Even in
such a case, it is possible to detect the polishing end point
because the singular point is translated in the same manner.
However, in a case of stopping the polishing process when the
conductive film reaches a predetermined thickness so as to leave a
part thereof, or in a case of switching to different conditions,
e.g., lower pressure or lower rotational speed, it is necessary to
detect a specific point where the signal value reaches a
predetermined value (Z2). In such a case of detecting the specific
point in accordance with the signal value, the drift can cause an
error of the polishing time to be detected because of a change in
the relationship between the output signal value of the eddy
current sensor and the film thickness.
[0013] In fabrication process of semiconductor devices, several
kinds of materials are deposited repeatedly in the form of film on
a silicon wafer to form a multilayer interconnect structure. In
order to form such a multilayer interconnect structure, CMP
(chemical mechanical polishing) is used. For example, a metal film
is formed on a surface of a substrate having interconnect trenches
formed thereon, and then CMP is performed so as to remove
unnecessary film, so that the metal film remains only in the
trenches to form metal interconnects.
[0014] In this process of forming the metal interconnects, the eddy
current sensor is widely used in order to detect whether or not the
unnecessary metal film has been removed (i.e., whether or not the
unnecessary metal film remains). However, in the substrate having
the multilayer interconnect structure, the interconnects existing
under the metal film to be polished could affect the output signal
of the eddy current sensor, thus preventing the detection of the
remaining film.
[0015] In order to eliminate such an influence of the interconnects
existing under the metal film, the following techniques have been
used.
[0016] (1) An average of the output signal of the eddy current
sensor obtained over the entire surface of the substrate is used to
determine the film thickness.
[0017] (2) A minimum output signal obtained in a predefined zone on
the substrate surface is used to determine the film thickness.
[0018] (3) A rotational speed ratio of the top ring to the
polishing table is adjusted such that paths of the eddy current
sensor described on the substrate surface are distributed
substantially uniformly over the entire circumference of the
substrate within a predetermined period of time (e.g., a moving
average time of the output signal of the eddy current sensor).
[0019] However, it is difficult to obtain film thickness
information for each of zones defined in the substrate surface with
the use of the conventional techniques described above.
SUMMARY OF THE INVENTION
[0020] The present invention has been made in view of the above
drawbacks. It is a first object of the present invention to provide
a polishing monitoring method and a polishing apparatus capable of
calibrating an eddy current sensor without lowering an operating
rate and capable of achieving highly-accurate film thickness
monitoring.
[0021] It is a second object of the present invention to provide a
method capable of obtaining film thickness information for each of
zones defined in a substrate surface using an eddy current sensor
while eliminating an influence of a metal lying under a film to be
polished, and capable of determining a polishing end point of the
substrate based on the film thickness information obtained.
[0022] It is a third object of the present invention to provide a
polishing apparatus capable of performing such a polishing end
point detection method.
[0023] A first aspect of the present invention for achieving the
above object is to provide a method of monitoring a thickness of a
conductive film on a substrate during polishing of the substrate
with use of an eddy current sensor provided in a polishing table.
The method includes: polishing the conductive film by pressing the
substrate against a polishing surface on the rotating polishing
table; obtaining output signal of the eddy current sensor during
polishing; calculating an amount of output adjustment of the eddy
current sensor using the output signal obtained when the substrate
is not present above the eddy current sensor; with use of the
amount of output adjustment, correcting the output signal obtained
when the substrate is present above the eddy current sensor; and
monitoring the thickness of the conductive film based on the
corrected output signal.
[0024] According to the present invention, the process of polishing
the conductive film on the substrate is started by pressing the
substrate against the polishing surface on the rotating polishing
table, and the output signal of the eddy current sensor is obtained
during polishing of the substrate. Subsequently, the output signal
obtained when the substrate is not present above the eddy current
sensor is used to calculate the amount of the output adjustment of
the eddy current sensor. Drift (translation) of the output signal
of the eddy current sensor may occur due to a change in operating
environment or a change in the eddy current sensor itself with
time. Such drift can be removed from the output signal by
correcting the output signal obtained when the substrate is present
above the eddy current sensor with use of the amount of the output
adjustment.
[0025] In a preferred aspect of the present invention, a resistance
component and reactance component of impedance of electric circuit
including a coil of the eddy current sensor are defined as
coordinates on a coordinate system, the coordinates are rotated and
moved such that a distance between an origin of the coordinate
system and a point specified by the coordinates is reduced in
accordance with a decrease in the thickness of the conductive film,
and the output signal of the eddy current sensor is represented by
the rotated and moved coordinates.
[0026] In a preferred aspect of the present invention, the
correcting of the output signal is performed by moving the origin
of the coordinate system.
[0027] According to the present invention, the drift can be removed
from the output signal by translating the origin of the coordinate
system on which the resistance component and the reactance
component of the impedance including the coil of the eddy current
sensor are plotted.
[0028] In a preferred aspect of the present invention, the
monitoring the thickness of the conductive film based on the
corrected output signal comprises monitoring the thickness of the
conductive film based on the distance between the moved origin of
the coordinate system and the point specified by the coordinates of
the impedance.
[0029] In a preferred aspect of the present invention, the method
further includes: obtaining resistance components and reactance
components of impedance of electric circuit including a coil of the
eddy current sensor at each of different thicknesses of the
conductive film under conditions of various distances between a
coil end of the eddy current sensor and the conductive film;
plotting the resistance components and the reactance components
onto rectangular coordinate axes; drawing preliminary measurement
linear lines each connecting points specified by coordinates
consisting of the resistance components and the reactance
components at each thickness of the conductive film; and
determining in advance a reference point at which the preliminary
measurement linear lines intersect with each other.
[0030] In a preferred aspect of the present invention, the
correcting of the output signal is performed by moving the
reference point that has been determined in advance.
[0031] The output signal of the eddy current sensor may drift due
to some causes, such as the change in the eddy current sensor
itself with time. Such drift causes a change in the angle between
the reference line extending through the reference point and the
line connecting the output signal of the eddy current sensor to the
reference point. According to the present invention, the preset
reference point is moved by a distance corresponding to the amount
of drift. Therefore, the drift can be removed from the output
signal.
[0032] In a preferred aspect of the present invention, the
monitoring the thickness of the conductive film based on the
corrected output signal comprises monitoring the thickness of the
conductive film based on an angle of a line connecting the moved
reference point to a point specified by coordinates of the
impedance.
[0033] In a preferred aspect of the present invention, the
correcting of the output signal is performed by using an average of
the output signal obtained when the substrate is not present above
the eddy current sensor while the polishing table makes N
revolutions.
[0034] In a preferred aspect of the present invention, the
calculating of the amount of output adjustment comprises
calculating the amount of output adjustment of the eddy current
sensor using only output signal obtained from a region where a top
ring for holding the substrate is not present on or above the
polishing surface, among the output signal obtained when the
substrate is not present above the eddy current sensor.
[0035] In a preferred aspect of the present invention, the
calculating of the amount of output adjustment comprises
calculating the amount of output adjustment of the eddy current
sensor using only output signal obtained from a region where a
dresser for dressing the polishing surface and an atomizer for
cleaning the polishing surface are not present on or above the
polishing surface, among the output signal obtained when the
substrate is not present above the eddy current sensor.
[0036] According to the present invention, the output signal
obtained when nothing exist on or above the polishing surface is
used. Therefore, only the signal that is obtained in a region that
does not affect the eddy current sensor can be used.
[0037] A second aspect of the present invention is to provide a
method of monitoring a thickness of a conductive film on a
substrate during polishing of the substrate with use of an eddy
current sensor provided in a polishing table. The method includes:
polishing the conductive film by pressing the substrate against a
polishing surface on the rotating polishing table; obtaining
resistance components and reactance components of impedance of
electric circuit including a coil of the eddy current sensor at
each of different thicknesses of the conductive film under
conditions of various distances between a coil end of the eddy
current sensor and the conductive film; plotting the resistance
components and the reactance components onto rectangular coordinate
axes; drawing preliminary measurement linear lines each connecting
points specified by coordinates consisting of the resistance
components and the reactance components at each thickness of the
conductive film; determining a reference point at which the
preliminary measurement linear lines intersect with each other;
correcting the reference point using output signal of the eddy
current sensor obtained during polishing, before polishing, or
after polishing; and monitoring the thickness of the conductive
film based on an angle of a line connecting the corrected reference
point to a point specified by coordinates of the impedance.
[0038] The output signal of the eddy current sensor may drift due
to some causes, such as the change in the eddy current sensor
itself with time. Such drift of the output single of the eddy
current sensor causes a change in the angle between the reference
line extending through the reference point and the line connecting
the output signal of the eddy current sensor to the reference
point. According to the present invention, the predetermined
reference point is corrected by the amount of drift, and the angle
between the reference line extending through the corrected
reference point and the line connecting the output signal of the
eddy current sensor and the corrected reference point is calculated
to thereby determine the thickness of the conductive film. In this
manner, the angle before and after the drift can be kept at the
same value by: determining the amount of drift of the output signal
value of the eddy current sensor; and shifting the reference point
by a distance corresponding to the amount of drift.
[0039] A third aspect of the present invention is to provide a
polishing apparatus, including: a rotatable polishing table having
a polishing surface; a top ring configured to press a substrate
against the polishing surface to polish a conductive film on the
substrate; an eddy current sensor arranged in the polishing table;
and a monitoring device for monitoring a thickness of the
conductive film based on output signal of the eddy current sensor,
wherein the monitoring device is configured to obtain the output
signal of the eddy current sensor during polishing, calculate an
amount of output adjustment of the eddy current sensor using the
output signal obtained when the substrate is not present above the
eddy current sensor, correct the output signal obtained when the
substrate is present above the eddy current sensor with use of the
amount of output adjustment, and monitor the thickness of the
conductive film based on the corrected output signal.
[0040] In a preferred aspect of the present invention, a resistance
component and reactance component of impedance of electric circuit
including a coil of the eddy current sensor are defined as
coordinates on a coordinate system, the coordinates are rotated and
moved such that a distance between an origin of the coordinate
system and a point specified by the coordinates is reduced in
accordance with a decrease in the thickness of the conductive film,
and the output signal of the eddy current sensor is represented by
the rotated and moved coordinates.
[0041] In a preferred aspect of the present invention, the
monitoring device is configured to correct the output signal by
moving the origin of the coordinate system.
[0042] In a preferred aspect of the present invention, the
monitoring device is configured to monitor the thickness of the
conductive film based on the distance between the moved origin of
the coordinate system and the point specified by the coordinates of
the impedance.
[0043] In a preferred aspect of the present invention, the
monitoring device is configured to: obtain resistance components
and reactance components of impedance of electric circuit including
a coil of the eddy current sensor at each of different thicknesses
of the conductive film under conditions of various distances
between a coil end of the eddy current sensor and the conductive
film; plot the resistance components and the reactance components
onto rectangular coordinate axes; draw preliminary measurement
linear lines each connecting points specified by coordinates
consisting of the resistance components and the reactance
components at each thickness of the conductive film; and determine
in advance a reference point at which the preliminary measurement
linear lines intersect with each other.
[0044] In a preferred aspect of the present invention, the
monitoring device is configured to correct the output signal by
moving the reference point that has been determined in advance.
[0045] In a preferred aspect of the present invention, the
monitoring device is configured to monitor the thickness of the
conductive film based on an angle of a line connecting the moved
reference point to a point specified by coordinates of the
impedance.
[0046] In a preferred aspect of the present invention, the
monitoring device is configured to correct the output signal by
using an average of the output signal obtained when the substrate
is not present above the eddy current sensor while the polishing
table makes N revolutions.
[0047] In a preferred aspect of the present invention, the
monitoring device is configured to calculate the amount of output
adjustment of the eddy current sensor using only output signal
obtained from a region where a top ring for holding the substrate
is not present on or above the polishing surface, among the output
signal obtained when the substrate is not present above the eddy
current sensor.
[0048] In a preferred aspect of the present invention, the
monitoring device is configured to calculate the amount of output
adjustment of the eddy current sensor using only output signal
obtained from a region where a dresser for dressing the polishing
surface and an atomizer for cleaning the polishing surface are not
present on or above the polishing surface, among the output signal
obtained when the substrate is not present above the eddy current
sensor.
[0049] A fourth aspect of the present invention is to provide a
method of detecting a polishing end point. The method includes:
rotating a top ring and a polishing table while the top ring is
pressing a substrate against a polishing pad on the polishing table
to polish a film of the substrate; during polishing of the
substrate, sweeping an eddy current sensor across a surface of the
substrate; obtaining resistance component X and inductive reactance
component Y of impedance of the eddy current sensor; plotting
coordinates X and Y, which consist of the resistance component X
and the inductive reactance component Y, onto a XY coordinate
system on which a plurality of impedance areas are defined in
advance, the plurality of impedance areas including a reference
impedance area and at least one offset impedance area; calculating
a plurality of film thickness index values in the plurality of
impedance areas, respectively, using plural pairs of coordinates X
and Y which belong respectively to the plurality of impedance
areas; and determining polishing end points of the substrate in the
plurality of impedance areas, respectively, using the plurality of
film thickness index values.
[0050] A fifth aspect of the present invention is to provide a
method of detecting a polishing end point. The method includes:
rotating a top ring and a polishing table while the top ring is
pressing a substrate against a polishing pad on the polishing table
to polish a film on the substrate; obtaining output signal of an
eddy current sensor provided in the polishing table while sweeping
the eddy current sensor across a surface of the substrate;
obtaining output signal of the eddy current sensor while sweeping
the eddy current sensor across the surface of the substrate in the
same path as that when the previous output signal is obtained;
calculating a film thickness index value from the output signal of
the eddy current sensor; and determining a polishing end point of
the substrate from a change in the film thickness index value.
[0051] A sixth aspect of the present invention is to provide a
method of detecting a polishing end point. The method includes:
rotating a top ring and a polishing table while the top ring is
pressing a substrate against a polishing pad on the polishing table
to polish a film on the substrate; during polishing of the
substrate, sweeping an eddy current sensor across a surface of the
substrate, the eddy current sensor being provided in the polishing
table; obtaining output signal of the eddy current sensor;
producing a film thickness profile from the output signal of the
eddy current sensor; judging whether a salient portion appearing in
the film thickness profile is due to the film remaining on the
substrate or due to metal lying under the film based on a change in
position of the salient portion appearing in the film thickness
profile; and determining a polishing end point of the substrate
based on a size of the salient portion that appears due to the film
remaining on the substrate.
[0052] A seventh aspect of the present invention is to provide a
polishing apparatus including: a rotatable polishing table for
supporting a polishing pad; a top ring configured to press a
substrate against the polishing pad on the rotating polishing table
while rotating the substrate; an eddy current sensor arranged in
the polishing table so as to sweep a surface of the substrate; and
a monitoring device for monitoring a film thickness of the
substrate from output signal of the eddy current sensor, wherein
the monitoring device is configured to obtain resistance component
X and inductive reactance component Y of impedance of the eddy
current sensor, plot coordinates X and Y, which consist of the
resistance component X and the inductive reactance component Y,
onto a XY coordinate system on which a plurality of impedance areas
are defined in advance, the plurality of impedance areas including
a reference impedance area and at least one offset impedance area,
calculate a plurality of film thickness index values in the
plurality of impedance areas, respectively, using plural pairs of
coordinates X and Y which belong respectively to the plurality of
impedance areas, and determine polishing end points of the
substrate in the plurality of impedance areas, respectively, using
the plurality of film thickness index values.
[0053] An eighth aspect of the present invention is to provide a
polishing apparatus including: a rotatable polishing table for
supporting a polishing pad; a top ring configured to press a
substrate against the polishing pad on the rotating polishing table
while rotating the substrate; an eddy current sensor arranged in
the polishing table so as to sweep a surface of the substrate; and
a monitoring device for monitoring a film thickness of the
substrate from output signal of the eddy current sensor, wherein
the monitoring device is configured to obtain output signal of the
eddy current sensor while the eddy current sensor is sweeping the
surface of the substrate, obtain output signal of the eddy current
sensor while the eddy current sensor is sweeping the surface of the
substrate in the same path as that when the previous output signal
is obtained, calculate a film thickness index value from the output
signal of the eddy current sensor, and determine a polishing end
point of the substrate from a change in the film thickness index
value.
[0054] According to the first to third aspects of the present
invention, the calibration of the eddy current sensor can be
performed on a software based on the output signal value of the
eddy current sensor during polishing of the conductive film on the
substrate, such as a semiconductor wafer. Therefore, accurate film
thickness monitoring can be performed continuously without lowering
the operating rate of the polishing apparatus.
[0055] According to the fourth and seventh aspects of the present
invention, each time the output signal of the eddy current sensor
is obtained, the coordinates consisting of the output signal X and
Y are sorted into one of the plurality of impedance areas in
accordance with the value of the coordinates. In other words, the
sensor output signal is sorted based on the degree of the influence
of the underlying metal into one of the plurality of impedance
areas. By providing the plurality of impedance areas in advance,
the variation in the sensor output signal (X, Y) can be divided,
i.e., can be small. Therefore, the film thickness index value
obtained from the sensor output signal in each impedance area
decreases gradually with the polishing time. The plurality of
impedance areas can be established in each zone defined in the
wafer surface, so that film thickness information can be obtained
in each zone in the wafer surface. Therefore, the polishing end
point can be detected in each of the multiple zones defined in the
wafer surface.
[0056] According to the fifth and eighth aspects of the present
invention, the film thickness index value is obtained when the eddy
current sensor sweeps the surface of the substrate in the same
path. Therefore, regardless of the presence of the underlying
metal, the film thickness index value decreases with the polishing
time at each measuring point on the surface of the substrate. That
is, the film thickness information can be obtained in each zone
defined in the substrate surface. Therefore, the polishing end
point can be detected in each of the multiple zones defined in the
wafer surface.
[0057] According to the sixth aspect of the present invention,
polishing of the substrate can be monitored based on the salient
portion appearing due to the residual film. Therefore, the
influence of the underlying metal is removed, and the accurate
polishing end point can be detected
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] FIG. 1 is a schematic view showing a whole structure of a
polishing apparatus;
[0059] FIG. 2 is a plan view showing a relationship between a
polishing table, an eddy current sensor, and a wafer;
[0060] FIG. 3 is a diagram showing an equivalent circuit for
illustrating a principle of the eddy current sensor;
[0061] FIG. 4 is a diagram showing a graph described by plotting X
and Y, which vary with polishing time, onto a XY coordinate
system;
[0062] FIG. 5 is a diagram showing a graph obtained by rotating the
graph in FIG. 4 in a counterclockwise direction through 90 degrees
and then translating the rotated graph;
[0063] FIG. 6 is a schematic view showing the eddy current
sensor;
[0064] FIG. 7 is a view of a structural example of a sensor coil of
the eddy current sensor shown in FIG. 6;
[0065] FIG. 8 is a schematic view of detailed structure of the eddy
current sensor;
[0066] FIG. 9A is a view showing the whole structure of the
polishing apparatus including a controller for the eddy current
sensor;
[0067] FIG. 9B is an enlarged cross-sectional view of a part of the
eddy current sensor;
[0068] FIG. 10A is a diagram showing a relationship between path of
the eddy current sensor when sweeping (scanning) a wafer surface
(i.e., a surface to be polished) and output of the eddy current
sensor;
[0069] FIG. 10B is a diagram showing relationship between rotation
of the polishing table and the output of the eddy current
sensor;
[0070] FIG. 11 is a diagram showing drift (translation) of the
output signal value of the eddy current sensor;
[0071] FIG. 12 is a diagraph showing an embodiment of a process
flow of monitoring a change in thickness of a conductive film on
the wafer while calibrating the output signal of the eddy current
sensor;
[0072] FIG. 13 is a diagram for illustrating a step of calculating
an amount of drift (an amount of correction);
[0073] FIG. 14 is a diagram for illustrating a step of moving an
origin O of the XY coordinate system by a distance corresponding to
the amount of drift (amount of correction);
[0074] FIG. 15 is a diagram showing another embodiment of the
process flow of monitoring the change in the thickness of the
conductive film on the wafer while calibrating the output signal of
the eddy current sensor;
[0075] FIG. 16 is a diagram showing the drift (or translation) of
the output signal value of the eddy current sensor;
[0076] FIG. 17 is a diagram for illustrating a step of shifting a
reference point by a distance corresponding to the amount of
correction;
[0077] FIG. 18 is a diagram showing paths of the eddy current
sensor when scanning the wafer;
[0078] FIG. 19 is a diagram illustrating an influence of underlying
interconnects that cause a change in film thickness index value
obtained from the output signal of the eddy current sensor;
[0079] FIG. 20A is a diagram showing an impedance curve in a case
where the influence of the underlying interconnects does not
exist;
[0080] FIG. 20B is a diagram showing the film thickness index value
obtained from the impedance curve shown in FIG. 20A;
[0081] FIG. 21A is a diagram showing an impedance curve in a case
where the influence of the underlying interconnects exists;
[0082] FIG. 21B is a diagram showing the film thickness index value
obtained from the impedance curve shown in FIG. 21A;
[0083] FIG. 22 is a diagram showing an example in which the wide
impedance curve shown in FIG. 21B is divided into four impedance
areas;
[0084] FIG. 23 is a diagram showing change in film thickness index
values determined from plural pairs of coordinates X and Y wherein
each pair belongs to each impedance area shown in FIG. 22;
[0085] FIG. 24 is a diagram showing a state in which first to third
offset impedance areas overlap a reference impedance area;
[0086] FIG. 25 is diagram showing change in the film thickness
index values determined from the coordinates X and Y belonging to
the respective overlapping four impedance areas shown in FIG.
24;
[0087] FIG. 26 is a view of five zones defined in the surface of
the wafer;
[0088] FIG. 27 is a diagram for illustrating a process of
calculating an angle .theta., which is the film thickness index
value, from the output signal X and Y of the eddy current
sensor;
[0089] FIG. 28 is a diagram showing an example in which the angle
.theta. varies due to the existence of the underlying interconnect
structure;
[0090] FIG. 29 is a diagraph illustrating an example of multiplying
the angle calculated in relation to the offset impedance area by a
coefficient;
[0091] FIG. 30 is a view showing paths of the eddy current sensor
described on the wafer when a top ring rotates at a speed of 77
min.sup.-1 and the polishing table rotates at a speed of 70
min.sup.-1;
[0092] FIG. 31 is a diagram showing a change in film thickness
profile on the same path of the eddy current sensor;
[0093] FIG. 32 is a diagram showing a residual film existing on a
wafer and film thickness profiles of the wafer;
[0094] FIG. 33 is a diagram showing film thickness profiles of a
wafer having the underlying interconnect structures and the
residual film;
[0095] FIG. 34 is a schematic view of a table rotation detector and
a top ring rotation detector;
[0096] FIG. 35 is a time chart illustrating a manner in which
time-measuring devices measure times of rotation of the polishing
table and the top ring upon receiving trigger signals;
[0097] FIG. 36 is a flowchart showing a process of detecting a
polishing end point;
[0098] FIG. 37 is a diagram for illustrating a specific example of
step 2 to step 5 shown in FIG. 36;
[0099] FIG. 38 is a cross-sectional view showing an example of the
top ring shown in FIG. 1; and
[0100] FIG. 39 is a diagram showing a relationship between signal
value of the eddy current sensor and polishing time (t) from when
polishing of a semiconductor wafer (substrate) is started until a
conductive film on the wafer is cleared (removed).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0101] Embodiments of the present invention will be described below
with reference to FIG. 1 to FIG. 38. The same or corresponding
elements are denoted by the same reference numerals and repetitive
explains will be omitted.
[0102] FIG. 1 is a schematic view showing a whole structure of a
polishing apparatus according to the present invention. As shown in
FIG. 1, the polishing apparatus has: a polishing table 1; and a top
ring 10 for holding a wafer W (i.e., a substrate to be polished)
and pressing the wafer W against a polishing pad 2 on the polishing
table 1. The polishing table 1 is coupled to a polishing table
rotating motor (not shown) through a table shaft 1a, so that the
polishing table 1 is rotated about the table shaft 1a. The
polishing table rotating motor is disposed below the polishing
table 1. A polishing pad 2 is attached to an upper surface of the
polishing table 1. The polishing pad 2 has an upper surface 2a that
provides a polishing surface for polishing the wafer W. A polishing
liquid supply nozzle 3 is installed above the polishing table 1 so
as to supply a polishing liquid (slurry) onto the polishing pad 2
on the polishing table 1. As shown in FIG. 1, an eddy current
sensor 50 is embedded in the polishing table 1.
[0103] The top ring 10 is coupled to a top ring shaft 11, which is
movable vertically relative to a top ring head 12. The vertical
movement of the top ring shaft 11 causes the top ring 10 in its
entirety to move vertically relative to the top ring head 12 and
enables positioning of the top ring 10. The top ring shaft 11 is
rotated by a top ring rotating motor (not shown). This rotation of
the top ring shaft 11 causes the top ring 10 to rotate about the
top ring shaft 11.
[0104] The top ring 10 is configured to be capable of holding the
wafer W, such as a semiconductor wafer, on its lower surface. The
top ring head 12 is configured to swing around a top ring head
shaft 13, so that the top ring 10, holding the wafer W on the lower
surface thereof, can move from a receiving position of the wafer W
to a position above the polishing table 1. The top ring 10 holds
the wafer W on its lower surface and presses the wafer W against
the surface (i.e., the polishing surface) of the polishing pad 2.
While pressing the wafer W, the top ring 10 and the polishing table
1 are rotated and the polishing liquid is supplied onto the
polishing pad 2 from the polishing liquid supply nozzle 3 that is
disposed above the polishing table 1. The polishing liquid contains
abrasive grains, such as ceria (CeO.sub.2) or silica (SiO.sub.2).
In this manner, the wafer W is pressed against the polishing pad 2
while the polishing liquid is supplied onto the polishing pad 2,
and the wafer W and the polishing pad 2 are moved relative to each
other to thereby polish a conductive film, e.g., a metal film, on
the wafer. Examples of the metal film include Cu film, W film, Ta
film, and Ti film.
[0105] As shown in FIG. 1, the polishing apparatus has a dressing
unit 20 for dressing the polishing pad 2. This dressing unit 20 has
a dresser arm 21, a dresser 22 rotatably mounted to a tip end of
the dresser arm 21, a pivot shaft 23 coupled to the other end of
the dressing arm 21, and a motor (not shown) as a driving device
for causing the dresser arm 21 to pivot on (swing about) the pivot
shaft 23. The dresser 22 has a lower portion that is constituted by
a dressing member 22a, which has a circular dressing surface. Hard
particles, such as diamond particles or ceramic particles, are
fixed to the dressing surface by means of electrodeposition or the
like. A motor (not shown) for rotating the dresser 22 is provided
in the dresser arm 21. The pivot shaft 23 is coupled to a vertical
actuator (not shown), so that the dresser arm 21 is lowered by the
vertical actuator to press the dressing member 22a against the
polishing surface 2a of the polishing pad 2 to thereby dress the
polishing pad 2. The dressing unit 20 is designed to be able to
dress the polishing pad 2 when polishing of the wafer is not
performed and further designed to be able to dress the polishing
pad 2 even when polishing of the wafer is being performed.
[0106] FIG. 2 is a plan view showing a relationship between the
polishing table 1, the eddy current sensor 50, and the wafer W. As
shown in FIG. 2, the eddy current sensor 50 is arranged in such a
position to pass through a center Cw of the wafer W when held by
the top ring 10 during polishing of the wafer W. Symbol CT
represents a center of rotation of the polishing table 1. For
example, the eddy current sensor 50 is capable of detecting a
thickness of the conductive film on the wafer W continuously on a
sweep path (i.e., scan line) while sweeping under the wafer W.
[0107] Next, the eddy current sensor 50 provided in the polishing
apparatus according to the present invention will be described in
more detail. There are two types of eddy current sensors: a
frequency type; and an impedance type. The frequency type is
designed to detect a conductive film from a change in oscillatory
frequency that is caused by an eddy current induced in the
conductive film. The impedance type is designed to detect a
conductive film from a change in impedance that is caused by an
eddy current induced in the conductive film. Measurement
information of the conductive film is obtained from the frequency
or the impedance. The eddy current sensor 50 is installed in the
polishing table 1 at a position near a surface of the polishing
table 1 as shown in FIG. 1, and is arranged so as to face the
wafer, to be polished, through the polishing pad in order to detect
a change in the conductive film from the eddy current flowing
through the conductive film on the wafer.
[0108] In the impedance-type eddy current sensor, signal output X
and Y, phase, and resultant impedance Z are extracted as will be
described below. Hereinafter, the impedance-type eddy current
sensor will be described more specifically. The eddy current sensor
50 is configured to pass a high-frequency alternating current to a
coil so as to induce the eddy current in the conductive film and
detect the thickness of the conductive film from the change in the
impedance due to a magnetic field produced by the induced eddy
current.
[0109] FIG. 3 is a diagram showing a circuit for illustrating the
principle of the eddy current sensor. When an AC power supply (a
voltage E [V]) passes a high-frequency alternating current I.sub.1
to a coil Q, magnetic lines of force, induced in the coil Q, pass
through the conductive film. As a result, mutual inductance occurs
between a sensor-side circuit and a conductive-film-side circuit,
and an eddy current I.sub.2 flows through the conductive film. This
eddy current I.sub.2 generates magnetic lines of force, which cause
a change in an impedance of the sensor-side circuit. The eddy
current sensor measures the thickness of the conductive film from
the change in the impedance of the sensor-side circuit.
[0110] In the sensor-side circuit and the conductive-film-side
circuit in FIG. 3, the following equations hold.
R.sub.1I.sub.1+L.sub.1dI.sub.1/dt+MdI.sub.2/dt=E (1)
R.sub.2I.sub.2+L.sub.2dI.sub.2/dt+MdI.sub.1/dt=0 (2)
[0111] where M represents mutual inductance, R.sub.1 represents
equivalent resistance of the sensor-side circuit including the coil
Q, L.sub.1 represents self-inductance of the sensor-side circuit
including the coil Q, R.sub.2 represents equivalent resistance
corresponding to eddy current loss, and L.sub.2 represents
self-inductance of the conductive film through which the eddy
current flows.
[0112] Letting I.sub.n=A.sub.ne.sup.j.omega.t (sine wave), the
above equations (1) and (2) are expressed as follows.
(R.sub.1+j.omega.L.sub.1)I.sub.1+j.omega.MI.sub.2=E (3)
(R.sub.2+j.omega.L.sub.2)I.sub.2+j.omega.MI.sub.1=0 (4)
[0113] From these equations (3) and (4), the following equations
are derived.
I 1 = E ( R 2 + j.omega. L 2 ) / [ ( R 1 + j.omega. L 1 ) ( R 2 +
j.omega. L 2 ) + .omega. 2 M 2 ] = E / [ ( R 1 + j.omega. L 1 ) +
.omega. 2 M 2 / ( R 2 + j.omega. L 2 ) ] ( 5 ) ##EQU00001##
[0114] Thus, the impedance .PHI. of the sensor-side circuit is
given by the following equation.
.PHI.=E/I.sub.1=[R.sub.1+.omega..sup.2M.sup.2R.sub.2/(R.sub.2.sup.2+.ome-
ga..sup.2L.sub.2.sup.2)]+j.omega.[L.sub.1-.omega..sup.2L.sub.2M.sup.2/(R.s-
ub.2.sup.2+.omega..sup.2L.sub.2.sup.2)] (6)
[0115] Substituting X and Y for a real part (i.e., a resistance
component) and an imaginary part (i.e., an inductive reactance
component) respectively, the above equation (6) is expressed as
follows.
.PHI.=X+j.omega.Y (7)
[0116] FIG. 4 is a diagram showing a graph drawn by plotting X and
Y, which change with a polishing time, on a XY coordinate system.
The coordinate system shown in FIG. 4 is defined by a vertical axis
as a Y-axis and a horizontal axis as a X-axis. Coordinates of a
point T.sup..infin. are values of X and Y when a film thickness is
infinity, i.e., R.sub.2 is zero. Where electrical conductivity of a
substrate can be neglected, coordinates of a point T0 are values of
X and Y when the film thickness is zero, i.e., R.sub.2 is infinity.
A point Tn, specified by the values of X and Y, moves in a circular
arc toward the point T0 as the film thickness decreases. A symbol k
in FIG. 4 represents coupling coefficient, and the following
relationship holds.
M=k(L.sub.1L.sub.2).sup.1/2 (8)
[0117] FIG. 5 shows a graph obtained by rotating the graph in FIG.
4 through 90 degrees in a counterclockwise direction and further
translating the resulting graph. Specifically, the point given by
the coordinates X and Y is rotated about the origin O of the XY
coordinate system, and the rotated point given by the coordinates
are further moved so as to create a graph in which a distance
between the origin O and the point specified by the coordinates X
and Y decreases in accordance with the decrease in the film
thickness. Hereinafter, a circular arc depicted by the point of the
coordinates X and Y will be referred to as an impedance curve.
[0118] FIG. 5 shows the case where the graph in FIG. 4 is rotated
through 90 degrees in the counterclockwise direction. Nevertheless,
it is noted that the rotation angle is not limited to 90 degrees.
For example, the rotation angle can be adjusted such that the
Y-coordinate corresponding to an upper limit of the film thickness
to be monitored is equal to the Y-coordinate of the point where the
film thickness is zero. As shown in FIG. 5, the point Tn, which is
specified by the values of X and Y, travels in a circular arc
toward the point T0 as the film thickness decreases. During
traveling, an impedance Z (=(X.sup.2+Y.sup.2).sup.1/2), which is
expressed as a distance between the origin O of the XY coordinate
system and the point Tn, decreases as the film thickness decreases,
so long as the point Tn is not located near the point T.infin.. The
output signal of the eddy current sensor 50 is sent to a monitoring
device 55, which calculates the impedance Z as a monitoring signal
that varies in accordance with the thickness of the conductive
film. Therefore, once a relationship between the impedance Z and
the film thickness is obtained in advance from experiences or
experiments, the monitoring device 55 can grasp the change in the
film thickness during polishing by monitoring the impedance Z.
[0119] Next, the eddy current sensor 50 will be described in more
detail. FIG. 6 is a schematic view showing the eddy current sensor.
This eddy current sensor 50 includes a sensor coil 102, an AC power
supply 103 connected to the sensor coil 102, and a synchronous
detector 105 configured to detect the resistance component X and
the inductive reactance component Y of an electric circuit
including the sensor coil 102 (the sensor-side circuit in FIG. 3).
A conductive film mf, which is a film to be detected in its
thickness, is a thin film on the wafer W. This thin film is made of
a conductive material, such as copper, aluminum, gold, tungsten,
tantalum, or titanium. A distance G between the sensor coil 102 and
the conductive film mf is in a range of 0.5 mm to 5.0 mm, for
example.
[0120] FIG. 7 is a view showing an example arrangement of the
sensor coil of the eddy current sensor shown in FIG. 6. The sensor
coil 102 includes a bobbin 111, and three coils 112, 113, and 114
wound on the bobbin 111. These coils 112, 113, and 114 form a
three-layer coil. The center coil 112 is an exciting coil connected
to the AC power supply 103. This exciting coil 112 produces a
magnetic field by an alternating current supplied from the AC power
supply 103 to thereby induce the eddy current in the conductive
film on the wafer. The detection coil 113 is located above the
exciting coil 112 (i.e., located at the conductive-film side). This
detection coil 113 is configured to detect a magnetic flux
generated by the eddy current flowing through the conductive film.
The balance coil 114 is located at an opposite side of the
detection coil 113.
[0121] The coils 113 and 114 preferably have the same number of
turns (1 to 500 turns), while the number of tunes of the coil 112
is not limited particularly. The detection coil 113 and the balance
coil 114 are connected in opposite phase to each other. When the
conductive film is present near the detection coil 113, the
magnetic flux produced by the eddy current flowing through the
conductive film is interlinked with the detection coil 113 and the
balance coil 114. Since the detection coil 113 is located closer to
the conductive film than the coil 114, induced voltages produced in
the coils 113 and 114 are unbalanced, whereby the interlinkage flux
generated by the eddy current in the conductive film can be
detected.
[0122] FIG. 8 is a schematic view showing the details of the eddy
current sensor. The AC power supply 103 includes an oscillator,
such as a quartz oscillator, generating a fixed frequency. For
example, the AC power supply 103 supplies an alternating current
having a fixed frequency of 1 to 50 MHz to the sensor coil 102. The
alternating current generated by the AC power supply (AC signal
source) 103 is supplied to the sensor coil 102 via a bandpass
filter 120. A terminal of the sensor coil 102 outputs a signal,
which is sent to the synchronous detector 105 via a bridge circuit
121 and a high-frequency amplifier 123. The synchronous detector
105 includes a cosine synchronous detection circuit 125 and a sine
synchronous detection circuit 126. A phase shift circuit 124
generates two signals: in-phase component (0 degree) and quadrature
component (90 degrees) from an oscillation signal generated by the
AC power source 103. These two signals are sent to the cosine
synchronous detection circuit 125 and the sine synchronous
detection circuit 126, respectively. The synchronous detector 105
extracts the resistance component and the inductive reactance
component of the impedance.
[0123] Low-pass filters 127 and 128 remove unwanted high-frequency
components (e.g., 5 kHz or more) from the resistance component and
the inductive reactance component outputted from the synchronous
detector 105. As a result, the signal X as the resistance component
and the signal Y as the inductive reactance component of the
impedance are outputted from the eddy current sensor 50. The
monitoring device 55 performs the same processes on the output
signal X and Y as described with reference to FIG. 5 (e.g., the
rotating process and the translating process) to thereby calculate
the impedance Z (see FIG. 5) as a film thickness index value.
Processing of the output signal X and Y of the eddy current sensor
50, e.g., the rotating process and the translating process, may be
performed electrically in the eddy current sensor 50 or may be
performed by the calculation in the monitoring device 55.
[0124] FIG. 9A and FIG. 9B are views showing an essential part of
the polishing apparatus including the eddy current sensor 50. More
specifically, FIG. 9A is a view showing a whole structure including
a controller for the eddy current sensor 50, and FIG. 9B is an
enlarged cross-sectional view of a part of the eddy current sensor.
As shown in FIG. 9A, the polishing table 1 is rotatable about its
own axis as indicated by arrow. The sensor coil 102 of the eddy
current sensor 50 is embedded in the polishing table 1. This sensor
coil 102 is a preamplifier-integrated sensor coil including the AC
power source and the synchronous detection circuit. A connection
cable of the sensor coil 102 extends through the table shaft 1a of
the polishing table 1 to the monitoring device 55 via a rotary
joint 150 provided on an end of the table shaft 1a. The monitoring
device 55 is coupled to a control device (controller) 56.
[0125] As shown in FIG. 9B, the eddy current sensor 50 has a
polishing-pad-side end surface that is covered with a coating
material 152 of fluororesin, such as polytetrafluoroethylene. This
coating material 152 can prevent the eddy current sensor from being
removed together with the polishing pad 2 when the polishing pad 2
is removed from the polishing table 1. The polishing-pad-side end
surface of the eddy current sensor 50 is located below an upper
surface (a polishing-pad-side surface) of the polishing table 1 by
a distance of 0 to 0.05 mm, so that the eddy current sensor 50 does
not contact the polishing pad 2. The difference between the upper
surface of the polishing table 1 and the upper end face of the eddy
current sensor 50 should preferably be as small as possible. In the
actual apparatus, the difference is typically set to around 0.02
mm. The height of the eddy current sensor 50 can be adjusted by any
adjustment means, such as a shim (thin plate) 151 or a screw.
[0126] Next, a method of monitoring the thickness of the conductive
film on the wafer during polishing in the polishing apparatus
having the eddy current sensor will be described. FIG. 10A is a
diagram showing a relationship between the path of the eddy current
sensor 50 when sweeping (scanning) the surface, to be polished, of
the wafer W and the output of the eddy current sensor 50. As shown
in FIG. 10A, the eddy current sensor 50 is configured to output the
signal value in response to the conductive film mf on the wafer W
while passing under the wafer W as the polishing table 1
rotates.
[0127] FIG. 10B is a diagram showing a relationship between
rotation of the polishing table 1 and the output of the eddy
current sensor 50. In FIG. 10B, horizontal axis represents
polishing time (t) and vertical axis represents the output value of
the eddy current sensor 50. As shown in FIG. 10B, when the eddy
current sensor 50 is in a region (A) in the wafer, the sensor
output forms an approximately rectangular pulse as a result of the
response to the conductive film mf on the wafer, and when the eddy
current sensor 50 is in a region (B) that is outside the wafer, the
sensor output is kept low in a constant level.
[0128] FIG. 11 is a diagram illustrating drift (translation) of the
output signal value of the eddy current sensor. Drift (i.e.,
translation) of the output signal value of the eddy current sensor
50 could occur due to a change in operating environment, such as
ambient temperature of the eddy current sensor or permeation of the
liquid into the polishing pad, or a change in the eddy current
sensor itself with time. As shown in FIG. 11, the output signal
value of the eddy current sensor 50 may drift as indicated by a
shift from a solid curve to a dotted curve. The drift of the output
signal value of the eddy current sensor 50 causes a change in the
impedance Z represented by a distance from the origin O of the XY
coordinate system (hereinafter the impedance Z may be called
distance Z). As a result, the relationship between the output
signal value of the eddy current sensor and the film thickness
varies.
[0129] Thus, in this embodiment, the monitoring device 55
calibrates the output signal of the eddy current sensor 50 so as to
monitor an accurate change in the film thickness.
[0130] Next, a method of monitoring the change in the film
thickness of the conductive film on the wafer while calibrating the
output signal of the eddy current sensor 50 during polishing will
be described.
[0131] FIG. 12 is a diagraph showing an embodiment of a process
flow of monitoring the change in thickness of the conductive film
on the wafer while calibrating the output signal of the eddy
current sensor 50. As shown in FIG. 12, at step 1, the wafer W is
held on the top ring 10, and the wafer W is pressed against the
polishing pad 2 while the polishing table 1 and the top ring 10 are
rotated, so that polishing of the conductive film on the wafer is
started. As shown in FIG. 10A and FIG. 10B, during polishing, the
eddy current sensor 50 passes through the region (A) in the wafer
and the region (B) off the wafer as the polishing table 1 rotates.
At step 2, the monitoring device 55 obtains data that are obtained
by the eddy current sensor 50 when the sensor 50 is in the region
(B) off the wafer. Specifically, after the polishing table 1 makes
one or more revolutions since polishing is started, the monitoring
device 55 obtains data of the region (B) off the wafer, and
continues to obtain the data until the polishing table 1 makes N
revolutions (N is integer). Then, at step 3, the monitoring device
55 calculates an amount of drift (i.e., an amount of correction)
based on an average of the output values of the eddy current sensor
50 with respect to the region (B) off the wafer that are obtained
until the polishing table 1 makes N revolutions.
[0132] The region off the wafer includes a region where the top
ring is not present, a region where the dresser is not present, and
a region where an atomizer and other structures are not present.
That is, the region off the wafer is a region where nothing is
present on the polishing table (the polishing pad).
[0133] FIG. 13 is a diagram for illustrating the step of
calculating the amount of drift (the amount of correction). As
indicated by curves in circular arc in FIG. 13, the output signal
value of the eddy current sensor 50 may drift from a solid line to
a dotted line.
[0134] This amount of drift (amount of correction) is calculated
from the following equations.
.DELTA.Xa=X11-X1,.DELTA.Ya=Y11-Y1
[0135] where X11 and Y11 are average of the output values of the
eddy current sensor 50 obtained in the off-wafer region (B), and X1
and Y1 are reference signal values for the correction, which are
similar to values when the thickness of the conductive film is
zero.
[0136] At step 4, the amount of drift (the amount of correction)
calculated in the step 3 is registered (or stored). Then, at step
5, the origin O of the XY coordinate system is translated by a
distance corresponding to the registered amount of drift (amount of
correction).
[0137] FIG. 14 is a diagram for illustrating the step of moving the
origin O of the XY coordinate system by a distance corresponding to
the amount of drift (amount of correction). As shown in FIG. 14,
the origin O of the XY coordinate system is translated from solid
line to dotted line. More specifically, X axis and Y axis,
indicated by solid lines, are translated by .DELTA.Xa and .DELTA.Ya
to X axis and Y axis indicated by dotted lines. Then the distance Z
from the origin O of the XY coordinate system defined by the X axis
and the Y axis indicated by the dotted lines is calculated. The
monitoring device 55 monitors the distance Z so as to grasp the
change in the film thickness during polishing.
[0138] FIG. 15 is a diagram showing another embodiment of the
process flow of monitoring the change in the thickness of the
conductive film on the wafer while calibrating the output signal of
the eddy current sensor 50. The drift of the output value of the
eddy current sensor may affect a film thickness monitoring method
other than the above-discussed method based on the distance Z as
well. For example, Japanese laid-open patent publication No.
2005-121616 discloses in FIG. 13 a method of monitoring a change in
film thickness during polishing from a change in an angle between a
reference line extending through a reference point (central point)
and a line extending through the reference point and a point
specified by output signal (X component and Y component) of the
eddy current sensor. This method includes the steps of: plotting,
onto rectangular coordinate axes, resistance components (X
components) and reactance components (Y components) of impedance
obtained under conditions of various distances between a sensor
coil end and the conductive film; drawing preliminary measurement
linear lines each connecting points specified by coordinates
consisting of the resistance components and the reactance
components at each thickness of the conductive film; determining a
reference point (central point) at which the preliminary
measurement linear lines intersect with each other; and determining
the thickness of the conductive film from an angle of a definitive
measurement linear line connecting the point specified by the
coordinates of the impedance to the reference point (central
point). This method can monitor the change in the film thickness
accurately regardless of a change in thickness of the polishing
pad. However, even in this method, the variation in the output
value of the eddy current sensor with time results in a change in
the angle, thus causing a shift in relationship between the output
signal value of the eddy current sensor and the film thickness.
[0139] FIG. 16 is a diagram showing the drift (translation) of the
output signal value of the eddy current sensor. As indicated by
curves in a circular arc in FIG. 16, the output signal value of the
eddy current sensor 50 may drift from a solid line to a dotted line
due to some causes including a change in the eddy current sensor
itself with time. Such drift of the output signal value of the eddy
current sensor causes the change in the angle between the reference
line extending through the reference point (central point) and the
line connecting the output signal of the eddy current sensor (the X
component and the Y component) to the reference point (central
point). Specifically, the angle is changed from "Angle 1" to "Angle
2". The reference point is a point at which the preliminary
measurement linear lines intersect with each other. The preliminary
measurement linear lines are obtained by: plotting onto the
rectangular coordinate axes the resistance components (X
components) and the reactance components (Y components) of
impedance obtained under the conditions of different distances
between the sensor coil end and the conductive film; and drawing
lines each connecting points specified by coordinates consisting of
the resistance components and the reactance components at each
thickness of the conductive film.
[0140] In this embodiment, as shown in FIG. 15, the processes from
step 1 of starting the polishing process to step 4 of registering
the amount of drift (amount of correction) are performed. The
processes from the step 1 to the step 4 are the same as those in
the process flow shown in FIG. 12. In the process flow shown in
FIG. 15, at step 5, the reference point is shifted by a distance
corresponding to the registered amount of drift (amount of
correction).
[0141] FIG. 17 is a diagram for illustrating the step of shifting
the reference point by a distance corresponding to the amount of
correction. As shown in FIG. 17, the reference point is shifted by
a distance corresponding to the amount of correction (.DELTA.Xa and
.DELTA.Ya) as illustrated by arrow. Subsequently, at step 6, the
angle ("Angle") of the impedance curve is calculated using the
corrected reference point. More specifically, the angle between the
reference line extending through the corrected reference point
(central point) and the line connecting the output signal (the X
component and the Y component) of the eddy current sensor to the
corrected reference point (central point) is calculated. The film
thickness can be determined from the angle calculated. In this
manner, the angle ("Angle") before and after the drift can be kept
at the same value by: determining the amount of drift of the output
signal value of the eddy current sensor; and shifting the reference
point by a distance corresponding to the amount of drift.
[0142] FIG. 18 is a diagram showing paths of the eddy current
sensor 50 when scanning the wafer W. As the polishing table 1
rotates, the eddy current sensor 50 scans the surface of the wafer
W while describing a path passing through the center C.sub.w of the
wafer W. Each time the eddy current sensor 50 sweeps the wafer
surface, the eddy current sensor 50 measures the film thickness of
the wafer W at plural measuring points. Typically, a rotational
speed of the top ring 10 is different from a rotational speed of
the polishing table 1. As a result, the path of the eddy current
sensor 50 on the surface of the wafer W varies as the polishing
table 1 rotates, as indicated by scan lines SL.sub.1, SL.sub.2,
SL.sub.3, . . . in FIG. 18. Even in this case, since the eddy
current sensor 50 is located so as to sweep the center C.sub.w of
the wafer W as described above, the path of the eddy current sensor
50 passes through the center C.sub.w of the wafer W in every
revolution. In this embodiment, timing of film-thickness measuring
by the eddy current sensor 50 is adjusted such that the film
thickness at the center C.sub.w of the wafer W is always monitored
by the eddy current sensor 50 in every revolution. In FIG. 18,
symbol MP.sub.m-n represents an n-th measuring point on an m-th
scan line SL.sub.m.
[0143] The output signal X and Y of the eddy current sensor 50
obtained at each measuring point is plotted as the coordinates X
and Y on the XY coordinate system. The output signal X and Y of the
eddy current sensor 50 varies in accordance with the film
thickness. Specifically, as shown in FIG. 5, the distance (i.e.,
impedance) Z (= (X.sup.2+Y.sup.2) between the origin O of the XY
coordinate system and the point Tn defined by the coordinates X, Y
decreases as the film thickness decreases. Therefore, it can be
said that the distance Z determined from the output signal X and Y
is an index value of the film thickness measured.
[0144] Although the film thickness of the wafer W can be determined
from the output signal X and Y of the eddy current sensor 50, a
great shift in the output signal of the eddy current sensor 50 may
occur due to existence of metal under the film. The wafer having
multilayer interconnect structure contains interconnects (i.e.,
metal) in each level of the multilayer interconnect structure. The
interconnects lying under the film could affect the output signal
of the eddy current sensor 50, thus preventing accurate measuring
of the film thickness.
[0145] FIG. 19 is a diagram illustrating the influence of the
underlying interconnects that cause the change in the film
thickness index value Z obtained from the output signal of the eddy
current sensor 50. A plurality of interconnect structures (e.g.,
integrated circuits) 200 lie under the film to be polished. In FIG.
19, these interconnect structures 200 are indicated by dotted lines
because they are covered with the film to be polished. The film
thickness index value Z decreases gradually in its entirety with
the polishing time. However, the eddy current sensor 50 senses not
only the film to be polished, but also the interconnect structures
200 lying under the film. As a result, the signal value of the eddy
current sensor 50 is affected by the underlying interconnect
structures 200.
[0146] As shown in FIG. 19, the path of the eddy current sensor 50
when the polishing table 1 is making N-th revolution differs from
the path of the eddy current sensor 50 when the polishing table 1
is making N+1-th revolution. Accordingly, arrangement of the
interconnect structures 200 sensed by the eddy current sensor 50
varies as the polishing table 1 rotates. This results in a
variation in a film thickness profile (i.e., a film thickness
distribution along radial direction of the wafer) which is produced
from the film thickness index value Z. In this manner, the output
signal X and Y of the eddy current sensor 50 is affected by the
underlying interconnect structures 200, and the impedance curve
described on the XY coordinate system fluctuates greatly.
[0147] FIG. 20A is a diagram showing the impedance curve in the
case where the influence of the underlying interconnect structures
does not exist, and FIG. 20B is a diagram showing the film
thickness index value Z obtained from the impedance curve shown in
FIG. 20A. When the influence of the underlying interconnect
structures does not exist, a width of the fluctuation (indicated by
dw) is small, although the impedance curve fluctuates to some
degree due to system noise. In this case, as shown in FIG. 20B, the
film thickness index value Z describes a line with a small width as
well. In FIG. 20B, vertical axis represents the film thickness
index value, and horizontal axis represents the polishing time. The
film thickness index value Z decreases with the polishing time.
Therefore, it is easy to detect a point where the film is removed,
i.e., the polishing end point.
[0148] In contrast, FIG. 21A shows the impedance curve in the case
where the influence of the underlying interconnect structures
exists, and FIG. 21B shows the film thickness index value Z
obtained from the impedance curve shown in FIG. 21A. When the
influence of the underlying interconnect structures exists, the
impedance curve fluctuates greatly. As a result, the width dw' of
the impedance curve becomes large. In this case, the film thickness
index value Z describes a wide line as well. This makes it
difficult to detect the polishing end point.
[0149] Thus, in this embodiment, the wide impedance curve as shown
in FIG. 21A is divided along its longitudinal direction into a
plurality of areas (which will hereinafter be referred to as
impedance areas). The film thickness index valve is calculated in
each of the impedance areas, and polishing of the wafer is
monitored in each of the impedance areas based on the film
thickness index value. FIG. 22 is a diagram showing an example in
which the wide impedance curve shown in FIG. 21A is divided into
four impedance areas. Hereinafter, the narrow impedance curve shown
in FIG. 20A will be referred to as a reference impedance area, the
wide impedance curve shown in FIG. 21A will be referred to as an
initial impedance area, and the impedance area, other than the
reference impedance area, of the divided impedance areas shown in
FIG. 22 will be referred to as offset impedance area.
[0150] The four impedance areas, i.e., a reference impedance area
r0, a first offset impedance area r1, a second offset impedance
area r2, and a third offset impedance area r3, have the same width,
which is the width dw of the reference impedance area r0 obtained
under the condition that no influence of the underlying
interconnect structures exists. However, the width of the offset
impedance areas r1-r3 may differ slightly from the width of the
reference impedance area r0.
[0151] The reference impedance area r0 is produced using only the
output signal (X, Y) of the eddy current sensor 50 obtained in the
center of the wafer. The eddy current sensor 50 always passes
through the center of the wafer every time the polishing table 1
makes one revolution. Therefore, the film thickness index value Z
obtained in the center of the wafer decreases with the polishing
time, regardless of the presence of the underlying metal, such as
interconnect structure. In other words, in the center of the wafer,
the underlying metal does not affect the temporal change in the
film thickness index value Z. Therefore, the narrow impedance area
as shown in FIG. 20A can be produced from the sensor output signal
(X, Y) obtained in the center of the wafer. This impedance area
obtained in the center of the wafer is defined as the reference
impedance area.
[0152] The width dw of the reference impedance area is given as a
difference between the minimum distance and the maximum distance
from a center of the circular arc of the reference impedance area.
More specifically, the width dw of the reference impedance area is
determined by: determining the center of the circular arc described
by the reference impedance area using a known technique, such as
least-squares method; and calculating the difference between the
minimum distance and the maximum distance from the determined
center. The width dw' of the wide initial impedance area shown in
FIG. 21A is also determined by calculation in the same manner.
Then, the initial impedance area is divided based on the width dw
of the reference impedance area. The number of impedance areas to
be divided is determined from the width dw' of the initial
impedance area. Specifically, the number of impedance areas is
determined by dividing the width dw' of the initial impedance area
by the width dw of the reference impedance area. In the example
shown in FIG. 22, the four impedance areas r0, r1, r2, r3,
including the reference impedance area, are produced. Depending on
the width of the initial impedance area, any one of the impedance
areas r1, r2, r3 may have a slightly different width.
[0153] The reference impedance area r0 and the offset impedance
areas r1, r2, r3 are obtained in advance by polishing a wafer
having the same structure as the wafer to be polished. Typically,
one of a plurality of wafers with the same structure belonging to
one lot is polished for producing the impedance areas r0, r1, r2,
r3 in advance.
[0154] The plurality of impedance areas, that have been produced as
described above, are defined on the XY coordinate system. Each time
the output signal X and Y of the eddy current sensor is obtained,
the coordinates consisting of the output signal X and Y are sorted
into one of the four impedance areas in accordance with value of
the output signal X and Y. In other words, based on the degree of
influence of the underlying interconnect structure, the sensor
output signal X and Y is sorted into one of the impedance areas r0,
r1, r2, r3.
[0155] FIG. 23 is a diagram showing change in film thickness index
values Z (each value Z is represented by the distance from the
origin O to the point of the coordinates X and Y) determined from
plural pairs of coordinates X and Y wherein each pair belongs to
each impedance area. The film thickness index values Z describe
four lines with the elapse of the polishing time. These four lines
correspond to the four impedance areas r0, r1, r2, r3 (see FIG. 22)
to which a position specified by the coordinates X and Y belongs.
Polishing of the wafer is monitored based on each of the four film
thickness index values corresponding to the four impedance areas,
and the polishing end point is determined based on the change in
each film thickness index value.
[0156] As shown in FIG. 24, the offset impedance areas r1, r2, r3
may be translated so as to overlap the reference impedance area r0.
A distance of the translation for each offset impedance area is
determined from a distance between the centers of the circular arcs
of the four impedance areas, i.e., the width dw of the reference
impedance area r0. Specifically, the first offset impedance area r1
is translated by a distance of dw.times.1, the second offset
impedance area r2 is translated by a distance of dw.times.2, and
the third offset impedance area r3 is translated by a distance of
dw.times.3. With these operations, the first to third offset
impedance areas r1, r2, r3 overlap the reference impedance area r0
as shown in FIG. 24.
[0157] FIG. 25 is diagram showing the change in the film thickness
index values Z (the distance from the origin O to the point of the
coordinates X and Y) determined from the plural pairs of
coordinates X and Y wherein the plural pairs belong to the
overlapping four impedance areas, respectively, shown in FIG. 24.
As can be seen from FIG. 25, the four film thickness index values
vary with the polishing time in the same manner, and the four film
thickness index values at each polishing time are closer to each
other, as compared with the film thickness index values shown in
FIG. 23.
[0158] The polishing end point of the wafer is determined in each
of the impedance areas. Specifically, the four film thickness index
values corresponding to the four impedance areas are monitored
separately. Points of time when the film thickness index values
have reached respective predetermined threshold values are
determined to be polishing end points in the impedance areas. The
threshold values are set for the four film thickness index values,
respectively. A final polishing end point may be a point of time
when at least one of the four film thickness index values has
reached the corresponding predetermined threshold value. For
example, the polishing end point may be set to a point of time when
the film thickness index value in the reference impedance area has
reached the predetermined threshold value, or a point of time when
the film thickness index values in all of the impedance areas have
reached the threshold values. Further, the polishing end point may
be set to a point of time when at least two of the film thickness
index values have reached the predetermined threshold values.
[0159] The first to third offset impedance areas r1, r2, r3 are
regions where the output signal of the eddy current sensor is under
the influence of the underlying interconnect structure. However, in
one offset impedance area, the output signal of the eddy current
sensor is affected equally by the underlying interconnect
structure. Therefore, the change in the film thickness index value
in one offset impedance area reflects the progress of polishing of
the wafer, regardless of the influence of the underlying
interconnect structure. Accordingly, accuracy of detecting the
polishing end point can be improved by monitoring polishing of the
wafer in each of the divided impedance areas.
[0160] The above-discussed plurality of impedance areas can be
produced for each of zones defined in the wafer surface. Therefore,
the polishing end point in each zone of the wafer can be determined
according to the above-described method. These zones can be defined
as desired in the surface of the wafer. FIG. 26 shows one example.
In this example, five zones C1, C2, C3, C4, and C5 are defined in
the surface of the wafer W. The four film thickness index values
are obtained in each one of the five zones C1 to C5. Therefore, 20
(5.times.4) film thickness index values are monitored during
polishing of the wafer.
[0161] As discussed previously, by providing in advance the
plurality of impedance areas including the reference impedance
area, the variation in the sensor output signal (X, Y) can be
divided, i.e., can be small. Therefore, the film thickness index
value obtained from the sensor output signal in each impedance area
decreases approximately with the polishing time. Because the
plurality of impedance areas can be established in each zone
defined in the wafer surface, film thickness information can be
obtained in each zone in the wafer surface. Therefore, the
polishing end point can be detected in each of the multiple zones
defined in the wafer surface.
[0162] In the above-described embodiment, the film thickness index
value Z (= (X.sup.2+Y.sup.2) is calculated from the output signal X
and Y of the eddy current sensor. In another embodiment, the film
thickness index value may be an angle calculated from the output
signal X and Y of the eddy current sensor. FIG. 27 is a diagram for
illustrating a process of calculating the angle, which is the film
thickness index value, from the output signal X and Y of the eddy
current sensor. As shown in FIG. 27, an angle .theta. is defined as
an angle between a reference line FL extending through a preset
reference point (fixed point) F and a line connecting the reference
point F to the point Tn determined from the output signal (the X
component and the Y component) of the eddy current sensor. The
angle .theta. varies as the point Tn moves, i.e., as the film
thickness decreases. Therefore, this angle .theta. can be used as
an index indicating the film thickness.
[0163] In general, the polishing pad 2 wears down gradually as the
number of wafers polished increases. As shown in FIG. 1, the eddy
current sensor 50 is embedded in the polishing table 1. Therefore,
the distance between the wafer W and the eddy current sensor 50
varies with the wear of the polishing pad 2. It is known that the
above-described angle .theta. varies depending on the film
thickness without depending on the distance between the wafer W and
the eddy current sensor 50 (see the Japanese laid-open patent
publication No. 2005-121616).
[0164] However, as shown in FIG. 28, the angle .theta. may be
changed due to the existence of the underlying interconnect
structure and, as a result, may not reflect the film thickness
accurately. Thus, the angles calculated for the offset impedance
areas r1, r2, r3 are multiplied by preset coefficients which are
such that the angles calculated for the offset impedance areas r1,
r2, r3 become equal to the angle calculated for the reference
impedance area r0, as shown in FIG. 29. These coefficients are
established in advance for the offset impedance areas r1, r2, r3,
respectively. Since the coefficients can vary depending on the
structure of the wafer, the coefficients are determined from
polishing results of wafer having the same structure as the wafer
to be polished. Based on the corrected angles, the polishing end
points can be detected in the impedance areas r0, r1, r2, r3,
respectively.
[0165] Next, still another embodiment of the present invention will
be described.
[0166] As shown in FIG. 19, the path of the eddy current sensor 50
when the polishing table 1 is making N-th revolution differs from
that when the polishing table 1 is making N+1-th revolution. The
arrangement of the interconnect structures 200 sensed by the eddy
current sensor 50 varies as the polishing table 1 rotates. As a
result, the film thickness profile obtained by the eddy current
sensor 50 varies depending on the path of the eddy current sensor
50.
[0167] Typically, the rotational speed of the top ring 10 differs
from the rotational speed of the polishing table 1. Under such a
condition, the path, described on the wafer surface by the eddy
current sensor 50, rotates about the center of the wafer. The path
of the eddy current sensor 50 makes one revolution on the surface
of the wafer while the polishing table 1 makes several revolutions.
The number of revolutions of the polishing table 1 necessary for
the sensor path to make one revolution on the surface of the wafer
is determined by a rotational speed ratio of the top ring 10 to the
polishing table 1.
[0168] FIG. 30 is a view showing the paths of the eddy current
sensor described on the wafer W when the top ring 10 rotates at a
speed of 77 min.sup.-1 and the polishing table 1 rotates at a speed
of 70 min.sup.-1. As shown in FIG. 30, under this condition, the
path of the eddy current sensor 50 rotates by 36 degrees each time
the polishing table 1 makes one revolution. Therefore, the path of
the eddy current sensor 50 makes one revolution each time the
polishing table 1 makes ten revolutions. In this case, the sensor
path when the polishing table 1 is making a first revolution is the
same as the sensor path when the polishing table 1 is making an
eleventh revolution.
[0169] FIG. 31 is a diagram showing a change in the film thickness
profile on the same path of the eddy current sensor 50. The film
thickness profile is a film thickness distribution along the radial
direction of the wafer. When the eddy current sensor 50 measures
the film thickness of the wafer along the same path, salient
portions appear in the film thickness profile at the same positions
due to the existence of the interconnect structures 200. Since the
eddy current sensor 50 scans the same part of the wafer, the
salient portions appear in the same positions. Therefore,
regardless of the existence of the underlying interconnect
structures 200, the film thickness profile in its entirety becomes
smaller gradually with the polishing time. That is, the film
thickness index value decreases with the polishing time in each
film thickness measuring point on the wafer. Therefore, the
polishing end point can be determined based on the change in the
film thickness profile (i.e., the film thickness index value).
[0170] If the purpose of polishing is to remove the metal film from
the wafer, the film thickness profile no longer varies after the
metal film is removed from the wafer. This is because the eddy
current sensor 50 does not react to the metal film any more.
Therefore, a point of time when the film thickness profile stops
changing (i.e., a point of time when the film thickness index value
stops decreasing) can be determined to be the polishing end point.
For example, the polishing end point may be a point of time when a
difference between a current film thickness index value and a
previous film thickness index value in the same location on the
wafer is reduced to a predetermined value.
[0171] The change in the film thickness profile (i.e., the change
in the film thickness index value) can be monitored in each of the
plural zones defined in advance on the surface of the wafer as
shown in FIG. 26. In each zone on the wafer, the film thickness
index value decreases with the polishing time, regardless of the
existence of the underlying interconnect structures. Therefore, the
film thickness index value obtained from the eddy current sensor 50
can be used to detect the polishing end point in each zone on the
wafer.
[0172] When the rotational speed of the top ring 10 differs from
the rotational speed of the polishing table 1, there are a
plurality of paths of the eddy current sensor 50 sweeping across
the surface of the wafer. In the example shown in FIG. 30, there
are ten paths since the sensor path makes one revolution about the
center of the wafer W each time the polishing table 1 makes ten
revolutions. The film thickness profile as shown in FIG. 31 may be
produced for each of the ten paths. In this case also, it is
possible to divide the wafer surface into five zones as in the
example shown in FIG. 26. Therefore, in this case, 50 (10.times.5)
polishing end points can be detected.
[0173] In the above-described example, the interconnect structure
lying under the film affects the output signal of the eddy current
sensor 50. The film to be polished can also cause the appearance of
the salient portion in the film thickness profile if the film
remains locally on the wafer. This example will be described with
reference to FIG. 32. FIG. 32 is a diagram showing the film
remaining locally on the wafer and the film thickness profiles of
the wafer. Typically, the residual film is an annular film, as
shown in FIG. 32. When such residual film exists on the wafer, the
eddy current sensor 50 reacts to the residual film, and the film
thickness index value becomes large. As a result, the salient
portions appear in the film thickness profile as well as the
example shown in FIG. 31.
[0174] The film thickness profile shown in FIG. 32 is different
from the film thickness profile shown in FIG. 31 in that the
salient portions always appear at constant positions regardless of
the path of the eddy current sensor 50. This is because the
residual film is an annular film extending in a circumferential
direction of the wafer. These salient portions of the film
thickness profile, indicating the existence of the residual film,
appear at the same locations every time the polishing table 1 makes
one revolution. The salient portions become smaller gradually with
the polishing time, and disappear when the residual film is
removed.
[0175] FIG. 33 is a diagram showing the film thickness profiles of
the wafer having both the underlying interconnect structures and
the residual film. The salient portions of the film thickness
profile due to the underlying interconnect structures appear in
different positions, so long as the sweep paths of the eddy current
sensor 50 are not the same. In contrast, the salient portions of
the film thickness profile due to the residual film appear in the
same positions each time the polishing table 1 makes one
revolution. Therefore, the monitoring device 55 can judge whether
the salient portion is one due to the residual film or one due to
the underlying interconnect structure from the position of the
salient portion appearing in the film thickness profile. Further,
the monitoring device 55 can determine the polishing end point from
the change in size of the salient portion that is due to the
residual film. For example, a point of time when the size of the
salient portion is reduced to zero or a predetermined threshold
value is determined to be the polishing end point.
[0176] The salient portion caused by the underlying interconnect
structure and the salient portion caused by the residual film can
be distinguished as follows. Each time the film thickness profile
is obtained, the number of salient portions in the film thickness
profile and the positions of the salient portions in the radial
direction of the wafer are obtained. As can be seen from FIG. 33,
every time the polishing table 1 makes one revolution, the salient
portion due to the residual film appears in approximately the same
position (or similar position) continuously, regardless of the
sensor path. In contrast, the salient portion due to the underlying
interconnect structure appears in approximately the same position
(or similar position) with a constant cycle. Therefore, the salient
portion appearing continuously in approximately the same position
can be judged to be the salient portion due to the residual film,
while the salient portion appearing in approximately the same
position with a constant cycle can be judged to be the salient
portion due to the underlying interconnect structure.
[0177] If the polishing table 1 and the top ring 10 rotate at the
same rotational speed, the eddy current sensor 50 sweeps the wafer
in the same path at all times. Therefore, the above-described
method cannot be used to distinguish the salient portions. In such
a case, it is possible to distinguish the salient portions based on
whether or not a peak value of each salient portion decreases with
the polishing time. More specifically, if the peak value of the
salient portion no longer decreases after the polishing time has
reached a certain point of time, such salient portion is judged to
be the salient portion due to the underlying interconnect
structure. In contrast, if the peak value of the salient portion
decreases (even gradually) with the polishing time, such salient
portion is judged to be the salient portion due to the residual
film.
[0178] As discussed above, the number of sweep paths of the eddy
current sensor 50 is determined by the ratio of the rotational
speed of the top ring 10 to the rotational speed of the polishing
table 1. In other words, by adjusting the rotational speed of the
top ring 10 and the rotational speed of the polishing table 1, the
eddy current sensor 50 can sweep the wafer in the same path each
time the polishing table 1 makes desired revolutions. However, the
top ring 10 and the polishing table 1 may not rotate at respective
set speeds. In other words, there may be a difference between a set
rotational speed and an actual rotational speed. Although this
difference is small, the eddy current sensor 50 does not sweep the
wafer in an expected path due to such difference. As a result, the
eddy current sensor 50 cannot obtain the film-thickness profile
with the salient portions appearing in the same position as shown
in FIG. 31.
[0179] Thus, in one embodiment, actual times in which the top ring
10 and the polishing table 1 make one revolution are measured, so
that the rotational speed of the top ring 10 and the rotational
speed of the polishing table 1 are calculated from the measured
actual times. FIG. 34 is a schematic view of a table rotation
detector 210 for measuring a time of one revolution of the
polishing table 1 and a top ring rotation detector 220 for
measuring a time of one revolution of the top ring 10. The table
rotation detector 210 has a sensor target 211 secured to a
circumferential surface of the polishing table 1, a sensor 212
configured to sense the sensor target 211, and a time measuring
device 213 coupled to the sensor 212.
[0180] The sensor target 211 is rotated together with the polishing
table 1, while the sensor 212 is fixed in its position. The sensor
212 is disposed in proximity to the sensor target 211 so as to
sense the sensor target 211 every time the polishing table 1 makes
one revolution. When the sensor 212 senses the sensor target 211,
the sensor 212 sends a trigger signal to the time measuring device
213, which measures a time from when the time measuring device 213
receives the trigger signal until the time measuring device 213
receives the next trigger signal. This measured time is a time
required for the polishing table 1 to make one revolution.
[0181] The top ring rotation detector 220 has a sensor target 221
secured to the top ring 10, a sensor 222 configured to sense the
sensor target 221, and a time measuring device 223 coupled to the
sensor 222. The sensor 222 is secured to the top ring head 12 (see
FIG. 1). Operations of the top ring rotation detector 220 are the
same as those of the above-described table rotation detector 210
and will be omitted.
[0182] FIG. 35 is a time chart illustrating a manner in which the
time measuring devices measure actual times per rotation upon
receiving the trigger signals. Upon receiving the trigger signals,
the time measuring devices 213 and 223 start measuring the time,
and upon receiving the next trigger signals, the time measuring
devices 213 and 223 stop measuring the time and simultaneously
start measuring the time again. Since the trigger signal is
inputted into the time measuring device 213 each time the polishing
table 1 makes one revolution, a time interval between the trigger
signal and the next trigger signal is the actual rotational time of
the polishing table 1. Similarly, since the trigger signal is
inputted into the time measuring device 223 each time the top ring
10 makes one revolution, a time interval between the trigger signal
and the next trigger signal is the actual rotational time of the
top ring 10.
[0183] The rotational speed (min.sup.-1) of the polishing table 1
and the rotational speed (min.sup.-1) of the top ring 10 can be
calculated from the measured actual rotational times, respectively.
In this manner, the actual rotational speed of the polishing table
1 and the actual rotational speed of the top ring 10 are obtained.
Therefore, the rotational speed ratio of the top ring 10 to the
polishing table 1 can be adjusted accurately. The eddy current
sensor 50 can sweep the surface of the wafer in the same path
accurately each time the polishing table 1 makes predetermined
revolutions. Either the top ring rotation detector 220 or the table
rotation detector 210 may be omitted. In this case, since the
actual rotational speed of the top ring 10 or the polishing table 1
cannot be measured, the set rotational speed is used instead of the
actual rotational speed.
[0184] Next, a process of detecting the polishing end point will be
described with reference to FIG. 36. FIG. 36 is a flow chart
showing the process of detecting the polishing end point. After
polishing of the wafer is started, the eddy current sensor 50 scans
the surface of the wafer each time the polishing table 1 makes one
revolution, and outputs the signal X as the resistance component
and the signal Y as the inductive reactance component of the
impedance. The monitoring device 55 receives film thickness data
including the output signal X and Y from the eddy current sensor 50
(step 1).
[0185] The monitoring device 55 receives the measured values of the
rotational time of the polishing table 1 and the rotational time of
the top ring 10 from the time measuring devices 213 and 223 (step
2). The monitoring device 55 calculates the actual rotational speed
of the top ring 10 and the actual rotational speed of the polishing
table 1 as discussed above. Further, the monitoring device 55
calculates the number of revolutions of the polishing table 1
required for the eddy current sensor 50 to describe the same path
from the rotational speed ratio of the top ring 10 to the polishing
table 1 (step 3).
[0186] The monitoring device 55 divides the film thickness data
into a plurality of film thickness data groups in accordance with a
plurality of zones (see FIG. 26) defined in advance on the wafer
surface (step 4), sorts the film thickness data group with respect
to each zone into a plurality of film thickness data in accordance
with the path of the eddy current sensor 50 (step 5), and creates
the film thickness profiles with respect to the sensor paths from
the respective film thickness data.
[0187] A specific example of the above steps 2 to step 5 will be
described with reference to FIG. 37. In this example, the actual
time of the one revolution of the top ring 10 is 2000 milliseconds,
and the actual time of the one revolution of the polishing table 1
is 1000 milliseconds. In this case, the rotational speed of the top
ring 10 is determined to be 30 min.sup.-1, the rotational speed of
the polishing table 1 is determined to be 60 min.sup.-1, and the
eddy current sensor 50 sweeps the surface of the wafer twice each
time the polishing table 1 makes one revolution. Therefore, the
number of paths of the eddy current sensor 50 in this case is two.
Five zones are defined in advance along each path on the surface of
the wafer.
[0188] The film thickness data obtained when the polishing table 1
is making a 2N-1-th revolution are D1.sub.2N-1, D2.sub.2N-1,
D3.sub.2N-1, D4.sub.2N-1, and D5.sub.2N-1, and the film thickness
data obtained when the polishing table 1 is making a 2N-th
revolution are D1.sub.2N, D2.sub.2N, D3.sub.2N, D4.sub.2N, and
D5.sub.2N. N is a natural number. These film thickness data are
divided into five data groups belonging to the respective five
zones on the wafer: a first data group D1.sub.2N-1, D1.sub.2N; a
second data group D2.sub.2N-1, D2.sub.2N; a third data group
D3.sub.2N-1, D3.sub.2N; a fourth data group D4.sub.2N-1, D4.sub.2N;
and a fifth data group D5.sub.2N-1, D5.sub.2N.
[0189] Further, each of the above data groups is sorted according
to the sensor path. Specifically, the first data group is sorted
into the film thickness data D1.sub.2N-1 and the film thickness
data D1.sub.2N, the second data group is sorted into the film
thickness data D2.sub.2N-1 and the film thickness data D2.sub.2N,
the third data group is sorted into the film thickness data
D3.sub.2N-1 and the film thickness data D3.sub.2N, the fourth data
group is sorted into the film thickness data D4.sub.2N-1 and the
film thickness data D4.sub.2N, and the fifth data group is sorted
into the film thickness data D5.sub.2N-1 and the film thickness
data D5.sub.2N. Then, the film thickness profiles are created from
the respective film thickness data.
[0190] Referring back to FIG. 36, the monitoring device 55 compares
a current film thickness obtained from each film thickness profile
with a previous film thickness so as to obtain a change in the film
thickness profile (step 6). More specifically, the monitoring
device 55 judges whether or not a difference between the current
film thickness and the previous film thickness is less than a
preset value, or whether or not a decreasing rate of the film
thickness is less than a preset value. In order to improve the
accuracy of the polishing end point detection, these preset values
are preferably determined based on the magnitude of system noise.
When the difference between the current film thickness and the
previous film thickness decreases below the preset value, or when
the decreasing rate of the film thickness decreases below the
preset value, the monitoring device 55 judges that the polishing
process of the wafer has reached the end point (step 7).
[0191] In order to further improve the accuracy of the polishing
end point detection, it is preferable that the monitoring device 55
judge that the polishing process of the wafer has reached the end
point when the polishing end point in the step 7 is detected in the
plural sensor paths. Alternatively, it is preferable that the
monitoring device 55 judge that the polishing process of the wafer
has reached the end point when the polishing end point in the step
7 is detected several times while the polishing table 1 makes
several revolutions.
[0192] The above-described embodiments can be applied to the top
ring capable of pressing the plurality of zones of the wafer
separately against the polishing pad. FIG. 38 is an example of the
top ring shown in FIG. 1. The top ring 10 has a top ring body 251
coupled to the top ring shaft 11 via a universal joint 250, and a
retainer ring 252 provided on a lower portion of the top ring body
251.
[0193] The top ring 10 further has a flexible membrane 256 to be
brought into contact with the wafer W, and a chucking plate 257
that holds the membrane 256. The membrane 256 and the chucking
plate 257 are disposed below the top ring body 251. Four pressure
chambers (air bags) P1, P2, P3, and P4 are provided between the
membrane 256 and the chucking plate 257. The pressure chambers P1,
P2, P3, and P4 are formed by the membrane 256 and the chucking
plate 257. The central pressure chamber P1 has a circular shape,
and the other pressure chambers P2, P3, and P4 have an annular
shape. These pressure chambers P1, P2, P3, and P4 are in a
concentric arrangement.
[0194] Pressurized fluid (e.g., pressurized air) is supplied into
the pressure chambers P1, P2, P3, and P4 or vacuum is developed in
the pressure chambers P1, P2, P3, and P4 by a pressure regulator
270 through fluid passages 261, 262, 263, and 264, respectively.
The pressures in the pressure chambers P1, P2, P3, and P4 can be
changed independently to thereby independently adjust loads on four
zones of the wafer W: the central portion; an inner intermediate
portion; an outer intermediate portion; and the peripheral portion.
Further, by elevating or lowering the top ring 10 in its entirety,
the retainer ring 252 can press the polishing pad 2 at a
predetermined load.
[0195] A pressure chamber P5 is formed between the chucking plate
257 and the top ring body 251. Pressurized fluid is supplied into
the pressure chamber P5 or vacuum is developed in the pressure
chamber P5 by the pressure regulator 270 through a fluid passage
265. With this operation, the chucking plate 257 and the membrane
256 in their entirety can move up and down. The retainer ring 252
is arranged around the wafer W so as to prevent the wafer W from
coming off the top ring 10 during polishing. The membrane 256 has
an opening in a portion that forms the pressure chamber P3, so that
the wafer W can be held by the top ring 10 via the vacuum suction
by producing vacuum in the pressure chamber P3. Further, the wafer
W can be released from the top ring 10 by supplying nitrogen gas or
clean air into the pressure chamber P3.
[0196] The monitoring device 55 determines target values of
internal pressure of the pressure chambers P1, P2, P3, and P4 based
on the film thickness index values in the zones on the wafer
surface corresponding to the pressure chambers P1, P2, P3, and P4.
The monitoring device 55 sends command signals of the target values
of internal pressure to the pressure regulator 270 so as to control
the pressure regulator 270 such that the internal pressures of the
pressure chambers P1, P2, P3, and P4 accord with the target values.
In this manner, the top ring 10 having the multiple pressure
chambers can press the respective zones on the wafer surface
separately in accordance with the polishing progress, and can
therefore polish the film uniformly.
[0197] The embodiments of the present invention have been descried
above. Nevertheless, the present invention is not limited to the
above-described embodiments and other embodiments can be made
within a technical concept of the present invention.
* * * * *