U.S. patent application number 12/379597 was filed with the patent office on 2009-07-30 for polishing apparatus.
Invention is credited to Makoto FUKUSHIMA, Osamu NABEYA, Tetsuji TOGAWA, Hozumi YASUDA.
Application Number | 20090191797 12/379597 |
Document ID | / |
Family ID | 36319267 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090191797 |
Kind Code |
A1 |
NABEYA; Osamu ; et
al. |
July 30, 2009 |
Polishing apparatus
Abstract
A polishing apparatus (1) has a polishing pad (22), a top ring
(20) for holding a semiconductor wafer (W), a vertical movement
mechanism (24) operable to move the top ring (20) in a vertical
direction, a distance measuring sensor (46) operable to detect a
position of the top ring (20) when a lower surface of the top ring
(20) is brought into contact with the polishing pad (22), and a
controller (47) operable to calculate an optimal position of the
top ring (20) to polish the semiconductor wafer (W) based on the
position detected by the distance measuring sensor (46). The
vertical movement mechanism (24) includes a ball screw mechanism
(30, 32, 38, 42) operable to move the top ring (20) to the optimal
position.
Inventors: |
NABEYA; Osamu; (Tokyo,
JP) ; TOGAWA; Tetsuji; (Tokyo, JP) ;
FUKUSHIMA; Makoto; (Tokyo, JP) ; YASUDA; Hozumi;
(Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
36319267 |
Appl. No.: |
12/379597 |
Filed: |
February 25, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11665648 |
Apr 18, 2007 |
|
|
|
PCT/JP2005/020334 |
Oct 31, 2005 |
|
|
|
12379597 |
|
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Current U.S.
Class: |
451/54 ; 451/288;
451/385 |
Current CPC
Class: |
B24B 37/20 20130101;
B24B 37/32 20130101; B24B 49/18 20130101; B24B 37/30 20130101; B24B
37/10 20130101; B24B 49/183 20130101; B24B 47/22 20130101; B24B
49/00 20130101; B24B 37/005 20130101; B24B 37/042 20130101; B24B
49/16 20130101; B24B 37/105 20130101 |
Class at
Publication: |
451/54 ; 451/385;
451/288 |
International
Class: |
B24B 1/00 20060101
B24B001/00; B24B 41/06 20060101 B24B041/06; B24B 7/22 20060101
B24B007/22 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 2004 |
JP |
2004-318581 |
Mar 18, 2005 |
JP |
2005-079166 |
May 18, 2005 |
JP |
2005-145566 |
Claims
1. A top ring for holding a substrate and pressing the substrate
against a polishing surface of a polishing pad on a polishing
table, said top ring comprising; a top ring body configured to
press the substrate against the polishing surface; and a retainer
ring configured to press the polishing surface, said retainer ring
being provided at a peripheral portion of said top ring body, said
retainer ring comprising an elastic membrane shaped so as to form a
pressure chamber therein, said elastic membrane being expandable
and contractible vertically while pressing the substrate against
the polishing surface, a holder for securing said elastic membrane
to said top ring body, said holder having a passage through which
said pressure chamber communicates with a fluid supply source, and
a ring member to be pressed against the polishing surface by said
pressure chamber supplied with a pressurized fluid therein, said
ring member being vertically movable independently of said top ring
body.
2. The top ring according to claim 1, wherein said elastic membrane
has bent portions.
3. The top ring according to claim 2, wherein said elastic membrane
comprises a rolling diaphragm.
4. The top ring according to claim 1, wherein said elastic membrane
is shaped so as to widen said pressure chamber when an inner
pressure in said pressure chamber is increased.
5. The top ring according to claim 1, further comprising an elastic
membrane attached to a lower surface of said top ring body and
shaped so as to contact substantially an entire upper surface of
the substrate.
6. The top ring according to claim 5, wherein a central chamber, a
ripple chamber, an outer chamber, and an edge chamber are formed by
said elastic membrane attached to the lower surface of said top
ring body.
7. The top ring according to claim 1, further comprising a retainer
ring wear detector configured to measure an amount of wear of said
retainer ring.
8. An apparatus for polishing a substrate, comprising: a polishing
table for supporting a polishing pad thereon; and a top ring
according to claim 1.
9. A method of polishing a substrate by providing a sliding contact
between the substrate and a polishing surface of a polishing pad on
a polishing table, said method comprising; rotating the polishing
table together with the polishing pad; pressing the substrate
against the polishing surface by a top ring while pressing a
retainer ring against the polishing surface by a pressure chamber
formed by an elastic membrane, said elastic membrane being
expandable and contractible vertically while pressing the substrate
against the polishing surface; during said pressing of the
substrate, rotating the top ring together with the substrate; and
adjusting a pressing force of the retainer ring against the
polishing surface by adjusting pressure of a pressurized fluid to
be supplied to the pressure chamber,
10. The method according to claim 9, wherein said elastic membrane
has bent portions.
11. The method according to claim 9, wherein said pressing of the
substrate against the polishing surface comprises pressing the
substrate against the polishing surface via a central chamber, a
ripple chamber, an outer chamber, and an edge chamber.
12. A polishing apparatus comprising: a polishing surface; and a
top ring for holding a substrate, said top ring having a retainer
ring for holding a peripheral portion of the substrate, wherein
said retainer ring includes an elastic membrane having a pressure
chamber formed therein, said elastic membrane being expandable and
contractible vertically, a passage for supplying a fluid to the
pressure chamber to vertically expand or contract said elastic
membrane, and a ring member vertically movable according to a
vertical movement of said elastic membrane, said ring member being
brought into contact with said polishing surface.
13. The polishing apparatus according to claim 12, wherein said
retainer ring further includes a cylinder housing said elastic
membrane therein, a holder configured to hold said elastic membrane
on said cylinder, and a piston vertically movable within said
cylinder, said piston being connected to said elastic membrane.
Description
[0001] This application is a divisional application of application
Ser. No. 11/665,648, which is the National Stage of International
Application No. PCT/JP2005/020334, filed Oct. 31, 2005.
TECHNICAL FIELD
[0002] The present invention relates to a polishing apparatus, and
more particularly to a polishing apparatus for polishing a
substrate such as a semiconductor wafer to a flat mirror
finish.
BACKGROUND ART
[0003] In recent years, semiconductor devices have become more
integrated, and structures of semiconductor elements have become
more complicated. Further, the number of layers in multilayer
interconnections used for a logical system has been increased.
Accordingly, irregularities on a surface of a semiconductor device
are increased, so that step heights on the surface of the
semiconductor device tend to be large. This is because, in a
manufacturing process of a semiconductor device, a thin film is
formed on a semiconductor device, then micromachining processes,
such as patterning or forming holes, are performed on the
semiconductor device, and these processes are repeated to form
subsequent thin films on the semiconductor device.
[0004] When the number of irregularities is increased on a surface
of a semiconductor device, the following problems arise. When a
thin film is formed on a semiconductor device, the thickness of the
film formed at portions having a step becomes relatively small.
Further, an open circuit may be caused by disconnection, or a short
circuit may be caused by insufficient insulation between
interconnection layers. As a result, good products cannot be
obtained, and the yield tends to be lowered. Further, even if a
semiconductor device initially works normally, reliability of the
semiconductor device is lowered after a long-term use. At the time
of exposure in a lithography process, if the irradiation surface
has irregularities, then a lens unit in an exposure system is
locally unfocused. Therefore, if the irregularities on the surface
of the semiconductor device are increased, then it becomes
problematically difficult to form a fine pattern itself on the
semiconductor device.
[0005] Further, as semiconductor devices have become more highly
integrated in recent years, circuit interconnections have become
finer and distances between those circuit interconnections have
become smaller. In the case of photolithography, which can form
interconnections that are at most 0.5 .mu.m wide, it is required
that surfaces on which pattern images are to be focused by a
stepper should be as flat as possible because the depth of focus of
an optical system is relatively small.
[0006] Thus, in a manufacturing process of a semiconductor device,
it increasingly becomes important to planarize a surface of the
semiconductor device. One of the most important planarizing
technologies is chemical mechanical polishing (CMP). Thus, there
has been employed a chemical mechanical polishing apparatus for
planarizing a surface of a semiconductor wafer. In a chemical
mechanical polishing apparatus, while a polishing liquid containing
abrasive particles such as silica (SiO.sub.2) therein is supplied
onto a polishing surface such as a polishing pad, a substrate such
as a semiconductor wafer is brought into sliding contact with the
polishing surface, so that the substrate is polished.
[0007] This type of polishing apparatus includes a polishing table
having a polishing surface formed by a polishing pad, and a
substrate holding device, which is referred to as a top ring
(substrate holding device), for holding a substrate such as a
semiconductor wafer. When a semiconductor wafer is polished with
such a polishing apparatus, the semiconductor wafer is held and
pressed against the polishing table under a predetermined pressure
by the top ring. At that time, the polishing table and the top ring
are moved relative to each other to bring the semiconductor wafer
into sliding contact with the polishing surface, so that the
surface of the semiconductor wafer is polished to a flat mirror
finish.
[0008] In such a polishing apparatus, the polishing pad is so
elastic that pressing forces applied to a peripheral edge portion
of the semiconductor wafer tend to be non-uniform. Accordingly, the
semiconductor wafer may excessively be polished at the peripheral
edge portion to thus cause edge rounding. In order to prevent such
edge rounding, there has been employed a top ring having a retainer
ring for holding a side edge portion of a semiconductor wafer and
pressing a polishing surface located outside of a peripheral edge
portion of the semiconductor wafer.
[0009] Further, when a polishing apparatus employs a polishing pad
made of resin, the polishing pad is worn out by dressing and
polishing. In this case, in order to prevent surface pressure
distribution from varying on a surface of a semiconductor wafer
held by a top ring, a constant distance should be maintained
between a surface of the top ring to hold the semiconductor wafer
and the polishing pad during polishing. When a retainer ring, which
holds a peripheral edge portion of a semiconductor wafer, is
provided, the retainer ring may be worn out according to progress
of polishing. When the retainer ring is thus worn out, a constant
distance should also be maintained between a surface of the top
ring to hold the semiconductor wafer and the polishing pad during
polishing.
[0010] In order to determine whether a polishing process is
performed normally in the aforementioned polishing apparatus, it is
necessary to monitor a pressing force to press a semiconductor
wafer, and concentration and flow rate of a polishing liquid.
However, for example, various devices such as a component analyzer
and a particle size distribution measuring device are required to
monitor a polishing liquid. Accordingly, cost of the polishing
apparatus is increased. Further, a polishing profile may also be
changed by wear of the polishing pad and the retainer ring. Thus,
monitoring only a pressing force and a polishing liquid is
insufficient to guarantee that a polishing process is normally
performed.
[0011] Further, a conventional retainer ring is configured to press
a polishing surface uniformly along its overall length in a
circumferential direction of the retainer ring. However, as
described above, since a polishing pad used to provide a polishing
surface is elastic, the polishing pad is elastically deformed so as
to produce extremely increased resistance at an outermost portion
of the retainer ring which is located upstream along a direction of
rotation of the polishing table. Accordingly, the retainer ring is
pressed downstream along the direction of rotation of the polishing
table so as to cause inclination of the retainer ring. In a
conventional polishing apparatus, when the retainer ring is thus
inclined, a pressure under which the retainer ring presses the
polishing surface is increased to prevent the semiconductor wafer
from being separated from the top ring. Further, non-uniformity of
the polishing profile which is caused by the inclination of the
retainer ring is improved with equalization by rotation of the
semiconductor wafer.
[0012] However, the conventional retainer ring has difficulty in
enhancing the controllability of the temperature of the polishing
pad and the polishing profile Accordingly, in order to further
enhance the controllability of the temperature of the polishing pad
and the polishing profile, it is required to control a pressure
under which the retainer ring presses the polishing surface along a
circumferential direction of the retainer ring.
DISCLOSURE OF INVENTION
[0013] The present invention has been made in view of the above
drawbacks. It is, therefore, a first object of the present
invention to provide a polishing apparatus which can polish a
substrate while a constant distance can be maintained between the
substrate and a polishing surface even if the polishing surface or
a retainer ring for holding a peripheral portion of the substrate
is worn out.
[0014] A second object of the present invention is to provide a
polishing apparatus in which an elastic membrane attached to a top
ring can readily be replaced.
[0015] A third object of the present invention is to provide a
polishing apparatus which can readily and inexpensively determine
whether polishing is normally conducted.
[0016] A fourth object of the present invention is to provide a
polishing apparatus capable of controlling a pressure under which a
retainer ring presses a polishing surface along a circumferential
direction of the retainer ring.
[0017] According to a first aspect of the present invention, there
is provided a polishing apparatus which can polish a substrate
while a constant distance can be maintained between the substrate
and a polishing surface even if the polishing surface or a retainer
ring for holding a peripheral portion of the substrate is worn out.
The polishing apparatus has a polishing surface, a top ring for
holding a substrate, a vertical movement mechanism operable to move
the top ring in a vertical direction, a position detector operable
to detect a position of the top ring when a lower surface of the
top ring or a lower surface of the substrate held by the top ring
is brought into contact with the polishing surface, and a position
calculator operable to calculate an optimal position of the top
ring to polish the substrate based on the position detected by the
position detector. The vertical movement mechanism includes a
movement mechanism operable to move the top ring to the optimal
position calculated by the position calculator.
[0018] With the above arrangement, even if the polishing surface is
worn out due to polishing, a constant distance can be maintained
between the top ring and the polishing surface during polishing.
Accordingly, a surface pressure of the substrate held by the top
ring can be made uniform. Further, with the movement mechanism, the
top ring can be moved accurately to an optimal position calculated
by a pad search process which will be described later. Accordingly,
a substrate can be polished in a state such that a constant
distance is maintained between the top ring and the polishing
surface.
[0019] The position detector may include a distance measuring
sensor for detecting the position of the top ring. In this case,
the polishing apparatus may further comprise a dresser for dressing
the polishing surface and a distance measuring sensor for detecting
a position of the dresser when the dresser is brought into contact
with the polishing surface to obtain a variation of a height of the
polishing surface. The vertical movement mechanism may be operable
to move the top ring so that the position of the top ring follows
the variation of the height of the polishing surface. The distance
measuring sensor may be provided on a dresser shaft to measure the
amount of wear of the polishing surface (polishing pad) during
dressing for each polishing process.
[0020] It is desirable that the vertical movement mechanism
includes a ball screw for moving the top ring in the vertical
direction and a motor for operating the ball screw. In this case,
it is also desirable that the motor comprises an AC servomotor.
With an AC servomotor, the number of revolutions of the motor can
be counted by an encoder to calculate a distance by which the top
ring is vertically moved. Accordingly, the position of the top ring
can be obtained based on the calculated distance.
[0021] It is desirable that the motor has a maximum current such
that a torque of the motor during polishing is larger than a torque
of the motor when the lower surface of the top ring or the lower
surface of the substrate held by the top ring is brought into
contact with the polishing surface. The maximum current may be
reduced before the lower surface of the top ring or the lower
surface of the substrate held by the top ring is brought into
contact with the polishing surface.
[0022] The position detector may include a current detector
operable to detect a current of the motor and determine when the
lower surface of the top ring or the lower surface of the substrate
held by the top ring is brought into contact with the polishing
surface based on a variation of the current of the motor. A dummy
wafer may be held as the substrate by the top ring when the
position of the top ring is detected by the position detector.
[0023] According to a second aspect of the present invention, there
is provided a polishing apparatus which can polish a substrate
while a constant distance can be maintained between the substrate
and a polishing surface even if the polishing surface or a retainer
ring for holding a peripheral portion of the substrate is worn out.
The polishing apparatus has a polishing surface, a top ring for
holding a substrate, a polishing liquid supply nozzle for supplying
a polishing liquid to the polishing surface, an ejection nozzle for
ejecting a gas toward the polishing surface to remove the polishing
liquid from a measurement portion of the polishing surface, and a
distance measuring sensor for detecting a position of the polishing
surface at the measurement portion.
[0024] With the above arrangement, a polishing liquid can be
removed from the polishing surface at a measurement portion by
ejection of a gas. Laser or ultrasonic wave can be applied to the
polishing surface at the measurement portion from the distance
measuring sensor. Accordingly, the laser or ultrasonic wave is not
reflected on the polishing liquid or water on the polishing
surface. Thus, it is possible to accurately detect a distance to
the polishing surface. As a result, a constant distance can be
maintained between the substrate and the polishing surface based on
the measured distance to the surface of the polishing surface.
[0025] According to a third aspect of the present invention, there
is provided a polishing apparatus which can polish a substrate
while a constant distance can be maintained between the substrate
and a polishing surface even if the polishing surface or a retainer
ring for holding a peripheral portion of the substrate is worn out.
The polishing apparatus has a polishing surface and a top ring for
holding a substrate. The top ring has a retainer ring for holding a
peripheral portion of the substrate. The retainer ring includes a
rolling diaphragm having a pressure chamber formed therein, a
passage for supplying a fluid to the pressure chamber to vertically
expand or contract the rolling diaphragm, and a ring member
vertically movable according to the rolling diaphragm. The ring
member is brought into contact with the polishing surface.
[0026] With the above arrangement, even if the ring member of the
retainer ring is worn out, only the retainer ring can be lowered.
Accordingly, a constant distance can be maintained between the top
ring and the polishing surface even if the ring member of the
retainer ring is worn out. Further, since the deformable rolling
diaphragm is connected to the ring member, which is brought into
contact with the polishing surface, no bending moment is produced
by offset loads. Accordingly, surface pressures by the retainer
ring can be made uniform, and the retainer ring becomes more likely
to follow the polishing surface.
[0027] The retainer ring may further include a cylinder housing the
rolling diaphragm therein, a holder configured to hold the rolling
diaphragm on the cylinder, and a piston vertically movable within
the cylinder. The piston is connected to the rolling diaphragm.
[0028] According to a fourth aspect of the present invention, there
is provided a polishing apparatus in which an elastic membrane
attached to a top ring can readily be replaced. The polishing
apparatus has a polishing surface, a top ring for holding a
substrate, and a top ring shaft movable in a vertical direction.
The top ring is connected to the top ring shaft. The top ring
includes an upper member connected to the top ring shaft, an
elastic membrane which is brought into contact with at least a
portion of the substrate, a lower member to which the elastic
membrane is attached, and a fastening member configured to
detachably fix the lower member to the upper member.
[0029] In a conventional top ring, it is necessary to remove the
entire top ring from a top ring shaft when an elastic membrane
attached to the top ring is replaced. Thus, troublesome processes
are required to replace the elastic membrane. According to the
present invention, since the lower member to which the elastic
membrane is attached can readily be removed from the upper member
by detaching the fastening member, it is not necessary to remove
the entire top ring from the top ring shaft to replace the elastic
membrane.
[0030] In this case, the top ring may further include a holder
configured to hold the elastic membrane on the lower member. The
holder has a hook. The top ring may include a stopper having an
engagement portion to engage with the hook of the holder. The
stopper may be cylindrical. It is desirable that the engagement
portion is formed partially in a circumferential direction of the
stopper. It is also desirable that the engagement portion is
gradually thickened along the circumferential direction of the
stopper. With this arrangement, the elastic membrane can readily be
removed from the lower member. Thus, replacement of the elastic
membrane is facilitated.
[0031] The top ring may further include a retainer ring for holding
a peripheral portion of the substrate and a seal member configured
to prevent a polishing liquid from being introduced between the
retainer ring and the upper member and/or the lower member.
[0032] According to the present invention, a substrate can be
polished while a constant distance can be maintained between the
substrate and a polishing surface even if the polishing surface or
a retainer ring for holding a peripheral portion of the substrate
is worn out. Further, an elastic membrane attached to a top ring
can readily be replaced.
[0033] According to a fifth aspect of the present invention, there
is provided a polishing apparatus which can readily and
inexpensively determine whether polishing is normally conducted.
The polishing apparatus has a polishing pad having a polishing
surface, a top ring body configured to press a substrate against
the polishing surface, and a retainer ring configured to press the
polishing surface. The retainer ring is provided at a peripheral
portion of the top ring body. The polishing apparatus also has a
dresser for dressing the polishing surface, a wear detector for
detecting wear of at least one component in the polishing
apparatus, and an arithmetical unit operable to calculate an amount
of wear of the least one component based on a signal from the wear
detector and determine whether polishing is normally conducted
based on the amount of wear for a polishing process or a plurality
of sets of polishing processes.
[0034] According to a sixth aspect of the present invention, there
is provided a polishing apparatus having a polishing pad having a
polishing surface, a top ring body configured to press a substrate
against the polishing surface, and a retainer ring configured to
press the polishing surface. The retainer ring is provided at a
peripheral portion of the top ring body. The retainer ring includes
a rolling diaphragm having a pressure chamber formed therein, a
passage for supplying a fluid to the pressure chamber to vertically
expand or contract the rolling diaphragm, and a ring member
vertically movable according to the rolling diaphragm. The ring
member is brought into contact with the polishing surface. The
retainer ring also includes a cylinder holding the rolling
diaphragm therein and a connection sheet capable of being expanded
and contracted in a vertical direction. The connection sheet
connects the cylinder and the ring member so as to cover a gap
between the cylinder and the ring member.
[0035] According to a seventh aspect of the present invention,
there is provided a polishing apparatus having a polishing pad
having a polishing surface, a top ring body configured to press a
substrate against the polishing surface, and a retainer ring
configured to press the polishing surface. The retainer ring is
provided at a peripheral portion of the top ring body. The
polishing apparatus also has an annular sheet member fixed to the
top ring body, a plurality of slide rings attached to the annular
sheet member, and a plurality of drive pins fixed to the retainer
ring. The drive pins are inserted into the slide rings so as to be
slidable within the slide rings.
[0036] According to an eighth aspect of the present invention,
there is provided a polishing apparatus having a polishing pad
having a polishing surface, a top ring body configured to press a
substrate against the polishing surface, and a retainer ring
configured to press the polishing surface. The retainer ring is
provided at a peripheral portion of the top ring body. The
polishing apparatus also has an elastic membrane provided at a
lower portion of the top ring body. The elastic membrane is brought
into contact with at least a portion of the substrate. The
polishing apparatus includes a seal member covering a gap between
the elastic membrane and the retainer ring.
[0037] According to a ninth aspect of the present invention, there
is provided a polishing apparatus having a polishing pad having a
polishing surface, a top ring body configured to press a substrate
against the polishing surface, and a retainer ring configured to
press the polishing surface. The retainer ring is provided at a
peripheral portion of the top ring body. The polishing apparatus
also has a pusher operable to receive the substrate from and
deliver the substrate to the top ring body and a retainer ring wear
detector for detecting wear of the retainer ring. The retainer ring
wear detector is provided in the pusher.
[0038] According to the present invention, it is possible to
determine whether polishing is normally conducted based on the
amount of wear of a component. Accordingly, a polishing process can
be monitored without any special devices. Thus, based on the
determination of the arithmetical unit, it is possible to guarantee
that polishing is normally conducted.
[0039] Further, the wear detector provided in the pusher can
directly measure the amount of wear of the retainer ring to thereby
obtain an accurate amount of wear. Accordingly, it is possible to
more accurately determine whether polishing is normally
conducted.
[0040] According to a tenth aspect of the present invention, there
is provided a polishing apparatus capable of controlling a pressure
under which a retainer ring presses a polishing surface along a
circumferential direction of the retainer ring. The polishing
apparatus has a polishing surface, a top ring body configured to
press a substrate against the polishing surface, and a retainer
ring configured to press the polishing surface. The retainer ring
is provided at a peripheral portion of the top ring body. The
retainer ring includes a pressure control mechanism operable to
control a pressure under which the retainer ring presses the
polishing surface so as to produce a non-uniform pressure
distribution along a circumferential direction of the retainer
ring.
[0041] The pressure control mechanism may include a ring member
which is brought into contact with the polishing surface, a
plurality of pressure chambers configured to press the ring member
against the polishing surface, and a plurality of passages for
supplying fluids independently controlled in pressure to the
plurality of pressure chambers. Alternatively, the pressure control
mechanism may include a lower ring member having an upper tapered
surface and a lower surface which is brought into contact with the
polishing surface and an upper ring member having a lower tapered
surface which is brought into contact with the upper tapered
surface of the lower ring member to convert a radial force applied
to the lower ring member into a downward force.
[0042] Further, the pressure control mechanism may include a lower
ring member having an upper tapered surface and a lower surface
which is brought into contact with the polishing surface, an upper
ring member having a lower tapered surface which is brought into
contact with the upper tapered surface of the lower ring member to
convert a radial force applied to the lower ring member into a
downward force, at least one pressure chamber configured to press
the upper ring member toward the polishing surface, at least one
passage for supplying a fluid controlled in pressure to the at
least one pressure chambers, and a restriction member which is
brought into contact with the upper ring member so as to restrict
vertical movement of the upper ring member.
[0043] The pressure control mechanism may be operable to control
the pressure under which the retainer ring presses the polishing
surface according to rotation of the top ring body so as to produce
a constant non-uniform pressure distribution in a static system.
The pressure control mechanism may be operable to control the
pressure under which the retainer ring presses the polishing
surface so that a portion located downstream in a rotation
direction of the polishing surface is pressed under a pressure
higher than a portion located upstream in the rotation direction of
the polishing surface.
[0044] According to the present invention, the pressure control
mechanism can produce a non-uniform pressure distribution along a
circumferential direction of the retainer ring. For example, the
pressure under which the retainer ring presses the polishing
surface can be controlled so that a portion located downstream in a
rotation direction of the polishing surface is pressed under a
pressure higher than a portion located upstream in the rotation
direction of the polishing surface.
[0045] The above and other objects, features, and advantages of the
present invention will be apparent from the following description
when taken in conjunction with the accompanying drawings which
illustrate preferred embodiments of the present invention by way of
example.
BRIEF DESCRIPTION OF DRAWINGS
[0046] FIG. 1 is a schematic view showing a polishing apparatus
according to a first embodiment of the present invention;
[0047] FIG. 2 is a schematic view showing the polishing apparatus
shown in FIG. 1 when a pad search process is performed;
[0048] FIG. 3 is a schematic view showing the polishing apparatus
shown in FIG. 1 when a semiconductor wafer is polished;
[0049] FIG. 4 is a schematic view showing a polishing apparatus
according to a second embodiment of the present invention;
[0050] FIG. 5 is a schematic view showing the polishing apparatus
shown in FIG. 4 when a pad search process is performed;
[0051] FIG. 6 is a schematic view showing a polishing apparatus
according to a third embodiment of the present invention;
[0052] FIG. 7 is a schematic view showing a portion of a polishing
apparatus according to a fourth embodiment of the present
invention;
[0053] FIG. 8 is a vertical cross-sectional view showing an example
of a top ring which is suitably used in the polishing apparatus in
the first through fourth embodiments of the present invention;
[0054] FIGS. 9 and 10 are vertical cross-sectional views of the top
ring shown in FIG. 8;
[0055] FIG. 11 is a plan view showing a lower member of the top
ring shown in FIG. 8;
[0056] FIG. 12A is a plan view showing a stopper in the top ring
shown in FIG. 8;
[0057] FIG. 12B is a vertical cross-sectional view of the stopper
shown in FIG. 12A;
[0058] FIG. 12C is a bottom view of the stopper shown in FIG.
12A;
[0059] FIG. 13 is an enlarged cross-sectional view showing a
variation of the top ring shown in FIG. 8;
[0060] FIG. 14 is a schematic view showing a polishing apparatus
according to a fifth embodiment of the present invention;
[0061] FIGS. 15 through 18 are cross-sectional views of a top ring
which is suitably used in the polishing apparatus shown in FIG.
14;
[0062] FIG. 19 is a plan view showing a lower member of the top
ring shown in FIGS. 15 through 18;
[0063] FIG. 20 is an enlarged view of a retainer ring shown in FIG.
15;
[0064] FIG. 21 is a plan view of a clamp in the retainer ring shown
in FIG. 20;
[0065] FIG. 22A is a perspective view showing another example of a
clamp in the retainer ring shown in FIG. 20;
[0066] FIG. 22B is a plan view showing a connection sheet used for
the clamp shown in FIG. 22A;
[0067] FIG. 23 is a partial cross-sectional view showing another
example of a top ring which is suitably used in the polishing
apparatus shown in FIG. 14;
[0068] FIG. 24 is a plan view of a lower member of the top ring
shown in FIG. 23;
[0069] FIG. 25 is a cross-sectional view showing a pusher having a
retainer ring wear detector;
[0070] FIGS. 26 through 29 are cross-sectional views explanatory of
operation of the pusher shown in FIG. 25;
[0071] FIG. 30 is a schematic view showing a top ring in a
polishing apparatus according to a sixth embodiment of the present
invention;
[0072] FIG. 31 is an enlarged view of a retainer ring in the top
ring shown in FIG. 30; and
[0073] FIG. 32 is a partial enlarged view showing a top ring in a
polishing apparatus according to a seventh embodiment of the
present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0074] Embodiments of a polishing apparatus according to the
present invention will be described below with reference to FIGS. 1
through 32. Like or corresponding parts are denoted by like or
corresponding reference numerals throughout drawings and will not
be described below repetitively.
[0075] FIG. 1 is a schematic view showing a polishing apparatus 10
according to a first embodiment of the present invention. As shown
in FIG. 1, the polishing apparatus 10 has a polishing table 12, a
top ring head 16 connected to an upper end of a support shaft 14, a
top ring shaft 18 mounted at a free end of the top ring head 16,
and a top ring 20 coupled to a lower end of the top ring shaft 18.
In the illustrated example, the top ring 20 is substantially in the
form of a circular plate.
[0076] The polishing table 12 is coupled via a table shaft 12a to a
motor (not shown) disposed below the polishing table 12. Thus, the
polishing table 12 is rotatable about the table shaft 12a. As shown
in FIG. 1, a polishing pad 22 is attached to an upper surface of
the polishing table 12. An upper surface 22a of the polishing pad
22 forms a polishing surface to polish a semiconductor wafer W.
[0077] Various kinds of polishing pads are available on the market.
For example, some of these are SUBA800, IC-1000, and
IC-1000/SUBA400 (two-layer cloth) manufactured by Rodel Inc., and
Surfin xxx-5 and Surfin 000 manufactured by Fujimi Inc. SUBA800,
Surfin xxx-5, and Surfin 000 are non-woven fabrics bonded by
urethane resin, and IC-1000 is made of rigid foam polyurethane
(single layer). Foam polyurethane is porous and has a large number
of fine recesses or holes formed in its surface.
[0078] The top ring shaft 18 is rotated by actuation of a motor
(not shown). By rotation of the top ring shaft 18, the top ring 20
is rotated about the top ring shaft 18. Further, the top ring shaft
18 is vertically moved by a vertical movement mechanism 24. By
vertical movement of the top ring shaft 18, the top ring 20 is
vertically moved with respect to the top ring head 16. A rotary
joint 25 is mounted on an upper end of the top ring shaft 18.
[0079] The top ring 20 is configured to hold a substrate such as a
semiconductor wafer W on its lower surface. The top ring head 16 is
pivotable (swingable) about the support shaft 14. Thus, the top
ring 20, which holds a semiconductor wafer W on its lower surface,
is moved between a position at which the top ring 20 receives the
semiconductor wafer W and a position above the polishing table 12
by pivotal movement of the top ring head 16. The top ring 20 is
lowered to press the semiconductor wafer W against a surface
(polishing surface) 22a of the polishing pad 10. At that time,
while the top ring 20 and the polishing table 12 are respectively
rotated, a polishing liquid is supplied onto the polishing pad 22
from a polishing liquid supply nozzle (not shown), which is
provided above the polishing table 12. The semiconductor wafer W is
brought into sliding contact with the polishing surface 22a on the
polishing pad 10. Thus, a surface of the semiconductor wafer W is
polished.
[0080] The vertical movement mechanism 24, which vertically moves
the top ring shaft 18 and the top ring 20, has a first frame 28
supporting the top ring shaft 18 in a manner such that the top ring
shaft 18 is rotatable via a bearing 26, a ball screw 32 threaded
into a nut 30 mounted on the first frame 28, a second frame 36
supporting the ball screw 32 in a manner such that the ball screw
32 is rotatable via a bearing 34, an AC servomotor 38 provided on
the second frame 36, and an air cylinder 40 supporting the second
frame 36.
[0081] The ball screw 32 is coupled via a belt 42 to the servomotor
38 disposed on the second frame 36. The top ring shaft 18 is
configured to be vertically movable together with the first frame
28. Accordingly, when the servomotor 38 is driven, the first frame
28 is vertically moved via the ball screw 32 with respect to the
second frame 36. As a result, the top ring shaft 18 and the top
ring 20 are vertically moved with respect to the second frame
36.
[0082] The air cylinder 40 is disposed on an upper surface of the
top ring head 16. The air cylinder 40 has a vertically movable rod
40a to support the second frame 36 on its upper end. The ball screw
32 is configured to be vertically movable together with the second
frame 36. Accordingly, when the rod 40a of the air cylinder 40 is
vertically moved, the second frame 36 is vertically moved with
respect to the top ring head 16. Further, the ball screw 32 and the
first frame 28 are vertically moved with respect to the top ring
head 16.
[0083] The top ring head 16 has a guide shaft 44 extending upward.
The guide shaft 44 is inserted into the second frame 36. When the
second frame 36 is vertically moved, the second frame 36 is guided
by the guide shaft 44. The guide shaft 44 has a stopper 44a at an
upper end thereof. Thus, upward movement of the second frame 36 is
restricted when an upper surface of the second frame 36 is brought
into contact with the stopper 44a.
[0084] As shown in FIG. 1, the polishing apparatus 10 has a
distance measuring sensor 46 serving as a position detector for
detecting a distance from the top ring head 16 to a lower surface
of the first frame 28, i.e., a position of the first frame 28. The
distance measuring sensor 46 detects the position of the first
frame 28 so as to detect the position of the top ring 20. Further,
the polishing apparatus 10 has a controller 47 operable to control
various devices, including the distance measuring sensor 46, the
servomotor 38, and the air cylinder 40, in the polishing apparatus
10. The controller 47 includes a storage device and a
computer-readable medium having a program recorded therein for
controlling the polishing apparatus 10.
[0085] When semiconductor wafers W are polished with the polishing
apparatus 10 thus constructed, the polishing pad 22 is worn out by
dressing and polishing. Accordingly, the thickness of the polishing
pad 22 is continuously varied. In this case, in order to prevent
surface pressure distribution from varying on a surface of a
semiconductor wafer W according to progress of the polishing
process, a constant distance should be maintained between the top
ring 20 and the surface of the polishing pad 22 during polishing.
Thus, in order to maintain a constant distance between the top ring
20 and the surface of the polishing pad 22, it is necessary to
detect the height (or position) of the surface of the polishing pad
22 and adjust a position to which the top ring 20 is lowered for
each lot of semiconductor wafers (e.g., 25 semiconductor wafers).
Such a process to detect the height (or position) of the surface of
the polishing pad 22 is referred to as a pad search process.
[0086] In the present embodiment, when the lower surface of the top
ring 20 is brought into contact with the polishing surface 22a of
the polishing pad 22, the position of the top ring 20 is stored in
the storage device. The height of the polishing surface 22a of the
polishing pad 22 is detected based on the stored position of the
top ring 20. Specifically, during a pad search process, as shown in
FIG. 2, the rod 40a of the air cylinder 40 is lowered so that the
second frame 36, the ball screw 32, the first frame 28, the top
ring shaft 18, and the top ring 20 are lowered due to gravity.
Thus, the lowering of the top ring 20 is stopped when the lower
surface of the top ring 20 is brought into contact with the surface
22a of the polishing pad 22. At that time, the distance measuring
sensor 46 detects the position of the first frame 28 to obtain the
height of the surface 22a of the polishing pad 22 based on the
detected position of the first frame 28. The controller 47 operates
an arithmetical unit (position calculator) therein so as to
calculate an optimal position of the top ring 20 to polish a
semiconductor wafer W based on the height of the surface 22a of the
polishing pad 22. The calculated optimal position of the top ring
20 is stored in the storage device.
[0087] When a semiconductor wafer W is to be polished, the
servomotor 38 is driven in a state shown in FIG. 1. Thus, the first
frame 28 and the top ring 20 which holds the semiconductor wafer W
are lowered as shown in FIG. 3. At that time, the controller 47
controls the servomotor 38 and stops the servomotor 38 when the top
ring 20 reaches the calculated optimal position. The semiconductor
wafer W held on the lower surface of the top ring 20 is pressed
against the polishing pad 22 and polished at the calculated optimal
position. In this case, the first frame 28 and the top ring 20 may
be lowered while the position of the first frame 28 is detected and
confirmed by the distance measuring sensor 46. The distance
measuring sensor 46 may comprise any type of sensors including a
laser sensor, an ultrasonic sensor, an eddy-current sensor, and a
linear scale sensor.
[0088] As described above, with a ball screw mechanism having the
servomotor 38 and the ball screw 32 in the present embodiment, the
top ring 20 can be moved accurately to an optimal position
calculated by a pad search process. Accordingly, a semiconductor
wafer W can be polished in a state such that a constant distance is
maintained between the top ring 20 and the polishing pad 22.
[0089] FIG. 4 is a schematic view showing a polishing apparatus 110
according to a second embodiment of the present invention. As shown
in FIG. 4, in the polishing apparatus 110 of the present
embodiment, the top ring shaft 18 is vertically movable with
respect to the top ring head 16 by a vertical movement mechanism
124. The vertical movement mechanism 124 has a first frame 128
supporting the top ring shaft 18 in a manner such that the top ring
shaft 18 is rotatable via a bearing 126, a ball screw 132 threaded
into a nut 130 mounted on the first frame 128, a second frame 136
fixed on the top ring head 16, and an AC servomotor 138 provided on
the second frame 136 for rotating the ball screw 132. The
controller 47 includes a current detector for detecting a current
flowing through the servomotor 138. The controller 47 includes a
storage device and a computer-readable medium having a program
recorded therein for controlling the polishing apparatus 110.
[0090] The top ring shaft 18 is configured to be vertically movable
together with the first frame 128. Accordingly, when the servomotor
138 is driven, the first frame 128 is vertically moved via the ball
screw 132 with respect to the top ring head 16. As a result, the
top ring shaft 18 and the top ring 20 are vertically moved with
respect to the top ring head 16.
[0091] In the present embodiment, as with the first embodiment, a
pad search process is performed by detecting the position of the
top ring 20 when the lower surface of the top ring 20 is brought
into contact with the polishing surface 22a of the polishing pad
22. The pad search process in the present embodiment is performed
without a distance measuring sensor. Specifically, during a pad
search process, the servomotor 138 is driven to lower the top ring
20 while the number of revolutions is counted by an encoder. As
shown in FIG. 5, when the lower surface of the top ring 20 is
brought into contact with the surface 22a of the polishing pad 22,
loads on the servomotor 138 are increased. Accordingly, a current
flowing through the servomotor 138 is also increased. The current
detector in the controller 47 detects a current flowing through the
servomotor 138 and determines that the lower surface of the top
ring 20 is brought into contact with the surface 22a of the
polishing pad 22 when a large current is detected. After it is
determined that the lower surface of the top ring 20 is brought
into contact with the surface 22a of the polishing pad 22, the
controller 47 calculates a distance by which the top ring 20 is
lowered based on the counted value of the encoder of the servomotor
138. The distance by which the top ring 20 is lowered is stored in
the storage device. The height of the surface 22a of the polishing
pad 22 is obtained based on the distance by which the top ring 20
is lowered. The controller 47 operates an arithmetical unit
(position calculator) so as to calculate an optimal position of the
top ring 20 to polish a semiconductor wafer based on the height of
the surface 22a of the polishing pad 22.
[0092] When a semiconductor wafer W is to be polished, the
servomotor 138 is driven in a state shown in FIG. 4 so as to lower
the first frame 128 and the top ring 20. At that time, the
controller 47 controls the servomotor 138 and stops the servomotor
138 when the top ring 20 reaches the calculated optimal position.
The semiconductor wafer W held on the lower surface of the top ring
20 is pressed against the polishing pad 22 and polished at the
calculated optimal position.
[0093] In the present embodiment, the top ring 20 holds a
semiconductor wafer W during a pad search process. In the first
embodiment, a pad search process may be performed in a state such
that the top ring 20 holds a semiconductor wafer W. In either case,
it is desirable that a dummy wafer is used rather than a product
wafer when a pad search process is performed. When a dummy wafer is
used during a pad search process, the lower surface of the top ring
20 is not exposed. Accordingly, components attached to the lower
surface of the top ring 20 are prevented from being brought into
direct contact with the polishing pad 22. Thus, slurry (polishing
liquid) is prevented from being attached to these components.
[0094] Further, it is desirable that the servomotor 138 is capable
of changing a maximum current of the motor. With such a servomotor,
for example, a maximum current of the motor is set to be about 5%
during a pad search process. When the lower surface of the top ring
20 or the surface of the semiconductor wafer (dummy wafer) W is
brought into contact with the polishing pad 22, extremely large
loads are prevented from being imposed on the semiconductor wafer
(dummy wafer) W, the top ring 20, the polishing pad 22, or the
like. In this case, if it is possible to predict when the top ring
20 is brought into contact with the polishing pad 22 based on a
period of time for which the top ring 20 is lowered or on a
distance by which the top ring 20 is lowered, then it is desirable
that the maximum current of the servomotor 138 is reduced before
the top ring 20 is brought into contact with the polishing pad 22.
This operation prevents the lower surface of the top ring 20 or the
semiconductor wafer W from being damaged.
[0095] FIG. 6 is a schematic view showing a polishing apparatus 210
according to a third embodiment of the present invention. As shown
in FIG. 6, the polishing apparatus 210 in the present embodiment
has a laser distance measuring sensor 246 for detecting the height
of the polishing pad 22, a polishing liquid supply nozzle 251 for
supplying slurry (polishing liquid) 250 onto the polishing pad 22,
and an ejection nozzle 252 for ejecting nitrogen gas or air toward
a surface of the polishing pad 22 to blow off the slurry 250 on the
polishing pad 22. The distance measuring sensor 246 may comprise an
ultrasonic distance measuring sensor.
[0096] With such an arrangement, the slurry 250 is removed from the
polishing pad 22 by ejection of nitrogen gas or air. A laser can be
applied from the laser distance measuring sensor 246 to a
measurement portion from which the slurry 250 is removed.
Accordingly, since the laser is not reflected on slurry or water on
the polishing pad 22, it is possible to accurately detect a
distance to the polishing pad 22. As a result, a constant distance
can be maintained between the semiconductor wafer W and the
polishing pad 22 based on the measured distance to the surface of
the polishing pad 22.
[0097] In the above embodiments, a pad search process is performed
for each lot of semiconductor wafers by detecting the height
(position) of the top ring 20. However, the pad search process is
not limited to this example. For example, when a product wafer
should not be used for a pad search process, or a dummy wafer
cannot be prepared for some reasons, then a portion of a pad search
process can be performed by a dresser, which dresses (conditions) a
polishing surface of a polishing pad.
[0098] FIG. 7 is a schematic view showing a portion of a polishing
apparatus according to a fourth embodiment of the present
invention. FIG. 7 mainly shows a dresser 50 having a function to
perform a pad search process. An air cylinder 53 is attached to a
dresser head 52 of the dresser 50. The dresser 50 is pressed
against the polishing pad 22 by actuation of the air cylinder
53.
[0099] Variation of the thickness of the polishing pad 22 is
measured by using the dresser 50. In this case, since polishing
pads have different thicknesses, a pad search process is performed
by using the top ring 20 when a polishing pad is replaced with a
new pad. At that time, components (e.g., elastic membranes)
attached to the lower surface of the top ring 20 may be brought
into direct contact with the polishing pad 22 without a product
wafer or a dummy wafer held by the top ring 20 because the
polishing pad that has not been used causes no problems to such
components.
[0100] The dresser head 52 of the dresser 50 has a distance
measuring sensor 54. Variations detected by the distance measuring
sensor 54 are used to follow wear of the polishing pad 22 for a
polishing process of each semiconductor wafer and for each lot of
semiconductor wafers. Specifically, the distance measuring sensor
54 detects a difference between an initial vertical position of the
dresser 50 and a measured vertical position of the dresser 50 to
determine the amount of wear of the polishing pad 22. The amount of
wear of the polishing pad 22 is sent to the controller 47. The
total amount of wear of the polishing pad 22 is determined based on
results of the pad search process performed with the top ring 20 at
the time of replacement of the polishing pad and on the variation
of the thickness of the polishing pad 22 which is detected by the
dresser 50. The top ring 20 is controlled in height so as to follow
the total amount of wear of the polishing pad 22. When variation of
the thickness of the polishing pad 22 is thus measured with the
dresser 50, a throughput can be increased as compared to a case
where a pad search process is performed for each lot of
semiconductor wafers (e.g., 25 semiconductor wafers) with the top
ring 20.
[0101] Next, a top ring which is suitably used as the top ring 20
in the first through fourth embodiments will be described below in
detail. FIGS. 8 through 10 are cross-sectional views showing an
example of the top ring 20 along a plurality of radial directions
of the top ring 20.
[0102] As shown in FIGS. 8 through 10, the top ring 20 has an upper
member 300 in the form of a circular plate, a retainer ring 302
attached to a peripheral portion of the upper member 300, an
intermediate member 304 attached to a lower surface of the upper
member 300, and a lower member 306 attached to a lower surface of
the intermediate member 304. The upper member 300 is connected to
the top ring shaft 18 by a bolt 308. Further, as shown in FIG. 10,
the intermediate member 304 is fixed to the upper member 300 by a
bolt 310 (fastening member), and the lower member 306 is fixed to
the upper member 300 by a bolt 312 (fastening member). Such
fastening members are not limited to bolts.
[0103] The top ring 20 has an elastic membrane 314 attached to a
lower surface of the lower member 306. The elastic membrane 314 is
brought into contact with a rear face of a semiconductor wafer held
by the top ring 20. The elastic membrane 314 is held on the lower
surface of the lower member 306 by an edge holder 316 disposed
radially outward and an annular ripple holder 318 disposed radially
inward of the edge holder 316. The edge holder 316 and the ripple
holder 318 are held on the lower surface of the lower member 306 by
stoppers 320 and 322, respectively. The elastic membrane 314 is
made of a highly strong and durable rubber material such as
ethylene propylene rubber (EPDM), polyurethane rubber, silicone
rubber, or the like.
[0104] The elastic membrane 314 has an opening 314a defined at a
central portion thereof. As shown in FIG. 8, the lower member 306
has a passage 324 communicating with the opening 314a. The passage
324 of the lower member 306 is connected to a fluid supply source
(not shown). Thus, a pressurized fluid is supplied through the
passage 324 to the central portion of the elastic membrane 314.
Further, the passage 324 is selectively connected to a vacuum pump
(not shown). When the vacuum pump is operated, a semiconductor
wafer is attracted to the lower surface of the lower member 306 by
suction.
[0105] The ripple holder 318 has claws 318b and 318c for holding
ripples 314b and 314c of the elastic membrane 314 on the lower
surface of the lower member 306. The ripple holder 318 has a
passage 326 communicating with a ripple chamber formed by the
ripples 314b and 314c of the elastic membrane 314. As shown in FIG.
10, the lower member 306 has a passage 328 communicating with the
passage 326 of the ripple holder 318. The intermediate member 304
has a passage 330 communicating with the passage 328 of the lower
member 306. An O-ring 332 is disposed as a seal member at a
connecting portion between the passage 328 of the lower member 306
and the passage 330 of the intermediate member 304. The passage 326
of the ripple holder 318 is connected via the passage 328 of the
lower member 306 and the passage 330 of the intermediate member 304
to a fluid supply source (not shown). Thus, a pressurized fluid is
supplied through the passages 330, 328, and 326 to the ripple
chamber of the elastic membrane 314.
[0106] As shown in FIG. 10, the edge holder 316 has claws 316d and
316e for holding edges 314d and 314e of the elastic membrane 314 on
the lower surface of the lower member 306. The edge holder 316 has
a passage 334 communicating with an edge chamber formed by the
edges 314d and 314e of the elastic membrane 314. The lower member
306 has a passage 336 communicating with the passage 334 of the
edge holder 316. The intermediate member 304 has a passage 338
communicating with the passage 336 of the lower member 306. An
O-ring 340 is disposed as a seal member at a connecting portion
between the passage 336 of the lower member 306 and the passage 338
of the intermediate member 304. The passage 334 of the edge holder
316 is connected via the passage 336 of the lower member 306 and
the passage 338 of the intermediate member 304 to a fluid supply
source (not shown). Thus, a pressurized fluid is supplied through
the passages 338, 336, and 334 to the edge chamber of the elastic
membrane 314.
[0107] As shown in FIG. 9, the elastic membrane 314 has openings
314f located between the ripple holder 318 and the edge holder 316.
The lower member 306 has a passage 342 communicating with the
openings 314f. The intermediate member 304 has a passage 344
communicating with the passage 342 of the lower member 306. An
O-ring 346 is disposed as a seal member at a connecting portion
between the passage 342 of the lower member 306 and the passage 344
of the intermediate member 304. The passage 342 of the lower member
306 is connected via the passage 344 of the intermediate member 304
to a fluid supply source (not shown). Thus, a pressurized fluid is
supplied through the passages 344 and 342 to an outer portion of
the elastic membrane 314. Further, the passage 342 is selectively
connected to a vacuum pump (not shown). When the vacuum pump is
operated, a semiconductor wafer is attracted to the lower surface
of the lower member 306 by suction.
[0108] As described above, with the top ring 20 in the present
embodiment, pressing forces to press a semiconductor wafer against
the polishing pad 22 can be adjusted at local areas of the
semiconductor wafer by adjusting pressures of fluids to be supplied
to the respective portions of the elastic membrane 314 (i.e., the
central portion, the ripple chamber, the outer portion, and the
edge chamber of the elastic membrane 314).
[0109] The intermediate member 304 has a cleaning liquid passage
348 formed at a peripheral portion thereof. The cleaning liquid
passage 348 of the intermediate member 304 is connected to a
cleaning liquid supply source (not shown). Thus, a cleaning liquid
is supplied through the cleaning liquid passage 348 to a space
between the retainer ring 302 and the intermediate member 304.
[0110] As shown in FIG. 9, the edge holder 316 has hooks 316a
provided at upper portions thereof. Each of the stoppers 320 for
holding the edge holder 316 is cylindrical and has an engagement
portion 320a provided at a lower end thereof. As shown in FIG. 11,
a plurality of stoppers 320 are arranged along a circumferential
direction of the top ring 20 at equal intervals. FIGS. 12A through
12C show details of the stopper 320. FIG. 12A is a plan view, FIG.
12B is a vertical cross-sectional view, and FIG. 12C is a bottom
view.
[0111] As shown in FIG. 12C, the engagement portion 320a is formed
partially in a circumferential direction of the stopper 320. The
engagement portion 320a has tapered portions T on opposite sides
thereof. Each of the tapered portions T is gradually thickened
along the circumferential direction of the stopper 320. Thus, when
the stopper 320 is rotated, the engagement portion 320a of the
stopper 320 is gradually engaged with the hook 316a of the edge
holder 316. Finally, the hook 316a of the edge holder 316 is fixed
to the lower member 306 by the engagement portion 320a of the
stopper 320. The stopper 320 has a groove 320b formed on its upper
surface so that a rotation tool can be inserted into the groove
320b of the stopper 320. Thus, an operator can attach the elastic
membrane 314 on and detach the elastic membrane 314 from the lower
member 306 with use of the rotation tool above the lower member
306.
[0112] Similarly, the ripple holder 318 has hooks 318a provided at
upper portions thereof. Each of the stoppers 322 for holding the
ripple holder 318 is cylindrical and has an engagement portion 322a
provided at a lower end thereof. The engagement portion 322a is
formed partially in a circumferential direction of the stopper 322.
The engagement portion 322a has tapered portions on opposite sides
thereof. Each of the tapered portions is gradually thickened along
the circumferential direction of the stopper 322. Thus, when the
stopper 322 is rotated, the engagement portion 322a of the stopper
322 is gradually engaged with the hook 318a of the ripple holder
318. Finally, the hook 318a of the ripple holder 318 is fixed to
the lower member 306 by the engagement portion 322a of the stopper
322. The stopper 322 has a groove 322b formed on its upper surface
so that a rotation tool can be inserted into the groove 322b of the
stopper 322. Thus, an operator can attach the elastic membrane 314
on and detach the elastic membrane 314 from the lower member 306
with use of the rotation tool above the lower member 306.
[0113] O-rings 350 and 352 are attached to the stoppers 320 and
322, respectively. The O-rings 350 and 352 seal pressurized fluids
supplied to the edge chamber and the ripple chamber of the elastic
membrane 314.
[0114] The retainer ring 302 serves to hold a peripheral edge of a
semiconductor wafer. As shown in FIG. 8, the retainer ring 302 has
a cylinder 400, a holder 402 attached to an upper portion of the
cylinder 400, an elastic membrane 404 held in the cylinder 400 by
the holder 402, a piston 406 connected to a lower end of the
elastic membrane 404, and a ring member 408 which is pressed
downward by the piston 406. An upper end of the cylinder 400 is
closed. The elastic membrane 404 is made of a highly strong and
durable rubber material such as ethylene propylene rubber (EPDM),
polyurethane rubber, silicone rubber, or the like.
[0115] The holder 402 has a passage 412 communicating with a
pressure chamber 410 formed by the elastic membrane 404. The
cylinder 400 has a passage 414 formed at an upper portion thereof.
The passage 414 of the cylinder 400 communicates with the passage
412 of the holder 402. The upper member 300 has a passage 416
communicating with the passage 414 of the cylinder 400. The passage
412 of the holder 402 is connected via the passage 414 of the
cylinder 400 and the passage 416 of the upper member 300 to a fluid
supply source (not shown). Thus, a pressurized fluid is supplied
through the passages 416, 414, and 412 to the pressure chamber 410.
Accordingly, by adjusting a pressure of a fluid to be supplied to
the pressure chamber 410, the elastic membrane 404 can be expanded
and contracted so as to vertically move the piston 406. Thus, the
ring member 408 of the retainer ring 302 can be pressed against the
polishing pad 22 under a desired pressure.
[0116] In the illustrated example, the elastic membrane 404 employs
a rolling diaphragm formed by an elastic membrane having bent
portions. When an inner pressure in a pressure chamber defined by
the rolling diaphragm is changed, the bent portions of the rolling
diaphragm are rolled so as to widen the pressure chamber. The
diaphragm is not brought into sliding contact with outside
components and is hardly expanded and contracted when the pressure
chamber is widened. Accordingly, friction due to sliding contact
can extremely be reduced, and a lifetime of the diaphragm can be
prolonged.
[0117] With the above arrangement, even if the ring member 408 of
the retainer ring 302 is worn out, only the retainer ring 302 can
be lowered. Accordingly, a constant distance can be maintained
between the lower member 306 and the polishing pad 22 even if the
ring member 408 of the retainer ring 302 is worn out. Further,
since the ring member 408, which is brought into contact with the
polishing pad 22, and the cylinder 400 are connected by the
deformable elastic membrane 404, no bending moment is produced by
offset loads. Accordingly, surface pressures by the retainer ring
302 can be made uniform, and the retainer ring 302 becomes more
likely to follow the polishing pad 22.
[0118] As shown in FIG. 11, the ring member 408 has a plurality of
vertically extending V-shaped grooves 418. The V-shaped grooves 418
are formed in an inner surface of the ring member 408 at equal
intervals. Further, a plurality of pins 349 project radially
outward from a peripheral portion of the lower member 306. The pins
349 are arranged so as to engage with the V-shaped grooves 418 of
the ring member 418. The pins 349 are vertically slidable within
the V-shaped grooves 418 relative to the ring member 408. The pins
349 allow rotation of the top ring 20 to be transmitted via the
upper member 300 and the lower member 306 to the ring member 408 so
as to integrally rotate the top ring 20 and the ring member 408.
Such an arrangement prevents torsion of the elastic membrane
(rolling diaphragm) 404 and allows the ring member 408 to be
pressed uniformly and smoothly against the polishing surface 22
during polishing. Further, a lifetime of the elastic membrane 404
can be prolonged.
[0119] As described above, pressing forces to press a semiconductor
wafer are controlled by pressures of fluids to be supplied to the
central portion, the ripple chamber, the outer portion, and the
edge chamber of the elastic membrane 314. Accordingly, the lower
member 306 should be located away upward from the polishing pad 22
during polishing. However, if the retainer ring 302 is worn out, a
distance between the semiconductor wafer and the lower member 306
is varied to change a deformation manner of the elastic membrane
314. Accordingly, surface pressure distribution is also varied on
the semiconductor wafer. Such a variation of the surface pressure
distribution causes unstable profiles of polished semiconductor
wafers.
[0120] In the illustrated example, since the retainer ring 302 can
vertically be moved independently of the lower member 306, a
constant distance can be maintained between the semiconductor wafer
and the lower member 306 even if the ring member 408 of the
retainer ring 302 is worn out. Accordingly, profiles of polished
semiconductor wafers can be stabilized.
[0121] In the illustrated example, when the elastic membrane 314 is
replaced with a new membrane, it is not necessary to remove the
entire top ring 20 from the top ring shaft 18. Specifically, when
the elastic membrane 314 is detached from the lower member 306, the
bolt 312 (see FIG. 10) is first removed to detach the lower member
306 from the upper member 300 and the intermediate member 304.
Then, a rotation tool is inserted into the groove 320b (see FIG. 9)
formed at the top of the stopper 320 to rotate the stopper 320.
Thus, the hook 316a of the edge holder 316 is disengaged from the
engagement portion 320a of the stopper 320. Accordingly, the edge
holder 316 can readily be detached from the lower member 306.
Similarly, a rotation tool is inserted into the groove 322b formed
at the top of the stopper 322 to rotate the stopper 322. Thus, the
hook 318a of the ripple holder 318 is disengaged from the
engagement portion 322a of the stopper 322. Accordingly, the ripple
holder 318 can readily be detached from the lower member 306.
[0122] When the edge holder 316 and the ripple holder 318 are
detached from the lower member 306 in the above manner, the elastic
membrane 314, which has been held by the edge holder 316 and the
ripple holder 318, can readily be detached from the lower member
306. The elastic membrane 314 can readily be attached to the lower
member 306 by a reverse operation to the above.
[0123] Since the O-rings 332, 340, and 346 are disposed as seal
members at the connecting portions between the passages of the
lower member 306 and the passages of the intermediate member 304,
the lower member 306 and the intermediate member 304 can be
connected to each other in a state such that these passages are
reliably sealed when the bolt 312 is fastened. Accordingly, special
extraction and insertion of pipes are not required to replace the
elastic membrane 314 with a new membrane.
[0124] In the illustrated example, the elastic membrane 314 is
disposed so as to be brought into contact with substantially the
entire surface of the semiconductor wafer. However, the elastic
membrane 314 may be brought into contact with at least a portion of
a semiconductor wafer.
[0125] FIG. 13 is an enlarged cross-sectional view showing a
variation of the top ring 20 shown in FIG. 8. In the example shown
in FIG. 13, an annular seal member 420 is provided between the
retainer ring 302 and the lower member 306. The seal member 420
prevents a polishing liquid from being introduced into the interior
of the top ring 20 and also prevents foreign matter from being
discharged from the interior of the top ring 20. The seal member
420 is made of a soft material and can be deformed according to
vertical movement of the retainer ring 302 and the lower member
306.
[0126] FIG. 14 is a schematic view showing a polishing apparatus
510 according to a fifth embodiment of the present invention. As
shown in FIG. 14, the polishing apparatus 510 has a polishing table
12, a top ring head 16 connected to an upper end of a support shaft
14, a top ring shaft 18 mounted at a free end of the top ring head
16, and a top ring 20 coupled to a lower end of the top ring shaft
18. In the illustrated example, the top ring 20 is substantially in
the form of a circular plate.
[0127] The polishing table 12 is coupled via a table shaft 12a to a
motor (not shown) disposed below the polishing table 12. Thus, the
polishing table 12 is rotatable about the table shaft 12a. As shown
in FIG. 14, a polishing pad 22 is attached to an upper surface of
the polishing table 12. An upper surface 22a of the polishing pad
22 forms a polishing surface to polish a semiconductor wafer W.
[0128] Various kinds of polishing pads are available on the market.
For example, some of these are SUBA800, IC-1000, and
IC-1000/SUBA400 (two-layer cloth) manufactured by Rodel Inc., and
Surfin xxx-5 and Surfin 000 manufactured by Fujimi Inc. SUBA800,
Surfin xxx-5, and Surfin 000 are non-woven fabrics bonded by
urethane resin, and IC-1000 is made of rigid foam polyurethane
(single layer). Foam polyurethane is porous and has a large number
of fine recesses or holes formed in its surface.
[0129] The top ring shaft 18 is rotated by actuation of a motor
(not shown). By rotation of the top ring shaft 18, the top ring 20
is rotated about the top ring shaft 18. Further, the top ring shaft
18 is vertically moved by a vertical movement mechanism 124. By
vertical movement of the top ring shaft 18, the top ring 20 is
vertically moved with respect to the top ring head 16. A rotary
joint 25 is mounted on an upper end of the top ring shaft 18.
[0130] The top ring 20 has a top ring body 500 for holding a
substrate such as a semiconductor wafer W on its lower surface and
pressing the substrate against the polishing pad 22 and a retainer
ring 502 for pressing the polishing pad 22. The retainer ring 502
is provided at a peripheral portion of the top ring body 500. The
top ring head 16 is pivotable (swingable) about the support shaft
14. Thus, the top ring 20, which holds a semiconductor wafer W on
its lower surface, is moved between a position at which the top
ring 20 receives the semiconductor wafer W and a position above the
polishing table 12 by pivotal movement of the top ring head 16. The
top ring 20 is lowered to press the semiconductor wafer W against a
surface (polishing surface) 22a of the polishing pad 10. At that
time, while the top ring 20 and the polishing table 12 are
respectively rotated, a polishing liquid is supplied onto the
polishing pad 22 from a polishing liquid supply nozzle (not shown),
which is provided above the polishing table 12. The semiconductor
wafer W is brought into sliding contact with the polishing surface
22a on the polishing pad 10. Thus, a surface of the semiconductor
wafer W is polished.
[0131] The vertical movement mechanism 124, which vertically moves
the top ring shaft 18 and the top ring 20, has a first frame
(bridge) 28 supporting the top ring shaft 18 in a manner such that
the top ring shaft 18 is rotatable via a bearing 126, a ball screw
132 threaded into a nut 130 mounted on the first frame 128, a
second frame (support stage) 136 supported by poles 135, and an AC
servomotor 138 provided on the second frame 136. The second frame
136, which supports the servomotor 138, is fixed to the top ring
head 16 via the poles 135.
[0132] The ball screw 132 is coupled to the servomotor 138. The top
ring shaft 18 is configured to be vertically movable together with
the first frame 128. Accordingly, when the servomotor 138 is
driven, the first frame 128 is vertically moved via the ball screw
132. As a result, the top ring shaft 18 and the top ring 20 are
vertically moved. The polishing apparatus 510 has a controller 47
operable to control various devices, including the servomotor 38,
in the polishing apparatus 510. The controller 47 includes a
storage device and a computer-readable medium having a program
recorded therein for controlling the polishing apparatus 510.
[0133] As shown in FIG. 14, the polishing apparatus 510 has a
dressing unit 540 for dressing the polishing surface 22a on the
polishing table 12. The dressing unit 540 includes a dresser 50
which is brought into sliding contact with the polishing surface
22a, a dresser shaft 51 to which the dresser 50 is connected, an
air cylinder 53 provided at an upper end of the dresser shaft 51,
and a swing arm 55 rotatably supporting the dresser shaft 51. The
dresser 50 has a dressing member 50a attached on a lower portion of
the dresser 50. The dressing member 50a has diamond particles in
the form of needles. These diamond particles are attached on a
lower of the dressing member 50a. The air cylinder 53 is disposed
on a support stage 57, which is supported by poles 56. The poles 56
are fixed to the swing arm 55.
[0134] The swing arm 55 is pivotable (swingable) about the support
shaft 58 by actuation of a motor (not shown). The dresser shaft 51
is rotatable by actuation of a motor (not shown). Thus, the dresser
50 is rotated about the dresser shaft 51 by rotation of the dresser
shaft 51. The air cylinder 53 vertically moves the dresser 50 via
the dresser shaft 51 so as to press the dresser 50 against the
polishing surface 22a of the polishing pad 22 under a predetermined
pressing force.
[0135] Dressing operation of the polishing surface 22a on the
polishing pad 22 is performed as follows. The dresser 50 is pressed
against the polishing surface 22a by the air cylinder 53.
Simultaneously, pure water is supplied onto the polishing surface
22a from a pure water supply nozzle (not shown). At that state, the
dresser 50 is rotated about the dresser shaft 51, and the lower
surface (diamond particles) of the dressing member 50a is brought
into contact with the polishing surface 22a. Thus, the dresser 50
removes a portion of the polishing pad 22 so as to dress the
polishing surface 22a.
[0136] The polishing apparatus 510 in the present embodiment
utilizes the dresser 50 to measure the amount of wear of the
polishing pad 22. Specifically, the dressing unit 540 includes a
displacement sensor (polishing pad wear detector) 60 for measuring
displacement of the dresser 50. The displacement sensor 60 is
provided on an upper surface of the swing arm 55. A target plate 61
is fixed to the dresser shaft 51. The target plate 61 is vertically
moved by vertical movement of the dresser 50. The displacement
sensor 60 is inserted into a hole of the target plate 61. The
displacement sensor 60 measures displacement of the target plate 61
to measure displacement of the dresser 50. The displacement sensor
60 may comprise any type of sensors including a laser sensor, an
ultrasonic sensor, an eddy-current sensor, and a linear scale
sensor.
[0137] In the present embodiment, the amount of wear of the
polishing pad 22 is measured as follows. First, the air cylinder 53
is operated to bring the dresser 50 into contact with a polishing
surface 22a of an unused polishing pad 22. At that state, the
displacement sensor 60 measures an initial position of the dresser
50 and stores the initial position in the storage device of the
controller (arithmetical unit) 47. After completion of a polishing
process for one or more semiconductor wafers W, the dresser 50 is
brought into contact with the polishing surface 22a. At that state,
the position of the dresser 50 is measured. Since the position of
the dresser 50 is shifted downward by the amount of wear of the
polishing pad 22, the controller 47 calculates a difference between
the initial position and the measured position of the dresser 50
after polishing to obtain the amount of wear of the polishing pad
22. Thus, the amount of wear of the polishing pad 22 is calculated
based on the position of the dresser 50.
[0138] In the controller 47, the total amount of wear of the
polishing pad 22 is compared with a predetermined set value. If the
total amount of wear of the polishing pad 22 exceeds the
predetermined set value, a signal to indicate that the polishing
pad 22 should be replaced is sent from the controller 47. The
amount of wear of the polishing pad 22 (the amount of polishing)
for a polishing process or sets of polishing processes is stored in
the controller 47 so that variation of the amount of wear can be
monitored by the controller 47. In this case, an operational recipe
of the dresser 50 (dressing conditions such as a dressing time, a
rotational speed of the dresser 50, and a pressing force to press
the dresser 50 against the polishing pad 22) may be changed by the
controller 47 to maintain a constant amount of wear of the
polishing pad 22 for each polishing process or each set of
polishing processes.
[0139] Based on the amount of wear of the polishing pad 22, the
controller 47 controls the servomotor 138 so that a distance
between the top ring 20 and the polishing surface 22a of the
polishing pad 22 is equal to a predetermined value. Specifically,
the controller 47 calculates an optimal position of the top ring 20
to polish a semiconductor wafer based on the amount of wear of the
polishing pad 22 (displacement of the polishing surface 22a) and
stores the optimal position in the storage device. When a
semiconductor wafer W is polished, the servomotor 138 is driven in
the state shown in FIG. 14 so as to lower the first frame 128 and
the top ring 20 which holds the semiconductor wafer W. At that
time, the controller 47 controls the servomotor 138 and stops the
servomotor 138 when the top ring 20 reaches the calculated optimal
position. The semiconductor wafer W held on the lower surface of
the top ring 20 is pressed against the polishing pad 22 and
polished at the calculated optimal position.
[0140] Next, a top ring which is suitably used as the top ring 20
in the fifth embodiment will be described below in detail. FIGS. 15
through 18 are cross-sectional views showing an example of the top
ring 20 along a plurality of radial directions of the top ring 20.
FIG. 19 is a plan view showing a lower member shown in FIGS. 15
through 18.
[0141] As shown in FIGS. 15 through 18, the top ring 20 has a top
ring body 500 for pressing a semiconductor wafer W against the
polishing surface 22a and a retainer ring 502 for directly pressing
the polishing surface 22a. The top ring body 500 includes an upper
member 600 in the form of a circular plate, an intermediate member
604 attached to a lower surface of the upper member 600, and a
lower member 606 attached to a lower surface of the intermediate
member 604.
[0142] The retainer ring 502 is attached to a peripheral portion of
the upper member 600. The upper member 600 is connected to the top
ring shaft 18 by a bolt 608. Further, the intermediate member 604
is fixed to the upper member 600 by a bolt (not shown), and the
lower member 606 is fixed to the upper member 600 by a bolt (not
shown). The top ring body 500 including the upper member 600, the
intermediate member 604, and the lower member 606 is made of resin
such as engineering plastics (e.g., PEEK).
[0143] The top ring 20 has an elastic membrane 614 attached to a
lower surface of the lower member 606. The elastic membrane 614 is
brought into contact with a rear face of a semiconductor wafer held
by the top ring 20. The elastic membrane 614 is held on the lower
surface of the lower member 606 by an edge holder 616 disposed
radially outward and annular ripple holders 618 and 619 disposed
radially inward of the edge holder 616. The elastic membrane 614 is
made of a highly strong and durable rubber material such as
ethylene propylene rubber (EPDM), polyurethane rubber, silicone
rubber, or the like.
[0144] The edge holder 616 is held by the ripple holder 618, and
the ripple holder 618 is held on the lower surface of the lower
member 606 by a plurality of stoppers 620. The ripple holder 619 is
held on the lower surface of the lower member 606 by a plurality of
stoppers 622. As shown in FIG. 19, the stoppers 620 and the
stoppers 622 are arranged along a circumferential direction of the
top ring 20 at equal intervals.
[0145] As shown in FIG. 15, a central chamber 660 is formed at a
central portion of the elastic membrane 614. The ripple holder 619
has a passage 624 communicating with the central chamber 660. The
lower member 606 has a passage 625 communicating with the passage
624. The passage 624 of the ripple holder 619 and the passage 625
of the lower member 606 are connected to a fluid supply source (not
shown). Thus, a pressurized fluid is supplied through the passage
625 and 624 to the central chamber 660 of the elastic membrane
314.
[0146] The ripple holder 618 has claws 618b and 618c for pressing a
ripple 614b and an edge 614c of the elastic membrane 614 against
the lower surface of the lower member 606. The ripple holder 619
has a claw 619a for pressing a ripple 614a of the elastic membrane
614 against the lower surface of the lower member 606.
[0147] As shown in FIG. 16, an annular ripple chamber 661 is formed
between the ripple 614a and the ripple 614b of the elastic membrane
614. A gap 614f is formed between the ripple holder 618 and the
ripple holder 619 of the elastic membrane 614. The lower member 606
has a passage 642 communicating with the gap 614f. Further, the
intermediate member 604 has a passage 644 communicating with the
passage 642 of the lower member 606. An annular groove 647 is
formed at a connecting portion between the passage 642 of the lower
member 606 and the passage 644 of the intermediate member 604. The
passage 642 of the lower member 606 is connected via the annular
groove 647 and the passage 644 of the intermediate member 604 to a
fluid supply source (not shown). Thus, a pressurized fluid is
supplied through the passages to the ripple chamber 661. Further,
the passage 642 is selectively connected to a vacuum pump (not
shown). When the vacuum pump is operated, a semiconductor wafer is
attracted to the lower surface of the elastic membrane 614 by
suction.
[0148] As shown in FIG. 17, the ripple holder 618 has a passage 626
communicating with an annular outer chamber 662 formed by the
ripple 614b and the edge 614c of the elastic membrane 614. Further,
the lower member 606 has a passage 628 communicating with the
passage 626 of the ripple holder 618 via a connector 627. The
intermediate member 604 has a passage 629 communicating with the
passage 628 of the lower member 606. The passage 626 of the ripple
holder 618 is connected via the passage 628 of the lower member 606
and the passage 629 of the intermediate member 604 to a fluid
supply source (not shown). Thus, a pressurized fluid is supplied
through the passages 629, 628, and 626 to the outer chamber 662 of
the elastic membrane 614.
[0149] As shown in FIG. 18, the edge holder 616 has a claw for
holding an edge 614d of the elastic membrane 614 on the lower
surface of the lower member 606. The edge holder 616 has a passage
634 communicating with an annular edge chamber 663 formed by the
edges 614c and 614d of the elastic membrane 614. The lower member
606 has a passage 636 communicating with the passage 634 of the
edge holder 616. The intermediate member 604 has a passage 638
communicating with the passage 636 of the lower member 606. The
passage 634 of the edge holder 616 is connected via the passage 636
of the lower member 606 and the passage 638 of the intermediate
member 604 to a fluid supply source (not shown). Thus, a
pressurized fluid is supplied through the passages 638, 636, and
634 to the edge chamber 663 of the elastic membrane 614.
[0150] As described above, with the top ring 20 in the present
embodiment, pressing forces to press a semiconductor wafer against
the polishing pad 22 can be adjusted at local areas of the
semiconductor wafer by adjusting pressures of fluids to be supplied
to the respective pressure chambers formed between the elastic
membrane 614 and the lower member 606 (i.e., the central chamber
660, the ripple chamber 661, the outer chamber 662, and the edge
chamber 663).
[0151] FIG. 20 is an enlarged view of the retainer ring 502 shown
in FIG. 15. The retainer ring 502 serves to hold a peripheral edge
of a semiconductor wafer. As shown in FIG. 20, the retainer ring
502 has a cylinder 700, a holder 702 attached to an upper portion
of the cylinder 700, an elastic membrane 704 held in the cylinder
700 by the holder 702, a piston 706 connected to a lower end of the
elastic membrane 704, and a ring member 708 which is pressed
downward by the piston 706. An upper end of the cylinder 700 is
closed. A connection sheet 720, which can be expanded and
contracted in a vertical direction, is provided between an outer
circumferential surface of the ring member 708 and a lower end of
the cylinder 700. The connection sheet 720 is disposed so as to
fill a gap between the ring member 708 and the cylinder 700. Thus,
the connection sheet 720 serves to prevent a polishing liquid
(slurry) from being introduced into the gap between the ring member
708 and the cylinder 700.
[0152] The elastic membrane 614 includes a seal portion 722
connecting the elastic membrane 614 to the retainer ring 502 at an
edge (periphery) of the elastic membrane 614. The seal portion 722
has a shape curved upward. The seal portion 722 is disposed so as
to fill a gap between the elastic membrane 614 and the ring member
708. The seal portion 722 is made of a deformable material. The
seal portion 722 serves to prevent a polishing liquid from being
introduced into the gap between the elastic membrane 614 and the
ring member 708 while allowing the top ring body 500 and the
retainer ring 502 to be moved relative to each other. In the
present embodiment, the seal portion 722 is formed integrally with
the edge 614d of the elastic membrane 614 and has a U-shaped
cross-section.
[0153] In a case where the connection sheet 720 or the seal portion
722 is not provided, a polishing liquid may be introduced into an
interior of the top ring 20 so as to inhibit normal operation of
the top ring body 500 and the retainer ring 502 of the top ring 20.
In the present embodiment, the connection sheet 720 and the seal
portion 722 prevent a polishing liquid from being introduced into
the interior of the top ring 20. Accordingly, it is possible to
operate the top ring 20 normally. The elastic membrane 704, the
connection sheet 720, and the seal portion 722 is made of a highly
strong and durable rubber material such as ethylene propylene
rubber (EPDM), polyurethane rubber, silicone rubber, or the
like.
[0154] The ring member 708 is divided into an upper ring member
708a and a lower ring member 708b. The upper ring member 708a is
brought into contact with the piston 706. The lower ring member
708b is brought into contact with the polishing surface 22a. The
upper ring member 708a and the lower ring member 708b have flange
portions extending in a circumferential direction on outer
circumferential surfaces of the ring members 708a and 708b. The
flange portions are held by a clamp 730 so that the upper ring
member 708a and the lower ring member 708b are fastened.
[0155] FIG. 21 is a plan view of the clamp 730 shown in FIG. 20.
The clamp 730 is made of a flexible material. An initial shape of
the clamp 730 is substantially linear. When the clamp 730 is
attached to the flange portions of the ring member 708, the clamp
730 is deformed into an annular shape having a notch 730a as shown
in FIG. 21.
[0156] FIG. 22A is a perspective view showing another example of
the clamp 730. A plurality of clamps 730 made of a hard material
are used in this example. FIG. 22A shows only one of the clamps
730. The upper ring member 708a has a plurality of flange portions
731a projecting outward on an outer circumferential surface of the
upper ring member 708a. The lower ring member 708b has a plurality
of flange portions 731b projecting outward on an outer
circumferential surface of the lower ring member 708b. Each clamp
730 has a shape curved along an outer circumferential surface of
the ring member 708.
[0157] These clamps 730 are attached to the ring member 708 as
follows. First, the upper ring member 708a and the lower ring
member 708b are brought into contact with each other in a state
such that the flange portions 731a and 731b are aligned with each
other. Then, the clamp 730 is located at a gap between adjacent
flange portions and moved horizontally to clamp the flange portions
731a and 731b. Thus, the upper ring member 708a and the lower ring
member 708b are fastened to each other by the clamp 730. In this
example, as shown in FIG. 22B, the connection sheet 720 has a
plurality of projections 720a formed on an inner circumferential
surface of the connection sheet 720. The projections 720a are
fitted into gaps between the flange portions. The connection sheet
720 is attached to the ring member 708 so that the projections 720a
are fitted into the gaps between the flange portions. Thus, the
clamps 730 are fixed in place.
[0158] As shown in FIG. 20, the holder 702 has a passage 712
communicating with a pressure chamber 710 formed by the elastic
membrane 704. The cylinder 700 has a passage 714 formed at an upper
portion thereof. The passage 714 of the cylinder 700 communicates
with the passage 712 of the holder 702. The upper member 600 has a
passage 716 communicating with the passage 714 of the cylinder 700.
The passage 712 of the holder 702 is connected via the passage 714
of the cylinder 700 and the passage 716 of the upper member 600 to
a fluid supply source (not shown). Thus, a pressurized fluid is
supplied through the passages 716, 714, and 712 to the pressure
chamber 710. Accordingly, by adjusting a pressure of a fluid to be
supplied to the pressure chamber 710, the elastic membrane 704 can
be expanded and contracted so as to vertically move the piston 706.
Thus, the ring member 708 of the retainer ring 502 can be pressed
against the polishing pad 22 under a desired pressure.
[0159] The elastic membrane 704 may have a plurality of separation
membranes (not shown) disposed along a circumferential direction so
as to form a plurality of pressure chambers 710, which are divided
in the circumferential direction, inside of the elastic membrane
704. It is desirable that the number of the pressure chambers 710
is not less than three. In this case, the passages 712, 714, and
716 are formed independently for each pressure chamber 710.
Pressure controllers (not shown) are provided for the respective
pressure chambers 710. Thus, fluids independently controlled in
pressure by the pressure controllers are supplied through the
passages 712, 714, and 716 into the respective pressure chambers
710. Accordingly, by adjusting pressures of fluids to be supplied
to the pressure chambers 710, the elastic membrane 704 can be
expanded and contracted so as to vertically move the piston 706.
Thus, the ring member 708 of the retainer ring 502 can be pressed
against the polishing pad 22 with a desired pressure
distribution.
[0160] In the above example, a non-uniform pressure distribution
can be produced along a circumferential direction of the retainer
ring 502 by independently adjusting pressures of fluids to be
supplied to a plurality of pressure chambers 710. Specifically, the
ring member 708 and a plurality of pressure chambers 710 to press
the ring member 708 against the polishing pad 22 serve as a
pressure control mechanism for producing a non-uniform pressure
distribution along a circumferential direction of the retainer ring
502.
[0161] For example, such a pressure control mechanism can control
pressures under which the retainer ring 502 presses the polishing
pad 22 so that portions located downstream in a rotation direction
of the polishing table 12 are pressed under pressures higher than
portions located upstream in the rotation direction of the
polishing table 12. In this case, it is necessary to dynamically
vary pressures to be supplied to the respective pressure chambers
710 according to rotation of the top ring 20. When the top ring 20
is rotated at a high rotational speed, it becomes difficult to
control pressures so as to follow the rotation. For example, in
order to overcome the difficulty of pressure control, pressure
control valves (not shown) may be provided for the respective
pressure chambers 710. The pressure control valves may be switched
according to the rotation of the top ring 20 so as to introduce
fluids having predetermined pressures into the respective pressure
chambers 710.
[0162] For example, a reference point (marking) may be provided on
the retainer ring 502. A plurality of proximity sensors may be
disposed around the retainer ring 502 at equal intervals. The
reference point may be detected by the proximity sensors when the
top ring 20 is rotated. In this case, pressures under which the
retainer ring 502 presses the polishing pad 22 can be controlled
based on detected results of the proximity sensors. It is desirable
that the number of the proximity sensors is not less than three.
Alternatively, vertical displacements of the retainer ring 502 or
actual pressing loads to press the polishing surface which
correspond to the respective pressure chambers 710 may be detected
to control pressures under which the retainer ring 502 presses the
polishing pad 22 based on the detected results.
[0163] In the illustrated example, the elastic membrane 704 employs
a rolling diaphragm formed by an elastic membrane having bent
portions. When an inner pressure in a pressure chamber defined by
the rolling diaphragm is changed, the bent portions of the rolling
diaphragm are rolled so as to widen the pressure chamber. The
diaphragm is not brought into sliding contact with outside
components and is hardly expanded and contracted when the pressure
chamber is widened. Accordingly, friction due to sliding contact
can extremely be reduced, and a lifetime of the diaphragm can be
prolonged. Further, pressing forces under which the retainer ring
502 presses the polishing pad 22 can accurately be adjusted.
[0164] With the above arrangement, only the retainer ring 502 can
be lowered. Accordingly, a constant distance can be maintained
between the lower member 606 and the polishing pad 22 even if the
ring member 708 of the retainer ring 502 is worn out. Further,
since the ring member 708, which is brought into contact with the
polishing pad 22, and the cylinder 700 are connected by the
deformable elastic membrane 704, no bending moment is produced by
offset loads. Accordingly, surface pressures by the retainer ring
502 can be made uniform, and the retainer ring 502 becomes more
likely to follow the polishing pad 22.
[0165] As shown in FIGS. 19 and 20, the upper ring member 708a has
a plurality of vertically extending V-shaped grooves 718. The
V-shaped grooves 718 are formed in an inner surface of the upper
ring member 708a at equal intervals. Further, a plurality of pins
649 project radially outward from a peripheral portion of the lower
member 606. The pins 649 are arranged so as to engage with the
V-shaped grooves 718 of the ring member 708. The pins 649 are
vertically slidable within the V-shaped grooves 718 relative to the
ring member 708. The pins 649 allow rotation of the top ring body
500 to be transmitted via the upper member 600 and the lower member
606 to the retainer ring 502 so as to integrally rotate the top
ring body 500 and the retainer ring 502. Such an arrangement
prevents torsion of the elastic membrane (rolling diaphragm) 704
and allows the ring member 708 to be pressed uniformly and smoothly
against the polishing surface 22 during polishing. Further, a
lifetime of the elastic membrane 704 can be prolonged.
[0166] Since rotation of the top ring body 500 is transmitted to
the retainer ring 502 by engagement of the pins 649 provided on the
top ring body 500 with the V-shaped grooves 718 of the retainer
ring 502, the pins 649 may be brought into sliding contact with the
V-shaped grooves 718 to form recesses in surfaces of the V-shaped
grooves 718. Such recesses may forcibly position the pins 649 so as
to cause unstable movement of the retainer ring 502. FIG. 23 is a
partial cross-sectional view showing a top ring capable of
resolving such a drawback. FIG. 24 is a plan view of a lower member
of the top ring shown in FIG. 23.
[0167] As shown in FIGS. 23 and 24, an annular sheet member 740 is
fixed to the lower member 606 of the top ring body 500 by pins 741.
A plurality of slide rings 744 are attached to peripheral portions
of the sheet member 740 at equal intervals. The upper ring member
708a of the retainer ring 502 has a plurality of drive pins 742
extending along a vertical direction at equal intervals. The drive
pins 742 are inserted into the slide rings 744 so as to be slidable
within the slide rings 744. Rotation of the top ring body 500 is
transmitted via the sheet member 740, the slide rings 744, and the
drive pins 742 to the retainer ring 502. Thus, the top ring body
500 and the retainer ring 502 are rotated integrally with each
other.
[0168] In this example, since the drive pins 742 are brought into
contact with the slide rings 744 with large contact areas, it is
possible to reduce wear of the drive pins 742 and the slide rings
744. Accordingly, the ring member 708 can be moved smoothly in the
vertical direction. Thus, it is possible to operate the retainer
ring 502 normally. Rubber is suitable for a material of the sheet
member 740. When the sheet member 740 is made of rubber, vibration
to be transmitted between the top ring body 500 and the retainer
ring 502 can be reduced.
[0169] As described above, pressing forces to press a semiconductor
wafer are controlled by pressures of fluids to be supplied to the
central chamber 660, the ripple chamber 661, the outer chamber 662,
and the edge chamber 663 of the elastic membrane 614. Accordingly,
the lower member 606 should be located away upward from the
polishing pad 22 during polishing. However, if the retainer ring
502 is worn out, a distance between the semiconductor wafer and the
lower member 606 is varied to change a deformation manner of the
elastic membrane 614. Accordingly, surface pressure distribution is
also varied on the semiconductor wafer. Such a variation of the
surface pressure distribution causes unstable profiles of polished
semiconductor wafers.
[0170] In the illustrated example, since the retainer ring 502 can
vertically be moved independently of the lower member 606, a
constant distance can be maintained between the semiconductor wafer
and the lower member 606 even if the ring member 708 of the
retainer ring 502 is worn out. Accordingly, profiles of polished
semiconductor wafers can be stabilized.
[0171] In the illustrated example, the elastic membrane 614 is
disposed so as to be brought into contact with substantially the
entire surface of the semiconductor wafer. However, the elastic
membrane 614 may be brought into contact with at least a portion of
a semiconductor wafer.
[0172] During polishing, since the retainer ring 502 of the top
ring 20 is brought into sliding contact with the polishing surface
22a, the retainer ring 502 (the lower ring member 708b) is
gradually worn out. When the retainer ring 502 is worn out to some
extent, the ring member 708 cannot be pressed against the polishing
surface 22a under a desired pressing force. As a result, profiles
of semiconductor wafers are varied. Accordingly, the present
embodiment employs a retainer ring wear detector provided on a
pusher to measure the amount of wear of the retainer ring 502.
[0173] FIG. 25 is a cross-sectional view showing a pusher having a
retainer ring wear detector. As shown in FIG. 25, the pusher 800
has a push stage 810 for lifting a semiconductor wafer to allow the
semiconductor wafer to be held on the elastic membrane 614 of the
top ring body 500, a retainer ring guide 815 for centering the top
ring 20 and the pusher 800, a first air cylinder 818 for vertically
moving the push stage 810, and a second air cylinder 819 for
vertically moving the push stage 810 and the retainer ring guide
815.
[0174] The push stage 810 is coupled via a first vertical shaft 821
to the first air cylinder 818. The first air cylinder 818 is
coupled via a second vertical shaft 822 to the second air cylinder
819. The first vertical shaft 821 is slidably supported by a slide
guide 826, which is housed in a housing 825. The retainer ring
guide 815 is supported via a spring 830 by the first vertical shaft
821. The retainer ring guide 815 has a recess 815a formed at its
upper end surface. The recess 815a is brought into contact with a
lower surface of the ring member 708 of the retainer ring 502. When
the second air cylinder 819 is operated to lift the retainer ring
guide 815 and the push stage 810, a lower portion of the ring
member 708 is fitted into the recess 815a. Thus, the top ring 20 is
centered on the pusher 800. At that time, the spring 830 is pressed
downward by the retainer ring guide 815 to absorb impact when the
top ring 20 is brought into contact with the pusher 800.
[0175] As shown in FIG. 25, an eddy-current sensor (retainer ring
wear detector) 840 is attached to the retainer ring guide 815. The
push stage 810 has a metal target plate 841 facing the eddy-current
sensor 840. The eddy-current sensor 840 measures a distance between
the push stage 810 and the retainer ring guide 815 with use of the
target plate 841. The retainer ring wear detector is not limited to
an eddy-current sensor and may comprise any type of sensors
including a laser sensor, an ultrasonic sensor, and a linear scale
sensor.
[0176] Two linear transporters 850 and 860 to transfer a
semiconductor wafer W and two wafer trays 870 and 880 held by the
linear transporters 850 and 860 are disposed between the top ring
20 and the pusher 800. Semiconductor wafers are loaded on or
unloaded from the top ring 20 via the wafer trays 870 and 880 by
the push stage 810. The linear transporters 850 and 860 serve to
transfer a semiconductor wafer W between the polishing apparatus
and a transfer robot (not shown). The linear transporters 850 and
860 are configured to be movable in a horizontal direction. The
linear transporter 850 is used for loading a semiconductor wafer,
whereas the linear transporter 860 is used for unloading a
semiconductor wafer. The linear transporter 850 is disposed above
the linear transporter 860. Although the linear transporter 850 and
the linear transporter 860 are illustrated as being vertically
aligned with each other in FIG. 25, the linear transporter 850 and
the linear transporter 860 are practically moved in parallel so as
to pass each other.
[0177] When a semiconductor wafer is loaded on the top ring 20, the
push stage 810 lifts the wafer tray 870 having a semiconductor
wafer W placed thereon to deliver the semiconductor wafer W to the
top ring 20. Then, the semiconductor wafer W is held on the top
ring 20. When a semiconductor wafer is unloaded from the top ring
20, the push stage 810 lifts the wafer tray 880 to receive a
semiconductor wafer W released from the top ring 20. Thus, the
semiconductor wafer W is placed on the wafer tray 880. The pusher
800 is disposed near the polishing table 12 (see FIG. 14). When a
semiconductor wafer is received or delivered by the pusher 800, the
support shaft 14 is rotated so that the top ring 20 is located
above the pusher 800.
[0178] Operation of the pusher 800 will be described with reference
to FIGS. 25 through 29. First, as shown FIG. 26, the linear
transporter 850 is moved so that the wafer tray 870, which has a
semiconductor wafer W to be polished, is located above the pusher
800. Then, as shown in FIG. 27, the second air cylinder 819 is
operated to lift the first air cylinder 818, the push stage 810,
and the retainer ring guide 815 so that the retainer ring guide 815
is brought into contact with the lower surface of the ring member
708. Further, as shown in FIG. 28, the first air cylinder 818 is
operated to lift the push stage 810. Thus, the wafer tray 870 is
lifted together with the semiconductor wafer W. Then, the
semiconductor wafer W is held on (or attracted to) the top ring 20.
Thereafter, the top ring 20 is moved to a position above the
polishing table 12. Thus, the semiconductor wafer W is polished on
the polishing table 12.
[0179] After completion of the polishing process, the support shaft
14 is rotated to move the top ring 20 to a position above the
pusher 800. At that time, the linear transporter 860 is moved so
that the wafer tray 880 is located above the pusher 800. Then, the
second air cylinder 819 is operated to lift the first air cylinder
818, the push stage 810, and the retainer ring guide 815 so that
the retainer ring guide 815 is brought into contact with the lower
surface of the ring member 708. At that time, as shown in FIG. 29,
a polished semiconductor wafer W is released from the top ring 20
and placed on the wafer tray 880. The second air cylinder 819 is
operated to lower the push stage 810 and the retainer ring guide
815. Then, the linear transporter 860 is moved to deliver the
semiconductor wafer W to a transfer robot (not shown).
[0180] When the retainer ring guide 815 is brought into contact
with the lower surface of the ring member 708 (see FIGS. 27 and
29), the position of the retainer ring guide 815, which is
supported by the spring 830, is varied according to the amount of
wear of the ring member 708. Since the push stage 810 is fixed to
the first vertical shaft 821, the position of the push stage 810 is
continuously fixed. The controller 47 is operable to compare a
distance between the retainer ring guide 815 and the push stage
810, which is measured by the eddy-current sensor 840, with a
reference value (initial distance) to calculate the amount of wear
of the ring member 708 (the retainer ring 502). The amount of wear
of the ring member 708 (the retainer ring 502) may be calculated
from a variation of measured values of the eddy-current sensor 840
(movement distance of the push stage 810) when the push stage 810
is lifted in a state such that the retainer ring guide 815 is
brought into contact with the retainer ring 502. Specifically, data
representing interrelationship between variations of measured
values of the eddy-current sensor 840 and the amount of wear of the
ring member 708 may be stored in a storage device of the controller
47 and used to calculate the amount of wear of the ring member 708
based on a variation of measured values of the eddy-current sensor
840.
[0181] In a conventional polishing apparatus, an eddy-current
sensor is embedded in a polishing table, and a metal target is
embedded in a retainer ring. The position of the target is detected
by the eddy-current sensor to measure the amount of wear of the
retainer ring. In this case, however, since a polishing pad is
located between the eddy-current sensor and the target, it is
necessary to consider the amount of wear of the polishing pad.
Accordingly, it is difficult to accurately measure the amount of
wear of the retainer ring. In the above example, the eddy-current
sensor 840 can perform measurement without influences from the
polishing pad or other components. Accordingly, the amount of wear
of the ring member 708 can accurately be measured.
[0182] The amount of wear of the ring member 708 is measured when a
semiconductor wafer is loaded or unloaded. When the total amount of
wear of the ring member 708 reaches a predetermined value, the
controller 47 issues a signal to indicate that the ring member 708
should be replaced. The amount of wear for a polishing process or
sets of polishing processes is recorded in the storage device of
the controller 47 so that variation of the amount of wear can be
monitored by the controller 47. If the amount of wear for a
polishing process or sets of polishing processes exceeds a
predetermined threshold value, then the controller 47 determines
that the polishing process is not normally performed. This
operation will be described below.
[0183] The amount of wear of the ring member 708 depends on various
factors including a pressing force applied to the ring member 708
(a pressure in the pressure chamber 710), concentrations of
principal components contained in a polishing liquid, a
concentration of abrasive particles in the polishing liquid, and a
flow rate of the polishing liquid. The amount of wear of the ring
member 708 (retainer ring 502) for a polishing process is
substantially constant unless these factors are changed.
Accordingly, when the amount of wear of the ring member 708 for a
polishing process exceeds a predetermined threshold value, it can
be seen that the polishing process has not been performed normally.
In this case, for example, when a pressure in the pressure chamber
710 and a flow rate of a polishing liquid are maintained at
predetermined values, it can be presumed that the components of the
polishing liquid or the concentration of the abrasive particles is
incorrect. Thus, with use of a plurality of sensors, it is possible
to specify causes of an abnormal polishing process.
[0184] Further, correlations between the amount of wear of the ring
member 708 and a polishing profile of a semiconductor wafer may be
stored as polishing characteristic data (correlation data) in the
storage device of the controller 47. Pressing forces of the ring
member 708 can be controlled during polishing based on the
correlation data by the controller 47. For example, in a case where
the amount of wear of the ring member 708 for a polishing process
is reduced, even if the ring member 708 is pressed against the
polishing pad 22 under the same pressing force as ever, a
sufficient pressure is not applied to the polishing pad 22 because
the total amount of wear of the ring member 708 is increased. In
such a case, it is desirable that the controller 47 corrects the
pressing force of the ring member 708 based on the correlation data
so as to prolong a lifetime of the ring member 708.
[0185] Further, a polishing simulation may be performed before a
polishing process is started. In this case, a suitable polishing
profile can be obtained by adjusting a pressing force of the ring
member 708 and inner pressures of the central chamber 660, the
ripple chamber 661, the outer chamber 662, and the edge chamber 663
based on data of results of the simulation and a desired polishing
profile.
[0186] Instead of the amount of wear of the ring member 708,
variation of wear of the polishing pad 22 may be monitored to
determine whether a polishing process is performed normally.
Specifically, the amount of wear of the polishing pad 22 for a
polishing process is substantially constant unless polishing
conditions such as a flow rate of the polishing liquid are changed.
Accordingly, variation of the polishing conditions may be detected
by monitoring variation of the amount of wear of the polishing pad
22. In this case, when the amount of wear of the polishing pad 22
for a polishing process or sets of polishing processes exceeds a
predetermined threshold value (e.g., a predetermined first
threshold value), it is determined that the polishing process has
not been performed normally. Further, recipes such as polishing
conditions including a rotational speed of the top ring 20 and a
pressing force of the ring member 708 may previously be prepared
according to the amount of wear of the ring member 708. The recipes
may be changed in response to a signal from the controller 47. In
such a case, it is possible to prolong a lifetime of the ring
member 708.
[0187] The dresser 50 shown in FIG. 14 brings needle diamond
particles, which are attached to the lower surface of the dresser
50, into sliding contact with the polishing pad 22 to remove a
portion of the polishing surface 22a. Accordingly, the diamond
particles are gradually worn out. If the diamond particles are worn
out to a certain extent, desirable surface roughness of the
polishing surface 22a cannot be obtained. As a result, the amount
of abrasive particles held on the polishing surface 22a is reduced,
so that a polishing process cannot be performed normally. In the
present embodiment, the amount of wear of diamond particles is
measured by the following method.
[0188] The amount of polishing pad 22 removed per unit time by the
dresser 50, which is hereinafter referred to as a cut rate, depends
on a pressing force under which the dresser 50 is pressed against
the polishing surface 22a and shapes of diamond particles.
Accordingly, a cut rate is reduced as the diamond particles are
worn out under conditions in which the dresser 50 is pressed under
a constant pressing force. In the present embodiment, a cut rate
(i.e., a displacement of the polishing surface 22a per unit time)
is measured by the aforementioned displacement sensor 60.
[0189] In the controller 47, a cut rate, i.e., a displacement of
the polishing surface 22a per unit time (the amount of wear of the
polishing pad 22) is calculated based on an output signal (measured
value) from the displacement sensor 60. Data representing
correlation between a cut rate and the amount of wear of the
dresser 50 (i.e., diamond particles) is previously inputted into
the controller 47. Then, the controller 47 calculates the amount of
wear of the dresser 50 from the data. When the total amount of wear
of the dresser 50 reaches a predetermined value, the controller 47
issues a signal to indicate that the dresser 50 should be replaced.
Thus, the displacement sensor 60 also serves as a dresser wear
detector to detect wear of the dresser 50.
[0190] As described above, when the diamond particles are worn out,
the amount of abrasive particles held on the polishing surface 22a
is reduced. Accordingly, it is presumed that the amount of wear
(removal) of the retainer ring 502 (ring member 708) for a
polishing process is also reduced. If the amount of wear of the
retainer ring 502 for a polishing process or sets of polishing
processes is lower than a predetermined threshold value (e.g., a
predetermined second threshold value), the controller 47 can
determine that the polishing process is not normally performed.
[0191] An operational recipe of the dresser 50 (dressing conditions
such as a dressing time, a rotational speed of the dresser 50, and
a pressing force to press the dresser 50 against the polishing pad
22) may be changed by the controller 47 according to the amount of
wear of the dresser 50.
[0192] As described above, a time-varied amount of wear is detected
while the amount of wear of worn-out components such as the ring
member 708, the polishing pad 22, and the dresser 50 is detected.
Accordingly, the following effects can be achieved.
[0193] 1) A lifetime of respective worn-out components can be
detected and prolonged. Timing of replacement of the worn-out
components can be detected and predicted.
[0194] 2) Polishing conditions including pressing conditions of the
worn-out components, internal pressures of the pressure chambers in
the top ring, conditions of the polishing liquid (temperature, pH,
and the like), a rotational speed of the top ring, a rotational
speed of the polishing table, and a relative speed between the
substrate and the polishing pad can suitably be controlled by
accumulated correlation data representing correlation between the
amount of wear of the worn-out components and a polishing
profile.
[0195] 3) Anomaly of a polishing process can be detected.
[0196] FIG. 30 is a schematic view showing a top ring 1020 in a
polishing apparatus according to a sixth embodiment of the present
invention. As shown in FIG. 30, the top ring 1020 has a retainer
ring 1302 including an upper ring member 1408a and a lower ring
member 1408b. FIG. 31 is an enlarged view of the upper ring member
1408a and the lower ring member 1408b. As shown in FIG. 31, the
lower ring member 1408b has a lower surface 1400 which is brought
into contact with the polishing surface 22a and an upper tapered
surface 1401. The upper ring member 1408a has a lower tapered
surface 1402 which is brought into contact with the upper tapered
surface 1401 of the lower ring member 1408b.
[0197] The retainer ring 1302, which is vertically movable, is
configured to be slightly movable in a radial direction of the
retainer ring 1302. Frictional forces produced between the retainer
ring 1302 and the polishing surface 22a and radial forces to hold
the substrate W are applied to the retainer ring 1302 during
polishing. Accordingly, the retainer ring 1302 is eccentrically
located downstream in a rotation direction of the polishing table
22 during polishing. In the present embodiment, as shown in FIGS.
30 and 31, the upper ring member 1408a and the lower ring member
1408b are brought into contact with each other on the tapered
surfaces 1402 and 1401 to convert a radial force F.sub.R applied to
the retainer ring 1302 into a downward force F.sub.D.
[0198] Thus, in the present embodiment, the upper ring member 1408a
having the tapered surface 1402 and the lower ring member 1408b
having the tapered surface 1401 serve as a pressure control
mechanism for producing a non-uniform pressure distribution along a
circumferential direction of the retainer ring 1302. Particularly,
pressing forces under which the retainer ring 1302 presses the
polishing pad 22 are controlled so that portions located downstream
in the rotation direction of the polishing table 12 are pressed
under pressures higher than portions located upstream in the
rotation direction of the polishing table 12. A roller may be
provided between the tapered surface 1401 and the tapered surface
1402 to smoothly produce a downward force.
[0199] FIG. 32 is a partial enlarged view showing a top ring in a
polishing apparatus according to a seventh embodiment of the
present invention. As shown in FIG. 32, the top ring has a retainer
ring 2302 into which the retainer ring 502 shown in FIG. 15 and the
retainer ring 1302 in the sixth embodiment are combined.
Specifically, the retainer ring 2302 has a ring member 2408 divided
into an upper ring member 2408a which is brought into contact with
the piston 706 and a lower ring member 2408b which is brought into
contact with the polishing surface 22a. The lower ring member 2408b
has a lower surface which is brought into contact with the
polishing surface 22a and an upper tapered surface 2401. The upper
ring member 2408a has a lower tapered surface 2402 which is brought
into contact with the tapered surface 2401 of the lower ring member
2408b. The retainer ring 1302 has a plurality of pressure chambers
710 divided along a circumferential direction of the retainer ring
1302.
[0200] In the present embodiment, since a pressure control
mechanism is formed by the upper ring member 2408a and the lower
ring member 2408b of the retainer ring 2302, it is not necessary to
provide a plurality of pressure chambers 710. Nevertheless, a
plurality of pressure chambers 710 may be provided in the retainer
ring 2302.
[0201] Since the pressure chambers 710 are located above the upper
ring member 2408a, the pressure chambers 710 absorb downward forces
produced by contact of the tapered surfaces 2402 and 2401 unless
vertical movement of the upper ring member 2408a is restricted. In
such a case, forces larger than those applied by the pressure
chambers 710 are not applied to the ring member 2408. Accordingly,
in the present embodiment, a restriction member 2800 is provided on
an inner circumferential surface of the cylinder 700. The
restriction member 2800 is brought into contact with the upper ring
member 2408a to restrict vertical movement of the upper ring member
2408a. For example, the restriction member 2800 may be made of
rubber having a large coefficient of friction.
[0202] With such a restriction member 2800, it is possible to
prevent the upper ring member 2408a from being lifted downstream in
the rotation direction of the polishing table 22. Accordingly,
forces produced by contact of the tapered surfaces 2402 and 2401
can be increased so as to be larger than forces produced by the
pressure chambers 710. Thus, pressing forces of the retainer ring
2302 can positively be increased at positions downstream in the
rotation direction of the polishing table 22. As with the sixth
embodiment, a roller may be provided between the tapered surface
2401 and the tapered surface 2402.
[0203] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
INDUSTRIAL APPLICABILITY
[0204] The present invention is suitable for use in a polishing
apparatus for polishing a substrate such as a semiconductor wafer
to a flat mirror finish.
* * * * *