U.S. patent application number 09/859641 was filed with the patent office on 2001-10-25 for polishing apparatus.
Invention is credited to Kozuki, Takaaki, Ootorii, Hiizu, Sato, Shuzo.
Application Number | 20010034186 09/859641 |
Document ID | / |
Family ID | 16841500 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010034186 |
Kind Code |
A1 |
Sato, Shuzo ; et
al. |
October 25, 2001 |
Polishing apparatus
Abstract
A polishing wheel is pushed up and down in the Z-axis direction
owing to a wafer surface shape. And the polishing amount depends on
the height of protrusions on a wafer surface. Where a spindle is a
rigid body in the Z-axis direction, the pressing force of the
polishing wheel caused by vertical movement of a tool varies
depending on the position on a wafer and hence polishing is not
performed uniformly To solve this problem, the spindle is provided
with a Z-axis parallel leaf spring mechanism. Push-up and push-down
actions of the polishing wheel are absorbed by displacement of the
parallel leaf spring mechanism. This enables uniform polishing.
Since the tool can be hardened, the flatness can also be
improved.
Inventors: |
Sato, Shuzo; (Kanagawa,
JP) ; Ootorii, Hiizu; (Tokyo, JP) ; Kozuki,
Takaaki; (Kanagawa, JP) |
Correspondence
Address: |
RADER FISHMAN & GRAUER PLLC
LION BUILDING
1233 20TH STREET N.W., SUITE 501
WASHINGTON
DC
20036
US
|
Family ID: |
16841500 |
Appl. No.: |
09/859641 |
Filed: |
May 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09859641 |
May 18, 2001 |
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09370225 |
Aug 9, 1999 |
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6280292 |
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Current U.S.
Class: |
451/9 |
Current CPC
Class: |
B24B 37/04 20130101;
B24B 41/042 20130101; B24B 49/16 20130101; B23Q 11/0032
20130101 |
Class at
Publication: |
451/9 |
International
Class: |
B24B 007/22 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 1998 |
JP |
P10-226202 |
Claims
What ts claimed is:
1. A polishing apparatus for polishing and finishing a
thin-plate-like object so that the object is made flat and uniform
in height by pressing the object being in contact with a surface of
a table that is provided parallel with a horizontal surface by
means of a polishing wheel that is opposed to the object,
comprising: a displacing mechanism section for displacing a support
side of the polishing wheel or the object in accordance with
working pressure; or a rotation speed correction mechanism section
for varying a relative rotation speed between the polishing wheel
and the object in accordance with the working pressure.
2. The polishing apparatus according to claim 1, further comprising
a Z-axis slide for supporting the polishing wheel so that the
polishing wheel is slidable in a Z-axis direction and a feed shaft
for feeding the polishing wheel in the Z-direction, wherein the
displacing mechanism section is a Z-axis parallel leaf spring
mechanism that is interposed between the Z-axis slide and the feed
shaft.
3. The polishing apparatus according to claim 1, wherein the
displacing mechanism section is a spindle slide mechanism that is
interposed between a spindle of the polishing wheel and a Z-axis
slide for supporting the spindle and that supports the spindle so
that it is inclined in an X-axis direction and is free or given
arbitrary elasticity in a Y-axis direction.
4. The polishing apparatus according to claim 1, wherein the
displacing mechanism section is a table damper mechanism for
supporting, elasto-plastically or by air pressure, the table that
is mounted with the object.
5. The polishing apparatus according to claim 1, wherein the
displacing mechanism section is a tilting table mechanism for
detecting a signal representing rotation torque of a spindle of the
polishing wheel and adjusting a height, in a Z-axis direction, of
the table that supports the object mounted thereon in accordance
with a detection value of the rotation torque signal, thereby
uniformizing the rotation torque.
6. The polishing apparatus according to claim 1, wherein the
rotation speed correction mechanism section is a table rotation
speed correction mechanism section for detecting a signal
representing rotation torque of a spindle of the polishing wheel
and adjusting a rotation speed of the table that supports the
object mounted thereon in accordance with a detection value of the
rotation torque signal, thereby uniformizing the rotation
torque.
7. A polishing apparatus in which a pad is stuck to a rotary table
that is provided parallel with a horizontal surface, an object that
is opposed to the pad is pressed against a pad side while rotating
the object, and a pad conditioner is provided that is in contact
with the pad, comprising: detecting means provided on an object
side and a pad conditioner side, for detecting a displacement of
the pad in a Z-direction; and swing units for adjusting inclination
angles from a Z-axis on the object side and the pad conditioner
side based on detection signals that are output from the detecting
means, respectively.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing apparatus for
polishing and finishing a thin-plate-like object such as a
semiconductor wafer or a glass plate for an LCD so that its surface
will be made flat and uniform in height.
[0003] 2. Description of the Related Art
[0004] FIGS. 1 and 2 show conventional polishing apparatuses for
polishing a thin-plate-like object such as a wafer. The polishing
apparatus 1 shown in FIG. 1 is composed of a table 3 that supports
a wafer 2 mounted thereon and can rotationally drive it, a
polishing wheel 5 supported by a spindle 4, and other parts. The
table 3 can be rotated in the horizontal plane by an X-axis slide 6
incorporating a rotational driving section as well as moved in the
X-axis direction by an X-axis slide mechanism section 7.
[0005] The X-axis slide mechanism section 7 is composed of an
X-axis ball-thread nut 8 that is fixed to the X-axis slide 6, an
X-axis ball-thread screw 9 that is threadedly engaged with the
X-axis ball-thread nut 8, an X-axis servo motor 10 for driving the
X-axis ball screw 9, and other parts. On the other hand, the
polishing wheel 5 is opposed to the table 3 and rotated in the
horizontal plane. A Z-axis slide 12 is fixed to the spindle 4 and
supported by a Z-axis guide so as to be slidable in the Z-axis
direction.
[0006] With the above configuration, the wafer 2 that is mounted on
the table 3 is polished by rotating the table 3 and the polishing
wheel 5 while pressing the polishing wheel 5 against the wafer 2.
The entire surface of the wafer 2 is polishing by moving the table
3 in the X-direction with the X-axis slide mechanism section 7.
[0007] On the other hand, in the polishing apparatus la shown in
FIG. 2, a pad 15 is fixed to the top surface of a surface table
(rotary table) 14 that is rotationally driven and a wafer 2 is
absorbed and fixed on a polishing head 16 via an absorption film
17. The wafer 2 is polished by rotating it while pressing it
against the pad 15 by means of a cylinder 18. To prevent scattering
of an abrasive 20 or a polishing powder, the wafer 2 is enclosed by
a retainer ring 19. A pad conditioner 21 for correcting roughening
of the pad 15 is pressed against the pad 15. The wafer 2 is
polished and finished by rotating the pad 15 together with the
surface table 14 and rotating the wafer 2.
[0008] As shown in FIG. 3(A), the surface of a wafer 2 is not flat
and is formed with many protrusions 22. To make the surface of the
wafer 2 flat and uniform in height, it is necessary to flatten the
protrusions 22. Conventionally, a static polishing/planarization
method shown in FIG. 3(B) and a dynamic polishing/planarization
method shown in FIG. 3(C) are employed as measures for removing the
protrusions 22. In the former method, the protrusions 22 are
removed by using a polishing pad 23 formed by bonding soft and hard
pads together. In the latter method, the protrusions 22 are removed
by adjusting the pressing force exerted on the protrusions 22 by
utilizing the frequency characteristic of an elastic tool. The
object of the polishing/planarization (CMP) is to flatten and
uniformize the height of the surface of the wafer 2. In general,
the flatness is represented by the difference A-B between height A
of the highest point and height B of the lowest point of the
protrusions 22 as measured from the base surface. On the other
hand, the height uniformity is a percent value obtained by dividing
dispersion of the polishing amount in the wafer 2 by an average
polishing amount over the entire surface. As shown in FIG. 4,
polishing/planarization is performed by removing the protrusions 22
while leaving large undulation of the entire surface of the wafer
2.
[0009] FIGS. 5(A)-5(D) show typical ones of various shapes of
polishing subject surfaces of wafers 2. FIG. 5(A)-5(D) show a taper
type, a sphere type, a chips type, and a twist type, respectively.
Naturally, there are composite types of those.
[0010] To polish the surface of a wafer 2, a polishing wheel or the
like is pressed against the surface of the wafer 2. In this case,
uniform polishing can be attained more easily when the pressing
force is constant.
[0011] When the surface of a wafer 2 is not flat as in the cases of
FIGS. 5(A)-5(D), there occurs an action that the polishing is
approximately in proportion to a push-up length or a push-down
length.
[0012] The push-up length and the push-down length are relatively
short in the cases of FIGS. 5(B)-5(D). On the other hand, in the
case of FIG. 5(A) the push-up length in a central portion is much
different from that in a peripheral portion. This causes a
difference between the degree of removal of the protrusions 22 in
the central portion of the wafer 2 and that in the peripheral
portion. In this case, it is particularly difficult to obtain a
polished surface that is flat and uniform in height.
[0013] On the other hand, as shown in FIG. 7, a deviation in
parallelism exists between a polishing axis 24 and a pad axis 25
and there is a squareness deviation of about {fraction (1/2,000)}
in the circumferential direction. Therefore, a wafer 2 and a pad 15
do not contact each other uniformly, which is one factor of
lowering the height uniformity in the surface of the wafer 2.
Further, in this state, the flatness of the pad 15 is lowered
faster and hence the pad 15 needs to be replaced more
frequently.
[0014] For example, Japanese Unexamined Patent Publication Nos.
Hei. 10-29153 and Hei. 10-73420 disclose polishing apparatuses for
polishing a wafer to obtain a flat surface. In the publication No.
Hei. 10-29153 entitled "Semiconductor Wafer Polishing Apparatus,"
an air room is provided behind a wafer holding plate for holding a
semiconductor wafer and prescribed pressing force is applied to the
wafer holding plate uniformly by controlling the inner pressure of
the air room. In the publication No. Hei. 10-73420 entitled
"Surface Shape Measuring Apparatus and Polishing Apparatus Using
It," an object is polished in such a manner that its inclination is
adjusted while its surface shape with respect to a reference glass
plate is detected.
[0015] Although the above conventional techniques are effective for
planarization of a wafer, the former technique is macroscopic and
cannot obtain a sufficient level of flatness for a wafer having
protrusions of different heights at many locations. Although the
latter technique employs a piezoelectric element as a surface
adjusting means, it cannot obtain a sufficient level of flatness
for a wafer having a surface shape as shown in FIG. 5(A). Further,
since the adjusting means of this technique is not so specific and
close as that of the invention as described in this specification,
this technique cannot provide sufficient levels of flatness and
height uniformity.
SUMMARY OF THE INVENTION
[0016] The present invention has been made in view of the above
circumstances in the art, and an object of the invention is
therefore to improve both of the flatness of a thin-plate-like
object and its height uniformity that is in tradeoff relationship
with the flatness, enable cost reduction through increase of the
polishing efficiency, dispense with a dummy pattern (an extra
wiring incorporated at the time of designing to compensate for
flatness defects) or the like, enable improvement of device
characteristics, increase of margins and freedom in designing,
etc., and elongate the life of a pad.
[0017] To attain the above object, the invention provides a
polishing apparatus for polishing and finishing a thin-plate-like
object so that the object is made flat and uniform in height by
pressing the object being in contact with a surface of a table that
is provided parallel with a horizontal surface by means of a
polishing wheel that is opposed to the object, comprising a
displacing mechanism section for displacing a support side of the
polishing wheel or the object in accordance with working pressure;
or a rotation speed correction mechanism section for varying a
relative rotation speed between the polishing wheel and the object
in accordance with the working pressure.
[0018] According to another aspect of the invention, there is
provided a polishing apparatus in which a pad is stuck to a rotary
table that is provided parallel with a horizontal surface, an
object that is opposed to the pad is pressed against a pad side
while rotating the object, and a pad conditioner is provided that
is in contact with the pad, comprising detecting means provided on
an object side and a pad conditioner side, for detecting a
displacement of the pad in a Z-direction; and swing units for
adjusting inclination angles from a Z-axis on the object side and
the pad conditioner side based on detection signals that are output
from the detecting means, respectively.
[0019] The object side or the side of the polishing wheel for
polishing the object is displaced through action of the displacing
mechanism section or the rotation speed correction mechanism
section that operates in accordance with the working pressure that
varies in accordance with protrusions of the object, to uniformize
the working pressure. Since the working pressure is uniformized,
the height uniformity of the object is improved. This makes it
possible to harden the polishing wheel side, thereby improving the
flatness.
[0020] By adjusting the inclination angle of the polishing wheel
side with respect to the object, the object and the polishing side
can be made parallel with each other, making it possible to improve
the flatness and the height uniformity.
[0021] Because of its relatively simple configuration, the
polishing apparatus of the invention can be implemented at a
relatively low cost. Further, since high-speed polishing is
enabled, the productivity can be increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a front view outlining the configuration of a
conventional polishing apparatus;
[0023] FIG. 2 is a front view outlining the configuration of
another conventional polishing apparatus having a pad and a pad
conditioner;
[0024] FIGS. 3(A)-3(C) schematically show a surface shape of a
wafer and methods for polishing it;
[0025] FIG. 4 schematically shows a manner of wafer polishing;
[0026] FIGS. 5(A)-5(D) are front views and side views showing
various surface shapes of wafers;
[0027] FIG. 6 is a front view and a side view showing how a tool is
pushed up in a wafer having a slant surface;
[0028] FIG. 7 schematically shows a deviation in parallelism
between the axes of a pad and a polishing wheel;
[0029] FIGS. 8(A) and 8(B) are partial front and side views,
respectively, showing a Z-axis parallel leaf spring mechanism of a
polishing apparatus according to the present invention;
[0030] FIG. 9 is a graph showing a relationship between the Z-axis
push length and the amount of removal by working;
[0031] FIGS. 10(A) and 10(B) are front and side views,
respectively, showing a spindle slide mechanism of a polishing
apparatus according to the invention;
[0032] FIGS. 11(A) is a plan view showing an arrangement of coil
springs interposed between a flange of a spindle and a Z-axis slide
of the spindle slide mechanism of FIGS. 10(A) and 10(B);
[0033] FIG. 11(B) is a partial enlarged view showing a detailed
structure of each coil spring shown in FIG. 10(A) and its
vicinity;
[0034] FIGS. 12(A) and 12(B) are front and side views,
respectively, showing an engagement state between a wafer and a
polishing wheel provided with the spindle slide mechanism of FIGS.
10(A) and 10(B);
[0035] FIGS. 13(A) and 13(B) are side and front views,
respectively, showing an engagement state between a wafer and the
polishing wheel provided with the spindle slide mechanism o f FIGS.
10(A) and 10(B);
[0036] FIG. 14 is a sectional view showing a table damper mechanism
of a polishing apparatus according to the invention;
[0037] FIGS. 15(A) and 15(B) are sectional views showing another
table damper mechanism of a polishing apparatus according to the
invention;
[0038] FIG. 16 is a sectional view showing a further table damper
mechanism of a polishing apparatus according to the invention;
[0039] FIG. 17 is a plan view showing an arrangement of actuators
of a tilting table mechanism of a polishing apparatus according to
the invention;
[0040] FIG. 18 is a sectional view taken so as to include the axis
and shows a detailed structure of the tilting table mechanism of
the polishing apparatus of the invention;
[0041] FIG. 19 is a graph showing a relationship between the
cylinder supply pressure and the displacement adjusting force in
the tilting table mechanism;
[0042] FIG. 20 is a graph showing a relationship between the
cylinder supply pressure and the stage displacement in the tilting
table mechanism;
[0043] FIG. 21 shows the configurations of control and detection
systems in a polishing apparatus having the tilting table
mechanism;
[0044] FIG. 22 are a plan view and a side view showing an
engagement state between a polishing wheel and a wafer in the
polishing apparatus having the tilting table mechanism;
[0045] FIG. 23 is a graph showing a relationship between the
cutting length and the spindle load output of the polishing
apparatus having the tilting table mechanism;
[0046] FIG. 24 is an operation chart showing a control method in
the polishing apparatus having the tilting table mechanism;
[0047] FIG. 25 is a schematic circuit diagram showing a signal
processing method in the polishing apparatus having the tilting
table mechanism;
[0048] FIG. 26 is a flowchart showing a control method in the
polishing apparatus having the tilting table mechanism;
[0049] FIG. 27 is a graph showing relationships between the
correction time and the residual TTV in the polishing apparatus
having the tilting table mechanism;
[0050] FIG. 28 is a plan view and a side view showing a function of
a rotation speed correction mechanism section of a polishing
apparatus according to the invention;
[0051] FIG. 29 is a graph showing spindle loads that occur when
portion A and portion B shown in FIG. 28 are polished;
[0052] FIGS. 30(A) and 30(B) are graphs showing relationships
between the polishing amount and the polishing speed in the
polishing apparatus having the rotation speed correction mechanism
section;
[0053] FIG. 31 is a front view showing a means for improving the
uniformity of wafer polishing in a polishing apparatus using a pad
and a pad conditioner;
[0054] FIG. 32 is a front view showing another means for improving
the uniformity of wafer polishing in a polishing apparatus using a
pad and a pad conditioner; and
[0055] FIG. 33 is a graph showing polishing results of the
polishing apparatuses of FIGS. 31 and 32.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0056] Embodiments of a polishing apparatus according to the
present invention will be hereinafter described in detail with
reference to the accompanying drawings. First, a description will
be made of height uniformization and planarization of a wafer 2 in
the polishing apparatus shown in FIG. 1. As described above, the
polishing subject surface of the wafer 2 has inclinations and
protrusions 22 (see FIG. 3(A)) and hence the working pressure
varies as the polishing proceeds. In the case of the wafer 2 shown
in FIG. 5(A), because of a large push-up length etc. the
protrusions 22 are not polished uniformly. It is necessary to vary
the height of the polishing wheel 5 in accordance with the push-up
length, and various displacing mechanism sections are employed for
this purpose.
[0057] Specific embodiments of the displacing mechanism section
according to the invention will be described below, which are a
Z-axis parallel leaf spring mechanism 26 shown in FIGS. 8(A) and
8(B) etc., spindle slide mechanism 27 shown in FIGS. 10(A) and
10(B) etc., a table damper mechanism shown in FIG. 14 etc., and a
tilting table mechanism 29 shown in FIG. 18 etc.
[0058] First, the Z-axis parallel leaf spring mechanism 26 will be
described. As shown in FIGS. 8(A) and 8(B), the spindle 4 of a
polishing wheel 5 is supported by a Z-axis slide 12, which is
supported by a Z-axis guide 13 so as to be slidable in the Z-axis
direction along the Z-axis guide 13. A Z-axis ball-thread screw 30
is provided in the vicinity of the Z-axis guide 13, and a
ball-thread nut 31 is threadedly engaged with the Z-axis
ball-thread screw 30. The Z-axis ball-thread screw 30 is driven by
a Z-axis servo motor 32.
[0059] The Z-axis parallel leaf spring mechanism 26 of the
invention is composed of parallel leaf springs 33 and 34 that are
suspended between the Z-axis guide 13 and the Z-axis ball-thread
screw 30, props 35 that are interposed between the parallel leaf
springs 33 and 34, and other parts. Specifically, the parallel leaf
spring 34 is fixed to the ball-thread nut 31 and the parallel leaf
spring 33 is fixed to the Z-axis guide 13. Displacement in the
Z-axis direction of the polishing wheel 5 is absorbed by bends of
the parallel leaf springs 33 and 34 that are supported by the props
35. The stiffness of the Z-axis parallel leaf spring mechanism 26
can easily be changed by changing the length of the props 35. For
example, the props 35 are shortened to increase the stiffness value
(i.e., to make the mechanism 26 stiffer) and elongated to decrease
the stiffness value (i.e., to make the mechanism 26 weaker).
[0060] As shown in FIG. 9, the Z-axis push length (.mu.m;
horizontal axis) is in proportion to the amount of removal by
polishing (.ANG.; vertical axis). Straight line {circle over (1)}
corresponds to a case where the Z-axis parallel leaf spring
mechanism 26 is not used. Straight line {circle over (2)}, which
corresponds to a case where the mechanism 26 is used, has a gentler
slope than straight line {circle over (1)}. That is, by
constructing the Z-axis parallel leaf spring mechanism 26 so that
its stiffness in the Z-axis direction follows straight line {circle
over (2)}, the protrusions 22 can be polished while the push-up
length depending on the surface shape of the wafer 2 is absorbed,
whereby the uniformity of polishing can be improved.
[0061] FIGS. 10(A) and 10(B) show a spindle slide mechanism 27. In
this embodiment, shims 37 and 38 are interposed between a flange 36
of a spindle 4 and a Z-axis slide 12, whereby the spindle 4 is
inclined in the X-axis direction as shown in FIG. 10(B). Further,
as shown in FIGS. 11(A) and 11(B), coil springs 39 are interposed
between the flange 36 and the Z-axis slide 12. The coil springs 39
may be omitted. As shown in FIG. 10(B), the shim 37 is taller than
the shim 38 and hence the spindle 4 is inclined in such a manner
that its left-hand side in the X-direction (see FIG. 10(B)) is
lower than its right-hand side. In this manner, the spindle 4 is
fixed in the X-direction.
[0062] On the other hand, as shown in FIG. 11(A), a plurality of
coil springs 39 are provided at regular intervals on the flange 36
of the spindle 4. The coil springs 39 are guided by respective rods
40. With the above structures, the spindle 4 is fixedly supported
in the X-direction and elastically supported in the Y-direction. If
the coil springs 39 are not provided, the spindle 4 is rendered
free in the Y-direction. As a specific example, where the TTV
(thickness dispersion) of the wafer 2 is about 5 .mu.m, the
inclination shown in FIG. 10(B) is set at 20-200 .mu.m.
[0063] When the surface of the wafer 2 is inclined in the X-axis
direction as shown in FIGS. 12(A) and 12(B), a push-up length in
the Z-axis direction can be absorbed even by the above-described
Z-axis parallel leaf spring mechanism 26, that is, even without
using the spindle slide mechanism 27 of this embodiment. When the
surface of the wafer 2 is inclined in the Y-axis direction as shown
in FIGS. 13(A) and 13(B), the use of the spindle slide mechanism 27
of this embodiment allows the spindle 4 to be supported freely or
elastically in the Y-axis direction. As a result, not influenced by
the inclination of the surface of the wafer 2, the polishing
apparatus can perform uniform polishing.
[0064] FIGS. 14-16 show table damper mechanisms 28, 28a, and 28b.
This type of mechanism is applied to a structure in which a wafer 2
is absorbed on and supported by a wafer chuck 41 made of highly
rigid ceramics or the like. The wafer 2 is polished in such a
manner that a polishing wheel 5 is rotated and moved in the
X-direction, for example, while being pressed against the top
surface of the wafer 2. Springs 43 as the table damper mechanism 28
are interposed between the bottom surface of the wafer chuck 41 and
a reference surface 42. The push-up length can be absorbed by the
above-described structure. Having a small plastic deformation
amount, the springs 43 can generate working pressure that is
approximately in proportion to the deformation amount of the
springs 43 that depends on the push length in the Z-direction. The
working amount can thus be controlled correctly.
[0065] In the table damper mechanism 28a of FIGS. 15(A) and 15(B),
a rubber member 44 is used instead of the above springs 43. Being
an elasto-plastic body, rubber has a feature that it generates
constant pressure irrespective of its deformation amount when used
under such pressure as to be deformed more than a certain limit. To
utilize this phenomenon, the wafer chuck 41 is supported via the
rubber member 44 that is pre-pressed to a certain extent. The
polishing apparatus of this embodiment has a feature that if the
rubber member 44 is pressed in the Z-axis direction by more than a
certain length, no pressure difference is generated even when
displacement due to wafer thickness dispersion occurs and hence a
constant working amount can be obtained.
[0066] The rubber member 44 is made of NBR, silicone rubber,
urethane rubber, or the like. As for the shape of the rubber member
44, it may be a solid member (see FIG. 15(A)), an O-ring (see FIG.
15(B)), a ring-like sheet (not shown), a perforated sheet (not
shown), divided sheets (now shown), etc. The stiffness (i.e., the
pressing force vs. displacement characteristic) can be adjusted to
an arbitrary value also in consideration of the thickness.
[0067] The table damper mechanism 28b of FIG. 16 is of such a type
as to be supported by air pressure of a chuck. Having no dispersion
relating to the materials of parts, this type of table damper
mechanism makes it possible to easily manufacture and duplicate
polishing apparatuses that behave in a manner as designed. Since
the working amount is determined by the air pressure irrespective
of the push length in the Z-direction, this type of table damper
mechanism enables complete constant-pressure working.
[0068] FIGS. 17, 18, etc. show a tilting table mechanism 29. In
this mechanism, a rotation torque signal of the spindle 4 is
detected and the amount of removal by working is uniformized by
making corrections to obtain constant torque, that is, by
decreasing the height of a wafer chuck 41 that absorbs and supports
a wafer 2 at a portion where the torque would otherwise be large
and increasing the height of the wafer chuck 41 at a portion where
the torque would otherwise be small. As shown in FIG. 17; this
mechanism has actuators 29a that are provided at a plurality of
positions (three positions in FIG. 17) that equally divide a circle
that is concentric with the circumference of the wafer chuck
41.
[0069] As shown in FIG. 18, the wafer chuck 41 that absorbs and
supports a wafer 2 (not shown) is supported by an X-axis slide 6
(see FIG. 1) via a table shaft 45. A rotary joint 46, which is
provided inside the table shaft 45, supplies pressure oil to a
tilting table mechanism 29 that is provided inside the wafer chuck
41.
[0070] Each actuator 29a of the tilting table mechanism 29 is
composed of a cylinder 47, a piston 48, a bolt 49 that is fixed to
the piston 48 and the wafer chuck 41, and other parts. Pressure
that is supplied to the cylinder 47 moves the piston 48 and
displaces the bolt 49 in the axial direction. This axial
displacement varies the height of the top surface of the wafer
chuck 41. The pressure that is supplied to the cylinder 47 is
controlled by external electropneumatic regulators via the rotary
joint 46.
[0071] FIG. 19 shows a relationship between the cylinder supply
pressure and the displacement adjusting force. Displacement
adjusting force corresponding to a pressure of 0.1 MPa is about
1,000 N, which is considerably strong. Therefore, the wafer chuck
41 is not displaced when a working load of about 500 N is applied
to it. FIG. 20 shows a relationship between the cylinder supply
pressure and the displacement of the stage (surface) of the wafer
chuck 41.
[0072] FIG. 21 shows the entire configuration of a polishing
apparatus having the actuators 29a of the tilting table mechanism
29 of this embodiment and its control and detection systems. As
described above, the wafer chuck 41 having the actuators 29a is
rotated by a table shaft motor 50 via a belt 51 and moved in the
X-axis direction via the X-axis slide 6. Slurry or pure water 53 is
supplied to a wafer 2 that is absorbed on and supported by the
wafer chuck 41 by means of a jetting nozzle 54 or the like. As
shown in FIG. 22, the wafer 2 is polished by rotation and pressing
of a polishing wheel 5. A working pan 52 is provided around the
wafer chuck 41 to prevent scattering of polishing powder, slurry,
or pure water.
[0073] An X-axis servo motor 10 and a Z-axis servo motor 32 are
connected to a CPU 58 via a motor driver 59 and controlled by the
CPU 58. The rotary joint 46 is connected to electropneumatic
regulators 55, which are controlled by the CPU 58. In this
embodiment, there are three electropneumatic regulator 55, that is,
electropneumatic regulator-1, -2, and -3 that control the actuators
29a of the tilting table mechanism 29 that are arranged on the
0.degree. axis, 120.degree. axis, and 240.degree. axis,
respectively.
[0074] An origin sensor 56, which is provided on the X-axis slide
6, detects the origin of the wafer chuck 41. The spindle 4 is
rotationally driven by a spindle torque motor 11, and the spindle
load is detected by the CPU 58 based on a torque signal that is
output from the spindle torque motor 11. FIG. 23 shows a
relationship between the cutting length (.mu.m) and the spindle
load output (mV). It is seen that the relationship is approximately
linear.
[0075] The point where the polishing wheel 5 that is descending
contacts the surface of the wafer 2 is made a zero point of
working. In practice, a spindle load output signal voltage is set
at the beginning in a state that the polishing wheel is located at
the lower limit point of a range where the wafer 2 is not worked,
and thereafter a point where the spindle load output signal voltage
is reached is employed as a zero point of working. Phase height
signals of the actuators 29a that adjust the wafer chuck 41 are
determined by averaging a spindle load output sampling signal over
the hatched regions having the 0.degree. axis, 120.degree. axis,
and 240.degree. axis of the wafer chuck 41 as the center lines.
FIG. 25 is a signal input/output diagram showing signal processing
that is performed by the polishing apparatus of FIG. 21.
[0076] Next, a control process will be described with reference to
FIGS. 24-26. First, resetting is performed and hysteresis is
eliminated. At this time, the regulator pressure of each
electropneumatic regulator 55 is zero.
[0077] Then, the polishing wheel 5 is caused to touch up the wafer
2. Then, a TTV judgement is performed; specifically, it is judged
whether a voltage variation width of a spindle load signal is
within a prescribed value. If the TTV judgment result is OK,
polishing is performed and finished.
[0078] On the other hand, if the TTV judgment result is NG, loads
of the 0.degree. axis, 120.degree. axis, and 240.degree. axis are
determined and a convergence judgment is performed. If the
convergence judgment result is OK, ordinary polishing is performed.
If it is NG, displacement-pressure conversion and pressure control
output are performed for each of the 0.degree. axis, 120.degree.
axis, and 240.degree. axis to cause the actuators 29a to operate.
This operation is repeated until the convergence judgment result
turns OK. FIG. 27 shows measurement results of actual
corrections.
[0079] Several embodiments of the displacing mechanism section have
been described above. A rotation speed correction mechanism section
will now be described. The top surface of a wafer 2 has a height
variation as shown in FIG. 28; portion A is high (the wafer 2 is
thick there) and portion B is low (the wafer 2 is thin there). As
shown in FIG. 29, when the polishing wheel 5 contacts portion A of
the wafer 2, the spindle load value becomes large. Conversely, when
the polishing wheel 5 contacts portion B, the spindle load value
becomes small.
[0080] FIGS. 30(A) and 30(B) are graphs showing relationships
between the radial positions on the wafer 2 (horizontal axis) and
the polishing amount (vertical axis). The rotation speed of the
polishing wheel 5 in the case of FIG. 30(B) is lower by about 20%
than that in the case of FIG. 30(A). As seen from FIGS. 30(A) and
30(B), the polishing amount decreases approximately in proportion
to the rotation speed. The dispersion of polishing amounts at the
respective points on the wafer 2 also decreases as the rotation
speed is decreased; the dispersion is 11.7% in the case of FIG.
30(A) and 3.8% in the case of FIG. 30(B). Based on these facts, the
rotation speed correction mechanism section has a control mechanism
for performing polishing in such a manner that the spindle load is
detected and the rotation speed is increased in a phase range where
the spindle load value is large and decreased in a phase range
where the spindle load value is small. A description of a specific
mechanism is omitted.
[0081] The height uniformity can be improved by using the above
displacing mechanism section and the rotation speed correction
mechanism section. The tool can be hardened so much more and hence
the flatness can be improved. Further, since the polishing is
performed smoothly, the polishing efficiency is increased, which
shortens the working time and reduces the cost of a product.
[0082] Next, a polishing apparatus according to an embodiment of
the invention corresponding to the polishing apparatus la shown in
FIG. 2 will be described with reference to FIGS. 31-33. The
polishing apparatus of this embodiment has generally the same
entire configuration as shown in FIG. 2. As described in the
background section in connection with FIG. 7, a slight deviation in
parallelism exists between the polishing axis 24 and the pad axis
25. The axis 60 (see FIG. 2) of the pad conditioner 21 and the pad
axis 25 also have a deviation in parallelism. If polishing is
performed in such a state, not only high-precision wafer working is
not expected but also a problem may occur that the pad surface is
damaged.
[0083] FIG. 31 shows a specific means for making adjustments to
correct such a deviation in parallelism (or squareness). The
polishing head 16 side and the pad conditioner 21 side are provided
with measuring devices 66 and 67 for measuring the surface shape of
the pad 15, respectively. On the other hand, arms 62 and 64 are
connected to the cylinder 18 of the polishing head 16 and the
cylinder 61 of the pad conditioner 21, respectively. Swing units 63
and 65 are connected to the respective arms 62 and 64.
[0084] The swing units 63 and 65 are so configured as to slightly
swing the arms 62 and 64 based on detection values of the surface
shape of the pad 15 that are output from the measuring devices 66
and 67, respectively. A description of their specific
configurations is omitted.
[0085] With the above configuration deviations in squareness of the
polishing axis 24 of the polishing head 16 and the axis 60 of the
conditioner 21 are corrected as shown in FIG. 31, whereby the wafer
2 and the pad conditioner 21 contact the pad 15 squarely.
[0086] FIG. 32 shows another embodiment. While in the embodiment of
FIG. 31 the arms 62 and 64 are swung, in this embodiment the arms
62 and 64 are fixed and the swing units 63 and 65 are swung. This
adjusting means can provide the same effect as in the embodiment of
FIG. 31. FIG. 33 shows a relationship between the rotation speed
(rpm; horizontal axis) of the polishing head 16 and the height
uniformity in the wafer surface (vertical axis). Marks
".circle-solid." correspond to a case where the adjusting means of
this embodiment is not used and marks ".box-solid." correspond to a
case where the adjusting means of this embodiment is used. It is
seen from FIG. 33 that the height uniformity is greatlv improved
for all rotation speed values of the polishing head 16. The
improvement in height uniformity is most remarkable at the highest
rotation speed value.
[0087] According to the invention, the height uniformity can be
improved and hence the production yield can be increased. The tool
can be hardened and hence the flatness can be improved. Since the
film forming thickness can be reduced, the working time can be
shortened, the error can be reduced, and the cost can be reduced.
Since a dummy pattern is no longer necessary, the device
characteristics can be improved. Further, margins and freedom of
designing can be increased. In the polishing apparatus using a pad
conditioner, the pad life can be elongated and hence the cost due
to consumption of pads can be reduced.
* * * * *