U.S. patent application number 09/895385 was filed with the patent office on 2002-02-14 for polishing method and apparatus, and device fabrication method.
Invention is credited to Kamono, Takashi.
Application Number | 20020019198 09/895385 |
Document ID | / |
Family ID | 18708114 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020019198 |
Kind Code |
A1 |
Kamono, Takashi |
February 14, 2002 |
Polishing method and apparatus, and device fabrication method
Abstract
The present invention concerns a polishing method of keeping a
polishing pad under a predetermined pressure and in contact with a
polished surface of a wafer and performing polishing while rotating
the wafer and the polishing pad, in which symmetry of a film on an
alignment mark for alignment of the wafer is measured after an end
of the polishing of the wafer or in the middle of the polishing and
in which polishing thereafter is carried out by controlling
rotation speeds of the wafer and polishing pad according to the
symmetry of the film on the alignment mark, thus measured, whereby
the film on the alignment mark of the wafer can be isotropically
polished in symmetry.
Inventors: |
Kamono, Takashi; (Tochigi,
JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
18708114 |
Appl. No.: |
09/895385 |
Filed: |
July 2, 2001 |
Current U.S.
Class: |
451/41 |
Current CPC
Class: |
B24B 37/005 20130101;
B24B 49/04 20130101; B24B 37/042 20130101; B24B 49/006
20130101 |
Class at
Publication: |
451/41 |
International
Class: |
B24B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2000 |
JP |
2000-212161 |
Claims
What is claimed is:
1. A polishing method comprising the steps of keeping a polishing
pad under a predetermined pressure and in a state of contact with a
device forming surface of a substrate and performing polishing
while rotating each of said substrate and said polishing pad,
wherein symmetry of a film on an alignment mark for alignment of
said substrate is measured after an end of the polishing of said
substrate or in the middle of the polishing and wherein a rotation
speed of at least either one of said substrate and said polishing
pad is controlled according to the symmetry of the film on the
alignment mark, thus measured.
2. The polishing method according to claim 1, wherein control is
implemented so as to change rotation speeds of said substrate and
said polishing pad and equate total numbers of rotations of said
substrate and said polishing pad from a start of the polishing to
the end of the polishing.
3. The polishing method according to claim 1, which comprises
setting a rotation speed of said substrate, a rotation speed of
said polishing pad, a polishing period, and a polishing pressure
and further setting a rotation speed switching time, performing
such calculation as to equate total numbers of rotations of said
substrate and said polishing pad from a start of the polishing to
the end of the polishing, based on these set rotation speed of said
substrate, rotation speed of said polishing pad, polishing period,
and rotation speed switching time, and driving said substrate and
said polishing pad at respective rotation speeds based on the
result of the calculation.
4. The polishing method according to claim 1, which comprises
storing a rotation speed switching time and either one or both of
rotation speeds of said substrate and said polishing pad and
performing such control as to equate total numbers of rotations of
said substrate and said polishing pad from a start of the polishing
to the end of the polishing.
5. A polishing apparatus comprising driving means for rotating a
substrate and driving means for rotating a polishing pad and
constructed to keep the polishing pad under a predetermined
pressure and in a state of contact with a device forming surface of
said substrate and perform polishing while rotating each of said
substrate and said polishing pad, said polishing apparatus
comprising measuring means for measuring symmetry of a film on an
alignment mark for alignment of said substrate or an input part for
inputting symmetry of a film on an alignment mark, and control
means for controlling a rotation speed of at least either one of
said substrate and said polishing pad according to the symmetry of
the film on the alignment mark, thus measured or inputted.
6. The polishing apparatus according to claim 5, wherein said
control means performs such control as to change rotation speeds of
said substrate and said polishing pad and equate total numbers of
rotations of said substrate and said polishing pad from a start of
the polishing to an end of the polishing.
7. The polishing apparatus according to claim 5, wherein said
control means comprises first input means for setting a rotation
speed of said substrate, a rotation speed of said polishing pad, a
polishing period, and a polishing pressure and second input means
for setting a rotation speed switching time, and said control means
further comprises an operation part for performing such calculation
as to equate total numbers of rotations of said substrate and
polishing pad from values inputted by said first and second input
means, and a control part for driving each of said substrate and
said polishing pad at respective rotation speeds based on the
rotation speeds inputted by said first input means and the result
of the calculation by said operation part.
8. The polishing apparatus according to claim 5, which comprises a
memory section for storing a rotation speed switching time and
either one or both of rotation speeds of said substrate and said
polishing pad, wherein control is implemented so as to equate total
numbers of rotations of said substrate and said polishing pad from
a start of the polishing to an end of the polishing.
9. A device fabrication method comprising: a step of forming a film
covering an alignment mark for alignment of a substrate on a device
forming surface of said substrate; and a step of keeping a
polishing pad under a predetermined pressure and in a state of
contact with said film and performing polishing while rotating each
of said substrate and polishing pad; said device fabrication method
comprising a step of measuring symmetry of the film on said
alignment mark after an end of the polishing of said substrate or
in the middle of the polishing and controlling a rotation speed of
the substrate and/or the polishing pad according to the symmetry of
the film on said alignment mark, thus measured.
10. The device fabrication method according to claim 9, wherein
control is implemented so as to change rotation speeds of said
substrate and said polishing pad and equate total numbers of
rotations of said substrate and said polishing pad from a start of
the polishing to the end of the polishing.
11. The device fabrication method according to claim 9, which
comprises setting a rotation speed of said substrate, a rotation
speed of said polishing pad, a polishing period, and a polishing
pressure and further setting a rotation speed switching time,
performing such calculation as to equate total numbers of rotations
of said substrate and said polishing pad from a start of the
polishing to the end of the polishing, based on these set rotation
speed of said substrate, rotation speed of said polishing pad,
polishing period, and rotation speed switching time, and driving
said substrate and said polishing pad at respective rotation speeds
based on the result of the calculation.
12. The device fabrication method according to claim 9, which
comprises storing a rotation speed switching time and either one or
both of rotation speeds of said substrate and said polishing pad
and performing such control as to equate total numbers of rotations
of said substrate and said polishing pad from a start of the
polishing to the end of the polishing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method and apparatus for
polishing of substrates such as semiconductor wafers of Si, GaAs,
InP, and so on, silica and glass substrates on the surface of which
a plurality of islandlike semiconductor regions are formed, or the
like, and to a device fabrication method.
[0003] 2. Related Background Art
[0004] With progress in microminiaturization and multilevel
metalization of semiconductor devices, there are needs for highly
precise flattening of outer surfaces of the substrates such as the
semiconductor wafers of Si, GaAs, InP, and so on, the silica and
glass substrates on the surface of which a plurality of islandlike
semiconductor regions are formed, or the like. Further, global
flattening of the outer surfaces of substrates is also demanded
from the emergence of SOI wafers and the necessity for
three-dimensional integration.
[0005] Chemical mechanical polishing (CMP) systems, for example, as
shown in FIG. 11 and FIG. 12, are conventionally known as the
flattening technology capable of microflattening as well as the
global flattening of such substrates.
[0006] Describing the chemical mechanical polishing system shown in
FIG. 11, the system has a wafer chuck 101 for holding a wafer W as
a work with a polished surface thereof facing down, and a polishing
table 105 which is placed so as to face the wafer W held on the
wafer chuck 101 and to which a polishing pad P, e.g., of
polyurethane, having the diameter greater than that of the wafer W,
is bonded, and is further provided with an abrasive supply 108 for
supplying abrasive (slurry) 107 onto the polishing pad P. The
polishing pad P is mainly made of a material having unevenness in
the surface, or a porous material, and grid-like grooves for supply
and discharge of the abrasive to and from the wafer W are scribed
in the surface of the polishing pad P.
[0007] In the chemical mechanical polishing system constructed in
this structure, the polished surface of the wafer W held on the
wafer chuck 101 is brought into contact onto the polishing pad P
bonded to the polishing table 105, the wafer W and polishing pad P
are rotated respectively in directions of arrows by unrepresented
driving means while the wafer W is kept under a predetermined
pressure, and, at the same time as it, the abrasive 107 is dropped
from the abrasive supply 108 onto the polishing pad P, thereby
polishing the polished surface of the wafer W. Concerning the
driving of the wafer W and the polishing pad P, when rotational
speeds (rpms) of the wafer W and the polishing pad P are set equal
to each other, the linear velocity of the polishing pad P becomes
constant at an arbitrary position on the wafer W, which is
desirable to the global flattening. However, the grid-like groove
pattern in the surface of the polishing pad P is transferred onto
the polished surface of the wafer W, which ends in failure of
microflattening. For this reason, it is common practice to perform
polishing with a shift of several % between the rotational speeds
of the wafer W and the polishing pad P.
[0008] On the occasion of this polishing, the abrasive (slurry) is
used for the purpose of increasing polishing amounts and is, for
example, an aqueous alkaline solution or the like in which fine
particles of SiO.sub.2 of micron order to submicron order are
dispersed in a stable state.
[0009] The chemical mechanical polishing system shown in FIG. 12
has a wafer chuck 201 for holding a wafer W as a work with a
polished surface thereof facing up, a wafer table 202 for
supporting the wafer chuck 201, and a polishing pad holder 205
which is disposed above the wafer table 202 so as to face the wafer
W held on the wafer table 202 and which holds a polishing pad P
having the diameter smaller than that of the wafer W, and is
arranged to supply the abrasive from the unrepresented abrasive
supply in communication with a small hole provided in the polishing
pad P, through the small hole to between the wafer W and the
polishing pad P. In the chemical mechanical polishing system
constructed in this structure, the polishing pad P of the smaller
diameter held on the polishing pad holder 205 is brought into
contact with the polished surface of the wafer W held through the
wafer chuck 201 on the wafer table 202, the polishing pad P is
rotated in a direction of an arrow and rocked by unrepresented
driving means while the polishing pad P is kept under a
predetermined pressure, and, at the same time as it, the abrasive
is supplied from the unrepresented abrasive supply to between the
polishing pad P and the wafer W, thereby polishing the polished
surface of the wafer W.
[0010] The semiconductor substrate such as the wafer or the like
having been polished by the polishing apparatus as described above
is conveyed through a cleaning step to a next device production
step and is then subjected to sequential processing steps to
produce devices. FIG. 13 shows a typical flow of device production
steps.
[0011] In FIG. 13, step S101 (oxidation) is a step of oxidizing the
surface of the wafer, step S102 (CVD) a step of forming an
insulating film on the wafer surface, step S103 (formation of
electrodes) a step of forming electrodes on the wafer by sputtering
or CVD, and step S104 (ion implantation) a step of injecting ions
into the wafer. Then step S105 (CMP) is a step of chemically and
mechanically polishing the surface of the wafer, step S106 (resist
process) a step of applying a resist onto the wafer, step S107
(exposure) a step of transferring a circuit pattern of a mask into
an array of shot areas in the wafer by a semiconductor exposure
system of a stepper or the like, step S108 (development) a step of
developing the exposed wafer, step S109 (etching) a step of
removing portions except for the resist image developed, and step
S110 (resist peeling) a step of removing the resist becoming
unnecessary after completion of the etching. The semiconductor
devices are produced by repeating these steps approximately 10 to
20 times as needed. Namely, the semiconductor substrate such as the
wafer or the like after completion of the CMP step (step S105) is
fed into the exposure step using an overlay inspection system, the
stepper, and so on.
[0012] Incidentally, in addition to patterns p forming
semiconductor devices, alignment marks m for positioning of an
alignment detecting system of the overlay inspection system, the
stepper, or the like are arranged on the polished surface of the
substrate such as the wafer or the like, as illustrated in FIG. 14.
In the polishing step, since a film s consisting of at least one
layer of insulator (dielectric) or the like is also formed, as
shown in FIG. 14, on the alignment marks m, the film on the
alignment marks is simultaneously polished together with the film
on the patterns p forming the semiconductor devices. In general,
the lengths of the device patterns p to be flattened by CMP are
fine patterns of not more than 1 .mu.m, but the lengths of the
alignment marks m are approximately 30 to 100 .mu.m. Since in the
CMP step the surface is polished with the pad of a viscoelastic
material like a polyurethane pad, non-dense portions of unevenness
are not flatly polished because of deformation of the pad during
polishing, thereby causing phenomena of so-called dishing and
thinning. For this reason, there remains slight unevenness in the
film layer on the alignment patterns m even after the flattening by
CMP, and reflection from this slightly remaining unevenness affects
alignment.
[0013] Describing this in further detail, most of methods now
practically used in the alignment detection systems of the overlay
inspection systems, steppers (exposure systems), and the like are
bright field image processing methods, and the alignment detection
systems of this type are constructed as schematically shown in FIG.
15 and arranged to detect an alignment mark m formed on the wafer
W, form an image thereof on CCD 301 as an image pickup device by an
optical system 303, and perform various signal processes on an
electric signal of the image, thereby implementing position
detection. In FIG. 15, numeral 302 designates a light source of the
alignment detection system, 303 an optical system including a beam
splitter of the alignment detection system, and 305 and 306 a
reticle and a projection lens of the stepper.
[0014] The imaging performance most required of the optical systems
of the alignment detection systems of this type is symmetry of
image. However, if the film s on the alignment mark m is asymmetric
as shown in FIG. 16A, light (A, B, C, D,. . . ) normally incident
to the alignment mark m is reflected at different angles as shown
in FIG. 16A and the reflected light (A', B', C', D',. . . ) travels
through the alignment optical system to be focused on the CCD as an
image pickup device, as shown in FIG. 16B. Since the angles of
reflection are different, positional deviation can occur because of
distortion of the image on the CCD. This becomes a factor of
degrading the alignment accuracy.
[0015] With the conventional polishing systems, as described above,
there was the problem that the asymmetric polishing of the film on
the alignment marks degraded the positioning accuracy in the
alignment detection systems of the overlay inspection systems, the
steppers, and so on. A conceivable reason of this asymmetric
polishing is that the film on the alignment marks is not polished
isotropically to become asymmetric because of execution of
polishing with the shift of several % between the rotational speeds
of the substrate, such as the wafer or the like, and the polishing
pad, occurrence of deformation of the polishing pad with a lapse of
time, and so on.
[0016] When the wafer surface is polished with the arbitrary shift
of several % between the rotational speeds of the wafer and
polishing pad, there occurs positional deviation of the alignment
marks on the wafer because of the difference between numbers of
rotations of the wafer and the polishing pad and directions of the
positional deviation are as shown in FIG. 17. Namely, if there is
the difference between numbers of rotations of the wafer and
polishing pad, the wafer will not be polished isotropically.
SUMMARY OF THE INVENTION
[0017] An object of the present invention is to provide a polishing
method and polishing apparatus of semiconductor substrate that can
polish the film layer on the alignment marks for positioning of the
overlay inspection system, the stepper, and the like in symmetric
shape to improve positioning accuracy thereby and that can prevent
the transfer of the grid-like groove pattern scribed in the surface
of the polishing pad, thereby improving microflatness.
[0018] A polishing method of a substrate according to the present
invention is a polishing method of keeping a polishing pad under a
predetermined pressure and in a state of contact with a device
forming surface of a substrate and performing polishing while
rotating each of the substrate and the polishing pad, wherein
symmetry of a film layer on an alignment mark for alignment of the
substrate is measured after an end of the polishing of the
substrate or in the middle of the polishing and wherein a rotation
speed of the substrate and/or the polishing pad is controlled
according to the symmetry of the film layer on the alignment mark,
thus measured.
[0019] In the polishing method of the substrate according to the
present invention, the control is preferably carried out so as to
change the rotation speeds of the substrate and the polishing pad
and equate total numbers of rotations of the substrate and the
polishing pad from a start of the polishing to the end of the
polishing.
[0020] In the polishing method of the substrate according to the
present invention, it is preferable to set the rotation speed of
the substrate, the rotation speed of the polishing pad, a polishing
period, and the polishing pressure, further set a rotation speed
switching time, perform calculation so as to equate the total
numbers of rotations of the substrate and the polishing pad from
the start of the polishing to the end of the polishing, based on
the rotation speed of the substrate, the rotation speed of the
polishing pad, the polishing period, and the rotation speed
switching time thus set, and drive the substrate and the polishing
pad at respective rotation speeds based on the result of the
calculation.
[0021] In the polishing method of the substrate according to the
present invention, it is preferable to store the rotation speed
switching time and either one or both of the rotation speeds of the
substrate and the polishing pad and the control is preferably
carried out so as to equate the total numbers of rotations of the
substrate and the polishing pad from the start of the polishing to
the end of the polishing.
[0022] A polishing apparatus of a substrate according to the
present invention is a polishing apparatus comprising driving means
for rotating a substrate and driving means for rotating a polishing
pad and constructed to keep the polishing pad under a predetermined
pressure and in a state of contact with a device forming surface of
the substrate and perform polishing while rotating each of the
substrate and the polishing pad, the polishing apparatus comprising
measuring means for measuring symmetry of a film layer on an
alignment mark for alignment of the substrate or an input portion
for inputting symmetry of a film layer on an alignment mark, and
control means for controlling a rotation speed of the substrate
and/or the polishing pad according to the symmetry of the film
layer on the alignment mark, thus measured or inputted.
[0023] In the polishing apparatus of the substrate according to the
present invention, the control means preferably performs the
control so as to change the rotation speeds of the substrate and
the polishing pad and equate total numbers of rotations of the
substrate and the polishing pad from a start of the polishing to an
end of the polishing.
[0024] In the polishing apparatus of the substrate according to the
present invention, preferably, the control means comprises first
input means for setting the rotation speed of the substrate, the
rotation speed of the polishing pad, a polishing period, and the
polishing pressure and second input means for setting a rotation
speed switching time, and the control means further comprises an
operation part for performing calculation so as to equate the total
numbers of rotations of the substrate and the polishing pad from
values inputted by the first and second input means, and a control
part for driving the substrate and the polishing pad at respective
rotation speeds based on the rotation speeds inputted by the first
input means and the result of the calculation by the operation
part.
[0025] In the polishing apparatus of the substrate according to the
present invention, it is preferable to comprise a memory part for
storing the rotation speed switching time and either one or both of
the rotation speeds of the substrate and the polishing pad and to
perform the control so as to equate the total numbers of rotations
of the substrate and the polishing pad from the start of the
polishing to the end of the polishing.
[0026] According to the present invention, the symmetry of the film
layer on the alignment mark for alignment of the substrate is
measured after the end of the polishing of the substrate or in the
middle of the polishing and the rotation speed of the substrate
and/or the polishing pad is controlled according to the symmetry of
the film layer on the alignment mark, thus measured, whereby it
becomes feasible to overcome the problem due to the difference
between the rotation speeds of the substrate and the polishing pad
and the temporal change of the polishing pad and to symmetrically
and isotropically polish the film layer on the alignment mark for
alignment on the polished surface of the substrate such as the
wafer or the like.
[0027] Further, the rotation speeds of the substrate and the
polishing pad are changed and the rotation speeds of the substrate
and polishing pad are controlled so as to equate the total numbers
of rotations of the substrate and the polishing pad from the start
of the polishing to the end of the polishing, whereby the polishing
can be carried out further more isotropically.
[0028] This enables symmetric polishing of the film layer on the
alignment mark and can improve the alignment accuracy and further
prevent the transfer of the grid-like groove pattern scribed in the
surface of the polishing pad, thereby improving the
microflatness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a layout diagram to show the schematic structure
of a polishing apparatus of substrate according to the first
embodiment of the present invention;
[0030] FIG. 2 is a view showing the structure of a polishing
mechanical section in the polishing apparatus of substrate
according to the first embodiment of the present invention;
[0031] FIG. 3 is a view showing the structure of the main part of
the polishing mechanical section in the polishing apparatus of
substrate according to the first embodiment of the present
invention;
[0032] FIG. 4 is a flowchart of a polishing method in the first
embodiment of the present invention;
[0033] FIG. 5 is a schematic diagram of an alignment mark symmetry
detecting system for measuring symmetry of a film layer on an
alignment mark in the polishing apparatus of substrate according to
the first embodiment of the present invention;
[0034] FIGS. 6A and 6B are drawings explaining a state of measuring
symmetry of a film layer on an alignment mark by the alignment mark
symmetry detecting system;
[0035] FIG. 7 is a timing chart for explaining a polishing method
in the second embodiment of the present invention;
[0036] FIG. 8 is a flowchart of the polishing method in the second
embodiment of the present invention;
[0037] FIG. 9 is a timing chart for explaining a polishing method
in the third embodiment of the present invention;
[0038] FIG. 10 is a flowchart of the polishing method in the third
embodiment of the present invention;
[0039] FIG. 11 is a schematic view of a conventional chemical
mechanical polishing apparatus;
[0040] FIG. 12 is a schematic view of another conventional chemical
mechanical polishing apparatus;
[0041] FIG. 13 is a flowchart showing ordinary device production
steps;
[0042] FIG. 14 is a schematic, cross-sectional view of a
semiconductor device in the step of forming the semiconductor
device;
[0043] FIG. 15 is a schematic view showing an ordinary alignment
detecting system;
[0044] FIGS. 16A and 16B are drawings showing the relation between
an alignment mark and an image on an image pickup device such as
CCD, based on asymmetry of a film layer on the alignment mark of
wafer; and
[0045] FIG. 17 is a drawing showing directions of positional
deviation of alignment marks on a wafer, appearing when the surface
of the wafer is polished with a shift of several % between rotation
speeds of the wafer and the polishing pad.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] (First Embodiment)
[0047] FIG. 1 is a layout diagram showing the schematic structure
of a polishing apparatus of substrate according to the first
embodiment of the present invention, FIG. 2 a view showing the
structure of a polishing mechanism section in the polishing
apparatus of substrate according to the first embodiment of the
present invention, and FIG. 3 a view showing the structure of the
main part of the same polishing mechanism section.
[0048] The polishing apparatus of substrate according to the
present invention is provided, as shown in FIG. 1, with a wafer
polishing section 51 for polishing a substrate, such as a
semiconductor substrate, a glass substrate, or the like (which will
be also referred to simply as a wafer), as a work, a cleaning
section 52 for cleaning the wafer after polished in the wafer
polishing section 51, a prealignment section 53 for effecting
prealignment of the wafer after cleaned in the cleaning section 52,
and a film symmetry measuring section 54 for measuring symmetry of
a film on alignment marks of the wafer after the prealignment.
Numeral 55 designates an XY.theta. stage, which holds the wafer
cleaned in the cleaning section 52 and which transfers the wafer to
the prealignment section 53 and the film symmetry measuring section
54. The prealignment section 53 performs positioning in the
rotational direction on the basis of a notch reference or an
orientation flat reference and positioning in the XY directions on
the basis of a wafer contour reference, and the film symmetry
measuring section 54 measures symmetry of the film on the alignment
marks. Numeral 56 denotes a wafer load-unload section for loading a
wafer stored in a wafer carrier into the polishing apparatus and
unloading the wafer from the apparatus, and numeral 57 a carry
robot for carrying the wafer.
[0049] Next, the polishing mechanism section of wafer in the
polishing apparatus will be described in detail with reference to
FIG. 2 and FIG. 3. The wafer polishing mechanism section is
provided with a wafer table 2 for holding a wafer W as a work
through a wafer chuck 1 with a polished surface of the wafer facing
up, and a polishing head 5 which is disposed above the wafer table
2 so as to face the wafer W held on the wafer table 2 and which has
the diameter larger than the diameter of the wafer W but smaller
than double the diameter of the wafer W. The polishing mechanism
section is further provided with a first driver 7 for rotationally
driving the polishing head 5 holding the polishing pad P in the
direction of arrow A about the axis thereof and a head vertical
motion driver 8 for vertically moving the polishing head 5 to press
the polishing pad P against the wafer W under pressure. On the
wafer table 2 holding the wafer W, as shown in FIG. 3, there are
provided a second driver 10 for rotationally driving the wafer
chuck 1 holding the wafer W, in the direction of arrow B about the
axis thereof, a third driver 11 consisting of a guide section 11a
and a power section 11b for rocking the wafer chuck 1 holding the
wafer W, in horizontal directions (arrow C), and an equalizing
mechanism 12 for pressing the entire surface of the wafer W against
the polishing pad P under a fixed pressure on the occasion of
polishing the wafer W by the polishing pad P. The polishing
mechanism section is further provided with an abrasive supply
mechanism 16 having an abrasive supply tube 15 in communication
with a small hole 14 provided in the central area of the polishing
head 5 and the polishing pad P so as to supply the abrasive
(slurry) to the region where the polished surface of the wafer W
and the polishing pad P face each other. If the polishing pad P is
made of a material that the abrasive S can penetrate, e.g., fabric
or polyurethane having large communicating holes, the small hole 14
does not have to be provided intentionally in the polishing pad
P.
[0050] The polishing mechanism section of the present embodiment is
further provided with a control unit 17 for controlling driving of
the foregoing first driver 7, head vertical motion driver 8, second
driver 10, third driver 11, etc. independently of each other or in
correlation with each other. The control unit 17 is composed of a
microcomputer and the like.
[0051] In the polishing mechanism section of the present
embodiment, the axis of autorotation of the polishing pad P is set
off the axis of autorotation of the wafer W, i.e., the axes of the
polishing pad P and the wafer W are located at different axis
positions, and the pad and the wafer are arranged so that the
entire surface of the wafer W never lies off the polishing pad P.
The polishing mechanism section is also constructed to keep the
wafer W from lying off the polishing pad P during rocking. In this
way the polishing mechanism section performs the polishing in a
state in which the polishing pad P is always in contact with the
whole of the polished surface of the wafer W. For that purpose, in
the present embodiment, the positions of the respective
autorotation axes are set so that the sum of the radius of the
wafer W and the distance between the autorotation axis of the
polishing pad P and the autorotation axis of the wafer W is not
more than the radius of the polishing pad P. For rocking the wafer
W, the rocking range is also determined so that the sum of the
radius of the wafer W and the maximum distance between the
autorotation axes during the rocking is not more than the radius of
the polishing pad P.
[0052] In the present embodiment, as shown in FIG. 3, the wafer W
is rocked by the third driver 11, but it is also possible to
construct the polishing mechanism section so as to rock the
polishing head P side by a rocking means provided on the polishing
head P side, or to construct the polishing mechanism section so as
to rock both the wafer W and the polishing head P. In either case,
however, it is necessary to keep the wafer W from lying off the
polishing pad P.
[0053] The abrasive used in the present embodiment is a polishing
solution in which fine particles, a material of which is selected
from silicon oxide, cerium oxide, aluminum oxide, oxide zeolite,
chromium oxide, iron oxide, silicon carbide, boron carbide, carbon,
ammonium salt, and so on and diameters of which are relatively
uniform in the range of several micron order to submicron order,
are dispersed in a solution selected from aqueous sodium hydroxide
solution, aqueous potassium hydroxide solution, aqueous ammonia
solution, isocyanurate solution, Br-CH.sub.3OH, hydrochloric acid
solution, and so on. The combination of these fine particles and
solution can be selected according to an object to be polished. For
example, the abrasive suitably applicable to polishing of Si
surface is one in which fine particles of silicon oxide, cerium
oxide, ammonium salt, manganese dioxide, or the like are dispersed
in the above-mentioned solution. The abrasive suitably applicable
to polishing of surface of SiO.sub.2 is one in which fine particles
of silicon oxide are dispersed in aqueous potassium hydroxide
solution. The abrasive suitably applicable to polishing of an
Al-surface wafer is one in which fine particles of silicon oxide
are dispersed in aqueous ammonia solution containing hydrogen
peroxide. In the present invention, films to be polished can be
insulators such as silicon oxide, silicon nitride, nitrided silicon
oxide, and the like, and these may be doped with boron or
phosphorus if necessary.
[0054] Next, the polishing method by the polishing apparatus
constructed as described above will be described below along the
flowchart shown in FIG. 4. In the present embodiment the polishing
is implemented by a control method of driving the wafer W as a work
and the polishing pad P in the same direction and at different
rotation speeds, and the respective rotation speeds of the wafer W
and the polishing pad P are selected in the range of not more than
1000 rpm and more preferably in the range of 50 to 300 rpm in the
same direction. The pressure for pressing the polishing pad P
against the wafer W by the head vertical motion driver 8 is set in
the range of 0 to 100 kPa.
[0055] The wafer is a substrate in which an insulating film is
formed on a device forming surface thereof so as to cover alignment
marks.
[0056] First, in step S1, a wafer W stored in the wafer carrier
placed in the wafer load-unload section 56 is carried to the wafer
polishing section 51 by the carry robot 57 according to a wafer
loading sequence and the surface of the insulating film formed on
the substrate is polished there (step S3). The mode of polishing is
as described above, and for the polishing, the polishing pressure,
the polishing period, the rotation speed of the wafer, the rotation
speed of the polishing pad, etc. are preliminarily set to arbitrary
values and are inputted through unrepresented input means. The
polishing is carried out according to these input values.
Desirably, the difference n between the rotation speeds of the
wafer and the polishing pad is approximately 1 to 10 rpm. The wafer
W after completion of the polishing is conveyed from the wafer
polishing section 51 to the cleaning section 52 by the carry robot
57 and the wafer W is cleaned and dried in the cleaning section 52
(step S4). After that, the wafer is transferred onto the XY.theta.
stage 55 by the carry robot 57. The wafer W on the XY.theta. stage
55 is transferred to the prealignment section 53 and in the
prealignment section 53 the wafer W is subjected to the alignment
in the rotational direction on the basis of the notch reference or
the orientation flat reference and the positioning in the XY
directions on the basis of the wafer contour reference as
prealignment (step S5). Then the wafer W is transferred to the film
symmetry measuring section 54 by the XY.theta. stage 55. According
to the positions and number of alignment marks preliminarily
inputted in step S6, the XY.theta. stage 55 is driven in the XY
directions to detect the alignment marks (step S7), and thereafter,
in step S8, symmetry is measured for the polished insulating film
on the alignment marks.
[0057] An alignment mark symmetry detecting system 60 shown in FIG.
5 is used for the measurement of symmetry of the insulating film on
the alignment marks m. The alignment mark symmetry detecting system
60 is configured to direct light emitted from a light source 62,
through an optical system 63 including a beam splitter, to an
alignment mark m on the wafer W and focus reflected light therefrom
through the optical system 63 on CCD 61 as an image pickup device.
A signal processing system processes an electric signal of the
alignment mark image focused on the CCD 61, thereby measuring
symmetry of the film on the alignment mark m. The measurement of
symmetry of film will be detailed later. The structure of the
optical system of this symmetry detecting system 60 is basically
similar to that of the bright field optical system of FIG. 15
described previously. The number of alignment marks m to be
measured can be preliminarily set to an arbitrary number from the
unrepresented computer section, and preferably set to approximately
2 to 18. On that occasion, the correction accuracy can be enhanced
by selecting a plurality of alignment marks on an identical
circle.
[0058] Based on the measured symmetry of each alignment mark thus
selected, the result is fed back to the difference between rotation
speeds of wafer W and polishing pad P for polishing of a next wafer
W (step S9), to appropriately correct the difference between the
rotation speeds of the polishing pad P and the next polished wafer
W (step S2). After completion of the measurement of symmetry of
alignment marks, the wafer W is unloaded according to a wafer
unloading sequence to be stored in a wafer carrier in the wafer
load-unload section 56 by the carry robot 57 (step S10).
[0059] Next, the measurement of symmetry of the film on the
alignment marks will be further described with reference to FIGS.
6A and 6B. When template matching is conducted so as to set the
measurement range for the alignment mark m imaged on the CCD 61 to
the positional relation of FIG. 6A, a measurement signal shown in
FIG. 6B is gained. The measurement signal obtained from the
alignment mark m in the central part of the measurement range
varies in a shape of two peaks in the measurement direction. The
measurement signal is sliced at a certain slice level to obtain two
intersections and determine an intermediate point between them for
each peak, a middle point between two intermediate points is
defined as a center position of the alignment mark, and a
difference between distances from that center position to tops of
the respective peaks is defined as symmetry of the alignment
mark.
[0060] Another method of measurement of symmetry is a method of
folding the measurement signal varying in the two-peak shape at the
center and taking a difference. The following measurement is
carried out for x of the measurement signal obtained as shown in
FIG. 6B. 1 M ( x ) = j = C - W / 2 C + W / 2 F ( x + j ) - F ( x -
j ) ( 1 )
[0061] A minimum is determined out of absolute values of M(x)
obtained by Eq (1) above and the minimum is divided by W. The
resultant of the division is defined as symmetry level.
symmetry level =M(x)/W. . .(2)
[0062] In the above equations, W and C represent coefficients
determined by the type of the alignment mark, the magnification of
the detection optical system, the number of pixels of CCD, and so
on.
[0063] Further, still another method of measurement of symmetry is
a method of comparing the actually measured signal with a waveform
with good symmetry preliminarily stored in a computer and
calculating the symmetry level, based on correlation between
them.
[0064] Described next is a method of correcting the difference n
between the rotation speeds of the wafer and polishing pad, based
on the symmetry level measured as described above.
[0065] When the polishing is carried out with the shift of several
% between the rotation speeds (rpms) of the wafer and polishing
pad, the film on the alignment marks is not polished isotropically
and thus the alignment mark detecting system measures positional
deviation. However, when the polishing is carried out with the
shift of several % between the rotation speeds of the wafer and
polishing pad, it becomes feasible on the other hand to correct the
positional deviation of the alignment marks due to the difference
between the rotation speeds of the wafer and polishing pad, the
temporal deformation of the polishing pad, and so on. In the
present embodiment, thus, actual polishing is preliminarily carried
out with change in the rotation speeds of the respective wafer and
polishing pad to several values, for films like insulating films on
the alignment marks on the wafer in the device process as an object
to be polished, and, based on results of measurement of the films
on the alignment marks at that time, the relation between symmetry
level and difference between rotation speeds of the wafer and
polishing pad is statistically processed and preliminarily stored
in a computer. Then the symmetry level obtained by the measurement
of symmetry is used for the operation in the computer to compute
the difference n between rotation speeds of the wafer and polishing
pad to be changed according to the measured symmetry level.
[0066] In the semiconductor fabrication process, it is common
practice to first run a test wafer for checking stability of the
system at the beginning of a fabrication lot. In the CMP apparatus,
a test wafer is also polished before polishing of the first wafer,
in order to check the stability of the expendable materials such as
the polishing pad, the abrasive, etc., thereby checking the
polishing rate, flatness, and so on. Then, the symmetry of the film
on the alignment marks is measured on the occasion of the polishing
of this test wafer and the rotation speed difference n can be
calculated according to this symmetry. Using the rotation speed
difference n calculated for this test wafer, the polishing is
carried out by setting the rotation speed of the wafer to N and the
rotation speed of the polishing pad to (N -n). This permits the
film on the alignment marks to be polished in symmetry, thereby
improving the alignment accuracy of wafer.
[0067] As described above, the polishing apparatus incorporates the
film symmetry measuring unit for measuring the symmetry of the film
on the alignment marks and is constructed to perform the polishing
while feeding back the data of the wafer polished one before,
whereby, even with change in such a factor as the temporal change
or the like of the polishing pad during processing of one lot, the
film on the alignment marks can be polished in symmetry in
accordance with the change. This improves the alignment accuracy,
prevents the transfer of the grid-like groove pattern scribed in
the surface of the polishing pad, and enhances the
microflatness.
[0068] (Second Embodiment)
[0069] The polishing method and apparatus of substrate according to
the second embodiment of the present invention will be described
below with reference to FIG. 7 and FIG. 8.
[0070] There are two conceivable reasons for the problem of
degradation of the alignment accuracy in the alignment detecting
system of the overlay inspection system, the stepper, etc. due to
the asymmetric polishing of the film on the alignment marks in the
polishing of the wafer. The first reason is that the film on the
alignment marks is not polished isotropically, so as to become
asymmetric, because the polishing is conducted with the shift of
several % between the rotation speeds (rpms) of the wafer and
polishing pad. The second reason is that the film on the alignment
marks is not polished isotropically, so as to become asymmetric,
because of the temporal deformation of the polishing pad.
[0071] In the present embodiment, thus, the rotation speeds of the
wafer and polishing pad are controlled in order to solve the former
and the difference between the rotation speeds of the wafer and
polishing pad is corrected in order to solve the latter. The
polishing apparatus used in the present embodiment is approximately
similar to the polishing apparatus described in the foregoing first
embodiment (FIG. 1 to FIG. 3) and the details of like members are
omitted herein.
[0072] First described is a method of controlling the rotation
speeds of the wafer and polishing pad in the present
embodiment.
[0073] When the wafer W and the polishing pad P are driven in the
same direction and at the same rotation speed as an ordinary
polishing method in polishing of wafers and the like, relative
peripheral velocity can be kept uniform at an arbitrary position on
the polished surface of wafer W and this enables implementation of
polishing while ensuring global uniformity. However, when the wafer
W and polishing pad P are driven in the same direction and at the
same rotation speed, satisfactory microflatness cannot be attained,
because the grid-like groove pattern for abrasive in the surface of
the polishing pad P is transferred to the wafer W. For this reason,
normally, the polishing is done with the shift of several % between
the rotation speeds of the wafer W and polishing pad P. The range
of the shift between the rotation speeds in this way is
approximately 0.1 to 10% relative to the rotation speed of either
one member and more preferably about 1 rpm. For example, let us
suppose that while the wafer W is rotated at 60 rpm, the polishing
pad P is rotated at 59 rpm and the film is polished for one minute.
In this case, the wafer W undergoes 60 rotations in total and the
polishing pad P 59 rotations in total. Thus the difference between
the total numbers of rotations of the wafer W and the polishing pad
P is calculated as 60-59=1 rotation and this is reduced to an
angular rotation difference of 360.degree.. When the grooves for
abrasive scribed in the polishing pad P are of the grid shape as
described previously, the transfer of the groove pattern can be
prevented if the rotation difference is not less than 90.degree..
If the grooves for abrasive scribed in the polishing pad P are
spiral, the transfer of the groove pattern can be averaged by the
rotation difference of 360.degree..
[0074] Incidentally, when the polishing is simply done with the
shift of several % between the rotation speeds of the wafer W and
polishing pad P, asymmetric polishing results from the rotation
speed difference. The mechanism of this polishing will be described
next. The relation between relative positions of the wafer W and
polishing pad P during rotation of the wafer W and polishing pad P
in the same direction and at the same rotation speed is equal to
that during revolving motion without autorotation, the radius of
which is the distance between the autorotation axis of the wafer W
and the autorotation axis of the polishing pad P. In this case, the
film layer on the alignment marks m on the wafer W is polished
isotropically. However, when the polishing is done with the shift
of several % between the rotation speeds of the wafer W and the
polishing pad P, autorotation motion occurs according to a
difference between their rotation numbers and the film on the
alignment marks m on the wafer W is polished on an asymmetric
basis. Accordingly, there occurs positional deviation of the
alignment marks as shown in FIG. 17.
[0075] Thus the polishing apparatus of the present embodiment
further comprises a control means for controlling the rotation of
the wafer W and polishing pad P so as to change the rotation speeds
(rpms) of the wafer W and the polishing pad P and equate the total
numbers of rotations of the wafer W and the polishing pad P from
the start of the polishing to the end of the polishing, this
control means comprises an input means for setting the rotation
speed of the wafer W, the rotation speed of the polishing pad P,
the polishing period, and the polishing pressure and an input means
for setting the rotation speed switching time, and the control
means further comprises an operation part for executing such
calculation as to equate the numbers of rotations of the wafer W
and polishing pad P and a control part for driving the wafer W and
the polishing pad P at their respective, predetermined rotation
speeds.
[0076] The control of the present embodiment will be described
below in detail with reference to FIG. 7 and FIG. 8. As shown in
the timing chart of FIG. 7, let T be the total polishing period, t
be the rotation speed switching time, N.sub.1 (rpm) be the rotation
speed of the wafer W before the rotation speed switching time t,
N.sub.2 (rpm) be the rotation speed of the wafer W after the
rotation speed switching, (N.sub.1-n) (rpm) be the rotation speed
of the polishing pad P before the rotation speed switching time t,
and N.sub.x (rpm) be the rotation speed of the polishing pad P
after the rotation speed switching. Then the rotation speed N.sub.x
(rpm) of the polishing pad P after the rotation speed switching can
be calculated by the equation below. Namely, from the fact that in
the total polishing period from the start of polishing to the end
of polishing the total number of rotations of the wafer W,
{N.sub.1.multidot.t+N.sub.2.multidot.(T-t)}, is equated to the
total number of rotations of the polishing pad P,
{(N.sub.1-n).multidot.t+N.sub- .x.multidot.(T-t)}, the following
equation holds.
N.sub.1.multidot.t+N.sub.2.multidot.(T-t)=(N.sub.1-n).multidot.t+N.sub.x.m-
ultidot.(T-t)
[0077] Therefore, we obtain the following equation.
N.sub.x=[N.sub.1.multidot.t+N.sub.2.multidot.(T-t)-(N.sub.1-n).multidot.t]-
/(T-t) . . . (3)
[0078] Namely, by giving input of respective values of the total
polishing period T, the rotation speed switching time t, the
rotation speed N.sub.1 (rpm) of the wafer W before the rotation
speed switching time t, the rotation speed N.sub.2 (rpm) of the
wafer W after the rotation speed switching, and the rotation speed
(N.sub.1-n) (rpm) of the polishing pad P before the rotation speed
switching time t by use of the input means, the operation part can
calculate the rotation speed N.sub.x (rpm) of the polishing pad P
after the rotation speed switching, based on Eq (3).
[0079] For example, suppose the total polishing period T is two
minutes, the rotation speed switching time t one minute, the
rotation speeds N.sub.1, N.sub.2 of the wafer W before and after
the rotation speed switching time t are both 60 rpm, and the
rotation speed (N.sub.1 -n) of the polishing pad P before the
rotation speed switching time t is (60-1=) 59 rpm. Then the
rotation speed N.sub.x (rpm) of the polishing pad P after the
rotation speed switching is calculated as follows by Eq (3)
described above.
N.sub.x={60.times.1+60 .times.(2-1)-59.times.1}/(2-1)=61
[0080] At this time, the numbers of rotations of the wafer W and
the polishing pad P are given as follows. the number of rotations
of the wafer ={60.times.1+60.times.(2-1)}=120 the number of
rotations of the polishing pad ={59 .times.1+61.times.(2-1)}120
[0081] Namely, though polishing is carried out with the shift of
several % between the rotation speeds of the wafer W and the
polishing pad P, the difference is 0 between the numbers of
rotations of the wafer W and the polishing pad P, so that isotropic
polishing is implemented.
[0082] When the rotation speed switching time t is half of the
polishing period T and rotating directions are switched (e.g., from
CW to CCW) between before and after the switching, velocity vectors
at each part on the wafer W cancel each other before and after the
switching time, thereby enabling implementation of further more
isotropic polishing.
[0083] It is needless to mention that the effect of the present
embodiment can also be achieved similarly by exchanging the speeds
of the wafer W and the polishing pad P in foregoing Eq (3) and
calculating the speed of the wafer W after the switching time, as
N.sub.x.
[0084] The apparatus may also be configured to store the rotation
speed switching time t, the speed N.sub.2 after switching, and the
difference n between rotation speeds of the wafer W and polishing
pad P as coefficients in the operation part.
[0085] A method of correction for the rotation speed difference n
between the rotational speeds of the wafer W and the polishing pad
P will be described below.
[0086] Against the phenomenon in which the film on the alignment
marks is not polished isotropically because of the difference
between the rotation speeds of the wafer W and the polishing pad P,
the desired effect can be achieved, as described above, by
controlling the rotation of the wafer W and the polishing pad P so
as to equate the total numbers of rotations thereof. However, even
if the rotation of the wafer W and polishing pad P is controlled so
as to equate the total numbers of rotations thereof, there are
cases where the film on the alignment marks is not polished
isotropically because of the temporal deformation of the polishing
pad P. Therefore, the difference n between the rotation speeds of
the wafer W and the polishing pad P is corrected according to the
symmetry of the film on the alignment marks after polishing,
whereby the film on the alignment marks can be polished
isotropically.
[0087] This will be described using the flowchart shown in FIG. 8.
The polishing apparatus in the present embodiment is approximately
similar to the polishing apparatus shown in FIG. 1 to FIG. 3, as
described previously, and thus reference is also made to FIG. 1 to
FIG. 3 in the description.
[0088] First, a wafer W is loaded into the polishing apparatus
(step S21) and then is conveyed to the wafer polishing section 51.
The input means also provides input of the preset total polishing
period T, rotation speed switching time t, rotation speed N.sub.1
(rpm) of the wafer W before the rotation speed switching time,
rotation speed N.sub.2 (rpm) of the wafer W after the rotation
speed switching, and rotation speed (N.sub.1-n) (rpm) of the
polishing pad P before the rotation speed switching time (step
S22), and then the rotation speed N.sub.x of the polishing pad P
after the rotation speed switching is calculated according to
aforementioned Eq (3) on the basis of the input values (step S23).
N.sub.x is set to a value satisfying
.vertline.N.sub.x-N.sub.2.vert- line..gtoreq.1 (steps S23 to S25).
Based on the values inputted and calculated as described above, the
wafer W is polished in step S26. After completion of the polishing,
the wafer W is cleaned and dried in the cleaning section 52 (step
S27) and thereafter, the wafer W is transferred onto the XY.theta.
stage 55 and moved to the prealignment section 53. In the
prealignment section 53 the wafer W is positioned by the alignment
in the rotational direction on the basis of the notch reference or
the orientation flat reference and the positioning in the XY
directions on the basis of the wafer contour reference as
prealignment (step S28).
[0089] Then the wafer W is transferred to the film symmetry
measuring section 54 by the XY.theta. stage 55 and, according to
the positions and the number of alignment marks preliminarily
inputted in step S29, the XY.theta. stage 55 is driven in the XY
directions to detect the alignment marks in step S30. After that,
symmetry of the film on the alignment marks is measured in step
S31. A corrected rotating speed N.sub.3 for a next polished wafer W
and the polishing pad P is calculated according to the symmetry
thus measured (step S32). This corrected rotating speed N.sub.3 is
used for determining the rotation speed N.sub.x of the polishing
pad P after the rotation speed switching in the polishing of the
next wafer W, as described hereinafter. After completion of the
measurement of symmetry of the alignment marks, the wafer W is
unloaded to be stored in the wafer carrier of the wafer load-unload
section 56 (step S33).
[0090] The corrected rotating speed N.sub.3 described above can be
obtained in similar fashion to the calculation of the rotation
speed difference n in the first embodiment. Namely, for films on
the alignment marks m on the wafer W as an object to be polished,
actual polishing is preliminarily carried out with change in each
rotation speed of the wafer W and the polishing pad P to several
values and, based on results of the measurement of the films on the
alignment marks m at that time, the relation between symmetry level
and rotation speed difference between the wafer W and the polishing
pad P is statistically processed and stored in a computer. Then the
symmetry level obtained by the measurement of symmetry is used for
the operation in the computer to calculate the corrected rotating
speed N.sub.3 according to the measured symmetry level.
[0091] For determining the rotation speed N.sub.x of the polishing
pad P after the rotation speed switching in the polishing of the
next wafer W by use of the corrected rotating speed N.sub.3, as
shown in the timing chart of FIG. 7, let T be the total polishing
period, t be the rotation speed switching time, N.sub.1 (rpm) be
the rotation speed of the wafer W before the rotation speed
switching time, N.sub.2 (rpm) be the rotation speed of the wafer W
after the rotation speed switching, and (N.sub.1-n) (rpm) be the
rotation speed of the polishing pad P before the rotation speed
switching time. Then the rotation speed N.sub.x (rpm) of the
polishing pad P after the rotation speed switching can be
calculated by Eq (4) below, using the corrected rotating speed
N.sub.3.
N.sub.x=[N.sub.1.multidot.t+N.sub.2.multidot.(T-t)-(N.sub.1-n).multidot.t+-
N.sub.3]/(T-t). . . (4)
[0092] In the present embodiment, as described above, the rotation
speeds of the wafer and the polishing pad are controlled to
implement the isotropic polishing of the film on the alignment
marks and the data of the wafer polished one before is fed back
whereby, even with change in such a factor as the temporal change
of the polishing pad or the like, the film on the alignment marks
can be polished in symmetry according to the change. This improves
the alignment accuracy and prevents the transfer of the grid-like
groove pattern scribed in the surface of the polishing pad, thereby
improving the microflatness.
[0093] Although in the first and second embodiments the film
symmetry measuring unit for measuring the symmetry of the alignment
marks for alignment is disposed in the polishing apparatus, it can
also be contemplated that the film symmetry measuring unit is
located outside the polishing apparatus, the wafer after completion
of polishing is subjected to the measurement of symmetry outside
the polishing apparatus, and the data of symmetry level obtained is
inputted through the input part provided in the polishing
apparatus.
[0094] (Third Embodiment)
[0095] The polishing method and apparatus of semiconductor
substrate according to the third embodiment of the present
invention will be described below with reference to FIG. 9 and FIG.
10.
[0096] In the third embodiment of the present invention, the
symmetry of the film on the alignment marks is measured in the
middle of polishing of a wafer and respective rotation speeds of
the wafer and polishing pad for the rest polishing are controlled
according to the symmetry of the film on the alignment marks as the
result of the measurement.
[0097] As shown in the timing chart of FIG. 9, the symmetry of film
on the alignment marks is measured after the first half of
polishing or primary polishing (which will be referred to
hereinafter simply as primary polishing), and based on the result,
the rest half of polishing or secondary polishing (which will be
referred to hereinafter simply as secondary polishing) is carried
out. In this case, let T.sub.f+T.sub.s be the total polishing
period, T.sub.f be a primary polishing period before the
measurement of symmetry, t.sub.f be a rotation speed switching time
in the primary polishing before the measurement of symmetry,
N.sub.1f (rpm) be a rotation speed of the wafer W before the
rotation speed switching time in the primary polishing, N.sub.2f
(rpm) be a rotation speed of the wafer W after the rotation speed
switching in the primary polishing, (N.sub.1f-n.sub.f) (rpm) be a
rotation speed of the polishing pad P before the rotation speed
switching time in the primary polishing, T.sub.s be a secondary
polishing period after the measurement of symmetry, t.sub.S be a
rotation speed switching time in the secondary polishing after the
measurement of symmetry, N.sub.1s (rpm) be a rotation speed of the
wafer W before the rotation speed switching time in the secondary
polishing after the measurement of symmetry, N.sub.2s (rpm) be a
rotation speed of the wafer W after the rotation speed switching in
the secondary polishing, and (N.sub.1s-n.sub.s) (rpm) be a rotation
speed of the polishing pad P before the rotation speed switching
time in the secondary polishing. When these are set as input
values, a rotation speed N.sub.xf (rpm) of the polishing pad P
after the rotation speed switching time in the primary polishing
before the measurement of symmetry and a rotation speed N.sub.xs
(rpm) of the polishing pad P after the rotation speed switching
time in the secondary polishing after the measurement of symmetry
can be calculated according to respective equations below. In the
equations, N.sub.3 is a corrected rotating speed similar to that in
the aforementioned second embodiment, and is a corrected rotating
speed calculated according to the symmetry measured by the
measurement of symmetry of the film on the alignment marks.
N.sub.xf=[N.sub.1f.multidot.t.sub.f+N.sub.2f.multidot.(T.sub.f-t.sub.f)-(N-
.sub.1f-n.sub.f).multidot.t.sub.f]/(T.sub.f-t.sub.f). . . (5)
N.sub.xs=[N.sub.1s.multidot.t.sub.s+N.sub.2s.multidot.(T.sub.s-t.sub.s)-(N-
.sub.1s-n.sub.s).multidot.t.sub.s+N.sub.3]/(T.sub.s-t.sub.s). . .
(6)
[0098] Preferably, N.sub.1f=N.sub.2f and t.sub.f is preferably half
of T.sub.f. Further, when T.sub.f=T.sub.s,
t.sub.f=t.sub.s,N.sub.1f=N.sub.1s- , N.sub.2f=N.sub.2s, and
(N.sub.1f-n.sub.f) =(N.sub.1s-n.sub.s), velocity vectors on the
wafer during polishing become more isotropic, so as to improve the
symmetry further.
[0099] In the present embodiment, the symmetry of the film on the
alignment marks is measured in the middle of the polishing and the
result is fed back to the polishing of the wafer itself, whereby
the isotropic polishing is implemented for each wafer without use
of a test wafer.
[0100] In general CMP involves the primary polishing being rough
polishing and the secondary polishing being finish polishing. In
this case, when the symmetry of the film on the alignment marks is
measured as described above between the rough polishing and the
finish polishing and the measurement result is fed back to the
finish polishing, it becomes feasible to isotropically polish the
film on the alignment marks. Namely, as shown in FIG. 10, the
measurement of symmetry of the film on the alignment marks, as well
as detection of an end point, is carried out between the primary
polishing and the secondary polishing. In FIG. 10, a wafer is
loaded in the polishing apparatus (step S41), the wafer is polished
by the primary polishing (step S42), then the wafer is prealigned
(step S43), and thereafter, the end is detected (step S44) and the
symmetry of the film on the alignment marks is also measured (steps
S45 to S46). The measurement result is fed back to the secondary
polishing carried out in the subsequent step (step S47). After
completion of the secondary polishing, the wafer is cleaned and
dried (step S48) and is unloaded (step S49).
[0101] As described above, the symmetry of film on the alignment
marks is measured in the middle of the polishing and the result of
the measurement is fed back to the polishing of the wafer itself
whereby it becomes feasible to implement the isotropic polishing
for each wafer, polish the film on the alignment marks in symmetry,
and enhance the alignment accuracy.
[0102] As described above, the present invention enables the
isotropic polishing of the film on the alignment marks for
alignment of the overlay inspection system, the stepper, etc. on
the polished surface of the semiconductor substrate such as the
wafer or the like. This permits the film on the alignment marks to
be polished in symmetry, improves the alignment accuracy, and
prevents the transfer of the grid-like groove pattern scribed in
the surface of the polishing pad, thereby improving the
microflatness and increasing the yields throughout the entire
production steps of semiconductor devices.
* * * * *