U.S. patent application number 13/080821 was filed with the patent office on 2011-10-20 for polishing method.
Invention is credited to Kenya Ito, Kenji Iwade, Takeo Kubota, Masayuki NAKANISHI, Masaya Seki.
Application Number | 20110256811 13/080821 |
Document ID | / |
Family ID | 44788542 |
Filed Date | 2011-10-20 |
United States Patent
Application |
20110256811 |
Kind Code |
A1 |
NAKANISHI; Masayuki ; et
al. |
October 20, 2011 |
POLISHING METHOD
Abstract
A polishing method can obtain a good polishing profile which,
for example, will not cause peeling of a semiconductor layer from a
silicon substrate. The polishing method includes: positioning a
polishing head at a position above a polishing start position in an
edge portion of a rotating substrate; lowering a polishing tool of
the polishing head until the polishing tool comes into contact with
the polishing start position in the edge portion of the rotating
substrate and a pressure between the polishing tool and the
polishing start position reaches a set pressure; allowing the
polishing tool to stay at the polishing start position for a
predetermined amount of time; and then moving the polishing head
toward a peripheral end of the substrate while keeping the
polishing tool in contact with the edge portion of the rotating
substrate at the set pressure.
Inventors: |
NAKANISHI; Masayuki; (Tokyo,
JP) ; Ito; Kenya; (Tokyo, JP) ; Seki;
Masaya; (Tokyo, JP) ; Iwade; Kenji;
(Hiratsuka-shi, JP) ; Kubota; Takeo; (Kuwana-shi,
JP) |
Family ID: |
44788542 |
Appl. No.: |
13/080821 |
Filed: |
April 6, 2011 |
Current U.S.
Class: |
451/41 |
Current CPC
Class: |
B24B 9/065 20130101;
B24B 21/002 20130101; B24B 21/04 20130101; B24B 37/042
20130101 |
Class at
Publication: |
451/41 |
International
Class: |
B24B 1/00 20060101
B24B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2010 |
JP |
2010-094732 |
Claims
1. A polishing method comprising: positioning a polishing head at a
position above a polishing start position in an edge portion of a
rotating substrate; lowering the polishing head and bringing a
polishing tool of the polishing head into contact with the
polishing start position in the edge portion of the rotating
substrate at a predetermined pressure; allowing the polishing tool
to stay at the polishing start position for a predetermined amount
of time; and then moving the polishing head toward a peripheral end
of the substrate while keeping the polishing tool in contact with
the edge portion of the rotating substrate at the predetermined
pressure.
2. The polishing method according to claim 1, herein the
predetermined amount of time is at least one second.
3. The polishing method according to claim 1, wherein the polishing
tool is a polishing tape which travels in one direction at a
predetermined speed when it polishes the edge portion of the
substrate.
4. The polishing method according to claim 1, wherein a bevel
portion of the substrate is polished while polishing the edge
portion of the substrate by keeping the polishing tool in contact
with the edge portion of the rotating substrate.
5. A polishing method comprising: positioning a polishing head at a
position above a polishing start position in an edge portion of a
rotating substrate; lowering a polishing tool of the polishing head
until the polishing tool comes into contact with the polishing
start position in the edge portion of the rotating substrate and a
pressure between the polishing tool and the polishing start
position reaches a set pressure; allowing the polishing tool to
stay at the polishing start position for a predetermined amount of
time; and then moving the polishing head toward a peripheral end of
the substrate while keeping the polishing tool in contact with the
edge portion of the rotating substrate at the set pressure.
6. The polishing method according to claim 5, wherein the
predetermined amount of time is at least one second.
7. The polishing method according to claim 5, wherein during a
period after contact of the polishing tool with the edge portion of
the substrate until the start of movement of the polishing head,
the contact pressure of the polishing tool on the edge portion of
the substrate is kept higher than the set pressure.
8. The polishing method according to claim 5, wherein after
lowering the polishing tool and bringing the polishing tool into
contact with the polishing start position in the edge portion of
the rotating substrate at a lower pressure than the set pressure,
the pressure of the polishing tool on the edge portion of the
substrate is increased to the set pressure.
9. The polishing method according to claim 5, wherein the polishing
tool is a polishing tape which travels in one direction at a
predetermined speed when it polishes the edge portion of the
substrate.
10. The polishing method according to claim 5, wherein a bevel
portion of the substrate is polished while polishing the edge
portion of the substrate by keeping the polishing tool in contact
with the edge portion of the rotating substrate.
11. A polishing method comprising: a first polishing including (a)
positioning a polishing head at a position above a polishing start
position in an edge portion of a rotating substrate, (b) lowering a
polishing tool of the polishing head until the polishing tool comes
into contact with the polishing start position in the edge portion
of the rotating substrate and a pressure between the polishing tool
and the polishing start position reaches a set pressure, and (c)
moving the polishing head toward a peripheral end of the substrate
at a first movement speed while keeping the polishing tool in
contact with the edge portion of the rotating substrate; and a
second polishing including (d) moving the polishing head toward the
peripheral end of the substrate at a second movement speed while
keeping the polishing tool in contact with the edge portion of the
rotating substrate.
12. The polishing method according to claim 11, wherein the second
movement speed of the polishing head is higher than the first
movement speed of the polishing head.
13. The polishing method according to claim 11, wherein when moving
the polishing head toward the peripheral end of the substrate at
the first movement speed, the contact pressure of the polishing
tool on the edge portion of the substrate is kept higher than the
set pressure.
14. The polishing method according to claim 11, wherein after
lowering the polishing tool and bringing the polishing tool into
contact with the polishing start position in the edge portion of
the rotating substrate at a lower pressure than the set pressure,
the pressure of the polishing tool on the edge portion of the
substrate is increased to the set pressure.
15. The polishing method according to claim 11, wherein the
polishing tool is a polishing tape which travels in one direction
at a predetermined speed when it polishes the edge portion of the
substrate.
16. The polishing method according to claim 11, wherein a bevel
portion of the substrate is polished while polishing the edge
portion of the substrate by keeping the polishing tool in contact
with the edge portion of the rotating substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing method for
polishing a peripheral portion (edge portion and bevel portion) of
a substrate, such as a semiconductor wafer, and more particularly
to a polishing method for polishing or grinding a peripheral
portion of a semiconductor wafer in the process of manufacturing a
semiconductor device in a surface of the semiconductor wafer.
[0003] 2. Description of the Related Art
[0004] A polishing apparatus, which uses a polishing tape having
abrasive particles fixed on a surface, is known as a polishing
apparatus for polishing a peripheral portion (edge portion and
bevel portion) of a substrate, such as a semiconductor wafer (see
Japanese Patent No. 4125148). In polishing of a peripheral portion
(edge portion and bevel portion) of a semiconductor wafer by the
use of a polishing tape, it is common practice to press a surface
of the polishing tape against the peripheral portion of the
semiconductor wafer, rotating in a horizontal plane, at a set
pressure while supplying a polishing liquid, such as pure water, to
a surface of the semiconductor wafer.
[0005] In a semiconductor wafer W shown in FIG. 1, for example, the
"bevel portion" herein refers to a portion B consisting of an upper
inclined portion P and a lower inclined portion Q of an upper
surface and a lower surface, respectively, of the semiconductor
wafer W, and a peripheral side surface portion R of the
semiconductor wafer W. The "edge portion" of the semiconductor
wafer W shown in FIG. 1, for example, herein refers to a portion E
lying between the boundary of the bevel portion B and a device area
D of the upper surface in which semiconductor devices are
formed.
[0006] A commonly-known polishing apparatus for polishing an edge
portion of a substrate with a polishing tape includes a
horizontally movable polishing head in which a polishing tape is
held movably in one direction. In operation of this polishing
apparatus, the polishing head is positioned immediately above a
polishing start position in an edge portion of a rotating
substrate, and the polishing tape is lowered and brought into
contact with the polishing start position in the edge portion of
the rotating substrate. When the contact pressure (load) of the
polishing tape on the edge portion of the substrate is found to
have reached a set pressure, the polishing tape is allowed to move
(scan) toward the peripheral end of the substrate at a
predetermined movement speed while keeping the polishing tape in
contact with the edge portion of the rotating substrate.
[0007] The applicant has proposed a polishing apparatus which can
polish a peripheral portion (edge portion) of a substrate,
including a flat portion, with a polishing tape while maintaining
the original angle of the peripheral portion (see Japanese Patent
Laid-Open Publication No. 2009-208214). The applicant has also
proposed a polishing apparatus which is suited for polishing of a
bevel portion of a substrate, can shorten the overall polishing
time and can facilitate replacement of polishing tape (see Japanese
Patent Laid-Open Publication No. 2009-154285).
[0008] It has recently been proposed to manufacture a bonded
substrate, such as an SOI (silicon-on-insulator) substrate, by a
bonding method which involves bonding, through heat treatment or
the like, two silicon substrates (a device substrate having
semiconductor devices and a supporting substrate). In a known
method for manufacturing a bonded substrate, such as an SOI
substrate, a first silicon substrate (device substrate), having a
surface semiconductor layer (SOI layer) and whose surface edge
portion has been polished away as necessary, and a second silicon
substrate (supporting substrate), facing each other, are bonded via
an insulting film, and then the back surface of the first silicon
substrate (device substrate) is polished or etched away, leaving
the semiconductor layer. Thereafter, an entire peripheral portion
of the semiconductor layer is polished away, and an edge portion of
the second silicon substrate is polished to a predetermined depth
(see Japanese Patent Laid-Open Publication No. H4-85827).
SUMMARY OF THE INVENTION
[0009] With reference to the conventional polishing apparatus which
includes a polishing head and in which a polishing tape is lowered
and brought into contact with a polishing start position in an edge
portion of a rotating substrate and, when the contact pressure of
the polishing tape on the edge portion of the substrate is found to
have reached a set pressure, the polishing tape is allowed to move
toward the peripheral end of the substrate at a predetermined
movement speed while keeping the polishing tape in contact with the
edge portion of the rotating substrate, it is generally difficult
to bring the polishing tape into contact with the polishing start
position in the edge portion of the substrate at a set pressure
upon the start of polishing and, in addition, the polishing tape
stays in the polishing start position generally for only a short
time. The conventional polishing apparatus, therefore, has the
problem that a polished surface of a substrate, at the boundary
with the non-polished surface, is likely to suffer from
insufficient polishing or uneven polishing.
[0010] Especially when manufacturing a bonded wafer, such as an SOI
substrate, by the above-described method in which a first silicon
substrate (device substrate), having a surface semiconductor layer,
and a second silicon substrate (supporting substrate), facing each
other, are bonded via an insulting film, and then the back surface
of the first silicon substrate (device substrate) is polished or
etched away, leaving the semiconductor layer, and thereafter the
entire peripheral portion of the semiconductor layer is polished
away, and the edge portion of the second silicon substrate is
polished to a predetermined depth, the semiconductor layer is
likely to peel off the second silicon substrate (supporting
substrate) if insufficient polishing or uneven polishing occurs at
the boundary of the polished surface with the non-polished
surface.
[0011] The present invention has been made in view of the above
situation. It is therefore an object of the present invention to
provide a polishing method which, e.g., when manufacturing a bonded
wafer, such as an SOI substrate, by the above-described method
comprising polishing away an entire peripheral portion of a
semiconductor layer of a first silicon substrate, and polishing an
edge portion of a second silicon substrate to a predetermined
depth, can obtain a good polishing profile which will not cause
peeling of the semiconductor layer from the second silicon
substrate.
[0012] In order to achieve the above object, the present invention
provides a polishing method comprising: positioning a polishing
head at a position above a polishing start position in an edge
portion of a rotating substrate; lowering the polishing head and
bringing a polishing tool of the polishing head into contact with
the polishing start position in the edge portion of the rotating
substrate at a predetermined pressure; allowing the polishing tool
to stay at the polishing start position for a predetermined amount
of time; and then moving the polishing head toward a peripheral end
of the substrate while keeping the polishing tool in contact with
the edge portion of the rotating substrate at the predetermined
pressure.
[0013] According to this polishing method, while keeping the
polishing tool in contact with a polishing start position in an
edge portion of a rotating substrate at a predetermined pressure,
the polishing tool is allowed to stay at the polishing start
position for a predetermined amount of time to polish the edge
portion at the polishing start position. This can prevent the
occurrence of insufficient polishing or uneven polishing at the
boundary of the polished surface with the non-polished surface,
making it possible to obtain a good polishing profile which, e.g.,
will not cause peeling of a surface film, such as a semiconductor
layer, from the substrate. Furthermore, even when a film to be
polished away is present in an edge portion of a substrate in an
uneven distribution in the circumferential direction, the film to
be polished away can be securely prevented from remaining in the
edge portion of the substrate by setting the polishing tool stay
time based on the location hardest to polish.
[0014] The present invention also provides a polishing method
comprising: positioning a polishing head at a position above a
polishing start position in an edge portion of a rotating
substrate; lowering a polishing tool of the polishing head until
the polishing tool comes into contact with the polishing start
position in the edge portion of the rotating substrate and a
pressure between the polishing tool and the polishing start
position reaches a set pressure; allowing the polishing tool to
stay at the polishing start position for a predetermined amount of
time; and then moving the polishing head toward a peripheral end of
the substrate while keeping the polishing tool in contact with the
edge portion of the rotating substrate at the set pressure.
[0015] According to this polishing method, while keeping the
polishing tool in contact with a polishing start position in an
edge portion of a rotating substrate at a set pressure, the
polishing tool is allowed to stay at the polishing start position
for a predetermined amount of time to polish the edge portion at
the polishing start position. This can prevent the occurrence of
insufficient polishing or uneven polishing at the boundary of the
polished surface with the non-polished surface, making it possible
to obtain a good polishing profile which, e.g., will not cause
peeling of a surface film, such as a semiconductor layer, from the
substrate.
[0016] In a preferred aspect of the present invention, the
predetermined amount of time is preferably at least one second.
[0017] In a preferred aspect of the present invention, during a
period after contact of the polishing tool with the edge portion of
the substrate until the start of movement of the polishing head,
the contact pressure of the polishing tool on the edge portion of
the substrate is kept higher than the set pressure.
[0018] Thus, the polishing rate can be increased when an edge
portion of a substrate is polished while allowing the polishing
tool to stay at the polishing start position in the edge portion of
the substrate for a predetermined amount of time. This can prevent
lowering of the throughput. In view of stress exerting on the
substrate, it is also possible to raise the rotational speed of the
substrate.
[0019] The present invention also provides a polishing method
comprising: a first polishing step including (a) positioning a
polishing head at a position above a polishing start position in an
edge portion of a rotating substrate, (b) lowering a polishing tool
of the polishing head until the polishing tool comes into contact
with the polishing start position in the edge portion of the
rotating substrate and a pressure between the polishing tool and
the polishing start position reaches a set pressure, and (c) moving
the polishing head toward a peripheral end of the substrate at a
first movement speed while keeping the polishing tool in contact
with the edge portion of the rotating substrate; and a second
polishing including (d) moving the polishing head toward the
peripheral end of the substrate at a second movement speed while
keeping the polishing tool in contact with the edge portion of the
rotating substrate.
[0020] By thus carrying out polishing of an edge portion of a
substrate in two steps at different polishing rates, a film to be
polished away, existing in the edge portion of the substrate, can
be polished under polishing conditions appropriate for the
particular film. Further, the inclination of a stepped portion,
formed at the boundary between the polished surface and the
non-polished surface of the substrate, can be arbitrarily changed
by changing polishing conditions.
[0021] The second movement speed of the polishing head is
preferably higher than the first movement speed of the polishing
head.
[0022] This can prevent the occurrence of insufficient polishing or
uneven polishing at the boundary of the polished surface of a
substrate with the non-polished surface, making it possible to
obtain a good polishing profile.
[0023] In a preferred aspect of the present invention, when moving
the polishing head toward the peripheral end of the substrate at
the first movement speed, the contact pressure of the polishing
tool on the edge portion of the substrate is kept higher than the
set pressure.
[0024] Thus, the polishing rate can be increased when the polishing
head is moving toward the peripheral end of the substrate at the
first movement speed. This can prevent lowering of the throughput.
In view of stress exerting on the substrate, it is also possible to
raise the rotational speed of the substrate.
[0025] In a preferred aspect of the present invention, after
lowering the polishing tool and bringing the polishing tool into
contact with the polishing start position in the edge portion of
the rotating substrate at a lower pressure than the set pressure,
the pressure of the polishing tool on the edge portion of the
substrate is increased to the set pressure.
[0026] This can minimize the stress exerting on the substrate when
the descending polishing tool comes into contact with the polishing
start position in the edge portion of the rotating substrate. In
the absence of a hard member, such as a stage, which supports an
edge portion of a substrate from below, a stress exerting on the
substrate could bend the substrate, which can result in the
formation of a crack in the substrate and, in the worst case,
breakage of the substrate. Such problems can be prevented by
minimizing the stress exerting on the substrate in the
above-described manner.
[0027] The polishing tool may preferably be a polishing tape which
travels in one direction at a predetermined speed when it polishes
the edge portion of the substrate.
[0028] In a preferred aspect of the present invention, a bevel
portion of the substrate is polished while polishing the edge
portion of the substrate by keeping the polishing tool in contact
with the edge portion of the rotating substrate.
[0029] The throughput can be increased by thus simultaneously
polishing the edge portion and the bevel portion of the substrate
while rotating the substrate.
[0030] A polishing apparatus may comprises: a substrate holding
section for holding and rotating a substrate in a horizontal
position; a horizontally movable polishing head including a
vertically movable polishing tool for polishing an edge portion of
the substrate by pressing it against the edge portion of the
rotating substrate held in a horizontal position by the substrate
holding section; and a control section for controlling the movement
of the polishing head, wherein the control section controls the
polishing head in such a manner that after the polishing tool has
come into contact with a polishing start position in the edge
portion of the rotating substrate and the contact pressure has
reached a set pressure, the polishing tool is allowed to stay at
the polishing start position for a predetermined amount of time,
and thereafter the polishing head moves toward the peripheral end
of the substrate while keeping the polishing tool in contact with
the edge portion of the rotating substrate at the set pressure.
[0031] Alternatively, a polishing apparatus may comprises: a
substrate holding section for holding and rotating a substrate in a
horizontal position; a horizontally movable polishing head
including a vertically movable polishing tool for polishing an edge
portion of the substrate by pressing it against the edge portion of
the rotating substrate held in a horizontal position by the
substrate holding section; and a control section for controlling
the movement of the polishing head, wherein the control section
controls the polishing head in such a manner that after the
polishing tool has come into contact with a polishing start
position in the edge portion of the rotating substrate and the
contact pressure has reached a set pressure, the polishing head
moves toward the peripheral end of the substrate at a first
movement speed while keeping the polishing tool in contact with the
edge portion of the rotating substrate, and thereafter the
polishing head moves toward the peripheral end of the substrate at
a second movement speed while keeping the polishing tool in contact
with the edge portion of the rotating substrate.
[0032] The polishing apparatuses may further comprise a bevel
polishing head for polishing a bevel portion of the rotating
substrate.
[0033] The present invention makes it possible to prevent the
occurrence of insufficient polishing or uneven polishing at the
boundary of a polished surface of a substrate with a non-polished
surface, and to obtain a good polishing profile which, e.g., will
not cause peeling of a surface film, such as a semiconductor layer,
from the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a cross-sectional view illustrating a bevel
portion and an edge portion of a semiconductor wafer;
[0035] FIG. 2 is a schematic front view of a polishing
apparatus;
[0036] FIG. 3 is a side view showing a tilt mechanism for tilting a
polishing head of the polishing apparatus shown in FIG. 2;
[0037] FIGS. 4A through 4D are diagrams illustrating, in a sequence
of process steps, the relationship between the polishing head and a
substrate upon polishing of an edge portion of the substrate in the
polishing apparatus shown in FIG. 2;
[0038] FIG. 5 is a graph showing an exemplary relationship between
the movement speed of the polishing head and time upon polishing of
an edge portion of a substrate in the polishing apparatus shown in
FIG. 2;
[0039] FIGS. 6A though 6C are graphs showing other exemplary
relationships between the movement speed of the polishing head and
time upon polishing of an edge portion of a substrate in the
polishing apparatus shown in FIG. 2;
[0040] FIG. 7 is a graph showing the relationship between polishing
amount and radial position on a substrate in Example 1;
[0041] FIG. 8 is a graph showing the relationship between polishing
amount and radial position on a substrate in Example 2;
[0042] FIG. 9 is a graph showing the relationship between polishing
amount and radial position on a substrate in Comp. Example 1
[0043] FIG. 10 is a photomicrograph of a substrate surface after
polishing (rough polishing) of an edge portion of a substrate,
showing a surface area around the boundary between the polished
surface and the non-polished surface;
[0044] FIG. 11 is a photomicrograph of a substrate surface after
polishing of an edge portion of a substrate in Example 3, showing a
surface area around the boundary between the polished surface and
the non-polished surface;
[0045] FIG. 12 is a photomicrograph of a substrate surface after
polishing of an edge portion of a substrate in Example 4, showing a
surface area around the boundary between the polished surface and
the non-polished surface;
[0046] FIG. 13 is a photomicrograph of a substrate surface after
polishing of an edge portion of a substrate in Comp. Example 2,
showing a surface area around the boundary between the polished
surface and the non-polished surface; and
[0047] FIG. 14 is a schematic view of another polishing
apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] Preferred embodiments of the present invention will now be
described in detail with reference to the drawings. FIG. 2 is a
schematic front view showing a polishing apparatus. As shown in
FIG. 2, this polishing apparatus includes a substrate holding
section 1 for holding and rotating a substrate W, such as a
semiconductor wafer, in a horizontal position, a polishing head 2
for polishing an edge portion of the substrate W held by the
substrate holding section 1, and a support section 3 for
supporting, from the back surface of the substrate W, the edge
portion of the substrate W held by the substrate holding section
1.
[0049] The substrate holding section 1 includes a substrate stage
11 for holding the substrate W, e.g., by vacuum attraction, and a
substrate rotating mechanism 12 for rotating the substrate stage
11. The substrate stage 11 has a smaller diameter than the
substrate W so that the substrate W is held with the edge portion
lying outside the substrate stage 11. The substrate rotating
mechanism 12 has a not-shown motor which is coupled to the
substrate stage 11. Thus, the substrate W held on the substrate
stage 11 rotates in a horizontal plane by rotating the motor of the
substrate rotating mechanism 12.
[0050] The polishing head 2 is provided with a polishing tape 10 as
a polishing tool for polishing the edge portion of the substrate W
by pressing it against the edge portion of the surface (upper
surface) of the substrate W. In this embodiment, the polishing tape
10 is used as a polishing tool. A polishing tape having abrasive
particles, such as diamond particles or SiC particles, fixed on one
surface of a base film, can be used as the polishing tape 10. The
surface of the polishing tape 10, on which the abrasive particles
are fixed, serves as a polishing surface. The abrasive particles of
the polishing tape 10 may be appropriately selected depending on
the type of the substrate W, the polishing performance required,
etc. For example, diamond particles or SiC particles, having an
average particle size in the range of 0.1 .mu.m to 5.0 .mu.m, can
be used as the abrasive particles. It is also possible to use a
belt-like polishing cloth having no abrasive particles. A film made
of a material having flexibility, such as polyester, polyurethane,
polyethylene terephthalate, etc., can be used as the base film.
[0051] The substrate holding section 1, the polishing head 2 and
the support section 3 are housed in a not-shown housing, and the
interior space of the hosing constitutes a polishing room. The
polishing tape 10 is fed to the polishing head 2 from a polishing
tape supply mechanism 15 which is disposed outside the polishing
room. The polishing tape supply mechanism 15 is secured to the
housing or a not-shown frame, so that the position of the mechanism
15 is fixed. The polishing tape supply mechanism 15 includes a tape
feeding mechanism 16 and a tape roll-up mechanism 17. The polishing
tape 10 is fed from the tape feeding mechanism 16 to the polishing
head 2, and is recovered from the polishing head 2 by the tape
roll-up mechanism 17. Because the polishing tape 10 is thus fed
continuously and gradually from the polishing tape supply mechanism
15 to the polishing head 2, polishing of the substrate W is
performed always by a new polishing surface.
[0052] The polishing head 2 includes a pressing pad 20 disposed on
the back side (opposite side from the polishing surface) of the
polishing tape 10, and a pressing mechanism 21, e.g., comprised of
a stepping motor or a servomotor, for applying a pressure to the
pressing pad 20. The position and the rotational speed of the
pressing mechanism 21 are controllable. The pressing pad 20 is
secured to a front end of a rod 22 which extends from the pressing
mechanism 21 and which is supported by a not-shown bearing slidably
in the longitudinal direction thereof. A pressure is applied by the
pressing mechanism 21 to the pressing pad 20 via the rod 22 so as
to press the polishing surface of the polishing tape 10 against the
surface of the substrate W. The pressure applied to the polishing
tape 10 is detected, e.g., by a pressure sensor provided between
the front end of the rod 22 and the pressing pad 20 or a torque
sensor which detects the motor torque, and is controlled, e.g., at
a set load (pressure), whereby the stop (stay) position of the
polishing tape 10 in the vertical direction is adjusted. Examples
of materials usable for the pressing pad 20 include elastic
materials such as silicone rubber, a silicone sponge, fluororubber,
etc., and rigid materials such as polybutylene naphthalate (PBN),
fluororesin, polyether ether ketone (PEEK), etc.
[0053] Instead of the above-described motor, it is possible to use
an air cylinder as a drive mechanism for the pressing mechanism 21.
Also in this case, it is possible to measure the pressure applied
to the polishing tape 10, e.g., with a pressure sensor provided
between the front end of the rod 22 and the pressing pad 20 or with
a pressure gauge which measures the air pressure in the air
cylinder, and to adjust the pressure on the polishing tape 10 to a
set load (pressure) by adjusting the pressure of air supplied to
the air cylinder, thereby accurately controlling the pressure of
the polishing tape 10 during polishing.
[0054] FIG. 3 is a side view showing a tilt mechanism for tilting
the polishing head 2. The polishing head 2 is coupled to a motor 29
via an arm 26, a belt 27 and pulleys 28A, 28B, so that by the
actuation of the motor 29, the polishing head 2 rotates (tilts)
around the peripheral end of the substrate W on the substrate
holding section 1. The arm 26, the belt 27, the pulleys 28A, 28B
and the motor 29 constitute a tilt mechanism for tilting the
polishing head 2.
[0055] The polishing head 2 is supported via the tilt mechanism by
a plate 30 which is provided on a sliding mechanism 31. The sliding
mechanism 31 allows the plate 30 to move in the longitudinal
direction of the sliding mechanism 31. The plate 30 is coupled to a
linear actuator 33 whose stop position and movement speed are
controllable, so that by the actuation of the linear actuator 33,
the polishing head 2 moves in the radial direction of the substrate
W held on the substrate holding section 1. Thus, the linear
actuator 33 constitutes a movement mechanism for moving the
polishing head 2 in the radial direction of the substrate W.
[0056] The polishing head 2 is disposed on the front surface (upper
surface) side of the substrate W held on the substrate holding
section 1, while the support section 3 is disposed on the back
surface (lower surface) side of the substrate W. Thus, the
polishing head 2 and the support section 3 are approximately
vertically symmetrical with respect to the substrate W. The support
section 3 supports the edge portion of the substrate W, which is
being pressed on by the polishing head 2, from the opposite side
(back side) of the substrate W from the edge portion by utilizing
the pressure of a fluid, as described below.
[0057] The support section 3 is coupled via a sliding mechanism 34
to the plate 30 that supports the polishing head 2. The sliding
mechanism 34 is coupled to a not-shown linear actuator mounted to
the plate 30. The support section 3 is thus movable in the radial
direction of the substrate W independently of the polishing head 2.
The support section 3 is connected to a liquid supply source 36 via
a pressure-reducing valve 35. A liquid, whose pressure is adjusted
by the pressure-reducing valve 35, is supplied to the support
section 3. The support section 3 has a nozzle 37 located near a
back surface portion opposite to the edge portion of the substrate
W. The liquid whose pressure has been adjusted by the
pressure-reducing valve 35 is ejected from the nozzle 37 toward the
edge portion of the back surface of the substrate W. Pure water is
preferably used as the liquid.
[0058] A polishing liquid supply nozzle 40 for supplying a
polishing liquid, such as pure water, onto the front surface (upper
surface) of the substrate W is disposed at a position above the
central portion of the substrate W held on the substrate holding
section 1. The polishing apparatus also includes a control section
42 for controlling the not-shown motor of the substrate rotating
mechanism 12, the pressing mechanism 21 of the polishing head 2,
and the linear actuator 33 which constitutes the movement mechanism
for moving the polishing head 2 in the radial direction of the
substrate W.
[0059] The control section 42 controls the rotational speed of the
not-shown motor of the substrate rotating mechanism 12, the
pressing load and the stop position of the pressing mechanism 21 of
the polishing head 2, the stop position and the movement speed of
the linear actuator 33, etc.
[0060] Polishing of an edge portion of a substrate by the polishing
apparatus of this embodiment will now be described with reference
further to FIGS. 4 and 5.
[0061] A substrate W is transported by a not-shown transport robot
into the polishing room of the polishing apparatus and placed on
the substrate stage 11 of the substrate holding section 1. The
substrate holding section 1, while performing centering of the
substrate W, holds the substrate W, e.g., by vacuum attraction and
rotates it in a horizontal plane. At the same time, a polishing
liquid, such as pure water, begins to be supplied from the
polishing liquid supply nozzle 40 onto the surface (upper surface)
of the substrate W.
[0062] Next, the polishing head 2, located in a stand-by position
beside the substrate W held on the substrate holding section 1, as
shown in FIG. 4A, is moved by the actuation of the linear actuator
33 to a position immediately above a polishing start position,
where the distance L.sub.1 from the peripheral end of the substrate
W to the pressing pad 20 is, e.g., 1.3 mm, in the edge portion of
the substrate W, as shown in FIG. 4B. By the actuation of the
linear actuator 33, the support section 3 moves to a position
immediately below the polishing start position in the edge portion
of the substrate W.
[0063] After the rotational speed of the substrate W is found to
have reached a predetermined rotational speed, the polishing tape
supply mechanism 15 is actuated to allow the polishing tape 10 to
travel from the tape feeding mechanism 16 to the tape roll-up
mechanism 17 via the polishing head 2 and to be rolled up by the
tape roll-up mechanism 17. At the same time, the pressing mechanism
21 is actuated to lower the pressing pad 20 and gradually bring the
polishing tape 10 into contact with the substrate W, as shown in
FIG. 4C, while a liquid is ejected from the nozzle 37 of the
support section 3 toward the edge portion of the lower surface of
the substrate W. Polishing of the edge portion of the substrate W
at a set pressure starts when the polishing tape 10 comes into
contact with the edge portion of the substrate W and the contact
pressure (load) reaches the set pressure.
[0064] Though the pressing pad 20 may be moved at a somewhat high
speed, the pressing mechanism 21 is preferably controlled so that
the load applied from the pressing pad 20 to the substrate W
increases gradually. This can minimize the stress exerting on the
substrate W when the descending polishing tape 10 comes into
contact with the polishing start position in the edge portion of
the rotating substrate W. In the absence of a hard member, such as
a stage, which supports an edge portion of a substrate from below,
a stress applied to a substrate could bend the substrate, which can
result in the formation of a crack in the substrate and, in the
worst case, breakage of the substrate. Such problems can be
prevented by minimizing the stress exerting on the substrate W in
the above-described manner.
[0065] As shown in FIG. 5, polishing is continued while keeping the
vertical position of the polishing tape 10 fixed and allowing the
polishing head 2 to stay at the position immediately above the
polishing start position in the edge portion of the substrate W for
a predetermined amount of time between time t.sub.1 and time
t.sub.2 (t.sub.2-t.sub.1), t.sub.1 being the time when the
polishing starts at the set pressure after the polishing tape 10
has come into contact with the edge portion of the substrate W and
the contact pressure has reached the set pressure. The
predetermined amount of time (t.sub.2-t.sub.1) is set based on the
location hardest to polish, and is generally at least about one
second, preferably at least 10 seconds, more preferably 20 to 40
seconds.
[0066] Thus, while keeping the polishing tape 10 in contact with
the polishing start position in the edge portion of the rotating
substrate W at the set pressure, the polishing tape 10 is allowed
to stay at the polishing start position for a predetermined amount
of time to polish the edge portion at the polishing start position.
This can prevent the occurrence of insufficient polishing or uneven
polishing at the boundary of the polished surface with the
non-polished surface, making it possible to obtain a good polishing
profile which, e.g., will not cause peeling of a surface film, such
as a semiconductor layer, from the substrate W. Furthermore, even
when a film to be polished away is present in the edge portion of
the substrate W in an uneven distribution in the circumferential
direction, the film to be polished away can be securely prevented
from remaining in the edge portion of the substrate W by setting
the stay time of the polishing tape 10 based on the location
hardest to polish.
[0067] The polishing tape 10 may be allowed to stay at the
polishing start position in the edge portion of the substrate W for
a predetermined amount of time while keeping the polishing tape 10
in contact with the polishing start position at a pressure higher
than the set pressure. According to this manner, the polishing rate
can be increased when the edge portion of the substrate W is
polished while allowing the polishing tape 10 to stay at the
polishing start position in the edge portion of the substrate W for
a predetermined amount of time. This can prevent lowering of the
throughput. In view of stress exerting on the substrate, it is also
possible to raise the rotational speed of the substrate W.
[0068] As shown in FIG. 5, after the predetermined amount of time
has elapsed (after time t.sub.2), the polishing head 2 is moved at
a predetermined speed V.sub.0 toward the peripheral end of the
substrate W while keeping the polishing tape 10 in contact with the
edge portion of the rotating substrate W at the set pressure to
continue polishing of the edge portion of the substrate W with the
polishing tape 10. During the polishing, the angle of the polishing
head 2 with respect to the substrate W may be changed by the tilt
mechanism, as necessary.
[0069] After the polishing head 2 has reached a polishing end
position where the distance L.sub.2 between the peripheral end of
the substrate W and the pressing pad 20 is, for example, 0.4 mm,
the polishing head 2 is moved at a high speed to the stand-by
position beside the substrate W, as shown in FIG. 4D.
[0070] As shown in FIG. 6A, polishing of the edge portion of the
substrate W may be carried out by a method comprising: carrying out
a first polishing step of moving the polishing head 2 at a first
movement speed V.sub.1, e.g., not more than 50 .mu.m/sec, toward
the peripheral end of the substrate W from time t.sub.1 when the
polishing tape 10 has come into contact with the edge portion of
the substrate W and the contact pressure reaches the set pressure,
while keeping the polishing tape 10 in contact with the edge
portion of the rotating substrate W; carrying out polishing for a
certain distance (up to time t.sub.3); and carrying out a second
polishing step of further moving the polishing head 2 at a second
movement speed V.sub.2, e.g., 50 .mu.m/sec to 100 .mu.m/sec, toward
the peripheral end of the substrate W while keeping the polishing
tape 10 in contact with the edge portion of the rotating substrate
W.
[0071] This polishing method can significantly shorten the
polishing time while preventing the occurrence of insufficient
polishing or uneven polishing at the boundary of the polished
surface with the non-polished surface. In addition, the polishing
amount can be made smaller in the surface area lying closer to a
peripheral end of a substrate. This polishing method is thus
especially effective for a substrate in which a film to be polished
away is thinner on the peripheral end side.
[0072] The contact pressure of the polishing tape 10 on the edge
portion of the substrate W during the movement of the polishing
head 2 at the second movement speed V.sub.2 may be changed from
that during the movement of the polishing head 2 at the first
movement speed V.sub.1. This can further shorten the polishing
time.
[0073] In this case, the first movement speed of the polishing head
2 may be increased linearly from the movement speed V.sub.1 to the
movement speed V.sub.2, as shown in FIG. 6B, or may be increased
gradually from the movement speed V.sub.1 to the movement speed
V.sub.2, as shown in FIG. 6C so as to avoid a rapid change in the
movement speed of the polishing head 2.
[0074] The accuracy of positioning of the polishing head 2 is very
important in the above-described embodiment. Because the movement
speed of the polishing head 2 is as low as about 1 .mu.m per
second, it is also very important to enhance the accuracy of the
movement speed (amount of change, error) of the polishing head 2.
It is, therefore, preferred to perform positioning of the polishing
head 2 with high accuracy and accurately control the movement speed
of the polishing head 2 by using, for example, a servomotor or a
stepping motor as the linear actuator 33.
[0075] Further, it is preferred that setting values for time to
stop the polishing head 2, the movement speed of the polishing head
2, etc. can be easily changed through program control by
digitalizing and inputting process sequence, process conditions,
etc.
Example 1
[0076] Polishing of an edge portion of a substrate was carried out
using the polishing apparatus shown in FIG. 2. A tape having #4000
diamond abrasive particles fixed thereon was used as a polishing
tape, and a resin pad whose lower end, which is to make contact
with the polishing tape, has a radius of curvature of 0.5 mm was
used as the pressing pad of the polishing head. While allowing the
polishing tape to travel at a speed of 10 mm/min, the polishing
tape was pressed against a polishing start position in the edge
portion of the substrate, rotating at 500 rpm, at a load of 10 N by
the pressing pad of the polishing head whose position was fixed,
thereby polishing the edge portion at the polishing start position
for 20 seconds. Thereafter, polishing was continued by pressing the
polishing tape against the edge portion of the substrate, rotating
at 500 rpm, at a load of 10 N while moving the polishing head
toward the peripheral end of the substrate at a movement speed of 5
.mu.m/min. The results of the polishing, i.e., the relationship
between polishing amount and radial position (measurement position)
on the substrate, are shown in FIG. 7.
[0077] In FIG. 7, the "notch" curve represents the polishing amount
on a line connecting the center and a notch of the substrate
(center-notch line); the "90.degree." curve represents the
polishing amount on a line corresponding to the center-notch line
as it is rotated by 90 degrees counterclockwise; the "180.degree."
curve represents the polishing amount on a line corresponding to
the center-notch line as it is rotated by 180 degrees
counterclockwise; and the "270.degree." curve represents the
polishing amount on a line corresponding to the center-notch line
as it is rotated by 270 degrees counterclockwise. This holds true
for FIGS. 8 and 9.
Example 2
[0078] Polishing of an edge portion of the same substrate was
carried out in the same manner as in Example 1 except that the edge
portion at the polishing start position was polished for 40
seconds. The results of the polishing, i.e., the relationship
between polishing amount and radial position (measurement position)
on the substrate, are shown in FIG. 8.
Comp. Example 1
[0079] Polishing of an edge portion of the same substrate was
carried out in the same manner as in Example 1 except that
polishing of the edge portion of the substrate was started by
pressing the polishing tape against the polishing start position in
the edge portion of the substrate, rotating at 500 rpm, at a load
of 10 N by the pressing pad of the polishing head and, immediately
after the start of polishing, the polishing head was moved toward
the peripheral end of the substrate at a movement speed of 5
.mu.m/min. The results of the polishing, i.e., the relationship
between polishing amount and radial position (measurement position)
on the substrate, are shown in FIG. 9.
[0080] As can be seen in FIGS. 7 through 9, the inclination at the
boundary between the polished surface and the non-polished surface
is steeper in Examples 1 and 2 than in Comp. Example 1. Further,
the inclination is steeper in Example 2 than in Example 1.
Example 3
[0081] First, an edge portion of a substrate was subjected to
polishing (rough polishing) with a polishing tape having #4000
diamond abrasive particles fixed thereon. FIG. 10 shows a
photomicrograph of a surface area around the boundary between the
polished surface and the non-polished surface of the substrate
after the rough polishing. Thereafter, polishing of the edge
portion of the substrate was carried out in the same manner as in
Example 1 except that the edge portion at the polishing start
position was polished for 10 seconds by using a polishing tape
having #12000 diamond abrasive particles fixed thereon and pressing
the polishing tape against the polishing start position of the
rotating substrate by the pressing pad of the polishing head whose
position was fixed. FIG. 11 shows a photomicrograph of a surface
area around the boundary between the polished surface and the
non-polished surface of the substrate after the polishing.
Example 4
[0082] Polishing of an edge portion of the same substrate was
carried out in the same manner as in Example 3 except that an edge
portion at the polishing start position was polished for 20
seconds. FIG. 12 shows a photomicrograph of a surface area around
the boundary between the polished surface and the non-polished
surface of the substrate after the polishing.
Comp. Example 2
[0083] Polishing of an edge portion of the same substrate was
carried out in the same manner as in Example 3 except that
polishing of an edge portion of the substrate was started by
pressing the polishing tape against the polishing start position in
the edge portion of the substrate, rotating at 500 rpm, at a load
of 10 N by the pressing pad of the polishing head and, immediately
after the start of polishing, the polishing head was moved toward
the peripheral end of the substrate at a movement speed of 5
.mu.m/min. FIG. 13 shows a photomicrograph of a surface area around
the boundary between the polished surface and the non-polished
surface of the substrate after the polishing.
[0084] As can be seen in FIGS. 11 through 13, sawtooth
irregularities due to uneven polishing were formed in the vicinity
of the boundary between the polished surface and the non-polished
surface of the substrate after the polishing in Comp. Example 2,
whereas no such irregularities were formed in Examples 3 and 4.
This demonstrates that the polishing method according to the
present invention can prevent the occurrence of uneven
polishing.
[0085] FIG. 14 schematically shows another polishing apparatus.
This polishing apparatus, in addition to the polishing head 2 of
the above-described embodiment for polishing an edge portion of a
substrate, further includes a bevel polishing head 50 for contact
with a bevel portion of a rotating substrate W to polish the bevel
portion. The bevel polishing head 50 is disposed lateral to the
substrate W held on the substrate stage 11 of the substrate holding
section 1. The bevel polishing head 50 includes a polishing tape
52, a pressing pad 54 disposed on a back side (opposite side from a
polishing surface) of the polishing tape 52, and a pressing
mechanism 56, e.g., comprised of a cylinder, for applying a
pressure to the pressing pad 54.
[0086] In operation, while supplying a polishing liquid from the
polishing liquid supply nozzle 40 onto a surface of a substrate W,
which is held on the substrate stage 11 and is rotating at a
predetermined rotational speed, the polishing tape 10 of the
polishing head 2 is pressed against the edge portion of the
substrate W at a predetermined pressure and the polishing tape 52
of the bevel polishing head 50 is pressed against the bevel portion
of the substrate W at a predetermined pressure to simultaneously
polish the edge portion and the bevel portion of the substrate W.
This embodiment can thus increase the throughput and, in addition,
can reduce the usage of a polishing liquid, thereby reducing the
production cost.
[0087] When there is a difference between the time it takes to
polish the bevel portion of the substrate W and the time it takes
to polish the edge portion of the substrate W, the polishing rate
can be lowered for the polishing head for the less time requiring
polishing. Thus, the traveling speed of the polishing tape can be
slowed down, or the usage of the polishing tape can be reduced.
This can reduce the polishing cost.
[0088] Further, the overall polishing time can be shortened. This
can reduce the risk of contamination of a substrate surface in
which devices are formed.
[0089] Further, when there is an imbalance in processing time
between polishing and other processing, the processing times can be
balanced by simultaneously carrying out polishing of an edge
portion of a substrate and polishing of a bevel portion of the
substrate. It thus becomes possible to operate the apparatus in the
most efficient manner.
[0090] While the present invention has been described with
reference to preferred embodiments, it is understood that the
present invention is not limited to the embodiments described
above, but is capable of various changes and modifications within
the scope of the inventive concept as expressed herein.
* * * * *