U.S. patent application number 17/347755 was filed with the patent office on 2022-01-20 for polishing apparatus and polishing method.
The applicant listed for this patent is DISCO CORPORATION. Invention is credited to Toshiyuki MORIYA, Takamasa SUZUKI.
Application Number | 20220016740 17/347755 |
Document ID | / |
Family ID | 1000005694652 |
Filed Date | 2022-01-20 |
United States Patent
Application |
20220016740 |
Kind Code |
A1 |
MORIYA; Toshiyuki ; et
al. |
January 20, 2022 |
POLISHING APPARATUS AND POLISHING METHOD
Abstract
A polishing apparatus for polishing a workpiece includes a chuck
table having a holding surface for holding the workpiece placed on
the holding surface under suction thereon, a polishing unit for
polishing the workpiece held on the chuck table with a polishing
pad while supplying a slurry to the workpiece, and a high-pressure
steam ejecting unit having a nozzle for ejecting high-pressure
steam to the holding surface of the chuck table. The high-pressure
steam ejecting unit ejects high-pressure steam to swarf produced
from polishing the workpiece and deposited on an outer
circumferential portion of the holding surface for thereby removing
the swarf from the holding surface.
Inventors: |
MORIYA; Toshiyuki; (Tokyo,
JP) ; SUZUKI; Takamasa; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DISCO CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
1000005694652 |
Appl. No.: |
17/347755 |
Filed: |
June 15, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 37/10 20130101;
B24B 53/017 20130101; B24B 37/20 20130101; B24B 37/30 20130101 |
International
Class: |
B24B 37/20 20060101
B24B037/20; B24B 53/017 20060101 B24B053/017; B24B 37/30 20060101
B24B037/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 14, 2020 |
JP |
2020-120358 |
Claims
1. A polishing apparatus for polishing a workpiece, comprising: a
chuck table having a holding surface for holding the workpiece
placed on the holding surface under suction thereon; a polishing
unit for polishing the workpiece held on the chuck table with a
polishing pad while supplying a slurry to the workpiece; and a
high-pressure steam ejecting unit having a nozzle for ejecting
high-pressure steam to the holding surface of the chuck table,
wherein the high-pressure steam ejecting unit ejects high-pressure
steam to swarf produced from polishing the workpiece and deposited
on an outer circumferential portion of the holding surface for
thereby removing the swarf from the holding surface.
2. A polishing method to be carried out by a polishing apparatus
including a chuck table for holding a workpiece placed on a holding
surface under suction and a polishing unit for polishing the
workpiece held on the chuck table with a polishing pad while
supplying a slurry to the workpiece, the polishing method
comprising: a holding step of placing the workpiece on the holding
surface and holding the workpiece on the chuck table; a polishing
step of polishing the workpiece held on the chuck table with the
polishing pad while supplying the slurry to the workpiece; an
unloading step of unloading the workpiece polished in the polishing
step from the chuck table; and a swarf removing step of ejecting
high-pressure steam to swarf produced from polishing the workpiece
and deposited on an outer circumferential portion of the holding
surface for thereby removing the swarf from the holding surface.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a polishing apparatus for
polishing a workpiece such as a semiconductor wafer and a polishing
method for polishing such a workpiece with a polishing
apparatus.
Description of the Related Art
[0002] According to a fabrication step for fabricating device chips
to be used in electronic equipment such as mobile phones and
computers, a plurality of devices such as integrated circuits (ICs)
or large-scale-integration (LSI) circuits are initially formed on a
face side of a semiconductor wafer. Next, a reverse side of the
semiconductor wafer is ground to thin the semiconductor wafer to a
predetermined thickness, and then the semiconductor wafer is
divided into individual device chips. When the reverse side of the
semiconductor wafer is ground, minute surface irregularities are
formed as grinding marks on the ground reverse side. Such minute
surface irregularities remain as they are on the device chips
divided from the semiconductor wafer. The minute surface
irregularities are responsible for a reduction in the flexural
strength of the device chips. It is known in the art to polish the
reverse side of the wafer according to a chemical mechanical
polishing (CMP) process or the like after the wafer has been ground
(see JP Hei 8-99265A).
[0003] A polishing apparatus for polishing a workpiece such as a
wafer includes a chuck table for holding the workpiece on a holding
surface thereof and a polishing unit having a polishing pad mounted
thereon for polishing the workpiece held on the chuck table. When
the workpiece is polished by the polishing apparatus, minute
surface irregularities on the ground surface of the wafer are
removed, giving the wafer a mirror finish. While the workpiece is
being polished on the polishing apparatus, the surface being
polished of the wafer is supplied with a slurry as a polishing
fluid. The slurry is a chemical fluid with abrasive grains
dispersed therein, for example. The slurry contributes not only to
the polishing of the wafer through chemical and mechanical actions,
but also to the discharging of swarf produced from polishing the
wafer. The slurry is supplied from a supply channel defined
centrally in the polishing pad, and travels between the polishing
pad and the workpiece to an outer circumferential edge of the
workpiece.
SUMMARY OF THE INVENTION
[0004] After having reached the outer circumferential edge of the
workpiece, the slurry that contains the swarf falls off the surface
being polished of the wafer and is deposited on and adheres to an
outer circumferential portion of the holding surface of the chuck
table. When the polished workpiece is unloaded from the chuck
table, therefore, the adhering swarf remains on the holding surface
of the chuck table in surrounding relation to an area of the
holding surface where the workpiece has been present.
[0005] When a workpiece to be polished by the polishing pad is to
be loaded onto the chuck table, the adhering swarf on the chuck
table tends to enter between the chuck table and the workpiece,
obstructing the loading of the workpiece onto the chuck table. One
solution is to supply cleaning water to the outer circumferential
portion of the holding surface of the chuck table in order to
remove the adhering swarf from the chuck table. However, it is not
easy to remove the adhering swarf from the chuck table with the
cleaning water. According to another solution, a sufficient amount
of cleaning water is supplied to the outer circumferential portion
of the holding surface of the chuck table while the workpiece is
being polished by the polishing pad in order to wash away the
slurry before the slurry containing the swarf that has reached the
outer circumferential portion of the holding surface adheres to the
holding surface. However, one problem with the latter solution is
that the supplied cleaning water is mixed with the slurry supplied
between the polishing pad and the workpiece, thinning down the
slurry to the extent that the polishing process cannot be performed
properly.
[0006] It is therefore an object of the present invention to
provide a polishing apparatus and a polishing method that are
capable of removing swarf produced from polishing a workpiece held
on a chuck table and adhering to an outer circumferential portion
of the chuck table.
[0007] In accordance with an aspect of the present invention, there
is provided a polishing apparatus for polishing a workpiece,
including a chuck table having a holding surface for holding the
workpiece placed on the holding surface under suction thereon, a
polishing unit for polishing the workpiece held on the chuck table
with a polishing pad while supplying a slurry to the workpiece, and
a high-pressure steam ejecting unit having a nozzle for ejecting
high-pressure steam to the holding surface of the chuck table. The
high-pressure steam ejecting unit ejects high-pressure steam to
swarf produced from polishing the workpiece and deposited on an
outer circumferential portion of the holding surface for thereby
removing the swarf from the holding surface.
[0008] In accordance with another aspect of the present invention,
there is provided a polishing method to be carried out by a
polishing apparatus including a chuck table for holding a workpiece
placed on a holding surface under suction and a polishing unit for
polishing the workpiece held on the chuck table with a polishing
pad while supplying a slurry to the workpiece, the polishing method
including a holding step of placing the workpiece on the holding
surface and holding the workpiece on the chuck table, a polishing
step of polishing the workpiece held on the chuck table with the
polishing pad while supplying the slurry to the workpiece, an
unloading step of unloading the workpiece polished in the polishing
step from the chuck table, and a swarf removing step of ejecting
high-pressure steam to swarf produced from polishing the workpiece
and deposited on an outer circumferential portion of the holding
surface for thereby removing the swarf from the holding
surface.
[0009] With the polishing apparatus and the polishing method
according to the above aspects of the present invention, the
workpiece is polished by the polishing pad while the slurry is
being supplied to the workpiece. When the workpiece is ground,
swarf produced from polishing the workpiece is deposited on the
outer circumferential portion of the holding surface of the chuck
table. The high-pressure steam is ejected to the swarf adhering to
the outer circumferential portion of the holding surface, softening
the swarf because the swarf is heated and water is applied to the
swarf. Therefore, when the high-pressure steam is continuously
ejected to the swarf, the adhering swarf can be removed relatively
and easily from the holding surface. Upon removal of the swarf from
the holding surface, a new workpiece can be placed on the holding
surface without fail.
[0010] According to the above aspects of the present invention,
consequently, there are provided a polishing apparatus and a
polishing method that are capable of removing swarf adhering to the
outer circumferential portion of the chuck table.
[0011] The above and other objects, features and advantages of the
present invention and the manner of realizing them will become more
apparent, and the invention itself will best be understood from a
study of the following description and appended claims with
reference to the attached drawings showing a preferred embodiment
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a perspective view schematically illustrating a
polishing apparatus according to an embodiment of the present
invention;
[0013] FIG. 2 is a perspective view schematically illustrating a
polishing wheel of the polishing apparatus;
[0014] FIG. 3 is a perspective view schematically illustrating a
manner in which a protective member is affixed to a face side of a
workpiece to be polished;
[0015] FIG. 4 is a perspective view schematically illustrating a
manner in which the workpiece is placed on a holding surface of a
chuck table of the polishing apparatus;
[0016] FIG. 5 is a perspective view schematically illustrating a
manner in which the workpiece is polished by the polishing
wheel;
[0017] FIG. 6 is a perspective view schematically illustrating a
manner in which the workpiece that has been polished is unloaded
from the holding surface of the chuck table;
[0018] FIG. 7A is a perspective view schematically illustrating a
manner in which an outer circumferential portion of the holding
surface of the chuck table is cleaned;
[0019] FIG. 7B is a perspective view schematically illustrating the
chuck table after the holding surface thereof has been cleaned;
[0020] FIG. 8A is a flowchart of a sequence of steps of an example
of a polishing method for polishing a workpiece;
[0021] FIG. 8B is a flowchart of a sequence of steps of another
example of the polishing method; and
[0022] FIG. 8C is a flowchart of a sequence of steps of still
another example of the polishing method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] A preferred embodiment of the present invention will be
described below with reference to the accompanying drawings. First,
a workpiece to be polished by a polishing apparatus and a polishing
method according to the preferred embodiment will be described
below with reference to FIG. 3. FIG. 3 schematically illustrates in
perspective a workpiece 1 such as a semiconductor wafer. The
workpiece 1 may include, for example, a wafer made of silicon,
silicon carbide (SiC), or other materials including a semiconductor
or the like, or a substrate shaped as a substantially circular
plate made of sapphire, glass, quartz, or the like. The workpiece 1
has a face side 1a where a plurality of areas are demarcated by a
grid of projected dicing lines or streets 5 established on the face
side 1a. A plurality of devices 7 such as ICs or LSI circuits are
formed respectively in the areas on the face side 1a. The workpiece
1 will be divided finally along the projected dicing lines 5 into
individual device chips including the respective devices 7.
[0024] The workpiece 1 is thinned down by having a reverse side 1b
thereof ground. The ground reverse side 1b of the workpiece 1 has
minute surface irregularities formed as grinding marks. If the
workpiece 1 with the minute surface irregularities left on the
reverse side 1b is divided along the projected dicing lines 5 into
individual device chips, then the minute surface irregularities
remain as they are on the device chips and are responsible for a
reduction in the flexural strength of the device chips. To
alleviate such a drawback, the ground reverse side 1b of the
workpiece 1 is polished to remove the minute surface irregularities
therefrom, making the reverse side 1b flat. Therefore, no minute
surface irregularities remain on the device chips divided from the
workpiece 1.
[0025] In preparation for the process of polishing the reverse side
1b of the workpiece 1, a protective tape 3 is affixed in advance to
the face side 1a of the workpiece 1 to protect the face side 1a.
The protective tape 3 protects the face side 1a of the workpiece 1
from shocks to be caused by polishing the reverse side 1b of the
workpiece 1 is polished, delivering the workpiece 1, and otherwise
handling or processing the workpiece 1. The protective tape 3 has a
flexible film-shaped base and a glue layer, i.e., an adhesive
layer, formed on a surface of the base. The base is made of
polyolefin, polyethylene terephthalate, polyvinyl chloride,
polystyrene, or the like, for example. The glue layer is made of
silicone rubber, an acrylic material, an epoxy material, or the
like, for example.
[0026] A polishing apparatus according to the present embodiment
for polishing the reverse side 1b of the workpiece 1 as a surface
to be polished will be described below. FIG. 1 illustrates a
polishing apparatus, denoted by 2, in perspective. As illustrated
in FIG. 1, the polishing apparatus 2 has a base block 4 supporting
various components thereof. The polishing apparatus 2 includes two
cassette rests 6a and 6b on an upper surface of a front portion of
the base block 4. A cassette 8a storing therein a plurality of
workpieces 1 to be polished is placed on the cassette rest 6a, for
example. A cassette 8b storing therein a plurality of workpieces 1
that have been polished is placed on the cassette rest 6b, for
example. A workpiece deliver robot 10 for delivering a workpiece 1
at a time is installed on the base block 4 adjacent to the cassette
rests 6a and 6b.
[0027] On the upper surface of the front portion of the base block
4, there are also disposed a positioning table 12 for adjusting the
position of a workpiece 1 by gripping the workpiece 1 with a
plurality of positioning pins and a workpiece loading mechanism or
arm 14 for placing a workpiece 1 on a chuck table 20. In addition,
a workpiece unloading mechanism or arm 16 for taking a polished
workpiece 1 from the chuck table 20 and a spinner cleaning device
52 for cleaning and spin-drying a polished workpiece 1 are disposed
on the upper surface of the front portion of the base block 4.
[0028] The base block 4 has an opening 4a defined in an upper
surface of a rear portion thereof. The opening 4a houses therein an
X-axis movable table 18 with the chuck table 20 placed on an upper
surface thereof for holding a workpiece 1 under suction thereon.
The X-axis movable table 18 is movable in X-axis directions, i.e.,
horizontal directions, by an X-axis moving mechanism, not
illustrated. The X-axis movable table 18 is selectively positioned
in a loading/unloading area 22 where a workpiece 1 can be placed on
and removed from the chuck table 20 and a processing area 24 where
a workpiece 1 held under suction on the chuck table 20 is polished.
The chuck table 20 includes a porous member shaped as a circular
plate having a diameter that is essentially the same as the
diameter of the workpiece 1. The porous member has an upper surface
exposed upwardly and defining an upper surface of the chuck table
20 as a holding surface 20a for holding the workpiece 1 thereon.
The chuck table 20 has a suction channel, not illustrated, defined
therein that has an end held in fluid communication with the porous
member and another end connected to a suction source, not
illustrated. When the suction source is actuated, it generates a
negative pressure that is transmitted through the suction channel
and the porous member to the workpiece 1 placed on the holding
surface 20a, holding the workpiece 1 under suction on the holding
surface 20a. The chuck table 20 is rotatable about an axis
perpendicular to the holding surface 20a.
[0029] A polishing unit 26 for polishing a workpiece 1 is disposed
above the processing area 24. The polishing unit 26 is supported on
a support wall 28 erected on a rear end of the base block 4 of the
polishing apparatus 2. Specifically, a pair of Z-axis guide rails
30 extending in Z-axis directions, i.e., vertical directions, are
mounted on a front vertical surface of the support wall 28. A
Z-axis movable plate 32 is vertically slidably mounted on the
Z-axis guide rails 30. A nut, not illustrated, is disposed on a
reverse side, i.e., rear surface, of the Z-axis movable plate 32
and operatively threaded over a Z-axis ball screw 34 extending
between and parallel to the Z-axis guide rails 30. The Z-axis ball
screw 34 has an end coupled to a Z-axis stepping motor 36. When the
Z-axis stepping motor 36 is energized, it rotates the Z-axis ball
screw 34 about its central axis, causing the nut to move the Z-axis
movable plate 32 in the Z-axis directions along the Z-axis ball
screw 34. The polishing unit 26 is fixedly mounted on a lower
portion of a face side, i.e., front surface, of the Z-axis movable
plate 32. Therefore, when the Z-axis movable plate 32 is moved in
the Z-axis directions, the polishing unit 26 is also moved in the
Z-axis directions in unison therewith.
[0030] The polishing unit 26 includes a spindle 40 movable about
its central axis extending vertically by an electric motor coupled
to a proximal end of the spindle 40 and a polishing wheel 44 fixed
by fasteners 46 to a wheel mount 42 disposed on a distal end of the
spindle 40. The electric motor is housed in a spindle housing 38 in
which the spindle 40 is rotatably supported. When the electric
motor is energized, it rotates the spindle 40 about its central
axis, causing the polishing wheel 44 to rotate in unison with the
spindle 40.
[0031] FIG. 2 schematically illustrates a polishing surface side of
the polishing wheel 44 in perspective. The polishing wheel 44
includes a polishing pad 44b made of felt of urethane or the like
and having a diameter larger than the diameter of the reverse side
1b of the workpiece 1 and a wheel base 44a having a surface to
which the polishing pad 44b is fixedly attached. The wheel base 44a
has a plurality of fastener holes, not illustrated, defined in a
surface thereof that is opposite the surface to which the polishing
pad 44b is fixedly attached. The fasteners 46 are threaded through
the wheel mount 42 into the respective fastener holes, fastening
the polishing wheel 44 to the wheel mount 42. The wheel base 44a
and the polishing pad 44b of the polishing wheel 44 have a through
hole defined therein that extends centrally thicknesswise
therethrough. The through hole has an end in the polishing pad 44b
that acts as a polishing fluid supply port 54.
[0032] As indicated by the broken lines in FIG. 1, the polishing
unit 26 has a polishing fluid supply passage 50 defined therein
that extends vertically in the Z-axis directions. The polishing
fluid supply passage 50 has an upper end connected to a polishing
fluid supply source 48 and a lower end connected to the polishing
fluid supply port 54. When the workpiece 1 is polished by the
polishing unit 26, a polishing fluid referred to as a slurry is
supplied from the polishing fluid supply source 48 through the
polishing fluid supply passage 50 to the polishing fluid supply
port 54 (see FIG. 2) defined centrally in the polishing pad 44b.
The slurry is a chemical fluid with abrasive grains dispersed
therein, and the material of the abrasive grains, the diameter of
the abrasive grains, the kind of a dispersion medium used, etc.,
are appropriately selected depending on the material of the
workpiece 1. The abrasive grains may be made of, for example,
silica, alumina, zirconia, manganese dioxide, ceria, colloidal
silica, fumed silica, boehmite, bayerite, diamond, or the like. The
dispersion medium may be made of, for example, an alkali aqueous
solution of potassium acetate, potassium chloride, potassium
hydroxide, sodium hydroxide, ammonium carbonate, potassium
hydrogencarbonate, sodium hydrogencarbonate, imidazole, pyrazole,
pyrazine, or the like. However, the materials that are contained in
the slurry are not limited to the above materials, and other
additives, etc., may be added to the slurry.
[0033] For polishing a workpiece 1 held on the chuck table 20
positioned in the processing area 24, the polishing pad 44b is
positioned above the workpiece 1 on the chuck table 20. Then, the
polishing wheel 44 and the chuck table 20 are rotated about their
respective axes extending vertically in the Z-axis directions, and
the polishing wheel 44 is lowered to bring the polishing pad 44b
into contact with the workpiece 1. At this time, the polishing
fluid supply source 48 is actuated to send the slurry to the
polishing fluid supply passage 50, thereby supplying the slurry
between the workpiece 1 and the polishing pad 44b.
[0034] FIG. 5 schematically illustrates in perspective the manner
in which the workpiece 1 is polished by the polishing unit 26. For
polishing the workpiece 1, the chuck table 20 is rotated at a speed
of approximately 300 rpm, and the polishing wheel 44 is rotated at
a speed of approximately 1000 rpm, for example. The chuck table 20
is positionally adjusted in advance such that the polishing fluid
supply port 54 in the polishing pad 44b is closed by the workpiece
1. Therefore, the slurry supplied from the polishing fluid supply
port 54 stays on the workpiece 1. When the polishing pad 44b and
the workpiece 1 are rotated about their respective axes extending
vertically in the Z-axis directions while they are being held
against each other, the slurry enters between the polishing pad 44b
and the surface to be polished, i.e., the reverse side 1b, of the
workpiece 1.
[0035] As the workpiece 1 is polished by the polishing pad 44b, the
surface being polished, i.e., the reverse side 1b, of the workpiece
1 produces swarf. The swarf is entrained in the slurry and
discharged toward the outside of the polishing pad 44b. A slurry,
denoted by 56 in FIG. 5, that has entrained the swarf reaches an
outer circumferential portion of the reverse side 1b of the
workpiece 1, and drops off onto an outer circumferential portion
20b of the holding surface 20a of the chuck table 20. Thereafter, a
part of the slurry 56 drops off the chuck table 20 and is
discharged from a drain port 4b (see FIG. 1) defined in the bottom
of the opening 4a in the base block 4 of the polishing apparatus 2.
On the other hand, another part of the slurry 56 that has dropped
off onto the outer circumferential portion 20b of the holding
surface 20a of the chuck table 20 dries on the outer
circumferential portion 20b and adheres together with the swarf to
the outer circumferential portion 20b. On the reverse side 1b of
the workpiece 1, the temperature of the slurry is kept relatively
high due to the heat generated by the polishing of the reverse side
1b. However, since the temperature of the slurry that has dropped
off onto the outer circumferential portion 20b of the holding
surface 20a falls quickly, the slurry tends to adhere soon to the
outer circumferential portion 20b. FIG. 6 schematically illustrates
in perspective the manner in which the workpiece 1 that has been
polished is unloaded from the holding surface 20a of the chuck
table 20. As illustrated in FIG. 6, an adhering swarf, denoted by
9, remains on the outer circumferential portion 20b of the holding
surface 20a of the chuck table 20.
[0036] While the polishing apparatus 2 is in operation, a plurality
of workpieces 1 stored in the cassette 8a are taken one after
another from the cassette 8a, loaded on the chuck table 20,
polished by the polishing unit 26, unloaded from the chuck table
20, cleaned and spin-dried by the spinner cleaning device 52, and
stored in the cassette 8b. The workpieces 1 to be polished are
placed successively on the holding surface 20a where the adhering
swarf 9 remains on the outer circumferential portion 20b. When the
workpieces 1 are repeatedly polished on the holding surface 20a by
the polishing unit 26, the swarf 9 is deposited in successively
layers on the outer circumferential portion 20b of the holding
surface 20a. When the amount of swarf 9 adhering to the outer
circumferential portion 20b of the holding surface 20a thus
increases, the swarf 9 is liable to enter between the workpiece 1
and the holding surface 20a. The swarf 9 that has entered between
the workpiece 1 and the holding surface 20a prevents the chuck
table 20 from appropriately holding a workpiece 1 to be polished
thereon, and hence the polishing unit 26 is unable to polish the
workpiece 1 properly.
[0037] One solution to the above problem is to eject water to the
deposited swarf 9 to clean the holding surface 20a of the chuck
table 20, for example. However, simply ejecting water has a low
cleaning effect and is unable to fully remove the swarf 9. A
process of mechanically polishing the holding surface 20a of the
chuck table 20 is another option, only the process tends to drag
the swarf 9 along the holding surface 20a and scratch the holding
surface 20a. The polishing apparatus 2 according to the present
embodiment solves the problem by cleaning the chuck table 20 where
the swarf 9 adheres to the holding surface 20a of the chuck table
20 with high-pressure steam. To that end, the polishing apparatus 2
includes, for example, a high-pressure steam ejecting unit 58
disposed in the vicinity of the loading/unloading area 22 where the
workpiece 1 is loaded and unloaded, for example.
[0038] FIG. 7A schematically illustrates in perspective the chuck
table 20 to which high-pressure steam is ejected from the
high-pressure steam ejecting unit 58. The high-pressure steam
ejecting unit 58 includes, for example, a pipe-shaped member
including a hollow shank 58a extending vertically in the Z-axis
directions, a hollow arm 58b extending horizontally from an upper
end of the shank 58a, and a nozzle 58c mounted on the distal end of
the arm 58b. The high-pressure steam ejecting unit 58 may be
arranged such that the shank 58a is angularly movable about its
central axis to turn the arm 58b to position the nozzle 58c at a
desired position over the chuck table 20. The shank 58a has a lower
end connected to a high-pressure steam supply source, not
illustrated. The high-pressure steam supply source includes a
heater, not illustrated, for heating water to a predetermined
temperature, for example, so that the high-pressure steam supply
source can supply steam at the predetermined temperature. The
high-pressure steam ejecting unit 58 ejects steam at a temperature
of approximately 105.degree. C. under a pressure of approximately
0.3 MPa to the outer circumferential portion 20b of the holding
surface 20a of the chuck table 20, for example.
[0039] For cleaning the outer circumferential portion 20b of the
holding surface 20a of the chuck table 20, the chuck table 20 is
rotated about its central axis at a speed of approximately 30 rpm,
for example. At the same time, the high-pressure steam ejecting
unit 58 ejects high-pressure steam 60 to the outer circumferential
portion 20b of the holding surface 20a fully therealong. When the
high-pressure steam 60 is ejected to the outer circumferential
portion 20b of the holding surface 20a, the high-pressure steam 60
is applied to the swarf 9 adhering to the outer circumferential
portion 20b, softening the swarf 9 because the swarf 9 is heated
and exposed to water. As the high-pressure steam ejecting unit 58
continuously ejects the high-pressure steam 60, the swarf 9 is
peeled off from the outer circumferential portion 20b and removed
therefrom. While the high-pressure steam ejecting unit 58 is
ejecting the high-pressure steam 60, water may be ejected from the
porous member that provides the holding surface 20a of the chuck
table 20. The ejected water prevents the swarf 9 peeled off from
the outer circumferential portion 20b from entering the porous
member, but discharges the swarf 9 outside of the holding surface
20a of the chuck table 20. Therefore, the peeled-off swarf 9 is
restrained from being deposited again on the holding surface
20a.
[0040] The nozzle 58c of the high-pressure steam ejecting unit 58
may be oriented downwardly in the vertical directions, i.e., the
Z-axis directions. Since steam has a tendency to ascend in the
atmosphere, when the high-pressure steam 60 is ejected to the outer
circumferential portion 20b of the holding surface 20a directly
from above, the high-pressure steam 60 acts efficiently on the
swarf 9. Alternatively, the nozzle 58c of the high-pressure steam
ejecting unit 58 may be inclined at a predetermined angle to the
Z-axis directions so as to face against the direction in which the
chuck table 20 rotates at the spot where the high-pressure steam 60
is applied to the outer circumferential portion 20b of the holding
surface 20a. The nozzle 58c thus inclined ejects the high-pressure
steam 60 in a direction opposite the direction of travel of the
swarf 9 on the outer circumferential portion 20b of the holding
surface 20a as the chuck table 20 rotates, so that the
high-pressure steam 60 acts intensively on the swarf 9. According
to the present invention, however, the nozzle 58c of the polishing
apparatus 2 is not limited to the downward or inclined
orientation.
[0041] As described above, the polishing apparatus 2 according to
the present embodiment is capable of easily removing the swarf 9
from the outer circumferential portion 20b of the holding surface
20a of the chuck table 20 by ejecting the high-pressure steam 60 to
the swarf 9 adhering to the outer circumferential portion 20b. FIG.
7B schematically illustrates in perspective the chuck table 20 from
which the swarf 9 has been removed from the outer circumferential
portion 20b of the holding surface 20a thereof. Since the chuck
table 20 whose holding surface 20a has been cleaned is able to hold
a new workpiece 1 under suction thereon without fail, the polishing
unit 26 can polish the workpiece 1 properly.
[0042] A polishing method according to the present embodiment for
polishing a workpiece on the polishing apparatus 2 and cleaning the
outer circumferential portion 20b of the holding surface 20a of the
chuck table 20 will be described below. FIG. 8A is a flowchart of a
sequence of steps of an example of the polishing method according
to the present embodiment.
[0043] In the polishing method according to the present embodiment,
holding step S10 is first carried out to place a workpiece 1 on the
holding surface 20a and hold the workpiece 1 on the chuck table 20.
FIG. 4 schematically illustrates holding step S10 in perspective.
In holding step S10, the X-axis movable table 18 is positioned in
the loading/unloading area 22, and the workpiece 1 that has been
adjusted in position by the positioning table 12 is loaded onto the
holding surface 20a by the workpiece loading mechanism 14. At this
time, the face side 1a of the workpiece 1 to which the protective
tape 3 is affixed is oriented downwardly toward the holding surface
20a, and the reverse side 1b of the workpiece 1 as a surface to be
polished is oriented upwardly. Then, the suction source connected
to the chuck table 20 is actuated to hold the workpiece 1 under
suction on the chuck table 20. Thereafter, the X-axis movable table
18 is moved to the processing area 24.
[0044] Next, polishing step S20 is carried out to polish the
workpiece 1 with the polishing pad 44b while supplying the slurry
to the workpiece 1 held on the chuck table 20. FIG. 5 schematically
illustrates polishing step S20 in perspective. In polishing step
S20, the chuck table 20 and the polishing wheel 44 are rotated
about their respective central axes. Then, while the polishing
fluid supply source 48 is supplying the slurry through the
polishing fluid supply passage 50 to the reverse side 1b of the
workpiece 1, the polishing unit 26 is lowered to bring the
polishing pad 44b into contact with the reverse side 1b of the
workpiece 1. At this time, the slurry enters between the polishing
pad 44b and the workpiece 1, and the reverse side 1b of the
workpiece 1 is polished to a flat surface. Swarf produced from the
workpiece 1, etc., when the workpiece 1 is polished by the
polishing pad 44b is entrained in the slurry and transferred to an
outer circumferential edge of the workpiece 1. The slurry, denoted
by 56, that has entrained the swarf drops off onto the outer
circumferential portion 20b of the holding surface 20a of the chuck
table 20, and some swarf from the slurry 56 adheres to the outer
circumferential portion 20b.
[0045] Next, unloading step S30 is carried out to unload the
workpiece 1 polished in polishing step S20 from the chuck table 20.
In unloading step S30, the X-axis movable table 18 is moved to the
loading/unloading area 22, the workpiece 1 is released from the
chuck table 20, as illustrated in FIG. 6, and the workpiece 1 is
delivered to the spinner cleaning device 52 by the workpiece
unloading mechanism 16. The spinner cleaning device 52 cleans and
spin-dries the workpiece 1, which is then stored in the cassette 8b
by the workpiece deliver robot 10.
[0046] In the example of the polishing method illustrated in FIG.
8A, after the workpiece 1 has been unloaded from the chuck table
20, swarf removing step S40 is carried out to remove the swarf 9
deposited on the outer circumferential portion 20b of the holding
surface 20a of the chuck table 20 by ejecting the high-pressure
steam 60 from the high-pressure steam ejecting unit 58 to the swarf
9 deposited on the outer circumferential portion 20b. FIG. 7A
schematically illustrates swarf removing step S40 in perspective.
In swarf removing step S40, the nozzle 58c of the high-pressure
steam ejecting unit 58 is oriented toward the outer circumferential
portion 20b of the holding surface 20a of the chuck table 20. Then,
the nozzle 58c ejects the high-pressure steam 60 toward the outer
circumferential portion 20b of the holding surface 20a. At this
time, the chuck table 20 is rotated about its central axis at a
predetermined speed. The swarf 9 adhering to the outer
circumferential portion 20b is now softened by being heated and
exposed to water, and then removed from the outer circumferential
portion 20b by following part of ejected high-pressure steam 60. In
swarf removing step S40, water is ejected from the porous member
that provides the holding surface 20a of the chuck table 20 to
prevent the swarf 9 removed from the outer circumferential portion
20b from entering the porous member. FIG. 7B schematically
illustrates in perspective the chuck table 20 that has been cleaned
to remove the swarf 9 therefrom. As described above, according to
the example of the polishing method illustrated in FIG. 8A, the
swarf 9 can be removed easily from the outer circumferential
portion 20b of the holding surface 20a.
[0047] In the polishing apparatus 2 according to the present
embodiment, the high-pressure steam ejecting unit 58 for ejecting
the high-pressure steam 60 to the holding surface 20a of the chuck
table 20 may be disposed in the vicinity of the processing area 24.
In the polishing method according to the present embodiment, swarf
removing step S40 may be carried out while polishing step S20 is
being carried out. FIG. 8B is a flowchart of a sequence of steps of
another example of the polishing method in which swarf removing
step S40 is carried out in polishing step S20. The high-pressure
steam ejecting unit 58 that is disposed in the vicinity of the
processing area 24 is capable of ejecting the high-pressure steam
60 to the outer circumferential portion 20b of the holding surface
20a of the chuck table 20 while the polishing unit 26 is polishing
the workpiece 1. In this case, the ejected high-pressure steam 60
can remove the swarf from the outer circumferential portion 20b
before the temperature of the slurry containing the swarf that has
reached the outer circumferential portion 20b becomes low enough to
dry the swarf and let it adhere to the outer circumferential
portion 20b.
[0048] In the present example of the polishing method, the
high-pressure steam 60 may possibly enter between the polishing pad
44b and the reverse side 1b of the workpiece 1, tending to lower
the concentration of the slurry. However, the amount of water
supplied in the form of steam from the high-pressure steam ejecting
unit 58 to the holding surface 20a of the chuck table 20 is
extremely small compared to the amount of ejected under high
pressure to the outer circumferential portion 20b of the holding
surface 20a. Therefore, any adverse effect that the ejected
high-pressure steam 60 has on the polishing process is minimum.
Further, inasmuch as a new workpiece can be loaded onto the chuck
table 20 after the polished workpiece 1 has been unloaded from the
chuck table 20, the example of the polishing method illustrated in
FIG. 8B is capable of efficiently polishing a plurality of
workpieces 1 in succession.
[0049] Further, in the polishing method according to the present
embodiment, swarf removing step S40 may be carried out prior to
holding step S10. FIG. 8C is a flowchart of a sequence of steps of
still another example of the polishing method in which swarf
removing step S40 is carried out prior to holding step S10. For
polishing a plurality of workpiece 1 one after another on the
polishing apparatus 2, when a new workpiece 1 is to be loaded onto
the chuck table 20, a problem arises out of swarf 9 deriving from
the workpiece 1 previously polished by the polishing unit 26 and
adhering to the outer circumferential portion 20b of the holding
surface 20a. To solve the problem, swarf removing step S40 may be
carried out prior to holding step S10 to clean the holding surface
20a with the high-pressure steam 60 ejected thereto.
[0050] Specifically, swarf removing step S40 may be considered to
be a step carried out in advance for properly polishing a workpiece
1. Swarf removing step S40 may also be considered to be a step for
removing swarf 9 produced from polishing a workpiece 1 in polishing
step S20 and adhering to the outer circumferential portion 20b of
the holding surface 20a. At any rate, the polishing method
according to the present embodiment applies the advantages of
appropriately holding a workpiece 1 on the chuck table 20 and
properly polishing the workpiece 1 to all workpieces to be polished
on the polishing apparatus 2. The polishing method reduces the
workload required to change and clean the chuck table 20 and the
downtime of the polishing unit 26, resulting in an increase in the
efficiency with which to process workpieces 1.
[0051] The present invention is not limited to the embodiment
described above, but many changes and modifications may be made in
the embodiment. For example, while the polishing of workpieces 1 on
the polishing apparatus 2 for polishing workpieces 1 has been
described in the above embodiment, the polishing apparatus 2 may
have a grinding unit, not illustrated, for grinding workpieces 1 in
addition to the polishing unit 26 for polishing workpieces 1. A
workpiece 1 held on the chuck table 20 may be ground by the
grinding unit and thereafter may be polished by the polishing unit
26. In this case, in addition to the swarf 9 produced from
polishing the workpiece 1, swarf produced from grinding the
workpiece 1 is also deposited on the outer circumferential portion
20b of the holding surface 20a of the chuck table 20. However, the
swarf 9 and the latter swarf can be removed by ejecting the
high-pressure steam 60 from the high-pressure steam ejecting unit
58 to the outer circumferential portion 20b. Accordingly, when a
new workpiece 1 is placed on the chuck table 20, the swarf 9 and
the latter swarf will not prevent the chuck table 20 from
appropriately holding the workpiece 1.
[0052] The present invention is not limited to the details of the
above described preferred embodiment. The scope of the invention is
defined by the appended claims and all changes and modifications as
fall within the equivalence of the scope of the claims are
therefore to be embraced by the invention.
* * * * *