U.S. patent application number 16/358102 was filed with the patent office on 2019-09-26 for grinding apparatus.
The applicant listed for this patent is DISCO CORPORATION. Invention is credited to Shinji YOSHIDA.
Application Number | 20190291239 16/358102 |
Document ID | / |
Family ID | 67984652 |
Filed Date | 2019-09-26 |
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United States Patent
Application |
20190291239 |
Kind Code |
A1 |
YOSHIDA; Shinji |
September 26, 2019 |
GRINDING APPARATUS
Abstract
A grinding apparatus includes a table having a holding surface,
a grinding unit grinding a wafer held on the holding surface, a
notification portion notifying an operator of information, an
imaging unit illuminating a ground surface of the wafer which is
held and ground with an illumination and imaging the ground
surface, a detecting portion detecting a cross line in an imaged
picture, a memory storing an X-axis and Y-axis coordinate position
of an intersection point of the cross line detected, a spotlight
illuminating the holding surface at the X-axis and Y-axis
coordinate position stored, and a controller causing the
notification portion to notify the operator that the cross line has
been detected and stopping grinding operations of the grinding
apparatus.
Inventors: |
YOSHIDA; Shinji; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DISCO CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
67984652 |
Appl. No.: |
16/358102 |
Filed: |
March 19, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 7/228 20130101;
B24B 41/068 20130101; B24B 49/12 20130101; B24B 27/0023
20130101 |
International
Class: |
B24B 49/12 20060101
B24B049/12; B24B 7/22 20060101 B24B007/22 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2018 |
JP |
2018-056173 |
Claims
1. A grinding apparatus comprising: a holding table including a
porous plate having a holding surface on which a wafer is held;
holding table rotation means rotating the holding table with a
center of the holding table as an axis for rotation; grinding means
grinding the wafer held on the holding surface with grinding
stones; notification means notifying an operator of various kinds
of information; imaging means illuminating a ground surface of the
wafer which is held on the holding surface and ground with the
grinding stones with an illumination and imaging the ground
surface; detecting means detecting a cross line in a picture imaged
by the imaging means; storage means storing an X-axis and Y-axis
coordinate position of an intersection point of the cross line
detected by the detecting means; a spotlight illuminating the
holding surface at the X-axis and Y-axis coordinate position stored
in the storage means; and control means causing the notification
means to notify the operator that the detecting means has detected
the cross line and stopping grinding operations of the grinding
apparatus.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a grinding apparatus for
grinding a workpiece such as a semiconductor wafer.
Description of the Related Art
[0002] In a grinding apparatus for grinding a wafer, the wafer is
held under suction on a holding surface of a holding table, the
holding surface being composed of a porous member, and a rotating
grinding stone is positioned in parallel to the holding surface,
whereby the wafer held on the holding surface is ground with a
grinding surface of the rotating grinding stone. When the wafer
held on the holding surface is ground with the grinding stone with
a minute substance such as a grinding swarf or an abrasive grain
got stuck between the holding surface of the holding table and a
lower surface of the wafer, a cross-shaped crack is formed on a
ground surface of the wafer directly above the minute substance. To
prevent the cross-shaped crack from being formed in the wafer, the
holding surface before the wafer is held under suction is cleaned
with a cleaning apparatus described in Japanese Patent No. 4079289
and Japanese Patent No. 5538971 so as not to cause a cross-shaped
crack to be formed in the wafer.
SUMMARY OF THE INVENTION
[0003] However, when the minute substance still remains on the
holding surface having been subjected to cleaning by use of the
cleaning apparatus described above, a cross-shaped crack is caused
to be formed. Accordingly, before the wafer is held under suction
on the holding surface of the holding table, it is required to
check whether a minute substance adhered to the holding surface is
present or not. In view of this, the holding surface is imaged with
an imaging camera. However, it is difficult for an operator to
determine whether a pattern detected on the holding surface is that
of a porous ceramic constituting the holding surface or the minute
substance, based on the imaged picture obtained.
[0004] To solve this problem, the grinding apparatus is configured
such that, when a cross-shaped crack is detected in a ground wafer,
an operator can immediately grasp a position of a holding surface
of a holding table (a position where a minute substance is adhered
onto the holding surface) corresponding to a position where the
cross-shaped crack is formed in the wafer to remove the adhered
substance from the holding surface, whereby further occurrence of a
cross-shaped crack in a wafer in the subsequent wafer grinding is
prevented.
[0005] It is therefore an object of the present invention to
provide a grinding apparatus capable of instantly removing an
adhered substance causing a cross-shaped crack from a holding
surface.
[0006] In accordance with an aspect of the present invention, there
is provided a grinding apparatus including a holding table
including a porous plate having a holding surface on which a wafer
is held, holding table rotation means rotating the holding table
with a center of the holding table as an axis for rotation,
grinding means grinding the wafer held on the holding surface with
grinding stones, notification means notifying an operator of
various kinds of information, imaging means illuminating a ground
surface of the wafer which is held on the holding surface and
ground with the grinding stones with an illumination and imaging
the ground surface, detecting means detecting a cross line in a
picture imaged by the imaging means, storage means storing an
X-axis and Y-axis coordinate position of an intersection point of
the cross line detected by the detecting means, a spotlight
illuminating the holding surface at the X-axis and Y-axis
coordinate position stored in the storage means, and control means
causing the notification means to notify the operator that the
detecting means has detected the cross line and stopping grinding
operations of the grinding apparatus.
[0007] According to the present invention, when a cross-shaped
crack is caused in the wafer which has been ground, it is possible
to illuminate the holding surface directly below the cross-shaped
crack with a spotlight, thereby enabling the operator to grasp
immediately a position where a grinding swarf, an abrasive grain,
or the like is adhered onto the holding surface after taking the
wafer off from the holding surface. Then, the operator removes the
minute substance adhered to the illuminated position of the holding
surface, so that the minute substance causing a cross-shaped crack
can be instantly removed from the holding surface.
[0008] 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 claim with
reference to the attached drawings showing a preferred embodiment
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a perspective view illustrating an example of a
grinding apparatus;
[0010] FIG. 2 is a cross-sectional view illustrating an example of
a holding table, cleaning means, and imaging means;
[0011] FIG. 3 is a cross-sectional view illustrating a state in
which a ground surface of a wafer which is held on a holding
surface and has been ground with grinding stones is imaged with the
imaging means while being illuminated with an illumination;
[0012] FIG. 4 is a plan view illustrating the state in which the
ground surface of the wafer which is held on the holding surface
and has been ground with the grinding stones is imaged with the
imaging means while being illuminated with the illumination;
and
[0013] FIG. 5 is an explanatory view illustrating a case in which a
cross line in a picture imaged by the imaging means is detected by
detecting means.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] A grinding apparatus 1 illustrated in FIG. 1 is an apparatus
for subjecting a wafer W held under suction on a holding table 30
to grinding processing. The wafer W illustrated in FIG. 1 is a
circular plate-shaped semiconductor wafer composed of a
silicon-based material, for example, and a front surface Wa of the
wafer W facing downward in FIG. 1 has a plurality of devices formed
thereon, with a protective tape T attached to the front surface Wa
to be protected. A back surface Wb of the wafer W facing upward is
a ground surface which is subjected to grinding processing. At an
outer peripheral edge of the wafer W, a notch N as a mark for
indicating crystal orientation of the wafer W is formed in such a
state as to be recessed radially inward toward a center of the
wafer W.
[0015] On a front side (-X direction side) of a base 10 of the
grinding apparatus 1, there is disposed inputting means 19 for
inputting processing conditions and the like with respect to the
grinding apparatus 1 by an operator. In addition, on the front side
on the base 10, there are disposed a first cassette 331 for storing
the wafer W before grinding and a second cassette 332 for storing
the wafer W after grinding. Between the first cassette 331 and the
second cassette 332, there is disposed a robot 330 including an
articulated arm which unloads the wafer W before grinding from the
first cassette 331 and loads the wafer W after grinding into the
second cassette 332.
[0016] In a movable region of the robot 330, there is provided a
temporary setting table 333a temporarily setting the wafer W before
processing thereon, and the temporary setting table 333a has
positioning means 333b disposed thereon. The positioning means 333b
positions (centers) the wafer W placed on the temporary setting
table 333a after being unloaded from the first cassette 331 at a
predetermined position by pushing the outer peripheral edge of the
wafer W with each of positioning pins which reduces a diameter.
[0017] On a lateral side of the temporary setting table 333a, a
detection portion 333c detecting the notch N of the wafer W is
disposed. The detection portion 333c includes a reflection type
optical sensor or a transmission type optical sensor, for example.
When the outer periphery of the wafer W passes through a detection
region (lower side) of the detection portion 333c along with
rotation of the temporary setting table 333a holding the centered
wafer W thereon, the detection portion 333c can detect the notch N
formed at the outer peripheral edge of the wafer W. Incidentally,
it may be configured such that, assuming that the detection portion
333c is constituted by a camera or the like, the detection portion
333c image-processes a picture imaged by the camera, so that the
notch N at the outer peripheral edge of the wafer W can be
detected. In addition, in the movable region of the robot 330,
cleaning means 334 cleaning the wafer W after grinding is disposed.
The cleaning means 334 is a single wafer spinner cleaning
apparatus, for example.
[0018] In a vicinity of the positioning means 333b, first transfer
means 335 is disposed, and second transfer means 336 is disposed in
a vicinity of the cleaning means 334. The first transfer means 335
transfers the wafer W before grinding, which is placed on the
temporary setting table 333a to be centered, to any one of the
holding tables 30 illustrated in FIG. 1, and the second transfer
means 336 transfers the wafer W after grinding which is held on any
one of the holding tables 30 to the cleaning means 334.
[0019] On a rear side of the first transfer means 335 on the base
10, a turn table 34 is disposed, and on an upper surface of the
turn table 34, for example, four holding tables 30 (only two
illustrated) are disposed to be spaced apart from one another at an
equal interval in a circumferential direction. The turn table 34
can rotate around an axial center of a Z-axis direction on the base
10. As a result of the rotation of the turn table 34, any of the
holding tables 30 are positioned close to the first transfer means
335 and the second transfer means 336.
[0020] As illustrated in FIG. 2, the holding table 30 has a
circular outer shape, for example, and includes a porous plate 300
which sucks the wafer W, and a frame body 301 which supports the
porous plate 300. The porous plate 300 communicates with a suction
source 39 of a vacuum generation apparatus or the like, and a
suction force generated as a result of suction by the suction
source 39 is transmitted to a holding surface 300a as an exposed
surface of the porous plate 300, so that the holding table 30 holds
the wafer W under suction on the holding surface 300a. The holding
surface 300a is formed in a conical shape having an extremely
gently inclined surface with its rotational center as an apex.
[0021] On a lower surface side of the holding table 30, holding
table rotation means 37 is connected, and the holding table 30 can
rotate around the axial center of the Z-axis direction by the
holding table rotation means 37 on the turn table 34 illustrated in
FIG. 1.
[0022] Also, an inclination adjusting mechanism 38 is disposed
through a coupling or the like below the holding table 30. The
inclination adjusting mechanism 38 can adjust an inclination
relative to a horizontal surface of the holding surface 300a of the
holding table 30.
[0023] The holding table rotation means 37 is a pulley mechanism
including a spindle 370 an axial direction of which is the Z-axis
direction and an upper end of which is connected to a lower surface
of the frame body 301 of the holding table 30, and a motor 371 as a
driving source rotating the holding table 30 with a center of the
holding table 30 as an axis for rotation. A main driving pulley 372
is mounted on a shaft of the motor 371, and an endless belt 373 is
wound around the main driving pulley 372. A driven pulley 374 is
mounted on the spindle 370, and the endless belt 373 is wound also
around the driven pulley 374. The motor 371 rotation-drives the
main driving pulley 372, and accordingly, the endless belt 373
moves rotationally in conjunction with the rotation of the main
driving pulley 372. As a result, the rotational movement of the
endless belt 373 rotates the driven pulley 374 and the spindle 370.
For example, the motor 371 has a rotary encoder 379 connected
thereto, the rotary encoder 379 detecting a rotation angle of the
motor 371, that is, a rotation angle of the holding table 30.
[0024] As illustrated in FIG. 1, a column 11 is erected on a rear
side of the base 10 (+X direction side). Rough-grinding feeding
means 35 and finish-grinding feeding means 36 are disposed adjacent
to each other on a front surface of the column 11. The
rough-grinding feeding means 35 causes rough grinding means 31 to
perform grinding-feeding with respect to the wafer W held on the
holding table 30. The finish-grinding feeding means 36 causes
finish grinding means 32 to perform grinding-feeding with respect
to the wafer W held on the holding table 30.
[0025] The rough-grinding feeding means 35 includes a ball screw
not illustrated, a pair of guide rails 351, a motor 352, and an
elevating portion 353. The ball screw has an axial center in a
vertical direction (Z-axis direction). The pair of guide rails 351
is disposed in parallel to the ball screw. The motor 352 is coupled
to the ball screw and causes the ball screw to rotationally move.
The elevating portion 353 has an internal nut screwed into the ball
screw and has a side portion thereof in sliding contact with the
guide rails 351. The motor 352 causes the ball screw to rotate, and
accordingly, the elevating portion 353 supporting the rough
grinding means 31 is guided with the guide rails 351 to move in the
vertical direction.
[0026] The finish-grinding feeding means 36 includes a ball screw
not illustrated, a pair of guide rails 361, a motor 362, and an
elevating portion 363. The ball screw has an axial center in the
vertical direction (Z-axis direction). The pair of guide rails 361
is disposed in parallel to the ball screw. The motor 362 is coupled
to the ball screw and causes the ball screw to rotationally move.
The elevating portion 363 has an internal nut screwed into the ball
screw and has a side portion thereof in sliding contact with the
guide rails 361. The motor 362 causes the ball screw to rotate, and
accordingly, the elevating portion 363 supporting the finish
grinding means 32 is guided with the guide rails 361 to move in the
vertical direction.
[0027] The rough grinding means 31 includes a rotary shaft 310
whose axial direction is the vertical direction, a housing 311, a
motor 312, a mount 313, and a grinding wheel 314. The housing 311
supports the rotary shaft 310 in a rotatable manner. The motor 312
rotation-drives the rotary shaft 310. The mount 313 is attached to
a lower end of the rotary shaft 310. The grinding wheel 314 is
detachably connected to the mount 313. A plurality of rough
grinding stones 314a in a substantially rectangular
parallelepipedic shape are annularly disposed on a bottom surface
of the grinding wheel 314. The rough grinding stones 314a are
formed by fixing diamond abrasive grains or the like thereto with a
predetermined bonding agent. The rough grinding stones 314a are,
for example, grinding stones containing relatively larger abrasive
grains.
[0028] For example, a flow passage not illustrated which
communicates with a grinding water supply source and serves as a
passage way for grinding water is formed within the rotary shaft
310 so as to penetrate in the axial direction of the rotary shaft
310. The flow passage opens in the bottom surface of the grinding
wheel 314 so as to be able to jet the grinding water toward the
rough grinding stones 314a.
[0029] The finish grinding means 32 can perform finish grinding
which enhances flatness with respect to the wafer W which is
thinned through rough grinding. More specifically, the finish
grinding means 32 further grinds the back surface Wb of the wafer W
which has been ground by the rough grinding means 31, with a
grinding wheel 314 including finish-grinding stones 324a and
rotatably mounted to the finish grinding means 32. Abrasive grains
contained in the finish-grinding stones 324a are smaller in grain
diameter than the abrasive grains contained in the rough grinding
stones 314a. Configurations other than the finish-grinding stones
324a in the finish grinding means 32 are similar to those in the
rough grinding means 31.
[0030] Disposed above a moving path of the holding table 30 is
cleaning means 8 cleaning the holding surface 300a of the holding
table 30. As illustrate in FIG. 2, this cleaning means 8 includes a
rotary shaft 80, a housing 81, a cleaning grinding stone 82,
elevating means 83. The rotary shaft 80 has an axial center in the
vertical direction. The housing 81 supports the rotary shaft 80 in
a rotatable manner. The cleaning grinding stone 82 is disposed at a
lower end of the rotary shaft 80. The elevating means 83 causes the
housing 81 to move in the vertical direction. The cleaning means 8
can be moved in a reciprocating manner in a Y-axis direction by
Y-axis moving means 89 illustrated in FIG. 1.
[0031] The Y-axis moving means 89 illustrated in FIG. 1 includes,
for example, a ball screw 890, a bridge portion 891, a movable
portion 892, and a motor not illustrated. The ball screw 890 has an
axial center in the Y-axis direction. The bridge portion 891
supports the ball screw 890. The movable portion 892 has an
internal nut screwed into the ball screw 890 and moves in a
reciprocating manner in the Y-axis direction on the ball screw 890.
The motor is coupled to one end of the ball screw 890 and
rotationally moves the ball screw 890. The cleaning means 8 is
disposed on a front surface of the movable portion 892.
[0032] The cleaning grinding stone 82 is, for example, a resin bond
grinding stone, or a grinding stone formed into a circular plate
shape with a resin material or a ceramic material to scrape off
contamination such as a grinding swarf adhered to the holding
surface 300a of the holding table 30. Incidentally, the cleaning
means 8 may include a cleaning brush instead of the cleaning
grinding stone 82. The elevating means 83 includes a rail 830 with
which the housing 81 is in sliding motion, and a motor and the like
provided inside the housing 81, for example, and causes the housing
81 to move in the vertical direction.
[0033] The grinding apparatus 1 includes imaging means 40 and a
spotlight 41. The imaging means 40 illuminates the ground surface
Wb of the wafer W held on the holding surface 300a of the holding
table 30 and ground with the finish-grinding stones 324a with an
illumination 400 (see FIG. 2) and images the ground surface Wb. The
spotlight 41 illuminates the holding surface 300a of the holding
table 30.
[0034] The imaging means 40 is a line sensor camera, for example,
and is disposed on a side surface of the housing 81 of the cleaning
means 8. The imaging means 40 can move with the cleaning means 8 in
the Y-axis direction and the Z-axis direction. As illustrated in
FIG. 2, the imaging means 40 includes a boxlike casing 401 which
blocks an external light, for example, and the illumination 400
illuminating the wafer W from above the wafer W is mounted on a
side surface of the casing 401. The illumination 400 is a light
emitting diode (LED) or a xenon lamp, for example, and light
generated from the illumination 400 is propagated inside the casing
401 through a transmission optical system such as an optical fiber
not illustrated. A light quantity of the light emitted from the
illumination 400 can be adjusted by an adjuster (not illustrated)
or the like.
[0035] The imaging means 40 includes a half mirror 402, an
objective lens not illustrated, and an imaging portion 403. The
half mirror 402 is disposed inside the casing 401 and reflects
downward the light emitted from the illumination 400 to change its
direction. The objective lens is disposed downstream of the half
mirror 402 in the casing 401, and the reflected light on the half
mirror 402 enters the objective lens. The imaging portion 403 is
disposed upstream of the half mirror 402 and photoelectrically
converts a reflection light reflected on the wafer W and captured
by the objective lens into an electrical signal to output the
electrical signal thus obtained as picture information.
[0036] The imaging portion 403 is configured such that a plurality
of light receiving elements such as a charge-coupled device (CCD)
are arranged side by side in a row in an X-axis direction, for
example. In the imaging portion 403, a length in its longitudinal
direction (X-axis direction) is substantially equal to a length of
a radius of the holding surface 300a of the holding table 30.
Accordingly, the imaging portion 403 has an imaging region with a
length equal to or greater than a radius of the wafer W. Data
transmitted by each pixel of the light receiving elements in
response to strength of the reflection light is expressed, for
example, with 8-bit gradation in luminance value, namely, in 256
graduations from 0 to 255.
[0037] The spotlight 41 is an LED light or the like capable of
illuminating the holding surface 300a of the holding table 30 like
a spot from above, for example, and mounted in a vicinity of the
imaging means 40, more specifically, on the side surface of the
housing 81 of the cleaning means 8 in the present embodiment. Note
that an incident angle of a spot light from the spotlight 41 can be
adjusted by adjusting means not illustrated, for example, and a
diameter of the spot light can also be narrowed to a desired value.
In addition, a disposition place of the spotlight 41 is also not
limited to examples illustrated in FIGS. 1 and 2.
[0038] As illustrated in FIGS. 1 and 2, the grinding apparatus 1
includes control means 9 constituted by storage means 90 such as a
central processing unit (CPU) and a memory and executing control of
the entire apparatus. The control means 9 is electrically connected
with the finish-grinding feeding means 36, the Y-axis moving means
89, the holding table rotation means 37, and the like, through
wiring lines not illustrated. Under control of the control means 9,
operations such as movement of the finish grinding means 32 in the
Z-axis direction by the finish-grinding feeding means 36,
positioning of the imaging means 40 in the Y-axis direction by the
Y-axis moving means 89, and rotation of the holding table 30 by the
holding table rotation means 37 are controlled. The grinding
apparatus 1 further includes notification means 17 notifying the
operator of various kinds of information. The notification means 17
displays the notified information on a monitor not illustrated or
activates an alarm.
[0039] A description will be given below regarding operation of the
grinding apparatus 1 in a case in which the wafer W is ground by
the grinding apparatus 1 illustrated in FIG. 1. First, in
accordance with rotation of the turn table 34 illustrated in FIG.
1, the holding table 30 with the wafer W not placed thereon
revolves around the rotation axis of the turn table 34.
Accordingly, the holding table 30 moves closer to the first
transfer means 335. The robot 330 takes one wafer W out of the
first cassette 331 to carry the wafer W onto the temporary setting
table 333a.
[0040] The positioning means 333b centers the wafer W on the
temporary setting table 333a, and then, the detection portion 333c
detects the notch N formed at the outer peripheral edge of the
wafer W. Then, the wafer W is rotated on the temporary setting
table 333a, so that the notch N is positioned at a predetermined
position in the circumferential direction. Next, the first transfer
means 335 causes the wafer W which has been centered and the notch
N of which has been positioned at the predetermined position in the
circumferential direction to be carried onto the holding table 30
so as not to displace the position of the notch N in the
circumferential direction which has been grasped.
[0041] For example, the holding table 30 may include a notch
alignment portion (alignment mark), not illustrated, for aligning
with the notch N on the holding table 30 when the wafer W is placed
on the holding table 30. On the holding table 30, the notch N of
the wafer W and the notch alignment portion of the holding table 30
are aligned with each other. In other words, since the position of
the notch N at the time at which the first transfer means 335 holds
the wafer W has been determined when the first transfer means 335
holds and carries the wafer W from the temporary setting table
333a, alignment is made in such a way that the holding table 30 is
rotated at a predetermined angle so as to cause the position of the
notch N of the wafer W which has been held on the temporary setting
table 333a and the notch alignment portion of the holding table 30
to align with each other. Thus, the wafer W is placed on the
holding surface 300a with the back surface Wb of the wafer W facing
upward in such a way that the center of the holding table 30 and
the center of the wafer W are substantially matched with each
other.
[0042] Then, the suction source 39 (see FIG. 2) is activated to
generate a suction force, and the generated suction force is
transmitted to the holding surface 300a of the porous plate 300, so
that the holding table 30 holds under suction the wafer W on the
holding surface 300a. Also, the position of the notch N of the
wafer W held under suction has been grasped by the control means
9.
[0043] Note that the position of the notch N of the wafer W held
under suction on the holding table 30 has been constantly grasped
at least until the second transfer means 336 described later
transfers the wafer W from the holding table 30. More specifically,
the rotary encoder 379 in the holding table rotation means 37
illustrated in FIG. 2 outputs an encoder signal (the number of
rotation of the motor 371) to the control means 9 when the holding
table 30 is rotated by the holding table rotation means 37.
According to the received encoder signal, the control means 9
performs feedback control of a rotation speed of the holding table
30 rotated by the holding table rotation means 37, and can
sequentially grasp the position of the notch N of the wafer W which
is being rotated on the holding table 30.
[0044] In a case in which an edge alignment of the wafer W is
carried out by use of the imaging means 40, grasping of the
position of the notch N of the wafer W on the holding table 30 may
be made along with the edge alignment. In the edge alignment, the
holding table 30 rotates, and the outer peripheral edge of the
wafer W held on the holding table 30 is imaged at a plurality of
locations by the imaging means 40. Then, coordinates of three
points on the outer peripheral edge of the wafer W, the three
points being spaced apart from one another, are detected, for
example, and an accurate center coordinate of the wafer W on the
holding table 30 is obtained through geometric arithmetic
processing based on the coordinates of the three points. In
addition, a coordinate position of the notch N is grasped from the
imaged picture obtained above.
[0045] After the holding table 30 holds under suction the wafer W,
the turn table 34 illustrated in FIG. 1 rotates in a clockwise
direction when it is seen from a +Z direction. As a result, the
holding table 30 on which the wafer W is held revolves around the
axis of the rotation of the turn table 34. Accordingly, the
rotation center of the rough grinding stones 314a of the rough
grinding means 31 shifts by a predetermined distance relative to a
rotation center of the wafer W, and the wafer W is positioned such
that a rotation locus of the rough grinding stones 314a passes
through the rotation center of the wafer W. Moreover, the
inclination of the holding table 30 is adjusted by the inclination
adjusting mechanism 38 (see FIG. 2) such that the holding surface
300a as the gently inclined conical surface becomes parallel to
grinding surfaces (lower surfaces) of the rough grinding stones
314a. Accordingly, along with the holding surface 300a, the back
surface Wb of the wafer W held under suction on the holding surface
300a becomes parallel to the grinding surfaces of the rough
grinding stones 314a.
[0046] The rough grinding means 31 is fed in a -Z direction by the
rough-grinding feeding means 35, and the rotating rough grinding
stones 314a are brought into contact with the back surface Wb of
the wafer W held on the holding table 30, so that rough grinding is
carried out. In addition, while the holding table rotation means 37
rotates the holding table 30 at a predetermined rotation speed, the
wafer W on the holding surface 300a is also rotated, and
accordingly, the rough grinding stones 314a carry out the rough
grinding processing on the entire surface of the back surface Wb of
the wafer W. During grinding, the grinding water is supplied to a
contact portion between the rough grinding stones 314a and the back
surface Wb of the wafer W to cool and clean the contact
portion.
[0047] After the wafer W is rough-ground close to a finished
thickness, the rough-grinding feeding means 35 causes the rough
grinding means 31 to move upward to be separated from the wafer
W.
[0048] Next, the turn table 34 rotates in the clockwise direction
when it is seen from the +Z direction, and the holding table 30
holding the wafer W under suction moves below the finish grinding
means 32. After positioning between the finish-grinding stones 324a
and the wafer W is carried out, the finish grinding means 32 is fed
downward by the finish-grinding feeding means 36, and the rotating
finish-grinding stones 324a are brought into contact with the back
surface Wb of the wafer W. In addition, along with rotation of the
holding table 30, the entire surface of the back surface Wb of the
wafer W is finish-ground.
[0049] After the finish grinding means 32 grinds the back surface
Wb of the wafer W to a finished thickness to thereby increase the
flatness of the back surface Wb of the wafer W and is then moved
away from the wafer W, the turn table 34 rotates in the clockwise
direction when it is seen from the +Z direction, and as a result,
the wafer W is moved closer to the second transfer means 336. Then,
the second transfer means 336 transfers the wafer W on the holding
table 30 to the cleaning means 334. After the wafer W is cleaned by
the cleaning means 334, the robot 330 transfers the wafer W from
the cleaning means 334 to load the wafer W into the second cassette
332. In the grinding apparatus 1, a series of grinding operations
thus described are repeatedly performed, and a plurality of wafers
W are ground.
[0050] When the wafer W is ground in the manner described above, a
grinding swarf or an abrasive grain which falls off enters between
the holding surface 300a of the holding table 30 illustrated in
FIG. 1 and the protective tape T attached to the wafer W
illustrated in FIG. 1, and the grinding swarf or the abrasive grain
may be adhered to the holding surface 300a, in some cases. When the
wafer W is ground in this state, a cross-shaped crack (cross line)
is caused in the wafer W. Moreover, when a subsequent wafer W is
held under suction on the holding surface 300a with this adhered
substance remained on the holding surface 300a and the back surface
Wb of the wafer W is ground, a cross-shaped crack is caused in the
subsequent wafer W as well.
[0051] In view of this, the cleaning means 8 moves in the Y-axis
direction by the Y-axis moving means 89 and causes the cleaning
grinding stone 82 to be positioned above the holding surface 300a
of the holding table 30 from which the wafer W is transferred.
Then, while the holding table rotation means 37 rotates the holding
table 30, the elevating means 83 causes the cleaning grinding stone
82 which is rotating to lower and press the holding surface 300a.
As a result of the pressing, the grinding swarf or the like which
protrudes from the holding surface 300a in an upward direction is
scraped off, and the holding surface 300a is cleaned.
[0052] For example, in a case in which the plurality of wafers W
are successively ground, while cleaning of the holding surface 300a
of the holding table 30 by use of the cleaning means 8 is
interposed at an appropriate timing, the adhered substance may
remain on the holding surface 300a on which cleaning has been
carried out by the cleaning means 8. This case results in forming
the cross line on the back surface Wb of the wafer W held on the
holding surface 300a by grinding.
[0053] To prevent the formation of the cross line, it is required
to prevent the plurality of wafers W from being ground with a risk
of forming the cross line in the wafer W. Thus, the grinding
apparatus 1 according to the present invention performs the
operation described below.
[0054] For example, after the predetermined n-th wafer W (n is two
or more) is ground to the finished thickness by finish-grinding and
the finish grinding means 32 illustrated in FIG. 1 is separated
from the wafer W, the turn table 34 rotates in the clockwise
direction when it is seen from the +Z direction. Also, the Y-axis
moving means 89 causes the imaging means 40 to move in the Y-axis
direction, and the imaging means 40 and the wafer W are positioned
such that the back surface Wb of the wafer W held under suction on
the holding table 30 is imaged by the imaging means 40. More
specifically, as illustrated in FIGS. 3 and 4, positioning of the
imaging means 40 and the wafer W is performed such that the imaging
portion 403 extends in a line shape between an upper side of a
center We of the wafer W and an upper side of the outer peripheral
edge of the wafer W. Note that, in FIGS. 3 and 4, configurations
other than the imaging portion 403 in the imaging means 40 are
omitted.
[0055] Next, the holding table rotation means 37 rotates the
holding table 30 by a predetermined angle under control of the
control means 9, and for example, as illustrated in FIG. 4, a
virtual line L1 passing through the center We of the wafer W and
the notch N is parallel to the X-axis direction, and the notch N is
positioned at a position on the +X direction side (at a 0-degree
position serving as an imaging start position).
[0056] Also, the imaging means 40 is operated, and focusing of the
objective lens not illustrated is performed in accordance with
vertical movement of the imaging means 40 by the elevating means 83
illustrated in FIG. 2. At the time point at which the objective
lens focuses on the back surface Wb of the wafer W, the elevating
means 83 stops the vertical movement of the imaging means 40.
[0057] In this state, as illustrated in FIGS. 3 and 4, the holding
table rotation means 37 rotates the holding table 30 at a
predetermined rotation speed in a counterclockwise direction when
it is seen from the +Z direction, for example. Also, the
illumination 400 of the imaging means 40 (see FIG. 2) irradiates
the back surface Wb of the wafer W with light through the half
mirror 402, and a reflected light from the back surface Wb of the
wafer W is captured by the objective lens not illustrated and
transmitted through the half mirror 402 to enter a light receiving
element in the imaging portion 403. Then, the back surface Wb of
the wafer W which relatively rotates relative to the imaging means
40 is successively imaged line by line from the center We of the
wafer W to its outer peripheral edge by the imaging means 40.
[0058] The imaging portion 403 sequentially sends the imaged
pictures in units of line to the control means 9 illustrated in
FIGS. 1 and 2. The imaged pictures in units of line are stored in
the storage means 90 in the control means 9 in order such that an
imaged picture on which the entire back surface Wb of the wafer W
is imaged can be configured. In addition, according to the encoder
signal received by the rotary encoder 379 (see FIG. 2) in the
holding table rotation means 37 which rotates the holding table 30,
the control means 9 associates an imaged picture indicating one
line on the back surface Wb of the wafer W with a rotation angle of
the holding table 30 from the imaging start position (0-degree
position) when the imaged picture indicating the one line is imaged
to store the imaged pictures in order in the storage means 90.
[0059] When the holding table rotation means 37 rotates the holding
table 30 at 360 degrees and the imaging means 40 has made one round
above the back surface Wb of the wafer W (the notch N is returned
to the imaging start position), an imaged picture on which the
entire surface of the back surface Wb of the wafer W is imaged is
formed. In addition, the rotation of the holding table 30 is
stopped.
[0060] A light quantity (light receiving quantity) of the reflected
light which has entered each of the light receiving elements in the
imaging portion 403 causes a difference in a case in which the
cross line is present on the back surface Wb of the wafer W. In
other words, in each of the light receiving elements in the imaging
portion 403, the light receiving quantity increases on a portion of
the back surface Wb of the wafer W with the cross line, and its
luminance value approaches 255 and becomes closer to white. On the
other hand, the light receiving quantity decreases in a region in
which the cross line is not present on the back surface Wb of the
wafer W, and its luminance value approaches 0 and becomes closer to
black. Accordingly, in an imaged picture G reflecting the entire
surface of the back surface Wb of the wafer W which is displayed on
a virtual output screen with a predetermined resolution illustrated
in FIG. 5, a cross line C on the back surface Wb of the wafer W is
indicated in white, for example, and the back surface Wb of the
wafer W around the cross line C is indicated in gray.
[0061] Incidentally, binarization processing may be executed on the
imaged picture G, so that the cross line C and the periphery
thereof can be clearly distinguished from each other.
[0062] As illustrated in FIGS. 1 and 2, the grinding apparatus 1
includes detecting means 91 detecting the cross line C in the
imaged picture G imaged by the imaging means 40. The detecting
means 91 is incorporated in the control means 9, for example. The
detecting means 91 counts a sum of white pixels in the Y-axis
direction and a sum of white pixels in the X-axis direction in the
back surface Wb of the wafer W (in a gray region) imaged on the
imaged picture G indicated in FIG. 5, to thereby detect the cross
line C and calculate a size of the cross line C. In addition, a
pixel at an intersection point of the cross line C is
identified.
[0063] Next, an X-axis and Y-axis coordinate position of the pixel
at the intersection point of the cross line C thus detected is
determined by the detecting means 91. A coordinate position of the
center We of the wafer W which substantially matches with a
rotation center of the holding table 30 is set as an origin
coordinate (0, 0), for example, and a virtual line L2 connecting
the origin coordinate (0, 0) and the intersection point of the
cross line C which has been identified is drawn. An angle .theta.1
between the virtual line L1 and the virtual line L2 is identical to
an angle at which the holding table 30 rotates from the imaging
start position when the imaged pictures in units of line with the
cross line C imaged thereon are imaged, and is a known value which
has been preliminarily stored in the storage means 90.
[0064] Also, a length of the virtual line L2 is calculated by
counting pixels from the origin coordinate (0, 0) to the pixel at
the intersection point of the cross line C (assuming the calculated
value is r, for example). Thus, the X-axis and Y-axis coordinate
position (x, y) of the pixel at the intersection point of the cross
line C detected is determined to be (r cos .theta.1, -r sin
.theta.1). Then, the X-axis and Y-axis coordinate position at the
intersection point of the cross line C, (r cos .theta.1, -r sin
.theta.1), is stored in the storage means 90.
[0065] Note that the determination of the X-axis and Y-axis
coordinate position (x, y) of the pixel at the intersection point
of the cross line C detected is not limited to the example
described above. For example, a virtual line L3 (not illustrated in
FIG. 5) which is orthogonal to the virtual line L1 is drawn from
the pixel at the intersection point of the cross line C, and an
X-axis coordinate of an intersection point between the virtual line
L1 and the virtual line L3 is determined by counting the pixels
from the origin coordinate (0, 0) to the intersection point between
the virtual line L1 and the virtual line L3. Then, by further
counting the pixels from the intersection point between the virtual
line L1 and the virtual line L3 to the intersection point of the
cross line C, a Y-axis coordinate position of the intersection
point of the cross line C is determined, and accordingly, the
X-axis and Y-axis coordinate position (x, y) of the intersection
point of the cross line C may be finally determined.
[0066] When the X-axis and Y-axis coordinate position at the
intersection point of the cross line C, (r cos .theta.1, -r sin
.theta.1), is stored in the storage means 90, the stored X-axis and
Y-axis coordinate position (r cos .theta.1, -r sin .theta.1) on the
back surface Wb of the wafer W is illuminated with the spotlight 41
illustrated in FIGS. 1 and 2. More specifically, under control of
the control means 9, movement of the spotlight 41 in the Y-axis
direction by the Y-axis moving means 89, movement of the spotlight
41 in the Z-axis direction by the elevating means 83, and/or
adjustment of an incident angle of the spot light irradiated from
the spotlight 41 by the adjusting means not illustrated are carried
out, so that the spotlight 41 illuminates the stored X-axis and
Y-axis coordinate position (r cos .theta.1, -r sin .theta.1) on the
back surface Wb of the wafer W at a predetermined spot diameter.
Note that the spot diameter of the spot light from the spotlight 41
is, for example, a diameter having a size of longitudinal and
lateral lengths of the cross line C.
[0067] As described above, when the detecting means 91 detects the
cross line C, the control means 9 sends the control signal to the
notification means 17, and the notification means 17 notifies the
operator that the cross line C has been detected on the wafer W.
Further, under control of the control means 9, grinding operations,
specifically, transferring the wafer W by the first transfer means
335 to a holding table 30 other than the holding table 30 holding
the wafer W in which the cross line C has been formed, rough
grinding processing (finish-grinding processing) on the wafers W
held on another holding table 30, transferring the wafer W in which
the cross line C has been formed from the holding table 30 to the
cleaning means 334 by the second transfer means 336, rotating the
turn table 34, and the like are stopped. As a result, the operator
removes the wafer W in which the cross line C has been formed from
the holding table 30, and thereafter, the grinding apparatus 1 is
in a state in which the adhered substance on the holding surface
300a of the holding table 30 can be removed.
[0068] Incidentally, in a case in which the cross line C is not
detected on the wafer W, similarly as described above, rotation of
the turn table 34 moves the wafer W closer to the second transfer
means 336, and the second transfer means 336 transfers the wafer W
on the holding table 30 to the cleaning means 334.
[0069] After the grinding operations in the grinding apparatus 1
are stopped as described above, suction of the wafer W with the
cross line C detected thereon by the holding table 30 is cancelled,
and the wafer W is no longer held on the holding table 30 to
thereby be transferred from the holding table 30 by the operator,
as a wafer unsuitable for a product wafer. Accordingly, the
spotlight 41 (see FIG. 2) illuminating the stored X-axis and Y-axis
coordinate position (r cos .theta.1, -r sin .theta.1) on the back
surface Wb of the wafer W at a predetermined spot diameter results
in illuminating the holding surface 300a directly below the X-axis
and Y-axis coordinate position (r cos .theta.1, -r sin .theta.1)
where the cross line C has been formed in the wafer W with the spot
light. In other words, the adhered substance on the holding surface
300a which has caused formation of the cross line C is in a state
of being illuminated by the spotlight 41 in a pinpoint manner.
[0070] The operator can immediately grasp the position where the
minute substance such as a grinding swarf and an abrasive grain is
adhered onto the holding surface 300a with the spot light emitted
from the spotlight 41. Hence, the operator can instantly remove the
adhered substance which causes the cross line C from the holding
surface 300a, for example, by use of a tool for removing the
adhered substances (a scraper or a cleaning brush, for
example).
[0071] After removal of the adhered substance from the holding
surface 300a by the operator is performed as described above, the
operator sets the grinding apparatus 1 such that the grinding
operations of the grinding apparatus 1 can be started again. Then,
the wafer W is held on the holding table 30 which turns into the
holding surface 300a in a state in which the cross line C is not
formed in the subsequent wafer W, and the grinding operations are
performed.
[0072] Note that the grinding apparatus 1 according to the present
invention is not limited to the embodiment described above, and the
configurations and the like in each of the apparatuses illustrated
in the attached drawings are also not limited thereto. Various
modifications and alterations can be made within the scope exerting
the effects of the present invention.
[0073] For example, the spotlight 41 may start to illuminate the
X-axis and Y-axis coordinate position at the intersection point of
the cross line C, (r cos .theta.1, -r sin .theta.1), which is
stored in the storage means 90, after the operator transfers the
wafer W in which the cross line C is detected, from the holding
table 30.
[0074] 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 claim and all changes and modifications as
fall within the equivalence of the scope of the claim are therefore
to be embraced by the invention.
* * * * *