FIELD OF THE INVENTION
[0001] This invention relates to a surface grinding apparatus, and more specifically, to
a surface grinding apparatus particularly adapted for grinding the surface of a semiconductor
wafer.
DESCRIPTION OF THE PRIOR ART
[0002] As is well known to those skilled in the art, the manufacturing of semiconductor
devices requires the grinding of the surface of a nearly disc-shaped semiconductor
wafer to make the thickness of the semiconductor wafer as required. In general, a
surface grinding apparatus as disclosed in the specification of Japanese Laid-Open
Patent Publication No. Sho 56-152562 (or U.S. Patent No. 4,481,738 or European Patent
Publication No. 0 039 209) is conveniently used as a surface grinding apparatus for
grinding the surface of a semiconductor wafer. This surface grinding apparatus comprises
a rotatably mounted support table, a plurality of semiconductor wafer holding chuck
tables fixed to the support table, a plurality of grinding wheels rotatably mounted
at intervals in the rotating direction of the support table, table rotating means
for rotating the support table and wheel rotating means for rotating the grinding
wheels.
[0003] In the aforesaid surface grinding apparatus, a semiconductor wafer to be ground on
its surface is held on the chuck table. Each of the plurality of grinding wheels is
rotated at a relatively high speed and the support table is also rotated at.a relatively
low speed. Consequently, the semiconductor wafer held on the chuck table fixed to
the support table is permitted passage beneath the plurality of rotating grinding
wheels successively, whereby the surface of the semiconductor wafer is ground with
the rotating grinding wheels.
[0004] As is understood from the description in the specification of Japanese Laid-Open
Patent Publication No. Sho 56-152562 (or U.S. Patent No. 4,481,738 or European Patent
Publication No. 0 039 209), the aforesaid surface grinding apparatus has various advantages
over other types of conventional surface grinding apparatuses. It is not, however,
fully satisfactory and it has problems to be solved that (a) a grinding wheel of an
annular shape as a whole is used in the aforesaid surface grinding apparatus and the
outer diameter of the grinding wheel needs to be sufficiently larger than the outer
diameter of a semiconductor wafer to be ground in order to uniformly grind the whole
surface of the semiconductor wafer with such a grinding wheel. Therefore, when a semiconductor
wafer is made large, the grinding wheel needs to be correspondingly made large. It
is not always easy, however, to produce a grinding wheel of a large diameter by bonding
super abrasive grains such as natural or synthetic diamond abrasive grains by a suitable
method in view of various aspects of the wheel production process; and (b) the relative
movement of a semiconductor wafer to the rotating grinding wheel in the grinding is
only the sending movement of the semiconductor wafer accompanied by the rotation of
the support table at the relatively low speed and the grinding trails by the grinding
wheel on the semiconductor wafer are simple arc-shaped ones defined by the movement
of the outer peripheral edge of the rotating grinding wheel. Therefore, the grinding
resistance is relatively large and it relatively largely varies according to the aforesaid
sending movement of the semiconductor wafer. Then, it is difficult to carry out a
sufficiently uniform grinding throughout the whole surface of the semiconductor wafer
and the grinding accuracy is limited.
SUMMARY OF THE INVENTION
[0005] It is a primary object of this invention to provide an improved surface grinding
apparatus, a surface grinding apparatus particularly adapted for grinding the surface
of a semiconductor wafer, in which a grinding wheel is not necessarily made large
in diameter even when a semiconductor wafer is made large in diameter and it is possible
to carry out a sufficiently uniform grinding throughout the whole surface of a semiconductor
wafer and obtain a required grinding accuracy.
[0006] It has now been found as a result of extensive investigations and experiments of
the present inventor that the aforesaid object can be attained by rotatably mounting
a workpiece holding chuck table on a support stand, by providing chuck table rotating
means for rotating this workpiece holding chuck table, and when grinding the surface
of a workpiece held on the chuck table with a grinding wheel, by rotating the grinding
wheel and also rotating the chuck table to rotate the workpiece held on the chuck
table although a workpiece holding chuck table has been fixed to a support stand such
as a support table in a conventional surface grinding apparatus.
[0007] According to this invention, there is provided a surface grinding apparatus comprising
a support stand, at least one workpiece holding chuck table rotatably mounted on the
support stand, a rotatably mounted grinding wheel for grinding the surface of a workpiece
held on the chuck table, chuck table rotating means for rotating the chuck table and
wheel rotating means for rotating the grinding wheel, wherein when grinding the surface
of the workpiece held on the chuck table with the grinding wheel, the grinding wheel
is rotated and the chuck table is also rotated to rotate the workpiece held on the
chuck table.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008]
Figure 1 is a simplified top plan view showing the major constituents of one embodiment
of the surface grinding apparatus constructed in accordance with this invention;
Figure 2 is a sectional view showing a part of the surface grinding apparatus of Figure
1;
Figure 3 and Figure 4 are simplified partial top plan views for explaining modifications
of the surface grinding manner by means of the surface grinding apparatus of Figure
1; and
Figure 5 is a sectional view, similar to Figure 2, showing a modified embodiment of
the chuck table rotating means.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0009] Preferred embodiments of the surface grinding apparatus constructed in accordance
with this invention will be described below in detail with reference to the accompanying
drawings.
[0010] Figure 1 simply illustrates the major constituents of one embodiment of the surface
grinding apparatus constructed in accordance with this invention. The illustrated
surface grinding apparatus is provided with a disc-shaped support table 4 of a relatively
large diameter mounted for rotation about the central axis 2 extending substantially
perpendicularly (vertically to the paper in Figure 1). A plurality of, four in the
illustrated embodiment, disc-shaped workpiece holding chuck tables 6 are rotatably
mounted on the support table 4 which constitutes a support stand at circumferentially
spaced positions. Conveniently, the plurality of chuck tables 6 are respectively arranged
at a plurality of positions whose radial distances from the central axis 2 are the
same one another and which are at equal intervals in the circumferential direction
of the support table 4 (i.e. at equal angular intervals).
[0011] Work stations A, B, C and D are respectively defined to the aforesaid plurality of,
four in the illustrated embodiment, positions spaced in the circumferential direction
of the support table 4. Conveniently, these work stations A, B, C and D are positioned
at equal intervals in the circumferential direction of the support table 4 (i.e. at
equal angular intervals) and the mutual angular interval between the work stations
A, B, C and D is consistent with the mutual angular interval between the plurality
of chuck tables 6. The work station A is a workpiece unloading and loading station.
In the workpiece unloading and loading station A, a workpiece ground on its surface
is taken out from the chuck table 6 by a suitable unloading means (not shown) and
a new workpiece to be ground on its surface is placed on the chuck table 6 by a suitable
loading means (not shown). The work stations B, C and D are a rough grinding station,
an intermediate grinding station and a finishing grinding station respectively. A
grinding wheel assembly having a grinding wheel 8 is disposed to each of these grinding
stations B, C and D. The surface of a workpiece held on the chuck table 6 is subjected
to a rough grinding in the rough grinding station B, an intermediate grinding in the
intermediate grinding station C and a finishing grinding in the finishing grinding
station D to be described in more detail hereinafter.
[0012] With reference to Figure 2 as well as Figure 1, the structure of the support table
4 and the chuck tables 6 mounted on the support table 4 is described in detail. In
the illustrated surface grinding apparatus, a static main support shaft (not shown)
extending substantially perpendicularly along the central axis 2 of the support table
4 is disposed and the support table 4 is rotatably mounted on the upper end portion
of this main support shaft. A table rotating means 10 such as an electric motor is
drivingly connected to the support table 4 through a suitable transmitting element
(not shown) and the support table 4 is intermittently or continuously rotated in the
direction shown by an arrow 12 in Figure 1 by the table rotating means 10 to be described
in more detail hereinafter. Four chuck table support blocks 14 (only one of them is
shown in Figure 2) are fixed to the peripheral edge portion of the substantially horizontal-upper
surface of the support table 4 at circumferentially equally spaced positions and the
chuck table 6 is rotatably mounted on each of these chuck table support blocks 14.
More specifically, a circular opening 16 open upwardly is formed in the chuck table
support block 14 which may be nearly cylindrical, and bearing members 18 and 20 are
disposed in this opening 16. The under surface of the bearing member 18 is caused
to abut against an annular shoulder portion formed in the opening 16, an annular spacer
member 22 is disposed between the bearing members 18 and 20, the internal peripheral
edge portion of the under surface of an annular support plate 23 fixed to the upper
surface of the chuck table support block 14 is caused to abut against the upper surface
of the bearing member 20, and thus the bearing members 18 and 20 are held at required
positions. The under portion of a rotating shaft 24 is inserted in the bearing members
18 and 20, and thus the rotating shaft 24 is rotatably mounted on the chuck table
support block 14. The chuck table 6 is fixed to the upper end of the rotating shaft
24 protruding upwardly beyond the chuck table support block 14. The illustrated chuck
table 6 has a disc-shaped main portion 26, a circular protrusion 28 formed on the
under surface of the main portion 26 and a connecting screw portion 30 extending downwardly
from the center of the circular protrusion 28. On the other hand, a circular depression
32 for receiving the circular protrusion 28 of the chuck table 6 and a screw hole
33 bored in the center of the circular depression 32 are formed in the upper surface
of the rotating shaft 24. The connecting screw portion 30 of the chuck table 6 is
screwed into the screw hole 33 of the rotating shaft 24 and thus the chuck table 6
is fixed to the upper end of the rotating shaft 24. In the state that the chuck table
6 is fixed to the rotating shaft 24 as required, there is a small interval between
the under surface of the circular protrusion 28 of the chuck table 6 and the bottom
surface of the circular depression 32 of the rotating shaft 24, and a closed space
34 is defined between the both. In the rotating shaft 24 is formed a passage 36 extending
axially from its upper end open to the bottom surface of the circular depression 32
to its lower end open to the under surface of the rotating shaft 24. A hollow manifold
38 is fixed to the central portion of the bottom surface of the opening 16 formed
in the chuck table support block 14 and the lower end of the passage 36 is adapted
for communication with this manifold 38. In the lower end portion of the chuck table
support block 14 is formed a passage 40 extending radially from its internal end adapted
for communication with the manifold 38 to its external end open to the outer peripheral
surface of the chuck table support block 14. The external end of the passage 40 is
connected to a vacuum source 46 and a supply source 48 of a liquid such as water through
a conduit 44 having a suitable switching valve 42. On the other hand, in the circular
protrusion 28 and the main portion 26 of the chuck table 5 are formed a plurality
of pores (not shown) extending from the under surface of the circular protrusion 28
to the upper surface of the main portion 26. When a workpiece such as a semiconductor
wafer is placed on the upper surface of the chuck table 6 in the workpiece unloading
and loading station A, the switching valve 42 is operated to connect the passage 40
to the vacuum source 46. Then, air is sucked through the plurality of pores (not shown)
formed in the chuck table 6, the space 34, the passage 36, the manifold 38, the passage
40 and the conduit 44 to thus hold the workpiece by suction onto the chuck table 6.
When the workpiece is taken out from the chuck table 6 in the workpiece unloading
and loading station A, the switching valve 42 is operated to connect the passage 40
to the supply source 48. Then, a liquid such as water is supplied to the upper surface
of the chuck table 6 through the conduit 44, the passage 40, the manifold 38, the
passage 36, the space 34 and the plurality of pores (not shown) formed in the chuck
table 6 to thus float up the workpiece which has been held by suction to the chuck
table 6.
[0013] In the illustrated surface grinding apparatus, a chuck table rotating means for rotating
the plurality of chuck tables 6 is also provided. With reference to Figure 2, a nearly
disc-shaped central support block 50 is fixed to the central portion of the substantially
horizontal upper surface of the support table 4. At the peripheral edge portion of
this central support block 50 is unitedly formed a cylindrical upright wall 52 extending
upwardly, and onto this upright wall 52 is fixed a disc-shaped support plate 54. In
the central portion of the upper surface of the central support block 50 is formed
a circular depression 56 and in the central portion of the support plate 54 is formed
a circular through opening 58 extending vertically. Bearing members 60 and 62 are
disposed in the depression 56 and the opening 58 respectively, and a central rotating
shaft 64 upwardly extending substantially perpendicularly from the depression 56 is
rotatably supported by these bearing members 60 and 62. In the upper surface of the
central support block 50 are further formed four circular depressions 66 correspondingly
positioned to the angular positions of the chuck tables 6 respectively, and in the
support plate 54 are formed four circular openings 68 coordinatively positioned with
these four depressions 66 respectively. (Only one depression 66 and one opening 68
are shown in Figure 2.) Bearing members 70 and 72 are disposed in the depressions
66 and openings 68 respectively, and rotating shafts 74 upwardly extending substantially
perpendicularly from the depressions 66 are rotatably supported by these bearing members
70 and 72. The upper end portion of the aforesaid central rotating shaft 64 extending
upwardly beyond the support plate 54 is drivingly connected to a rotating source 76
such as an electric motor through a suitable transmitting element (not shown). The
rotating source 76 may be mounted on the support table 4 through a suitable support
frame (not shown) or may be mounted at a suitable position separate from the support
table 4. A gear 78 is fixed to the central rotating shaft 64 at its middle portion
between the central support block 50 and the support plate 54. On the other hand,
gears 80 are fixed to the rotating shafts 74 respectively at their middle portions
between the central support block 50 and the support plate 54, and each of these gears
80 is engaged with the gear 78. Toothed pulleys 82 are fixed to the rotating shafts
74 respectively at their upper end portions protruding upwardly beyond the support
plate 54. Toothed pulleys 84 are also fixed to the rotating shafts 24 respectively
to which the chuck tables 6 are fixed, and endless toothed belts 86 are wound around
the corresponding toothed pulleys 82 and 84 respectively. Consequently, as is understood,
when the common rotating source 76 is energized to rotate the central rotating shaft
64, for example, in the direction shown by an arrow 88 in Figure 1, each of the plurality
of chuck tables 6 is caused to rotate in the direction shown by an arrow 90 in Figure
1 through common drive connecting means (i.e. the gear 78) and drive connecting means
(i.e. the gear 80, the toothed pulley 82, the toothed belt 86 and the toothed pulley
84) provided with respect to each of the plurality of chuck tables 6.
[0014] In the illustrated embodiment, protect covers 92, 94 and 96 are also disposed on
the support table 4 by suitable support means (not shown). These protect covers 92,
94 and 96 prevent a cooling liquid such as water used when grinding the workpiece
held on the chuck table 6 with the grinding wheel 8 to be described hereinafter or
produced grinding chips from coming into the above-described various rotation supporting
constituents and drive connecting elements disposed on the support table 4.
[0015] In each of the grinding stations shown by letters B, C and D in Figure 1, a grinding
wheel assembly is disposed adjacent to the support table 4. (Only the grinding wheels
8 in the grinding wheel assemblies are simply shown by two-dot chain line in Figure
1 for clearness of the drawing.) The structures of the grinding wheel assemblies disposed
to the grinding stations B,C and D may be substantially the same and only one grinding
wheel assembly is shown in Figure 2. With reference to Figure 2, the illustrated grinding
wheel assembly shown generally by a numeral 98 has a static support base stand 100
positioned adjacent to the peripheral edge of the support table 4. A horizontally
moving block 102 is mounted on the base stand 100 by suitable support means (not shown)
for substantially horizontal movement in the right-and-left direction in Figure 2.
Conveniently, the moving direction of the horizontally moving block 102 is substantially
consistent with a radial direction of the support table 4. A first wheel moving means
104 including a driving source such as an electric motor exists between the base stand
100 and the horizontally moving block 102, and the horizontally moving block 102 is
moved by this first wheel moving means 104. A perpendicularly moving block 106 is
mounted on the horizontally moving block 102 by suitable support means (not shown)
for substantially perpendicular movement in the up-and-down direction. A second wheel
moving means 108 including a driving source such as an electric motor exists between
the horizontally moving block 102 and the perpendicularly moving block 106, and the
perpendicularly moving block 106 is vertically moved by this second wheel moving means
108. A rotating shaft 110 is rotatably mounted on the perpendicularly moving block
106. A grinding wheel assemblage 112 which is conveniently a so-called cup-shaped
grinding wheel assamblage is fixed to the lower end of the rotating shaft 110 protruding
downwardly from the perpendicularly moving block 106. The illustrated grinding wheel
assemblage 112 consists of a reversed- cup-shaped support member 114 fixed to the
lower end of the rotating shaft 110 and the grinding wheel 8 fixed to an annular open
end of the support member 114. The grinding wheel 8 is conveniently of an annular
shape as a whole, but it is not limited to one continuously extending annularly as
illustrated, and one which is made annular as a whole by fixing a plurality of arc-shaped
pieces to the annular open end of the support member 114 at circumferentially spaced
positions may also be conveniently used. The rotating shaft 110 is drivingly connected
to a wheel rotating means 116 such as an electric motor mounted on the perpendicularly
moving block 106, and the rotating shaft 110 and the grinding wheel assemblage 112
fixed thereto are rotated about the central axis 118 of the rotating shaft 110 by
this wheel rotating means 116. The central axis 118 may extend substantially perpendicularly.
If desired, the central axis 118 may be inclined in a predetermined direction, for
example, in the right direction as one faces down in Figure 2 by a small angle (for
example, 0.004° to 0.01
0). Conveniently, the grinding wheel 8 itself is one formed by bonding super abrasive
grains such as natural or synthetic diamond grains or cubic boron nitride grains by
a suitable method. Preferably, the grain size of the grinding wheel 8 used in the
rough grinding station B is relatively large, the grain size of the grinding wheel
8 used in the intermediate grinding station C is intermediate and the grain size of
the grinding wheel 8 used in the finishing grinding station D is relatively small.
[0016] In the next place, surface grinding manners of a semiconductor wafer by the above-described
surface grinding apparatus are described.
[0017] In the first surface grinding manner, the support table 4 is intermittently rotated
every 90
0 in the direction shown by the arrow 12 from the angular position illustrated in Figure
1. Consequently, each of the four chuck tables 6 mounted on the support table 4 is
positioned to the workpiece unloading and loading station A, the rough grinding station
B, the intermediate grinding station C and the finishing grinding station D successively.
While the chuck table 6 is positioned to the workpiece unloading and loading station
A, a semiconductor wafer W which has been ground on its surface is taken out of the
chuck table 6 by the suitable unloading means (not shown) as described hereinbefore.
Then, a new semiconductor wafer W to be ground on its surface is placed on the chuck
table 6 by the suitable loading means (not shown) as illustrated by two-dot chain
line in Figure 1 and Figure 2, and held by suction onto the chuck table 6 as described
hereinbefore. In these unloading and loading of a semiconductor wafer W, it is necessary
to stop the rotation of the chuck table 6 itself, and therefore, the rotation of the
chuck tables 6 is not started for a predetermined time after the support table 4 is
rotated by 90
0 and stopped at a specific angular position, and during this time the unloading and
loading of a semiconductor wafer W is carried out in the workpiece unloading and loading
station A. Subsequently, the rotation of the chuck tables 6 is started for the grinding
in the grinding stations B, C and D.
[0018] The grinding in each of the grinding stations B, C and D may be carried out by the
following procedure. Mainly with reference to Figure 1, when the rotation of the support
table 4 is stopped to stop the support table 4 at the specific angular position, the
grinding wheel 8 is situated over a semiconductor wafer W held on the chuck table
6 in each of the grinding stations B, C and D. As illustrated in Figure 1 and Figure
2, the relative position of the grinding wheel 8 to the semiconductor wafer W is preferably
where the grinding edge of the grinding wheel 8 is caused to pass over the substantial
center of the surface of the nearly disc-shaped semiconductor wafer W. (Generally,
the semiconductor wafer W is substantially circular except for a straight-line periphery
called an orientation flat.) In order to meet this requirement, in Figure 1 and Figure
2, the central axis 118 (Figure 2) of the grinding wheel 8 is shifted outwardly in
a radial direction of the support table 4 with reference to the central axis (extending
vertically to the paper in Figure 1 and extending in an up-and-down direction in Figure
2) of the semiconductor wafer W. If desired, however, it may be shifted in another
direction, for example, in a circumferential direction of the support table 4 as illustrated
in Figure 3. In order to grind the surface of the semiconductor wafer W, the chuck
table 6 and the semiconductor wafer W held thereon are rotated in the direction shown
by the arrow 90 (or in its reverse direction) at, for example, 1 to 100 r.p.m. by
the chuck table rotating means 76 (Figure 2). Simultaneously, the grinding wheel 8
is rotated in the direction shown by an arrow 120 (or in its reverse direction) at
a relatively high speed of, for example, 500 to 5000 r.p.m. by the wheel rotating
means 116 (Figure 2). In addition, the perpendicularly moving block 106 is lowered
at a relatively low speed of, for example, 0.001 to 1.0 mm/min. by the second wheel
moving means 108 (Figure 2) to thus lower the grinding wheel 8 toward the semiconductor
wafer W. As a result, the rotating grinding wheel 8 acts on the rotating semiconductor
wafer W, whereby the surface of the semiconductor wafer W is ground with a gradually
increased grinding depth. The grinding depth of the surface of the semiconductor wafer
W is determined by the lowered amount of the grinding wheel 8. In this kind of surface
grinding manner, if there is a small offset between the grinding edge of the grinding
wheel 8 and the substantial center of the surface of the semiconductor wafer W, as
is easily understood, a small unground projection remains in the central area of the
surface of the semiconductor wafer W. In this case, after the grinding wheel 8 is
lowered by a predetermined amount, the horizontally moving block 102 is reciprocated
to some extent to reciprocate the grinding wheel 8 to some extent against the surface
of the semiconductor wafer W, whereby the unground projection can be ground and disappear.
When the surface of the semiconductor wafer W is ground as required, the grinding
wheel 8 is raised, and the rotation of the grinding wheel 8 and the rotation of the
chuck table 6 and the semiconductor wafer W held thereon are stopped. Subsequently,
the support table 4 is rotated by
900.
[0019] In place of the above-described first surface grinding manner, the following second
surface grinding manner may be carried out. In this second surface grinding manner,
in the beginning of the grinding, the grinding wheel 8 is situated outside the semiconductor
wafer W held on the chuck table 6 as shown by a two-dot chain line 8A in Figure 4.
The vertical position of the grinding wheel 8 is set up at a required grinding depth,
namely, is set up so that the lower end of the grinding wheel 8 is below the surface
of the semiconductor wafer W by the required grinding depth. In a similar way as in
the first surface grinding manner, the chuck table 6 and the semiconductor wafer W
held thereon are rotated in the direction shown by the arrow 90 (or in its reverse
direction) at a relatively high speed and the grinding wheel 8 is rotated in the direction
shown by the arrow 120 (or in its reverse direction) at a relatively high speed. Furthermore,
the horizontally moving block 102 is moved in the left direction in Figure 4 at a
relatively low speed of, for example, 100 to 500 mm/min. by the first wheel moving
means 104 to thus move the grinding wheel 8 in the direction shown by an arrow 122
from the position shown by the two-dot chain line 8A to the position shown by a two-dot
chain line 8B in Figure 4. The position of the grinding wheel 8 shown by the two-dot
chain line 8B in Figure 4 may be the same with the position of the grinding wheel
8 shown by two-dot chain line in Figure 1. As a result, the rotating grinding wheel
8 successively acts on the semiconductor wafer W from its peripheral edge toward its
center according to its movement in the direction shown by the arrow 122 to grind
the surface of the semiconductor wafer W. The grinding depth of the surface of the
semiconductor wafer W is defined by the initially established grinding depth of the
grinding wheel 8.
[0020] In place of the above-described first and second surface grinding manners, the following
third surface grinding manner may be carried out. Mainly with reference to Figure
1, while in the first and second surface grinding manners the support table 4 is stopped
at the specific angular position during the grinding, in the third surface grinding
manner the support table 4 is continuously rotated in the direction shown by the arrow
12 at a relatively low speed of, for example, 100 mm/min. to 500 mm/min. in the moving
speed of the semiconductor wafer W held on the chuck table 6 in the direction shown
by the arrow 12 to continuously move the semiconductor wafer W held on the chuck table
6 in the direction shown by the arrow 12 and to permit its passage beneath the grinding
wheels 8 at least in the grinding stations B, C and D. On the other hand, the grinding
wheel 8 is set up at a required grinding depth, namely, is set up so that the lower
end of the grinding wheel 8 is below the surface of the semiconductor wafer W by the
required grinding depth, at the position shown by two-dot chain line in Figure 3 (or
at the position shown by two-dot chain line in Figure 1 or a position a little inside
than that in the radial direction). Similarly as in the first and second surface grinding
manners, the semiconductor wafer W held on the chuck table 6 is rotated in the direction
shown by the arrow 90 (or in its reverse direction) at a relatively high speed and
the grinding wheel 8 is rotated in the direction shown by the arrow 120 (or in its
reverse direction) at a relatively high speed. As a result, when the semiconductor
wafer W held on the chuck table 6 is permitted passage beneath the grinding wheel
8 by the continuous rotation of the support table 4, the rotating grinding wheel 8
acts on and grinds the surface of the rotating semiconductor wafer W. The grinding
depth of the surface of the semiconductor wafer W is defined by the initially established
grinding depth of the grinding wheel 8.
[0021] As is clear from the above description about the one embodiment of the surface grinding
apparatus constructed in accordance with this invention, in the surface grinding apparatus
constructed in accordance with this invention, the grinding wheel 8 is rotated and
a workpiece such as a semiconductor wafer W is also rotated when grinding the surface
of the workpiece. Therefore, although the grinding wheel 8 having a considerably larger
outer diameter than the outer diameter of the workpiece is used in the illustrated
embodiment, even if the outer diameter of the grinding wheel 8 is nearly the same
with, or somewhat smaller than, the outer diameter of the workpiece, the whole surface
of the workpiece can be uniformly ground. Then, for example, even if the semiconductor
wafer W is made large in diameter, it is not always necessary to make the grinding
wheel 8 large in diameter accordingly. Furthermore, since the relative movement of
the workpiece and the grinding wheel 8 in the grinding is defined by at least both
of the rotation of the grinding wheel 8 and the rotation of the workpiece, the grinding
trails on the surface of the workpiece by the grinding wheel 8 extend in various directions
throughout the whole surface of the workpiece and become very complicated. Therefore,
the grinding resistance is relatively small and the fluctuations of the grinding resistance
are sufficiently small. It is possible to carry out a sufficiently uniform grinding
throughout the whole surface of the workpiece.
[0022] Figure 5 illustrates a modified embodiment of the chuck table rotating means. In
this modified embodiment, a central support block 200 is fixed to the central portion
of the substantially horizontal upper surface of the support table 4. This central
support block 200 has a disc-shaped base portion 202 and a cylindrical support portion
204 upwardly extending substantially perpendicularly from the central portion of the
upper surface of this base portion 202. On the other hand, at the lower portion of
a central rotating shaft 206 is formed a large-diameter portion 208, and in this large-diameter
portion 208 is formed a circular depression 210 open downwardly. The large-diameter
portion 208 of the central rotating shaft 206 is rotatably mounted on the cylindrical
support portion 204 of the central support block 200 through bearing members 212 and
214. Specifically, the under surface of the bearing member 212 is caused to abut against
the upper surface of the base portion 202 of the central support block 200, an annular
spacer member 216 is disposed between the bearing member 212 and the bearing member
214, the upper surface of the bearing member 214 is caused to abut against the bottom
surface (upper surface) of the circular depression 210, and thus the bearing members
212 and 214 are held at required positions. The upper end portion of the central rotating
shaft 206 is drivingly connected to the rotating source 76 such as an electric motor
through a suitable transmitting element (not shown). An annular flange 218 is formed
on the outer peripheral surface of the large-diameter portion 208 of the central rotating
shaft 206 and a gear 220 is fixed onto this annular flange 218.
[0023] To the upper surface of the support table 4 are also fixed four support blocks 222
correspondingly positioned to the angular positions of the four workpiece holding
chuck tables 6 respectively. (Only one support block 222 is illustrated in Figure
5.) Each of the support blocks 222 is provided with drive connecting elements including
pneumatic clutchs. Specifically, each of the support blocks 222 has a lower large-diameter
cylindrical portion 224 and an upper small-diameter cylindrical portion 226. A nearly
cylindrical rotating member 232 is rotatably mounted on the upper small-diameter cylindrical
portion 226 through bearing members 228 and 230. Specifically, the under surface of
the bearing member 228 is caused to abut against the upper surface of the large-diameter
cylindrical portion 224, an annular spacer member 234 is disposed between the bearing
member 228 and the bearing member 230, the upper surface of the bearing member 230
is caused to abut against the under surface of an annular flange 236 formed on the
inner peripheral surface of the rotating member 232, and thus the bearing members
228 and 230 are held at required positions. An annular member 238 is fixed to the
upper surface of the upper small-diameter cylindrical portion 226, and the annular
flange 236 of the rotating member 232 is restrained by the under surface of this annular
member 238 to prevent the rotating member 232 from moving upwardly. An annular flange
240 is formed on the outer peripheral surface of the rotating member 232 and a gear
242 is fixed onto this annular flange 240. This gear 242 is engaged with the aforesaid
gear 220. To the upper end of the rotating member 232 is fixed an annular friction
plate 244 made of a material having a high friction coefficient such as synthetic
rubber. On the other hand, in the lower large-diameter cylindrical portion 224 of
the support block 222 is formed a circular depression 246 open downwardly. The under
surface of this circular depression 246 is closed by the support table 4 and the circular
depression 246 works as a cylinder of a pneumatic mechanism as will be clear from
a description hereinafter. A through hole 248 extending substantially perpendicularly
is further formed in the support block 222 and a shaft 254 is slidably mounted in
this through hole 248 for movement in the perpendicular direction. The shaft 254 extends
upwardly beyond the upper surface of the upper small-diameter cylindrical portion
226 and a gear 262 is rotatably mounted on the upper end portion of the shaft 254
by a bearing member 258 and a stop ring 260 so that the gear 262 cannot move in the
axial direction with respect to the shaft 254. On the under surface of the gear 262
is formed an annular projection 264 facing to the friction plate 244. To the lower
end of the shaft 254 located in the circular depression 246 is fixed a disc 266 which
works as a piston of a pneumatic cylinder mechanism. A spring means 268 such as a
plurality of flat springs is disposed between the upper surface of the support table
4 and the disc 266, and this spring means 268 spring y biases upwardly the disc 266,
accordingly the shaft 254 and the gear 262 mounted thereon. On the other hand, in
the lower large-diameter cylindrical portion 224 of the support block 222 is formed
a passage 270 extending from its internal end open to the upper end of the circular
depression 246 to its external end open to the outer peripheral surface of the lower
large-diameter cylindrical portion 224. The external end of the passage 270 is adapted
for selective communication with a compressed air supply source 276 or the atmosphere
through a conduit 274 having a suitable switching valve 272. Upon communication of
the passage 270 with the compressed air supply source 276, the disc 266 is lowered
to the illustrated position against the springy biasing action of the spring means
268 by compressed air supplied to the circular depression 246. Therefore, the shaft
254 and the gear 262 are lowered to the connection position shown by real line. In
this connection position, the annular projection 264 formed on the under surface of
the gear 262 is pressed against the friction plate 244 to thus frictionally connect
the gear 262 to the rotating member 232. On the other hand, upon communication of
the passage 270 with the atmosphere, the disc 266 is raised by the springy biasing
action of the spring means 268. Therefore, the shaft 254 and the gear 262 are raised
to the release position shown by two-dot chain line. In this release position, the
annular projection 264 formed on the under surface of the gear 262 is kept apart upwardly
from the friction plate 244 to thus release the connection of the gear 262 with the
rotating member 232. Furthermore, a gear 278 is fixed to the rotating shaft 24 to
which the chuck table 6 is fixed, and this gear 278 is engaged with the gear 262.
Since the structure in the modified embodiment illustrated in Figure 5 such as the
mounting manner of the chuck table 6 is substantially the same with that in the embodiment
illustrated in Figure 2 except for the above-described structure, its description
is omitted in this specification.
[0024] In the modified embodiment illustrated in Figure 5, the drive connecting means disposed
between the common driving source 76 and each of the plurality of (four) chuck tables
6 includes a clutch means (i.e. the friction plate 244 fixed to the rotating member
232, the annular projection 264 formed on the gear 262 and the like). As a result,
the rotation of each of the plurality of chuck tables 6 can be independently controlled.
Specifically, when the gear 262 is lowered to the connection position shown by real
line, the rotation of the driving source 76 is transmitted to the chuck table 6 through
the central rotating shaft 206, the gear 220, the gear 242, the rotating member 232,
the friction plate 244, the gear 262 and the gear 278 to thus rotate the chuck table
6. When the gear 262 is raised to the release position shown by two-dot chain line,
the connection between the friction plate 244 and the gear 262 is released, and thus
the rotation of the chuck table 6 is stopped. If desired, in order to immediately
stop the rotation of the chuck table 6 when the gear 262 is raised to the release
position shown by two-dot chain line, a brake means (not shown) which works on the
chuck table 6 synchronously with the raise of the gear 262 may also be provided. In
the modified embodiment illustrated in Figure 5, since the rotation of each of the
plurality of chuck tables 6 can be independently controlled, for example, the grinding
operations can be carried out in the grinding stations B, C and D (Figure 1) respectively
while rotating three chuck tables 6 existing in the grinding stations B, C and D respectively,
while the workpiece unloading and loading operations can be carried out in the workpiece
unloading and loading station A (Figure 1) while stopping the chuck table 6 existing
in the workpiece unloading and loading station A, and thus the operation efficiency
can be improved. If desired, a position detector (not shown) may be additionally provided
to each of the chuck tables 6 to automatically control the connection and release
of the clutch means, to rotate the chuck tables 6 while each of the chuck tables 6
exists at least in the grinding stations B, C and D and to stop the chuck tables 6
while each of the chuck tables 6 exists at least in the workpiece unloading and loading
station A.
[0025] While this invention has been described in detail hereinabove with reference to the
accompanying drawings showing specific embodiments of the surface grinding apparatus
constructed in accordance with this invention, it should be understood that this invention
is not limited to these specific embodiments, and various changes and modifications
are possible without departing from the scope of this invention.
1. A surface grinding apparatus comprising a support stand (4), at least one workpiece
holding chuck table (6) rotatably mounted on the support stand (4), a rotatably mounted
grinding wheel (8) for grinding the surface of a workpiece (W) held on the chuck table
(6), chuck table rotating means (76) for rotating the chuck table (6) and wheel rotating
means (116) for rotating the grinding wheel (8), wherein when grinding the surface
of the workpiece (W) held on the chuck table (6) with the grinding wheel (8), the
grinding sheel (8) is rotated and the chuck table (6) is also rotated to rotate the
workpiece (W) held on the chuck table (6).
2. A surface grinding apparatus according to claim 1 wherein the grinding wheel (8)
is of an annular shape as a whole and the central axis (118) of rotation of the grinding
wheel (8) is disposed generally parallel to the central axis of rotation of the chuck
table (6).
3. A surface grinding apparatus according to claim 1 wherein the support stand comprises
a rotatably mounted support table (4), and table rotating means (76) is provided for
rotating the support table (4).
4. A surface grinding apparatus according to claim 3 wherein the grinding wheel (8)
is mounted for movement in the direction of its central axis (118) of rotation, wheel
moving means (108) is provided for moving the grinding wheel (8) in the direction
of its central axis (118) of rotation, and when grinding the surface of the workpiece
(W) held on the chuck table (6) with the grinding wheel (8), the support table (4)
is stopped at a predetermined angular position so that the workpiece (W) held on the
chuck table (6) has a predetermined relationship with the grinding wheel (8), and
the grinding wheel (8) is moved toward the chuck table (6) by the wheel moving means
(108) to thus gradually increase the grinding depth of the surface of the workpiece
(W).
5. A surface grinding apparatus according to claim 4 wherein the workpiece is nearly
disc-shaped, and when . the support table (4) is stopped at the predetermined angular
position, the workpiece (W) is positioned with respect to the grinding wheel (8) so
that the outer peripheral edge of the grinding wheel (8) passes through the substantial
center of the workpiece (W).
6. A surface grinding apparatus according to claim 3 wherein when grinding the surface
of the workpiece (W) held on the chuck table (6) with the grinding wheel (8), the
support table (4) is continuously rotated by the table rotating means (76) to permit
passage of the workpiece (W) held on the chuck table (6) beneath the grinding wheel
(8).
7. A surface grinding apparatus according to claim 3 wherein the grinding wheel (8)
is mounted for movement in a direction generally perpendicular to its central axis
(118) of rotation, wheel moving means (104) is provided for moving the grinding wheel
(8) in the direction generally perpendicular to its central axis (118) of rotation,
and when grinding the surface of the workpiece (W) held on the chuck table (6) with
the grinding wheel (8), the support table (4) is stopped at a predetermined angular
position and the grinding wheel (8) is moved from the peripheral edge toward the center
of the workpiece (W) held on the chuck table (6) by the wheel moving means (104) to
thus gradually grind the surface of the workpiece (W) from its peripheral edge toward
its center.
8. A surface grinding apparatus according to claim 7 wherein the workpiece (W) is
nearly disc-shaped and the grinding wheel (8) is moved by the wheel moving means (104)
up to the position where its outer peripheral edge passes through the substantial
center of the surface of the workpiece (W).
9. A surface grinding apparatus according to claim 3 wherein the support table (4)
is provided with a plurality of workpiece holding chuck tables (6) at circumferentially
spaced positions and the chuck table rotating means (76) includes one common driving
source and a plurality of drive connecting means disposed between the common driving
source and each of the plurality of chuck tables (6) respectively.
10. A surface grinding apparatus according to claim 9 wherein each of the plurality
of drive connecting means has clutch means for controlling connection and release.
11. A surface grinding apparatus according to claim 10 wherein the clutch means is
a pneumatic clutch controlled by pressurized air.
12. A surface grinding apparatus according to claim 10 wherein one workpiece unloading
and loading station (A) and a plurality of grinding stations (B, C, D) are defined
at circumferentially spaced positions of the support table (4) and a grinding wheel
(8) is provided in each of the plurality of grinding stations (B,C, D).
13. A surface grinding apparatus according to claim 12 wherein while each of the plurality
of chuck tables (6) exists at least in either of the plurality of grinding stations
(B, C, D), the clutch means is connected and each of the plurality of chuck tables
(6) is rotated, whereas while each of the plurality of chuck tables (6) exists at
least in the workpiece unloading and loading station (A), the clutch means is released
and the rotation of each of the plurality of chuck tables (6) is stopped.
14. -A surface grinding apparatus according to claim 13 wherein the support table
(4) is continuously rotated by the table rotating means (76), whereby each of the
plurality of chuck tables (6) is continuously moved through the workpiece unloading
and loading station (A) and the plurality of grinding stations (B, C, D).
15. A surface grinding apparatus according to claim 1 wherein the workpiece (W) is
a semiconductor wafer.