Wafer abrasive machine

Details Wafer abrasive machine Wafer abrasive machine

2002-02-22

2004-02-17

Nguyen, Dung Van (Department: 3723)

Abrading

Machine

Rotary tool

C451S289000, C451S388000

Reexamination Certificate

active

06692342

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a wafer abrasive machine, more precisely relates to a wafer abrasive machine, in which a surface of a wafer held by a holding plate is pressed onto an abrasive face of an abrasive plate and relatively moved with respect thereto so as to abrade the surface of the wafer.
An example of a conventional abrasive machine for abrading silicon wafers for semiconductor devices is shown in
FIGS. 9 and 10
.
FIG. 9
is a partial sectional view of the conventional machine;
FIG. 10
is a partial enlarged view of the machine shown in FIG.
9
.
In the abrasive machine shown in
FIGS. 9 and 10
, an abrasive face
22
is constituted by an abrasive cloth
21
adhered on an upper face of an abrasive plate
20
.
A top ring “T” is headed toward the abrasive face
22
and provided to a lower end of a rotary shaft
28
, which is rotated by a motor
64
with gears
66
and
68
. The top ring “T” and the rotary shaft
28
are vertically moved by a cylinder unit
56
.
A through-hole
30
is formed in the rotary shaft
28
, and a suction pipe
18
, which is connected to a connecting port
74
communicated with a vacuum generator, runs through the through-hole
30
. A space between the suction pipe
18
and an inner face of the through-hole
30
is an air path
32
, which is connected to a connecting port
76
communicated with an air compressor. Therefore, compressed air, which is a pressure fluid, runs through the air path
32
.
The top ring “T” provided to the lower end of the rotary shaft
28
includes a head member
24
, which is fixed to the rotary shaft
28
, and a holding plate
10
, which is held and accommodated in a concave section
26
of the head member
24
and whose lower face
11
faces the abrasive face
22
of the abrasive plate
20
. The lower face
11
of the holding plate
10
acts as a holding face capable of sucking and holding a silicon wafer “W”. A plurality of holes
12
are opened in the holding face
11
of the holding plate
10
. As shown in
FIG. 10
, the holes
12
are mutually communicated by a horizontal connecting path
14
formed in the holding plate
10
. The connecting path
14
is communicated to the suction pipe
18
via a connector
16
. With this structure, the wafer “W” can be sucked and held on the holding face
11
of the holding plate
10
by driving the vacuum generator.
The holding plate
10
, whose holding face
11
faces the abrasive face
22
of the abrasive plate
20
, is suspended and accommodated in the concave section
26
of the head member
24
by a elastic sheet member
38
, which is formed into a donut-shape and made of rigid rubber. A symbol “h” stands for a length of projecting the holding plate
10
from the concave section
26
.
An elastic O-ring
34
, which is made of rubber or the like, is provided between an outer circumferential face
10
a
of the holding plate
10
accommodated in the concave section
26
and an inner circumferential face
24
a
of the concave section
26
. The O-ring
34
contacts the both faces
10
a
and
24
a
. With this structure, the holding plate
10
can be slightly moved in the horizontal direction and capable of absorbing a horizontal functional force which is generated while the wafer “W” is abraded.
A ring-shaped restraint member
36
, which is made of resin, e.g., acetyl resin, is fitted in the concave section
26
so as not to damage the holding plate
10
. The restraint member
36
restrains the horizontal movement of the holding plate
10
, which is accommodated in the concave section
26
, within a prescribed range.
By the O-ring
34
and the restraint member
36
, the horizontal movement of the holding plate
10
is limited, the vertical movement thereof is allowed.
An outer edge of the elastic sheet member
38
, which suspends the holding plate
10
in the concave section
26
, contacts an upper face of a step section
24
b
, which is formed along an outer edge of an inner upper face of the concave section
26
, and is air-tightly fixed thereto by a fixing plate
40
and screws
42
. An inner edge of the elastic sheet member
38
is air-tightly fixed to an upper face of the holding plate
10
as well. With this structure, a space
50
is formed between the elastic sheet member
38
and the inner upper face of the concave section
26
. The air path
32
for introducing the compressed air is communicated to the space
50
.
When the air compressor is driven and the compressed air is introduced into the space
50
via the air path
32
, inner pressure of the space
50
rises. If the inner pressure is greater than elastic force of the elastic sheet member
38
which biases the holding plate
10
toward the inner upper face of the concave section
26
, the lower end part of the holding plate is further projected from the concave section
26
as shown in
FIG. 11. A
symbol “h” shown in
FIG. 11
stands for the length of projecting the holding plate
10
, which has been further projected by the compressed air. Of course, the length “h” is longer than the length “h” (see FIG.
10
).
In the case of abrading the wafer “W” by the abrasive machine shown in
FIGS. 9 and 10
, the wafer “W” is sucked and held on the holding face
11
of the holding plate
10
, and a bottom surface of the wafer “W” is headed toward the abrasive face
22
of the abrasive plate
20
. Then the wafer “W” and the abrasive plate
20
are relatively moved so as to abrade the bottom surface of the wafer “W”. While the abrasion, a pressing force of the cylinder unit
56
and the inner pressure of the space
50
are adjusted so as to press the bottom surface of the wafer “W” onto the abrasive face
22
of the abrasive plate
20
with proper force.
To easily control the length of projecting the holding plate
10
from the concave section
26
of the head member
24
, the elastic sheet member
38
made of soft rubber was used instead of that made of the rigid rubber. In this case, the elastic sheet member
38
was excessively extended despite the inner pressure of the space
50
was slightly risen. To properly extend the elastic sheet member
38
when an external force is applied, the elastic sheet member
38
is reinforced by a cloth-formed reinforcing member
41
as shown in FIG.
12
A.
The cloth-formed reinforcing member
41
is shown in FIG.
12
B. When external forces F
1
are applied to warps
41
a
and woofs
41
b
in parallel, the reinforcing member
41
is less deformed. On the other hand, when external forces F
2
are diagonally applied to the warps
41
a
and woofs
41
b
, the reinforcing member
41
is fairly deformed. Degree of extension of the cloth-formed reinforcing member
41
is varied by the direction of the external force.
Since the holding plate
10
is suspended by the elastic sheet member
38
whose degree of extension is varied by the direction of the external force, the movement of the holding plate
10
is varied by the direction of the external force applied while the holding plate
10
is rotated. By the variation of the movement of the holding plate
10
, a gravity center of the wafer “W”, which is held and pressed by the holding plate
10
, is shifted from a rotational axis thereof, so that an edge of the wafer “W” is apt to be abraded diagonally.
If density of fibers, i.e., warps and woofs, of the reinforcing member
41
is made higher, the variation of the deformation of the elastic sheet member
38
, which depends on the direction of the external force, can be made small, but the problem caused by the variation still exists. Further, the reinforcing member
41
whose density of fibers is high is apt to peel from the rubber constituting the elastic sheet member
38
.
In the top ring “T” shown in
FIGS. 9 and 10
, the O-ring
34
made of rubber and the restraint member
36
made of acetyl resin are provided between the outer circumferential face
10
a
of the holding plate
10
and the inner circumferential face
24
a
of the concave section
26
so as to limit the horizontal movement of the holding plate
10
.
However, the O-ring
34
and the restraint m

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