Abrasive machine

Details Abrasive machine Abrasive machine

1999-09-08

2001-08-28

Banks, Derris H. (Department: 3723)

Abrading

Machine

Rotary tool

C451S262000, C451S288000, C451S285000

Reexamination Certificate

active

06280304

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an abrasive machine, more precisely relates to an abrasive machine, which sandwiches a work piece between a lower plate and an upper plate and relatively moves the two plates so as to abrade the work piece therebetween.
Conventionally, a thin plate work piece, e.g., a silicon wafer, is abraded by a lapping machine and polished by a polishing machine.
In the conventional lapping machine, for example, an external gear, which acts as a sun gear, and an internal gear are rotated at different angular velocity, so that each carrier plate, which holds the work pieces in through-holes, is rotated on its axis and moved round. Each carrier plate acts as a planet gear. The work pieces held by the carrier plates are sandwiched between an upper plate and a lower plate, which are respectively provided on the upper side and the lower side of the carrier plates. An abrasive agent (slurry) is supplied to spaces between the work pieces and the upper and lower plates. The upper and lower plates are relatively moved (rotated and/or swung) with respect to the work pieces, so that an upper face and a lower face of the work pieces can be simultaneously lapped.
By using the lapping machine, the work pieces can be precisely flatly lapped. Further, by simultaneously lapping the both faces of the work piece, working efficiency can be improved. The lapping machine has been employed, for example, to lap silicon wafers for semiconductor chips.
The conventional polishing machine generally has a rotary polishing plate, whose upper face is covered with a polishing cloth, and a holding unit including a holding plate. The holding plate is rotatably provided above the polishing plate, movable in the vertical direction and capable of holding the work pieces on a bottom face. Note that, the polishing plate corresponds to the lower plate; the holding plate corresponds to the upper plate. In the conventional polishing machine, the slurry is supplied, and the polishing plate is relatively moved with respect to the work pieces to polish a surface of the work pieces like mirror faces.
An example of the conventional lapping machine will be explained with reference to FIG.
6
.
A bottom face of an upper plate
20
is an abrasive face, which laps upper faces of work pieces
10
(silicon wafers). Keys
21
are provided on an upper face of the upper plate
20
.
A cylinder unit
22
, e.g., a hydraulic cylinder unit, is provided to an upper part of a gate-shaped frame
14
. The upper plate
20
is connected to a lower end of a piston rod
22
a
of the cylinder unit
22
by a rotary plate
23
and connecting rods
27
. With this structure, the upper plate
20
is rotatably suspended. A connecting section
22
b
is fixed to the rotary plate
23
, the piston rods
22
a
is not rotatable, and the rotary plate
23
and the upper plate
20
, which are mutually connected by the connecting rods
27
, are rotatably connected to the piston rod
22
b
without falling therefrom. The upper plate
20
applies a pressing force, which is caused by weight of the upper plate
20
, to a lower plate
30
. The pressing force can be adjusted by controlling a lifting force of the cylinder unit
22
.
The keys
21
of the upper plate
20
are engaged with key grooves of a rotary member
54
, which is rotated by a motor
70
, so the upper plate
20
is rotated by the motor
70
. A shaft
54
a
is downwardly extended from a lower end of the rotary member
54
. A gear
54
b
is fixed to a lower end of the shaft
54
a
, and an idle gear
63
is engaged with the gear
54
b
and a gear
64
, which is fixed to a spindle
60
. With this structure, power of the motor
70
is transmitted to the upper plate
20
via the rotary member
54
. By connecting the upper plate
20
to the rotary member
54
with the keys
21
, a wide space for maintenance and setting the work pieces
10
can be formed between the upper plate
20
and the lower plate
30
.
An external gear
50
is engaged with carrier plates
40
. A first hollow shaft
50
a
, which is coaxial to the rotary shaft
54
a
, is connected to the external gear
50
. A gear
50
b
of the first hollow shaft
50
a
is engaged with a gear
65
of the spindle
60
.
A second hollow shaft
30
b
, which is coaxial to the first hollow shaft
50
a
, is connected to the lower plate
30
. A gear
30
b
, which is fixed to a mid part of the second hollow shaft
30
a
, is engaged with a gear
61
of the spindle
60
.
An internal gear
52
is engaged with the carrier plates
40
. A third hollow gear
52
a
, which is coaxial to the second hollow shaft
30
a
, is connected to the internal gear
52
. A gear
52
b
of the third hollow shaft
52
a
is engaged with a gear
62
of the spindle
60
.
The spindle
60
is connected to a reduction gear system
69
, and the reduction gear system
69
is connected to the motor, e.g., an electric motor, an oil motor, by a belt.
With the above described structure, the power of the motor
70
is transmitted by the reduction gear system
69
, the gears and the shafts, so that the upper plate
20
, the lower plate
30
, the external gear
50
and the internal gear
52
are rotated.
In the conventional lapping machine, the pressing force of the upper plate
20
, which is caused by the weight of the upper plate
20
and which presses the lower plate
30
, is adjusted by controlling the lifting force of the cylinder unit
22
. If fluid pressure in a lower chamber of the cylinder unit is made higher, the piston rod
22
a
is retracted into the cylinder unit
22
and the pressing force of the upper plate
20
, which presses the lower plate
30
, can be reduced. Namely, the maximum pressing force of the upper plate
20
is equal to the weight of the upper plate
20
.
When silicon wafers are lapped by the lapping machine, there are minute projections and holes in surfaces of the silicon wafers
10
. Firstly, the fluid pressure in the lower chamber of the cylinder unit
22
is made high so as to reduce the pressing force of the upper plate
20
. The surfaces of the silicon wafers
10
are lapped with lower pressing force. Then, the fluid pressure in the cylinder unit
22
is gradually reduced so as to gradually increase the pressing force of the upper plate
20
. By this control, the surfaces of the silicon wafers
10
are smoothly lapped and the silicon wafers have uniform thickness. In this state, the pressing force can be uniformly applied to the whole surfaces of the silicon wafers
10
. Then, the entire weight of the upper plate
20
is applied to the lower plate
30
as the pressing force. Adjusting the pressing force should be executed smoothly.
However, in the conventional lapping machine, the pressing force of the upper plate
20
is adjusted by changing the fluid pressure in the cylinder unit
22
, so mechanical resistance in the cylinder unit
22
influences the adjustment. Namely, it is difficult to precisely and linearly control the pressing force. Namely, the pressing force of the upper plate
20
is directly changed according to tensile stress of the piston rod
22
a
, and the pressing force of the upper plate
20
is changed while a bottom lapping face of the upper plate
20
contacts the work pieces
10
. Thus, a stroke of a piston (not shown) in the cylinder unit
22
is equal to the sum total of amount of lapping (abrading) the wafer
10
and minute elastic elongation of the piston rod
22
a
. Namely, it is very very short.
It is difficult to perfectly smoothly move the piston due to friction between the piston and an inner circumferential face of the cylinder unit
22
, so the piston is braked in the stroke. This phenomenon is called knocking. Even if the braking action is minute, the stroke of the piston is very very short, so the non-smooth action of the piston influences the pressing force of the upper plate
20
. Therefore, it is very difficult to smoothly adjust the pressing force of the upper plate
20
. The piston usually slides on the inner circumferential face of the cylinder unit
22
together with sealing membe

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