Drying and gas or vapor contact with solids – Process – Diverse types of drying operations
Reissue Patent
1999-11-30
2002-04-09
Gravini, Stephen (Department: 3749)
Drying and gas or vapor contact with solids
Process
Diverse types of drying operations
C034S058000, C034S186000
Reissue Patent
active
RE037627
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a centrifugal wafer drying apparatus used for drying after washing a semiconductor wafer such as a silicon wafer.
FIGS. 1A and 1B
show a prior art centrifugal wafer drying apparatus having carriers
2
each receiving silicon wafers in a stack. Each of the carriers
2
has grooves
3
for accomodating wafers
1
. Each of the grooves
3
extends along substantially half a periphery of a wafer
1
, and has clearance with respect to the thickness of the wafer, e.g., it has a thickness of two to three times the thickness of the wafer to facilitate loading (insertion) and unloading (removal) of the wafer. The apparatus further comprises a cylindrical container
4
, and cradles
5
made of stainless-steel disposed in the container
4
to hold the carriers
2
. The cradles
5
are mounted on a rotor
6
, which is fixed to a rotor shaft
7
. The rotor shaft
7
is driven by a motor
8
, so that the rotor
6
rotates together with the cradles mounted thereon. Water remaining on the wafers disperse due to the centrifugal force and the wafers
1
are thereby dried.
FIG.
2
A and
FIG. 2B
are a plan view and a partial side view of the rotor
6
. The rotor
6
, disposed in the container
4
has an opening
6
a, through which clean air, which has passed a filter (not shown) provided in a lid
4
a of the container
4
, is supplied into the rotor
6
and air streams
11
(
FIG. 3
) are created along the surfaces of the wafers
1
, being limited by walls
6
b acting as guides. The air streams also serve to disperse water from the surfaces of the wafers
1
.
Each of the cradles
5
is pivotably mounted on a pivot pin
5
a extending at right angles with the rotor shaft
7
and with the direction of a radius from the axis of rotation RX which is an extension of the axis of the rotor shaft
7
. Each of the cradles
5
is pivotable between the positions A and B, about 90°, as indicated by an arrow C. At the position A, the rotor is at rest and carriers
2
are loaded in or unloaded from the cradle
5
. For this purpose, the cradles
5
each have an opening
5
b which faces upward for loading and unloading of the carrier. Each of the carriers
2
has an opening
2
a for loading and unloading of wafers in and out of the grooves
3
. The opening
2
a of the carrier
2
also faces upward when the cradle is at the position A. The cradle
5
is at the position B while the rotor
6
is rotating.
When the cradle
5
is at the position B, the opening
2
a of the carrier
2
faces the axis of rotation RX of the rotor. At the position B, half the periphery of each wafer that is covered by the groove is positioned on the radially outer side with respect to the axis RX of rotation of the rotor
6
. At the position B, the cradle
5
is engaged with a cradle stopper
9
. The stopper
9
is provided to hold the cradle
5
in such a position that the surfaces of the wafers
1
are substantially orthogonal to the axis of rotation of the rotor
6
.
Examples of prior art references showing this type of drying apparatus are Japanese Patent Application Laid-open No. 36930/1984, Japanese Patent Application Laid-open No. 160130/1982 and Japanese Patent Application Laid-open No. 8823/1981.
The above-described apparatus however has a disadvantage. This is explained with reference to
FIG. 3
, which is a section view taken along the periphery of wafers as received by the grooves. When the rotor
6
is at rest, the wafers
1
are at positions D where the lower surfaces
1
a of the wafers
1
abut upwardly-facing edges
3
a of the grooves
3
. This is due to gravity. When the rotor
6
is rotating, the centrifugal force acts in the direction F, substantially parallel with the surfaces of the wafers
1
, so that the wafers
1
vibrate between the position D, and the position E where the upper surfaces
1
b abut the downwardly-facing edges
3
b of the grooves
3
. The actual condition which the individual wafers assume is affected by the air stream or wind caused by the rotation of the rotor. Thus, the resultant vibration of the wafers generates dust from the parts of the wafers
1
and the grooves
3
where they collide with each other. The vibration of the wafer also causes the air stream
11
to be unstable, and the effect of the water removal by the air stream
11
is reduced. The result is an unsatisfactory drying.
SUMMARY OF THE INVENTION
An object of the invention is to prevent vibration of the wafers, thereby to reduce generation of dust and to improve the effect of removing water.
According to the invention, grooves holding the wafers are inclined with respect to a plane normal to the axis of rotation so that during rotation, each of the wafers is held against one of the edges, for instance downwardly-facing edge of the groove. The grooves can be inclined by inserting a spacer between the cradle stopper and the cradle. The angle of inclination is preferably within the range of 2.5° to 30°.
With the above structure, the wafers are stably held in the grooves abutting one of the edges by the action of the centrifugal force. Accordingly, vibration of the wafers is prevented. As a result, the generation of dust is reduced. Moreover, the air streams around the wafers are stabilized and the effect of removing water is improved.
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patent: 3727620 (1973-04-01), Orr
patent: 3769992 (1973-11-01), Wallstad
patent: 3990462 (1976-11-01), Elftmann et al.
patent: 4132567 (1979-01-01), Blackwood
patent: 4677759 (1987-07-01), Inamura
patent: 4907349 (1990-03-01), Aigo
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Special Edition/Recent Super LSI Technology and Manufacturing Device—Spin Dryer For Super LSI; Ref. No.: 66098.0017, Mar. 1983.
Two-Position Device Allowing A centrifugal Machine Spinning About A Vertical Axis to Be Automatically Loaded With-Two Wafer Carriers;IBM Technical Disclosure Bulletin;vol. 29, No. 5; Oct. 1986.
FSI Turntable Drawing Part No. 2971-002, FSI Corporation, 1981.
Sales Document Back Order Part No. 2971-002 To National Semiconductor, Jul. 1982.
Sales Document Back Order Part No. 2971-002 To Dryden Engineering Co., May 1982.
FSI Turntable Drawing, Part No. 2930, 1982.
FSI Turntable Drawing, Part No. 2952, 1981.
FSI Turntable Drawing, Part No. 2958, 1981.
FSI Turntable Drawings, 1982.
FSI Turntable Catalog, Jul., 1984, pp. 3, 4, 6, 8, 18, 20, 22, 29, 31.
Gravini Stephen
Oki Electric Industry Co. Ltd.
Rabin & Champagne, P.C.
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