Wafer-fetching sensing device for wafer storage apparatus

Details Wafer-fetching sensing device for wafer storage apparatus Wafer-fetching sensing device for wafer storage apparatus

1999-02-18

2001-05-22

Hofsass, Jeffery (Department: 2632)

Communications: electrical

Condition responsive indicating system

Specific condition

C340S556000, C250S559430, C250S559120, C414S935000

Reexamination Certificate

active

06236327

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a wafer-fetching sensing device for wafer storage apparatus, and more particularly to an apparatus that upgrades the wafer positioning detection from a linear sensing level to a plane sensing level for increasing the production yield.
2. Description of the Prior Art
In semiconductor industry, transportation and storage of wafers in the IC fabrication process usually involve a wafer storage apparatus for storing a plural number of wafers and a robot for fetching the wafer. The wafers are arranged, at a predetermined order, into the wafer storage apparatus before an automation process can begin. In a fabrication site, the wafer storage apparatus usually locates beside a workstation or a group of workstations, and includes a wafer access opening for the robot to access and fetch the wafer thereinside.
FIG. 1
illustrates a conventional wafer storage apparatus
1
which includes a housing
100
providing an interior accommodation space
11
for orderly storing a plurality of wafers
3
therein; for example, to store wafers
3
upon a plurality of movable racks
13
. By providing the movable racks
13
, the wafers
3
then can be sequentially fetched out by the robot, through an access opening
50
of the housing
100
, where the access opening
50
is arranged parallel to a normal storage state of wafer
3
.
In order to make sure that each wafer
3
in the wafer storage apparatus
1
can be fetched out through the access opening
50
safely and right at an acceptable access level
10
formed parallel to the normal storage state of wafers
3
, a first sensor unit
5
is installed at the access opening
50
for sensing whether or not the wafer
3
is posed by the normal storage state at the access level
10
. Generally, the access opening
50
and the access level
10
is coplanar.
Referring now to
FIG. 2
, the first sensor unit
5
includes a first emitter
17
located at the access opening
50
for sending a signal to a first receiver
15
along a first measuring line
101
on the access level
10
. The first measuring line
101
may coincide with the center axis of the access opening
50
. When the first sensor unit
5
detects the wafer
3
is properly positioned and leveled, the robot may proceed to start the fetching operation to move out the wafer
3
through the access opening
50
.
However, there are some occasions in which a wafer
3
may be improperly positioned and may deviate from its normal state upon the rack
13
. Upon occurring such an occasion, a wafer-fetching problem that the first sensor unit
5
fails to detect the misplacement may arise.
FIG. 3
illustrates one of such occasions. Due to any possible operation error (e.g. by putting the wafer
3
a
with two lateral sides anchored at different levels of racks
13
, the wafer
3
a
is tilted about the first measuring line
101
(also symbolized by the position of the first receiver
15
) in the center of the access level
10
, and forms an angle with the access level
10
, but still keeps the center line of the tilted wafer
3
a
coinciding with the first measuring line
101
. Under such a situation shown in
FIG. 3
, the first sensor unit
5
can still decide that the wafer
3
a
is posed at the normal storage state, and then proceeds to issue a normal signal for the robot to fetch out the wafer
3
a.
However, both lateral sides of the wafer
3
a
have deviated from the access level
10
and thus may result in the wafer
3
a
hitting the storage wall of the housing
10
or dropping to the floor, while being fetched out. It may cause damage (either minor or major) to the wafer
3
a
or even sequentially shut down whole production operation.
SUMMARY OF THE INVENTION
In view of aforesaid disadvantages, it is therefore an object of this invention to provide a wafer-fetching sensing device for wafer storage apparatus capable of detecting if a wafer is correctly positioned for fetch out from the wafer storage apparatus, so that wafer damage incident may be avoided.
It is another object of this invention to provide a wafer-fetching sensing device for wafer storage apparatus that enhances the wafer level detection from conventional linear mode to a planar mode, so that the wafer level detection accuracy can be greatly improved, the wafer damage problem can be greatly reduced, and the total production yield can be increased.
The apparatus according to this invention uses a planar detection means at the access level of the access opening of the wafer storage apparatus to make sure that a wafer is precisely positioned by a normal storage state before moving the robot to fetch the wafer. The planar detection means implements a second sensor unit besides the first sensor unit of a conventional one set forth above. There are two pairs of emitters and receivers for measuring two spaced (and preferably parallel) measuring lines on the access level of the wafer. Thus, the wafer-tilting problem may be easily detected and alarmed before any further damage occurs. Wafer damage and production interruption problem thus may be reduced, and production yield may be enhanced.


REFERENCES:
patent: 4803373 (1989-02-01), Imamura
patent: 4895486 (1990-01-01), Baker
patent: 5225691 (1993-07-01), Powers
patent: 5466945 (1995-11-01), Brickell
patent: 5690744 (1997-11-01), Landau

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