Wafer transport device

Details Wafer transport device Wafer transport device

1999-06-08

2001-03-27

Ellis, Christopher P. (Department: 3651)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Article handling

C414S937000, C414S331140, C414S331180

Reexamination Certificate

active

06208909

ABSTRACT:

DESCRIPTION
1. Technical Field
The present invention relates to a wafer transfer apparatus for taking out a wafer from a wafer cassette and transfer it to another apparatus, if necessary, in order to inspect it or subject it to a subsequent process.
2. Background Art
FIG. 9
shows an example of conventional wafer transfer apparatuses for taking out a wafer from a wafer cassette by means of a transfer arm. More specifically, a wafer cassette
4
storing a number of wafers
3
one on another is mounted on a cassette base
2
movable up and down by an elevator mechanism portion
1
, such that a wafer-inlet/outlet side faces a transfer arm
5
having an attracting portion
6
.
An operation of the conventional wafer transfer apparatus will be described in brief. First, the cassette base
2
is moved down by the elevator mechanism portion
1
, and the number of detected wafers is counted by a sensor (not shown), thereby detecting a wafer
3
to be transferred. After the sensor detects the wafer
3
, the cassette base
2
is moved up by a predetermined amount, and then the transfer arm
5
is moved toward the wafer cassette
4
and inserted under the wafer
3
to be transferred. After the transfer arm
5
is inserted, the cassette base
2
is moved down by a predetermined amount by means of the elevator mechanism portion
1
, so that the wafer to be transferred is placed on the transfer arm
5
. Then, the wafer
3
to be transferred is attracted by the attracting portion
6
, the transfer arm
5
is drawn out of the wafer cassette
4
, and the wafer
3
to be transferred is extracted and transferred to a next step, such as an inspecting step.
In the wafer transfer apparatus described above, a plurality of slot grooves
7
, for holding the wafers
3
horizontally, are formed in both side walls in the wafer cassette
4
for storing the wafers
3
. A view encircled in a right portion of
FIG. 8
is an enlarged view showing slot grooves
7
in the right side wall of the wafer cassette
4
viewed from the wafer
3
-inlet/outlet side. Thus, the slot grooves
7
hold circumferential edge portions of the wafers
3
, so that the wafer can be stored in the wafer cassette
4
keeping the wafers
3
horizontal.
Therefore, if the wafers
3
are stored in the wafer cassette
4
always horizontally at regular intervals, the transfer arm
5
can be smoothly inserted under the wafer
3
to be transferred by the transfer arm
5
.
However, when the wafer
3
is first stored in the wafer cassette
4
, it is generally inserted by hand, and the wafer
3
may be inserted in the slot grooves at different heights on the left and right. In this case, the inserted wafer
3
is inclined. Due to the inclination of the wafer
3
, when the transfer arm
5
is inserted under the wafer
3
, the transfer arm
5
may collide with the wafer
3
, resulting in a problem that the wafer is damaged.
To solve this problem, for example, as disclosed in Published Japanese Patent No. 2606423, it is proposed that an inserted condition of each wafer
3
to be transferred is detected by a sensor, and if the wafer
3
is inclined, the insertion of the transfer arm
5
is stopped, thereby preventing collision. More specifically, a sensor for detecting a wafer
3
is provided, and a cassette base is moved down relative to the sensor by an elevator mechanism portion, so that the sensor detects each wafer
3
to be transferred. A position where the sensor starts detection of the wafer is regarded as a wafer lowermost surface, and a position where the sensor ends detection of the wafer is regarded as a wafer uppermost surface. The distance of movement of the cassette base from the detection start position to the detection end position is detected as a thickness of the wafer. If (the original thickness of the wafer)=(the detected thickness of the wafer), it is determined that the wafer is stored correctly and the transfer process is started. If (the original thickness of the wafer)<(the detected thickness of the wafer), it is determined that the wafer is not stored correctly and the transfer process is stopped.
By the way, recently, as the wafer becomes larger and thinner, a problem of bend of a wafer stored in the wafer cassette is posed. For example, an amount of bend is defined as the difference in level between the circumferential edge portion held by the slot groove and the most bent portion, i.e., the central portion.
FIGS. 10A and 10B
show the relationship between the thickness and the amount of bend in the cases of 6-inch and 8-inch wafers.
According to
FIG. 10B
, for example, as regards 8-inch wafers, when the amount of bend of a wafer of the conventional standard thickness, 0.6 mm, is compared to the amount of bend of a wafer of the recent standard thickness, 0.1 mm, the amount of bend is increased by about 5 mm with the decrease in the amount of bend of the wafer.
The bend due to the decrease in thickness poses the following new problems.
First, in the conventional means for detecting an inclination of a wafer as a thickness by a sensor, a bend of the wafer is not taken into account. Therefore, according to the conventional art, the amount of bend is determined as a thickness, and even if the wafer is correctly inserted in left and right slot grooves on the same stage, it is erroneously determined that the wafer is not correctly stored and the transfer process is ended. Thus, a wafer having a bend cannot be transferred.
Secondly, when the wafer to be transferred is attracted on and lifted up by the transfer arm in the wafer cassette, if the bend of the wafer is not taken into account, the upper surface of the wafer to be transferred will be brought into contact with the lower surface of the bent wafer located above, resulting in a damage or crack of the wafer surface.
Thirdly, when an inspection or the like is completed and the wafer is restored in the wafer cassette by the transfer arm, if the bend of the wafer is not taken into account, a peripheral portion of the wafer may collide with the slot due to the bend in the peripheral portion, resulting in a crack of the wafer.
DISCLOSURE OF INVENTION
The present invention was made in consideration of the above situations. An object of the present invention is to provide a wafer transfer apparatus in which a bend of a wafer is taken into account, so that a crack of the wafer is surely prevented when the wafer is transferred.
The present invention provides a wafer transfer apparatus for taking out a wafer from a wafer cassette having grooves on both ends for holding circumferential edge portions of a plurality of wafers by moving a wafer taking out arm in height directions and back and forth directions relative to the wafer cassette, the wafer transfer apparatus comprising: bend detecting means for detecting bend of a wafer; and transfer means for inserting the wafer taking out arm into the wafer cassette, based on the bend, placing the wafer on the arm, and taking out the wafer from the cassette.
It is preferable that the transfer means comprise inserting means for determining, based on the bend, a position in which the wafer taking out arm is inserted into the wafer cassette, and inserting the arm in the determined position, and that the transfer means further comprise extracting means for determining, based on the bend, an amount of movement of the arm in a height direction of the cassette required to lift circumferential edge portions of the wafer from grooves, moving the arm inserted in the cassette in the height direction of the wafer cassette by the determined amount of movement, and extracting the arm from the cassette.
Further, it is preferable that the extracting means determine whether extraction is possible without contacting with another wafer, and that the inserting means determine whether the wafer taking out arm can be inserted in the wafer cassette without contacting with another wafer.
With the wafer transfer apparatus described above, positional information of a wafer in the wafer cassette is detected, and bend of the wafer is calculated. Based on t

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