Measuring and testing – Testing of apparatus
Reexamination Certificate
2002-05-06
2003-07-22
Kwok, Helen (Department: 2856)
Measuring and testing
Testing of apparatus
C206S710000, C292S068000, C049S031000
Reexamination Certificate
active
06595075
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and an apparatus for testing the operation of a cassette pod for storing and transporting semiconductor wafers and more particularly, relates to a method and an apparatus for testing the operation of a cassette pod door or the unlatching torque of a cassette pod door during a door opening procedure.
BACKGROUND OF THE INVENTION
The high level of automation used in fabricating semiconductor devices relies on sophisticated handling and transport equipment for moving semiconductor wafers between various processing stations. Most handling and transport operations are conducted under automatic control using a programmed computer which issues control signals for operating the equipment with little or no intervention by an operator. In many systems, standard mechanical interface (SMIF) pods are used to transport batches of wafers that are stored in cassettes. These pods include a base upon which the cassettes rest, and a cover removably secured to the base and completely enclosing the cassette. The cover protectively surrounds the cassette, and thus the wafers, from the surrounding environment which may contain airborne, contamination particles. SMIF pods are most often used to transport cassettes from one clean room environment to another, where during the transport movement, the wafers, if not covered, are exposed to the contaminating environment. In more recent development, FOUPs (front open unified pod) are used for storing and transporting 12″ wafers.
After a pod has reached the vicinity of a processing station within a protected, clean room environment, it is necessary to remove the cover so that automated wafer transfer robots can access the individual wafers held in the cassette. The cover is held on the pod by one of various types of latching mechanisms which is automatically actuated to latch and unlatch the cover by means of actuating controls positioned at each processing station. Thus, when a pod is transported to a processing station, control mechanisms engage the latch mechanism on the pod to unlatch the cover, following which either an operator or a robotic mechanism removes the cover to expose the cassette. After the batch of wafers in the cassette is processed, the cover is reinstalled on the pod base, either manually or robotically, and the control mechanism is again actuated to latch the cover onto the base (for SMIF) or onto the back (for FOUP) before the pod leaves the processing station.
In spite of the fact that positive latch mechanisms are designed to lock the cover on the pod base, occasions arise when, for a variety of reasons, the latch fails to lock the cover onto the pod base. This may occur, for example, when a foreign article becomes lodged between the cover and the base or when the cassette becomes tilted on the base, thus interfering with the proper seating of the cover. In other cases, the control mechanism for actuating the latch may malfunction. Frequently, such failure of the latch mechanism to lock the cover on the pod base goes undetected by process operators. As a result, it is possible that contaminants may pass through between the pod base and cover when the pod leaves the clean room environment, resulting in possible contamination of the wafers.
Accordingly, there is a clear need in the art for an improved pod construction which insures that the cover is properly locked onto the pod. The present invention is directed toward satisfying this need in the art.
FIG. 1
illustrates a cassette pod such as a FOUP that is installed on a process machine. The cassette pod
10
is positioned on a loadport
12
of the process machine
14
. The loadport
12
is normally equipped with a plurality of locating pins
16
for the proper positioning of the cassette pod
10
.
A detailed perspective view of the cassette pod, i.e. the FOUP
10
, is shown in FIG.
4
. The FOUP
10
is constructed by a body portion
18
and a cover portion
28
. The body portion
18
is provided with a cavity
46
equipped with a multiplicity of partitions
48
for the positioning of 25 wafers of the 300 mm size. The body portion
18
is further provided with sloped handles
50
on both sides of the body for ease of transporting. On top of the body portion
18
is provided a plate member
52
for gripping by a transport arm (not shown) of an overhead hoist transport system. It should be noted that, for simplicity reasons, the latching mechanism for opening and closing the FOUP door, or the cover portion
28
, is not shown in FIG.
2
.
In the conventional cover member, or door
28
of the FOUP
10
, the door opening/closing mechanism is shown in
FIG. 3
in a plane view. Locking tabs
20
a
,
20
b
,
22
a
and
22
b
are provided at the top and at the bottom of the cover member
28
. Circular drive plates
24
a
and
24
b
are connected to the locking tabs
20
a
-
22
b
by mechanical linkage
26
a
and
26
b
and operated by latch holes
28
a
and
28
b
. A pair of latch keys (not shown) that are part of the door opener mechanism of the loadport (not shown) are inserted into the latch holes
28
a
and
28
b
and turned by a DC motor to lock or unlock the cover member
28
to the loadport opening. As shown in
FIG. 3
, when the drive plates
24
a
and
24
b
are turned in a clockwise direction, the locking tabs
20
a
,
20
b
,
22
a
and
22
b
are withdrawn into the frame of the cover member
28
and therefore, unlocking the cover member
28
from the body member
18
of the cassette pod
10
(shown in FIG.
2
). Conversely, when the drive plates
24
a
and
24
b
are turned by the DC motor in a counter-clockwise direction, the locking tabs
20
a
,
20
b
,
22
a
and
22
b
are extended out of the frame of the cover member
28
to engage receptacles (not shown) in the body member
18
and thus, locking the cover member
28
to the body member
18
of the cassette pod
10
.
Problems occur when operating the conventional door opening/closing mechanism shown in
FIG. 3
installed on a FOUP. For instance, the latch keys (not shown) that are turned by the DC motor sometimes are misaligned with the latch holes
28
a
and
28
b
and thus, the door opening or closing operation cannot be carried out. Secondly, the torque of the DC motor cannot always be precisely controlled such that the angle of turning, i.e. such as a 90° angle, cannot be precisely controlled. A door opening or closing mechanism can not be completely executed when the angle of rotation is not exactly 90°. For instance, during a door locking operation if the latch holes
28
a
and
28
b
are not turned to a perfect vertical position in order to lock the cover member
28
to the body member
18
and when the FOUP
10
is later positioned on another process equipment, a similar set of door opening latch keys can not be inserted into the latch holes
28
a
and
28
b
and thus, the cover member
28
cannot be opened or unlocked from the body member
18
.
In the operation of cassette pods for the 300 mm diameter wafers, i.e. the FOUP, an error message is frequently observed during the unlatching of a FOUP door from the FOUP. The error message occurs when a torque required to open the FOUP door is detected to be larger than 80 in-lb. A higher than normal torque reading indicates one of many possible defective conditions of the FOUP. For instance, a distortion in the latch mechanism of the FOUP door and thus, excessively high torque is required to unlatch the door from the FOUP. Other defective conditions may include a misalignment between the latch key of the door opener in the loadport and the latch holes in the FOUP door. The misalignment may also be caused by a distorted FOUP door which occurs after extended usage.
Conventionally, a DC motor is used to unlatch the FOUP door. When a torque reading of the DC motor, during the unlatching operation, exceeds 80 in-lb, the DC motor is stopped to prevent any possible damage that may be caused in the motor. The FOUP is then manually removed from the loadport for the operator to diagnose the cause of the
Lo Fu-Sun
Peng Ray-Chung
Shien Kwen-Mu
Kwok Helen
Rogers David
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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