Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-01-16
2001-01-16
Grant, William (Department: 2786)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S169000, C701S023000, C701S025000
Reexamination Certificate
active
06175777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method for transferring wafer cassettes between semiconductor device process equipment and an Automated Guide Vehicle (AGV) at a semiconductor fabrication facility. More specifically, the present invention relates to a method that includes steps for checking the mode of the process equipment and changing the mode, if necessary, to a mode more suitable for the transfer that is to take place.
2. Description of the Related Art
The processes employed during the fabrication of semiconductor devices have become increasingly automated. Until recently, however, the transfer of semiconductor wafer cassettes among pieces of processing equipment has been a manual process involving a human operator. With the increasing integration of semiconductor devices, particles generated by the human body, formerly not considered to be a problem, have become a main cause of contamination. Consequently, much research and development has gone into automating the transfer of wafer cassettes. Automated Guide Vehicles (AGVs) have been developed to deliver cassettes under the remote control of a computer. Although great advances have been made, current systems still suffer some disadvantages. For example, if the process equipment is not in the correct mode when the cassette delivery unit arrives, the transfer may be initiated nonetheless. The result is that cassettes may not be transferred at all, or, worse, cassettes can be dropped and wafers spilled and broken.
FIG. 1
is a schematic diagram of a current wafer transfer system using communications links between an AGV and its controller and between the AGV and some semiconductor fabrication process equipment. The system includes transfer equipment
10
, process equipment
20
, and a host computer
30
. The transfer equipment
10
includes a controller
11
that itself is connected to and controlled by the host computer
30
. The transfer equipment
10
also includes an AGV
13
that operates under radio control by the controller
11
through a radio link represented by the arrow
12
. The process equipment
20
is simultaneously controlled by the host computer
30
through a second controller (not shown). The host computer
30
communicates with the transfer controller
11
and the process equipment controller (not shown) according to a Semiconductor Equipment Communication Standard (SECS). The AGV
13
communicates with the process equipment
20
through a communications link represented by another arrow
15
. In the current system, a photo-coupled Parallel Input/Output (PPIO) link serves as the communications link
15
.
A cassette transfer occurs when a wafer cassette (not shown) is loaded into the process equipment
20
from the AGV
13
or when a wafer cassette is unloaded from the process equipment
20
to the AGV
13
. The process equipment
20
includes a loading/unloading cassette stage
21
(
FIG. 2
) used when wafer cassettes are transferred between the process equipment
20
and the AGV
13
.
FIG. 2
is a schematic diagram showing the loading/unloading cassette stage
21
of the process equipment
20
. The stage
21
contains a sensor S
1
that can detect the presence of a cassette when the cassette is placed in a preferred location A on the stage
21
.
The operation of the current wafer cassette transfer system will be described with reference to FIG.
1
and FIG.
2
. Starting with
FIG. 1
, a command to transfer a wafer cassette is issued by the host computer
30
which communicates the command through the connections to the transfer equipment controller
11
and to the controller (not shown) of the process equipment
20
according to SECS. The transfer equipment controller
11
then utilizes the radio link
12
to instruct the AGV
13
to move toward the process equipment
20
. As a result the AGV
13
arrives at the process equipment
20
adjacent to its loading/unloading cassette stage
21
.
After arrival at the process equipment
20
, the AGV
13
begins to communicate with the process equipment
20
via the communications link
15
. In the case of the PPIO link, the communications protocol is defined by the Semiconductor Equipment and Material International (SEMI) standard. The process equipment
20
has internal mechanisms (not shown) that must be deployed in a certain fashion for loading or unloading operations. For example, the process equipment
20
may have a door that must be opened, or the process equipment
20
may have a robot arm that must be unfolded during loading and unloading. In addition, the cassette stage
21
must be occupied by a cassette to allow unloading to occur, or the stage
21
must be empty to allow loading to occur. The state of such various internal mechanisms and the state of occupancy of the stage
21
constitute the transfer mode of the process equipment
20
. In the conventional wafer transfer system of
FIG. 1
, the process equipment
20
is considered to be in a mode suitable for the transfer as commanded by the host computer
30
when the AGV
13
arrives and begins communicating, regardless of whether the wafer transfer system is actually ready to load or unload a cassette.
For various reasons, however, the process equipment
20
may not be in a suitable transfer mode when the AGV begins communicating. When transfer begins while the processing equipment
20
is not in a suitable mode, for example, if the door is not completely open, or the robot arm is not completely unfolded, the cassette might not be placed on the stage
21
at the preferred location A in FIG.
2
.
FIG. 2
shows that when a cassette is placed at the preferred location A on the stage
21
, the sensor S
1
can detect its presence. However, if the cassette is placed near the preferred location but not in the view of the sensor S
1
, the sensor S
1
may indicate to the process equipment controller that the stage is empty. In this case, the process equipment controller will not clear the stage upon receiving the load command from the host computer
30
. When the AGV
13
attempts to perform the load operation, the cassettes collide and the transfer operation fails. This faulty detection of cassette stage
21
occupancy is a main cause of failure for the transferring operations. In addition, cassettes may collide with a door that is not open or a robot arm that is not unfolded. For any of these reasons a cassette may be dropped during the failure of the transfer operation and wafers may be spilled. The current system is unable to check whether there are problems with the stage
21
occupancy or the internal mechanisms of the process equipment
20
prior to transferring wafer cassettes.
A need exists, therefore, for a wafer cassette transfer system that will not transfer cassettes if the process equipment is not in a suitable mode.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method for transferring a wafer cassette between an AGV and process equipment in a semiconductor fabrication facility. The method comprises transmitting a first signal from the AGV to the process equipment indicative of a cassette transfer request, and checking whether the process equipment is in a suitable mode for the transfer request. If the process equipment was not already in a suitable mode, the next step sets the process equipment to the suitable mode. Then transferring the cassette between the AGV and the process equipment occurs.
In another version of the invention, the method includes transmitting a second signal from the process equipment indicating authorization for the transfer of the cassette before the actual transferring occurs. In another version the checking step further comprises the step of sensing the position of the cassette on a cassette stage of the process equipment using a plurality of sensors.
In another aspect of the invention, a system for exchanging a cassette between an AGV and process equipment using the method comprises a host computer, an AGV controller, an AGV, process equipment, and a communications li
Bahta Kidest
Grant William
Jones Volentine, LLC
Samsung Electronics Co,. Ltd.
LandOfFree
Method for transferring wafer cassettes after checking... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for transferring wafer cassettes after checking..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for transferring wafer cassettes after checking... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2528260