Data processing: generic control systems or specific application – Specific application – apparatus or process – Article handling
Reexamination Certificate
1998-09-28
2001-10-02
Valenza, Joseph E. (Department: 3651)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Article handling
C414S941000, C901S040000, C901S047000
Reexamination Certificate
active
06298280
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor wafer handling and processing equipment, and in particular, to a method and apparatus for positioning and orienting an end effector of a wafer handling robot with respect to a wafer to be extracted from a cassette, and for thereafter reading an indicial mark on the wafer.
2. Description of the Related Art
Standardized mechanical interface (SMIF) systems, first proposed by the Hewlett-Pac card Company and disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389, have now become accepted clean room equipment for semiconductor manufacturing. The purpose of the SMIF system is to reduce particle fluxes onto articles, for example, semiconductor wafers. This end is accomplished, in part, by mechanic ay ensuring that during transportation and storage the gaseous medium (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafer cassettes; (2) canopies placed over cassette pots and wafer processing areas of processing stations so that the environments inside the pods and canopies (upon being filled with clean air) become mixture clean spaces; and (3) a transfer mechanism to load/unload wafer cassettes from the sealed pods to the processing equipment without contamination of the wafers in the wafer cassette from external environments.
SMIF pods are in general comprised of a pod door which mates with a pod shell to provide a sealed environment in which wafers may be stored and transferred. So called “bottom opening” pods are known, where the pod door is horizontally provided at the bottom of the pod, and the wafers are supported in a cassette which is in turn supported on the pod door. It is also known to provide “front opening” pods, in which the pod door is located in a vertical plane, and the wafers are supported either in a cassette mounted within the pod shell, or to shelves mounted in the pod shell itself.
In order to transfer wafers between a SMIF pod and a process tool within a wafer fab, a pod typically loaded either manually or automatedly onto a load port on a from of the tool. The process tool includes an access port which, in the absence of a pod, is covered by a port door. Once the pod is positioned on the load port, mechanisms within the port door unlatch the pod door from the pod shell and move the pod door and port door together into the process tool where the doors are then moved away from the wafer transfer path and stowed. The pod shell remains in proximity to the interface port so as to maintain a clean environment including the interior of the process tool and the pod shell around the wafers. A wafer handling robot within the process tool may thereafter access particular wafers supported in wafer slots in the pod or cassette for transfer between the pod and the process tool. Alternatively, a bare cassette (without the pod) may be loaded directly onto the interface load port and transferred into the processing station by the wafer handling robot.
As wafers move through the various processing chambers within a semiconductor wafer fab, it is desirable to be able to track and locate a particular wafer at any given time. Moreover, it is desirable to be able to identify a particular wafer during wafer fabrication to ensure that the wafer is subjected only to processes appropriate for that wafer. This wafer tracking is accomplished by marking each wafer with an optical character recognition (OCR) mark, or similar indicia mark, which mark is read for each wafer prior to locating a wafer within a processing station. The indicial mark is typically a number or letter sequence etch into an upper surface of a wafer near the outer circumference by a laser or other suitable etching means. The indicial mark may alternatively be a bar code or a two dimensional dot matrix at an outer circumference of the wafer.
In order to read the indicial mark on a particular wafer, the indicial mark is conventionally positioned under an image identifying device such as a video camera, which acquires a computer-recognizable image of the indicial mark. The indicial mark must be precisely positioned under the video camera in order for the camera to acquire the image. This requirement is made more difficult by the fact that indicial marks are very small, so as not to take up space on the wafer otherwise sable for circuit devices.
Before an indicial mark may be read, the mark must first be located. When a wafer is seated within a wafer cassette, the orientation of the wafer to the cassette and to a tool for extracting and supporting the wafer is generally unknown. attempts have been made to align the indicial mark of each wafer at a particular rotational orientation within the cassette. However, because wafers move within a cassette upon handling and transfer of the cassette between processing stations, alignment of the indicial marks prior to transportation has not proved feasible. Conventionally, a separate operation has been devoted to orienting a wafer to a known location, locating the indicial mark, and aligning the indicial ark under the camera at or immediately prior to each station where it is desired to identify the particular wafers to be processed in that station.
In order to locate an indicial mark, wafers are conventionally formed with a notch, or flat on the outer edge of a wafer. For each wafer being processed, the indicial mark is located in a fixed, known relation to the notch, and by finding the notch, the precise location of the indicial mark may be determined. Conventionally, in order to locate the notch, the center of the wafer first has to be identified Thereafter, the wafer is rotated on center until a sensor proximate to the rotating wafer edge detects the notch.
FIG. 1
shows a conventional station
20
for performing this operation of wafer centering, notch location, and indicial mark reading. Such stations are conventionally located immediately upstream or as part of each processing station in the wafer fabrication process where the indicial mark is to be read. The station
20
includes a wafer handling robot
22
for accessing and transferring wafers
40
from a cassette
38
. The robot
22
includes a shaft
26
mounted for rotation and translation along a z-axis concentric with the shaft axis of rotation. The robot
22
further includes a first arm
28
affixed to an upper end of shaft
26
for rotation with the shaft, and a second arm
30
pivotally attached to the opposite end of the first arm
28
. The wafer handling robot further includes an end effector
32
Pivotally attached to the second arm
30
. The robot
22
is controlled by a computer
36
such that end effector
32
slides into the wafer cassette
38
underneath one of the wafers
40
, rises up to support the wafer
40
, and thereafter retracts from the cassette with the wafer
40
supported thereon.
The robot
22
next transfers the wafer to an alignment module
42
. The module
42
includes a table
44
capable of rotation and translation in a direction indicated arrow A—A in FIGS.
1
and
2
A-
2
C. The robot
22
deposits the wafer on pins
52
FIGS. 2A-2C
) around table
44
, which pins thereafter retract to rest the w the table
44
. Wafer
40
is then rotated on table
44
t o determine the radial of the wafer (i.e., the distance by which the center of the wafer deviates from the axis of rotation of table
44
).
In order to determine the radial run out of wafer
44
, the module
42
includes a sensor
48
having a plurality of optical transmitters
44
a
and a plurality of optical receivers
48
b
. After table
44
rotates wafer
40
360°, the computer
36
is able to determine the center of wafer
40
via the sensor
48
.
Thereafter, the table rotates to align the axis of maximum radial runout with the direction translation of the table
44
(arrow A—A).
Bonora Anthony C.
Cookson Mike
Davis Mark R.
Fosnight William J.
Swamy Krishna D.
Asyst Technologies, Inc.
Fliesler Dubb Meyer & Lovejoy LLP
Tran Khoi H.
Valenza Joseph E.
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