Optically aligning a loadport on a process machine by...

Details Optically aligning a loadport on a process machine by... Optically aligning a loadport on a process machine by...

2001-04-18

2003-04-01

Allen, Stephone B. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

With circuit for evaluating a web, strand, strip, or sheet

C414S217100

Reexamination Certificate

active

06541787

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for aligning a loadport on a process machine and more particularly, relates to an apparatus for aligning a loadport on a process machine which consists of a base plate and an alignment block with an aperture therethrough for passage of an alignment laser beam and a method for using the apparatus.
BACKGROUND OF THE INVENTION
In the fabrication of a product, the product is usually processed at many work stations or processing machines. The transporting or conveying of partially finished products, or work-in-process (WIP) parts, is an important aspect in the total manufacturing process. The conveying of semiconductor wafers is especially important in the manufacturing of integrated circuit chips due to the delicate nature of the chips. Furthermore, in fabricating an IC product, a multiplicity of fabrication steps, i.e., as many as several hundred, is usually required to complete the fabrication process. A semiconductor wafer or IC chips must be transported between various process stations in order to perform various fabrication processes.
For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, implantation, etching and passivation must be carried out before the chip can be packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e. a chemical vapor deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a semiconductor fabrication facility is therefore an important aspect of the total fabrication process.
Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically guided vehicles or overhead transport vehicles that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes pods, such as SMIF (standard machine interface) or FOUP (front opening unified pod), and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rail of the conveying vehicle.
In an automatic material handling system (AMHS), stockers are used in conjunction with automatically guided or overhead transport vehicles, either on the ground or suspended on tracks, for the storing and transporting of semiconductor wafers in SMIF pods or in wafer cassettes. For instance, three possible configurations for utilizing a stocker may be provided. In the first case, a stocker is utilized for storing WIP wafers in SMIF pods and transporting them first to tool A, then to tool B, and finally to tool C for three separate processing steps to be conducted on the wafers. After the processing in tool C is completed, the SMIF pod is returned to the stocker for possible conveying to another stocker. The configuration in the first case is theoretically workable but hardly ever possible in a fabrication environment since the tools or processing equipment cannot always be arranged nearby to accommodate the processing of wafers in the stocker.
In the second case, a stocker and a plurality of buffer stations A, B and C are used to accommodate different processes to be conducted in tool A, tool B and tool C. A SMIF pod may be first delivered to buffer station A from the stocker and waits there for processing in tool A. Buffer stations B and C are similarly utilized in connection with tools B and C. The buffer stations A, B and C therefore become holding stations for conducting processes on the wafers. This configuration provides a workable solution to the fabrication process, however, requires excessive floor space because of the additional buffer stations required. The configuration is therefore not feasible for use in a semiconductor fabrication facility.
In the third case, a stocker is provided for controlling the storage and conveying of WIP wafers to tools A, B and C. After a SMIF pod is delivered to one of the three tools, the SMIF pod is always returned to the stocker before it is sent to the next processing tool. This is a viable process since only one stocker is required for handling three different processing tools, and in that no buffer station is needed. This configuration illustrates that the frequency of use of the stocker is extremely high since the stocker itself is used as a buffer station for all three tools. The accessing of the stocker is therefore more frequent than that required in the previous two configurations.
FIG. 1
illustrates a schematic of a typical automatic material handling system
20
that utilizes a central corridor
22
, a plurality of bays
24
and a multiplicity of process machines
26
. A multiplicity of stockers
30
are utilized for providing input/output to bay
24
, or to processing machines
26
located on the bay
24
. The central corridor
22
designed for bay lay-out is frequently used in an efficient automatic material handling system to perform lot transportation between bays. In this configuration, the stockers
30
of the automatic material handling system become the pathway for both input and output of the bay. Unfortunately, the stocker
30
frequently becomes a bottleneck for internal transportation. It has been observed that a major cause for the stockers
30
to be the bottleneck is the input/output ports of the stockers.
In modern semiconductor fabrication facilities, especially for the 200 mm or 300 mm FAB plants, automatic guided vehicles (AGV) and overhead hoist transport (OHT) are extensively used to automate the wafer transport process as much as possible. The AGV and OHT utilize the input/output ports of a stocker to load or unload wafer lots, i.e. normally stored in POUFs.
FIG. 2
is a perspective view of an overhead hoist transport system
32
consisting of two vehicles
34
,
36
that travel on a track
38
. An input port
40
and an output port
42
are provided on the stocker
30
. As shown in
FIG. 2
, the overhead transport vehicle
36
stops at a position for unloading a FOUP
44
into the input port
40
. The second overhead transport vehicle
34
waits on track
38
for input from stocker
30
until the first overhead transport vehicle
36
moves out of the way.
Similarly, the OHT system is used to deliver a cassette pod such as a FOUP to a process machine. This is shown in
FIG. 3. A
cassette pod
10
of the FOUP type is positioned on a loadport
12
of a process machine
14
. The loadport
12
is frequently equipped with a plurality of locating pins
16
for the proper positioning of the cassette pod
10
. A detailed perspective view of 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 with a plate member
52
for gripping by a transport arm (not shown) of the OHT system (not shown).
When an OHT system is utilized to transport a cassette pod to a process machine, problems arise when the loadport of the process machine is not in alignment with the OHT system. Mis-positioned cassette pods on a loadport not only affects the operation of loading/unloading from the pod, but also in severe instances may cause the cassette pod to tip over and cause breakage of the wafers. Conventionally, a laser surveying instrument is used to align the cassette pod, i.e. or the l

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