FIMS interface without alignment pins

Details FIMS interface without alignment pins FIMS interface without alignment pins

2000-11-28

2002-07-16

Bratlie, Steven A. (Department: 3652)

Material or article handling

Apparatus for moving material between zones having different...

C414S217100, C414S805000, C414S939000

Reexamination Certificate

active

06419438

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the transfer of workpieces such as semiconductor wafers from a storage and transport pod to a process tool, and in particular to a system for ensuring proper registration of the pod door against the port door on the load port assembly without the use of guide pins on the port door.
2. Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (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, scaled pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled “SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,” by Mihir Parikh and Ulrich Kaempf,
Solid State Technology
, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (&mgr;m) to above 200 &mgr;m. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half &mgr;m and under. Unwanted contamination particles which have geometries measuring greater than 0.1 &mgr;m substantially interfere with 1 &mgr;m geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 &mgr;m and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles and molecular contaminants become of interest.
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 arc supported in a cassette which is in turn supported on the pod door. It is also known to provide front opening pods referred to as front opening unified pods, or FOUPs, 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.
In order to transfer wafers between a FOUP and a process tool within a wafer fab, the FOUP is typically loaded either manually or automatedly onto a pod advance plate, which then advances the FOUP toward the process tool. The process tool includes an access port which, in the absence of a pod, is covered by a port door. Upon advance of the FOUP toward the process tool, the pod door aligns against the 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 stowed away from the wafer transfer path. 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 the pod for transfer between the pod and the process tool.
The load port includes several mechanisms for ensuring that the pod and port doors properly align along the X (horizontal) and Z (vertical) axes so as to properly mate with each other. For example, the pod advance plate includes three kinematic pins that mate within respective slots on the bottom of the FOUP to ensure a precise and repeatable seating of the pod on the load port. Additionally, the port door includes a pair of latch keys, which latch keys fit within slots within the front surface of the pod door. It is the latch keys which rotate to unlatch the pod door from the pod shell and at the same time latch the pod door to the port door. The port door further includes a pair of guide pins which mate within holes in the front surface of the pod door. It is further known to provide a vacuum source around the guide pins to hold the pod door against the port door. A prior art system including the above features is disclosed in U.S. Pat. No. 5,772,386, entitled “Loading and Unloading Station for Semiconductor Processing Installations”, which patent is assigned to Jenoptik A. G. Such a system is shown in FIG.
1
. As seen therein, there is a pair of latch keys
10
, a pair of guide pins
12
and a pair of suction cups
14
surrounding the guide pins, each for positioning the pod on the load port assembly.
The above-described mechanisms for positioning the pod with respect to the port door assembly amount to an over-constraint of the FOUP on the load port. This over-constraint has at least two significant drawbacks. First, by providing additional alignment or guiding mechanisms, this provides additional sources for particulates when the pod door is transferred to and from the port door. As indicated above, the geometries of the devices formed on semiconductor wafers are so small today that particulates of even extremely small sizes can adversely effect or ruin a device geometry on the wafer. A second drawback of over-constraint results from the fact that FOUPs occasionally deform or are improperly constructed, and tilt slightly (i.e., 10 to 30 mils) to the side while supported on the kinematic pins. When the FOUP door is aligned over the guide pins, the pins force the pod into a straightened position on the load port. This can generate particulates. Additionally, when the door is removed, the pod shell may return to its unrestrained tilted position. Thus, the FOUP door may not properly align with the FOUP shell upon return of the door to the shell. This misalignment may result in the generation of particulates, or may prevent the door from being properly returned to the shell entirely. It may also happen that FOUP sits properly on the kinematic pins, but the pod door is misaligned within the pod shell. In this event, when the pod door seats over the guide pins, particulates can be generated.
SUMMARY OF THE INVENTION
It is therefore an advantage of the present invention to provide a load port assembly that does not include excessive constraints for positioning a FOUP on the load port assembly.
It is another advantage of the present invention to minimize the amount of particulates and contaminants that may otherwise be generated as a result of contact between the pod door and guide pins.
It is a further advantage of the present invention to allow the pod door to be returned to the pod in substantially the same position from which is was acquired.
These and other advantages are provided by the present invention, which in preferred embodiments relates to a front opening interface mechanical standard, or “FIMS” system for ensuring proper registration of a pod door against a port door on a load port assembly without the use of guide pins on the port door. In a preferred embodiment, the load port assembly includes registration features

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