Special receptacle or package – Holder for a removable electrical component – For a semiconductor wafer
Reexamination Certificate
1998-05-05
2002-06-04
Brahan, Thomas J. (Department: 3652)
Special receptacle or package
Holder for a removable electrical component
For a semiconductor wafer
Reexamination Certificate
active
06398032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to SMIF pods, and more particularly to a SMIF pod shell enclosing an independently supported cassette allowing precise, controllable and repeatable positioning of wafers with respect to a surface on which the pod is supported.
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, sealed 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 Paikh 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.
In practice, a SMIF pod is set down on various support surfaces within a wafer fab, such as for example at a load port to a minienvironment, whereupon interface mechanisms in the load port open the pod door to allow access to the wafers within the pod. Additionally, a pod may be supported at a storage location while awaiting processing at a particular tool. Such storage locations may comprise a local tool buffer in the case of metrology or high throughput tools, or may alternatively comprise a stocker for storing large numbers of pods within a tool bay. A pod may additionally be positioned at a stand-alone purge station.
Whether a tool load port, local tool buffer, stocker or purge station, the support surfaces typically include registration or kinematic pins protruding upward from the support surface. In 300 mm pods, a bottom surface of the pods includes radially extending grooves for receiving kinematic pins. Once the pod is positioned so that the grooves engage their respective kinematic pins, the grooves settle over the pins to establish six points of contact between the pod and support platform (at the grooves and pins) to kinematically couple the pod to the support platform with fixed and repeatable accuracy. Such a kinematic coupling is for example disclosed in U.S. Pat. No. 5,683,118, entitled “Kinematic Coupling Fluid Couplings and Method”, to Slocum, which patent is incorporated by reference herein in its entirety. The size and location of the kinematic pins are standardized so that the pods of various suppliers are compatible with each other. The industry standard for the location and dimensions of the kinematic coupling pins are set by Semiconductor Equipment and Materials International (“SEMI”).
In general, wafers may be supported within a pod according to one of two configurations. In a first configuration, the wafers may be seated within a removable cassette including a plurality of shelves for supporting the wafers in a planar orientation. The cassette in general includes kinematic pins or grooves on its bottom surface for mating with respective kinematic grooves or pins provided on an upper surface of the bottom of the pod. Thus, in the first configuration, wafers are supported by the wafer cassette, which is in turn supported within the pod, which is in turn supported on a support surface. The second configuration for supporting wafers within a pod is the so-called cassetteless pod. Such pods are used exclusively for front opening applications, and include a plurality of shelves formed on the side walls of the pod itself for supporting the wafers in a planar orientation. An example of such a pod is disclosed in U.S. Pat. No. 5,476,176 to Gregerson entitled, “Reinforced Semiconductor Wafer Holder”.
Pods are typically formed of plastics and various polymers such as for example polycarbonate. These materials allow the pods to be efficiently and inexpensively manufactured of a lightweight material which is easily transported, and are typically transparent to allow viewing of the wafers seated therein. While it is conceivable that pods may be manufactured from various metals, metal pods are in general disfavored within wafer fabs owing in part to their weight and potential for ionic contamination.
The desired material characteristics of the wafer cassettes for supporting the wafers are different than those of the pods. It is desirable that the wafer cassettes be more rigid, temperature and wear resistant than the pods, and that the wafer cassettes be static dissipative. For at least these reasons, the pods and wafer cassettes are typically formed of different materials. One preferred material from which the wafer cassettes are formed is polyetheretherkeytone, or “PEEK”. Owing in part to its weight, expense and lack of transparency, PEEK is in general not a good material for use in forming a pod.
Once the pods and wafer cassettes are independently formed, the pod shells and wafer supports are generally affixed together in front opening pods to thereby constrain the wafer cassette against movement with respect to the pod shell in all six degrees of movement. That is, the wafer support is prevented from translating along X, Y, and Z cartesian axes, and is prevented from rotating about the X, Y and Z cartesian axes, with respect to the pod shell. The rigidity of the pod shell is relied upon to stabilize and maintain the wafer support in a proper position.
However, conventional pod shells have proven somewhat ineffective in providing a precise, controllable and repeatable positioning of the wafer supports within the pods. One reason is that inherent stresses within the pod shell cause the pod shell to slightly warp or deform over time. Additionally, mechanisms are provided at support surfaces such as for example those at load ports for physically grasping and securing the pod in tight engagement with both the horizontal support surface and the vertical load port. Such grasping and engagement of the pod may further cause deformation of the pod shell. Further still, pods weigh on the order of about twenty pounds. When the pods are lifted from a handle mounted on a top of the pod, as they often are, the pod shells may elongate slightly in the vertical direction, pulling the sides of the pod shell inward. Deformation of the pod shell as a result of any of the above described conditions is communicated directly to the wafer support, which as described above is typically connected to
Bonora Anthony C.
Fosnight William J.
Martin Raymond S.
Peterson Perry
Asyst Technologies, Inc.
Brahan Thomas J.
O'Melveny & Myers LLP
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