Material or article handling – Apparatus for charging a load holding or supporting element...
Reexamination Certificate
1997-07-11
2003-06-17
Brahan, Thomas J. (Department: 3652)
Material or article handling
Apparatus for charging a load holding or supporting element...
C414S281000, C414S940000
Reexamination Certificate
active
06579052
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the transport and storage of semiconductor wafers, and in particular to a system capable of storing wafer-carrying pods and/or cassettes and capable of transferring wafer-carrying pods and/or cassettes to and from a semiconductor processing tool, which system provides a high degree of flexibility, operates with a minimum amount of hardware and software control and makes efficient use of space.
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.
The SMIF system provides a clean environment for articles by using a small volume of particle-free gas which is controlled with respect to motion, gas flow direction and external contaminants. Further details of one proposed 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 present geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.2 &mgr;m and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest.
A SMIF system includes a minimum volume, sealed pod used for storing and transporting wafers or other workpieces. Within a wafer fab, a first automated transport system is provided for transferring the SMIF pods from one processing tool bay to another (interbay delivery systems) and a second automated transport system may be provided for transferring the pods around within each particular bay (intrabay delivery systems). Tool bays are typically on the order of about 80 feet long, and consist in general of a number of processing tools for performing various wafer fabrication functions, metrology tools for monitoring or testing a wafer or wafers from within a wafer lot, and at least one stocker for storing the pods before or after processing.
Some processing tools within a tool bay are typically high throughput tools which are capable of performing their particular wafer process at a relatively higher rate than other processing tools. Similarly, as metrology tools only sample one wafer per lot, these tools also are capable of handling substrate carriers at a much higher rate than typical processing tools. Presently, a semiconductor wafer fab may cost in excess of $1.6 billion, and approximately 80% of that cost is the cost of equipment. It is therefore desirable to maximize the yield of this equipment, and substantial efforts are devoted to minimizing the time that the tools sit idle.
In order to prevent significant idle time for high throughput and metrology tools, it is known to include a local tool buffer adjacent the tool load ports of high throughput and metrology tools. In this way, pods may be stored locally adjacent such tools and quickly transferred to the tool load port without having to constantly retrieve a pod from the remotely located stocker, or depend on timely delivery therefrom. A conventional local tool buffer is shown generally at
10
adjacent a process tool
12
in FIG.
1
A. As shown therein, a pod handling robot
14
is capable of transferring pod
16
between a plurality of local shelves
18
and the tool load ports
20
on the process tool. The pod handling robot
14
includes a base
21
mounted to a track
22
so as to translate along the z-axis. First and second arms
24
and
26
and a gripper
28
are attached to the base
21
and are controlled by computer to grip a pod
16
for transfer between the shelves
18
and the tool load ports
20
.
Conventional local buffers, such as that shown in
FIG. 1A
, have several shortcomings. First, it is the nature of the robot used therein that it can only reach one carrier space to its left or right. Thus, the storage spaces available to such a robot are limited to being directly adjacent the robot. A second significant shortcoming of conventional local buffers is that they utilize three-dimensional transport of the pods. That is, the pods are transported outside of the X-Z plane in which they are stored. The footprint of such conventional buffers must be large enough to accommodate this three-dimensional transport.
A still further shortcoming to conventional local buffers relates to the storage density of such systems. Storage density refers to the ratio of storage space available to the overall footprint required by the local buffer.
FIG. 1B
is a graphical representation of the storage density of the local buffer shown in
FIG. 1A
(each box represents a space capable of being occupied by a single wafer-carrying pod), with the outline of the robot provided thereon. As shown, storage spaces are available in the lower left and right positions
1
and
2
of the buffer. As the track
22
must be off-set from the robot in order to allow pods to be passed in front of the robot (i.e., between the robot and the buffer wall), the lower middle space is utilized for vertical pod travel and is unavailable for pod storage. Similarly, the spaces to the left and right of the robot base (in the top center) are inaccessible due to the position of the stored pod and track
22
. Thus the resulting storage density for a two-deep local buffer is 2 to 6, or 33%.
A mechanism similar to that shown in
FIG. 1A
may be used as a stocker for pod storage. Such conventional stockers may additionally include a second bank of storage spaces juxtaposed to the first bank. The storage density of this system is graphically represented in FIG.
1
C. As shown, the robot may be configured to translate in the direction of arrow A—A. By adding the additional bank, the storage density improves to 4 to 9, or about 45%. However, this is still a relatively low ratio, and it comes at the expense of a large footprint.
SUMMARY OF THE INVENTION
It is therefore an advantage of the present invention to provide a process tool storage, delivery and retrieval system for supplying pods to semiconductor process and metrology tools.
It is another advantage of the present invention to provide two-dimensional transport of a wafer carrier, wherein a carrier is transported in the same plane in which it is stored
It is a further advantage of the present invention to provide a storage space for wafer carriers having a maximum storage density within a minimum incremental footprint relative to the process tool's original footprint without the buffer.
It is a still further advantage of the present invention to provide a tool integrated pod storage, delivery and retrieval system having a small overall footprint.
It is another advantage of the present invention to provide a tool integrated pod storage, delivery and retrieval system which may be easily scaled to different sizes.
It is a further advantage of the present invention to provide a highly reliable tool integrated pod storage, delivery and retrieval system.
It is anothe
Bonora Anthony C.
Fosnight William J.
Martin Raymond S.
Mosier Terry
Netsch Robert
Asyst Technologies, Inc.
Brahan Thomas J.
O'Melveny & Myers LLP
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