Data processing: generic control systems or specific application – Specific application – apparatus or process – Article handling
Reexamination Certificate
2000-08-16
2003-07-08
Choules, Jack (Department: 2177)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Article handling
C700S225000
Reexamination Certificate
active
06591162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the fabrication of integrated circuits on semiconductor wafers, and in particular to a system capable of monitoring a plurality of performance characteristics of wafer carriers and to a system for managing carrier operation on a fab-wide basis.
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 carriers, or 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 carriers 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 carriers are in general comprised of a carrier door which mates with a carrier shell to provide a sealed environment in which wafers may be stored and transferred. So called “bottom opening” carriers are known, where the carrier door is horizontally provided at the bottom of the carrier, and the wafers are supported in a cassette which is in turn supported on the carrier door. It is also known to provide “front opening” carriers, in which the carrier door is located in a vertical plane, and the wafers are supported either in a cassette mounted within the carrier shell, or to shelves mounted in the carrier shell.
A typical wafer fab has several different types of tools into which wafers from a carrier are loaded. Processing tools are used to form patterned layers of silicon, silicon compounds and metals on the wafer to define the individual IC devices. Metrology tools are used for performing various tests on wafers to ensure the wafers are fabricated to specification. Carrier cleaning tools are used to periodically clean the interior surfaces of a carrier to remove particulates and contaminants that accumulate within a carrier with use. Another tool found in a wafer fab is a sorter, which performs various functions including the transfer of wafers between the various carriers positioned on the wafer sorter, the mapping of wafer location within a carrier cassette, and wafer identification.
In order to transfer wafers between a SMIF carrier and the various tools within a wafer fab, a carrier is typically loaded either manually or automatedly onto a load port assembly on a front of the tool. Each load port assembly includes an access port which, in the absence of a carrier, is covered by a port door. The SMIF carrier is seated on the load port so that the carrier door and port door lie juxtaposed to each other. In a front opening system, the carrier is seated on a carrier advance plate which advances the carrier to the port so that the respective carrier and port doors lie adjacent to each other. Registration pins are provided on the port door that mate with grooves in the carrier door to assure a proper alignment of the carrier door with respect to the port door.
Once the carrier is positioned against the port door, mechanisms within the port door unlatch the carrier door from the carrier shell and move the carrier door and port door together into the process tool where the doors are then stowed away from the wafer transfer path. The carrier shell remains in proximity to the interface port so as to maintain a clean environment including the interior of the process tool and the carrier shell around the wafers. A wafer handling robot within the process tool may thereafter access particular wafers supported in the carrier for transfer between the carrier and the process tool.
Wafer carriers are manufactured to relatively narrow tolerances and are tested prior to initial use within a wafer fab to ensure they have been manufactured to specifications. However, carriers are subject to wear, deformation, breakage and improper maintenance in use, and several performance characteristics of each carrier should be monitored over the life of the carrier as it transports various wafer lots around the fab. These performance characteristics which should be monitored include the following:
Seal Performance
One or more elastomeric seals are provided between the carrier shell and the carrier door to prevent fluids from traveling into or out of the carrier when the door is sealed within the shell. These elastomeric seals wear over time and gradually become less effective in isolating the environment within the carrier from the environment surrounding the carrier.
Seal performance refers to how effective an elastomeric seal in a carrier is at a given point in the life of a carrier at preventing fluid flow around the seal between the carrier shell and carrier door.
Cleanliness
Cleanliness relates to the amount of contaminants found within a carrier at a given time. Contaminants may be grouped into two classes, and there are different removal and monitoring systems for each. The first type of contaminant includes relatively large particles, for example bigger than 0.02&mgr;, which adhere to surfaces within the carrier. These particles are generally removed by injecting a cleaning solution onto the surfaces of the carrier to flush away the particles. A second type of contaminant relates to relatively small particles, for example smaller than 0.02&mgr;. These particles may be airborne or adhered to surfaces. Such smaller particles may be removed by including a particle filter within the carrier, which removes particles that come into contact with the filter as they float around the interior of the carrier. These small particle contaminants are also removed from surfaces by the cleaning solution injected into the carrier.
Sources of contaminants within a carrier include worn elastomeric seals in a wafer carrier, fluids injected into the carrier and instances where the carrier is opened for maintenance or other purposes. As indicated above, it is important to monitor the cleanliness of the interior of a carrier, as particles can interfere with the device geometries formed on the wafers.
Relative Humidity
Wafer carriers are formed of various materials including plastics such as polycarbonate which absorb moisture. Thus, after a carrier is cleaned with a wet cleaning soluti
Asyst Technologies, Inc.
Choules Jack
O'Melveny & Myers LLP
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