1. Field of the Invention
The invention relates generally to semiconductor processing equipment and more specifically to systems that permit the multiple processing of semiconductor wafers in a single cluster.
2. Description of the Prior Art
The fabrication of semiconductors and the handling of silicon wafers requires extreme cleanliness. Cleanrooms provide such clean environments, but are costly to construct and maintain. Therefore, each square foot in a cleanroom is very valuable and the semiconductor processing equipment placed in a cleanroom must make the most of the space it occupies by processing the wafers more effectively.
Cluster tools have evolved over the years that surround a wafer transfer arm, an endifector, with wafer cassette modules and process modules. The central cluster tool controller moves the wafers in and out of the various cassette and process modules. Such an arrangement can make for a very large assembly that consumes a lot of cleanroom space. The wafer transfer arm becomes a limiting factor in how fast wafers can be moved through the cluster tool. Since the single arm visits all the modules, contamination in one module can be distributed to all the modules.