Third-Generation CMP Equipment

Orbital motion offers the capability of achieving high relative velocities without sacrificing tool footprint. This point is especially important as the semiconductor industry prepares to make the transition to 300-mm wafers. Several CMP tool concepts have been developed based on orbital motion. Some orbit the carrier while rotating the platen [13]. Others orbit the polishing pad while rotating the carrier [14]. Another design involves orbital (as well as arbitrary nonrotational) motion on a fixed polish pad [15]. 

A polish technology that is just emerging from development by several CMP capital equipment suppliers is the pad feed polisher. This equipment is based on some fairly recently developed polish pad rolls. These polish pads are in a roll similar to 35-mm camera film. The pad is fed out to the wafer polish table, a wafer is polished, the pad is conditioned, the pad is incremented forward, and then the next wafer is polished. 

Successful polishing with such a methodology strongly relies on the pad characteristics being consistent from beginning to end. This method is particularly useful for pads with very consistent first polishes, but whose characteristics degrade rapidly with subsequent wafer polishes. 

Aside from the basic approach to polishing, the most critical component of a CMP tool is the wafer earrier. As with CMP tools, wafer carriers have evolved from roots in lens grinding and in the silicon wafer polishing industries to meet requirements specific to polishing silicon-based integrated circuits. 

Baker [17] derived an elegant description of the edge effect based on the mechanics of the pad and of the wafer. He argued that the peak in the edge exclusion region is proportional to where C is the slope of 

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