Scheduling Dedicated Lithography Equipment

Friday, September 27, 2002 - 9:30am - 10:20am
Keller 3-180
Robert Leachman (University of California, Berkeley)
A common strategy to achieve a successful and stable process for the fabrication of advanced digital semiconductors involves what is termed the dedication of lithography equipment. In order to maximize registration of multiple mask layers, the same machine may be required to be used for the exposure of critical layers. Moreover, only certain machines matched to a given machine may be used at other layers. This strategy poses a considerable challenge for scheduling lot releases. Lots must be assigned to machines before release, and, once released, cannot be re-assigned. It is difficult to balance utilization of lithography equipment, resulting in situations where some machines have large queues yet others are idle.

A scheduling system based on integer goal programming has been developed and implemented to cope with this challenge. Multiple objective functions for minimizing machine overloads and balancing equipment workloads are optimized. Implementation in one advanced fabrication facility reduced average queue times at lithography by about 40%, resulting in product flow time reduction of about 36 hours.