Yield Improvements In Semiconductor Manufacturing

A dispatching scheme that implements composite scheduling policies is developed to maintain a high average outgoing quality level (AOQL) at every stage of the wafer fabrication process. The dispatching scheme selects the jobs to be processed next by periodically alternating between a selected scheduling rule such as first in first out (FIFO) or a job due-date based priority rule (slack) and last in first out (LIFO) priority rule. This dispatching scheme captures many of the quality benefits of JIT while permitting adequate work-in process to smooth out work flow. The dispatching scheme also enables defect detection as quickly as possible and corrective action to be taken at the preceding process.