The impact of operation-to-tool dedications on factory stability

It is essential, or should be, that the pricey machines that support the process steps in the fabrication of semiconductor wafers be designed so as to achieve optimal, or near optimal, performance. Performance, in turn, is typically measured by average cycle time, capacity, yield, and cost. One metric of particular importance is, however, seldom considered. This is that of the stability of the machines, workstations, and production line as a whole. While too often ignored, it is vital that the components of the factory exhibit stable performance when exposed to everyday changes (e.g., minor fluctuations in product mix, slight changes in factory throughput). We examine, herein, the stability of the reentrant workstations that employ operation-to-machine dedications when those dedications are produced by either (a) optimization, (b) heuristics, or (c) genetic algorithms. The results of a multi-year effort reveal there is a significant difference in the stability of the resultant facility.