Scheduling approach for a wafer fab with re-entrant flows and photo dedication constraints

In this research, we consider a scheduling problem for a wafer fab with dedication constraints of photolithography equipments. In a fab, wafer lots have to visit the serial operations (clean, diffusion, photolithography, etch and so on) to construct multi (L≥2) layers of semiconductor chips. Therefore, there are re-entrant wafer lots (j-th pass lot, 2≤j≤L) in a fab. Then, the re-entrant lots have to be operated in the photolithography equipments that the lot (first-pass lot) was operated in the first flow, which is called as dedication constraint. For the exact circuit alignments among layers of a wafer, the dedication constraint of photolithography equipment is very important, and we fulfill the dedication constraint of photolithography equipment. In this paper, we approach the concepts of heuristic algorithms considering the dedication load balance, and the objective function of this scheduling problem can be represented as minimizing the total flow time and so on.