Scheduling of Wet Etch and Furnace Operations with Next Arrival Control Heuristic

Abstract

In wafer fabrication facilities, it is critical to schedule batching operations efficiently. Most previous studies in scheduling these operations have the objective to efficiently create the batches with the given jobs at the batching operation and decide whether to start a partial batch or to wait for the next arrival to make a full batch. Typical batch operations in wafer fab can be found in the diffusion area which is mainly composed of pre-cleaning (wet etch) and furnace. Glassey and Weng (Dynamic batching heuristic for simultaneous processing. IEEE Trans Semicond Manuf 4(2), May 1991) first introduced the concept of using future arrival information and called it look-ahead. Fowler et al. (Real-time control of multiproduct bulk-service semiconductor manufacturing processes. IEEE Trans Semicond Manuf 1992) expanded the concept to multiple products and created the heuristic method called next arrival control heuristic (NACH). NACH considers only the next arrival and makes the decision whether to start the batch now or to wait for the next arrival. The new proposed scheduling system called NACH+ tries to control the incoming inventory into the batch operation. The preliminary batches are scheduled to arrive at the batch operation just in time so that any unnecessary waiting time does not happen. In this paper, NACH+ is compared to the minimum batching size rule.