(A) study on the production control policies considering WIP balance and setup time in a semiconductor fabrication line

Abstract

This paper mainly deals with the problem determining workloads in a semiconductor fabrication line. A mathematical model is proposed to determine the amount and type of wafers which will be processed on equipment used in photolithography process. Photolithography process is main bottleneck process in the fabrication line, especially on the steppers. It is assumed that this stepper process is the most significant bottleneck process and others are non-bottleneck processes It is the goal of the proposed MIP model to control WIP level in the buffer of stepper to the target WIP level considering the setup time The ratio test between imbalance of actual WIP to the target WIP and setup time in the objective function was performed, and hence the most reasonable ratio was proposed. This test was performed using OPL Studio. Because of the long computation time of MIP model, it is necessary to suggest heuristic methods. LP relaxation and two direct stepper allocation methods are suggested. Among them LP relaxation method gives the solution near the optimal solution. The difference between optimal solution and the solution of LP relaxation is less than 10%.