Yield improvement planning for the recycle processes of test wafers

Abstract

Test wafers are used to measure the process quality in semiconductor manufacturing. Test wafers are reusable by recycle cleaning and can be downgraded to the downstream processes. Most previous studies on test wafers aimed to reduce the use of test wafers by making appropriate operational decisions. Yet, the effective improvement of yield in the recycle process of test wafers is seldom explored. This paper formulates a decision problem and proposes two solution methods for selecting the yield improvement alternatives in the test wafer recycle processes. The decision problem is to determine the yield improvement target for each recycle process in order to minimize the use of test wafers, under a given budget for yield improvement. The two solution methods involve a genetic algorithm and a marginal allocation algorithm. The two methods yield very close solutions, but the marginal allocation method is better because it requires less computation time.