Pull system for control and dummy wafers

Abstract

Various CD wafers (Control and Dummy wafers) are used in wafer fabrication to enhance product quality and process stability. Most wafer fabs downgrade used CD wafers into other functional ones and then recycle them to reduce costs. Wafer costs increase with wafer diameter, and thus the downgrading mechanisms and inventory control of CD wafers have become increasingly important to fab performance. Wafer fabs now are willing to seriously consider CD wafer management but CD wafer management remains neglected in the literature. This study presents a novel pull system focusing on inventory and downgrading management of CD wafers. The proposed system in this study intends to reduce the WIP level of CD wafers, increase recycled usages (number of times CD-wafer lots are recycled) before scraping, and reduce machine delay ratio without lowering the product wafer throughput rate.