Downgrading and release rules for control and dummy wafers

Abstract

A variety of control and dummy wafers (CD wafers) are utilized in wafer fabrication to enhance product quality and process stability. Wafer fabs downgrade and recycle used CD wafers for cost-down purposes. Downgrading and release rules therefore become crucial issues in CD-wafer management activities but only few studies covered this topic. This study presents a CD-wafer management system, the push system, focusing on downgrading and release rules. The push system attempts to reduce machine delay time, increase recycled usages of CD-wafer lots, and attain a reasonable CD-wafer work-in-process (WIP) level without lowering the throughput rate of product wafers. This study also employs a simulation model of a simplified fab to analyze the performance of the proposed push system. Simulation results demonstrate that the push system leads to efficient utilization of CD wafers. Significance: This work proposes a systematic system, the push system, for downgrading and releases of control and dummy wafers in wafer fabrication. The issue discussed in this study is crucial and practical for wafer fabrication but is seldom cited in research papers.