Setting daily production targets with novel approximation of target tracking operations for semiconductor manufacturing

Daily production target setting based on machine capacities and available wafer-in-process (WIP) is an important practice in a semiconductor fab characterized by re-entrant process steps sharing individual machine group capacities. Operations of individual machine groups will track their respective target guidance through detailed machine allocation and lot dispatching (MALD), inducing variations of wafer flow. Existing approaches do not explicitly address such target-induced variations (TIV), and the resultant target setting may incur throughput loss and prolonged cycle times. A novel design of target-setting algorithm considering TIV called TaTIV is proposed to take TIV into account for setting daily targets systematically. TaTIV integrates three innovations: i) a Bernoulli trial model for approximating TIV of MALD at a process step under a given target, ii) a hybrid and recursive tandem queue approximation of multiple-step target-induced wafer flows and flow times given initial WIPs and machine group capacities of the day, and iii) a fixed-point iteration between target setting and target-induced wafer flow estimation. Analyses and simulations exploiting fab data show that TaTIV sets targets closer to what are actually achieved at individual steps than those set without considering TIV, reduces inter-step variations of machine allocation, and improves fab throughput and cycle times.