Capacity planning with sequential time constraints under various controlpolicies in the back-end of wafer fabrications

Abstract

To ensure final product yield, engineers have to set up queue time limits forparticular sequential machines during wafer processing; we name these as‘sequential time constraints’ (STCs). This issue can be observed atthe back-end of the copper interconnect process. Moreover, wafers can only bescrapped or given a mark, but cannot be reworked, when queue time limits areexceeded at these stages. To eradicate difficulties with STCs, capacity planningmust be addressed. This study presents a capacity determination model employingthe GI/G/m queuing model to eliminate the difficulties caused by STCs.The probability that waiting time exceeds queue time constraints under a certaincapacity level can be calculated by proposed model. Hence, we can get therequired capacity that can achieve the probability target set in advance.Furthermore, the inferences of different control policies on capacity planningare discussed. The proposed model is also adjusted to calculate the effects anddetermine required capacity under various policies. The simulation experimentssupport that the proposed could resolve the issues of STCs effectively.Moreover, under various control rules, the experiments results indicate thatdifferent capacity level may not be required, but varied performance will beperformed.