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ABSTRACT
Time constraints related issues are unavoidable tasks in wafer fabrications, especially for back-end copper-interconnect process while the wafers are processed through sets of continuous operations associate with various time constraints. We shall address ourselves to capacity planning in order to eradicate the difficulties of sequential time constraints. This paper proposed a tool portfolio determination model to determine the required quantity and type of tools for ensuring pre-defined target yield could be achieved. The workstations are modeled as GI/G/m queuing network, and the analysis of rate of wafers exceeding queue time is adopted to determine the required capacity. Furthermore, a virtual customer was introduced into the model to adjust system service rate to character the machine failure. By this approach, the influence of downtime duration at fixed machine availability could be observed. The results support that the proposed model can more effectively resolve the issues of sequential time constraints. Moreover, the analysis results indicate that the current capacity expansion policy of the semiconductor industry should be re-examined.