Scheduling Setup Operations For Bottleneck Facilities In Semiconductor Manufacturing

In this paper, a scheduling heuristic was developed to aid the semiconductor fabs\u27 operators in choosing what type of lots to process next and whether to change machine setup in order to reduce cycle time. Specifically, this study focused on developing a scheduling heuristic for ion implanter facilities at Cirent Semiconductor (currently Agere Systems) in Orlando, Florida where implanters facility groups are considered to be a bottleneck. The re-entrant flow of production passes several times through the implanters at different stages of the wafer production, requiring changes to the current settings of the workstations and thus incurring a significant setup time. The scheduling heuristic developed in this research aims at balancing workload levels for implanters processing lots at different stages of the wafer production lifecycle. This is accomplished by processing those lots that contribute most to increasing inventory levels at the bottleneck facility. The measures used to evaluate the performance of the proposed heuristic were mean cycle time, mean work in process (WIP), and standard deviation of cycle time. The performance of the proposed heuristic was compared against the scheduling rules currently in use and against other commonly used dispatching rules using a valid simulation model. Simulation results showed that the heuristic developed in this research performs better than all other rules in terms of mean cycle time and WIP in all cases, and better in terms of standard deviation of cycle time for most cases tested. The heuristic can be used at any bottleneck facility that processes products at different stages of their production cycle and that requires a significant setup time