Cycle Time Analysis at Wet Stations

In a complex manufacturing environment, such as a semiconductor wafer fab, small variations of system operating factors, implemented at any production step, may have a significant impact on the overall fab performance. Cycle time (CT) reductions obtained at critical tools could generate considerable productivity improvements which eventually lead to a capacity increase at no investment cost. In this study, a simulation model is developed to analyse CT performance at wet tools. The model developed captures the production dynamics of a wet station operating in a real wafer fab; its flexibility allows reproducing the behaviour of different wet tools configurations. The model is used to compare the efficiency of two different assignment strategies, which are based on a workload balance concept and an “Earliest Finish” concept, respectively. The impact of these strategies on CT is also analysed through the effect that these strategies have on the relationships between three different operating factors and CT itself. The factors investigated include wet tool dedication policies, batching parameters and wet tool capacity limits. The model results are used to draw conclusions on sub-optimal operational settings at the wet station modelled; based on these settings, a 19% CT reduction could be achieved.