Effect of Reduced Equipment Downtime Variability on Cycle Time in a Conventional 300mm Fab

The semiconductor industry is pursuing further cycle time and cost reductions through an initiative termed 300 mm Prime. One key area of focus is improving process tool availability. Equipment downtime-particularly unscheduled down time due to a failure-causes disruptions to production, loss of productivity, and higher costs. This paper focuses on fab productivity improvements resulting from the reduction of tool downtime variability. Preventive maintenance can reduce the risk of unscheduled downtime. Discrete-event simulation is used to investigate the relationship between downtime variability and overall cycle time in a conventional 300 mm fab with batch tools. Variance reduction is modeled by reducing the standard deviation of the time to repair a failed tool and by increasing the portion of tool downtime reserved for regularly scheduled preventive maintenance. Also, the effect of reserving capacity in the form of additional tools is assessed and compared to the effect of reduced downtime variability.