bottleneck

A bottleneck is the process step or tool with the least capacity relative to demand, limiting overall fab throughput regardless of other tools' capacity. Identification methods: (1) Queue analysis—longest WIP queues indicate bottleneck; (2) Utilization analysis—highest utilized tool (approaching 100%); (3) Throughput analysis—step with lowest effective throughput relative to demand; (4) Theory of Constraints—systematic identification. Bottleneck characteristics: WIP accumulates before bottleneck, any capacity loss at bottleneck is lost forever (can't be recovered), downstream tools starve. Bottleneck types: (1) Constraint—single limiting resource; (2) Floating bottleneck—moves based on product mix; (3) Temporary bottleneck—caused by failures, PM, qual wafer runs. Bottleneck management (drum-buffer-rope): (1) Drum—bottleneck pace sets production rate; (2) Buffer—WIP buffer before bottleneck ensures it never starves; (3) Rope—release wafers at bottleneck rate. Bottleneck improvement priority: (1) Maximize bottleneck uptime; (2) Increase bottleneck UPH; (3) Offload work (split operations); (4) Add capacity (new tools). Non-bottleneck focus: improving non-bottleneck doesn't increase output, but reducing variability helps protect bottleneck. Dynamic nature: as bottleneck is improved, another step becomes the new bottleneck—continuous improvement cycle.