There are many factors that affect cycle time in wafer fabs: utilization, lot size, hot lots, tool dedication, variability, and so on. Understanding these issues is key to improving wafer fab cycle time. FabTime’s cycle time management newsletter has discussed many of these issues in detail. Some of these articles have left people thinking “OK, I understand that utilization and variability and tool dedication and all these things influence fab cycle times, but what do I do about it?” In Issue 3.06 of FabTime’s newsletter, we propose three distinct cycle time management styles, and describe how each can be used to improve cycle time under certain conditions. We have named these three styles: The Traffic Cop; The Shepherd; and The Relay Coach.
The Traffic Cop approach involves managing starts to control utilization and thus keep cycle times lower for all lots. The Shepherd approach involves managing inactive lots, to reduce variability in the fab, and thus reduce both cycle times and cycle time variability. The Relay Coach approach involves focusing close attention on a small number of hot lots. This gets those particular lots through with very low cycle times, though at the expense of other lots.
These approaches all require access to accurate, real-time data about fab behavior, along with management authority to make recommendations or changes. These approaches can be used together (with some trade-offs required), and can be used in conjunction with other cycle time improvement efforts such as variability reduction programs. To read the full article, please subscribe to FabTime’s cycle time management newsletter.
What follows here is a series of graphical examples, using standard charts from FabTime’s cycle time management software. These are examples of the kinds of analysis we have seen people go through when applying the cycle time management styles. We have added many of these charts to our FabTime® software specifically to facilitate this type of analysis.
All of the sample charts are taken from the same set of demo data. The demo was derived from simulated output using an adapted version of one of the SEMATECH testbed datasets. The SEMATECH datasets were derived from actual wafer fab data, scrubbed to maintain confidentiality. Move transactions for the demo were generated using the Factory Explorer® simulation engine, distributed by Wright Williams & Kelly
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