Golden nuggets of AMHS modeling and design for semiconductor wafer fabrication

This paper presents the “golden nuggets” or principles for modeling and designing automated material-handling systems (AMHS) for semiconductor wafer fabrication. Discrete-event simulation, analytical, and spreadsheet models were developed to model the performance, reliability, and cost/benefit of conventional cleanroom material handling including manual and automated systems. The components of a conventional cleanroom material-handling system include an overhead monorail system for interbay (bay-to-bay) transport, work-in-process (WIP) stockers for lot storage, and manual systems for intrabay movement. Suggestions for selecting simulation software and a list of the steps required to develop an AMHS performance model are also presented. One of the most beneficial principles for optimizing AMHS performance is to shorten the distance traveled when transporting lots. The second most beneficial principle is to minimize the congestion of a lot in transport. Both of these principles can be implemented through an effective layout of processing equipment and by using design rules for the effective use of AMHS track options such as turntables and customized track configurations. Examples of track configurations include spine-based, perimeter-based and custom layouts. The reliability of WIP stockers is vital to the overall system reliability, especially in comparison to other components. Several principles of operator behavior are also discussed including operator response times and a subjective work aura radius. These nuggets are useful in determining WIP stocker location and in integrating manual and automated material-handling systems