Flexible simulation of a complex semiconductor manufacturing line using a rule-based system

Rule-based systems have been used to produce fast, flexible simulation models for semiconductor manufacturing lines. This paper describes such a rule-based simulator for a semiconductor manufacturing line, and the language in which it is written. The simulator is written in a rule-based declarative style that uses a single-rule “template” to move thousands of product lots through various process steps; the rule is customized as needed with data for each step, route, lot, tool, manpower skill, etc. Since line or product changes require only reading new data from a database, without reprogramming, this provides a modeling environment that is simple, flexible, and maintainable. The model is implemented in ECLPS (Enhanced Common Lisp Production System), also known as a knowledge-based or expert systems language. It handles very large models (thousands of data elements, or more) well and is very fast. Subsequent changes improved the speed several orders of magnitude over that of an older version of the model, primarily through use of a preprocessor to eliminate duplicate and redundant data, and by enforcing data typing to take advantage of special techniques for very fast processing of extremely large matches (hashed indices). ECLPS also provides a built-in simulated time clock and other constructs to simplify simulation applications. The model runs daily at the IBM semiconductor manufacturing plant in Yasu, Japan, where it has been in use for many years, currently on three different semiconductor manufacturing lines.