EPAS: an emitter piloting advisory expert system for IC emitter deposition

Emitter piloting is a difficult diffusion process in IC manufacturing. The decision for the adjustment of the piloting drive cycle is a heuristic-oriented task. An expert system, the emitter piloting advisory system (EPAS), is used at Harris Semiconductor to advise fab operators on how to adjust piloting cycle time for emitters based on knowledge extracted from the most experienced engineer. EPAS consists of an input filter to validate the input parameter values; a knowledge base containing the knowledge extracted from the domain expert; a limited learning mechanism for dynamically calculating a better estimate of initial drive time for the next lot; a convergence control mechanism to control the rule inference so that the result of an inference is always closer to the conclusion; a user facility module containing many LISP-based modules developed to let the expert, engineers, and operators maintain the system by themselves; and a user-friendly interface. One EPAS operation example is provided