An expert system for real-time process characterization and control [photolithography]

An expert system for photolithography is described. It is designed to monitor, characterize, and control front-end photoresist cells towards optimal product throughput, quality, and yield. A key feature of this expert system is its ability to detect out-of-control products while continuously improving the process aim and tightening the process variation. Techniques of statistical process control combined with customer requirements and the expertise of photolithographic engineers make up the expert system's rule base. Technical aspects of the expert system are discussed, along with the problems involved in allowing a process to control itself. The physical computer implementation is explained, and detailed descriptions of major decision points are given. A discussion of statistical process control as implemented in this system is also included