Statistical control of VLSI fabrication processes

Random fluctuations in very large scale integrated circuit (VLSIC) fabrication processes cause the parametric production yield to fall below acceptable levels, resulting in a loss of competitive edge. To address this problem, a framework for an integrated computer-aided-design-computer-aided-manufacturing (CAD-CAM) system that will enable the design, fabrication, control, and diagnosis of present and future VLSICs to be carried out profitably is proposed. It is argued that the inefficiencies of present-day CAM systems are due to the lack of appropriate methodologies for process monitoring and statistical techniques to analyze the in-process and end-of-process data. Methodologies for monitoring lots in fabrication lines, using in situ measurements, and for controlling lots, using the multivariate distribution of observable in-process parameters, are discussed. These methodologies attempt to eliminate the pitfalls of the previous statistical process control algorithms. The software system that implements the algorithms has shown encouraging results when applied to industrial fabrication lines.