This Small Business Innovation Research Phase I project will develop the technology for closed loop process control in semiconductor device fabrication. In current practice, fixed set point control is used for process steps. Here, reactor recipes are set so that a parameter value (as determined by measurements on 1 in 25 or 1 in 50 wafers) matches a target specification, and the process is run until the parameter value is outside preset limits. Then the process is stopped and the reactor is retuned. This practice results in down time for process retuning, scrapped material which is produced before the process is stopped (often the measurements are not made immediately), and wider variations in the product specifications than necessary. Higher quality products, with tighter specifications produced at lower cost, with reduced scrap can be achieved by the application of closed loop process control in which measurements are made on every wafer, and recipe changes are continuously made to keep the wafer state parameters on target. The objective of this project is to develop the technology for wafer-by-wafer control in the fabrication of epitaxial silicon. On-Line technologies, Inc. (On-Line) has developed a thin film metrology (TFM) tool which integrates with the fabrication tool for epitaxial silicon (epi), allowing the measurement of the quality of every epi film produced without any delay in the process. Work at the Massachusetts Institute of Technology (MIT) has developed the data analysis and control algorithms which can be employed in a cell controller. Phase I will develop a cell controller which integrates an Applied Materials, Inc. Centura epi fabrication tool, an On-Line epi TFM tool, and MlT's analysis and control algorithms. This system will be used to demonstrate improvements in the epi thickness specifications using wafer-by-wafer control of the deposition time. Phase I will provide the foundation for a cell controller to be constructed and tested in Phase II which will control the complete fabrication recipe to ensure both epi thickness precision and uniformity. The implementation of closed loop control can provide parameter specification improvements of factors of 2 to 10 without requiring any improvements in the fabrication tool. This improvement in product quality can be achieved with increased tool availability, reduced scrap, and lower personnel costs. The proposed technology will be applicable to fabrication tools with a total value of $9.6 billion/yr. in the year 2000. The cost for metrology is predicted to be 10% of the fabrication tool costs, or $960 million/yr. A market of similar size is expected for the cell controllers which will compliment and add significantly to the value of the metrology tools.
