Exhaust Gas Monitoring for Process Control and Pollution Reduction in Semiconductor Manufacturing

Perfluorocarbons (PFCs), known greenhouse gases, are used widely in semiconductor manufacturing. Several options for reducing the emissions of PFCs are being considered, including: (1) optimizing the process; (2) reducing the nonproduction operation of the fabrication tool; (3) recovering and recycling the unused PFCs; (4) using alternative etch gases; and (5) postprocess abatement (combustion). This project will address the first two reduction procedures by developing a new process control and fault detection system for wafer etching, tool cleaning, and other fabrication processes. The key system component will be the improved process knowledge obtained by infrared monitoring of the exhaust gas composition. Exhaust gas composition knowledge provides information concerning the processing or cleaning step. Comparison of run-to-run variations can provide methodologies for improved process control and fault detection and classification (FDC). Process exhaust gas measurements provide information on deposition and etch rates, etch and clean endpoints, plasma behavior, contamination levels, first wafer, and chamber wall effects. This information is useful for tool and process development, equipment installation and qualification, process tuning, chamber matching, maintenance, troubleshooting, process control, and FDC. On-Line Technologies, Inc.'s proposed technology will reduce PFC emissions by using the exhaust gas data for: (1) active process control to optimize the etch effectiveness and minimize emissions per product wafer, and (2) increasing the overall equipment effectiveness (OEE) to reduce emissions during nonproductive tool operation. In Phase I, a Fourier transform infrared spectrometer will be used to collect exhaust data. Phase I will demonstrate feasibility by monitoring a Lam etch tool at Lam Research Corporation. A commercial system prototyped in Phase II will employ a low-cost, filter-based system monitoring one to three significant gases.The benefits of the proposed system could be enormous for emission reductions and improved manufacturing efficiency. According to SEMATECH, the average OEE for semiconductor microelectronics manufacturing equipment is only 43 percent. During the nonproductive time, the tool is running test wafers, and being tuned up and operated for troubleshooting. This nonproductive tool time creates emissions and wastes valuable production capacity. If an advanced control and FDC system costing $50,000 can increase OEE from 43 percent to 65 percent, it can increase the value of a $2 million tool by $1 million and reduce energy consumption and emissions by up to 50 percent. In addition, improvements in development and yield learning times also can reduce emissions. With the high benefit-to-cost ratio, sales of such systems are expected to reach more than $1 billion by 2004.