9531816 Pearsall The goal of this project is to achieve new fundamental understanding of thin film deposition from the gas phase through non-invasive monitoring and to determine how this information can improve real-time control of chemistry in gas-phase semiconductor processing. Nearly all semiconductor manufacturing involves etching or deposition of thin films via gasphase chemistry. There is wide agreement that in-situ, non-invasive process monitoring and real-time control will improve manufacturing yield and throughput, and that more research is needed to develop suitable methods. For example, in recent (8/94) review the editor of Semiconductor International remarked, "Real-time monitoring remains a highly desirable, but somewhat distant goal". The key is a robust, quantitative technique that tracks the chemical reactions occurring at or near the surface of a semiconductor wafer. A method based on ultra-violet (UV) spectroscopy is focus of the proposed work. Simultaneous tests of control strategies will determine whether the measurements have enough information to be of practical use. The experimental environment will be an existing chemical beam expitaxy reactor with calibrated flow, pressure, and wafer temperature monitoring. It supports processing conditions from ultra-high vacuum (10-10 Torr) to 10-4 Torr pressure. A co-located chemical vapor deposition reactor allows additional experiments in the pressure range 10-4 Torr to atmospheric pressure. Experiments will determine whether UV spectroscopy can provide positive identification and quantitation of multiple chemical components at realistic operating conditions. This method has sufficient sensitivity to be used in ultra-high vacuum deposition conditions where the gas density is lowest. Quantitation depends on an accurate baseline for the optical signal, so a new nonclouding window will be used in combination with techniques that compensate for drift in source intensity and optical transparency. Mechanis tic modeling will provide the basis for estimation of unmeasured parameters and for feedback control. Linear and non-linear model-based control methods will be used. Initial work will test the system's ability to track time-varying setpoints for compositions of 1 to 3 dilute reactants in an excess of another, and to provide uniform temperature across the wafer surface. The system will then be used to control deposition of compounds of GaAs with Al and In. Experiments will determine where the UV beam should be located (relative to the wafer surface) in order to optimize the information content. The efficacy of the control strategy will be measured by independent (off-line) chemical analysis of the deposited film. ***
