<title>Laser-Based Studies Of Chemical Vapor Deposition</title>

Abstract

W. G. Breiland, M. E. Coltrin, Pauline HoSandia National Laboratories, Division 1126Albuquerque, New Mexico 87185AbstractPulsed laser -Raman spectroscopy and laser -excited fluorescence have been used to profilereactive species concentrations inside a chemical vapor deposition cell. Experimentaldata and theoretical calculations indicate that gas -phase chemical kinetics plays animportant role in the deposition process.IntroductionThe chemical vapor deposition (CVD) process has been developed into a very sophisticatedand widely -used technological tool. However, very little is known about the fundamentalphysical and chemical mechanisms that are responsible for CVD film growth. As CVD pro-cesses become more complicated, and as film -property tolerances become more stringent,it will be increasingly difficult to optimize experimental conditions using the standardempirical methods that have been successful in the past. A fundamental understanding ofthe CVD process, coupled with accurate diagnostic techniques, would greatly accelerate theoptimization procedure and could also lead to novel deposition methods. We are currentlydeveloping experimental techniques for in -situ measurement of the reactive chemical speciesconcentrations in a CVD reactor. This effort is closely coupled to a theoretical programaimed at developing a realistic, predictive model based on basic laws of physics andchemistry. Our current efforts are directed at defining the role that gas -phase fluiddynamics and gas -phase chemistry play in the deposition mechanism. We have found that gas -phase chemical kinetics is more important than has been previously recognized.Analytical measurements inside a CVD reactor during deposition pose a difficult chal-lenge to the experimentalist. The ideal probe for such measurements must be non -intrusive,selective, sensitive enough to measure sub -torr partial pressures, quantitative, general,and capable of high spatial resolution in the presence of rapidly changing chemical andtemperature fields. Optical methods that employ a crossed -beam arrangement such as Ramanspectroscopy and laser- excited fluorescence come very close to meeting all these require-