Abstract

This is a program to develop and demonstrate laser diagnostics of compound semiconductor processing systems, such as the metal-organic chemical-vapor deposition (MOCVD) of III–V and II–VI materials. It focuses on tunable infrared diode-laser absorption, a technique capable of high-sensitivity quantitative measurements of absolute concentrations of both radicals and stable molecules. A long-path plasma reactor is used to generate easily detectable amounts of a wide variety of radical species in plasmas that include organoarsine compounds or methane. These latter systems have their own intrinsic interest because of their applications in diamond and hard-carbon deposition, as well as gallium arsenide etching. In addition, they contain the hydrocarbon species that are also important in MOCVD. Results to date in methane plasma observations include measurements of the methane dissociation fraction and rotational temperature and the measurement of the absolute concentrations of the decomposition products CH₃, C₂H₄, and C₂H₂. The dissociation fraction is large, reaching about 0.9 at applied powers above 500 W. C₂H₂ and C₂H₄ concentrations are large, but CH₃ concentrations are much smaller, on the order of 10⁴ of the total. Plasma temperatures are low, under400 K for all conditions observed to date. Also planned are observations of arsenic hydride species, which may play a key role in suppressing carbon incorporation in MOCVD.

© 1990 Optical Society of America