Abstract

Plasma-enhanced deposition and etching methods are finding applications in materials processing, thermal management, microstructure fabrication, and optics. Dry etching methods are mandatory for high yield microcircuits when the required features are <3 μm. Glow discharge preparation and processing of materials depend not only on the method of coupling the electrical energy into the plasma, but also on various other parameters such as the gas mixture, gas residence time, substrate bias, substrate position, and power into the plasma. The films grow or are etched in contact with the plasma or adjacent to it. Their properties are affected by the plasma species and, hence, by the homogeneous reactions occurring in the discharge, and by the heterogeneous reactions at the surface. The need for clarification of the more important of these reactions has given impetus to several new optical diagnostics. This paper reviews recent progress in Stark spectroscopy of the time-varying fields in the plasma sheaths (including Rydberg state spectroscopy), the fields of the different regions of dc glow discharges, emission and tunable laser diode absorption spectroscopy, photodetachment spectroscopy, and laser-induced fluorescence. Optical methods that may have future application are also mentioned. The data derived from the diagnostics permit the determination of the principal mechanisms involved in the deposition and etching of thin films. Taking amorphous silicon as an example, the results are compared with kinetic models that use the Boltzmann transport equation to calculate the plasma reactor dissociation, ionization, and conductivity. Combined with other collision experiments, the results permit interpretation of the influences of buffer gas, gas mixture, residence time, and applied frequency.

© 1986 Optical Society of America