Microstructural and Electronic Properties of Hydrogenated Amorphous Silicon Films Deposited by Magnetron Reactive Sputtering.

Abstract

Hydrogenated amorphous silicon (a-Si:H) films have been deposited by dc magnetron reactive sputtering in an Ar+H₂ working gas. In this process, the hydrogen content A controlled by two independent variables: the substrate temperature and the hydrogen partial pressure in the deposition chamber. For a wide range of deposition conditions studied, it is shown that total hydrogen content of the films, as inferred from IR absorption, is uniquely related to the hydrogen bonding and the microstructure. We report films of high electronic quality, deposited between 200–300 °C, in which hydrogen bonding varies from predominantly SiH to mixed SiH and SiH₂ modes as the hydrogen content is increased. This struciral change is reflected in hydrogen evolution spectra. In addition to peaks at ˜500 and ˜600 ° C, a low-temperature peak (350–400 C) has been observed for the films which have high hydrogen content and consequently are rich in SiH₂. The low temperature peak is absent in SiH dominant films. However, the low-temperature peak is not associated with a columnar morphology because SEM images of fracture cross-sections are featureless for SiH dominant films and have a “bumpy” texture for high SiH₂ content films. We propose that in our SiH₂ rich films, excess hydrogen leads to a void rich but non-columnar morphology. Preliminary measurements of the Staebler-Wronski effect using AM-1 light show a low susceptibilty to degradation in both types of films. The different electronic properties of the films indicate that the quality of magnetron sputtered films does not necessarily correlate with the IR absorption peaks in a simple manner.