Microstructure of thin films prepared by plasma-enhanced chemical vapour deposition of helium-diluted silane

The present paper describes an investigation on the microscopic structure of silicon thin films made by plasma-enhanced chemical vapour deposition (PECVD) in conditions different from those typically applied in the preparation of hydrogenated amorphous silicon. Gas mixtures containing helium silane, and diborane have been used. High radiofrequency power densities have been applied, so that a quasi-equilibrium is reached between film growth and selective etching due to ion bombardment. The specimens have been analysed using infrared-absorption spectroscopy, atomic-force microscopy, X-ray diffraction, Raman spectroscopy and photothermal-deflection spectroscopy. The results clearly indicate two phases in the material: microcrystalline and amorphous. The preparation approach can, thus, be considered an alternative to hydrogen dilution for making microcrystalline-silicon thin films. (C) 1999 Elsevier Science B.V. All rights reserved.