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 o f silicon thin films made by plasma-enhanced chemical vapour deposition (PE CVD) in conditions different from those typically applied in the preparatio n 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 se lective etching due to ion bombardment. The specimens have been analysed us ing infrared-absorption spectroscopy, atomic-force microscopy, X-ray diffra ction, Raman spectroscopy and photothermal-deflection spectroscopy. The res ults clearly indicate two phases in the material: microcrystalline and amor phous. 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.