Tailoring the Structure of Low-Temperature-Deposited Microcrystalline Silicon Films by Biasing the Substrate

Abstract

ABSTRACTBiasing the substrate during deposition and the substrate's surface morphology may both have major effects on the structural properties of thin films. We present the results of structural investigations (Raman and FTIR spectroscopy, XRD, SAXS) of thin silicon films that were prepared at low temperatures by electron-cyclotron resonance (ECR) chemical-vapor deposition. The effect of substrate bias during the deposition was investigated for positive DC susceptor biases VB ranging from 0 to 45 V. For stainless steel substrates with an artificially enlarged surface roughness (smart substrates), an increase of the crystallinity could be observed with Raman spectroscopy. Films prepared under a susceptor bias of +15 V exhibited a texture inversion of preferential (220)- to (111)- oriented grains, which was accompanied by an increase in grain size from 18 to 42 nm. Small-angle X-ray scattering (SAXS) revealed the films as deposited on Al foil to exhibit significant free volume fractions (microvoids). The ability of tailoring the structure of thin Si films by applying a bias is discussed in terms of controlling the energy and intensity of ion flux to the surface of the growing film. This can efficiently be achieved in an ECR system, where the mean free path of gas particles exceeds the thickness of the plasma sheath.