Comparison of Different Methods to Characterize Thin a-Si:H Films

The objective of this work is to determine the materials properties of thin layers typically deposited for wall conditioning in fusion devices. As reference material, a sequence of thin amorphous hydrogenated silicon layers with different thicknesses were produced on polished glassy carbon by Plasma Chemical Vapour Deposition PCVD. The films were characterised using AES, AFM, EPMA, ellipsometry, interference fringe analysis and RBS. A second aim was to study the accuracy and reliability of EPMA and RBS measurements. The techniques applied provided values for refractive index, absorption coefficient, roughness, thickness and elemental areal density. From the latter two, the density of the film could be determined. It turned out that the density derived by combining the results from different techniques was in good agreement. For the range of thickness investigated, the combination of ellipsometry and EPMA gave the most consistent values for the density with a maximum uncertainty of ±5%.