Thickness and strain determinations of thin film systems by x-ray analysis

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Virginia Polytechnic Institute and State University


X-ray diffraction techniques were used to determine thicknesses, and strains in sputtered polycrystalline thin films of molybdenum and titanium on silicon single crystal substrates. The thickness determination method used was an extension of a previous method wherein the orientation function determined from experimental data obtained in only a part of the angular range in chi could be fitted with Legendre polynomials and extrapolated to chi=90°. The fitted orientation functions were then used to accurately calculate the thickness of the thin films. The method proved to be theoretically consistent.

The residual strain measurements completed on the thin films were determined using the sin²x method of analysis. Strains were determined from x-ray peak shifts and then plotted against sin²x. Tensile stresses were found to be present in the titanium sample while compressive stresses were present in the molybdenum sample. Lattice expansions were recorded in both film samples (as received condition). These expansions were correlated to the presence of argon as reported by previous authors. Other effects which could have produced additional residual strains were also noted (i.e., thermally induced dislocations, etc.).