INFLUENCE OF ANNEALING TEMPERATURE ON STRUCTURAL, ELECTRICAL AND OPTICAL-PROPERTIES OF WSI2

WSi2 polycrystalline films of different thickness were prepared by low pressure chemical vapor deposition on silicon wafers, and their crystallization properties were studied as a function of the annealing temperature. Structural measurements were performed by X-ray diffraction, detailing for the first time the phase transition from the amorphous to the hexagonal structure at an annealing temperature 380-degrees-C and from hexagonal to tetragonal above 700-degrees-C. The electrical sheet resistance showed the same transition temperatures. Optical characterization was performed by spectroscopic ellipsometry, and the real and imaginary part of the complex refractive index were obtained as a function of the annealing temperature in the 0.25-0.9-mu-m wavelength range. A broad optical band was found for samples annealed up to 700-degrees-C, while for higher annealing temperatures a transparency region for wavelengths greater than 0.5-mu-m and some significant structures appear. A corresponding behavior was observed in the infrared reflectance spectra. Furthermore, it was shown that the determination of the thickness of SiO2 grown on WSi2 requires a multilayer model, taking into account the transparency of tetragonal WSi2.