Characterization of Silicide Formation of LPCVD-W By Means of Rutherford Backscatrering Spectrometry and X-Ray Diffractometry

Tungsten disilicide (WSi2 ) was formed by annealing 185 nm and 750 nm thick LPCVD-W films deposited on <100>-Si substrates. The thickness of the formed WSi2 was observed by Rutherford backscattering measurements (RBS) to increase parabolically with the annealing time. This agrees with the behavior reported in the literature for sputter deposited or evaporated W films. However, a higher stlicide growth rate was found in this work. An activation energy of 2.6 eV/atom was measured, which is smaller than those for sputter deposited or evaporated W films. The crystal structures of the formed WSi2 and the unreacted W films were analyzed using X-ray diffraction (XRD) technique. The thermal history of the samples was found to play an important role for the crystal structure of the unreacted W and formed WSi2. The as-deposited W films became more oriented to the <100> direction with increasing film thickness, while the unreacted W films on top of the formed WSi2, from the samples annealed at temperatures from 700 to 800°C, became more <100> direction dominated with decreasing W film thickness. The preferred orientation of the grown WSi2 films also varied with the silicidation conditions. These observations indicate that the simple method of determining W film thickness by comparing the W diffraction peak heights of the remaining W films after heat treatment to a reference sample will unavoidably introduce large errors. A compensation technique was suggested where both the W and WSi2 diffraction signals were used. A parameter x, a function of reacted W thickness, was introduced to fit the compensation procedure. The conclusion of this study is that attention should be paid to the orientation change of W and WSi2 films during heat treatment if XRD is employed to study the kinetics of WSi2 formation.