COMPARISON OF MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF HYDROGEN AND SILANE REDUCED LOW-PRESSURE CHEMICAL VAPOR-DEPOSITED TUNGSTEN FILMS

We have compared the physical, mechanical, microstructural, and structural properties of tungsten thin films produced by reducing tungsten hexaflouride by silane and hydrogen. We show that despite similarities in chemical composition and film density, the films exhibit differing film hardness and elastic compliances. The origin of the differences is shown to arise from the differences in film growth rate and the incorporation of impurities during film growth. Hydrogen reduction results in the formation of second phase W20O58 particles in the tungsten bulk, which leads to film hardening. Silane reduced films show strong texture in the [110] direction, which decays with increasing film thickness. Silane films also show a larger tensile stress and faulted microstructure. Extensive transmission electron microscopy analysis has been carried out and the results have been correlated to x-ray diffraction studies. We also have studied the surface morphology of the films and show clustering of grains which results in a larger surface feature, compared to the average grain size of the film. As a result of this study, we show the need to complete film characterization prior to changing chemistries to meet specific macroscopic film properties such as film step coverage.