David Winfield Woodruff

Chemical vapor deposition of fine-grained equiaxed tungsten films

Abstract A method is described whereby fine-grained equiaxed tungsten films can be deposited by chemical vapor deposition (CVD). Special techniques are required to obtain the equiaxed grain structure and are generally not known. The method described here consists of a high velocity jet of reactant gases directed at the substrate from close proximity. The equiaxed structure results from gas phase formation of tungsten particles which are impinged on and become part of the depositing surface. These particles become the renucleation sites which are necessary to avoid the more common columnar grain structure. The grain size as measured by scanning electron microscopy ranges from 0.04 to 5 μm depending on deposition conditions and is equiaxed. Aerosol capture theory has been applied to this process and predicts correctly the velocity gradient at which the process becomes effective at producing equiaxed films.