The chemical vapor deposition process was used to produce tungsten single crystalline layers of tungsten.This method is based on the reduction of tungsten hexafluoride (WF_6) by hydrogen in a heated reactor to deposit a controlled layer of single crystalline tungsten.The substrates used were molybdenum single crystals.The exhaust gases were cleaned by a commercial scrubber prior to release into the atmosphere.Substrate temperature,reaction chamber pressure,and flow rates of WF_6 and H_2,are critical process parameters during deposition.A comprehensive analysis of the effects of these parameters on single crystal layer growth has been processed and optimized growth conditions have been obtained.Different orientations of the substrate show different deposition rates for tungsten.A low index plane has a high index plane.The kinetics of the deposition process have also been investigated,illustrating that the growth rate is not limited by surface diffusion.Scanning electron microscopy surface analysis indicates that the single crystal layer is smooth in macroscale and is rough and has a step-growth format in micro-scale.
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