GROWTH-KINETICS OF TUNGSTEN MICROSTRUCTURES PRODUCED VIA THE HYDROGEN REDUCTION OF TUNGSTEN HEXAFLUORIDE ON LASER-HEATED SUBSTRATES

Laser-assisted chemical vapor deposition of tungsten microstructures (dots, stripes, or films) has been accomplished via the H-2 reduction of WF6 on polycrystalline silicon-coated quartz substrates irradiated with a focused cw argon-ion laser beam. Tungsten dots were grown on the substrates via a pyrolytic process occurring within the laser-heated zone of about 200-mu-m in diameter. The morphology and height of these dots were determined as functions of deposition parameters by profilometer measurements. The effects of WF6 and H-2 partial pressures on the morphology and deposition rate of W dots were investigated at a laser-induced surface temperature ranging from 340 to 950-degrees-C. The deposition rate of flat-topped dots was independent of the deposition temperature and proportional to the WF6 partial pressure. The deposition rate of W dots with a Gaussian profile was independent of the WF6 partial pressure. At low temperatures (340-670-degrees-C) and high H-2 partial pressures (50-700 Torr), the deposition rate of Gaussian W dots was proportional to the square root of the H-2 partial pressure. At high temperatures (750-950-degrees-C) and reduced H-2 partial pressures (20-80 Torr), the deposition rate of these dots was proportional to the H-2 partial pressure. This reaction order equal to 1 was interpreted on the basis of the Rideal model involving a direct reaction between H-2 molecules and fluorinated adspecies on the W surface. The nature of the fluorinated adsorbed phase on the metal surface was discussed in terms of coordination number of W and F atoms. A new reaction mechanism for the H-2 reduction of WF6 promoted by laser irradiation of the deposition zone or accomplished in a conventional furnace-type reactor is discussed and proposed.