Growth kinetics of tungsten microstructures produced via the hydrogen reduction of tungsten hexafluoride on laser-heated substrates

Abstract

Laser-assisted chemical vapor deposition of tungsten microstructures (dots, stripes, or films) has been accomplished via the H2 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 μm in diameter. The morphology and height of these dots were determined as functions of deposition parameters by profilometer measurements. The effects of WF6 and H2 partial pressures on the morphology and deposition rate of W dots were investigated at a laser-induced surface temperature ranging from 340 to 950 °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 °C) and high H2 partial pressures (50–700 Torr), the deposition rate of Gaussian W dots was proportional to the square root of the H2 partial pressure. At high temperatures (750–950 °C) and reduced H2 partial pressures (20–80 Torr), the deposition rate of these dots was proportional to the H2 partial pressure. This reaction order equal to 1 was interpreted on the basis of the Rideal model involving a direct reaction between H2 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 H2 reduction of WF6 promoted by laser irradiation of the deposition zone or accomplished in a conventional furnace-type reactor is discussed and proposed.