Hot-Wire Assisted ALD: A Study Powered by In Situ Spectroscopic Ellipsometry

Hot-wire assisted atomic layer deposition (HWALD) is a novel energy-enhancement technique. HWALD enables formation of reactive species (radicals) at low substrate temperatures, without the generation of energetic ions and UV photons as by plasma. This approach employs a hot wire (tungsten filament) that is heated up to a temperature in the range of 1300–2000 °C to dissociate precursor molecules. HWALD has the potential to overcome certain limitations of plasma-assisted processes. This work investigates the ability of a heated tungsten filament to catalytically crack molecular hydrogen or ammonia into atomic hydrogen and nitrogen-containing radicals. The generation of these radicals and their successful delivery to the wafer (substrate) surface are experimentally confirmed by dedicated tellurium-etching and silicon-nitridation experiments. It further reports on deposition of low-resistivity oxygen-free tungsten films by using HWALD, as well as on the effect of hot-wire-generated nitrogen radicals and atomic hydrogen in deposition of aluminum nitride and boron nitride films. In parallel, this work provides important illustrative examples of using in situ real-time monitoring of deposition and etching processes, together with extracting a variety of film properties, by spectroscopic ellipsometry technique.