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

Abstract

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.

Electrical characterization of hot-wire assisted atomic layer deposited Tungsten films

“…Secondly, multiple reactions take place in plasma: the wafer may be exposed to unwanted radicals, atoms, ions, or UV photons [13]. Recently, we developed a novel approach to ALD, the so-called Hot Wire assisted ALD (HWALD) [14]. A hot wire takes the place of the plasma as the radical source.…”

From radical-enhanced to pure thermal ALD of gallium and aluminium nitrides

“…A plasma power of 2 kW, process temperature of 350 o C, and reactor pressure of 1 mbar were maintained during the experiments, unless otherwise mentioned. (111) wafers were used as substrates. Prior to ALD, they were cleaned from organic and metallic contaminants using 99 %-and 69 %-by-vol.…”

“…Three plasma compositions were used for surface pre-treatment: NH3-, N2-H2-, and H2-plasmas. Si (111) substrates were used in all cases. The composition, the pre-treatment duration, and the plasma power had varying effects on the AlN polycrystallinity ( Fig.…”

“…The molecules impinge on the heated filament surface and catalytically dissociate into radicals 110 , which then take part in the film-forming reactions. Such an ALD process is termed 'hot-wire assisted ALD' (HWALD) 111 . In this thesis, all three activation techniques (namely, thermal, plasma and hot-wire) have been explored for the ALD of (Al)GaN films.…”

Conduction and Electric Field Effect in Ultra-Thin Tungsten Films

“…Secondly, multiple reactions take place in plasma: the wafer may be exposed to unwanted radicals, atoms, ions, or UV photons [13]. Recently, a novel approach to ALD was developed, the so-called hot-wire assisted ALD (HWALD) [14]. A hot-wire takes the role of the plasma as the radical source.…”