Nucleation and growth during tungsten atomic layer deposition on SiO 2 surfaces

Abstract

The nucleation and growth during tungsten (W) atomic layer deposition (ALD) on SiO 2 surfaces was examined using Auger electron spectroscopy (AES) techniques. Tungsten ALD was performed on a hydroxylated silica (SiO 2) surface using repeated exposures to disilane (Si 2H 6) and tungsten hexafluoride (WF 6) in an ABAB… sequence at 573 K. The AES measurements revealed that W growth is slow during the first ∼10 AB reaction cycles using ∼10 5 Langmuir reactant exposures. Following this initial nucleation period, the tungsten film grew linearly at 2.5 Å per AB cycle. The W and Si AES signals dramatically oscillated in magnitude versus the sequential Si 2H 6 and WF 6 exposures in the linear growth regime. Comparison of the experimental AES signals with predicted AES signals assuming different growth mechanisms determined that tungsten grows in a layer-by-layer fashion following the Frank–van der Merwe mechanism. Quantitative modeling indicated that electron backscattering effects must be included to describe the absolute experimental AES signals during W ALD. Simulations also revealed that the mechanism of tungsten nucleation during the first ∼10 AB reactions cycles will affect the surface roughness of the tungsten films. More rapid nucleation of W ALD was achieved using a larger initial Si 2H 6 exposure of >10 10 Langmuir, or by repeatedly probing the same location on the SiO 2 surface with the AES electron beam.