Nucleation and growth during tungsten atomic layer deposition on SiO2 surfaces

The nucleation and growth during tungsten (W) atomic layer deposition (ALD) on SiO2 surfaces was examined using Auger electron spectroscopy (AES) tech niques. Tungsten ALD was performed on a hydroxylated silica (SiO2) surface using repeated exposures to disilane (Si2H6) and tungsten hexafluoride (WF6 ) in an ABAB... sequence at 573 K. The AES measurements revealed that W gro wth is slow during the first similar to 10 AB reaction cycles using similar to 10(5) Langmuir reactant exposures. Following this initial nucleation pe riod, the tungsten film grew linearly at 2.5 Angstrom per AB cycle. The W a nd Si AES signals dramatically oscillated in magnitude versus the sequentia l Si2H6 and WF6 exposures in the linear growth regime. Comparison of the ex perimental AES signals with predicted AES signals assuming different growth mechanisms determined that tungsten grows in a layer-by-layer fashion foll owing the Frank-van der Merwe mechanism. Quantitative modeling indicated th at electron backscattering effects must be included to describe the absolut e experimental AES signals during W ALD. Simulations also revealed that the mechanism of tungsten nucleation during the first similar to 10 AB reactio ns cycles will affect the surface roughness of the tungsten films. More rap id nucleation of W ALD was achieved using a larger initial Si2H6 exposure o f > 10(10) Langmuir, or by repeatedly probing the same location on the SiO2 surface with the AES electron beam. (C) 2001 Published by Elsevier Science B.V. All rights reserved.