A Self-Limited Atomic Layer Deposition of WS2 Based on the Chemisorption and Reduction of Bis(t-butylimino)bis(dimethylamino) Complexes

A novel self-terminating chemical approach for the deposition of WS2 by atomic layer deposition based on chemisorption of bis(t-butylimino)bis-(dirnethylamino)tungsten(VI) followed by sulfurization by H2S is reported. A broad spectrum of reaction parameters including temperatures of the reaction chamber and the precursor and durations of every atomic layer deposition (ALD) step are investigated and optimized to reach a high growth per cycle of 1.7 angstrom and a high quality of the deposited thin films. The self-terminating behavior of this reaction is determined by the variation of the dose of the precursors. Surface- and bulk-sensitive techniques prove that highly pure and well-defined WS2 layers can be synthesized by ALD. Imaging methods show that WS2 grows as platelets with a thickness of 6-10 nm and diameter of 30 nm, which do not vary dramatically with the number of ALD cycles. A low deposition temperature process followed by a postannealing under H2S is also investigated to produce a conformal WS2 film. Finally, a reaction mechanism could be proposed by studying the chemisorption of bis(t-butylimino)bis(dimethylamino)tungsten(VI) onto silica and the thermal and chemical reactivities of chemisorbed species by small-molecule analyses.