Surface Chemistry during Atomic-Layer Deposition of Nickel Sulfide from Nickel Amidinate and H2S

Abstract

Atomic-layer deposition (ALD) of metal-sulfide thin films has recently been developing very fast, and many new metal-sulfide ALD processes have emerged during the past several years. Surface chemistry plays a key role in ALD, but it remains yet to be investigated for many recently developed sulfide ALD processes. We herein report our study on the surface chemistry of the ALD of nickel sulfide from bis(N,N′-di-tert-butylacetamidinato)nickel(II) and H2S, using the in situ characterization techniques of X-ray photoelectron spectroscopy, low-energy ion scattering, quartz crystal microbalance, and quadrupole mass spectrometry. The surface chemistry is found to deviate from the conventional ligand-exchange ALD scheme, and a formation of a nonvolatile acid–base complex from acidic surface sulfhydryl and basic amidine is suggested during the H2S half-cycle. Since the precursors used herein are fairly representative, the findings should be of valuable reference for many other metal-sulfide ALD processes.