Nucleation and Growth During Tungsten Atomic Layer Deposition on Oxide Surfaces

ABSTRACTNucleation and growth has been studied during tungsten (W) atomic layer deposition (ALD) on oxide surfaces. Auger electron spectroscopy (AES) was utilized to examine the deposition of W during the sequential (A) WF6 and (B) Si2H6 reaction cycles that define W ALD. The AES results displayed an initial nucleation period of ∼10 AB cycles to deposit one tungsten monolayer on SiO2. Subsequently, the W and Si AES signals grew and oscillated dramatically versus WF6 and Si2H6 exposures. The increase in the W AES signal in the growth region was consistent with a W ALD growth rate of 3.5 Å per AB cycle. An examination of the oxygen and tungsten AES signals versus AB cycles indicated that W ALD displayed nearly ideal “layer-by-layer”, Frank- van der Merwe growth after the nucleation period. On Al2O3, the AES results displayed a much shorter nucleation period for W ALD. Only 3 AB cycles were required to deposit one tungsten monolayer. Subsequently, the tungsten film grew at a rate of 3.6 Å per AB cycle. The initial nucleation period and growth mechanism during ALD are important because they will affect the roughness of the resulting ALD film.