Selective atomic layer deposition of MoSix on Si (0 0 1) in preference to silicon nitride and silicon oxide

Abstract

Highly selective deposition of MoSix on Si in preference to SiO2 and SiNx was achieved via atomic layer deposition (ALD) using MoF6 and Si2H6 at 120 °C. The selectivity was enabled by the lack of chemical reactivity between the reactants and the SiO2 and SiNx substrates. In contrast, MoF6 nucleated in a self-limiting manner on H-terminated Si, and a following Si2H6 exposure reduced MoFx to Mo0 which is consistent with Mo-Si bond formation. X-Ray photoelectron spectroscopy (XPS) revealed that the 5 ALD cycles of MoF6 and Si2H6 selectively deposited a substoichiometric MoSi2 film on the Si substrate in contrast to previous results showing a nearly pure Mo deposition. Extra Si2H6 doses on the substoichiometric MoSi2 film incorporated more Si into the film without disturbing the inherent selectivity over SiO2 and SiNx. A depth-profiling study showed that the bulk of the film has Si/Mo = 1.7–1.9 with <10% F and O impurities. The data is consistent with higher pressure Si2H6 doses inducing silicide formation instead of metal deposition. To verify selectivity on the nanoscale, the selective deposition of MoSix was investigated on a patterned Si wafer containing three-dimensional (3D) nanoscale SiO2 and SiNx features. Cross-sectional transmission electron microscopy (TEM) showed that selective MoSix deposition was achieved on nanoscale 3D structures. AFM documented that there were less than 10 nuclei/µm2 on SiO2.; since SiO2 has ∼106/µm2 OH groups, this corresponds to an intrinsic selectivity of about 106:1 between the OH groups on SiO2 and Si-H groups on Si. This inherent substrate-dependent selectivity for silicide deposition allows the elimination of pre-positioning of passivants.