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

Highlights: • A highly selective MoSi_x deposition has been achieved on Si in preference to SiO₂ and SiN_x using MoF₆ and Si₂H₆. • MoF₆ nucleates on H-terminated Si in a self-limiting manner but shows inherent non-reactivity on SiO₂ and SiN_x substrates. • MoSi_x film was atomically conformal and flat with a RMS roughness of 1.7–2.8 Å. • Atomic Force Microscopy records that there were 9 nuclei/µm² after MoSi_x deposition on SiO₂ which is 10⁶:1 selectivity between OH-SiO₂ and H-Si. • This extreme selectivity was verified on nanoscale 3D structures. Highly selective deposition of MoSi_x on Si in preference to SiO₂ and SiN_x 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 SiN_x substrates. In contrast, MoF₆ nucleated in a self-limiting manner on H-terminated Si, and a following Si₂H₆ exposure reduced MoF_x 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 SiN_x. 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 MoSi_x was investigated on a patterned Si wafer containing three-dimensional (3D) nanoscale SiO₂ and SiN_x features. Cross-sectional transmission electron microscopy (TEM) showed that selective MoSi_x 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.