Atomic layer deposition of silicon nitride barrier layer for self-aligned gate stack

The surface chemical processes needed to optimize subsequent deposition steps and to grow self-aligned structures have been investigated for gate dielectric formation. UV-Cl ₂ exposures were used to terminate bare silicon surfaces with chlorine atoms (10% Cl ₂ in N ₂ at 150°C and 100 Torr for 10 min, 1000 W Xe arc lamp). Exposure to NH ₃ and UV-NH ₃ chemistries (10% NH ₃ in N ₂ at 80°C for 10 min) replaced the chlorine atoms with amine (-NH ₂) groups, intended as the foundation of a silicon nitride diffusion barrier. By providing a more reactive surface, ALD of silicon nitride occurs at lower temperatures (<100°C) and with better initial deposition rates compared to deposition on hydrogen terminated silicon. Surface activation by UV-Cl ₂ is selective for Si over SiO ₂, enabling deposition of self-aligned nitride and dielectric films. The amine surface coverage saturates at less than one monolayer and is equilibrium limited. UV illumination increased amine coverage at similar conditions.