Enhancement of SiN-induced compressive and tensile strains in Si free-standing microstructures by modulation of SiN network structures

Strain-induced enhancement of carrier mobility is essential for achieving high-speed transistors. The effects of thermal-annealing (temperature: 400-1150°C) and ultraviolet (UV) laser-annealing (wavelength: 248 nm, temperature: 30-400°C) on strain-enhancement in Si-pillars covered with Si ₃N ₄ stress-liners by plasma-enhanced chemical vapor deposition are investigated. Before annealing, the Si ₃N ₄ stress-liners induce a tensile strain (∼0.5%) in Si. After thermal-annealing (> 800°C), the strain becomes highly compressive (> ∼0.4%), because of dehydrogenation-induced structural relaxation in Si ₃N ₄ films. On the other hand, the tensile strain becomes large (>~0.7%) after UV laser-annealing at 400°C, due to non-equilibrium dehydrogenation in Si ₃N ₄ films. This strain-enhancement technique is useful for the realization of advanced high-speed three-dimensional transistors.