Stress-relaxation mechanism in ultra-thin SiGe on insulator formed by H⁺ irradiation-assisted Ge condensation method

The mechanism for the stress-relaxation in the Ge condensation induced by H⁺ irradiation-assisted oxidation method was investigated. Relaxation ratio of Si_0.7Ge_0.3 (thickness: 28 nm) formed by medium dose H⁺ irradiation (5 × 10¹⁵ cm^{- 2}) and oxidation at 1100 °C was limited to 35%. Post-annealing (1200 °C) improved this value significantly (70%), though defect density was found to be kept at low density (< 10⁶ cm^{- 2}). However, the height of cross hatches was increased (from 0.6 nm to 4.1 nm) after post-annealing. Based on these results, local-area slipping model was proposed, where slipping at SiGe/SiO₂ interface of local areas surrounded by cross hatches enhanced stress-relaxation. This model could quantitatively explain the stress-relaxation enhanced by combination of H⁺ irradiation, oxidation-induced Ge condensation, and post-annealing.