Relaxation mechanism of SiGe-on-insulator by oxidation-induced Ge condensation with H⁺ irradiation and postannealing

Stress-relaxation phenomena in SiGe-on-insulator (SGOI) layers during the oxidation-induced Ge condensation process have been comprehensively investigated as a function of several parameters (SiGe thickness, Ge fraction, oxidation temperature, and oxidation time). Final SiGe thickness-dependent relaxation ratio was found, i.e., complete relaxation for thick (<100 nm) SGOI layers, and abrupt decrease in relaxation ratio with decreasing SiGe thickness below 100 nm, e.g., the relaxation ratio of 30% for the SiGe thickness of 30 nm. An improved method combined with H+ irradiation (5× 10¹⁵ cm ^-2) and postannealing (1200°C) has been examined to enhance the stress-relaxation. This achieved a high relaxation ratio (70%) and a low defect density (1× 10⁶ cm^-2) in the ultrathin (28 nm) SGOI with a Ge fraction of 30%. A local-area slipping model was proposed, where SiGe/ SiO₂ interface slipping occurred during postannealing in local areas surrounded by cross hatches. This model quantitatively explained the enhanced relaxation ratio of the SGOI layers obtained by the Ge condensation method combined with H+ irradiation and postannealing.