Structural inhomogeneity and silicon enrichment of buried SiO2 layers formed by oxygen ion implantation in silicon

The microstructure and electrical properties of buried ${\mathrm{SiO}}_{\mathrm{2}}$ layers produced in silicon by the implantation of oxygen ions are analyzed in terms of implantation parameters and supplemental incorporation of oxygen. The buried oxides show inhomogeneous etching in aqueous HF, revealing the presence of a crystalline oxide phase and Si-enriched regions. Silicon enrichment in ${\mathrm{SiO}}_{\mathrm{2}}$ is found in the form of Si inclusions and oxygen deficient network defects. The former are found to be sensitive to the oxygen implantation profile, and may arise as a result of a blockage of Si outdiffusion by crystalline oxide inclusions. The network defects, in turn, are predominantly generated during high temperature postimplantation annealing, caused possibly by some mechanism of silicon transport from the interfaces into the bulk of oxide. The electron trapping and electrical conduction characteristics of buried oxides are found to correlate with the density and size of the inhomogeneities. By contrast, hole trapping and the generation of positive charge at the Si/oxide interfaces by exposure to hydrogen at elevated temperature are controlled by the network defects in the bulk of the oxide and in the near interfacial layers, respectively.