Composition of Ge+ and Si+ implanted SiO2/Si layers: Role of oxides in nanocluster formation

Abstract

X-ray photoelectron spectroscopy (XPS) has been used to examine the atomic content of implanted SiO2/Si layers. In particular, an XPS analysis permits to identify elemental Ge and Si, as well as GeO2 precipitations in SiO2 matrices. The XPS results reveal valuable information not only about the formation mechanism of Ge and Si nanoclusters but also on the annealing kinetics of SiO2 whose properties are known to be significantly altered during the process of ion implantation and subsequent annealing. The composition of ion beam-modified SiO2 layers strongly depends on the annealing temperature. With respect to germanium implanted samples a possibility of Ge nanocrystals formation appears at high (above 1000°C) annealing temperatures. It has been shown that an intermediate step in the Ge oxide formation is necessary for the creation of Ge nanoclusters. Additionally, the presence of a subsurface zone GeOx (about 100nm thick) predicted in kinetic three-dimensional lattice simulations has been confirmed. In the case of Si+ implanted samples substoichiometric silicon oxide lines in the XPS spectra of a SiO2 layer for all samples have been observed. No evidence of a line connected to the Si–Si bonding has been observed even at the highest annealing temperatures, at which only stoichiometric SiO2 has been detected.