Role of ion energy in ion beam oxidation of semiconductors: Experimental study and model

Abstract

Ion beam oxidation (IBO) is a low temperature growth technique where a directional low energy (≤1 keV) ion beam introduces the oxygen into the substrate and athermally activates the chemical reaction leading to the oxide growth. In this work, IBO of Si, Ge, Si1−xGex was investigated experimentally as a function of ion energy from 100 eV to 1 keV. The results show a strong dependence of the materials properties such as phase formation, stoichiometry, and thickness upon the ion energy. To investigate the kinetics of IBO and to account for the observed relationship between ion energy and films properties, three models were successively developed taking progressively into account: (1) ion implantation and sputtering (model IS), (2) replacement and relocation events, i.e., ion beam mixing effects (model ISR) and (3) oxygen diffusion (model ISRD). The simulation results show that the model IS based only on implantation and sputtering cannot explain the oxide thickness dependence upon ion energy observed experimentally, but can give qualitative information on the phases formed by IBO. Ion beam mixing effects in the model ISR lead to spatial redistribution of the elements in compound targets and account for the evolution of stoichiometry as a function of depth. Thermal and point defect mediated diffusion of free oxygen and the strong driving force for oxidation must be considered to account for the observed thicknesses, sharp interfaces and kinetics of IBO growth in three stages.