18O studies of altered layers formed in Si and SiO 2 by ion bombardment

Abstract

(100) silicon targets have been bombarded by an 18O + 2 beam in-situ in a SIMS instrument. Bombardment was carried out at normal incidence at a variety of energies between 2 and 14 keV. The target behaviour was monitored by following negative secondary ions until a steady state had been achieved. Following oxygen bombardment the modified layer was then depth profiled by SIMS, in-situ, using a low energy Xe primary and negative secondary ions. The thickness of the synthesised oxide was determined from these Xe analyses. Within this energy range the thickness of the synthesised layer falls, with an energy dependence approximately proportional to E 0.75. 18O + 2 beams were also used to bombard a natural thermal oxide on silicon to simulate the bombardment which occurs once a synthesised oxide has formed. The isotope ratio of the sputtered oxygen flux has been measured as a function of fluence for normal incidence and at a variety of angles at 15 keV. The equilibrium isotope concentration of the sputtered flux is found to be dependent upon the angle of bombardment. These changes in isotope ratio are related to the changes in sputter rate for the different bombardment conditions.