The Bombardment Angle Dependence of the Sputtering and Secondary Ion Yield for Oxygen Ion Bombardment of Silicon

Abstract

From theoretical considerations, we have derived a mathematical relationship which correlates the angle of bombardment with the sample sputtering yield, the incorporated concentration of the bombarding ion and secondary ion intensities. Data from other researchers was then used to provide points of reference for the derived relationships.If silicon is bombarded with oxygen and no additional oxygen flooding takes place, the following implications on instrument performance can be concluded. It appears from experiment that instruments with a large deviation of the angle of incidence from the target normal give a relatively large sputter yield S together with small values of the ion yield S+. Here the steady state is characterized by a relatively large sputter yield of 1,8 and a correspondingly large value of the sputter rate ż. On the other hand, the oxygen coverage is small, θ = 0,6. The latter as has been reported before (MORGAN and WERNER [1], DELINE, et al., [2], implies a low degree of ionization ο+. Consequently, the secondary ion current will be relatively low. Instruments which are operated with normal incidence were found to have a small sputtering yield, a relatively high ion yield and secondary ion intensity. This can be understood from the deviations which show a low value for the sputtering rate and a large value for the surface concentration of oxygen. Therefore, a decrease in the rate of atom ejection as determined by the sputtering yield will lead to a significantly larger ion yield and secondary ion intensity due to the power function dependence of secondary ion yields on the implanted oxygen concentration. With oxygen bombardment oxygen flooding, the trend is the same, but the difference between the two modes is not as pronounced.