Secondary ion mass spectrometry and atomic force spectroscopy studies of surface roughening, erosion rate change and depth resolution in Si during 1 keV 60° O2+ bombardment with oxygen flooding

Abstract

Oxygen flooding during secondary ion mass spectrometry (SIMS) depth profiling is often used to achieve very short surface transients. However, for low-energy and obliquely incident O2+ primary beams, oxygen flooding can be detrimental. In this work we have measured as a function of depth the erosion rates, surface topographies and depth resolution for B and Ge in Si bombarded by 1 keV 60° O2+ with and without oxygen flooding. Using B and Ge deltas we showed that the erosion rate under oxygen flooding was not constant. The effect was most pronounced at intermediate flooding pressures; at saturation pressures, a drop of 25%–30% was found within ∼25 nm below the surface. Atomic force microscopy measurements revealed that the erosion rate change was related to the onset of surface roughening. Oxygen flooding influenced the depth resolution in terms of the decay length for B and Ge in different ways. With oxygen flooding, the Ge decay length was larger than without flooding due to oxide-enhanced segregation; while the B decay length was smaller, due to swelling of the sample. In terms of the delta peak width, best depth resolution was always obtained without flooding. This study showed that oxygen flooding impedes accurate ultrashallow SIMS depth profiling.