Sputtering rate change and surface roughening during oblique and normal incidence O2+ bombardment of silicon, with and without oxygen flooding

Abstract

A sample of low-temperature epitaxial Si grown with five B delta-doped layers 5.4 nm apart has been profiled using secondary ion mass spectrometry under a variety of O2 bombardment conditions. Energies from 400 eV to 1.5 keV were used with angles of incidence from 0° to 70°. Analyses were performed using oxygen flooding of the sample surface during analysis, as well as without using oxygen flooding. The apparent spacing between the B delta layers was used to determine the magnitude and extent of increased sputtering rate at the beginning of an analysis. Changes in depth resolution due to sputter-induced surface roughening are reflected in variations in the apparent width of the B delta layers. It was found that sputtering with 500 eV O2 at an angle of 50° while flooding with oxygen produced no measurable change in sputtering rate and resulted in no unexpected shift towards the surface of the B delta layers. These analysis conditions also resulted in a depth resolution which was as good as that obtained using 400 eV O2 bombardment at 0° incidence without oxygen flooding. The 0° method of analysis, however, resulted in a 1.1 nm shift of the topmost B delta layer toward the surface, and the 0° method had a sputtering rate only 1/5 that of the 50° method of analysis.