The effect of oxygen flooding during ultrashallow depth profiling using secondary ion mass spectrometry (SIMS) was studied on a silicon sample implanted with 2 keV boron. SIMS depth profiles were obtained on a Cameca IMS6f using low energy (1 keV) O-2(+) primary beams at 56 degrees incident angle. Different oxygen flooding conditions were used to investigate the dependence of crater bottom composition and roughening on oxygen partial pressure. The development of surface oxidation state and the thickness of the silicon oxide layer formed at the crater bottom during sputtering were determined using small area high resolution x-ray photoelectron spectroscopy. It is shown that the oxidation states during sputtering are dominated by Si-0 (elemental Si) and Si4+(SiO2) with small contributions from other silicon suboxides, i.e., Si1+(Si2O), Si2+(SiO), and Si3+(Si2O3). The calculated equilibrium oxide thickness was found to increase with oxygen partial pressure. The sputtering induced surface roughening on the crater bottom was characterized using atomic force microscopy as a function of depth and oxygen partial pressure. Surface roughening appears to be suppressed under higher oxygen partial pressures, and is related to the nature of the oxide formed.