Reduction in surface roughness during secondary ion mass spectrometry depth profiling with an ion-milling method J.Effects of oxygen flooding on crater bottom composition and roughness in ultrashallow secondary ion mass spectrometry depth profiling Secondary ion mass spectrometry analysis of through-oxide ion implantation in silicon often exhibits strong matrix effects across the SiO 2 /Si interface. In this study we explored the analytical conditions that required minimal correction for the variation in the relative sensitivity factors and the sputtering rates across the interface. We found that an O 2 ϩ beam at 1 keV and 46°provided an equal sputtering erosion rate for SiO 2 and Si. Under these sputtering conditions, the SiO 2 surface remained smooth, but Si became rough ϳ50 nm below the SiO 2 /Si interface. A complete depth profile of B implantation through oxide was obtained by utilizing the 1 keV 46°O 2 ϩ beam in SiO 2 and across the SiO 2 /Si interface and a 1 keV 60°O 2 ϩ beam deeper in the Si substrate. The data exhibited an apparent drop in the concentration of the implanted B at the SiO 2 /Si interface which was attributed to a phase transition in the matrix from amorphous to crystalline. In addition, analyses of an ion-beam synthesized oxide ͑5 keV O 2 ϩ at normal incidence͒ confirmed the occurrence of outdiffusion of B in the altered layer. Also, the results indicated preferential sputtering of B at the surface.