Sputter rates for sub-keV primary beam energies are investigated with atomic force microscopy measurements of crater step heights. Using a 800 eV O-2(+) sputtering beam at an incidence angle of 50 degrees with oxygen flooding, the surface swells as the implanted oxygen forms an altered layer. After a fluence of 1E17 O/cm(2), the sputter rate reaches equilibrium. Characteristic parameters such as the depth scale offset, z(d)(0), and the apparent initial silicon surface z(Si)(0), are extracted from the data (0.6 and -1.3 nm, respectively), and the magnitude of the profile shift is discussed in terms of the final profile accuracy.