Si(100) wafers with oxide thicknesses of 40 and 200 Å were implanted with ${\mathrm{Ge}}^{+}$ and ${\mathrm{As}}^{+}$ ions with energies from 20 keV to 1 MeV. Low ion doses, ∼${10}^{11}$ ions/${\mathrm{cm}}^2$, were used to avoid overlap of collision cascades. The extent of cascade damage at the ${\mathrm{SiO}}_2$/Si interface due to single ion impacts was examined by scanning tunneling microscopy after the oxide layer was removed by HF. The surface topography in the form of craters was found to relate to the cascade damage rather than to the removal of atoms by sputtering. There is a 1:1 correlation between the number of ion impacts and the number of craters. The crater diameter as a function of implant-ion energy agrees well with theoretical estimates of the lateral extent of the cascade due to nuclear energy deposition at the interface.

• Received 27 April 1988

DOI:https://doi.org/10.1103/PhysRevB.38.8444