The HF-chemical etching process near theSiO2/Si(111)interface(<1&hthinsp;nm)is investigated by scanning reflection electron microscopy and microprobe Auger electron spectroscopy. The HF etching of theSiO2layer thermally grown on an atomically flatSi(111)-7×7surface progresses in a layer-by-layer manner, and then the final layer of oxide(∼0.3&hthinsp;nm)is removed in a two-dimensional void expansion with the H-terminated Si surface. This very uniform HF etching is thought to reflect the structural anisotropy of theSiO2layer formed near theSiO2/Si(111)interface. ©1998 American Institute of Physics.