Three-dimensional B impurity profiles in substrates were measured, with a resolution of 10nm, via the scanning tunnelling microscopy of cleaved surfaces which had been progressively etched with HF-HNO3-H2O mixtures. The optimum composition had a volume ratio of 1:100:25, and could be applied to dopant concentrations of between 1016 and 1020/cm2. The etching rate exhibited no dependence upon the crystallographic orientation. It was noted that this technique revealed the active B impurity content rather than the implanted B concentration.

T.Takigami, M.Tanimoto: Applied Physics Letters, 1991, 58[20], 2288-90