Ultrashallow depth profiling using ozone oxidation and HF etching of silicon

A new approach for semiconductor ultrashallow depth profiling is presented. In this technique, the compositional and structural properties in the near-surface region of a silicon sample were measured by Rutherford backscattering spectroscopy, and the chemical and electrical properties by x-ray photoelectron spectroscopy (XPS). The measurements were repeated after the removal of a few atomic layers of silicon via ozone oxidation followed by a hydrofluoric acid etch of the oxide. The depth distributions of composition and surface potential were then determined. The etch-depth per cycle of this treatment was estimated by measuring the oxide thickness formed in each ozone oxidation with XPS, and was calibrated to be 0.5 nm of silicon per cycle by applying the technique to a Si/Ge/Si sample with a known silicon overlayer thickness. This profiling technique, therefore, provides a depth resolution of better than 0.5 nm. The applicability of the technique is demonstrated by showing the compositional profiling results on a p-Si (100) sample treated with reactive ion etching, and the surface potential profiling data on an n-Si (100) sample bombarded by 1 keV Ar.