Roughening of Si (111) surface under high-temperature thermal cycling

High-resolution low-energy electron diffraction has been used to study the generation of defects on the surface of commercial Si (111) wafers under high-temperature thermal cycling in ultrahigh vacuum. We observed a gradual increase of single-atomic step density from 0.15 to 0.30% after several thermal annealings at ∼1200 °C. However, a reduction of step density, accompanied by a change of step height from single-atomic to double-atomic step height, was observed after the sample was annealed to near melting temperature (∼1400 °C). At the same time, the surface was broken into micrograins having a small mosaic orientation. Due to the limited instrumental resolution, these low-density step structures and the small-angle mosaic structures cannot be resolved by using the conventional low-energy electron diffraction technique.