Atomically flat germanium (111) surface by hydrogen annealing

In germanium (Ge) MOSFET technology, surface planarization is a serious concern for mobility enhancement at high carrier density, reliability improvement of gate dielectrics and morphology control for non-planar FETs. In this work, (111)-oriented Ge substrates were annealed at 350-750°C in pure H₂ atmosphere, and the surface structure and morphology were analyzed with atomic force microscopy. A step and terrace structure was observed on the surface after the H₂ annealing above 500°C. The terrace width is controllable by the off-angle of the initial surface within 0.3° at least. The roughness root mean square (RMS) at 100 × 100 nm on single terrace is ∼0.05 nm which is almost our detection limit, which implies that the single terrace on H₂ annealed Ge (111) is atomically flat. Furthermore, even though the initial surface roughness RMS is intentionally increased up to 0.6 nm, atomically flat terrace structure could be obtained by the H₂ annealing.