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 350-750oC 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 500oC. The terrace width is controllable by the off-angle of the initial surface within 0.3o at least. The roughness root mean square (RMS) at 100 x 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.