Atomic-layer etching of Ge using an ultraclean ECR plasma

Self-limited atomic-layer etching of Ge(100) has been investigated by alternated chlorine adsorption and Ar+ ion irradiation using an ultraclean ECR plasma. With short Ar+ ion irradiation, about a quarter of atomic-layer thickness was etched in each cycle under the saturated adsorption condition, which corresponds with the case of Si(100). With increasing irradiation amount of Ar+ ions, the etch rate per cycle increases and tends to saturate to the atomic-layer thickness of Ge(100). Taking Ar+ ion induced reaction into consideration, a simple exponentially-saturating equation well describes the atomic-layer etch rate of Ge. From measured Ar+ ion flux density distribution, it is estimated that the energy of Ar+ ions predominantly contributing to the atomic-layer etching of Ge is higher than the order of ∼13 eV.