Ga+ focused-ion-beam implantation-induced masking for H 2 etching of ZnO films

摘要

Gallium implantation of ZnO by a focused-ion beam is used to create a mask for ZnO dry etching with hydrogen. Effects of Ga~+ fluence on the etch stop properties and the associated mechanisms are investigated. The fluence of 2.8 × 10~(16) cm~(-2) is determined to be optimum to render the best mask quality. While lower fluences would cause less etching selectivity, higher fluences would cause erosion of the surface and particles to be precipitated on the surface after H2 treatment at high temperature. In contrast to the commonly adopted gallium oxide formation on Si, transmission electron microscopy analysis reveals that, for the fluences ≤2.8 × 10~(16) cm~(-2), Ga~+ ions are incorporated as dopants into ZnO without any second phases or precipitates, indicating the Ga-doped ZnO layer behaves as a mask for H_2 etching due to the higher electronegativity of Ga+ towards oxygen. However, for the fluences ≥4.6 × 10~(16) cm~(-2), the surface particles are responsible for the etch stop and are identified as ZnGa_2O _4. We finally demonstrate a complicated pattern of 'NCKU' on ZnO by using this technique. The study not only helps clarify the related mechanisms, but also suggests a feasible extension of the etch stop process that can be applied to more functional material.