Step-free profiles by controlling the mask taper angle and ion incident angle in ion milling

In this study, we investigated ion milling using Ar ions to clarify the fundamental material-removal mechanisms using both experimental and analytical approaches. In the experiments, a SiO 2 layer and mask patterns were formed on Si substrates, and mask taper angles ranging from 40 to 80 degrees were controlled by thermal treatment. Processing experiments were performed by varying the ion incident angle, and the resulting surface morphology and profile evolution were evaluated. Numerical simulations were also conducted to analyze SiO 2 profile evolution as a function of the mask taper angle. The results reveal that the formation of the step structure in the SiO 2 profile is governed by the relationship between the mask taper angle and ion incident angle. In particular, shadowing effects play a dominant role, leading to intermediate steps when the ion incident angle exceeds the mask taper angle. The results provide a systematic understanding of ion-milling mechanisms and offer insights for achieving high-precision profile control.