Ar+-ion milling characteristics of III-V nitrides

TLDR

Thin‑film GaN, InN, AlN, and InGaN were ion‑milled with 100–500 eV Ar⁺ ions at incidence angles from 0° to 75° to study milling behavior. The single‑crystal nitrides exhibited mill rates about half those of GaAs and InP, while polycrystalline InN matched GaAs/InP rates; surfaces remained smooth without preferential N sputtering or amorphization, indicating that the slow etch rates limit the technique to shallow‑mesa applications and that alternative dry‑etch or ion‑implantation methods are preferable for device patterning.

Abstract

Ion milling of thin-film GaN, InN, AlN, and InGaN was performed with 100–500 eV Ar+ ions at beam angles of incidence ranging from 0° to 75° from normal incidence. The mill rates normalized to the Ar+ beam current for the single-crystal GaN, AlN, and InGaN were typically a factor of 2 lower than for GaAs and InP. For the polycrystalline InN, the mill rates were similar to those of GaAs and InP. The surface morphology of the ion-milled nitrides was smooth even at 500 eV Ar+ energy, with no evidence for preferential sputtering of the N, a result confirmed by Auger electron spectroscopy. The surface region was not amorphized by extended ion milling (35 min) at 500 eV with the samples held at 10 °C, as determined by Rutherford backscattering. Since the ion mill rates are slow for single-crystal nitrides and less than the mill rates of common masking materials (SiO2, SiNx, photoresist) it appears this technique is useful only for shallow-mesa applications, and that dry etching methods involving an additional chemical component or ion implantation isolation are more practical alternatives for device patterning.