AR+-ION MILLING CHARACTERISTICS OF III-V NITRIDES

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-degrees to 75-degrees 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-degrees-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, SiN(x), 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.