Ion Milling and Reactive Ion Etching of III-V Nitrides

Abstract

Dry patterning of GaN, InN, AlN and InGaN grown by MOMBE on GaP, Al₂ O₃ or GaAs substrates was performed with 100–500 eV Ar⁺ ions at beam angles of incidence ranging from 0–75° from the normal, or with ECR discharges of BCl₃/Ar, CH₄/H₂ or Cl₂/H₂. The mill rates normalized to the Ar⁺ beam current were typically a factor of 2 lower than for GaAs and InP (i.e. maximum values of 300–500 Å·min^-1·mA^-1·cm^-2 at 400eV Ar⁺ beam energy and 60° angle with respect to the beam normal). The surface morphology of the ion milled nitrides was smooth even at 500 eV Ar⁺ energy, with no evidence for preferential sputtering of N as determined by AES. The ECR dry etch rates were fastest with elevated temperature Cl₂/H₂discharges, although both of the other chemistries investigated provide smooth, anisotropie pattern transfer. 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.