Dry etching of GaN and related materials: comparison of techniques

The etch rates and feature anisotropy for GaN, AlN, and InN etched in Cl₂-Ar plasmas with four different techniques were examined. Conventional reactive ion etching produces the slowest etch rates, even when high dc self-biases (>-900 V) are employed, and this leads to mask erosion and sloped feature sidewalls during ridge waveguide fabrication. Two high-ion-density techniques, inductively coupled plasma and electron cyclotron resonance, provide the highest etch rates and most anisotropic features through their combination of high-ion flux and moderate-ion energy. Etch selectivities of GaN to AlN and InN are typically ⩽4 in these tools. Reactive ion beam etching utilizing a high density (ICP) source is also an attractive option for pattern transfer in the nitrides, although its etch rates are slower than for ICP or ECR due to its lower operating pressure