Neutral-beam etching with high selectivity and low damage for GaN-based materials

Neutral-beam etching (NBE) provides a charge-free, low-damage approach for the dry processing of wide-bandgap semiconductors. By neutralizing plasma ions and precisely controlling bias power, NBE delivers reactive radicals without UV-induced damage or charging effects. We systematically compare the etching of GaN, AlGaN, and SiN under Cl₂, Cl₂/BCl₃, and SF₆ neutral beams. The gallium nitride (GaN) etch rate ranges from <0.5 nm min⁻¹ at the sputtering threshold to 28.9 nm min⁻¹ at 100 W bias. Cl₂/BCl₃ beams yield AlGaN/GaN selectivity >25, while SF₆ beams achieve SiN/GaN selectivity >675 at 10 W. Post-etch atomic force microscopy shows an rms roughness of 0.3–0.7 nm, in some cases smoother than as-grown surfaces. These results demonstrate that NBE combines high material selectivity with atomically smooth and reproducible profiles. The reduced defect density and stable etch depth directly benefit GaN high-electron-mobility transistor fabrication, enabling precise gate recesses and suppressing threshold-voltage shifts and gate leakage. Our findings establish NBE as a versatile tool for the next generation of GaN device processing.