CH4/H2/Ar etching study of N-polar GaN for micro-LED applications

Inductively coupled plasma (ICP) etching of N-polar n-doped gallium nitride (GaN) with a CH4/H2/Ar chemistry was investigated as a function of CH4 ratio in the gas mixture, DC bias voltage, ICP source power, pressure, and total gas flow. Two etching modes are evidenced when varying CH4 ratio in the gas mixture, the DC bias voltage at fixed source power or the total gas flow. Moreover, the etch rate increases with increasing DC bias voltage at 1000 W source power, increasing source power or decreasing pressure. In some conditions, the formation of a polymer film onto the GaN surface was observed. Etch rates as high as 65 nm/min was achieved. Based on the competition between GaN etching and polymer layer deposition observed from the etch rate study, an etching mechanism of GaN with a CH4/H2/Ar chemistry is proposed. This study proposes an overview of etching performances of GaN with both Cl2/Ar and CH4/H2/Ar chemistries. The luminescence properties and GaN surface chemistry for a given set of plasma parameters in the CH4-based chemistry were investigated by cathodoluminescence, x-ray photoelectron spectroscopy, and hard x-ray photoelectron spectroscopy, respectively. The GaN properties after etching were compared to the ones obtained after a Cl2/Ar etching chemistry. Preliminary results suggest that the CH4-based etched samples exhibit improved electro-optical performance.