In situ surface analysis of an ion-energy-dependent chlorination layer on GaN during cyclic etching using Ar⁺ ions and Cl radicals

Gallium nitride (GaN) semiconductor devices must be fabricated using plasma etching with precise control of the etching depths and minimal plasma-induced damage on the atomic scale. A cyclic process comprising etchant adsorption and product removal may be suitable for this purpose but an understanding of the associated etching surface reactions is required. The present work examined the formation of a chlorinated layer based on Cl radical adsorption on a GaN surface in conjunction with Ar ion irradiation. This research employed beam experiments and in situ x-ray photoelectron spectroscopy. The results show that N atoms are preferentially desorbed during exposure to Ar ions to produce Ga-rich layers at depths of 0.8 and 1.1 nm at an Ar ion dosage on the order of 10¹⁶ cm⁻² and ion energies of 116.0 and 212.6 eV, respectively. Subsequent exposure of the irradiated Ga-rich layer to Cl radicals removes some Ga atoms and produces a chlorinated layer over the GaN surface. This chlorinated layer has a thickness on the order of 1 nm following Cl radical dosages on the order of 10¹⁹ cm⁻². This study of plasma-treated surfaces is expected to assist in developing means of controlling the etching depth during the atomic layer etching of GaN via Ar ion bombardment.