Etch characteristics of GaN using inductively coupled Cl2/Ar and Cl2/BCl3 plasmas

Abstract

In this study, Cl2/Ar and Cl2/BCl3 inductively coupled plasmas were used to etch GaN and the effects of etch parameters such as gas combination and operation pressure on the characteristics of the plasmas and etch properties of GaN were investigated. The characteristics of the plasmas were estimated using a Langmuir probe and optical emission spectroscopy. Surface residue remaining after the etch was investigated using x-ray photoelectron spectroscopy (XPS). The increase of Ar and BCl3 in Cl2 generally reduced GaN etch rates except for the small addition of Ar or BCl3. With the addition of 10% Ar or 10% BCl3 to Cl2, the GaN etch rates showed the maximum etch rates. Also, the increase of operational pressure up to 30 mTorr increased the GaN etch rates. By optimizing etch process parameters, etch conditions having smooth and nearly vertical etch profiles with the etch rates close to 8500 A/min and the selectivity over SiO2 higher than 3.5 could be obtained with Cl2-rich Cl2/BCl3 gas combinations. The change of Cl radical density measured by optical emission spectroscopy as a function of gas combination showed the same trend as the change of GaN etch rates, therefore, chemical reactions between Ga in GaN and Cl from Cl2 appear to be one of the most important factors controlling the GaN etch rates. Ga/N ratios of the etched GaN surfaces measured by angle resolved XPS were less than 1 for all of the etch conditions used in the experiment. However, when Ar was added to Cl2, Ga/N ratio increased and, when BCl3 was added, the Ga/N ratio decreased from that of the GaN surface etched using pure Cl2.