ETCH CHARACTERISTICS OF GAN USING INDUCTIVELY-COUPLED CL-2 AR AND CL-2/BCL3 PLASMAS/

In this study, Cl-2/Ar and Cl-2/BCl3 inductively coupled plasmas were used to etch GaN and the effects of etch parameters such as gas combin ation 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 spe ctroscopy. Surface residue remaining after the etch was investigated u sing x-ray photoelectron spectroscopy (XPS). The increase of Ar and BC l3 in Cl-2 generally reduced GaN etch rates except for the small addit ion of Ar or BCl3. With the addition of 10% Ar or 10% BCl3 to Cl-2, th e GaN etch rates showed the maximum etch rates. Also, the increase of operational pressure up to 30 mTorr increased the GaN etch rates. By o ptimizing etch process parameters, etch conditions having smooth and n early vertical etch profiles with the etch rates close to 8500 A/min a nd the selectivity over SiO2 higher than 3.5 could be obtained with Cl -2-rich Cl-2/BCl3 gas combinations. The change of Cl radical density m easured by optical emission spectroscopy as a function of gas combinat ion showed the same trend as the change of GaN etch rates, therefore, chemical reactions between Ga in GaN and Cl from Cl-2 appear to be one of the most important factors controlling the GaN etch rates. Ga/N ra tios of the etched GaN surfaces measured by angle resolved XPS were le ss than 1 for all of the etch conditions used in the experiment. Howev er, when Ar was added to Cl-2, Ga/N ratio increased and, when BCl3 was added, the Ga/N ratio decreased from that of the GaN surface etched u sing pure Cl-2. (C) 1998 American Vacuum Society.