Temperature dependence on plasma-induced damage and chemical reactions in GaN etching processes using chlorine plasma

Abstract

Plasma-induced damage (PID) on GaN was optimally reduced by high-temperature chlorine plasma etching. Energetic ion bombardments primarily induced PID involving stoichiometry, surface roughness, and photoluminescence (PL) degradation. Chemical reactions under ultraviolet (UV) irradiation and chlorine radical exposure at temperatures higher than 400 °C can be controlled by taking into account the synergism of simultaneous photon and radical irradiations to effectively reduce PID.

Reaction mechanisms between chlorine plasma and a spin-on-type polymer mask for high-temperature plasma etching

“…A high-temperature plasma etcher, which has been described in detail in other reports, was used in our experiments. [1][2][3][4][5][6] Pure Cl 2 gas was introduced through a showerhead at a flow rate of 50 sccm. The pressure was maintained at 20 Pa using an automatic pressure controller (VAT PM-4).…”

“…19) A medium-frequency (3.2 MHz) bias power of 15 W with a peak-to-peak voltage of about 237 V was applied to the SiC stage. Negative DC bias voltage as the self-bias voltage was measured to be close to −90 V. [2][3][4][5][6] Samples were set on the stage. An infrared lamp (Thermo Riko GV) was used to heat the stage in the range from 300 to 500 °C.…”

“…1) The etching of GaN in a range of 400-500 °C with Cl 2 plasma provides less ion-induced damage and a smooth surface without vacuum ultraviolet photon-induced deterioration. [2][3][4][5][6] To realize a pattern transfer with dimensions on the order of 10 nm scale during etching processes at this temperature, mask materials with high thermal and etching resistance are required. Although 193 nm ArF photoresists are generally used as mask materials during plasma etching in lowtemperature etching processes, [7][8][9][10][11] they will rapidly reflow or deform at high temperatures because their main constituents of methacrylate polymers, which have excellent transparency at 193 nm, 12) usually have low glass transition temperatures (T g ) of 100-200 °C.…”