Selective atomic layer reaction between GaN and SiN in HBr neutral beam etching

We investigated higher selective etching between SiN and GaN using an HBr neutral beam (NB) and found that it exhibited a more selective reaction compared to Cl₂ NB. The etching rate of GaN mainly depended on the desorption rate of the etching product (GaCl_x or GaBr_x) assisted by the bombardment of NB. As a result, in the case of the HBr neutral beam, the GaN etching rate was drastically decreased at the atomic layer level because the vapor pressure of the etching product, GaBr_x, was much lower than that of GaCl_x. On the other hand, the dominant etching progression of SiN was mainly caused by neutral beam bombardment energy, and the desorption of the etching products (SiCl_x or SiBr_x) was almost the same in both cases because the vapor pressures of the etching product, SiCl_x and SiBr_x. In particular, in the case of the HBr neutral beam, the neutral beam energy dependence of the surface reaction layer of SiN was larger than that of Cl₂ NB. As a result, the etching selectivity between SiN and GaN in HBr NB improved to 2.1 at 10 W of bias power, whereas that with Cl₂ NB was saturated at 0.41 at more than 10 W of bias power. We found that the surface atomic layer etching reaction could precisely control the desorption rate of the etching product by optimizing the neutral beam bombardment energy and gas chemistry. The HBr neutral beam process can achieve atomic layer level selective reactions on the SiN/GaN structure.