Selective isotropic etching of SiO(2) over Si(3)N(4) using NF(3)/H(2) remote plasma and methanol vapor

In this study, an isotropic etching process of SiO(2) selective to Si(3)N(4) using NF(3)/H(2)/methanol chemistry was investigated. HF was formed using a NF(3)/H(2) remote plasma, and in order to remove the F radicals, which induces spontaneous etching of Si-base material, methanol was injected outside the plasma discharge region. Through this process, etch products were formed on the surface of SiO(2), and then the (NH(4))(2)SiF(6) was removed by following heating process. When the H and F radicals were abundant, the highest SiO(2) etch per cycle (EPC) was obtained. And, the increase of H(2) and methanol percentage in the gas chemistry increased the etch selectivity by decreasing the F radicals. The etch products such as (NH(4))(2)SiF(6) were formed on the surfaces of SiO(2) and Si(3)N(4) during the reaction step and no noticeable spontaneous etching by formation of SiF(4) was observed. By optimized conditions, the etch selectivity of SiO(2) over Si(3)N(4) and poly Si higher than 50 and 20, respectively, was obtained while having SiO(2) EPC of ~ 13 nm/cycle. It is believed that the cyclic process using NF(3)/H(2) remote plasma and methanol followed by heating can be applied to the selective isotropic SiO(2) etching of next generation 3D device fabrication.