Angular dependences of Si3N4 etch rates and SiO2-to-Si3N4 etch selectivity in C4F6/Ar/O2/CH2F2 plasmas

摘要

Si3N4 films are usually used as a protecting layer of a poly silicon gate during the etching of a contact hole. An increase in the etch rates of Si3N4 at its curved surface lowers the etch selectivity of SiO2 with respect to Si3N4 [1, 2], resulting in device failure. Therefore, it is important to control the angular dependence of Si3N4 etch rates and SiO2-to-Si3N4 etch selectivity. In this work, the angular dependences of the Si3N4 etch rate and SiO2-to-Si3N4 etch selectivity in a C4F6/Ar/O2/CH2F2 plasma were investigated using a speciallydesigned Faraday cage system. The Faraday cage allowed one to control the ion-incident angles. Etching was conducted by varying the ratio of CH2F2 flow rate to study a role of steadystate fluorocarbon films formed on the surface of the Si3N4 substrate during etching.