SELECTIVE SIO2-TO-SI3N4 ETCHING IN INDUCTIVELY-COUPLED FLUOROCARBON PLASMAS - ANGULAR-DEPENDENCE OF SIO2 AND SI3N4 ETCHING RATES

In the fabrication of microstructures in SiO2, etch selectivity of SiO 2 to masking, etch stop, and underlayer materials need to be maintaine d at corners and inclined surfaces. The angular dependence of the SiO2 -to-Si3N4 etch selectivity mechanism in a high density fluorocarbon pl asma has been studied using V-groove structures. The SiO2 etch rate on 54.7 degrees inclined surfaces is lower than on hat surfaces, while t he SiO2 etch yield (atoms/ion) is a factor of 1.33 higher. The results are consistent with a chemical sputtering mechanism. The Si3N4 etch y ield is greater by a factor of 2.8 for 54.7 degrees inclined surfaces than for flat surfaces. This large enhancement is explained by a fluor ocarbon surface passivation mechanism that controls Si3N4 etching. The fluorocarbon deposition is decreased at 54.7 degrees whereas the fluo rocarbon etching rate is increased at 54.7 degrees. This produces a th inner steady-state fluorocarbon film on the inclined Si3N4 surface, an d results in a large enhancement of the Si3N4 etch yield. (C) 1998 Ame rican Vacuum Society. [S0734-2101(98)05706-6].