Influence of different etching mechanisms on the angular dependence of silicon nitride etching

Results from etching experiments where Si3N4 films have been bombarded by argon ions at different angles of incidence, with or without a simultaneous exposure to XeF2 molecules, are presented. The experiments have been performed using a Kaufman-type ion beam source. With these experiments, one obtains the angular dependence of physical sputtering and ion enhanced chemical etching by fluorine. The results are compared with reactive ion beam etching (RIBE) of silicon nitride, silicon dioxide, and polysilicon using CHF3+O2 in order to find the influence of a polymer layer that may be formed on the surface of silicon nitride during etching. Such a polymer layer will strongly affect the angular dependence of the etching process. The formation of the polymer layer, responsible for the variations in the angular dependence, is a result of the flux of polymer precursors, atomic fluorine, and energetic particles to the etched surface. This means that the angular dependence of the RIBE process can be changed by varying the process parameters. This offers a possibility to tailor a process with a specific angular dependence that can be used to etch structures with controlled sidewall profiles.