Fabrication of controlled sidewall angles in thin films using isotropic etches

Abstract

Angular structures in thin films have applications in microelectronics and optoelectronics. In this study we analyze isotropic etching of a two-layer system for the fabrication of angular sidewalls. Such a process is attractive because of its bulk processing capability. The isotropic etch process is demonstrated to provide good control of the sidewall angle. Theoretical analysis along with numerical simulation of the slope etching process is used to understand profile evolution. The numerical simulations showed that to obtain a flat angular sidewall face, reaction controlled etching is needed. Angular sidewalls are fabricated in plasma enhanced chemical vapor deposition (PECVD) silicon oxide with PECVD silicon nitride as the sacrificial layer using an isotropic, buffered hydrofluoric acid based, wet chemical etch. PECVD silicon nitride is shown to be a good material for use as the sacrificial layer because of its etch rate controllability through deposition conditions. Controlled angles ranging from 5° to 50° are demonstrated using this isotropic etch technique. Penetration of the etchant between the photoresist and the sacrificial silicon nitride layers is determined to be the cause of the limited range of the angles that could be etched. The rms roughness of the etched faces ranged from 79 to 389 Å.