Low-Temperature Etching for Deep-Submicron Trilayer Resist

The effects of Cl2 addition to O2 plasma used for deep-submicron trilayer resist etching are investigated. The bottom-layer organic resist is etched using a low-temperature microwave plasma etcher. With O2+Cl2 etching gas, highly anisotropic etching is achieved at higher temperatures than with pure O2. Cl2 concentrations above 25% reduce resist selectivity relative to the SOG intermediate layer. Vertical 0.1-µm-wide resist patterns are achieved with O2+25% Cl2 at -60°C. Broadened resist patterns with tapered side walls are produced at lower temperatures and at higher Cl2 concentrations; this is thought to be caused by chlorine passivation and polymer deposition on the side walls.