Quartz etch optimization

Abstract

Studies on photomask quartz etching in a gas system consisting of SF6, O2, and He were carried out using an inductively coupled plasma (ICP) photomask etcher. A profilometer was used for etch rate uniformity characterization. Quartz etch was performed in the same chamber as was used for MoSi etching. The defectivity influence was also investigated so that the feasibility of MoSi and quartz etches in the same chamber was examined and discussed. Process optimization was studied by changing the Cr layer thickness, the O2, SF6, and He flow rates and gas composition, the ICP power and bias power, and the pressure. It was found that ICP power, bias power, pressure, O2 flow rate, and He flow rate played an important role in determining etch performance. Plasma stability and etch performance were also investigated. An empirical kinetic equation was proposed based on experimental data and a quartz etch mechanism was also explained. Systematic etch non-uniformity resulting from radial and the side-to-side errors were also investigated in this study. High CD resolution (down to 100 nm), good etch rate linearity, extremely low etch rate dependency on photomask patterns with different loading, and repeatable etch rate produced an optimal etch process suitable for 90 nm and below technology node.