Plasma Etching of Deep High-Aspect Ratio Features Into Fused Silica

This paper reports research performed on developing and optimizing a process recipe for the plasma etching of deep high-aspect ratio features into fused silica (fused quartz) material using an inductively coupled plasma reactive-ion etch process. As part of this effort, we performed a design of experiments (DOE), wherein the etch recipe parameters having the most impact on the etch process were varied over fixed ranges of predetermined values, while the other etch recipe process parameters were unchanged. Subsequently, the etched samples were analyzed so as to quantify the etch outcomes. Using the experimental data collected during the DOE, we then performed multiple regression analysis on this data to determine optimal etch tool parameters in order to achieve the desired etch results. Based on this work, we have demonstrated the ability to etch very deep features into fused silica of over 100 microns, having nearly vertical sidewalls, and with aspect ratios of over 10 to 1 using the optimized etch process. The ability to fabricate deep high-aspect ratio features into fused silica has important implications for a number of micro-electromechanical systems applications. The etch technology developments presented herein are applicable to fused silica, as well as to other silicon-dioxide-based materials including crystalline quartz.