Atomic Force Metrology

We present a study of the micro-trenching caused by different quartz etch processes during the fabrication of phaseshift photomasks.. Six different photomasks with quartz etches 320nm – 720nm deep were measured nondestructively by Atomic Force Microscopy (AFM) to explore the details of micro-trenching that occurs at the base of vertical walls. Results of etch profiles obtained using AFM metrology are correlated with electromigration (EM) modeling of alternating aperture phase shift masks for use with KrF 4X reduction steppers. The metrology and EM modeling results clearly differentiate each of the generic etch processes and predict the process window changes resulting from modeled micro-trenching relative to an ideal etch case. In particular, the ICP + wet etches show 50 percent less micro-trenching relative to three of the four RIE-only etch processes. Comparisons of micro-trenching lengths measured during these experiments with the results of trenching bias across different etched space widths as reported by McCallum, et al. (1) suggest that micro-trenching is a universal phenomenon...