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5 September 2001 Atomic force metrology and 3D modeling of microtrenching in etched photomask features
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Proceedings Volume 4409, Photomask and Next-Generation Lithography Mask Technology VIII; (2001)
Event: Photomask and Next Generation Lithography Mask Technology VIII, 2001, Kanagawa, Japan
We present a study of the micro-trenching caused by different quartz etch processes during the fabrication of phase-shift photomasks. Six different photomasks with quartz etches 320nm - 720nm deep were measured non-destructively 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. suggest that micro-trenching is a universal phenomenon occurring during quartz etches. We propose that micro-trenching more correctly defines the geometries responsible for trenching bias. Finally, to show the effect of local geometry to the extent which trenching occurs, we study the depth detail in the vicinity of an unusually shaped phase bump defect. Trenching is more than 50 percent greater at the base of concave or acute defects as compared to convex defects. Local trenching may make repair more difficult for phase bump defects near or touching a vertical trench wall.
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Bradley Todd, Kirk Miller, and Thomas V. Pistor "Atomic force metrology and 3D modeling of microtrenching in etched photomask features", Proc. SPIE 4409, Photomask and Next-Generation Lithography Mask Technology VIII, (5 September 2001);

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