Corner-rounding study

Precise measurement of pattern corner rounding is essential for determining the quality of current and next-generation photomask reticles. Using an appropriate test target with precise critical dimensions (CDs) and feature sizes, photomasks were written on an ETEC CORE 2564 laser writer with changes in focus from -1.0 to 1.0 micrometers at various exposure doses (mj/cm2). Using this methodology, the corner rounding of the CORE 2564 imaged feature was changed and compared to the ETEC MEBES III system generated pattern. The KLA 239HRS photomask inspection system was used to examine the effects of corner rounding at 0.25 micrometers with its most sensitive detectors at a 0.05 tolerance level. The optimization of writing tool performance and process parameters was enabled in two ways: by using the KLA 239HRS system, which did on-line biasing and rounding in 0.12 micrometers increments; and by using the Leitz AMS200 CD measurement tool, Micron Focused-Ion-Beam (FIB) system, and a binary image system, which measured the rounding of the mask features.