Study of pupil filters for depth of focus enhancement in printing contact holes

Chun-Ming Albert Wang; Shinn Sheng Yu; Anthony Yen

doi:10.1117/12.354396

26 July 1999 Study of pupil filters for depth of focus enhancement in printing contact holes

Chun-Ming Albert Wang, Shinn Sheng Yu, Anthony Yen

Proceedings Volume 3679, Optical Microlithography XII; (1999) https://doi.org/10.1117/12.354396
Event: Microlithography '99, 1999, Santa Clara, CA, United States

Abstract

In this paper, we investigate depth of focus (DOF) improvement using radially symmetric pure phase pupil filters. Optimization of such filters starts by requiring their corresponding point spread function be flat in the axial direction. it is found that DOF for 0.18micrometers contact holes using an optimized filter is about 1micrometers , while printing them without filters is hardly feasible, using a binary mask. however, this filter introduces 2/3 intensity loss and therefore affects the processing throughput. We also apply the optimized filter to the imaging of 0.15micrometers contact holes and 0.18micrometers lines and spaces. For 0.15micrometers contact holes, it still performs better than other case, but normalized image log-slopes are low for all cases. From the simulation data of 0.18micrometers lines and spaces, pure phase filters may not be good candidates for improving their DOF. Other DOF enhancing techniques such as quadrupole illumination may be required.

Citation Download Citation

Chun-Ming Albert Wang, Shinn Sheng Yu, and Anthony Yen "Study of pupil filters for depth of focus enhancement in printing contact holes", Proc. SPIE 3679, Optical Microlithography XII, (26 July 1999); https://doi.org/10.1117/12.354396

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KEYWORDS

Image filtering

Nanoimprint lithography

Printing

Point spread functions

Optical filters

Bessel functions

Binary data

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