25 June 1999 UV thermoresists: sub-100-nm imaging without proximity effects
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Abstract
Thermoresists offer the possibility of greatly enhanced resolution and process window, mainly depth of focus, using conventional masks and modified conventional steppers. Unlike photoresists, which respond to total exposure, thermoresists ignore all exposures below their threshold provided that the exposures are separated in time by more than a few tens of nanoseconds. This allows thermoresists to ignore sidelobes and stray light that result from improving the resolution and depth of focus if nearby features are not imaged at the same time. Conventional steppers can be modified by adding a piezoelectrically-scanned microlens array above the mask and by adding an apodizing function to the reduction lens system. The microlens array eliminates all optical proximity effects by breaking the image into an array of dots that are moved between pulses of the stepper's laser, causing image features to be separated in time as well as space. Thermoresists also offers an advantage when imagin on non-planar materials if the intensity of the exposure is adjusted so that image spots will only reach the threshold of the resist when they are in focus. By making multiple image exposures with the focus shifted towards and away from the resist, a high-resolution image can be produced on a rough surface.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Dan Gelbart, Valentin A. Karasyuk, "UV thermoresists: sub-100-nm imaging without proximity effects", Proc. SPIE 3676, Emerging Lithographic Technologies III, (25 June 1999); doi: 10.1117/12.351148; https://doi.org/10.1117/12.351148
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