Dual-wavelength photoresist for sub-200-nm lithography

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Abstract
Dry developable bilayer resist systems offer high resolution capability and wide focus windows due to the thin imaging photoresist layer that is applied on top of a thick light- absorbing and planarizing bottom resist. Since 1995, Siemens uses the CARL bilayer resist process as a commercial available i-line version in its high-volume DRAM and logic IC production for patterning of half-micron features over severe topography. For application of this process in high resolution lithography, the chemical biasing of photoresist structures, achieved by a separate silylation step, can be used for a dramatic increase in focus latitudes at k1 <EQ 0.5, even with standard illumination and COG masks. In our paper we will discuss this effect and focus on first results with a further developed CARL resist system for application in 248 nm and 193 nm lithography, respectively. With such a dual-wavelength bilayer resist, early process development and optimization is possible for the 193 nm technology by using the already implemented 248 nm exposure tools. Consequently rapid and easy access to sub-150 nm structure dimensions is given by simply switching the exposure wavelength from 248 to 193 nm at a time when the 193 nm exposure tools are mature for production.

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