Joerg Rottstegge

Ultrathin film imaging at 157 nm

In future lithography the 157 nm wavelength is expected to succeed the 193 nm wavelength in 2004. So an early CARL resist for sub 100 nm resolution was developed at Infineon Technologies within the German BMBF project Laserbasierte Ultraprazisionstechnik - 157 nm Lithographie. Common 248 and 193 nm resist materials have a high absorbance (7- 12 μm-1) A main challenge at this short exposure wavelength is the development of a transparent base polymer or the imaging has to be done alternatively with ultra thin films. In contrast to a high transparency of the polymer a high quantum yield for the photo chemicals is required. CARL is a bilayer resist system developed by Siemens/Infineon Technologies. A modified CARL version is presented here for exposures at 157 nm, consisting of a silicon free top resist (Si free CARL) as thin imaging layer. A separate silylation step of the structured top resist after exposure and wet development provides a high etch resistance in the dry development step and allows imaging of ultra-thin films with a film thickness of ca. 50 nm. An oxygen plasma is taken to transfer these top resist structures into the up to 300 nm thick underlying Novolac type bottom resist. In dry development. The bottom resist itself provides high etch resistance also for aggressive substrate etch processes.

Novel fluoro copolymers for 157-nm photoresists: a progress report

Several fluoro-substituted polymers consisting of acid cleavable methacryoic or cinnamic acid tert.-butyl ester compounds copolymerized with maleic acid anhydride derivatives were synthesized by radical copolymerization. Vacuum ultraviolet transmission measurements of the samples reveal absorbances down to 5micrometers -1 despite of the strongly absorbing anhydride moiety which serves as silylation anchor for the application of the Chemical Amplification of Resist Lines (CARL) process, one of the promising approaches for sub-90nm pattern fabrication. Some of the samples exhibit resolutions down to 110nm dense at 157nm exposure using an alternating phase shift mask. The feasibility of the CARL principle including the silylation reaction after development has been demonstrated with selected fluorinated polymer samples.