Chromatic aberration-free TTL alignment system for 193-nm step-and-scan exposure system by using phase conjugate waves

Abstract

A TTL(through-the-lens) alignment system using the holographic phase conjugation in photopolyrner films for application to ArF step-and-scan exposure system was designed, and the TTL alignment signals were obtained. The optical setup is similar to the DFWM(degenerate four-wave mixing). The recording materials were HRF 150 photopolymer films of Du Pont corporation, and the recording wavelength was 476 nm of argon ion laser with 400mW output power. The diffraction efficiencies of photopolymer film were typically around 50%. Fine patterns as small as imicron were imaged successfully by the phase conjugate waves generated by DFWM holography. For TTL alignment, the 'X' or chevron patterns ofthe 1 or 2 micron linewidths were recorded as hologram and the reconstructed phase conjugate beams were used as the align beam through the projection lens which has strong chromatic aberration. TTL alignment signals were obtained by scanning the wafer with alignment mark under the align beam.