<title>Exploration of fabrication techniques for phase-shifting masks</title>

Abstract

Techniques for fabrication and testing of phase-shifting masks have been explored. The masks were formed using quartz blanks with both directly etched-in phase-shifters as well as deposited SiO2 films and photoresist for the phase-shifting layer. The etched-in phase- shifters were fabricated by standard lithographic patterning and dry etching of the quartz mask surface. Phase-shifters consisting of photoresist were applied and important resist properties such as index of refraction and absorption were determined. A technique for precise control of the etched phase step using a self-terminated plasma etch into CVD SiO2 has also been explored. Printed patterns using the masks showed the expected benefits of phase-shifting. We also investigated the effect of fabrication tolerances. For example, misalignment of the auxiliary phase-shifters surrounding a contact hole has little impact on printed resist patterns. Phase-shifter parameters deviating from the optimum value were explored both experimentally and using the optical simulator SPLAT. Sloping side walls as well as absorption and interference in the phase-shifter show varying influence depending on the specific feature and the lens reduction. The tolerance in phase-shift magnitude has been examined in a number of cases, and is generally found to be in the neighborhood of 30 degree(s).