Aluminum oxides as imaging materials for 193-nm excimer laser lithography

Abstract

Aluminum oxide films deposited over amorphous carbon(a-C:H) planarizing layers have been investigated as imaging layers for 193-nm excimer laser lithography. The AlOx films were deposited by ion beam deposition, e-beam evaporation, or sputter deposition. The films have been analyzed by Auger electron spectroscopy and x-ray photoelectron spectroscopy. Depending on the deposition conditions, AlOx films with compositions varying from metallic to fully oxidized Al can be formed. The optical appearance of these films varies from highly reflective for metallic Al to highly transparent for fully oxidized layers. Using pulsed 193-nm radiation from an ArF excimer laser, the single-pulse self-development threshold energy is similar for films with different compositions when the film reflectivity is taken into account. It was found that pure Al films and highly oxidized Al films do not provide good adhesion on a-C:H layers and have a tendency to peel during laser exposure. In contrast, films with intermediate compositions consisting of a mixture of Al and aluminum oxides provide good adhesion, high etch resistance during O2 reactive ion etching, and submicrometer resolution when exposed with the 193-nm excimer laser. Features as small as 0.1 μm have been patterned on these films in projection, and can be transferred through a 1-μm-thick a-C:H planarizing layer with vertical profiles.