Graded transmission dielectric optical masks by laser ablation

Dielectric interference layer systems designed for high reflectivity at 248 nm are patterned by ArF-excimer laser ablation (193 nm). Each single pulse ArF-laser exposure in vacuum at a fluence of about 0.2 J/cm(2) causes ablation of a bilayer of the HfO2/SiO2 multilayer system. As the reflectivity of the system depends on the number of remaining layers, the local transmission after laser treatment will depend on the number of applied laser pulses in this area. A spatially well defined irradiation procedure leads to a graded transmission system, which can be applied as a projection mask for KrF-laser ablation (248 nm). Using this mask, according to the specific ablation rate vs, fluence dependence, a defined ablation profile is achieved with a single pulse or with several pulses without any movement of laser beam, mask, or sample. This is demonstrated by ablating a multistep surface structure in a polymer material. (C) 1998 Elsevier Science B.V.