Investigation of attenuated phase-shifting mask material for 157-nm lithography

This work was done to identify viable materials for attenuated phase-shift masks (Att-PSMs) for use with 157-nm lithography. Earlier studies proposed Si-based and Zr-based materials as potential contenders for use as Att-PSMs for 157-nm lithography. This report proposes new Ta-based materials for Att-PSMs, and evaluates the irradiation durability of Ta-group bilayer films (Ta and TaSiO) and Si film to F2 laser light. The Ta-based mask is a bilayer structure consisting of an absorption film (AF) layer and a transparent film (TF) layer. Ta is used for the AF, while TaSiO is used for the TF. The Cr of the Si-based mask is used for the AF layer. The TF layer is etched substrate. The transmittance of the Cr-based mask is readily controlled by the thickness of the Cr layer. The phase angle is controlled by the depth of etching substrate. It was found that the Ta- based bilayer films, and the Cr-based films exhibit good irradiation durability for irradiation to 157-nm light. We demonstrated that the Ta-based and Cr-based Att-PSMs are practical for use in 157-nm lithography.