Reducing EUV mask 3D effects by alternative metal absorbers

Abstract

Over the recent years EUV lithography has demonstrated the patterning of ever shrinking feature sizes (enabling the N7 technology node and below), while the EUV mask has remained unaltered using a 70nm Ta-based absorber. This has led to experimentally observed Mask 3D (M3D) effects at wafer level, which are induced by the interaction between the oblique incident EUV light and the patterned absorber with typical thickness values in the order of several wavelengths. In this paper we exploit the optical properties of the absorber material of the EUV mask as M3D mitigation strategy. Using rigorous lithographic simulations, we screen potential single element absorber materials for their optical properties and their optimal thickness for minimum best focus variation through pitch at wafer level. In addition, the M3D mitigation by absorber material is evaluated by process window comparison of foundry N5 specific logic clips. In order to validate the rigorous simulation predictions and to test the processing feasibility of the alternative absorber materials, we have selected the candidate single elements Nickel and Cobalt for an experimental evaluation on wafer substrates. In this work, we present the film characterization as well as first patterning tests of these single element candidate absorber materials.