Mask roughness impact on extreme UV and 193nm immersion lithography

Abstract

The contribution of mask absorber line edge roughness on printed resist lines is studied for extreme UV and 193nm immersion lithography. Programmed roughness modules were designed for roughness transfer function evaluation on 88nm pitch line space patterns. The tested modules were designed applying variations of roughness amplitude and spatial frequency. Power spectral density analysis was performed on top-down SEM images. The effect of frequency roughness filtering by the lithographic optical system was studied with different illumination settings. It was found that, except for the degradation of the aerial image due to the filtering effect, less performing illuminations show an increased deterioration of the aerial image quality and thus contribute further to line edge roughness. A comparison with previous work was completed on different mask architectures and photoresist platforms. Resist performance can attenuate the roughness transfer from mask but at the cost of worse chemical gradient at the edges of the exposed regions.