Thin film stress control of absorber stack materials for EUVL reticles

Abstract

Extreme ultraviolet lithography (EUVL) is the leading candidate for next generation lithography with the potential for extendibility beyond the 50-nm node. The three-layer absorber stack for EUVL reticles consists of an absorber, repair buffer and etch-stop layers, while a two-layer absorber stack eliminates the etch-stop layer. A portion of the mask pattern distortion can be assigned to the absorber stack's film stress. Ideally, the absorber stack films would have zero stress uniformly across the mask, which would produce zero pattern distortion when the films were removed during the pattern transfer processes. Maintaining adequate thin film stress control and uniformity relies on accurate thin film thickness measurements. The thin film deposition parameters can have a significant influence on the metrology technique's ability to measure the thin film's thickness. We have studied resistive and photonic metrology techniques for absorber stack thin film thickness measurement and stress control.