Effect of Attenuated Phase Shift Mask Structure on Extreme Ultraviolet Lithography

Abstract

Optimization of the absorber stack is becoming a critical issue in extreme ultraviolet (EUV) lithography. The attenuated phase shift mask (att-PSM) can be a long-term solution for continued technological improvements. The designed structure is based on the Fabry–Perot structure that consists of a TaN attenuator, an Al2O3 spacer, and a Mo phase shifter. The total thickness of the absorber stack is 52 nm. The characteristics of the designed att-PSM are an EUV reflectivity (9.5% at 13.5 nm) and phase shift effect (180° at 13.5 nm) that maximize the image contrast in EUV exposure, and a low deep ultraviolet (DUV) reflectivity (1.72% at 257 nm) for high efficiency DUV inspection. All the simulations were carried out with the EM-Suite simulation tool. As a result, we determined that the att-PSM shows a higher image contrast, a larger process window, and a lower horizontal–vertical (H–V) CD bias than a binary image mask.