Actinic patterned mask inspection for high-NA EUV lithography

Abstract

Lasertec released an actinic patterned mask inspection (APMI) system named ACTIS in 2019 and has since been providing it as an EUV mask inspection solution for use at mask shops and semiconductor fabs in high-volume manufacturing. Actinic inspection is a type of inspection that utilizes 13.5nm EUV, the wavelength of light used in EUV lithography. ACTIS performs high-resolution, high-throughput inspection of EUV masks and detects mask defects that print on wafers in the lithography process (printable defects). One of the key advantages offered by APMI is its ability to perform highresolution through-pellicle inspection. EUV pellicles are expected to be used in semiconductor fabs, and ACTIS can detect printable defects on EUV masks even when a pellicle is attached to them.High-NA EUV lithography will be used at the technology nodes of N2 and beyond. The projection optics of high-NA EUV lithography are anamorphic optics, which have different scales of magnification for the horizontal and vertical axes. Lasertec has developed a next-generation model of ACTIS for high-NA mask inspection. It uses higher NA objective optics to meet the requirements of high-NA EUV mask inspection.This paper discusses the next-generation ACTIS for high-NA EUV lithography and its inspection performance on programmed defect masks that are similar to actual production masks. The paper also discusses the characteristics of a light source and illumination optics required for APMI.