Enabling EUVL high-volume manufacturing with actinic patterned mask inspection

As extreme ultraviolet lithography (EUVL) enters high volume manufacturing (HVM), the integrated circuit (IC) industry considers actinic patterned mask inspection (APMI) to be the last major EUV mask infrastructure gap. For over 20 years, there have been calls for an APMI tool for both the final qualification of EUV masks in the mask shop and for the requalification of EUV masks in the wafer fab1. Actinic, in this context, is matching the 13.5 nm scanner wavelength to that of the inspection tool so that all types of EUV mask defects can be detected. In order to enable EUVL HVM, we have developed and introduced the world's first commercially available APMI tool. Actinic inspection enables HVM EUVL by ensuring that the EUV mask going to the EUV scanner is free from EUVprintable defects that may have been overlooked during EUV blank manufacturing or occurred during EUV mask manufacturing, cleaning and use. In this paper we will review EUV mask defect requirements from the maskshop and fab perspective, as well as capabilities of different inspection methods available for HVM. Further, we will provide an overview of the history of APMI tool development and highlight challenges and successes made when designing major components for the tool. APMI enables reliable detection of all classes of EUV-printable mask defects: small absorber defects, phase and amplitude defects in the multi-layer, In this paper, inspection performance of the APMI tool will be reviewed using representative cases from programmed defect masks with designs resembling real production cases. Finally, we will provide an outlook for the next steps in tool development including Die-to-Database inspection, throughpellicle inspection and platform extendibility to high NA EUVL.