Inspection and repair of EUV

Abstract

Fabricating masks for extreme ultraviolet lithography (EUVL) is challenging. New design features have been introduced because of the high absorption of most materials at 13.4 nm and the small critical dimension (70 nm and below). The novel mask features introduced with EUVL include the reflective design, new film combinations, and stringent defect specifications. This paper focuses on one aspect of the mask build process that must be detected, understood, and minimized: defects. We obtain our EUV mask blanks with the multi-layers already in place. While the deposition of usable Mo/Si multilayers is a challenge in itself, our pursuit of a clean EUV mask process begins with the buffer layer. From that point, the basic mechanics of the mask build is: deposit the buffer layer, deposit the absorber layer, apply and pattern the resist, and etch the absorber. The buffer layer is left to protect the multi-layers during inspection and repair. Careful attention to cleaning, inspection, and repair will be required to meet the ITRS Roadmap's 55 nm maximum defect size (at the 70 nm node). Our inspection methodology, defect data and repair options will be presented in detail.