EB alignment function for defect mitigation of EUV blank

Abstract

Availability of Defect-free blank is one of the most critical issues for high volume mask production in EUV lithography. Blank defects will disrupt the structure of multi-layers and will cause phase defects in EUV lithography. Phase defects caused by the disruption in the structure of multi-layers are difficult to repair after identified by the pattern inspection tools. Defect density in blanks are improving year by year, but the current progress is still insufficient [1][2] . All EUV blanks should be inspected for qualification before blank suppliers can establish manufacture processes for defect-free EUV blanks with higher productivity. There are also techniques in EUV blank alignment to relax the specification of defect density on a blank [3][4] . The origin of the alignment is the coordinate defined by the fiducial marks which are prepared on the glass of low thermal expansion material (LTEM) or on the multi-layer of EUV mask substrate. A limited number of defects can be covered by absorber film of a pattern in this technique. We developed an optional function for EBM-8000 [5] to precisely align a blank based on the fiducial marks by electron beam (EB) prior to pattern writing. Two possible structures of fiducial marks, advocated by SEMI standard 4580, can be considered to be used for fiducial marks in EUV blanks. In this paper, the alignment accuracy of blanks will be discussed through alignment experiments with actual EUV blanks.