Mask defect printability in the Self-Aligned Quadruple Patterning (SAQP) process

The Self-Aligned Quadruple Patterning (SAQP) process is one of the most suitable techniques for the patterning of under-20 nm half-pitch lines and spaces (L/S) patterns because it requires only one lithography step, resulting in a relatively low process cost. A serious problem when applying the SAQP process to real devices is the printability of defects in the photomask to the wafer because the effect of the mask defects may be enlarged when the defects are transferred to the spacer pattern. In this study, we evaluate the mask defect printability for both opaque and clear defects in the SAQP process in order to clarify the limit size of the defects on the photomask and to clarify whether the acceptable mask defect size given by ITRS was too small. The defect sizes of both the opaque and clear defects were relaxed as the wafer process progressed from lithography to SAQP. The acceptable mask defect size in the SAQP process found to be 70 nm, which is relaxed from that in ITRS2013.