Mark design challenge of cut layer in FinFet

The requirement of overlay performance, which is determined by alignment process during exposure and overlay measurement process, is getting tighter as technology node shrinks in integrated circuit. Mark design has drawn a lot of attention since appropriately designed marks can guarantee process compatibility and sufficient device performance tracking property. Cut layers are widely used in FinFet to define active area formed by SADP (Self-aligned double patterning) or SAQP (Self-aligned quadruple patterning), of which the mark design is especially challenging for diffusion break layer since it is a cut layer that landing on three dimensional fin structure and will be aligned to. In this paper, mark design of diffusion break layer is investigated, including alignment marks and overlay marks with various substrates and segmentations. It’s recommended that the whole process from mark definition by lithography to final formation of mark after etch should be well taken into consideration during mark design, along with substrate and segmentation to avoid defect and achieve qualified signal as well.