RET for optical maskless lithography

Abstract
Due to the ever-increasing mask cost, Optical Maskless Lithography provides an attractive alternative to mask-based lithography, especially for low-volume runs. In order to offer a seamless mix-and-match solution with mask-based scanners, or a complete transfer from mask-based to maskless lithography, the imaging performance of a maskless tool must at least match the performance of a regular scanner. This paper reports results from simulations showing very good agreement with a mask-based scanner at the 65 nm design node, including semi-isolated lines of 50 nm (AttPSM), 45 nm (CPL), and 35 nm (phase edge). Due to a new enhanced rasterization, the results show minor or no influence at all from the pixel grid. The results also indicate that a maskless tool can use the same OPC model as a mask-based scanner, including phase-shifting.