Model based high NA anamorphic EUV RET

With the announcement of the extension of the Extreme Ultraviolet (EUV) roadmap to a high NA lithography tool that utilizes anamorphic optics design, an investigation of design tradeoffs unique to the imaging of anamorphic lithography tool is shown. An anamorphic optical proximity correction (OPC) solution has been developed that models fully the EUV near field electromagnetic effects and the anamorphic imaging using the Domain Decomposition Method (DDM). Clips of imec representative for the N3 logic node were used to demonstrate the OPC solutions on critical layers that will benefit from the increased contrast at high NA using anamorphic imaging. However, unlike isomorphic case, from wafer perspective, OPC needs to treat x and y differently. In the paper, we show a design trade-off seen unique to Anamorphic EUV, namely that using a mask rule of 48nm (mask scale), approaching current state of the art, limitations are observed in the available correction that can be applied to the mask. The metal pattern has a pitch of 24nm and CD of 12nm. During OPC, the correction of the metal lines oriented vertically are being limited by the mask rule of 12nm 1X. The horizontally oriented lines do not suffer from this mask rule limitation as the correction is allowed to go to 6nm 1X. For this example, the masks rules will need to be more aggressive to allow complete correction, or design rules and wafer processes (wafer rotation) would need to be created that utilize the orientation that can image more aggressive features. When considering VIA or block level correction, aggressive polygon corner to corner designs can be handled with various solutions, including applying a 45 degree chop. Multiple solutions are discussed with the metrics of edge placement error (EPE) and Process Variation Bands (PVBands), together with all the mask constrains. Noted in anamorphic OPC, the 45 degree chop is maintained at the mask level to meet mask manufacturing constraints, but results in skewed angle edge in wafer level correction. In this paper, we used both contact (Via/ block) patterns and metal patterns for OPC practice. By comparing the EPE of horizontal and vertical patterns with a fixed mask rule check (MRC), and the PVBand, we focus on the challenges and the solutions of OPC with anamorphic High-NA lens.