Mask phase and transmission variation effects on wafer critical dimensions for nodes 65nm and 45nm

In microelectronic industry, mainly from the 65nm node, phase shift photomasks (PSM) are increasingly used for critical layers, optical properties of the shifter (MoSi) giving a better control of critical dimensions (CD) in photoresist. Fab-users and maskshops have committed on specifications that restrict phase and transmission variations within certain limits. The goal of this study is to validate and/or update these previously admitted limits. A specific test reticle has been jointly designed with several structures representative of 65nm and 45nm nodes and then manufactured with a specific process in order to voluntarily degrade the phase and transmission uniformity within the mask. Knowing all CD and their related phase and transmission on mask, CD variations seen on wafers have been directly linked to phase and transmission variations. In parallel, rigorous simulations have been performed using Panoramic software in order to predict effects of phase and transmission variations on wafer. This reticle has been also used for early studies to evaluate the impact of phase and transmission variations on optical proximity correction (OPC) model.