Orthogonal functional method for optical proximity correction of thermal processes in optical lithography

The patterning of very small features is a difficult challenge for current lithography technology. The thermal process is an easy and simple solution involving no any additional processes. This process is one of extension techniques for 248 nm KrF and 193 nm ArF lithography equipment and chemically amplified resists (CARs). However, thermal effects are severe, thus, more critical approaches are needed for small pattern formation. In this paper, thermal processes are described and modelled for evaluating property changes in 248 and 193 nm CARs. The simulated results agree well with experimental results. Those processes can be used to shrink not only contact hole patterns but also space patterns. For the optical proximity correction (OPC) of thermal effects, an orthogonal functional method is introduced. These orthogonal functions depend on pattern types such as contact holes and spaces. By using this method, underbaked postexposure bake and thermal reflow are performed for the below-45-nm contact hole pattern for a 248 nm KrF CAR and the 32 nm contact hole pattern for a 193 nm ArF CAR. Thus, an orthogonal functional method is useful for carrying out the OPC for thermal effects.