Simulation based OPC for contact pattern using 193 nm lithography

For state of the art technologies, rule based optical proximity correction (OPC) together with conventional illumination is commonly used for contact layers, because it is simple to handle and processing times are short. However, as geometries are getting smaller it becomes more difficult to accurately control critical dimension (CD) variations influenced by nearby pattern. This applies in particular for irregularly arranged contact holes. Here simulation based OPC is more effective. We present a procedure for application of simulation based OPC for a 193 nm lithography contact hole layer with rectangular contact holes of different sizes in different proximities, using attenuated phase shift masks. In order to further improve the accuracy of the simulation based OPC process, characteristics of the mask, like mask comer rounding are. incorporated in the OPC process. We build an OPC model, use it for OPC processing of DRAM design data and investigate the process window of the printing contacts. The results show an overlapping process window for length and width of isolated and dense small contact holes of different length and width, which is sufficient for volume production.