Flare and lens aberration requirements for EUV lithographic tools

EUV lithographic tools can support the 32 nm MPU manufacturing node and beyond. In order to meet the stringent requirements on CD control and overlay for such technology generations, wavefront error and flare of the EUV exposure systems have to be well controlled. The cross field variations of wavefront errors and flare need to be in the acceptable range in order to improve the common Depth of Focus (DoF) across the field. The impacts of lens aberration and flare to the aerial image at the system level are studied for the 32nm MPU technology node using Intel's aerial image simulation tool. The focus control budget of the exposure tools has been estimated. Useable Depth of Focus (UDoF) has been defined, and focus margin between UDoF and focus control budget from the exposure tool has been calculated for various cases. Focus margin has been used to determine the flare and lens aberration requirements for the 32nm MPU node. It is found that <10% intrinsic flare and <0.75nm rms lens aberration are required for the 32nm MPU node. Process window as a measure of individual aberration terms for the 32nm node has been also investigated.