Predicting Pattern Surface Distortions of Extreme Ultraviolet Lithography Masks due to Particle Entrapment during Exposure Chucking

An extreme ultraviolet lithography (EUVL) system employs nontelecentric illumination, and thus the flatness requirement for the EUVL masks during exposure chucking is a key issue in minimizing image placement errors at the wafer level. Particle generation during mask handling and chucking in the exposure tool poses a serious threat to successful pattern transfer. This research characterizes and predicts the effect of particle-induced reticle distortion during exposure chucking via the use of numerical and analytical models. Finite element (FE) models have been developed to simulate the micro-scale response of the reticle / particle / chuck system. Experimental indentation testing to identify relevant nano-scale material properties has also been performed. To capture the macro-scale response, global FE models have been generated to simulate exposure chucking under typical clamping conditions. The local FE models have been benchmarked against suitable test cases, and the validity of the predictions of the global FE models have been verified analytically. The contribution of the particle-induced reticle distortion toward the image placement error has also been evaluated.