Evaluation of Particle Protection Capability of Extreme Ultraviolet Lithography Mask Carrier in Vacuum Transfer by Experiment and Calculation

In extreme ultraviolet lithography (EUVL), particle-free mask handling is a critical issue. We have studied particle protection capability of a dual pod, which consists of an outer pod and an inner pod that holds the mask. Our experiment and calculation demonstrated that a dual pod prevents particle addition in a quality area of 142×142 mm2 at the center of the mask, because particles entering the inner pod stopped near the edges. Our experiments showed 8 particle adders (≥46-nm polystyrene latex particle equivalent) for 1850-cycle transfer tests, and the dual pod satisfied the pre-production tool specification. Our measurement repeatability was 0.0015(σ)/cycle with a binominal distribution; however, we found that the accuracy was insufficient for an estimated specification of a high-volume machine. We discussed the necessary handling cycles and a method to improve repeatability by inspecting the area outside the quality area.