Thermal distortion of EUV reticle during exposure

Extreme ultraviolet lithography (EUVL) is one of all candidate next-generation lithography technologies targeting 45 nm features, the industrial throughput should be more than 80 wafers-per-hour. As the throughput requirements are increased, the incident EUV power on reticle density rise. About 100% the incident power is absorbed by the absorber layer and 35% is absorbed by Mo/Si multi-layers to result in a significant thermal distortion in the reticle. Such effects can contribute to reticle-wafer overlay error, so it is necessary to quantify the reticle distortion. In this work, detailed three-dimensional thermal and structure models have been developed using finite element methods. The results show that the maximum in-plane distortion in x-y plane and z indirection are respectively about 1.11 nm and 0.26 nm when the sensitivity of the resist and the EUV power density are respectively 7 mJ/cm² and 259.24 W/cm², and they are respectively about 0.71 nm and 0.19 nm when the sensitivity and the power density are 5 mJ/cm² and 184.38 W/cm² respectively.