Thermal and structural deformation of projection optics and its influence on optical imaging performance for 22 nm extreme ultraviolet lithography

Extreme ultraviolet lithography (EUVL) is the next generation lithography for the semiconductor manufacturer to achieve 22 nm node and below. In the process of exposure, the 35%~40% incident power will be absorbed by multilayers of extreme ultrauiolet (EUV) optics, resulting in the thermal and structural deformation of the mirror, and consequently affecting the optical performance of the projection optics (PO). It is based on a six-mirror PO designed for EUVL at 22 nm technology generation with an image numerical aperture of 0.3. Finite element analysis (FEA) method is used for the deformation analysis of the six-mirror PO, and then the deformation is introduced to CODE V to evaluate its effect on the PO. The results show that the maximum temperature increase is 9.77°C, and the maximum deformation at clear aperture is 5.89 nm, with the beam power of 321 mW onto the wafer and wafer throughtput reaches 100 wafers per hour. While it is partial coherently illuminated (partial coherent factor 0.5), the distortions of 22 nm line and space is 6.956 nm, critical dimension (CD) error is 3.414%.