Measurement of Wavefront Aberration of Extreme Ultraviolet Lithographic Projection Lens Based on Ptychography

Ptychography, a phase retrieval technology based on scanning coherent diffractive imaging, shows such advantages as simple experimental setup and strong anti-noise ability. Ptychography is used in the field of wavefront metrology for projection lens. The formulas of optical field propagation, the conditions of discretion, and the experimental configurations are analyzed in detail for projection lenses with different numerical apertures. Numerical simulations and experimental results show that to achieve reasonable convergence and measurement accuracy, the transmittance of the object should be set between 45% and 80%. Increasing the complexity of the object pattern and adding registration process of probe and object into the iterative algorithm can also improve the convergence speed and the recovery accuracy. The wavefront aberration measurement accuracy can reach 10~(-3)lambda or less. It is feasible to use ptychography in wavefront aberration measurement for extreme ultraviolet lithographic projection lenses.