Comparison of wavefront reconstruction with modal method and zonal method for the inspection of catadioptric projection optics using Hartmann wavefront sensor

Rapid progress of exposure systems for IC manufacturing is pushing their performance from sub-micrometer to nanometer and catadioptric projection optics have been developed to fulfill this trend. The catadioptric projection optics will produce an annular wavefront. In our system with catadioptric projection optics, the Hartmann wavefront sensor is employed for the test. The wavefront reconstruction method is essential to the accuracy of inspection. For typical annular wavefronts with smaller and larger obscuration ratios, the wavefront reconstructed via modal method with Zernike annular polynomials, modal method with Zernike circular polynomials and zonal method are compared. Simulation results show that both the modal method with Zernike annular polynomials and zonal method are qualified to guarantee the accuracy of reconstruction in both cases. While the modal method with Zernike circular polynomials fail in the case of larger obscuration ratios. The wavefront reconstruction with different terms of Zernike annular polynomials, Zernike circular polynomials and the wavefront fit following the zonal method with a different number of Zernike polynomials are conducted as well.