论文信息 - Comparison of EUV interferometry methods in EUVA project

Comparison of EUV interferometry methods in EUVA project

We are developing an at-wavelength interferometer for EUV lithography systems. The goal is the measurement of the wavefront aberration for a six-aspherical mirror projection optic. Among the six methods that EEI can measure, we selected CGLSI and PDI for comparison. PDI is a method well-known for its high accuracy, while CGLSI is a simple measurement method. Our comparison of PDI and CGLSI methods, verified the precision of the CGLSI method. The results show a difference between the methods of 0.33nm RMS for terms Z5-36. CGLSI measurement wavefronts agree well with PDI for terms Z5-36, and it is thought of as a promising method. Using FFT analysis, we estimated and then removed the impact of flare on the wavefront. As a result of having removed the influence of flare, the difference between CGLSI and PDI improved to only 0.26nm RMS in Zernike 5-36 terms. We executed PDI wavefront retrieval with FFT, which has not been used till now. By confirming that the difference between methods using FFT and Phase shift is 0.035nm RMS for terms Z5-36, we have proven that PDI wavefront analysis with FFT is possible.

[1] M. Takeda,et al. Lateral aberration measurements with a digital Talbot interferometer. , 1984, Applied optics.

[2] Kazuya Ota,et al. Advanced point diffraction interferometer for EUV aspherical mirrors , 2001, SPIE Advanced Lithography.

[3] Kazuya Ota,et al. Development of an experimental EUV interferometer for benchmarking several EUV wavefront metrology schemes , 2003, SPIE Advanced Lithography.