Wavefront Sensing for Evaluation of Extreme Ultraviolet Microscopy.

Area of Science:

• Optics and Photonics
• Metrology
• Extreme Ultraviolet (EUV) Lithography

Background:

• Wavefront analysis is a key technique for optical system alignment and characterization across various spectral regions.
• High-numerical-aperture (NA) systems, particularly those used in extreme ultraviolet (EUV) lithography, present unique challenges for traditional wavefront analysis.
• Schwarzschild objectives are critical for achieving small foci in EUV photolithography, necessitating highly precise alignment.

Discussion:

• A high-NA Hartmann wavefront sensor was utilized at the free electron laser FLASH to characterize a Schwarzschild objective.
• The study addresses the challenges of applying wavefront analysis to optical systems with NA > 0.1.
• The characterization was performed on a Schwarzschild objective, a component vital for EUV photolithography.

Key Insights:

• The performance of a high-NA Hartmann wavefront sensor was evaluated for characterizing EUV optics.
• Two distinct wavefront analysis methods, centroid calculation and Fourier demodulation, were employed.
• Both analysis methods yielded consistent wavefront maps, demonstrating negligible discrepancies and validating the measurement approach.

Outlook:

• This work validates wavefront analysis techniques for high-NA EUV optical systems.
• The findings support the precise alignment of Schwarzschild objectives for advanced photolithography applications.
• Future research may explore further refinements in wavefront sensing for even more demanding optical metrology.