Analysis and experiments of the thermal-optical performance for a kinematically mounted lens element

Area of Science:

• Optical Engineering
• Materials Science
• Mechanical Engineering

Background:

• Lithographic projection lenses are critical for semiconductor manufacturing.
• Thermal variations can degrade optical performance and manufacturing precision.
• Kinematic mounts are proposed to mitigate thermal effects in optical systems.

Purpose of the Study:

• To evaluate the thermal-optical performance of a kinematic mounting system for lithographic projection lenses.
• To quantify surface figure and wavefront changes under thermal load.
• To assess the mount's ability to reduce thermally induced aberrations.

Main Methods:

• Experimental measurements of lens element temperature, surface figure, and wavefront.
• Numerical simulations to model thermal load and optical response.
• Comparison of experimental and simulation data to validate the methodology.

Main Results:

• Non-uniform temperature distribution observed, with edge temperatures rising significantly.
• Thermal inhomogeneity induced RMS changes in optical surface figure (9.622 nm) and index inhomogeneity (71.905 nm), dominated by Zernike terms Z4, Z9, and Z16.
• Kinematic mounting demonstrated radial flexibility, limiting asymmetric aberrations (e.g., trefoil) to <2% of total wavefront changes.
• Experimental and simulation results showed excellent agreement (Zernike coefficient differences <2 nm).

Conclusions:

• The kinematic mounting exhibits good thermal adaptability for lithographic projection lenses.
• The employed evaluation method for thermal-optical characteristics is effective and validated.
• This approach provides a reliable means to assess optical system performance under thermal stress.