This work delves into designing and implementing an optimized self-centering lens mounting technique for the collimator and coupler lenses in the Universal Light Source (ULS) by ASML. The ULS aims to meet the growing demand for smaller logic nodes and higher throughput in optical metrology sensors. To achieve precise alignment and stability, the light source utilizes a supercontinuum spectral shaping method based on a highly non-linear hollow core anti-resonance photonic crystal fiber filled with a high-pressure noble gas.
This research identifies the limitations of the existing lens mounting design in terms of manufacturing, stability, and adhesive usage. To address these challenges, a self-centering design is proposed, leveraging the geometrical relationship between thread angle, barrel and retaining ring diameters, and lens clearance. By optimizing these parameters, the centering error is substantially reduced, demonstrating a considerable improvement in centering precision compared to the current method. Additionally, thermal effects are mitigated through a symmetrical design and local flexibility, reducing the impact of temperature fluctuations during operation and transportation.
An analytical assessment of five different collimator and coupler lens mount concepts are presented to identify an optimal design meeting specific operating temperature, stresses, eigenfrequency, and manufacturability criteria. Numerical analysis is employed to evaluate the performance of each design concept relative to the currently employed mounting designs.
The resulting optimized self-centering coupler and collimator lens mount exhibits centering errors influenced by various tolerances. These tolerances have a deviation of ±0.2% for the lens radial surface, ±1° for the thread angle, and ±0.2 mm for the remaining parameters. The calculated centering errors for coupler lens and collimator lens 1 and 2 are 6.27 μm, 8.24 μm, and 6.98 μm, respectively. However, it is crucial to acknowledge that these results are purely theoretical and necessitate validation through experimental data to ascertain their accuracy.
Overall, this optimized self-centering technique offers enhanced stability, relaxed manufacturing tolerances, and eliminates the need for adhesives when compared to the current flexure design. These significant findings contribute to the advancement of optomechanical engineering and provide valuable insights into the implementation of self-centering mounts, thereby enhancing precision while relaxing manufacturing requirements in optomechanical mounting.