Solid Immersion Lens Position Control via Casimir Force Compensation
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Solution Overview
Problem
Current techniques for reducing the size and improving the accuracy of metrology/inspection targets in lithographic processing face challenges in maintaining accuracy and reducing target size due to constraints related to the measurement of small gap distances and varying surface topographies, particularly when using solid immersion lenses (SILs) in close proximity to substrates.
Innovation Solution
The method involves calculating and compensating for the Casimir force and stiffness between the SIL and the substrate surface to maintain a precise gap distance, using estimated Casimir effects to stabilize the control loop and improve positioning accuracy, thereby enabling more accurate and reliable measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a solid immersion lens is positioned in close proximity to the substrate surface to achieve high numerical aperture and improved measurement accuracy, then measurement precision is improved, but positioning stability deteriorates due to Casimir forces and stiffness variations
Solution Approach 1:
The patent implements a feedback control mechanism that continuously monitors the gap distance between the solid immersion lens and substrate surface, and adjusts the lens position to compensate for Casimir force variations. This feedback loop maintains stable positioning despite the strong attractive forces at nanometer-scale gaps, enabling both high measurement precision and positioning stability
Solution Approach 2:
The patent compensates for Casimir force effects by dynamically adjusting positioning parameters based on the measured gap distance. By calculating the expected Casimir force at each gap distance and adjusting the lens position accordingly, the system maintains stable positioning while operating at the small gap distances required for high numerical aperture measurements
2Measurement precision
If the gap distance between the solid immersion lens and substrate is reduced to enable high numerical aperture measurements, then measurement precision is improved, but measurement reliability deteriorates due to varying surface topographies and Casimir forces
Solution Approach 1:
The patent performs preliminary measurement of the surface topography before the actual measurement process. This advance characterization of the surface allows the system to pre-calculate expected Casimir force variations and adjust positioning parameters in advance, ensuring reliable measurements even over varying topographies
Solution Approach 2:
The patent employs dynamic positioning adjustment during the measurement process, continuously adapting the lens position to follow the surface topography while maintaining the optimal gap distance. This dynamic compensation for surface variations ensures measurement reliability across different topographic features
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise control of the SIL's position relative to the substrate, enhancing measurement accuracy and stability, even at small gap distances, which is crucial for advanced lithographic processes.
Implementation Method 1
calculating and compensating for the Casimir force and stiffness between the SIL and the substrate surface
Data Source
AI summary
A method and apparatus for position control of a component relative to a surface is disclosed. The method may include calculating an estimated effect of, or derived from, Casimir force acting between the component and the surface, and compensating positioning of the component relative to the surface using the estimated effect.