Goos-Hanchen Error Compensation Autofocus
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Solution Overview
Problem
The Goos-Hanchen effect causes significant errors in autofocus systems due to variations in substrate patterns and coating thicknesses, making it difficult to accurately measure surface height, and existing compensation methods like ellipsometry are complex and resource-intensive.
Innovation Solution
A method that compensates for Goos-Hanchen errors by using a broadband light spectrum filtered across wavelengths and polarizations to minimize error variations, either through an 'analog' approach with physical filters or a 'digital' approach with software-based spectral and polarization filtering, allowing for accurate substrate position determination without complex optical systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ellipsometry is used to determine substrate film structure and estimate GH error, then measurement precision is improved, but device complexity increases significantly
Solution Approach 1:
The patent extracts only the essential information needed for GH error compensation by using a simplified optical setup that measures substrate reflectance at multiple wavelengths, rather than implementing the full ellipsometry system. This extraction approach achieves the necessary measurement precision without the complex optical components and computational requirements of ellipsometry.
Solution Approach 2:
The patent creates a simplified model of the substrate optical properties by measuring reflectance at multiple wavelengths and using this data to estimate the GH error. This copying approach replicates the essential functionality of ellipsometry for GH error compensation while using a much simpler optical system that does not require complex polarizing optics or sophisticated data analysis.
2Measurement precision
If broadband light spectrum is filtered dynamically, then Goos-Hanchen errors are minimized, but device complexity increases
Solution Approach 1:
The patent implements periodic action by sequentially switching between different bandpass filters to illuminate the substrate at different wavelength ranges. This time-multiplexed approach allows the system to gather spectral information needed for GH error compensation using a single detector, avoiding the need for complex simultaneous multi-wavelength detection systems while achieving effective error minimization.
3Measurement precision
If multiple wavelength bands are used to compensate GH errors, then measurement precision is improved, but loss of time increases due to sequential measurement
Solution Approach 1:
The patent applies partial action by selecting and measuring only the most informative wavelength bands that provide the greatest contribution to GH error compensation. Rather than measuring across the entire spectrum or using equal weighting for all wavelengths, the system identifies and measures specific wavelength ranges that are most sensitive to the substrate optical properties, thereby achieving effective compensation with reduced measurement time.
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 method effectively reduces Goos-Hanchen errors to nearly arbitrary low levels without the need for ellipsometry, providing accurate substrate height measurements across various substrate conditions using either the analog or digital filtering approaches.
Implementation Method 1
The Goos-Hanchen (GH) effect produces a shift of a beam when incident on an optical interface (e.g. a substrate that is imaged by an imaging optical system in the production of a semiconductor wafer)
Implementation Method 2
reflected light from the substrate is provided at a plurality of wavelengths and polarizations
Implementation Method 3
reflected light from the substrate is provided at a plurality of wavelengths and polarizations, detected and used to make corrections
Data Source
AI summary
Prediction of a distribution of light in an illumination pupil of an illumination system includes identifying component(s) of the illumination system the adjustment of which affects this distribution and simulating the distribution based on a point spread function defined in part by the identified components. The point spread function has functional relationship with configurable setting of the illumination settings.