White Light Interferometer Height Mapping via Principal Component Analysis
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Solution Overview
Problem
Existing white light interferometry methods for determining height maps are prone to inaccuracies due to vibrations of the sample relative to the interferometer, which affect phase differences and result in unreliable height maps, and known vibration damping methods are costly and insufficient.
Innovation Solution
A method using principal component analysis of a stack of interferograms to separate random phase shifts caused by vibrations from phase shifts related to the sample height, allowing for a height map determination with reduced dependency on vibrations, achieved through a white light interferometer with a broad band light source, optical sensor, and processor configured to perform the method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vibration dampers are used to isolate the white light interferometer from vibrational effects, then the reliability of height map determination is improved, but the overall costs increase and the dampers may not sufficiently reduce the effect of vibrations
Solution Approach 1:
The patent replaces the mechanical vibration isolation system (vibration dampers) with a signal processing approach using principal component analysis. Instead of physically isolating the interferometer from vibrations, the method processes the interferogram data to separate vibration-induced phase shifts from actual height information, thereby reducing dependency on mechanical damping while lowering costs and complexity.
Solution Approach 2:
The patent changes the approach from modifying physical parameters (mechanical isolation) to transforming data parameters through mathematical processing. By applying principal component analysis to the interferogram stack, the system transforms the raw measurement data into separated components that distinguish between vibration effects and true surface height, achieving reliability improvement without mechanical modifications.
2Measurement precision
If vibration dampers are used to reduce vibrational effects, then the measurement precision is improved, but the overall costs increase and the dampers may not sufficiently reduce the effect of vibrations
Solution Approach 1:
The patent substitutes mechanical vibration damping with a computational method that processes interferogram stacks. The principal component analysis separates vibration-induced phase variations from height-related phase information, achieving improved measurement precision through data processing rather than mechanical isolation, thereby avoiding increased costs and device complexity.
Solution Approach 2:
The patent takes multiple copies of the interferogram (creating a stack of interferograms at different vertical positions) and processes them together. By analyzing the stack rather than single interferograms, the method extracts height information while filtering out vibration effects that vary between frames, achieving precision improvement without additional mechanical damping equipment.
3Reliability
If a stack of interferograms is processed using principal component analysis, then the dependency on vibrations is reduced, but the processing complexity increases
Solution Approach 1:
The patent segments the interferogram stack into distinct components through principal component analysis. The first principal component captures the dominant height-related phase information, while the second principal component captures vibration-induced phase variations. This segmentation allows selective use of the height-related component for measurement, reducing vibration dependency through systematic data decomposition.
Solution Approach 2:
The patent introduces principal component analysis as an intermediary processing step between raw interferogram acquisition and final height map generation. This intermediary transformation converts the complex, vibration-contaminated interferogram stack into separated components, with the first principal component serving as the cleaned height information source, thereby reducing vibration impact without requiring complex hardware modifications.
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
The method effectively reduces the impact of vibrations on height map accuracy by isolating random phase shifts, resulting in improved precision and reliability of the height map determination.
Implementation Method 1
Both light beams interfere with each other which results in an interference pattern and allows the interferometer to measure an interferogram associated with the sample surface
Data Source
AI summary
The invention relates to a method for determining a height map of a surface of a sample through white light interferometry wherein use is made of a white light interferometer with a broad band light source and an optical sensor including pixels. The invention further relates to a white light interferometer including a broad band light source, an optical sensor including pixels and a processor configured for performing the method of the invention. The invention further relates to a digital data carrier including a computer program which, when run on a processor of a white light interferometer according to the invention, causes the white light interferometer to perform the method according to the invention.