Low Coherence Interferometry System Error Compensation

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Solution Overview

Problem

Scanning white light interferometry (SWLI) signals are degraded by optical aberrations and dispersion, leading to reduced accuracy and difficulty in characterizing thin films due to overlapping interference patterns from multiple interfaces.

Innovation Solution

The method involves characterizing system errors in the frequency domain and correcting SWLI signals by subtracting or dividing known phase and amplitude errors, allowing for improved signal quality by reducing imperfections such as source spectrum distortions and nonlinear dispersion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a light source with large bandwidth is used in SWLI, then the resolution and measurement capability are improved, but the signal quality is degraded due to optical aberrations and dispersion

Engineering Contradiction:

ImproveresolutionVSAvoidsignal quality

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent performs preliminary characterization of the interferometer system to determine system errors including optical aberrations and dispersion effects. This preliminary action enables subsequent correction of the interference signal by removing the identified errors, thereby maintaining high resolution while improving signal quality.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the harmful effects of optical aberrations and dispersion into correctable parameters by characterizing them during system setup. The identified aberration and dispersion characteristics are then used to generate correction terms that are applied to the interference signal, transforming these previously detrimental effects into manageable and correctable factors.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Adaptability or versatility

If a light source with large bandwidth is used in SWLI, then the usable bandwidth is extended, but source spectrum distortions and nonlinear dispersion reduce measurement accuracy

Engineering Contradiction:

Improveusable bandwidthVSAvoidmeasurement accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent changes the parameters of the interference signal by applying correction terms that compensate for source spectrum distortions and nonlinear dispersion. These parameter changes include adjusting the phase and amplitude characteristics of the signal to eliminate the effects of spectral distortions, thereby maintaining measurement accuracy across the extended bandwidth.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs feedback by using the characterized system errors to generate correction terms that are applied to subsequent measurements. The system continuously accounts for the identified distortions and dispersion effects, adjusting the signal processing to maintain accuracy across the full bandwidth range.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If SWLI is used to characterize thin films, then the ability to measure spatial properties is improved, but overlapping interference patterns from multiple interfaces make signal extraction difficult

Engineering Contradiction:

Improvespatial property determinationVSAvoidsignal extraction difficulty

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent performs preliminary system characterization to identify and quantify system errors before measuring thin film samples. This preliminary action enables the development of correction methods that can be applied to the interference signals from thin films, making it easier to extract accurate information from overlapping interference patterns by removing the confounding system error contributions.

Inventive Principle:

Principle #10Preliminary action

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 enhances the accuracy of SWLI measurements by extending the usable bandwidth of light sources, improving resolution, and enabling better separation of signals from different interfaces, particularly for thin films, without substantial loss in signal-to-noise ratio.

Implementation Method 1

an imaging interferometer configured to receive light from the light source, to direct a portion of the light to reflect from a measurement object, to direct another portion of the light to reflect from a reference object, and to combine the light reflected from the measurement and reference objects to produce an output beam

Methodology Applied

Scientific EffectInterference: Interference

Data Source

PatentUS7522288B2Compensation of systematic effects in low coherence interferometry

Publication Date: 2009.04.21 ZYGO CORP

AI summary

In general, in one aspect, the invention features a method that includes transforming interferometry data acquired for a test sample using a low coherence imaging interferometry system to a frequency domain and, at a plurality of frequencies in the frequency domain, reducing contributions to the transformed interferometry data due to imperfections in the imaging interferometry system thereby producing compensated interferometry data. The errors are reduced based on variations between interferometry data acquired using the low coherence imaging interferometry system for a calibration sample and model interferometry data corresponding to data acquired for the calibration sample using a model interferometry system.