Optical Inspection Correction for Dynamic Condition Errors
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Solution Overview
Problem
Optical systems, particularly those using solid immersion lenses (SIL) or micro-SIL, face challenges in maintaining accurate positioning and stability due to dynamic condition errors such as focus errors, thermal changes, and mechanical vibrations, leading to aberrations and inaccuracies in measurements.
Innovation Solution
A method and apparatus that correct for dynamic condition errors by calculating and applying a correction to the radiation distribution in real-time, using a processor to observe and adjust for deviations caused by errors such as focus errors, thermal conditions, and mechanical distortions, allowing for more accurate property determination of structures without the need for high computational recalculations of diffraction-based models.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a solid immersion lens (SIL) is used to increase the range of scattering angles, then measurement capability is improved, but positioning accuracy deteriorates due to dynamic condition errors
Solution Approach 1:
The patent implements a feedback mechanism where condition errors (focus errors, thermal changes, mechanical vibrations) are detected and used to generate correction values that are applied to the measured radiation distribution. The processor continuously monitors the optical system conditions and adjusts the measurement corrections in real-time, creating a closed-loop system that maintains positioning accuracy despite dynamic changes.
Solution Approach 2:
The patent changes the parameters of the measurement system by introducing correction values that account for dynamic condition errors. Instead of using a fixed calibration, the system adapts the correction parameters based on real-time detection of focus errors, thermal conditions, and mechanical vibrations, allowing the same optical system to maintain accuracy across varying conditions.
2Measurement precision
If dynamic condition errors are corrected through computational recalculations, then measurement accuracy is improved, but computational burden increases
Solution Approach 1:
The patent performs preliminary actions by pre-calculating and storing correction values for different condition error states. Instead of performing complex computational recalculations during measurement, the system uses pre-computed correction data that can be quickly applied to the measured radiation distribution, significantly reducing real-time computational requirements.
Solution Approach 2:
The patent creates a simplified representation of the complex optical system by using correction values that capture the essential effects of condition errors without requiring full physical modeling. These correction values serve as a simplified copy of the complex computational models, allowing for fast application during measurements without the heavy computational burden of the underlying physics simulations.
3Device complexity
If focus errors and thermal changes are not compensated, then device complexity is reduced, but measurement reliability deteriorates
Solution Approach 1:
The patent implements self-service by enabling the optical system to automatically detect and correct its own condition errors. The system monitors its own focus state, thermal conditions, and mechanical vibrations, then applies appropriate corrections without requiring external intervention or complex additional hardware, maintaining simplicity while improving reliability.
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 measurement accuracy by compensating for dynamic condition errors, reducing the impact of aberrations and improving the precision of property determination in optical systems, particularly in scatterometry, without increasing computational burden or requiring custom-made optics.
Implementation Method 1
measure one or more properties of the scattered radiation—e.g., intensity at a single angle of reflection
Implementation Method 2
diffraction based overlay can be measured using such apparatus
Implementation Method 3
a solid immersion lens (SIL) or miniature SIL (micro-SIL) can be provided between an objective lens and the target structure
Data Source
AI summary
An optical system and detector capture a distribution of radiation modified by interaction with a target structure. The observed distribution is used to calculate a property of the structure (e.g. CD or overlay). A condition error (e.g. focus error) associated with the optical system is variable between observations. The actual condition error specific to each capture is recorded and used to apply a correction for a deviation of the observed distribution due to the condition error specific to the observation. The correction in one practical example is based on a unit correction previously defined with respect to a unit focus error. This unit correction can be scaled linearly, in accordance with a focus error specific to the observation.