Optical Measurement System for Nanostructure Critical Dimension Analysis
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Solution Overview
Problem
Current measurement methods for nanoscale objects, such as scanning electron microscopes and atomic force microscopes, are inefficient and costly when dealing with semiconductor structures of small critical dimensions, while optical methods like ellipsometry and scatterometry face challenges in accuracy and speed.
Innovation Solution
An optical measurement system utilizing an optical transfer function (OTF) for defocused image analysis, which includes an optical module, OTF measurement, optical system parameter control, defocused image calculation, and CD evaluation modules to accurately determine the critical dimension of nanostructured surfaces by comparing registered and calculated defocused images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement methods (SEM, AFM) are used for nanoscale objects, then measurement accuracy can be maintained, but measurement speed is slow and cost is high
Solution Approach 1:
The patent replaces mechanical measurement systems (SEM, AFM) with an optical measurement system that uses light interference and optical transfer functions to measure critical dimensions. This substitution enables faster, non-contact measurement while maintaining accuracy through optical field analysis rather than mechanical scanning or electron beam scanning.
Solution Approach 2:
The patent changes the measurement parameters by using optical wavelength and interference patterns instead of mechanical position scanning. By measuring the optical transfer function at different defocus positions and analyzing interference fringes, the system extracts critical dimension information optically, achieving both speed and accuracy.
2Productivity
If optical methods (ellipsometry, scatterometry) are used for CD measurement, then measurement speed improves, but measurement accuracy deteriorates for structures smaller than Rayleigh limit
Solution Approach 1:
The patent moves from two-dimensional image analysis to three-dimensional optical field analysis by measuring the optical transfer function through defocused image analysis. By capturing and analyzing interference patterns in the optical path (adding the dimension of optical field phase information), the system can resolve structures below the Rayleigh limit with high accuracy while maintaining fast measurement speed.
Solution Approach 2:
The patent introduces the optical transfer function as an intermediary that bridges the gap between optical measurement and critical dimension extraction. By measuring how the optical system transfers spatial frequencies through defocused images and analyzing interference fringes, the system accurately determines CD values for sub-Rayleigh structures without direct imaging.
3Device complexity
If defocused image analysis without OTF measurement is used, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent implements self-service by having the optical measurement system automatically measure its own optical transfer function using interferograms from the same optical path. The system characterizes its own aberrations and uses this information to correct and improve CD measurement accuracy, eliminating the need for external calibration equipment while enhancing precision.
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 provides a fast, accurate, and cost-effective method for measuring critical dimensions of nanoscale objects, improving reliability and precision by using OTF measurement and defocused image analysis, enabling the determination of precise CD values with enhanced accuracy.
Implementation Method 1
an optical module including an optical system and configured to illuminate a sample and to register a defocused image of a nanostructured surface of the sample
Implementation Method 2
The OTF measurement module may be further configured to analyze interferograms that correspond to an illumination light aberrated by the optical measurement system and a reference light
Data Source
AI summary
Provided is an optical measurement system. The optical measurement system includes: an optical module which includes an optical system and which is configured to illuminate a sample and register a defocused image of a nanostructured surface of the sample, an optical system parameter control module configured to set optical parameters of the optical system, an optical transfer function (OTF) measurement module configured to measure an OTF, a defocused image calculation module configured to calculate the defocused image based on the measured OTF and the optical parameters, and a critical dimension (CD) evaluation module configured to compare the registered defocused image with the calculated defocused image of the nanostructured surface of the sample and to output a CD value of the nanostructured surface.