Charged-Particle Beam Image Aberration Correction by Defocus Series
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Solution Overview
Problem
Charged-particle beam tools, such as electron beam inspection tools, face challenges in maintaining high spatial resolution due to aberrations in the probe spot profile, which affect the detection of micro and nano-sized defects on semiconductor wafers, leading to reduced yield and throughput in IC chip manufacturing.
Innovation Solution
A method is developed to determine and correct aberrations in charged-particle beam tools by obtaining multiple images under varying measurement conditions, selecting an estimated aberration parameter, evaluating an error function, and iteratively updating the parameter to achieve the smallest error value, thereby improving image quality and tool settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a focused probe spot of primary electrons is used to generate secondary electrons for imaging, then the spatial resolution of the image is improved, but aberrations in the probe spot profile reduce the spatial resolution
Solution Approach 1:
The patent applies preliminary action by measuring aberrations at multiple known defocus values before final imaging. The system performs defocus series measurements to determine aberration parameters (astigmatism, field curvature, distortion) in advance, then uses these parameters to correct the probe spot profile for high-resolution imaging.
Solution Approach 2:
The patent implements feedback by using measured aberration parameters to adjust and correct the probe spot profile. The system continuously monitors aberrations through defocus series and feeds this information back to optimize the imaging conditions, ensuring the probe spot maintains optimal focus and resolution.
2Measurement precision
If multiple images are obtained at different measurement conditions to determine aberrations, then the accuracy of aberration correction is improved, but the measurement time and complexity increase
Solution Approach 1:
The patent applies partial action by selecting only the essential aberration parameters (astigmatism, field curvature, distortion) that most significantly affect image quality. Instead of measuring all possible aberrations, the system focuses on these key parameters to achieve effective correction without excessive measurement time.
Solution Approach 2:
The patent uses parameter changes by varying the defocus value across multiple measurements. The system changes the defocus parameter systematically to obtain defocus series data, which enables determination of aberration parameters through mathematical analysis of the focus variations.
3Measurement precision
If iterative updating of aberration parameters is performed to minimize error function, then the image quality is improved, but the computational complexity and processing time increase
Solution Approach 1:
The patent implements feedback through iterative optimization where the error function (difference between measured and simulated images) is continuously minimized by adjusting aberration parameters. The system uses this feedback loop to converge on the optimal parameter set that best explains the observed defocus series data.
Solution Approach 2:
The patent applies copying by creating simulated images based on theoretical models and comparing them with actual measured images. The simulation copies the expected imaging behavior under different aberration conditions, enabling quantitative comparison and parameter optimization without requiring complex physical adjustments.
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 spatial resolution of images obtained by charged-particle beam tools, improving the detection of defects and increasing the yield and throughput in IC chip manufacturing by effectively correcting aberrations and optimizing tool settings.
Implementation Method 1
a beam of primary electrons having a relatively high energy is decelerated to land on a sample at a relatively low landing energy and is focused to form a probe spot thereon
Implementation Method 2
Due to this focused probe spot of primary electrons, secondary electrons will be generated from the surface
Data Source
AI summary
A method of determining aberrations in images obtained by a charged-particle beam tool, comprising: a) obtaining two or more images of a sample, wherein each image is obtained at a known relative difference in a measurement condition of the charged-particle beam tool; b) selecting an estimated aberration parameter for the aberrations of a probe profile representing the charged-particle beam used by the charged-particle beam tool; c) evaluating an error function indicative of the difference between the two or more images and two or more estimated images that are a function of the estimated aberration parameter and the known relative difference in the measurement condition; d) updating the estimated aberration parameter; e) performing processes c) and d) iteratively; f) determining the final aberration parameter as the estimated aberration parameter that provides the smallest value of the error function.