Anisotropic Aperture Filtering for Multi-Beam SEM Image Contrast
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Solution Overview
Problem
Current multi-beam charged particle microscopes face challenges in achieving high imaging contrast due to limitations in secondary electron yield and angular distribution, which affects the accuracy of semiconductor feature inspection.
Innovation Solution
The implementation of anisotropic filtering of secondary electron beamlets using selected aperture filters, such as elongated rectangular or elliptical shapes, and active multi-aperture arrays to selectively block or deflect secondary electrons, enhancing image contrast by filtering out unwanted signals from underlying features or backgrounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If anisotropic filtering with selected aperture filters is applied to secondary electron beamlets, then image contrast is improved, but device complexity increases
Solution Approach 1:
The detection system is divided into multiple independent detector elements, each associated with a specific aperture filter. This segmentation allows parallel processing of different angular components of secondary electrons without requiring complex sequential operations, thereby improving image contrast while managing system complexity through modular architecture.
Solution Approach 2:
Different aperture filters with specific anisotropic shapes are assigned to different detector elements based on their spatial positions and the local imaging requirements. This local optimization allows each detector element to enhance contrast for specific features or regions, improving overall measurement precision without requiring uniform complexity across the entire system.
2Measurement precision
If anisotropic filtering is applied to enhance image contrast, then measurement accuracy is improved, but the system becomes more sensitive to noise
Solution Approach 1:
The system applies anisotropic filtering selectively to specific angular components and spatial regions rather than uniformly to all secondary electrons. This partial action approach enhances contrast for relevant features while preserving sufficient signal levels in other regions, thereby improving measurement accuracy without excessively amplifying noise across the entire image.
Solution Approach 2:
The system incorporates feedback mechanisms that monitor the detected signal levels and adjust the filtering parameters dynamically. This feedback control allows the system to optimize the balance between contrast enhancement and noise suppression, maintaining measurement accuracy while compensating for noise sensitivity in real-time operation.
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 significantly improves image contrast and measurement accuracy for semiconductor features, allowing for more precise wafer inspection with higher reliability and efficiency.
Implementation Method 1
an objective lens for focusing during use the plurality of primary charged particle beamlets into an image plane
Implementation Method 2
secondary electron beamlets, which are generated in parallel during use at the interaction volumes of the plurality of primary charged particle beamlets with a surface of a wafer
Implementation Method 3
an aperture filter configured to anisotropically filter at least one secondary electron beamlet
Data Source
AI summary
A multi-beam charged particle system and a method of operating a multi-beam charged particle system can provide improved image contrast. The multi-beam charged particle system comprises a filter element or an active array element in a detection system, which can provide improved, anisotropic image contrast. The disclosure can be applied for applications of multi-beam charged particle system, where higher requirements on beam uniformity and throughput may be relevant.