SEM Autofocus via Symmetric Detector Signal Merging
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Solution Overview
Problem
Existing scanning electron microscopes face challenges in achieving accurate autofocus adjustment when dealing with specimens that have features detectable only by specific detectors, particularly when the contrast is low or when foreign matter and patterns are present, leading to difficulties in focus positioning.
Innovation Solution
A scanning electron microscope system equipped with multiple detectors for secondary electron signals, where the detectors are arranged axially symmetrically, and a data calculation unit combines signals to adjust the electron beam focus based on evaluation values derived from combined secondary signal data, allowing for stable autofocus adjustment even in low-contrast images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single detector is used for autofocus adjustment, then the device complexity is reduced, but the measurement precision deteriorates when dealing with low-contrast features or foreign matter detectable only by specific detectors
Solution Approach 1:
The patent combines signals from multiple detectors (secondary electron detector and reflected electron detector) to create a composite image for autofocus adjustment. This merging of detection channels allows the system to leverage the complementary strengths of each detector type, improving focus positioning accuracy for various specimen features including low-contrast patterns and foreign matter.
Solution Approach 2:
The patent implements a multi-functional detection system where multiple detectors serve both specific detection purposes and contribute to the overall autofocus function. The system can selectively use different detector signals depending on the specimen type, making the autofocus system universally applicable to various features including pattern edges, foreign matter, and low-contrast structures.
2Adaptability or versatility
If multiple detectors are used to detect different types of signals, then the adaptability improves for detecting various foreign matter and defects, but the difficulty of detecting and measuring increases due to signal combination requirements
Solution Approach 1:
The patent implements an automatic signal combination system that autonomously processes signals from multiple detectors. The autofocus adjustment unit automatically evaluates combined signals from secondary electron and reflected electron detectors, performing the complex signal combination task without manual intervention, thereby maintaining high adaptability while reducing operational difficulty.
Solution Approach 2:
The patent dynamically adjusts detection parameters and signal combination weights based on the specimen being observed. By changing the relative contribution of different detector signals according to the specific detection task, the system optimizes its adaptability for different defect types while managing the complexity of multi-signal processing.
3Productivity
If autofocus adjustment is performed on low-contrast images, then the productivity increases by enabling inspection of difficult-to-observe features, but the measurement precision deteriorates due to reduced image contrast
Solution Approach 1:
The patent combines images from multiple detectors to create a composite image with enhanced contrast for low-contrast features. By merging the complementary information from secondary electron and reflected electron detectors, the system maintains focus accuracy even when inspecting difficult-to-observe features, enabling high-speed inspection without sacrificing 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
The system enables stable autofocus adjustment across various specimens by creating a combined image from multiple detector signals, effectively addressing the limitations of single-image focus adjustment and improving inspection efficiency in semiconductor wafer analysis.
Implementation Method 1
a secondary electron emitted from a specimen when irradiated with an electron beam
Implementation Method 2
a reflected electron is defined as having an energy of 50 eV or more, has a property of reflecting the shape of the irradiated material
Data Source
AI summary
A technique executes autofocus adjustment stably even when a plurality of patterns or foreign matter capable of being imaged only by a specific detector are included independently. Such an image as a concavo-convex image having a weak contrast can be picked up. The technique can automatically focus such an image even when it is difficult to find a focus position in the image. A scanning electron microscope includes a plurality of detectors for detecting secondary signals from a specimen when irradiated with an electron beam, and a calculation unit for combining the signals obtained from the detectors. At least two of the detectors are provided to be symmetric with respect to the electron beam. The focus of the electron beam is adjusted based on the signals of the detectors or on a signal corresponding to a combination of the signals.