Dual SE Detector STEM Imaging for Depth Localization
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Solution Overview
Problem
Existing scanning transmission electron microscopes (STEM) struggle to provide morphology information for features embedded deep within thick samples, as secondary electrons emitted from these features are attenuated and their signals are suppressed, limiting depth information, especially for features with low atomic numbers.
Innovation Solution
A STEM system with two secondary electron detectors positioned above and below the sample plane, allowing simultaneous detection of secondary electrons scattered in different directions, enabling comparison of signal amplitudes to derive depth information, which is then merged with the STEM image data to provide three-dimensional localization of features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single secondary electron detector is used above the sample plane, then the detector can detect secondary electrons from surface features, but features embedded deep within the sample exhibit suppressed signals due to attenuation
Solution Approach 1:
The invention divides the detection function into two separate detectors: one positioned above the sample plane to detect secondary electrons scattered in one direction, and another positioned below the sample plane to detect secondary electrons scattered in the opposite direction. This segmentation allows each detector to capture signals from features at different depths, with the below-sample detector being particularly effective for detecting electrons from deep-embedded features that would be attenuated in a single-detector configuration.
Solution Approach 2:
The invention adds a spatial dimension to the detection system by positioning detectors on both sides of the sample plane (above and below). This dimensional change enables the system to compare signal amplitudes from opposite directions, providing depth information through the ratio or difference of signals, thereby transforming a two-dimensional surface detection problem into a three-dimensional depth-resolved measurement.
2Length of stationary object
If the sample is thick, then more depth information is needed, but secondary electrons from deep features are attenuated and cannot be detected effectively
Solution Approach 1:
The invention uses the sample itself as an intermediary medium. By positioning a detector below the sample plane, the system utilizes the sample's transmission properties to detect secondary electrons that have traveled through the sample thickness. The signal amplitude from the below-sample detector serves as a mediator that provides information about the depth and composition of features, with lower atomic number features generating fewer secondary electrons that can be detected after traversing thick sample material.
3Quantity of substance
If features have low atomic number, then they generate fewer secondary electrons, but this makes depth determination more difficult
Solution Approach 1:
The invention implements a feedback mechanism by comparing the signal amplitudes from both above-sample and below-sample detectors. For features with low atomic number that generate fewer secondary electrons, the system uses the ratio or difference of signals from the two detectors to compensate for the low yield. This feedback comparison provides depth information even when the absolute signal intensity is low, as the relative signal distribution between the two detectors remains informative about feature depth.
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 configuration enhances the ability to visualize features within thick samples by providing accurate depth information and morphology details, overcoming the limitations of single-detector systems, and allowing virtual slicing of samples.
Implementation Method 1
An electron source 15 produces an electron beam 20
Implementation Method 2
The electron beam 20 is focused by a focusing element such as an upper electron objective pole piece 40
Implementation Method 3
The upper objective pole piece 40 steers the electron beam 20 across the sample plane 30
Implementation Method 4
A primary electron beam 25, having passed through the sample plane, is collected by a lower objective pole piece 70
Implementation Method 5
secondary electrons 60 may also be scattered from features within the sample
Implementation Method 6
These secondary electrons 60 can provide additional information about a sample
Implementation Method 7
the STEM detector 80 generating a signal at each position or continuously throughout a scan
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
Scanning transmission electron microscope (sTEM) 200, having a sample plane 30, the sTEM comprising a primary electron beam source 15 arranged to provide a primary electron beam 20 to a sample located at the sample plane of the sTEM, and an sTEM detector 80, wherein the sample plane is located between the primary electron beam source and the sTEM detector. A first secondary electron (SE) detector 50 is located between the primary electron beam source and the sample plane of the sTEM. A second SE detector 220 is located between the sample plane and the sTEM detector. Signal acquisition circuitry configured to acquire simultaneously a first signal from the first SE detector, a second signal from the second SE detector, and a third signal from the sTEM detector. There is also a method for generating an image from the sTEM by merging depth information from the first and second SE detector signals with the sTEM detector signal data.