Wide-Bandgap BSE Sensor for Low-Energy SEM Detection
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Solution Overview
Problem
Existing BSE detectors in scanning electron microscopes are susceptible to thermal noise from thermal photons and are insensitive to BSEs with energies less than 4 keV, limiting their operating range and excluding the detection of light elements and sensitive samples.
Innovation Solution
Incorporation of a semiconductor-based charged particle sensor with a wide bandgap material (≥2.0 eV) as an acceptor layer, such as sp3 hybridized carbon or other materials like silicon carbide and diamond, to detect BSEs without detecting thermal photons, and a bias voltage of 0.1 V to 5 kV is applied across the acceptor layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a narrow bandgap semiconductor material (e.g., doped-silicon with 1.1 eV bandgap) is used as the acceptor layer, then the detector is sensitive to a wide range of BSE energies including low energies, but it detects thermal photons (infrared spectrum) as noise, reducing measurement precision
Solution Approach 1:
The patent changes the fundamental parameter of the semiconductor material's bandgap energy from narrow (1.1 eV for silicon) to wide (≥2.0 eV). This parameter change allows the detector to reject thermal photons while maintaining BSE detection capability, resolving the contradiction between measurement precision and detection range
Solution Approach 2:
The patent employs composite material structures combining wide bandgap semiconductor acceptor layers with specific conducting layers. This composite approach enables simultaneous achievement of thermal photon rejection and adequate BSE detection sensitivity across a broad energy range
2Measurement precision
If an aluminum-covered scintillator detector is used to reduce thermal noise, then thermal photon detection is reduced, but the detector becomes insensitive to BSEs with energies less than 4 keV, limiting the detection energy range
Solution Approach 1:
The patent replaces the scintillator-photon conversion mechanism with a direct semiconductor charge generation mechanism. Wide bandgap semiconductors directly convert BSE energy to electrical signals without requiring scintillator conversion, enabling detection of low-energy BSEs while maintaining thermal noise rejection
Solution Approach 2:
The patent changes the detection mechanism parameter from indirect scintillator conversion to direct semiconductor charge generation. This parameter change enables sensitivity to BSE energies below 4 keV while maintaining immunity to thermal photon interference
3Adaptability or versatility
If the sample stage is heated to high temperatures for sample analysis, then sample processing capability is improved, but thermal photons are emitted that generate electron-hole pairs in the detector, increasing noise and reducing measurement precision
Solution Approach 1:
The patent converts the harmful thermal photon emission from heated samples into a beneficial design criterion. By selecting wide bandgap materials with bandgaps ≥2.0 eV, the detector is specifically designed to be insensitive to the thermal photon spectrum emitted at elevated temperatures, thus converting the thermal environment from a noise source to a manageable operating condition
Solution Approach 2:
The patent changes the detector material parameter (bandgap energy) to match and exceed the thermal photon energy distribution at elevated temperatures. This parameter selection allows the detector to operate in high-temperature environments while maintaining measurement 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 sensor effectively detects BSEs with energies up to 30 keV while maintaining sensitivity at elevated sample temperatures, reducing thermal artifacts and expanding the operating range of BSE microscopy.
Implementation Method 1
a photon having a wavelength shorter than 1127 nm, in the infrared spectrum, is energetic enough to generate electron-hole pairs in doped-silicon having a bandgap of about 1.1 eV
Implementation Method 2
Thermal photons emitted by a heated sample and/or sample stage are energetic enough to induce the formation of electron-hole pairs in some semiconductor-based BSE detectors
Data Source
AI summary
Charged particle microscopy systems, sensors, and techniques are provided. A charged particle sensor can include a housing, configured to be incorporated into a scanning electron microscope (SEM). The charged particle sensor can include a detector cell, mechanically coupled with the housing. The detector cell can include an acceptor layer including a semiconducting material characterized by a bandgap equal to or greater than about 2.0 eV. The acceptor layer can define a first surface and a second surface opposing the first surface. The detector cell can include a first conducting layer disposed on the first surface, a second conducting layer disposed on the second surface, a first contact, electrically coupled with the first conducting layer, and a second contact, electrically coupled with the second conducting layer.