SEM Adaptive Dwell Time Control for Faster Low-Damage Imaging
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Solution Overview
Problem
Conventional scanning electron microscopes (SEMs) face inefficiencies in material analysis due to fixed dwell times, leading to prolonged acquisition times and potential sample damage from electron beams, especially for samples like biological specimens, and issues with image quality from fixed electronic gain and offset settings.
Innovation Solution
Adaptive dwell times are implemented in SEMs, adjusting dwell times per image pixel based on detected particle counts, using variable staircase patterns and multiple detectors to optimize scanning, and incorporating multi-pass scanning to reduce exposure and acquisition time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fixed dwell times are used in SEM scanning, then the scanning process is simple and stable, but the acquisition time is prolonged and sample damage increases
Solution Approach 1:
The patent implements dynamic dwell time adjustment where the dwell time at each pixel is varied based on detected particle counts rather than using a fixed dwell time. The system monitors particle emissions in real-time and adapts the dwell time accordingly, allowing faster scanning of regions with sufficient signal and reduced exposure of sensitive regions, thereby reducing both acquisition time and sample damage
Solution Approach 2:
The system incorporates feedback mechanisms where particle detection results from previous scans inform dwell time decisions in subsequent scans. The dwell time for each pixel is adjusted based on cumulative particle counts and signal quality metrics, creating a closed-loop control system that optimizes both speed and sample preservation through iterative refinement
2Measurement precision
If fixed electronic gain and offset settings are used, then the system operation is stable, but image quality deteriorates for diverse sample structures
Solution Approach 1:
The patent applies local quality optimization by adjusting electronic gain and offset settings independently for different regions of the sample based on their specific characteristics. The system divides the sample into zones with similar signal properties and optimizes parameters for each zone, enabling high-quality imaging of diverse structures while managing complexity through regional grouping
Solution Approach 2:
The system dynamically changes electronic parameters (gain and offset) based on detected signal characteristics and dwell time variations. By coordinating parameter adjustments with adaptive dwell times, the system maintains optimal image quality across varying sample regions while the underlying complexity is managed through automated control algorithms
3Loss of information
If X-ray detection is performed at all scanning locations, then complete compositional information is obtained, but the acquisition time increases to several minutes or hours
Solution Approach 1:
The patent segments the scanning process into multiple passes with different objectives. Initial passes use longer dwell times to identify regions of interest based on particle emission patterns, while subsequent passes perform targeted X-ray detection only in selected regions. This segmentation allows complete compositional information to be obtained efficiently by concentrating measurement resources on informative areas
Solution Approach 2:
The system performs preliminary scanning and particle detection before conducting full X-ray analysis. By using initial scans to pre-identify regions with interesting compositional characteristics, the system prepares a targeted list of locations for detailed X-ray measurement, thereby obtaining complete compositional information for relevant regions while minimizing total acquisition time
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 reduces sample damage and acquisition time while improving image quality by dynamically adjusting dwell times, ensuring efficient and effective imaging of diverse sample structures.
Implementation Method 1
Backscattered electrons (BSE) originate from the primary electron beam, which, as the name suggests, are reflected back (e.g., out of the sample) via elastic scattering on the sample atoms.
Implementation Method 2
characteristic X-rays are emitted when primary electrons cause the ejection of an electron in an inner shell of a sample atom, creating an electron hole. This electron hole is then filled by another electron from an outer atomic shell through the emission of an X-ray photon.
Implementation Method 3
monitoring, by at least using a detector of the microscope, a first cumulative number of particles associated with the first scanning location of the sample and detected at the first scanning location of the scan pattern
Data Source
AI summary
A method for adaptive pixel dwell time usage in a microscope that includes scanning a beam emitted by a beam source over a sample in a scan pattern such that the beam interacts with the sample at a first scanning location according to the scan pattern. In some examples, the method includes monitoring, by at least using a detector of the microscope, a first cumulative number of particles associated with the first scanning location of the sample such that the first cumulative number of particles correspond to an interaction of the beam with the sample at the first scanning location. In some examples, the method includes moving, after a first dwell time and before a first dwell period elapses, the beam to a second scanning location of the sample according to the scan pattern if a signal criterion is met such that the signal criterion is based on the first cumulative number of particles.