2D Pixelated Detector Tracking for SEM Beam Spot Drift
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Solution Overview
Problem
In scanning electron microscope (SEM) systems, the retrace period is underutilized, leading to reduced throughput due to charge accumulation and beam spot shifts caused by sample surface charging, which affects the accuracy and efficiency of secondary electron beam spot detection and imaging.
Innovation Solution
Implementing a method to track and adjust secondary beam spots in real-time during the retrace period using a detector's sensing elements, allowing for continuous data acquisition and compensation for beam spot changes, and employing virtual apertures to maintain detection efficiency and reduce cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the primary beam performs raster scan on the sample surface with retrace periods, then the sample surface charging is reduced by diverting the beam, but the throughput of the system decreases due to lost detection time during retrace
Solution Approach 1:
The patent enables continuous useful action by utilizing the retrace period for secondary beam spot detection. Instead of leaving the detector idle during retrace, the system continuously detects secondary electron beam spots throughout both forward scan and retrace periods, eliminating detection gaps and maintaining productive operation during previously wasted time.
Solution Approach 2:
The patent applies preliminary action by detecting secondary beam spots during the retrace period before the forward scan begins. This allows the system to prepare detection data in advance during the retrace interval, ensuring continuous detection coverage without interrupting the primary imaging process.
2Loss of information
If the primary beam scans repeatedly over the sample, then imaging data is collected, but charge accumulates on the sample surface causing secondary beam spot shifts and detection accuracy degradation
Solution Approach 1:
The patent implements feedback by detecting the position of secondary electron beam spots during scanning and using this information to identify and correct beam spot shifts. The system continuously monitors beam spot positions and can compensate for drifts caused by surface charging, maintaining measurement precision throughout extended imaging sessions.
Solution Approach 2:
The system performs self-service by using its own secondary electron emission during normal operation to detect and track beam spot positions. The secondary electrons naturally produced during primary beam scanning serve as the detection signal, eliminating the need for separate calibration procedures or additional hardware.
3Productivity
If the retrace period is used for secondary beam spot detection, then throughput is improved by eliminating idle time, but the system complexity increases due to additional detection and processing requirements
Solution Approach 1:
The patent applies universality by making the detector perform multiple functions: detecting secondary electrons during both forward scan and retrace periods, and serving both imaging and beam spot tracking purposes. The same detector hardware and signal processing path are used for both functions, avoiding the need for separate detection systems and reducing overall complexity.
Solution Approach 2:
The patent merges the forward scan detection and retrace detection into a unified continuous detection process. By combining these operations into a single detection stream that processes signals throughout the entire scanning cycle, the system achieves high throughput without requiring separate complex processing paths for each scanning phase.
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
Enhances the throughput of SEM systems by utilizing the retrace period for real-time beam spot tracking and adjustment, improving detection accuracy and reducing the impact of charge accumulation and beam spot shifts, thereby maintaining high collection efficiency and minimizing cross-talk.
Implementation Method 1
detecting beam intensity as a primary charged particle beam moves along a first direction
Implementation Method 2
a detector that receives charged particles projected from a sample and that outputs detection signals
Data Source
AI summary
A method of detecting charged particles may include detecting beam intensity as a primary charged particle beam moves along a first direction; acquiring a secondary beam spot projection pattern as the primary charged particle beam moves along a second direction; and determining a parameter of a secondary beam spot based on the acquired secondary beam spot projection pattern. A method of compensating for beam spot changes on a detector may include acquiring a beam spot projection pattern on the detector, determining a change of the beam spot projection pattern, and adjusting a parameter of a detector cell of the detector based on the change. Another method may be provided for forming virtual apertures with respect to detector cells of a detector.