Charged Particle Beam Scanning Using Triangular Waveform
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Solution Overview
Problem
Scanning Electron Microscope (SEM) systems face challenges in achieving efficient data throughput and maintaining linearity of the primary beam positioning during scanning, particularly due to the high slew rate requirements and bandwidth demands in the retrace part of the scan signal, which limits the scan rate and data throughput.
Innovation Solution
The method involves a 'shark tooth' scanning technique where the charged particle beam is deflected in a specific pattern to reduce oscillations and retrace time, allowing for efficient scanning of both directions with reduced bandwidth and transient response requirements, thereby increasing scan rate and data throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a traditional sawtooth scan signal is used with fast retrace, then the scan rate can be increased, but the retrace part requires very high slew rate and bandwidth which complicates the scan system and limits the achievable scan rate
Solution Approach 1:
Instead of using a traditional sawtooth waveform with fast retrace, the patent inverts the approach by using a triangular waveform where both forward and backward scans are utilized for data acquisition. This eliminates the need for high-speed retrace to a single direction, reducing the slew rate and bandwidth requirements of the scan system while maintaining high scan rates.
Solution Approach 2:
The patent makes the backward scan direction useful by acquiring data during both forward and backward movements of the electron beam. This continuous useful action during the entire scan cycle eliminates wasted retrace time and reduces the demand for extremely fast retrace performance, thereby lowering system complexity.
2Productivity
If the retrace time is reduced to increase data throughput, then the scan duty cycle improves, but the high slew rate required for fast retrace demands wider bandwidth which limits the practical improvement
Solution Approach 1:
The patent inverts the traditional scanning approach by utilizing both forward and backward scan directions for data acquisition. This eliminates the need for extremely fast retrace to a single position, reducing slew rate requirements and allowing for more relaxed bandwidth constraints while maintaining high scan duty cycle and data throughput.
Solution Approach 2:
The patent changes the scan waveform parameters from a sawtooth pattern with asymmetric fast retrace to a triangular pattern with symmetric, slower transitions in both directions. This parameter change reduces the maximum slew rate requirement while maintaining acceptable scan linearity and improving overall data throughput.
3Manufacturing precision
If the scan system uses high bandwidth to achieve fast retrace, then the scan linearity can be maintained, but the system complexity and cost increase
Solution Approach 1:
Instead of achieving fast retrace in one direction with high bandwidth, the patent inverts the approach by making both directions useful scan directions with moderate, symmetric bandwidth requirements. This reduces the peak bandwidth demand while maintaining beam positioning linearity through the symmetric triangular waveform.
4Productivity
If the retrace part is optimized for speed, then the scan duty cycle increases, but oscillations and ringing occur which degrade image quality
Solution Approach 1:
The patent eliminates the harmful fast retrace oscillations by inverting the traditional scan approach to use symmetric triangular waveforms where both directions are utilized. This removes the need for abrupt retrace transitions that cause ringing and oscillations, while maintaining high scan duty cycle through continuous useful scanning in both directions.
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 'shark tooth' scanning method enhances scan rate and data throughput while improving linearity, reducing the need for high bandwidth and transient response, resulting in a more efficient SEM system with minimized scan direction-dependent distortions.
Implementation Method 1
The primary beam moving over the target (scanning) is usually implemented through application of electrical or magnetic field
Implementation Method 2
The primary beam moving over the target (scanning) is usually implemented through application of electrical or magnetic field
Implementation Method 3
high energy primary electrons hit the target and cause emission of secondary electrons
Data Source
AI summary
A method for scanning an object with a charged particle beam, the method may include repeating, for each pair of scan lines out of multiple pairs of scan lines, the stages of: (i) deflecting the charged particle beam along a first direction, thereby scanning the object along a first scan line of the pair of scan lines; (ii) collecting electrons emitted from the object during the scanning of the object along a majority of the first scan line; (iii) deflecting the charged particle beam along a second direction that is normal to the first direction; (iv) deflecting the charged particle beam along a third direction that is opposite to the first direction, thereby scanning the object along a second scan line of the pair of scan lines; (v) collecting electrons emitted from the object during the scanning of the object along a majority of the second scan line; and (vi) deflecting the charged particle beam along the second direction that is normal to the third direction.