Electron-Beam Deflection Calibration Using 1D Diffraction Grating
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Solution Overview
Problem
Conventional electron-beam length measurement systems face challenges in achieving high accuracy, particularly with insulating materials and those prone to deformation, due to the lack of precise pitch size arrangement in two-dimensional lattice samples and low secondary-electron signals from low-current beams, leading to calibration accuracy degradation.
Innovation Solution
The system employs a one-dimensional diffraction grating for calibration, with separate methods for perpendicular and parallel directions, using secondary-electron signal waveforms to determine pitch size and adjust beam deflection, ensuring accurate calibration by maximizing secondary-electron signal intensity and using superlattice structures for precise pitch determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a two-dimensional arrangement lattice sample is used for calibration, then the calibration can be performed, but the pitch size cannot be arranged precisely in the transverse and longitudinal directions, leading to degradation in calibration accuracy
Solution Approach 1:
The patent divides the calibration process into two separate one-dimensional calibrations instead of using a two-dimensional lattice sample. By segmenting the calibration into perpendicular and parallel directions relative to the electron beam scanning direction, each calibration can be performed independently with higher precision, avoiding the complexity of arranging precise two-dimensional pitch sizes.
Solution Approach 2:
The patent transitions from two-dimensional lattice sample calibration to one-dimensional diffraction grating calibration. By changing the dimensionality from 2D to 1D, the system simplifies the pitch size arrangement requirement to a single direction, making it feasible to achieve precise pitch sizes using standard fabrication techniques while maintaining high calibration accuracy.
2Object-affected harmful factors
If a low-current electron beam is used to minimize beam damage to insulating materials, then beam damage is reduced, but the secondary-electron signals become small in number, resulting in worse accuracy
Solution Approach 1:
The patent changes the calibration target from point lattice structures to extended one-dimensional diffraction grating structures. This parameter change in the target geometry allows low-current beams to accumulate sufficient secondary-electron signals across the extended grating structure, maintaining measurement accuracy while using beam currents low enough to minimize damage to insulating materials.
3Ease of operation
If the electron beam is scanned at an angle set to the lattice-point arrangement, then the scanning can be performed, but the locations at which the beam and lattice points coincide decrease in number, causing a decrease in acquired secondary-electron signals
Solution Approach 1:
The patent replaces two-dimensional lattice point sampling with one-dimensional diffraction grating sampling. This dimensional change ensures that during linear scanning, the electron beam continuously intersects with the grating lines, maximizing the number of coincidence locations and the resulting secondary-electron signal count, while maintaining simple scanning operation.
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 enables high-accuracy deflection calibration in electron-beam systems, even with low-acceleration and low-current beams, ensuring precise length measurements and minimizing beam damage, with calibration accuracy improved to 1 nm or less.
Implementation Method 1
the precise pitch size of the one-dimensional diffraction grating can be determined from diffraction-angle measurement on diffraction light diffracted thereby
Implementation Method 2
the pitch size of the diffraction grating is determined from a secondary-electron signal waveform acquired by scanning the electron beam
Data Source
AI summary
There is provided an electron-beam calibration technology whereby deflection calibration used in the electron-beam system can be performed with a high accuracy. A one-dimensional diffraction grating is located such that direction of the grating becomes parallel to an electron-beam scanning direction. Next, the electron-beam scanning is horizontally performed while displacing the electron-beam scanning in the perpendicular direction so that the electron-beam scanning displacement quantity will coincide with pitch size of the grating. From a secondary-electron signal image acquired, based on the presence or absence of moiré interference fringes, it can be judged whether or not the deflection calibration in the direction perpendicular to the electron-beam scanning has been correctly performed.