Particle Beam Focusing via Stage Current Extrema
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Solution Overview
Problem
Conventional methods for focusing particle beams in scanning electron microscopes (SEMs) are subjective, difficult to automate, and rely on discernible edge features, which are not always present, making it challenging to achieve precise and automated focusing, especially in nanoprobe environments.
Innovation Solution
The method involves measuring absorbed or secondary current from a sample to determine the extrema of the current profile, allowing for iterative adjustment of working distance and stigmator controls to achieve a tight beam spot, independent of surface patterns and suitable for both electron and ion beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If conventional focusing techniques relying on image observation by trained operators are used, then focusing can be achieved when discernible edge features are present, but the process is subjective, difficult to automate, and not reproducible
Solution Approach 1:
The patent replaces the manual visual inspection mechanism with an automated electrical measurement system. Instead of operators visually observing images to determine focus, the system uses automated measurement of absorbed or secondary current to objectively determine beam focus through extrema detection in current profiles
Solution Approach 2:
The system performs self-diagnosis and self-adjustment by automatically measuring current extrema and using this information to determine optimal focus settings without requiring external operator intervention or subjective judgment
2Adaptability or versatility
If conventional focusing techniques relying on discernible edge features are used, then focusing can be performed with operator judgment, but the method fails when such features are not present on the sample surface
Solution Approach 1:
The patent extracts the focusing determination criterion from dependence on sample surface features. Instead of relying on edge features present on the sample, the system uses electrical current measurements that are independent of sample morphology, making the method applicable to any sample type regardless of surface characteristics
Solution Approach 2:
The current measurement-based focusing method serves as a universal approach that works across different sample types, materials, and beam energies without requiring adjustment for the presence or absence of specific surface features, unlike conventional image-based methods
3Manufacturing precision
If iterative scanning of working distance and stigmator controls is performed to achieve tight beam spot, then focusing precision below 10 nm is achieved, but measurement time and complexity increase
Solution Approach 1:
The system implements feedback by measuring current at multiple working distance settings, identifying extrema in the current profile, and using this information to guide iterative adjustment of focus controls. The feedback loop continues until optimal focus is achieved, with each iteration informed by previous measurements
Solution Approach 2:
The system performs preliminary scanning of the working distance range to identify the approximate location of current extrema before performing detailed iterative optimization. This preliminary action narrows the search space and reduces the time required for subsequent precision focusing
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 reproducible and automated focusing with resolution below 10 nm, independent of surface features, and is applicable to a range of materials and beam energies, effectively addressing the limitations of conventional focusing techniques.
Implementation Method 1
measuring absorbed or secondary current from a sample receiving a particle beam
Data Source
AI summary
Apparatus and methods are disclosed for particle beam focusing, suitable for use in sample preparation or test environments, including SEM-based nanoprobing platforms. With a particle beam incident on a sample surface, stage current is used as an indicator of spot size. By scanning or searching settings of a working distance control, a control value having maximum (or minimum) stage current is used to set the beam waist at the sample surface. Alternatively, minima (or maxima) of reflected current can be used. Stigmator controls can be adjusted similarly to reduce astigmatism. The scan of control settings can be performed concurrently with sweeping the beam across a region of interest on the sample. Curved sweep patterns can be used. Energy measurements can be used as an alternative to current measurement. Applications to a nanoprobing workflow are disclosed.