Objective Lens Hysteresis Correction for Stable Electron Beam Imaging
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Solution Overview
Problem
Existing charged particle beam devices, such as scanning electron microscopes, face challenges in accurately estimating the magnetic field due to magnetic hysteresis, leading to errors in deflection magnification and image rotation, and reduced throughput due to frequent lens reset operations to correct these errors.
Innovation Solution
A charged particle beam device that includes a control unit to estimate the magnetic field using hysteresis characteristic information and history information of the coil current, with additional correction values for coil current changes, reducing the need for lens reset operations and improving throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If lens reset operation is performed frequently to correct magnetic field estimation errors, then measurement precision is improved, but productivity deteriorates
Solution Approach 1:
The system uses feedback from hysteresis characteristic information and coil current history to continuously refine magnetic field estimation. The control unit compares estimated magnetic field values with actual measurements and adjusts the estimation algorithm accordingly, reducing the need for frequent lens reset operations while maintaining accuracy.
Solution Approach 2:
The system performs preliminary characterization of the objective lens by measuring hysteresis characteristics and storing them in advance. This pre-acquired information is then used during normal operation to estimate magnetic field without requiring frequent reset operations, thereby improving throughput while maintaining measurement precision.
2Measurement precision
If lens reset operation is performed to correct magnetic field errors, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The control unit continuously monitors coil current changes and uses hysteresis characteristic feedback to estimate magnetic field in real-time. This eliminates the need for time-consuming lens reset operations while maintaining accurate magnetic field estimation throughout the measurement process.
Solution Approach 2:
The system maintains continuous magnetic field estimation using hysteresis information and coil current history, avoiding interruptions caused by lens reset operations. This continuous operation reduces time loss while sustaining measurement precision throughout the imaging process.
3Stability of the object's composition
If coil current is greatly changed during lens reset operation, then magnetic field relationship is stabilized, but eddy current is generated causing response delay
Solution Approach 1:
The system replaces the mechanical lens reset operation with a computational approach using hysteresis characteristic information and coil current history to estimate magnetic field. This substitution eliminates the need for large coil current changes, maintaining magnetic field stability without generating eddy currents that would delay response.
Solution Approach 2:
Instead of changing coil current dramatically during lens reset, the system changes the estimation parameters by utilizing hysteresis characteristic data and historical coil current information. This allows magnetic field stabilization through parameter optimization rather than physical current disruption, avoiding eddy current generation.
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
Accurate estimation of the magnetic field is achieved while minimizing errors in deflection magnification and image rotation, thereby enhancing the throughput of the device.
Implementation Method 1
an objective lens in which coil current is inputted to focus the charged particle beams on a sample
Implementation Method 2
the relationship between the coil current and the magnetic field generated by the objective lens is not uniquely determined due to the influence of the magnetic hysteresis
Implementation Method 3
since the coil current input to the objective lens is greatly changed, there is a problem that an eddy current is generated in the magnetic circuit, the response of the magnetic field is delayed
Data Source
AI summary
This charged particle beam device comprises: a charged particle beam source that generates charged particle beams; an objective lens in which coil current is inputted to focus the charged particle beams on a sample; a control unit that controls the coil current; a hysteresis characteristics storage unit that stores hysteresis characteristics information of the objective lens; a history information storage unit that stores history information relating to the coil current; and an estimating unit that estimates the magnetic field generated by the objective lens based on the coil current, the history information, and the hysteresis characteristic information, and has a magnetic field correction unit that, when the absolute value of the change amount of the coil current is greater than a prescribed value, further adds to the magnetic field estimated by the estimating unit a correction value according to the coil current and its change amount, correcting the magnetic field generated by the objective lens.