Reflective Energy Filter Beam-Adjusting Lens for LVSEM Contrast
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Solution Overview
Problem
Existing energy filters in low-voltage scanning electron microscopes (LVSEM) face challenges in achieving fine energy-discrimination power and high uniformity of energy-discrimination powers over a large field of view due to their energy-angle-depending and position-depending filtering, which limits image contrast and throughput.
Innovation Solution
An energy filter of reflection type is designed with a beam-adjusting lens to make the charged particle beam incident onto a potential barrier as a substantially parallel beam, allowing for fine energy-discrimination power at the center and high uniformity over the entire field of view, and separate detectors are used to detect secondary electrons and backscattered electrons within different energy ranges for enhanced image contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an energy filter is used to filter charged particles by energy, then energy-discrimination power is improved, but uniformity of energy-discrimination power over field of view deteriorates due to position-depending filtering
Solution Approach 1:
A beam-adjusting lens is introduced as an intermediary component between the charged particle source and the potential barrier. This lens adjusts the trajectories of charged particles from different field of view positions to ensure they all approach the potential barrier at substantially the same angle, thereby eliminating position-dependent variations in energy discrimination while maintaining fine energy resolution at the center.
2Ease of operation
If conventional electron detectors are used to detect signal electrons, then detection simplicity is improved, but image contrast deteriorates due to low sensitivity to electron energies
Solution Approach 1:
The detection system is segmented into multiple independent detectors, each configured to detect specific energy ranges of secondary electrons and backscattered electrons. This segmentation enables energy-discrimination detection, where different detectors capture electrons with different energy characteristics, thereby improving image contrast through energy-sensitive detection while maintaining operational simplicity through modular detector design.
3Measurement precision
If energy-angle-depending filtering is used in the energy filter, then energy filtering capability is improved, but position-depending filtering occurs that limits image contrast
Solution Approach 1:
The beam-adjusting lens serves as a mediator that decouples the energy filtering function from angular dependence. By adjusting particle trajectories before they reach the potential barrier, the lens ensures that particles from different positions and angles are normalized to a common incident angle, allowing the potential barrier to perform pure energy filtering without position-dependent artifacts that would degrade image contrast.
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 configuration improves image contrast and resolution by providing fine energy-discrimination power and high uniformity over a large field of view, enabling the simultaneous detection of topography, material, and voltage contrasts, thereby enhancing the defect inspection and yield management in semiconductor manufacturing.
Implementation Method 1
a beam-adjusting lens below the grid electrode and adjusting an incident electron beam of the energy filter to become a substantially parallel beam to be incident onto the potential barrier
Implementation Method 2
a grid electrode being set at a first potential to form a potential barrier, while a first plurality of particles of the charged particle beam, which has initial kinetic energies higher than a specific value and thus is able to cross the potential barrier, passes through the grid electrode
Data Source
AI summary
This invention provides a method for improving performance of a reflective type energy filter for a charged particle beam, which employs a beam-adjusting lens on an entrance side of a potential barrier of the energy filter to make the charged particle beam become a substantially parallel beam to be incident onto the potential barrier. The method makes the energy filter have both a fine energy-discrimination power over a large emission angle spread and a high uniformity of energy-discrimination powers over a large FOV. A LVSEM using this method in the energy filter can obviously improve image contrast. The invention also provides multiple energy-discrimination detection devices formed by using the advantages of the method.