Multi-Detector Electron Optics for Higher Signal Collection
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Solution Overview
Problem
Existing electron microscopes struggle with low combined detection efficiencies of secondary and backscattered electrons, leading to inadequate image quality for high accuracy and high throughput defect inspection and metrology of complex structures.
Innovation Solution
An electron beam apparatus is designed with a compound objective lens and multiple electron detectors strategically positioned to enhance signal electron collection efficiency. The apparatus includes a magnetic lens with a cavity for the primary electron beam, and electron detectors are placed to detect signal electrons generated from a sample, with the first detector located upstream from the polepiece of the magnetic lens.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple electron detectors are used to maximize collection efficiency of secondary and backscattered electrons individually, then the detection efficiency of each electron type is improved, but the combined detection efficiency remains low
Solution Approach 1:
The patent positions detectors at multiple locations along the optical axis (upstream inside the magnetic lens cavity, downstream outside the cavity, and in-lens positions) rather than just at the traditional downstream position. This spatial distribution in the axial dimension allows different detectors to collect electrons from different angular ranges and energy levels, significantly improving combined detection efficiency while maintaining manageable system complexity through systematic positioning
2Measurement precision
If detectors are positioned downstream from the sample, then the structural arrangement is simple, but the detection efficiency of signal electrons is insufficient
Solution Approach 1:
The patent places a detector upstream inside the magnetic lens cavity before the electron beam passes through the polepiece. This preliminary positioning allows the detector to capture signal electrons early in their trajectory, before they are deflected by the magnetic field, thereby improving detection efficiency without requiring complex post-deflection detection arrangements
3Measurement precision
If the opening of the first electron detector is made smaller than the polepiece opening, then the detection precision is improved, but the field-of-view is reduced
Solution Approach 1:
The patent compensates for the reduced field-of-view from the smaller first detector opening by adding additional detectors at different axial positions (upstream inside cavity, downstream outside cavity, and in-lens positions). This multi-dimensional detector arrangement ensures that while each individual detector has a focused view, the combined system maintains comprehensive coverage of the sample area
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 apparatus significantly improves the detection efficiency of signal electrons, resulting in enhanced image quality and increased throughput for defect inspection and metrology of complex structures, including 3D NAND devices.
Implementation Method 1
a magnetic lens comprising a cavity configured to allow the primary electron beam to pass through
Implementation Method 2
a compound objective lens comprising a magnetic lens and an electrostatic lens
Implementation Method 3
an electron source configured to generate a primary electron beam along a primary optical axis
Data Source
AI summary
Systems and methods of imaging a sample using a charged-particle beam apparatus are disclosed. The charged-particle beam apparatus may include a compound objective lens comprising a magnetic lens and an electrostatic lens, the magnetic lens comprising a cavity, and an electron detector located immediately upstream from a polepiece of the magnetic lens and inside the cavity of the magnetic lens. In some embodiments, deflectors may be located between the electron detector and the opening of the polepiece adjacent to the sample to achieve a large field of view. Electron distributions among the detectors can be manipulated without changing the landing energy by changing the potential of the control electrode(s) in the electrostatic objective lens. The electron source can be operated with several discrete potentials to cover different landing energies, while the potential difference between electron source and the extractor is fixed.