Objective Lens Assembly for Backscatter Detection With Lower Cross-Talk
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Solution Overview
Problem
Current multi-beam inspection systems rely primarily on secondary electron detection, limiting their ability to effectively image backscattered signals and increasing cross-talk, which prevents the efficient detection of backscattered charged particles and reduces throughput for inspecting buried defects and overlay targets.
Innovation Solution
A charged particle-optical device is configured to project a multi-beam of charged particles onto a sample using an objective lens array with aligned apertures and a detector array positioned proximate to the sample to capture and repel secondary charged particles, allowing direct detection of backscattered charged particles with reduced cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If secondary electron detection is used in multi-beam inspection systems, then detection capability for surface features is improved, but cross-talk increases and detection of backscattered particles is limited
Solution Approach 1:
The detection system is segmented into multiple independent detectors, each associated with a specific beam aperture. This segmentation allows each detector to capture signals primarily from its corresponding beam, reducing cross-talk between adjacent beams while maintaining detection capability for both secondary and backscattered electrons
Solution Approach 2:
The patent extracts and detects backscattered electrons separately from secondary electrons by positioning detectors close to the sample surface and using electrostatic lenses to selectively collect backscattered particles. This extraction enables independent detection of backscattered signals that were previously overwhelmed by secondary electron noise
2Measurement precision
If detector array is positioned proximate to the sample, then direct detection of backscattered particles is improved, but secondary particle interference increases
Solution Approach 1:
Different regions of the detection system are assigned different functions: detectors positioned proximate to the sample capture backscattered particles, while electrostatic lenses and aperture structures selectively filter and direct specific particle types. This local differentiation allows simultaneous optimization for both backscattered particle detection and secondary particle rejection
Solution Approach 2:
The system changes the energy parameter of detected particles by using electrostatic lenses with specific voltages to selectively accelerate or decelerate particles based on their energy. This allows the detector to respond preferentially to backscattered electrons with higher energy while rejecting lower-energy secondary electrons
3Productivity
If multi-beam configuration is used, then inspection throughput is improved, but cross-talk between beams increases
Solution Approach 1:
The multi-beam system is segmented into independent beam-detector pairs, with each beam having its own dedicated detector and aperture. This segmentation maintains high throughput by processing multiple beams simultaneously while reducing cross-talk through physical and electrostatic isolation between beam paths
Solution Approach 2:
Electrostatic lenses serve as intermediary elements between the multi-beam source and detectors. These lenses selectively focus and direct electrons from specific beam apertures to corresponding detectors, acting as mediators that prevent cross-contamination between adjacent beam paths while maintaining efficient signal collection
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 enables the effective detection of backscattered charged particles, improving the inspection of buried defects and overlay targets by reducing secondary particle interference and enhancing detection throughput.
Implementation Method 1
the objective lenses are configured to accelerate the charged particle sub-beams along the sub-beam paths
Implementation Method 2
a detector array configured to be proximate the sample and configured to capture charged particles emitted from the sample
Implementation Method 3
the charged particle-optical device is configured to repel secondary charged particles emitted from the sample away from the detector
Data Source
AI summary
The embodiments of the present disclosure provide various techniques for detecting backscatter charged particles, including accelerating charged particle sub-beams along sub-beam paths to a sample, repelling secondary charged particles from detector arrays, and providing devices and detectors which can switch between modes for primarily detecting charged particles and modes for primarily detecting secondary particles.