Sample Charge Control via Mesh Biasing in SEM
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Solution Overview
Problem
Conventional techniques for controlling sample charges in scanning electron microscopy are inadequate, particularly with insulating materials, leading to imaging issues like excessive and non-uniform darkness, distortion, and arcing, and are not suitable for compact electron-beam inspection systems due to the lack of precise charge control and the need for space-consuming Kelvin probes.
Innovation Solution
A system and method that includes a vacuum chamber with an electron gun, a mesh, and voltage supplies to bias the electron gun, mesh, and sample holder, allowing for precise control of electron beam parameters to manage and measure sample charges in-situ, without the use of Kelvin probes, thereby optimizing imaging conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a flood gun is used for surface preparation, then charging coverage is improved, but charge control precision deteriorates
Solution Approach 1:
The charging system is segmented into multiple independently controllable electron guns (flood gun for broad coverage and spot gun for precise control). The flood gun covers large areas while the spot gun provides precise charge control at specific locations, resolving the contradiction between coverage area and control precision.
Solution Approach 2:
A mesh structure is introduced as an intermediary between the electron guns and the sample surface. The mesh enables selective electron transmission and facilitates precise charge deposition while maintaining broad coverage capability, acting as a mediator that reconciles the conflicting requirements.
2Productivity
If a flood gun is used for surface preparation, then charging efficiency is improved, but imaging sensitivity deteriorates
Solution Approach 1:
The system separates charging and imaging functions using different electron guns. The flood gun performs efficient charging while the separate imaging gun maintains imaging sensitivity by operating independently without being overwhelmed by flood gun charges.
Solution Approach 2:
Surface charging is performed as a preliminary action before imaging. The flood gun charges the surface first, then the imaging process follows with adjusted parameters to account for the pre-applied charge, preventing charge interference during imaging.
3Measurement precision
If Kelvin probes are used for charge measurement, then charge measurement capability is improved, but device complexity increases
Solution Approach 1:
The electron beam itself is used to measure surface charge through interaction effects, eliminating the need for separate Kelvin probe apparatus. The system uses its own imaging beam to gather charge information, making the measurement capability inherent to the existing system rather than requiring additional complex equipment.
4Volume of stationary object
If the vacuum chamber volume is reduced for compactness, then system compactness is improved, but charge control capability deteriorates
Solution Approach 1:
Multiple functions (charging, imaging, charge measurement) are merged into a single compact vacuum chamber environment. The electron guns and associated control systems are integrated within the limited space, achieving both compactness and full charge control capability through functional integration.
Solution Approach 2:
The system uses dynamic voltage control and adjustable electron beam parameters to achieve precise charge control within the compact chamber. By dynamically adjusting operating conditions rather than relying on fixed large-scale apparatus, the system maintains control precision in a reduced volume.
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 precise control of sample charging, improving image quality by providing a desirable voltage potential and charge profile, allowing for better defect visibility and eliminating the need for Kelvin probes, thus enhancing the visibility of defects and reducing imaging artifacts.
Implementation Method 1
a charged particle beam source (302) having an effective source point (304)
Implementation Method 2
an objective lens system (312) that focuses the charged particle beam into a small spot
Implementation Method 3
The specimen interacts with the primary beam and generates secondary and backscattered electrons
Implementation Method 4
The specimen interacts with the primary beam and generates secondary and backscattered electrons
Implementation Method 5
a sample holder (132) that is biased to a voltage level by a voltage supply (260)
Implementation Method 6
a mesh (220) that is biased by a voltage supply (240)
Data Source
AI summary
A system and method for characterizing and charging a sample. The system includes a vacuum chamber, a first apparatus in the vacuum chamber and configured to characterize a sample, and a second apparatus in the vacuum chamber and configured to charge the sample. The second apparatus includes an electron gun configured to provide an electron beam to the sample and including an emission cathode biased to a first voltage relative to a reference voltage, a sample holder configured to support the sample, and a mesh located between the electron gun and the sample holder. Additionally, the second apparatus includes a first voltage supply configured to bias the mesh to a second voltage relative to the sample holder, and a second voltage supply configured to bias the sample holder to a third voltage relative to the reference voltage.