Magnetic Immersion Lens Electron Beam Column Design
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Solution Overview
Problem
Conventional electron beam inspection systems face limitations in throughput due to aberrations and electron-to-electron interactions, primarily caused by substantial spherical and chromatic aberrations in the electrostatic electron gun and objective lens, leading to image blur, especially at high beam current conditions.
Innovation Solution
The innovative electron beam column design incorporates a magnetic immersion lens, a combined mechanism for the gate valve and beam-current selection apertures, and a deep immersion objective lens, which reduces the column length, decreases electron-to-electron interactions, and minimizes image blur by focusing the electron beam more precisely onto the substrate surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrostatic electron gun and objective lens are used, then the electron beam can be focused onto the substrate surface, but substantial spherical and chromatic aberrations occur leading to image blur
Solution Approach 1:
The patent changes the fundamental operating parameters of the electron lens system by transitioning from electrostatic to magnetic immersion lenses. This parameter change enables the system to achieve the required beam focusing while dramatically reducing spherical and chromatic aberrations, thereby improving image clarity without sacrificing beam focus capability
Solution Approach 2:
The patent substitutes the electrostatic field-based focusing mechanism with a magnetic field-based immersion lens system. This substitution replaces the problematic electrostatic electron gun and lens combination with a magnetic immersion lens that provides superior focusing performance with reduced aberrations, directly addressing the image blur issue
2Productivity
If conventional electron beam column design is used, then the system can operate, but the column length is substantial leading to increased electron-to-electron interactions
Solution Approach 1:
The patent extracts and eliminates the unnecessary intermediate components and extended column structure from the conventional design. By using magnetic immersion lenses that achieve focusing in a shorter distance, the patent removes the excess column length that causes electron-to-electron interactions, thereby improving throughput while reducing harmful interactions
Solution Approach 2:
The patent changes the spatial dimension of the electron beam path by implementing a more direct, compact column architecture. The magnetic immersion lens system enables the beam to be focused onto the substrate surface in a shorter axial distance, effectively reducing the interaction path length and improving system productivity
3Productivity
If high beam current is used, then the scanning speed and throughput increase, but image blur increases due to aberrations
Solution Approach 1:
The patent changes the lens type parameter from electrostatic to magnetic immersion lenses, which fundamentally alters the aberration characteristics of the system. This parameter change allows the system to maintain high beam current for fast scanning while keeping aberrations low, thus preserving image clarity at high throughput conditions
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 design significantly increases the throughput of electron beam inspection systems by reducing image blur and aberrations, allowing for more accurate and efficient scanning of the substrate surface with reduced electron-to-electron interactions.
Implementation Method 1
A magnetic immersion lens is positioned outside of the first vacuum chamber and is configured to immerse the electron source in a magnetic field so as to focus the emitted electrons into the primary electron beam
Implementation Method 2
An objective lens is configured to focus the primary electron beam onto a beam spot on a substrate surface so as to produce scattered electrons from the beam spot
Implementation Method 3
Controllable deflectors are configured to scan the beam spot over an area of the substrate surface
Implementation Method 4
The electron source includes a cathode configured to emit electrons, and an anode configured to accelerate the emitted electrons through an opening of the anode
Data Source
AI summary
In one embodiment, a first vacuum chamber of an electron beam column has an opening which is positioned along an optical axis so as to pass a primary electron beam that travels down the column. A source that emits electrons is positioned within the first vacuum chamber. A beam-limiting aperture is configured to pass a limited angular range of the emitted electrons. A magnetic immersion lens is positioned outside of the first vacuum chamber and is configured to immerse the electron source in a magnetic field so as to focus the emitted electrons into the primary electron beam. An objective lens is configured to focus the primary electron beam onto a beam spot on a substrate surface so as to produce scattered electrons from the beam spot. Controllable deflectors are configured to scan the beam spot over an area of the substrate surface. Other features and embodiments are also disclosed.