Backside-Illuminated Photoelectron Source for Multi-Beam Writing
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Solution Overview
Problem
Existing electron beam writing techniques face challenges in achieving high throughput and efficient utilization of excitation light due to the difficulty in implementing multi-beam configurations, particularly when the photocathode is irradiated from its surface, leading to low light utilization efficiency.
Innovation Solution
A photoelectron source configuration where excitation light is incident on the back surface of the photocathode, utilizing a reflecting or focusing mirror to focus the light and extract photoelectrons through an extraction hole, allowing for efficient light utilization and easier implementation of multi-beam systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the photocathode is irradiated from the surface with excitation light, then the structure is simple, but the light utilization efficiency is low and multi-beam implementation is difficult
Solution Approach 1:
The patent inverts the conventional illumination direction by irradiating the photocathode from the back surface instead of the front surface. This allows the excitation light to pass through the transparent substrate and reach the photocathode material directly, improving light utilization efficiency while enabling multi-beam implementation through the substrate
2Loss of energy
If the photocathode is irradiated from the back surface with excitation light, then the light utilization efficiency is improved, but the structural complexity increases due to requiring transparent substrate and focusing optics
Solution Approach 1:
The transparent substrate serves multiple functions: it allows excitation light to pass through from the back surface, provides mechanical support for the photocathode, and enables the extraction electrode to collect photoelectrons. The focusing mirror also serves dual purposes by both focusing the excitation light and acting as the extraction electrode for photoelectrons
Solution Approach 2:
The transparent substrate acts as an intermediary that allows the excitation light to pass through while providing a platform for mounting the photocathode and extraction electrode. This mediator enables the back-surface illumination configuration without requiring direct contact between the light source and photocathode
3Use of energy by moving object
If a thin photocathode is used to allow excitation light to reach the surface, then the light can penetrate, but the electron emission efficiency decreases
Solution Approach 1:
By inverting the illumination direction to back-surface irradiation, the patent eliminates the need for thin photocathodes. The excitation light passes through the transparent substrate and reaches the photocathode material from the back, allowing both thick photocathodes (for high electron emission efficiency) and effective light penetration
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 efficient use of excitation light and facilitates the implementation of multi-beam systems, improving throughput and reducing defects, while maintaining high resolution in electron beam writing processes.
Implementation Method 1
a photocathode which emits photoelectrons when irradiated with excitation light
Implementation Method 2
a reflecting mirror disposed at a position opposed to the photocathode on the surface side of the substrate configured to reflect and focus the excitation light which has passed through the substrate to the photocathode
Data Source
AI summary
In one embodiment, a photoelectron source includes a photocathode supported on a surface side of a substrate, a light source emitting excitation light from a back surface side of the substrate, and a reflecting mirror disposed at a position opposed to the photocathode on the surface side of the substrate configured to reflect and focus the excitation light which has passed through the substrate to the photocathode and include an extraction hole through which photoelectrons emitted from the photocathode due to irradiation of the excitation light pass.