Boron-Coated Silicon Field Emitter for Stable Electron Sources
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Solution Overview
Problem
Current electron sources for scanning electron microscopes, such as thermionic and Schottky emitters, face limitations including inefficient power consumption, wide energy spread, short lifetime, and instability due to contamination, while silicon field emitters are hindered by oxidation and reactivity, limiting their commercial use in high-resolution semiconductor inspection and lithography.
Innovation Solution
A boron-coated silicon field emitter with a pyramid or rounded whisker structure, where a high-purity boron layer hermetically seals the silicon surface, allowing for stable operation at room temperature with reduced oxidation and enhanced emission current density, brightness, and longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If silicon field emitters are used to achieve high brightness and low energy spread, then electron source performance is improved, but oxidation and reactivity of silicon limit their stability and commercial use
Solution Approach 1:
The patent uses a composite structure combining silicon field emitter with a protective coating layer (such as diamond-like carbon or other inert materials). This composite approach allows the silicon to provide high brightness and low energy spread while the protective coating prevents oxidation and enhances stability, enabling commercial use.
Solution Approach 2:
The patent creates an inert environment by applying a protective coating that acts as a barrier between the reactive silicon and the surrounding atmosphere. This prevents oxidation of the silicon surface while maintaining the field emitter's performance characteristics.
2Ease of manufacture
If thermionic emitters are used to achieve ease of manufacture, then device complexity is reduced, but power consumption increases and lifetime decreases
Solution Approach 1:
The patent changes the operating parameters from thermionic emission (requiring high temperatures >1300K) to field emission (operating at room temperature or near-room temperature). This parameter change maintains ease of manufacture while dramatically reducing power consumption and extending emitter lifetime.
3Quantity of substance
If Schottky emitters are used to enhance thermionic emission, then current density is improved, but operating temperature must be maintained above 1000K increasing energy consumption
Solution Approach 1:
The patent replaces the thermal field emission mechanism (Schottky emission requiring high temperature) with a pure field emission mechanism. This substitution eliminates the need for high operating temperatures while maintaining or enhancing current density through quantum tunneling effects in the field emission regime.
4Productivity
If high speed inspection is performed using UV light, then inspection speed is improved, but detection sensitivity for small defects decreases
Solution Approach 1:
The patent makes the electron microscope system capable of performing both high-speed inspection and high-resolution review functions. By using a stable, high-brightness field emitter that can operate continuously, the system can quickly scan large areas for defects and then immediately perform high-resolution imaging of detected defects without requiring separate instrumentation.
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 boron-coated silicon field emitter provides a stable, high-brightness electron source with improved current density and longevity, overcoming the limitations of previous technologies by preventing oxidation and maintaining high performance in semiconductor inspection and lithography applications.
Implementation Method 1
a boron layer hermetically disposed on at least a tip of the field emitter
Implementation Method 2
Field emission takes place when the applied electric field is high enough to reduce the potential barrier on the tip-vacuum interface so that electrons can tunnel through this barrier at a temperature close to room temperature
Implementation Method 3
electrons can tunnel through this barrier at a temperature close to room temperature (i.e., quantum-mechanical tunneling)
Implementation Method 4
allowing for stable operation at room temperature with reduced oxidation
Data Source
AI summary
An electron source is formed on a silicon substrate having opposing first and second surfaces. At least one field emitter is prepared on the second surface of the silicon substrate to enhance the emission of electrons. To prevent oxidation of the silicon, a thin, contiguous boron layer is disposed directly on the output surface of the field emitter using a process that minimizes oxidation and defects. The field emitter can take various shapes such as pyramids and rounded whiskers. One or several optional gate layers may be placed at or slightly lower than the height of the field emitter tip in order to achieve fast and accurate control of the emission current and high emission currents. The field emitter can be p-type doped and configured to operate in a reverse bias mode or the field emitter can be n-type doped.