Polyhedral Schottky Emitter Tip for Stable Probe Current

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Solution Overview

Problem

The shape of the tip end of Schottky electron sources changes over time due to diffusion of atoms, leading to unstable probe current and reduced spatial resolution in scanning electron microscopes.

Innovation Solution

A charged particle source with a tip end portion featuring a first flat surface perpendicular to the optic axis, multiple second flat surfaces parallel to the optic axis, and third flat surfaces between them, maintaining a stable polyhedral shape to stabilize the {100} plane and reduce diffusion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a Schottky electron source is used to achieve both current stability and high spatial resolution, then the probe current becomes unstable over long operation times due to shape changes from atom diffusion, but using a different electron source type would restore shape stability

Engineering Contradiction:

Improveprobe current stabilityVSAvoidelectron source shape stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent applies parameter changes by modifying the geometric parameters of the electron source tip - specifically creating a polyhedral shape with controlled face angles (40-60 degrees) and edge lengths. This geometric parameter optimization reduces the surface area and minimizes atom diffusion, thereby maintaining shape stability and probe current consistency during prolonged operation

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material structure by combining a refractory metal (tungsten or molybdenum) substrate with a low work function coating (barium oxide or calcium oxide) on the emission surface. This composite structure achieves both thermal stability from the refractory metal and electron emission efficiency from the coating, while the overall polyhedral geometry provides shape stability

Inventive Principle:

Principle #40Composite materials

2Reliability

If the electron source operates at high temperature to maintain stability, then surrounding gas molecules are difficult to be adsorbed and work function remains constant, but energy dispersion of emitted electrons increases causing chromatic aberration

Engineering Contradiction:

Improvework function constancyVSAvoidspatial resolution

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies local quality by creating a polyhedral electron source tip with specific geometric characteristics - multiple flat faces at controlled angles (40-60 degrees) that localize the emission area. This localized geometric structure concentrates the electron emission from specific crystallographic planes, reducing energy dispersion while maintaining the thermal stability benefits of high-temperature operation

Inventive Principle:

Principle #3Local quality

3Reliability

If the tip end shape changes over time due to atom diffusion, then the electric field intensity continuously changes and emission current is reduced, but maintaining a fixed shape would require preventing natural diffusion processes

Engineering Contradiction:

Improveemission current stabilityVSAvoidoperation time

Core Design Contradiction:

ReliabilityVSDuration of action of moving object

Solution Approach 1:

The patent applies preliminary anti-action by pre-shaping the electron source tip into a polyhedral geometry with optimized face angles (40-60 degrees) and controlled edge lengths before operation. This pre-optimized shape is specifically designed to resist atom diffusion during thermal operation, creating a geometric configuration that maintains its integrity and electrical field distribution over extended operation periods

Inventive Principle:

Principle #9Preliminary anti-action

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 stable shape maintains a consistent electric field, ensuring a stable probe current and reduced energy dispersion, thus enhancing spatial resolution and throughput in scanning electron microscopes.

Implementation Method 1

a thermal electron source that accelerates and emits electrons excited by heating

Methodology Applied

Scientific EffectThermionic emission: Thermionic Emission

Implementation Method 2

a field emission electron source that emits electrons by a tunnel effect due to an action of an electric field

Methodology Applied

Scientific EffectField emission: Electron Avalanche

Implementation Method 3

an electron source that accelerates and emits electrons excited by heating

Methodology Applied

Scientific EffectThermal excitation: Heating

Data Source

PatentUS20250385065A1Charged Particle Source, Charged Particle Gun, and Charged Particle Beam Device

Publication Date: 2025.12.18 HITACHI HIGH TECH CORP

AI summary

The purpose of the present disclosure is to stabilize the probe current of a charged particle source over long periods of time. In a charged particle source according to the present disclosure, an emitter tip has a first flat surface perpendicular to an optical axis, a plurality of second flat surfaces parallel to the optical axis, and a plurality of third flat surfaces each disposed between the first flat surface and a second flat surface. Among the plurality of second flat surfaces, a first distance between second flat surfaces located at positions facing each other across the optical axis is greater than the outer diameter of the boundary portion between the tip and a needle.