SEM Electrostatic Lens for Secondary Electron Energy Resolution

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Solution Overview

Problem

In scanning electron microscopes (SEMs), the energy dispersion of secondary electrons is challenging when using the retarding method, as it deteriorates spatial resolution and changes the energy resolution and focus position of secondary electrons, making it difficult to maintain a consistent number of electrons injected into the spectrometer and energy resolution when adjusting the retarding voltage.

Innovation Solution

The SEM incorporates an electrostatic lens between the secondary electron deflector and spectrometer, allowing for overlapping converging and deflecting actions, and a voltage control unit to adjust the electrostatic lens voltage based on the retarding voltage applied to the sample, ensuring a consistent number of electrons and energy resolution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a spectrometer is placed between the objective lens and sample to perform energy dispersion of secondary electrons, then energy analysis is enabled, but the distance between the objective lens and sample cannot be reduced, deteriorating spatial resolution

Engineering Contradiction:

Improveenergy analysis capabilityVSAvoidspatial resolution

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The invention introduces a second deflector that operates in a different spatial dimension (deflecting secondary electrons to the outside of the optical axis) rather than placing the spectrometer in the primary electron path between the objective lens and sample. This dimensional change allows energy analysis without compromising the spatial resolution maintained by the objective lens-sample distance.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Adaptability or versatility

If retarding voltage Vr is changed to adjust observation target energy, then different energy ranges can be analyzed, but the focus position of secondary electrons changes and energy resolution varies

Engineering Contradiction:

Improveenergy range adjustmentVSAvoidenergy resolution and focus position

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The invention employs a feedback mechanism where the voltage applied to the electrostatic lens is controlled based on the retarding voltage Vr. When Vr changes to adjust the energy range, the electrostatic lens voltage is automatically adjusted in response, maintaining constant energy resolution and focus position despite the change in observation target energy.

Inventive Principle:

Principle #23Feedback

3Quantity of substance

If secondary electrons are deflected to the outside of the optical axis and convergence mechanism is applied to increase electron number, then more electrons are injected into the spectrometer, but the system complexity increases

Engineering Contradiction:

Improvenumber of electrons injected into spectrometerVSAvoidconvergence mechanism

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The invention merges the deflecting action (moving electrons to outside optical axis) with the converging action (increasing electron number) by using the electrostatic lens to perform both functions simultaneously. This combination eliminates the need for separate convergence mechanisms, reducing system complexity while maintaining the quantity of electrons injected into the spectrometer.

Inventive Principle:

Principle #5Merging (Combining)

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 allows for energy dispersion of secondary electrons without changing the number of electrons injected into the spectrometer or energy resolution, even when the retarding voltage is adjusted, maintaining high spatial and energy resolution.

Implementation Method 1

an electrostatic lens provided between the second deflector and the spectrometer

Methodology Applied

Scientific EffectElectrostatic lens: Electrostatic Lens

Implementation Method 2

The electrostatic lens allows for overlapping converging and deflecting actions

Methodology Applied

Scientific EffectElectric field: Electric Field

Implementation Method 3

a spectrometer for dispersing the secondary electron

Methodology Applied

Scientific EffectEnergy dispersion:

Implementation Method 4

a voltage applying unit that applies a negative voltage to the sample to decelerate the primary electron beam

Methodology Applied

Scientific EffectRetarding voltage:

Data Source

PatentUS10014160B2Scanning electron microscope and method for controlling same

Publication Date: 2018.07.03 HITACHI HIGH TECH CORP

AI summary

The scanning electron microscope includes: an electron source; a first deflector for deflecting a primary electron beam emitted from the electron source; a second deflector for focusing the primary electron beam deflected by the first deflector and deflecting a second electron from a sample, which is generated the focused primary electron beam, to the outside of the optical axis; a voltage applying unit for applying a negative voltage to the sample to decelerate the primary electron beam; a spectrometer for dispersing the secondary electron; a detector for detecting the secondary electron passing through the spectrometer; an electrostatic lens provided between the second deflector and the spectrometer; and a voltage control unit that controls the voltage applied to the electrostatic lens based on the negative voltage applied to the sample. The electrostatic lens allows the deflecting action to be overlapped with the converging action.