Scanning Electron Microscope Lattice Calibration via Aperture Angle
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Solution Overview
Problem
Scanning electron microscopes face challenges in achieving high-accuracy dimensional calibration at magnifications of 1,000,000× or more due to insufficient dimensional pitch of microscales and limited resolution with general commercial scanning electron microscopes, which restricts the observation of samples with small lattice spacing.
Innovation Solution
A scanning transmission electron microscope is equipped with an electron source, deflector, objective lens, detector, and aperture to acquire a lattice image with a known crystalline structure, allowing for high-accuracy dimensional calibration by adjusting the beam convergence semi-angle and detection angle to optimize image contrast and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the scanning area of the primary electron beam is widened to decrease observation magnification, then the scanning width increases, but the observation magnification decreases
Solution Approach 1:
The patent changes the detection angle parameter of scanning transmission electrons by adjusting the aperture position and orientation. By detecting electrons at optimized angles, the system achieves improved measurement precision for dimensional calibration without requiring changes to the scanning width or magnification settings.
2Ease of manufacture
If a microscale with known dimensions is used for dimensional calibration, then the calibration process is simplified, but the minimum dimensional pitch is limited to about 100 nm which is insufficient for high magnification calibration
Solution Approach 1:
The patent uses a lattice image of a thin single crystal sample as a reference standard for dimensional calibration. The known crystalline structure and lattice spacing of the crystal serve as a natural ruler, replacing the need for manufactured microscales. This copying approach allows calibration at much finer dimensional pitches limited only by the crystal structure itself, not by manufacturing capabilities.
Solution Approach 2:
The patent optimizes the detection angle of scanning transmission electrons to enhance the visibility and measurement accuracy of lattice structures. By adjusting the aperture to detect electrons at specific angles, the system achieves high-precision dimensional calibration using the crystal lattice as a reference, overcoming the pitch limitations of conventional microscales.
3Measurement precision
If the accelerating voltage is increased to 100 kV or more to acquire high-resolution scanning transmission images, then the resolution improves, but general commercial scanning electron microscopes are limited to 30 kV maximum
Solution Approach 1:
The patent optimizes the detection angle of scanning transmission electrons as a compensating parameter. By detecting electrons at specifically optimized angles using the existing 30 kV accelerating voltage, the system achieves image quality and resolution comparable to what would require 100 kV or higher, thus overcoming the hardware limitation without increasing device complexity.
4Measurement precision
If the beam convergence semi-angle is increased to improve resolution, then the image contrast may deteriorate, but decreasing it reduces the beam diameter and limits resolution
Solution Approach 1:
The patent optimizes the detection angle of scanning transmission electrons as a compensating parameter for beam convergence settings. By detecting electrons at specifically optimized angles, the system maintains high image contrast even when using beam convergence angles optimized for resolution, thus resolving the trade-off between resolution and contrast.
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
Enables high-accuracy dimensional calibration and magnification calibration using lattice images, even with general-purpose scanning electron microscopes, overcoming limitations in resolution and pitch, particularly at high magnifications.
Implementation Method 1
an electron source which generates an electron beam
Implementation Method 2
an objective lens which focuses the electron beam on the sample
Implementation Method 3
scans the sample with the primary electron beam through a magnetic field deflector or an electric field deflector
Implementation Method 4
scans the sample with the primary electron beam through a magnetic field deflector or an electric field deflector
Implementation Method 5
a detector which detects a scanning transmission electron transmitted through the sample
Implementation Method 6
an aperture which is disposed between the sample and the detector to control a detection angle of the scanning transmission electron
Data Source
AI summary
Conventionally, in a general-purpose scanning electron microscope, the maximum accelerating voltage which can be set is low, and hence thin crystal samples which can be observed under normal high-resolution observation conditions are limited to samples with large lattice spacing. For this reason, there has no means for accurately performing magnification calibration. As means for solving this problem, the present invention includes an electron source which generates an electron beam, a deflector which deflects the electron beam so as to scan a sample with the electron beam, an objective lens which focuses the electron beam on the sample, a detector which detects an elastically scattered electron and an inelastically scattered electron which are transmitted through the sample, and an aperture disposed between the sample and the detector to control detection angles of the elastically scattered electron and the inelastically scattered electron. The electron beam enters the sample at a predetermined convergence semi-angle, and a lattice image is acquired at a second convergence semi-angle larger than a first convergence semi-angle at which a beam diameter is minimized on the sample.