In Situ FIB-SEM Lamella Preparation for High-Resolution Ptychography
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Solution Overview
Problem
Current methods for imaging samples in particle-optical apparatuses, such as SEMs, require thinning samples, which can lead to oxidation, handling difficulties for very thin samples, and limited resolution, especially for samples less than 20 nm thick, due to the need for air exposure and complex reinsertion processes.
Innovation Solution
A method utilizing a focused ion beam column within a particle-optical apparatus for in situ thinning and imaging, maintaining samples under vacuum to prevent surface modification, and employing ptychographic imaging techniques with iterative processes and seed images to enhance throughput and resolution, allowing for detailed imaging of very thin samples without reinsertion and oxidation risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sample is thinned and inserted into the SEM, then imaging can be performed, but oxidation or surface modification is likely to occur
Solution Approach 1:
The patent combines the FIB preparation chamber and the SEM imaging chamber into a single integrated system. The sample remains in the same vacuum environment throughout the entire process from thinning to imaging, eliminating the need to expose the sample to air or change environments. This merging of functions prevents oxidation and surface modification while maintaining high imaging precision.
2Measurement precision
If the sample is made very thin (less than 20 nm), then higher resolution imaging is possible, but handling and transporting becomes difficult and results in damage or loss
Solution Approach 1:
The integrated FIB-SEM system allows the sample to remain clamped on the manipulator throughout the entire process. The sample is thinned in situ by the FIB, then immediately imaged by the SEM without being removed from the chamber or manipulator. This eliminates handling difficulties and prevents damage to ultra-thin samples while achieving high resolution imaging.
Solution Approach 2:
The system performs both preparation and imaging functions within the same chamber, making the sample self-contained throughout the process. The manipulator holds the sample securely, and both the FIB column and SEM column operate on the same sample without requiring removal or repositioning, enabling the sample to 'serve itself' through the complete workflow.
3Ease of manufacture
If the sample is removed from the vacuum chamber for thinning, then processing can be done, but reinsertion is time-consuming and complex
Solution Approach 1:
The patent integrates the FIB thinning chamber and SEM imaging chamber into one system with a common vacuum environment. The sample remains in the chamber throughout the entire process, eliminating the need for removal and reinsertion. This merging of functions saves significant time and simplifies the workflow while maintaining full processing capability.
4Ease of operation
If conventional SEM imaging is used with focused beam, then imaging is straightforward, but resolution is limited to 1.2 nm due to spot diameter
Solution Approach 1:
The patent employs ptychographic imaging with an underfocused beam instead of a focused spot. By changing the focusing parameter from zero (focused) to negative (underfocused), the beam diameter at the sample increases to 20-40 nm, but the diffraction pattern contains higher spatial frequency information that can be reconstructed to achieve 0.236 nm resolution, significantly improving measurement precision.
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-resolution imaging of samples as thin as 20 nm or less without surface modification, improves handling and imaging efficiency by maintaining samples in vacuum, and allows for precise localization and phase information analysis, including dopant concentration determination without further thinning.
Implementation Method 1
a focused ion beam column mounted on the sample chamber for producing a focused ion beam, the focused ion beam for machining the sample
Implementation Method 2
a camera system for forming an electron image of the diffraction pattern caused by electrons transmitted through the sample
Implementation Method 3
The SEM is equipped to produce a beam of electrons, in this example a beam of 30 keV electrons, and comprises an objective lens for focusing the beam
Data Source
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AI summary
The invention relates to a method of preparing and imaging a sample (101) using a particle-optical apparatus (100), equipped with an electron column (120) and an ion beam column (140), a camera system (110), a manipulator (160) the method comprising the steps of Deriving a first ptychographic image of the sample from a first electron image, then thinning the sample, and forming a second ptychographic image of the sample. In an embodiments of the invention the seed image used for the second image is the first ptychografic image. In another embodiment the second ptychographic image is the image of the layer removed during the thinning, In yet another embodiment the inner potential of the sample is determined and dopant concentrations are determined.