Wedged Lamella Preparation Using SEM-Guided Ion Beam Thinning
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Solution Overview
Problem
Preparing a wedged lamella with a thickness of a few nanometers for high-resolution transmission electron microscopy is challenging due to unpredictable sample twist and bend, requiring precise control of milling to achieve a desired thickness.
Innovation Solution
A method and system using a dual-beam charged particle microscopy system, where an ion beam mills sample slices from opposing sides, and an electron beam acquires images to estimate the distance between structures, stopping milling when the distance reaches a threshold to achieve a tapered wedged lamella.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional milling methods are used to prepare a lamella, then the sample can be thinned to a few nanometers, but the sample twist and bend become unpredictable and difficult to control
Solution Approach 1:
The milling process is divided into multiple sequential steps with intermediate imaging and measurement. The lamella is milled in stages, with the ion beam removing material in controlled increments. Between milling steps, the system pauses to capture images and measure thickness, allowing the process to be segmented into manageable phases rather than a single continuous operation. This segmentation enables better control over the final thickness and reduces cumulative errors that lead to twist and bend.
Solution Approach 2:
The system implements a closed-loop feedback mechanism where the ion beam milling process is continuously monitored through intermediate imaging. The measured thickness from captured images is fed back to the control system, which then adjusts subsequent milling parameters accordingly. This feedback loop allows real-time correction of thickness variations and prevents over-milling, thereby reducing sample distortion and improving both precision and reliability.
2Manufacturing precision
If the ion beam removes multiple sample slices to achieve desired thickness, then the lamella thickness can be reduced, but the process time increases due to repeated imaging and measurement
Solution Approach 1:
The system performs preliminary rough milling to remove the bulk of the material before transitioning to precision milling. This preliminary action reduces the total amount of material that needs to be removed in the slow, incremental precision steps. By pre-establishing the approximate thickness and removing excess material upfront, the system reduces the number of iterative imaging and measurement cycles required, thereby decreasing total preparation time while maintaining final thickness precision.
Solution Approach 2:
The milling process uses periodic imaging and measurement at strategically chosen intervals rather than after every single milling step. The system employs a rhythm of milling followed by periodic verification, where measurements are taken at key milestones during the thinning process. This periodic approach balances the need for precision control with the need to minimize process time, avoiding excessive intermediate measurements while ensuring adequate monitoring of thickness progression.
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 approach allows for the precise and automatic preparation of wedged lamellas with controlled thickness, reducing sample twist and bend, and ensuring optimal sample quality for TEM imaging.
Implementation Method 1
removing multiple sample slices from at least one side of a sample with an ion beam
Implementation Method 2
acquiring an image of a sample surface with an electron beam, and estimating a distance between a first structure and a second structure
Data Source
AI summary
Wedged lamella can be prepared by milling multiple sample slices from at least one side of a sample. The milling is monitored based on an SEM image acquired after removing one or more of the sample slices. The milling may be terminated responsive to an estimated distance between a first structure and a second structure along the height of the milled sample not greater than a threshold distance.