Automated Endpointing for Focused Ion Beam Milling
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Solution Overview
Problem
Automating nanoscale charged particle beam processes is challenging due to the difficulty in precisely controlling and observing features at the nanometer scale, as conventional methods are time-consuming and labor-intensive, and inconsistent across operators, especially when thinning samples for transmission electron microscopy.
Innovation Solution
A system that uses focused ion beam milling and electron beam imaging to analyze exposed surfaces, repeatedly milling and imaging until predefined criteria are met, employing edge recognition software for precise endpointing and closed-loop feedback to automate the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual observation and stopping is used during sample thinning, then the feature can be observed on TEM, but the process is time consuming and labor intensive
Solution Approach 1:
The system continuously monitors secondary particle emission during ion beam thinning and uses this feedback signal to automatically detect when the feature is exposed, eliminating manual observation and enabling automated endpoint detection
Solution Approach 2:
The system uses the secondary particles naturally emitted during the thinning process itself as the detection signal, so the thinning process provides its own monitoring data without requiring separate measurement systems
2Measurement precision
If manual observation and stopping is used during sample thinning, then the feature can be observed on TEM, but the results are inconsistent from operator to operator
Solution Approach 1:
The automated feedback system provides objective, consistent detection of feature exposure based on secondary particle emission signals, eliminating subjective human judgment and ensuring reproducible results across different operators
Solution Approach 2:
The manual mechanical observation process is replaced with an automated electronic detection system that monitors secondary particle emission, providing consistent and reproducible measurements independent of human operators
3Ease of manufacture
If secondary particles are collected at glancing angle for lamella formation, then the image can be formed, but the image is rough because particles from deep in the trench are not detected well
Solution Approach 1:
Instead of using glancing angle incidence that misses deep trench particles, the system uses normal incidence ion beam that effectively detects secondary particles from the entire trench depth, inverting the traditional approach to improve detection sensitivity
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 enables automated and precise control of nanoscale processes, reducing human error and improving yield and throughput by ensuring accurate exposure of features, even at sub-100 nm scales, facilitating efficient preparation of samples for TEM observation.
Implementation Method 1
a thin portion of the sample is milled using a focused ion beam (FIB)
Implementation Method 2
the focused ion beam (FIB) mills a thin portion of the sample
Implementation Method 3
an electron beam image of the exposed surface is analyzed
Implementation Method 4
secondary particles are collected as the ion beam thins the lamella, and the image formed from the secondary particles
Data Source
AI summary
To expose a desired feature, focused ion beam milling of thin slices from a cross section alternate with forming a scanning electron image of each newly exposed cross section. Milling is stopped when automatic analysis of an electron beam image of the newly exposed cross section shows that a predetermined criterion is met.