FIB Cross-Section Fiducials for Slice Thickness and Drift Control
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Solution Overview
Problem
Current charged particle beam (CPB) systems require excessive time to image large volume samples at high resolution, and are prone to sample drift due to mechanical and thermal variations, making it challenging to acquire high-resolution images of large areas efficiently.
Innovation Solution
A selective high-resolution imaging method where a CPB system acquires a low-resolution image of a large sample area, allowing the operator to identify regions of interest, which are then imaged at higher resolution, and using alignment vernier notches to adjust the milling rate and maintain accuracy, along with multi-digital to analog circuit control for precise beam deflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a CPB system images large volume samples at high resolution across the entire area, then image quality is improved, but imaging time becomes excessively long
Solution Approach 1:
The patent divides the large sample area into multiple regions of interest (ROIs) and images only those specific regions at high resolution, rather than scanning the entire large area. This segmentation approach maintains high measurement precision for the selected ROIs while dramatically reducing the total imaging time by excluding non-critical areas from high-resolution scanning.
2Area of stationary object
If the beam scans across large areas for extended periods, then comprehensive coverage is improved, but sample drift increases due to mechanical and thermal variations
Solution Approach 1:
By segmenting the imaging task into discrete regions of interest rather than continuous full-area scanning, the patent reduces the total scan time and beam exposure duration. This minimizes the opportunity for mechanical drift and thermal variations to accumulate, thereby maintaining better reliability and image accuracy for the covered areas.
Solution Approach 2:
The system employs periodic re-alignment and drift compensation procedures between imaging different regions of interest. This periodic correction of beam position and sample drift ensures that each ROI is imaged with high accuracy despite the extended overall process time, maintaining reliability across the full coverage area.
3Productivity
If the milling rate is increased to reduce sectioning time, then productivity is improved, but positioning accuracy deteriorates
Solution Approach 1:
The patent implements dynamic adjustment of the milling rate based on real-time feedback from thickness measurement systems. The system can operate at higher milling rates when thickness control is less critical, then slow down or pause for precise measurement and adjustment, optimizing both productivity and manufacturing precision through adaptive rate changes.
Solution Approach 2:
The system uses feedback from thickness measurement systems (such as interferometric or capacitive sensors) to continuously monitor and adjust the milling rate. When the measured thickness deviates from the target, the feedback loop automatically adjusts the milling parameters to correct the error, maintaining precision even at higher overall productivity levels.
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
Significantly reduces the time required for imaging large volume samples while maintaining high accuracy by focusing on specific regions of interest and using advanced control systems for precise beam positioning and milling.
Implementation Method 1
These ion beams, when directed onto a sample, will eject charged particles, which include secondary electrons, secondary ions (i+ or i−), and neutral molecules and atoms from the exposed surface of the sample
Implementation Method 2
the FIB can be operated as an 'atomic scale milling machine,' for selectively removing, or sputtering, materials wherever the beam is placed
Implementation Method 3
Electron beam 43 is focused to a fine spot by means of a condensing lens 56 and an objective lens 58
Implementation Method 4
Electron beam 43 is emitted from a cathode 52 by applying voltage between cathode 52 and an anode 54
Data Source
AI summary
Linear fiducials including notches or chevrons with known angles relative to each other are formed such that each branch of a chevron appears in a cross-sectional face of the sample as a distinct structure. Therefore, when imaging the cross-section face during the cross-sectioning operation, the distance between the identified structures allows unique identification of the position of the cross-section plane along the Z axis. Then a direct measurement of the actual position of each slice can be calculated, allowing for dynamic repositioning to account for drift in the plane of the sample and also dynamic adjustment of the forward advancement rate of the FIB to account for variations in the sample, microscope, microscope environment, etc. that contributes to drift. An additional result of this approach is the ability to dynamically calculate the actual thickness of each acquired slice as it is acquired.Linear fiducials including notches or chevrons with known angles relative to each other are formed such that each branch of a chevron appears in a cross-sectional face of the sample as a distinct structure. Therefore, when imaging the cross-section face during the cross-sectioning operation, the distance between the identified structures allows unique identification of the position of the cross-section plane along the Z axis. Then a direct measurement of the actual position of each slice can be calculated, allowing for dynamic repositioning to account for drift in the plane of the sample and also dynamic adjustment of the forward advancement rate of the FIB to account for variations in the sample, microscope, microscope environment, etc. that contributes to drift. An additional result of this approach is the ability to dynamically calculate the actual thickness of each acquired slice as it is acquired.