Optical Metrology for X-ray Laminography Alignment
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Solution Overview
Problem
High-resolution imaging systems such as micro-CT or nano-CT face challenges in maintaining alignment accuracy due to mechanical stage errors, which are beyond the resolution of traditional mechanical rotation stage accuracy, requiring additional alignment steps beyond simple calibration.
Innovation Solution
A metrology system that uses an imaging system to monitor alignment features on the sample or sample holder, providing real-time shift and rotation data for alignment routines, comprising an illumination source, objective lens, and spatially resolved detector to compensate for errors and produce accurate 3D reconstructions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical rotation stage is used for high-resolution imaging, then imaging resolution is improved, but alignment accuracy deteriorates due to mechanical stage errors exceeding resolution
Solution Approach 1:
The patent replaces mechanical alignment measurement methods with an optical imaging-based metrology system. An optical microscope with high numerical aperture (0.1 to 0.9) captures images of alignment features on the sample holder, and sub-pixel analysis algorithms determine positions with precision better than 100 nanometers, eliminating reliance on mechanical stage accuracy
Solution Approach 2:
The patent introduces alignment features (such as grid patterns or crosshair markers) fabricated on the sample holder as intermediary reference objects. These features serve as mediators between the mechanical stage and the imaging system, allowing optical measurement of stage position and orientation errors without direct mechanical sensing
2Manufacturing precision
If traditional calibration is used for mechanical rotation stage, then systematic shift error is corrected, but asynchronous error exceeds resolution in high-resolution systems
Solution Approach 1:
The patent implements a feedback-based alignment correction system. The optical metrology system continuously monitors the positions of alignment features during sample rotation, and the measured deviations from the ideal rotation center are fed back to correct the projection images. This closed-loop approach compensates for both systematic and asynchronous errors in real-time
Solution Approach 2:
The patent performs preliminary optical calibration by capturing images of alignment features at multiple known rotation angles before actual imaging. This preliminary action establishes the relationship between optical feature positions and mechanical stage angles, creating a calibration map that compensates for stage errors during subsequent high-resolution imaging
3Reliability
If alignment features are introduced into the sample, then alignment accuracy is improved, but sample modification is required
Solution Approach 1:
The patent separates the alignment measurement function from the sample itself by placing alignment features on the sample holder rather than modifying the sample. This segmentation allows the sample to remain unchanged while the sample holder carries the alignment features, eliminating the need for sample modification while maintaining alignment accuracy
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
The metrology system achieves precise alignment and improved 3D image reconstruction by capturing and compensating for shifts and rotations, ensuring high-resolution images with resolutions better than 100 nanometers, effectively addressing mechanical stage alignment errors in high-resolution imaging systems.
Implementation Method 1
The illumination source produces infra-red light, visible light, or ultra-violet light
Implementation Method 2
an objective lens, a spatially resolved detector for detecting an image of the alignment target formed by the objective lens
Implementation Method 3
a spatially resolved detector for detecting an image of the alignment target formed by the objective lens
Implementation Method 4
X-ray radiation is typically used in these applications as it provides a good combination of high penetration, low scattering, and relatively simple absorption characteristics
Data Source
AI summary
A metrology system that uses an imaging system to monitor alignment features on the sample or sample holder of an X-ray laminography or tomography system. the metrology system has the capability to provide both sample shift and sample rotation movement data to a data acquisition system. These shift and rotation data can be used in alignment routines to produce 3D reconstructions from the X-ray images/projections. The metrology system is based on an imaging and focusing measurement of intrinsic feature of the sample or artificial features fabricated on the sample or sample holder.