Metrology System Non-Recurring Pattern Z-Height Precision
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Precision non-contact metrology systems face challenges in achieving high accuracy and reliability for Z-height measurements due to the complexity of determining the best focus position, which often results in lower precision compared to X and Y measurements.
Innovation Solution
A metrology system that includes an objective lens with varying magnification, a pattern projection component with non-recurring pattern portions, and a camera to acquire an image stack, determining focus curve data to identify 3D positions of surface points on a workpiece surface, utilizing a pattern with a broad spectrum of spatial frequencies to enhance contrast and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a best focus position is determined using traditional autofocus tools combining multiple images, then Z-height measurements can be obtained, but the precision and reliability are lower compared to X and Y measurements
Solution Approach 1:
The patent applies optical contrast enhancement by projecting a pattern onto the workpiece surface and analyzing the contrast variations in captured images. The pattern projection creates optical 'color' or intensity variations that enhance the detectability of focus position, thereby improving measurement precision and reliability of Z-height measurements.
Solution Approach 2:
The patent introduces a pattern projection component as an intermediary element between the light source and the workpiece surface. This intermediary pattern serves as a reference for analyzing focus position through contrast variations, enabling more precise and reliable Z-height measurements without directly modifying the workpiece or the imaging sensor.
2Measurement precision
If multiple images are combined and compared to determine best focus position, then Z-height information can be extracted, but the process becomes relatively complex
Solution Approach 1:
By projecting a known pattern onto the workpiece and analyzing contrast variations in the captured images, the system simplifies the autofocus process. The pattern provides inherent reference features that make focus determination more straightforward compared to combining and comparing multiple raw images without such references.
3Ease of manufacture
If a pattern with recurring intervals is used for projection, then the pattern structure is simple, but it limits the broad spectrum of spatial frequencies needed for high precision measurements
Solution Approach 1:
The patent employs an asymmetric, non-recurring pattern design that breaks the regular periodicity of traditional patterns. This asymmetric structure generates a broader spectrum of spatial frequencies when projected, enhancing the system's ability to measure diverse surface features with high precision while remaining manufacturable through standard photolithographic techniques.
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 system improves the accuracy and reliability of Z-height measurements by providing focus curve data that indicates 3D positions of surface points, overcoming the limitations of existing systems by maintaining high precision across different magnifications and objective lens cutoff frequencies.
Implementation Method 1
light from the light source is configured to be transmitted toward the pattern to form pattern light that is transmitted through the objective lens to form a projected pattern on a workpiece surface
Implementation Method 2
The camera is configured to receive image light transmitted along the imaging optical path and provide images of the workpiece surface including the projected pattern
Data Source
AI summary
A metrology system is provided including a projected pattern for points-from-focus type processes. The metrology system includes an objective lens portion, a light source, a pattern projection portion and a camera. Different lenses (e.g., objective lenses) having different magnifications and cutoff frequencies may be utilized in the system. The pattern projection portion includes a pattern component with a pattern. At least a majority of the area of the pattern includes pattern portions that are not recurring at regular intervals across the pattern (e.g., as corresponding to a diverse spectrum of spatial frequencies that result in a relatively flat power spectrum over a desired range and with which different lenses with different cutoff frequencies may be utilized). The pattern is projected on a workpiece surface (e.g., for producing contrast) and an image stack is acquired, from which focus curve data is determined that indicates 3 dimensional positions of workpiece surface points.