Scan Lens Metrology With VFL Focus for Fast 3D Z-Height Measurement
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Solution Overview
Problem
Existing precision metrology systems face challenges in achieving micron or sub-micron accuracy for Z-height measurements, particularly in determining best focus positions, which can be time-consuming due to the need for multiple stage movements, limiting overall process throughput.
Innovation Solution
A metrology system incorporating a mirror configuration and a variable focal length (VFL) lens to rapidly adjust fields of view and focus positions, allowing for rapid image acquisition using a points-from-focus type process without mechanical stage movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple stage movements are used to inspect different workpiece areas, then measurement coverage is improved, but process time increases
Solution Approach 1:
The patent replaces mechanical stage movements with optical field-of-view changes. By using a variable focal length lens to rapidly switch between wide-field and narrow-field views, the system inspects different workpiece areas without moving the mechanical stage, thereby reducing process time while maintaining measurement coverage.
Solution Approach 2:
The patent introduces an optical dimension (field-of-view scaling) to replace the mechanical dimension (stage movement). By varying the focal length to switch between wide and narrow fields of view, the system accesses different spatial scales of the same workpiece area, achieving comprehensive inspection without mechanical displacement.
2Measurement precision
If best focus position is determined through complex multi-image processes, then measurement precision is improved, but process complexity increases
Solution Approach 1:
The patent acquires multiple images at different focus positions (excessive action) but processes them efficiently by comparing corresponding pixels across images to determine the best focus position. This approach maintains high measurement precision while simplifying the overall process through automated pixel-level comparison rather than complex multi-step analysis.
Solution Approach 2:
The patent creates multiple copies of the same field of view at different focus positions and compares corresponding pixels across these copies. By replicating the imaging process at varying focal lengths and systematically comparing the copies, the system determines the optimal focus position with high precision through a standardized, repeatable process.
3Productivity
If variable focal length lens is used to rapidly adjust focus position, then productivity is improved, but device complexity increases
Solution Approach 1:
The patent employs a variable focal length lens that can dynamically adjust between different focal lengths during the measurement process. This dynamic optical system allows rapid switching between wide-field and narrow-field views, as well as adjustment of focus positions, significantly improving measurement throughput despite the added optical complexity.
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
Enhances measurement throughput by enabling rapid adjustment to multiple fields of view and focus positions, achieving high accuracy in Z-height measurements without the need for mechanical stage movement.
Implementation Method 1
The VFL lens is included in the imaging optical path, wherein image light travels from the mirror configuration along the imaging optical path and through the VFL lens to the camera. The VFL lens is configured to be controlled to vary an optical power of the VFL lens so as to vary a focus position of the metrology system.
Implementation Method 2
The scan lens is included in the imaging optical path and is configured to input image light arising from the workpiece as illuminated by the lighting configuration.
Implementation Method 3
The mirror configuration is included in the imaging optical path and is configured to direct image light from the scan lens along the imaging optical path.
Data Source
AI summary
A metrology system is provided including a lighting configuration, a camera, a scan lens, a mirror configuration and a variable focal length (VFL) lens. The mirror configuration is utilized to adjust to different imaged fields of view as corresponding to different view positions through the scan lens. For each imaged field of view, the camera is utilized to acquire a corresponding image set including images of the workpiece, wherein the VFL lens is controlled to rapidly vary the focus position of the metrology system for acquiring the images (e.g., wherein each image corresponds to different focus position data). For each corresponding image set, focus position data is determined that indicates three dimensional positions of a plurality of surface points on the workpiece that are within the corresponding field of view (e.g., enabling determinations of measurements of workpiece features that are within the corresponding field of view).