Circular Workpiece Edge Metrology With Tilted Illumination
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Solution Overview
Problem
Existing metrology systems struggle to accurately measure the edge of a circular workpiece, such as a semiconductor wafer, due to issues like edge damage, contamination, and distortion caused by misalignment and halo/ringing effects, which affect measurement precision and accuracy.
Innovation Solution
A metrology system with a tilted illumination configuration and image sensor setup, where the illumination direction is angled relative to the objective lens axis, combined with a telecentric aperture to reduce edge distortion, and an adjustable illumination tilt to align with the workpiece surfaces, providing clear edge images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional illumination configuration is used (illumination direction parallel to lens optical axis), then the system structure is simple, but edge distortion and halo/ringing effects occur reducing measurement precision
Solution Approach 1:
The illumination configuration is tilted at a specific angle (e.g., 45 degrees) relative to the lens optical axis, creating an asymmetric illumination path. This asymmetric configuration eliminates edge distortion and halo/ringing effects by changing the angle at which light interacts with the workpiece edge, thereby improving measurement precision without excessive complexity
Solution Approach 2:
The solution introduces a new dimensional parameter - the tilt angle of the illumination configuration - to resolve the measurement precision issue. By adding this angular dimension to the traditionally coaxial illumination setup, the system achieves distortion-free edge measurements while maintaining reasonable structural complexity
2Measurement precision
If illumination direction is tilted relative to lens optical axis, then edge distortion is minimized improving measurement accuracy, but system alignment complexity increases
Solution Approach 1:
The system utilizes specific parameter values for the tilt angle (e.g., 45 degrees) and positions of optical components to achieve optimal measurement accuracy. By establishing standardized parameter values, the system balances improved edge measurement accuracy with manageable alignment requirements through repeatable configuration
3Reliability
If conventional coaxial illumination is used, then system structure is simple, but halo effects and ring artifacts reduce image quality
Solution Approach 1:
The illumination path is configured asymmetrically with a tilt angle relative to the lens optical axis, which eliminates the symmetric halo effects and ring artifacts that plague conventional coaxial illumination systems. This asymmetric arrangement ensures reliable edge imaging by preventing artifact formation while maintaining reasonable optical path 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
This configuration enhances measurement accuracy by minimizing edge distortion and halo effects, allowing for precise determination of edge dimensions and profiles, improving the overall precision and reliability of edge inspection.
Implementation Method 1
The illumination configuration is configured to provide illumination in an illumination direction toward at least a portion of an edge of a circular workpiece that is along the optical path
Implementation Method 2
The objective lens configuration directs illumination toward the image sensor configuration which is configured to provide an image corresponding to the edge of the circular workpiece
Data Source
AI summary
A metrology system includes an illumination configuration having an illumination source, an objective lens configuration, and an image sensor configuration including an image sensor. The objective lens configuration includes an objective lens and has a lens optical axis. The illumination configuration, the objective lens configuration and the image sensor configuration form an optical path along which illumination from the illumination configuration travels. The illumination configuration provides illumination in an illumination direction toward at least a portion of an edge of a circular workpiece that is along the optical path. At least part of the illumination configuration is tilted relative to the objective lens configuration such that the illumination direction is at a first tilt angle in relation to the lens optical axis. The objective lens configuration directs illumination toward the image sensor configuration which is configured to provide an image corresponding to the edge of the circular workpiece.