Aperture Alignment in Scatterometry Metrology
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Solution Overview
Problem
Existing scatterometry metrology tools face accuracy and repeatability issues due to misalignment of apertures, leading to significant overlay errors that affect measurement precision and reliability.
Innovation Solution
A method is developed to align apertures to the optical axis of a scatterometry metrology tool using correction terms derived by minimizing an overlay variation measure calculated from periodic structure measurements, enabling highly sensitive misalignment metrics for calibration or real-time alignment, thus enhancing accuracy to a few or tens of nanometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional resolution-based methodologies are used for aperture alignment, then the measurement process is simpler, but the alignment accuracy and repeatability are insufficient
Solution Approach 1:
The patent replaces traditional mechanical alignment adjustment methods with an optical measurement and computational correction approach. By using scatterometry to measure overlay variations and applying mathematical models to calculate misalignment, the system achieves high-precision aperture alignment without complex mechanical adjustment mechanisms.
Solution Approach 2:
The patent changes the approach from direct mechanical positioning to parameter-based correction. By measuring overlay variations and using these parameters to calculate misalignment correction terms, the system achieves precise alignment through computational methods rather than mechanical complexity.
2Reliability
If aperture misalignment is present, then the measurement process is simpler to implement, but overlay errors increase significantly
Solution Approach 1:
The patent implements a feedback mechanism where scatterometry measurements of overlay variations are used to calculate misalignment correction terms. These corrections are then applied to realign the aperture, creating a closed-loop system that ensures reliable and repeatable overlay measurements by continuously monitoring and correcting alignment.
Solution Approach 2:
The patent performs preliminary alignment calibration using scatterometry measurements before actual overlay measurements are taken. By pre-measuring overlay variations and calculating correction terms, the system prepares the aperture alignment in advance, ensuring that subsequent measurements are accurate and repeatable.
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 approach significantly improves aperture alignment accuracy, reduces misalignment sensitivity, and allows for precise measurement of non-overlay features like critical dimension, outperforming traditional resolution-based methodologies by providing quicker and more accurate results.
Implementation Method 1
aligning at least one aperture to an optical axis of a scatterometry metrology tool using at least one correction term derived by minimizing an overlay variation measure calculated with respect to overlay measurements of a periodic structure
Data Source
AI summary
Methods and algorithms are provided, as well as new metrics for misalignment of apertures with respect to the optical axis of a metrology system. The methods comprise aligning aperture(s) to an optical axis of a scatterometry metrology tool using correction term(s) derived by minimizing an overlay variation measure calculated with respect to overlay measurements of a periodic structure. These methods result in highly sensitive misalignment metrics, which may be used in calibration stages or on the fly to align the system's apertures, and enable reducing target size due to the resulting enhanced alignment accuracy.