Scanning Scatterometry Overlay Metrology with Moiré Signal Detection
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Solution Overview
Problem
Existing overlay metrology systems face challenges in achieving accurate and efficient measurements due to the need for static image-based systems that suffer from throughput limitations and underfilled illumination, which fail to capture position-dependent differences in Moiré structures, particularly in Moiré grating targets with varying grating pitches.
Innovation Solution
The implementation of scanning scatterometry overlay metrology systems that utilize time-varying interference signals from Moiré structures, captured by photodetectors in the pupil plane, to determine overlay errors by scanning the sample or illumination beam relative to the target, allowing for high-throughput measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a move and measure (MAM) approach with static sample during measurement is used, then measurement accuracy is improved, but throughput is reduced due to stage settling time requirements
Solution Approach 1:
The patent applies dynamics by transitioning from static sample measurement to dynamic scanning measurement. The sample is continuously scanned through the measurement field while measurements are taken during motion, eliminating the need for stage settling time. This is achieved by using a scanning confocal reflectometry system that captures depth information while the sample is in motion, thereby improving throughput without sacrificing measurement accuracy.
2Ease of operation
If traditional image-based metrology systems are used, then ease of operation is maintained, but measurement precision is reduced due to underfilled illumination and inability to capture position-dependent Moiré structure differences
Solution Approach 1:
The patent applies dimensionality change by transitioning from 2D image-based measurement to 3D depth-resolved measurement using confocal reflectometry. The system captures depth information through axial scanning, enabling detection of position-dependent Moiré structure differences that cannot be resolved by traditional 2D imaging. This provides precise overlay measurement while maintaining ease of operation through automated scanning procedures.
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 enables accurate and efficient overlay measurements by capturing position-dependent overlay information through time-varying interference signals, reducing the need for stage settling times and enabling smaller target sizes with improved signal-to-noise ratio and measurement efficiency.
Implementation Method 1
a first photodetector located in a pupil plane at a first location to capture at least one of Moiré diffraction orders or overlapping diffraction orders from the Moiré structures
Implementation Method 2
the overlay target, in accordance with the metrology recipe, includes one or more cells having Moiré structures formed as overlapping grating structures with different pitches
Implementation Method 3
a controller to receive time-varying interference signals from the first and second photodetectors associated with the Moiré structures
Data Source
AI summary
An overlay metrology system may include an illumination an illumination source to generate an illumination beam, one or more illumination optics to direct the illumination beam to an overlay target on a sample as the sample is scanned relative to the illumination beam along a scan direction, the target including one or more cells having Moiré structures. The system may also include two photodetectors at locations of a pupil plane associated with Moiré or overlapping diffraction orders from the Moiré structures. The system may then generate overlay measurements based on time-varying interference signals captured by the detector as the sample is scanned.