Scanning Diffraction Overlay Scatterometry Without Stage Settling
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Solution Overview
Problem
Existing overlay metrology systems face challenges with low throughput due to stage settling times and the need for high-sensitivity cameras, leading to increased costs and time-consuming measurements.
Innovation Solution
A scanning diffraction-based overlay metrology system using photodetectors positioned to capture time-varying interference signals from overlapping diffraction orders, allowing for rapid measurements without stage acceleration and deceleration, and utilizing a controller to determine differential signals for accurate overlay measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a move and measure approach with translation stage is used to sequentially move metrology targets into measurement field of view, then measurement coverage is improved, but throughput deteriorates due to stage settling time
Solution Approach 1:
The patent transitions from static measurement to dynamic scanning measurement. The translation stage continuously scans the sample through the measurement field of view, and the system captures interference signals during this motion without requiring the stage to settle between measurements. This dynamic approach eliminates settling time delays while maintaining comprehensive measurement coverage.
Solution Approach 2:
The patent implements continuous measurement during the scanning process. Instead of stopping the translation stage to capture each target sequentially, the system continuously captures interference signals as the sample scans through the field of view. This continuous action eliminates idle settling time and maximizes throughput while maintaining measurement accuracy.
2Measurement precision
If image-based scatterometry with high sensitivity camera is used, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the image-based optical detection system with a photodetector-based interference signal detection system. Instead of using a high-sensitivity camera to capture images and process them to extract overlay information, the system uses photodetectors to directly detect interference signals generated by diffracted light. This substitution simplifies the detection hardware while maintaining measurement precision.
Solution Approach 2:
The patent changes the detection parameter from image intensity to interference signal phase. Instead of analyzing the intensity distribution of diffracted light orders as captured by a camera, the system measures the phase information encoded in the interference signals detected by photodetectors. This parameter transformation enables simpler hardware while achieving equivalent or superior measurement precision.
3Measurement precision
If two separate measurements per direction are used in image-based scatterometry, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent merges multiple measurement operations into a single simultaneous measurement. Instead of performing separate measurements for different directions sequentially, the system captures interference signals for multiple diffraction orders simultaneously using multiple photodetectors. This concurrent measurement approach reduces total measurement time while maintaining the precision required for accurate overlay measurement.
Solution Approach 2:
The patent performs preliminary signal capture during the scanning motion itself, rather than requiring separate stationary measurements. The interference signals are captured in advance during the continuous scan, eliminating the need for subsequent separate measurement operations. This preliminary action during motion significantly reduces total measurement time.
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 provides high-throughput and sensitive overlay metrology by capturing interference signals as the sample is scanned, reducing measurement time and costs while maintaining accuracy.
Implementation Method 1
one or more illumination beams are directed to an overlay target... 0-order diffraction overlaps with first-order diffraction in a collection pupil
Implementation Method 2
receiving time-varying interference signals from the first photodetector and the second photodetector
Implementation Method 3
a first photodetector located in a pupil plane at a location of overlap between 0-order diffraction from the overlay target and +1-order diffraction from the overlay target
Data Source
AI summary
A method includes illuminating an overlay target with a plurality of measurement cells. The method further includes receiving time-varying interference signals from a first and second photodetector as an overlay target is scanned along a stage-scan direction by a translation stage when implementing a metrology recipe. The overlay target may include a plurality of measurement cells, where each measurement cell includes a grating-over-grating structures including a first-layer grating feature on a first layer of the sample and a second-layer grating feature on a second layer of the sample in an overlapping region. The first-layer grating feature and the second-layer grating feature may have a similar pitch. The method includes determining one or more differential signals between the first photodetector and the second photodetector for each measurement cell of the plurality of measurement cells. The method includes determining an overlay measurement based on the determined one or more differential signals.