Moiré Overlay Targets for Tool-Induced Shift Prediction
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Solution Overview
Problem
Overlay metrology measurements suffer from inaccuracies due to tool-induced shifts (TIS) and other systematic errors, degrading measurement accuracy and sensitivity.
Innovation Solution
A metrology system utilizing Moiré structures with different pitches in overlapping layers to generate both Moiré and non-Moiré regime images, enabling simultaneous overlay measurements and systematic error determination through machine learning or closed-form techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If overlay metrology measurements are performed using conventional methods, then overlay alignment data can be obtained, but measurement accuracy is degraded due to tool-induced shifts and systematic errors
Solution Approach 1:
The patent introduces Moiré structures as an intermediary element between the overlay features and the measurement process. These Moiré structures act as a mediator that amplifies the overlay signal while providing reference information, enabling the measurement system to distinguish between actual overlay variations and tool-induced systematic errors. The Moiré structures convert subtle overlay misalignments into larger, more measurable optical interference patterns.
Solution Approach 2:
The patent changes the measurement parameter from direct imaging of overlay features to detection of Moiré interference patterns. By transforming the measurement into the Moiré regime, the system can simultaneously extract overlay information and systematic error data from the same image, improving both accuracy and reliability without requiring additional measurement steps.
2Measurement precision
If Moiré structures with different pitches are used in overlapping layers, then both overlay measurements and systematic error determination can be achieved, but device complexity increases
Solution Approach 1:
The overlay target is segmented into multiple functional regions: Moiré structures for overlay measurement, and non-Moiré structures for systematic error determination. Each region is optimized for its specific function, with the Moiré structures using overlapping layers of different pitches to generate interference patterns, while the non-Moiré structures provide reference measurements for error characterization.
Solution Approach 2:
The Moiré structures serve multiple functions simultaneously: they provide the overlay measurement signal through interference patterns, and they also enable systematic error determination when imaged in the non-Moiré regime. This multi-functionality reduces the need for separate measurement targets and procedures, offsetting the increased structural complexity with measurement efficiency.
3Measurement precision
If first-layer features and second-layer features with different pitches are made to at least partially overlap, then Moiré pitch can be resolved in images, but the features become unresolved individually
Solution Approach 1:
The patent exploits optical interference (analogous to vibration principles) where the overlapping periodic structures create Moiré fringes that represent the beat frequency between the two different pitches. This interference phenomenon transforms the unresolvable fine details into a resolvable lower-frequency pattern that can be easily detected and measured.
Solution Approach 2:
The measurement transitions between two regimes: in the Moiré regime, the overlapping features produce interference patterns that are resolvable and provide overlay information; in the non-Moiré regime, the same structures appear as unresolved features that provide systematic error information. The system leverages both regimes from the same structural configuration.
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 accuracy by resolving tool-induced shifts and other systematic errors, improving the precision of overlay metrology.
Implementation Method 1
the overlay target includes one or more Moiré structures, where a respective one of the one or more Moiré structures includes first-layer features on a first layer of the sample and further includes second-layer features on a second layer of the sample, where the first-layer features and the second-layer features in the respective one of the one or more Moiré structures have different pitches and at least partially overlap
Data Source
AI summary
A metrology system may receive one or more first images of an overlay target on a sample from a first detector, where the overlay target includes one or more Moiré structures, which may be formed as first-layer features and second-layer features that at least partially overlap and have different pitches. In the first images, the first-layer features and the second-layer features may be unresolved, but a Moiré pitch may be resolved. The system may further receive one or more second images of the overlay target from a second detector, where at least one of the first-layer features or the second-layer features are resolved in the one or more second images. The controller may generate a metrology measurement based on the one or more first images and generate a measurement of a systematic error associated with the metrology measurement based on the one or more second images.