Self-Calibrating Metrology Targets for Edge Placement Error
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Solution Overview
Problem
In lithographic device manufacturing, precise measurement of edge placement errors (EPE) is challenging due to difficulties in directly measuring features formed by lithography, especially when using different imaging devices or measuring at different stages, which affects the accuracy of overlay and critical dimension (CD) measurements.
Innovation Solution
The implementation of self-calibrating metrology targets with multiple sub-units having the same features at different offsets allows for the determination of edge placement errors without direct measurements, using imaging systems like SEMs, by analyzing positional relationships and symmetries in images, enabling accurate detection of overlay and CD errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement methods are used to measure edge placement errors, then measurement capability is achieved, but measurement precision deteriorates due to difficulties in directly measuring features formed by lithography
Solution Approach 1:
The patent introduces intermediary target structures with known geometries and symmetries that serve as mediators between the lithography features and the measurement system. These target structures include reference features with precise, known dimensions and positions that can be easily imaged and measured, allowing indirect determination of edge placement errors through comparison with the actual lithography features
Solution Approach 2:
The patent creates copied reference features within the target structures that replicate the expected geometry and position of actual lithography features. By comparing the imaged reference features (which are easily measurable) with the actual features, the system can determine edge placement errors without directly measuring the difficult-to-measure lithography features themselves
2Adaptability or versatility
If multiple imaging devices or different measurement stages are used, then measurement flexibility is improved, but measurement precision deteriorates due to inconsistencies between different imaging devices
Solution Approach 1:
The patent designs universal target structures that can be imaged by multiple different imaging devices (optical microscopes, electron microscopes, scatterometers) and at different measurement stages. The target structures include features with known geometries that serve as common reference points across different measurement systems, enabling consistent edge placement error determination regardless of which imaging device or measurement stage is used
Solution Approach 2:
The patent incorporates homogeneous reference features with uniform, known geometries throughout the target structures. These homogeneous reference features provide consistent measurement benchmarks that can be used across different imaging devices and measurement stages, ensuring measurement consistency and eliminating device-specific variations
3Measurement precision
If self-calibrating target structures with multiple sub-units at different offsets are implemented, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the target structures into multiple sub-units, each containing reference features at different known offsets from a reference position. This segmentation allows the measurement system to compare features at multiple offset positions and determine edge placement errors through analysis of the positional relationships, improving measurement precision while keeping each individual sub-unit relatively simple
4Manufacturing precision
If direct distance measurements are performed, then measurement capability is achieved, but manufacturing precision requirements increase due to the need for highly accurate direct measurements
Solution Approach 1:
The patent incorporates reference features with pre-determined, known dimensions and positions directly into the target structures during the lithography process. These reference features serve as pre-calibrated measurement benchmarks that eliminate the need for complex post-fabrication calibration procedures, making the measurement process easier while maintaining high manufacturing precision
Data Source
AI summary
A metrology method comprising: performing a first exposure on a substrate to form a first patterned layer including a plurality of first target units, each first target unit comprising a first target feature; performing a second exposure on the substrate to form a second patterned layer comprising second target units overlying respective ones of the first target units, each of the second target units having a second target feature, wherein ones of the second target units have the second target feature positioned at respectively different offsets relative to a reference position: imaging the second target units overlaid on the first target units; and determining an edge placement error based on positions of edges of second target features in second target units relative to edges of the first target feature of the underlying first target unit.