Multi-Design Diffraction Targets for Small-Feature Metrology
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Solution Overview
Problem
Existing metrology methods in lithographic processes face challenges in achieving high throughput, flexibility, and accuracy, particularly in measuring small target structures, and there is a need for improved techniques that can read out such structures using dark-field image-based methods.
Innovation Solution
The use of diffraction measurement targets with multiple sub-targets having different designs, including varying pitches, feature widths, space widths, and segmentations, and the application of radiation to detect scattered radiation for measuring lithographic process parameters, along with the incorporation of assist features to reduce intensity peaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional single-target metrology methods are used, then measurement simplicity is maintained, but measurement precision and accuracy are insufficient for small target structures
Solution Approach 1:
The metrology target is divided into multiple sub-targets (first sub-target, second sub-target, etc.), each with different designs such as varying pitches, feature widths, and segmentations. This segmentation allows each sub-target to be optimized for specific measurement conditions, thereby improving overall measurement precision while managing complexity through modular design
Solution Approach 2:
Different sub-targets are designed with locally optimized characteristics - for example, sub-targets with different pitches and feature widths are positioned to measure specific process parameters. This local quality approach enables each region of the target to provide optimal measurement data for particular lithographic process variations, enhancing overall measurement accuracy
2Measurement precision
If multiple measurement methods are employed to achieve comprehensive process control, then measurement accuracy improves, but measurement time and throughput decrease
Solution Approach 1:
Multiple measurement capabilities are merged into a single metrology target by incorporating multiple sub-targets with different designs. This allows a single measurement process to extract multiple process parameters simultaneously, thereby maintaining high measurement accuracy while improving throughput by eliminating the need for separate measurement steps
Solution Approach 2:
The metrology target is designed as a multi-functional structure where different sub-targets serve different measurement purposes. For example, sub-targets with different pitches can measure different critical dimensions, and sub-targets with different segmentations can measure various overlay parameters. This universality allows one target to replace multiple specialized targets, improving both accuracy and throughput
3Adaptability or versatility
If dark-field image-based techniques are used for small target detection, then measurement flexibility improves, but interference from intensity peaks reduces measurement reliability
Solution Approach 1:
The patent converts the harmful intensity peaks in dark-field images into beneficial features by strategically positioning sub-targets with different designs. These sub-targets are arranged so that their diffraction patterns create intensity distributions that enhance rather than interfere with measurement signals, transforming potential measurement artifacts into useful measurement information
Solution Approach 2:
Sub-targets are designed with asymmetric features including different pitches, feature widths, and segmentations. This asymmetry creates distinct diffraction patterns for each sub-target, allowing the measurement system to differentiate between various process parameters and reducing interference effects that would occur with symmetric, identical targets
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 throughput, flexibility, and accuracy by allowing the detection of small target structures with improved precision and reduced interference, facilitating better process control in lithographic processes.
Implementation Method 1
detecting radiation scattered by at least the first and second sub-targets
Implementation Method 2
the first and second sub-targets each comprise a pair of periodic structures
Data Source
AI summary
A diffraction measurement target that has at least a first sub-target and at least a second sub-target, and wherein (1) the first and second sub-targets each include a pair of periodic structures and the first sub-target has a different design than the second sub-target, the different design including the first sub-target periodic structures having a different pitch, feature width, space width, and/or segmentation than the second sub-target periodic structure or (2) the first and second sub-targets respectively include a first and second periodic structure in a first layer, and a third periodic structure is located at least partly underneath the first periodic structure in a second layer under the first layer and there being no periodic structure underneath the second periodic structure in the second layer, and a fourth periodic structure is located at least partly underneath the second periodic structure in a third layer under the second layer.