Adaptive Metrology Apparatus for Overlay Measurement Accuracy
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Solution Overview
Problem
Existing methods for measuring multiple structures on a substrate face challenges due to variations in processing, such as thickness of thin film stacks, leading to inconsistent intensity asymmetry measurements, which can result in errors in overlay determination.
Innovation Solution
A method and apparatus that individually select radiation properties, such as wavelength, for each structure based on measured properties to optimize measurement accuracy, using a dual measurement process to adapt illumination conditions for precise overlay measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed radiation wavelength is used for measuring all structures on a substrate, then the measurement process is simple and fast, but measurement accuracy deteriorates due to processing variations between different structures
Solution Approach 1:
The patent applies local quality by selecting different radiation wavelengths for different structures on the substrate based on their individual properties. Each structure is characterized by measuring its reflectivity or scattering properties, and then a specific wavelength is chosen that optimizes the intensity asymmetry for that particular structure. This ensures high measurement accuracy for each local region while accounting for processing variations in thin film stacks and other structure-specific parameters.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the radiation wavelength parameter based on the measured properties of each structure. The system measures a first property (such as reflectivity or scattering characteristics) of each structure, then selects a radiation wavelength that optimizes a second measurement property (intensity asymmetry). This adaptive parameter adjustment resolves the contradiction by allowing the measurement system to optimize for accuracy on a per-structure basis rather than using a fixed wavelength for all structures.
2Measurement precision
If individual wavelength selection is performed for each structure, then measurement accuracy is improved, but measurement time and process complexity increase
Solution Approach 1:
The patent applies preliminary action by first measuring a property of each structure (such as reflectivity or scattering characteristics) before performing the overlay measurement. This preliminary measurement provides information about the structure's specific conditions, including thin film stack thickness variations. Based on this preliminary data, the system pre-selects the optimal radiation wavelength for each structure before the actual overlay measurement, thereby optimizing accuracy without requiring trial-and-error adjustments during the measurement process.
Solution Approach 2:
The patent implements feedback by using the measured first property of each structure to inform the selection of radiation wavelength for the second measurement. The system creates a feedback loop where the initial measurement data about structure properties (reflectivity, scattering characteristics, thin film thickness) is used to adjust and optimize the measurement parameters for subsequent measurements. This feedback mechanism ensures that each structure is measured under optimal conditions while maintaining efficient measurement throughput.
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 reduces measurement errors and improves accuracy by tailoring radiation properties to each structure's specific conditions, enhancing the precision of overlay measurements across the substrate.
Implementation Method 1
These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation
Implementation Method 2
intensity at a single angle of reflection, or over a range of angles of reflection
Implementation Method 3
Diffraction-based overlay using dark-field detection of the diffraction orders enables overlay measurements on smaller targets
Data Source
AI summary
Methods and apparatuses for measuring a plurality of structures formed on a substrate are disclosed. In one arrangement, a method includes obtaining data from a first measurement process. The first measurement process including individually measuring each of the plurality of structures to measure a first property of the structure. A second measurement process is used to measure a second property of each of the plurality of structures. The second measurement process includes illuminating each structure with radiation having a radiation property that is individually selected for that structure using the measured first property for the structure.