Lithographic Metrology Using Time-Delayed Scattered Radiation
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Solution Overview
Problem
Current metrology techniques in lithographic processes face challenges in accurately measuring small product structures due to limitations in spectral resolution and the need for larger metrology targets, which can lead to inaccurate results and increased manufacturing costs.
Innovation Solution
The method involves providing a time-delayed copy of the illuminating radiation to optimize the spectral resolution of the metrology system by controlling the time delay between scattered radiation, allowing for improved measurement performance on smaller targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the wavelength of radiation used during metrology is decreased (moving towards soft X-ray spectrum), then measurement performance improves and radiation can penetrate further into product structures, but the spectral resolution requirement of the metrology system increases significantly
Solution Approach 1:
The broadband radiation spectrum is segmented into multiple wavelength components, each interacting with different depths of the multi-layer target structure. By measuring the spectral distribution of scattered radiation across these segmented wavelength components, the system achieves high measurement precision without requiring the entire system to resolve extremely fine spectral details at a single wavelength.
Solution Approach 2:
The patent transitions from resolving spectral details in the frequency dimension to resolving spatial/depth information by utilizing the natural wavelength-dependent penetration depth. Different wavelengths naturally probe different depths of the multi-layer structure, converting a spectral resolution challenge into a spatial measurement advantage.
2Manufacturing precision
If the size of metrology targets is reduced to match modern product structures, then measurement accuracy improves, but the targets become too small for effective optical metrology and require much larger features
Solution Approach 1:
The patent changes the measurement parameters by using broadband radiation with a wide wavelength range instead of monochromatic light. This allows the metrology system to resolve small target features through wavelength-dependent interaction, where shorter wavelengths probe smaller features and penetrate less deeply, while longer wavelengths provide complementary information from different depths.
Solution Approach 2:
The target structure is treated as a composite multi-layer system where each layer has different optical properties. By illuminating with broadband radiation, the system exploits the composite nature of the target to extract information from multiple layers simultaneously, achieving accurate measurements of small features without requiring large target areas.
3Ease of operation
If larger metrology targets are used, then optical metrology can effectively image them, but the measurement results become indirectly related to the dimensions of real product structures and may be inaccurate
Solution Approach 1:
The patent applies local quality by allowing different wavelength components of the broadband radiation to interact with different local regions and depths of the target structure. Each wavelength component provides localized information about specific features at specific depths, and the combined spectral measurement reconstructs the complete three-dimensional structure with high precision.
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 enhances the spectral resolution and accuracy of measurements, reducing the size of metrology targets and improving overlay performance by optimizing the properties of the combined scattered radiation.
Implementation Method 1
illuminating a target structure with the illuminating radiation resulting in at least a first and a second scattered radiation
Data Source
AI summary
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). The lithographic apparatus has an inspection apparatus with an illumination system that utilizes illuminating radiation with a wavelength of 2-40 nm. The illumination system includes an optical element that splits the illuminating radiation into a first and a second illuminating radiation and induces a time delay to the first or the second illuminating radiation. A detector detects the radiation that has been scattered by a target structure. The inspection apparatus has a processing unit operable to control a time delay between the first scattered radiation and the second scattered radiation so as to optimize a property of the combined first and second scattered radiation.