Lithographic Overlay Metrology via Scatterometry Asymmetry
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Solution Overview
Problem
Current lithographic processes face challenges in accurately measuring small features due to limitations in traditional metrology techniques, which struggle to image structures with dimensions smaller than the wavelength of radiation used, leading to inefficiencies and increased costs with scanning electron microscopes.
Innovation Solution
The method involves using zeroth-order light scattered by target structures with specifically designed bias amounts to derive measurements of parameters like overlay error through angle-resolved scatter spectra, optimizing the wavelength for strength and linearity of asymmetry in the spectra.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional optical metrology techniques are used to measure small features, then the measurement process is simple and fast, but the measurement precision deteriorates because the features are smaller than the wavelength of radiation used
Solution Approach 1:
The patent replaces direct imaging methods with scatterometry, using scattered light analysis instead of direct optical imaging to measure sub-wavelength features. This substitution enables measurement of features smaller than the wavelength by analyzing the scattering pattern rather than attempting to directly image the features.
Solution Approach 2:
The patent changes the measurement parameter from direct spatial imaging to angular distribution of scattered light. By measuring the intensity distribution of scattered light at different angles and wavelengths, the system can derive feature dimensions that are smaller than the illumination wavelength.
2Measurement precision
If scanning electron microscopes are used to measure small features, then the measurement precision improves, but the productivity deteriorates due to time-consuming measurements and increased costs
Solution Approach 1:
The patent replaces scanning electron microscopy with optical scatterometry, substituting a slow, expensive sequential scanning method with a faster optical technique. The scatterometry system uses optical detection of scattered light patterns to achieve comparable measurement precision without the time and cost constraints of electron beam scanning.
Solution Approach 2:
The patent creates optical copies or representations of the feature scattering patterns that can be analyzed without physically scanning the features with an electron beam. The scattered light intensity distribution serves as a computational copy that contains the dimensional information needed for measurement.
3Productivity
If targets with features much larger than product features are used for metrology, then the measurement process becomes easier and faster, but the measurement precision deteriorates because the targets do not represent the actual product structures
Solution Approach 1:
The patent applies local quality by creating target structures that locally replicate the critical dimensions and material composition of the actual product features. The targets use the same sub-wavelength feature sizes and material layers as the products, ensuring that the scattering characteristics accurately represent the features being measured in production.
Solution Approach 2:
The patent creates accurate optical copies of the product structures at the target location, using identical feature dimensions and material compositions. This copying approach ensures that the scatterometry measurements on targets directly reflect the conditions and dimensions of the actual product features, enabling precise overlay and critical dimension measurement.
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 enables efficient and cost-effective metrology measurements for small features by leveraging asymmetry in scatter spectra, improving the accuracy of overlay error determination and reducing the reliance on time-consuming and expensive scanning electron microscopes.
Implementation Method 1
obtaining an angle-resolved scatter spectrum of the first target structure and an angle-resolved scatter spectrum of the second target structure
Data Source
AI summary
A substrate has first and second target structures formed thereon by a lithographic process. Each target structure has two-dimensional periodic structure formed in a single material layer on a substrate using first and second lithographic steps, wherein, in the first target structure, features defined in the second lithographic step are displaced relative to features defined in the first lithographic step by a first bias amount that is close to one half of a spatial period of the features formed in the first lithographic step, and, in the second target structure, features defined in the second lithographic step are displaced relative to features defined in the first lithographic step by a second bias amount close to one half of said spatial period and different to the first bias amount. An angle-resolved scatter spectrum of the first target structure and an angle-resolved scatter spectrum of the second target structure is obtained, and a measurement of a parameter of a lithographic process is derived from the measurements using asymmetry found in the scatter spectra of the first and second target structures.