Forbidden Diffraction Order Metrology for Edge Roughness
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Solution Overview
Problem
Current metrology techniques struggle to efficiently measure edge placement errors and local critical dimension uniformity (LCDU) parameters, particularly Line Edge Roughness (LER), due to limitations in measuring smaller features using visible or ultraviolet radiation, which restricts the ability to monitor and control these critical parameters in advanced lithographic processes.
Innovation Solution
A metrology apparatus and method utilizing a radiation system to measure the intensity of forbidden diffraction orders from a metrology target with repetitive patterns, allowing for the determination of edge roughness parameters like LCDU and LER, by controlling destructive interference and optimizing measurement settings with shorter wavelengths such as EUV or SXR radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If visible or ultraviolet radiation is used for metrology measurements, then the measurement system can operate with conventional optics, but the smallest features that can be measured are limited
Solution Approach 1:
The patent changes the fundamental parameter of radiation wavelength from visible/ultraviolet to extreme ultraviolet (EUV) and soft x-ray ranges (1-100 nm). This parameter change enables measurement of smaller features (below 10 nm) that are inaccessible to conventional optical systems, directly resolving the contradiction between measurement precision and wavelength adaptability.
2Measurement precision
If scatterometry is used to measure LCDU and LER parameters, then non-contact measurement is achieved, but measurement accuracy for edge placement errors is insufficient
Solution Approach 1:
The patent uses scatterometry to pre-measure diffraction patterns and extract LCDU parameters before final edge placement error determination. This preliminary action provides critical input data that enhances the accuracy of subsequent EPE measurements while maintaining measurement efficiency through automated processing.
Solution Approach 2:
The patent introduces LCDU (local critical dimension uniformity) as an intermediary parameter that mediates between raw scatterometry data and final EPE measurements. By measuring LCDU through diffraction pattern analysis and using it to correct or refine EPE calculations, the system achieves higher measurement accuracy without sacrificing productivity.
3Measurement precision
If conventional diffraction patterns are used for measurement, then simple intensity detection is possible, but sensitivity to edge roughness is insufficient
Solution Approach 1:
The patent extracts and isolates the forbidden diffraction order from the complete diffraction pattern, focusing measurement sensitivity specifically on this particular diffraction component. By taking out only the relevant forbidden order information and analyzing its intensity, the system achieves high sensitivity to edge roughness and LCDU parameters without requiring complex analysis of the entire diffraction spectrum.
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 more efficient and accurate measurement of edge placement errors and LCDU parameters, improving process control and minimizing Line Edge Roughness, thereby enhancing the precision and reliability of lithographic processes.
Implementation Method 1
measuring intensity of a forbidden diffraction order being diffracted by a metrology target at the measurement position when the metrology target is illuminated by the spot of radiation
Implementation Method 2
the metrology target comprising a repetitive pattern being configured to control an amount of destructive interference that leads to forbidding of the diffraction order
Data Source
AI summary
A method of determining an edge roughness parameter has the steps: (1010) controlling a radiation system to provide a spot of radiation at a measurement position for receiving a substrate; (1020) receiving a measurement signal from a sensor for measuring intensity of a forbidden diffraction order (such as a second order) being diffracted by a metrology target at the measurement position when the metrology target is illuminated by the spot of radiation, the metrology target comprising a repetitive pattern being configured by configuration of a linewidth/pitch ratio (of about 0.5) to control an amount of destructive interference that leads to forbidding of the diffraction order, the sensor being configured to provide the measurement signal based on the measured intensity; and (1040) determining an edge roughness parameter based on the measured intensity of the forbidden diffraction order.