EUV Scatterometry for Edge Roughness Measurement
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Solution Overview
Problem
Current methods for determining edge roughness parameters in lithographic processes, such as CD-SEM and hard X-ray scatterometry, are slow, insensitive to low-frequency variations, and not suitable for small feature sizes due to limitations in wavelength range and source availability, making it difficult to accurately measure Line Edge Roughness (LER) and Line Width Roughness (LWR) in modern lithographic processes.
Innovation Solution
A method involving the use of a radiation beam to obtain a scattering signal from a periodic structure and determining edge roughness parameters based on the distribution of the scattering signal around non-specular diffraction orders, utilizing radiation sources like high-harmonic generation (HHG) for EUV/SXR wavelengths, which allows for more precise measurement of LER and LWR even at small product pitches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If visible or ultraviolet radiation is used for inspection, then the inspection apparatus can operate with available radiation sources, but the smallest features that can be measured are limited
Solution Approach 1:
The patent changes the wavelength parameter of the radiation beam from visible/ultraviolet to extreme ultraviolet (EUV) range (1-100 nm), enabling measurement of smaller features while maintaining inspection capabilities through scatterometry techniques
2Measurement precision
If CD-SEM is used to measure line edge roughness, then edge roughness parameters can be determined, but the measurement process is slow
Solution Approach 1:
The patent replaces the mechanical scanning electron microscope system with a scatterometry-based optical system that uses radiation scattering patterns to determine edge roughness parameters, enabling faster non-contact measurement
Solution Approach 2:
The patent measures scattering signals at multiple angles and wavelengths to obtain sufficient data for edge roughness determination, using partial measurements at different conditions rather than complete scanning to achieve faster results
3Measurement precision
If hard X-ray scatterometry is used for measurement, then small feature sizes can be measured, but the technique is insensitive to low-frequency variations
Solution Approach 1:
The patent measures scattering signals at multiple angles including both specular and non-specular diffraction orders, using partial measurements at different angular positions to capture both high-frequency and low-frequency roughness variations that would be missed by single-angle measurements
4Productivity
If EUV/SXR wavelengths are used with HHG sources, then small feature sizes and fast measurement are achieved, but the radiation source complexity increases
Solution Approach 1:
The patent uses high-harmonic generation (HHG) as an intermediary process that converts infrared laser radiation into EUV/SXR wavelengths through interaction with a gaseous medium, enabling access to required wavelength range while using commercially available laser technology
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 faster and more accurate determination of edge roughness parameters, improving the measurement of LER and LWR, particularly for small feature sizes, by utilizing EUV/SXR wavelengths and non-specular diffraction order analysis, overcoming the limitations of existing techniques.
Implementation Method 1
obtaining a scattering signal from a radiation beam scattered from the periodic structure
Implementation Method 2
determining an edge roughness parameter based on a distribution of the scattering signal around a non-specular diffraction order
Data Source
AI summary
In a method of determining an edge roughness parameter of a periodic structure, the periodic structure is illuminated (602) in an inspection apparatus. The illumination radiation beam may comprise radiation with a wavelength in the range 1 nm to 100 nm. A scattering signal (604) is obtained from a radiation beam scattered from the periodic structure. The scattering signal comprises a scattering intensity signal that is obtained by detecting an image of a far-field diffraction pattern in the inspection apparatus. An edge roughness parameter, such as Lined Edge Roughness and/or Line Width Roughness is determined (606) based on a distribution of the scattering intensity signal around a non-specular diffraction order. This may be done for example using a peak broadening model.