EUV Illumination Source for Lithography Metrology
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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 wavelength range and spectral resolution, particularly with deep ultraviolet (DUV) and extreme ultraviolet (EUV) radiation sources, leading to inaccurate and indirect measurement results.
Innovation Solution
A method for generating an illuminating radiation beam using a higher harmonic generation radiation source, where a driving radiation beam is split into two pluralities of pulses, with controlled characteristics to manage the output wavelength spectrum, allowing for improved spectral resolution and penetration into product structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If visible or near-IR radiation is used for metrology, then the pitch of the grating can be much coarser, but the measurement accuracy for small product structures deteriorates
Solution Approach 1:
The patent changes the wavelength parameter of the radiation from visible/near-IR to EUV range, which fundamentally alters the diffraction behavior and enables accurate measurement of sub-10nm structures. This parameter change allows the use of smaller grating pitches while maintaining measurement accuracy.
Solution Approach 2:
The patent employs pulsed radiation delivery with specific pulse durations (e.g., 100 fs to 10 ps) and repetition rates (e.g., 1 kHz to 1 MHz). This periodic action enables time-gated detection that separates the signal from background noise, improving measurement precision for small features.
2Measurement precision
If EUV radiation is used for metrology, then measurement accuracy for small structures improves, but spectral resolution requirements increase
Solution Approach 1:
The patent uses dynamically controllable pulse parameters including pulse duration (adjustable from femtoseconds to picoseconds) and repetition rate (adjustable from kHz to MHz). This dynamic control allows optimization of the spectral resolution based on the specific measurement requirements, reducing the fixed spectral resolution burden.
Solution Approach 2:
The patent segments the broadband EUV spectrum into multiple wavelength bands using dispersive elements. This segmentation allows selective enhancement of specific wavelength ranges that are most useful for particular measurement applications, effectively reducing the required spectral resolution across the entire spectrum.
3Measurement precision
If scanning electron microscopy is used for direct imaging, then small product structures can be resolved, but measurement time increases significantly
Solution Approach 1:
The patent replaces the mechanical scanning process of SEM with a stationary optical measurement system using EUV radiation. The entire wafer surface can be measured simultaneously or in large fields of view without mechanical scanning, achieving both high resolution and high speed.
Solution Approach 2:
The patent uses preliminary pulse shaping and pre-characterization of the EUV source to optimize the measurement process. By preparing the radiation pulses with specific temporal and spectral properties in advance, the actual measurement requires minimal processing time, achieving high productivity.
4Reliability
If radiation wavelength is decreased for better penetration, then measurement performance improves, but spectral resolution requirements increase
Solution Approach 1:
The patent employs dynamically adjustable pulse parameters including duration and repetition rate that can be optimized for different penetration depths. This dynamic control allows the system to adapt to different measurement scenarios without requiring fixed high spectral resolution across all conditions.
Solution Approach 2:
The patent applies local quality enhancement by selectively optimizing the spectral characteristics for specific wavelength ranges that are most useful for particular measurement applications. Different regions of the EUV spectrum can be enhanced according to their specific utility, reducing the overall spectral resolution burden.
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 measurement accuracy and utility by providing a broader spectral width, enabling more precise metrology measurements and improved reconstruction accuracy for critical dimensions and overlay errors.
Implementation Method 1
a higher harmonic generation radiation source, wherein a driving radiation beam is processed to generate the illuminating radiation
Data Source
AI summary
An method for generating illuminating radiation in an illumination apparatus for use in an inspection apparatus for use in lithographic processes is described. A driving radiation beam is provided that comprises a plurality of radiation pulses. The beam is split into first and second pluralities of driving radiation pulses. Each plurality of driving radiation pulses has a controllable characteristic. The first and second pluralities may be used to generate an illuminating radiation beam with an output wavelength spectrum. The first and second controllable characteristics are controlled so as to control first and second portions respectively of the output wavelength spectrum of the illuminating radiation beam.