Inverse Compton Scattering EUV Source for Semiconductor Metrology
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Solution Overview
Problem
Current metrology techniques for measuring critical dimensions in lithographic processes are limited by the need for large metrology structures and lack of suitable radiation sources for high-volume, high-speed measurement of small targets, particularly in semiconductor manufacturing, where features are becoming increasingly smaller and require higher resolution.
Innovation Solution
A method and apparatus utilizing inverse Compton scattering to generate a bright, controllable EUV radiation source with wavelengths between 0.1 to 125 nm, enabling high-volume metrology on small targets by adapting the radiation source to deliver a wide range of wavelengths, including EUV, UV, and visible, for precise measurement of critical dimensions and other parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optical wavelengths are used for metrology measurements, then measurement speed and throughput are improved, but measurement precision and resolution deteriorate due to the inability to resolve small target features
Solution Approach 1:
The patent changes the wavelength parameter of the radiation used in metrology measurements from optical wavelengths to EUV wavelengths (0.1-125 nm). This parameter change enables both high throughput and high resolution measurements because EUV radiation provides the short wavelength needed to resolve small target features while maintaining the non-contact, rapid measurement capability of optical methods.
Solution Approach 2:
The patent replaces the mechanical/electronic scanning systems of SEM with a radiation-based scatterometry system using EUV sources. This substitution eliminates the need for physical scanning and sample preparation while achieving comparable or superior resolution through the fundamental physics of short-wavelength radiation interaction with the target structures.
2Measurement precision
If EUV radiation is used to achieve higher resolution measurements on small targets, then measurement precision is improved, but productivity deteriorates due to lack of suitable radiation sources for high-volume manufacturing
Solution Approach 1:
The patent develops tunable EUV radiation sources that can operate at different wavelengths (0.1-125 nm) and pulse frequencies. By optimizing the source parameters including pulse duration, repetition rate, and wavelength selection, the system achieves both high resolution measurements and high throughput suitable for high-volume manufacturing environments.
Solution Approach 2:
The patent employs pulsed EUV radiation sources operating at high repetition frequencies. The periodic pulsed operation allows for rapid sequential measurement of multiple targets or multiple parameters on the same target, thereby achieving high measurement throughput while maintaining the resolution benefits of EUV radiation.
3Measurement precision
If dedicated metrology structures with large dimensions are used, then measurement capability is improved, but adaptability to real product structures deteriorates due to the indirect nature of measurements
Solution Approach 1:
The patent changes the scale parameter of metrology targets from large dedicated structures to small product-like structures by using EUV radiation. The short wavelength of EUV enables direct measurement of actual product features at their true dimensions, eliminating the need for scaled-up metrology targets and providing measurements that directly reflect product quality.
Solution Approach 2:
The patent measures actual product structures or realistic replicas of product structures directly, rather than using simplified or scaled metrology targets. The EUV radiation enables accurate measurement of the true product geometry, creating a direct copy of the product features being measured rather than an indirect representation through larger surrogate structures.
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 allows for faster, more accurate measurement of small targets with higher resolution, improving the throughput and precision of metrology in semiconductor manufacturing and other applications, enabling the use of smaller metrology targets and adapting to future lithographic technology nodes.
Implementation Method 1
A bright, compact x-ray source has recently been described based on the phenomenon of inverse Compton scattering (ICS). This is described by W S Graves et al, in 'Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz'
Data Source
AI summary
A target structure (T) made by lithography or used in lithography is inspected by irradiating the structure at least a first time with EUV radiation (304) generated by inverse Compton scattering. Radiation (308) scattered by the target structure in reflection or transmission is detected (312) and properties of the target structure are calculated by a processor (340) based on the detected scattered radiation. The radiation may have a first wavelength in the EUV range of 0.1 nm to 125 nm. Using the same source and controlling an electron energy, the structure may be irradiated multiple times with different wavelengths within the EUV range, and/or with shorter (x-ray) wavelengths and/or with longer (UV, visible) wavelengths. By rapid switching of electron energy in the inverse Compton scattering source, irradiation at different wavelengths can be performed several times per second.