Compact EUV Light Source for Metrology
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Solution Overview
Problem
Current EUV metrology methods face challenges in achieving high brightness, stability, and coherence, particularly for coherent scattering applications, with existing light sources being either too large or lacking in power and reliability, making them unsuitable for efficient actinic mask inspection.
Innovation Solution
A compact light source based on electron beam accelerator technology, optimized for EUV range, featuring a 3-dimensional storage ring and booster design with undulator periods of 16 mm, providing high stability, brightness, and coherence, and minimizing footprint and maintenance costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional EUV light sources (DPP or LPP) are used to achieve high brightness, then brightness is improved, but device size becomes large and stability deteriorates
Solution Approach 1:
The patent replaces conventional thermal plasma-based EUV sources (DPP/LPP) with an accelerator-based light source that uses electron beam acceleration and undulator radiation. This substitution of the fundamental generation mechanism enables compact size while maintaining high brightness and improving stability through precise electron beam control and continuous top-up injection.
Solution Approach 2:
The patent changes the operating parameters by using a storage ring with continuous electron beam circulation and top-up injection, maintaining optimal beam parameters (energy, current, emittance) for EUV generation. This enables stable, repeatable operation that improves reliability compared to pulsed plasma sources.
2Illumination intensity
If accelerator-based light sources are used to achieve high brightness, then brightness is improved, but device complexity increases
Solution Approach 1:
The storage ring serves multiple functions simultaneously: it stores and circulates electron beams for continuous EUV generation, enables top-up injection for stability, provides beam manipulation capabilities, and supports various undulator configurations. This multi-functionality reduces the need for separate systems and simplifies the overall device architecture.
3Power
If high power EUV sources are used to achieve sufficient flux, then flux is improved, but operational costs increase
Solution Approach 1:
The storage ring enables continuous electron beam circulation and continuous EUV photon generation, eliminating the need for high-power pulsed operation. The top-up injection maintains optimal beam parameters continuously, enabling sustained high flux at lower average power consumption, thereby reducing operational costs.
4Area of stationary object
If compact design is implemented to reduce footprint, then device size is reduced, but achieving high brightness becomes difficult
Solution Approach 1:
The patent employs a nested configuration where the undulator is positioned within the storage ring aperture, and the beam line components are integrated within the ring structure. This space-efficient nesting enables compact footprint while maintaining the interaction length and geometry needed for high brightness EUV generation.
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
The solution delivers extremely high intensity stability and brightness, enabling efficient coherent diffraction imaging and actinic mask inspection with a compact footprint, suitable for conventional lab settings and reducing operational costs.
Implementation Method 1
A compact light source based on accelerator technology for metrology application in the EUV range
Implementation Method 2
featuring a 3-dimensional storage ring and booster design with undulator periods of 16 mm, providing high stability, brightness, and coherence
Implementation Method 3
A compact light source based on electron beam accelerator technology, optimized for EUV range, featuring a 3-dimensional storage ring and booster design
Data Source
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AI summary
It is the objective of the present invention to provide a compact and cost effective light source based on a storage ring that can deliver sufficient power, superior stability and high coherence for metrology methods in the EUV range using coherent scattering methods. This objective is achieved according to the present invention by a compact light source (LS) based on electron beam accelerator technology, comprising a storage ring (SR), a booster ring (BR), a linear accelerators and an undulator (UN) for providing light having the characteristics for actinic mask inspection at 13.5 nm,wherein: a) the intensity of the electron beam is maintained down to a level of 10-3; b) a compact multi-bend magnet structure is used for the storage ring (SR) to generate a small emittance leading to high brilliance and large coherent content of the light; c) the booster ring (BR) and the storage ring (SR) are located at different levels in a concentric top view arrangement in order to keep the required floor space small and to reduce interference effects; d) quasi-continuous injection, respectively enhanced top-up injection is implemented to reach the high intensity stability and to combat lifetime reductions due to elastic beam gas scattering and Touschek scattering; e) the injection into the storage ring (SR) and extraction from the booster ring (BR) are performed diagonal in the plane which is defined by the parallel straight section orbits of the booster ring (BR) and the storage ring (SR); and f) for the top-up injection from the booster ring (BR) into the storage ring (SR) two antisymmetrically arranged Lambertson septa are used. These measures result in a very compact source that fits into conventional labs or their maintenance areas and has quite low maintenance requirements and low cost of ownership. The wavelength of the light emitted by the undulator ranges from 6 to 30 nm. The light beam has an extreme intensity stability in a range of 10-3, a sufficient power on the mask larger than 10 mW and a high brightness larger than 10 kW/mm2/sr. The parameter space of electron beam energy, undulator period length, number of undulator periods are optimized to provide the required wavelength, photon flux and coherence for lensless metrology applications and coherent scattering methods. The concept of concentric rings enables minimal footprint of the source. A combination of enhanced top-up injection into the storage ring with a low gap undulator provides extremely high intensity stability and satisfies the coherence need for the specific application of coherent scattering methods.