Plasma Radiation Source Brightness and Lifetime
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Solution Overview
Problem
Current plasma-based radiation sources, such as xenon arc-discharge lamps, have a short lifetime due to thermal stresses and solarization, and their design leads to astigmatism issues, limiting their brightness and spectral bandwidth in applications like lithographic metrology.
Innovation Solution
A radiation source apparatus with a container pressurized with a gaseous medium, where plasma radiation is generated and filtered to remove unwanted wavelengths, using inlet and outlet radiation transmitting elements, including plane parallel plates, to enhance brightness and extend the lifetime by reducing thermal stresses and astigmatism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a xenon arc-discharge lamp is used as the light source, then the apparatus can provide illumination for metrology measurements, but the source brightness is insufficient and the lifetime is short due to thermal stresses and solarization
Solution Approach 1:
The patent changes the physical parameters of the light source by transitioning from a xenon arc-discharge lamp to a plasma-based radiation source. This involves changing the operating conditions, gas composition, and excitation method (using laser energy instead of electrical discharge) to achieve higher brightness while reducing thermal stresses and solarization effects that limit lamp lifetime.
Solution Approach 2:
The patent replaces the mechanical/electrical arc-discharge system with a plasma-based system excited by laser energy. This substitution eliminates the need for electrical arcs and associated thermal stresses, thereby extending source lifetime while maintaining or improving brightness through controlled plasma generation in a pressurized gaseous medium.
2Adaptability or versatility
If the spectral bandwidth is increased and sensor transmittance is reduced, then the measurement capability is improved, but the measurement time increases unless source brightness is significantly improved
Solution Approach 1:
The patent changes the radiation source parameters to produce higher brightness output across a broad spectral range. The plasma-based source with laser excitation generates intense radiation that compensates for reduced sensor transmittance, allowing increased spectral bandwidth without extending measurement time.
3Illumination intensity
If plasma-based light sources are used to increase brightness, then the source brightness improves, but the lifetime is reduced due to thermal stresses and solarization in conventional designs
Solution Approach 1:
The patent uses an inert pressurized gaseous medium (such as xenon or other noble gases) in which plasma is generated. This inert environment prevents oxidation and solarization of the container walls, eliminating the degradation mechanisms that limit lifetime in conventional lamps while allowing high brightness plasma operation.
Solution Approach 2:
The patent introduces a pressurized gaseous medium as an intermediary between the laser energy and the radiation output. This medium absorbs the laser energy, generates plasma, and emits broadband radiation, while the pressure and composition are optimized to reduce thermal stresses and prevent solarization, thereby extending lifetime.
4Power
If conventional plasma source design is used, then the apparatus can generate radiation, but astigmatism issues limit the brightness and quality of the output radiation
Solution Approach 1:
The patent addresses astigmatism by carefully designing the symmetric geometry of the plasma generation region and container. The laser beam is focused symmetrically into the pressurized gas, and the container dimensions are optimized to ensure uniform radiation emission in all directions, eliminating astigmatic distortion in the output radiation.
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 provides higher brightness and extended lifetime of the radiation source, enabling improved spectral bandwidth and reduced measurement time in lithographic metrology, while minimizing thermal stress and astigmatism issues.
Implementation Method 1
A radiation source apparatus includes a container for being pressurised with a gaseous medium in which plasma which emits plasma emitted radiation is generated following excitation of the gaseous medium by a driving radiation
Implementation Method 2
Lasers are used to drive the photon source. The laser light is focused into a gas-filled container to create plasma
Implementation Method 3
The container is operable substantially to remove radiation with a wavelength of 10-400 nm from said plasma emitted radiation before said plasma emitted radiation exits said container as output radiation
Data Source
AI summary
A radiation source apparatus comprising: a container for being pressurized with a gaseous medium in which plasma which emits plasma emitted radiation is generated following excitation of the gaseous medium by a driving radiation, wherein said container is operable substantially to remove radiation with a wavelength of 10-400 nm from said plasma emitted radiation before said plasma emitted radiation exits said container as output radiation. In an embodiment the container comprises: an inlet radiation transmitting element operable to transmit said driving radiation from outside said container to inside said container, and an outlet radiation transmitting element operable to transmit at least some of said plasma emitted radiation from inside said container to outside said container as output radiation; wherein at least one of said inlet and outlet radiation transmitting elements comprises a plane parallel plate.