EUV Source Debris Control via Laser Steering and Buffer Gas
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Solution Overview
Problem
The generation of extreme ultraviolet (EUV) radiation in plasma-based systems results in undesirable by-products such as out-of-band radiation, high energy ions, and debris, which degrade the optical elements and reduce their useful lifetime, and also lead to target material deposition on the vessel walls, affecting the efficiency and longevity of EUV sources.
Innovation Solution
A source control loop is established using temperature sensors to optimize debris flux and deposition while maintaining EUV generation conditions, by adjusting the laser targeting and target material positioning within the plasma chamber, utilizing a laser steering system and target material delivery system, and incorporating an EUV radiation metrology system to monitor and control the interaction of laser radiation and target material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If laser radiation is used to generate EUV radiation by irradiating target material, then EUV radiation is produced, but debris and target material are deposited on optical elements and vessel walls, degrading their performance and reducing lifetime
Solution Approach 1:
A buffer gas (hydrogen or deuterium) is introduced into the vacuum chamber as an intermediary substance between the laser irradiation region and the optical elements. This buffer gas absorbs and slows down the high-energy debris particles generated during laser-induced plasma formation, preventing them from directly impacting and degrading the optical elements. The buffer gas thus mediates the interaction between the plasma generation process and the optical components, protecting the latter while allowing the former to continue.
2Duration of action of stationary object
If buffer gas is introduced to protect optical elements from debris, then optical element lifetime is extended, but EUV radiation efficiency may be reduced due to gas absorption
Solution Approach 1:
The system dynamically adjusts the buffer gas pressure parameters to optimize the balance between protection and efficiency. By controlling the buffer gas pressure within specific ranges (e.g., 0.1-10 mbar), the system ensures sufficient debris mitigation while minimizing EUV radiation absorption. This parameter optimization allows the buffer gas to provide adequate protection without excessively compromising the EUV generation efficiency.
3Object-affected harmful factors
If laser beam is steered to adjust target material flux direction, then debris deposition is minimized, but system complexity increases
Solution Approach 1:
The laser beam steering system is made dynamic and adjustable, allowing real-time modification of the beam direction and focal point. This dynamic capability enables the system to adapt to varying debris patterns and target material flux directions, optimizing debris mitigation without requiring a completely complex fixed infrastructure. The adjustability provides flexibility in managing debris deposition while maintaining reasonable system complexity.
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 extends the lifetime of EUV sources and optical elements by minimizing debris deposition and maintaining the directionality of target material flux, effectively managing by-products and ensuring optimal EUV production.
Implementation Method 1
the required plasma can be produced by using a laser beam to irradiate a target material having the required line-emitting element
Implementation Method 2
creating a highly ionized plasma with electron temperatures of several 10's of eV
Implementation Method 3
H2 gas is introduced into the vacuum chamber to slow down the energetic debris (ions, atoms, and clusters) of target material created by the plasma. The debris is slowed down by collisions with the gas molecules.
Implementation Method 4
a near-normal-incidence mirror (often termed a 'collector mirror' or simply a 'collector') is positioned to collect, direct, and, in some arrangements, focus at least a portion of the radiation
Data Source
AI summary
Disclosed is an EUV system in which a source control loop is established to maintain and optimize debris flux while not unduly affecting optimum EUV generation conditions. One or more temperature sensors, e.g., thermocouples may be installed in the vessel to measure respective local gas temperatures. The respective local temperature as measured by the one or more thermocouples can be used as one or more inputs to the source control loop. The source control loop may then adjust the laser targeting to permit optimization of debris generation and deposition while not affecting EUV production, thus extending the lifetime of the source and its collector.