LPP EUV Light Source Cooling via Rotating Target and Magnetic Seal
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Solution Overview
Problem
High-brightness EUV light sources with fast rotating targets face limitations in achieving high output power and brightness due to heat removal challenges, which lead to debris contamination and reduced operational efficiency.
Innovation Solution
A high-brightness EUV light source with a rotating target assembly featuring a large surface area disk with high emissivity coatings, a liquid-cooled heat exchanger, and a magnetic fluid seal for efficient thermal management, combined with gas blowing through a narrow slit gap and convection air cooling, to effectively mitigate debris and maintain target temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a fast rotating liquid metal target is used to mitigate debris, then debris mitigation is improved, but heat removal becomes more difficult due to centrifugal forces and rotation speed limitations
Solution Approach 1:
The cooling system is segmented into multiple independent channels: internal cooling channels within the target structure, external heat exchangers, and separate debris mitigation systems. This allows optimization of each subsystem independently - the target can rotate fast for debris mitigation while cooling channels efficiently remove heat without being affected by centrifugal forces
Solution Approach 2:
A magnetic field is introduced as an intermediary to mitigate debris particles without requiring physical contact or slowing down the rotating target. The magnetic field selectively deflects charged debris particles away from the optical path, allowing the target to maintain high rotation speeds for both debris mitigation and effective cooling
2Object-generated harmful factors
If the target rotation speed is increased to improve debris mitigation, then debris redirection is improved, but heat removal efficiency decreases due to centrifugal forces
Solution Approach 1:
The system replaces purely mechanical cooling methods with a hybrid approach combining magnetic field-based debris mitigation and thermally-driven cooling systems. Heat removal is achieved through thermal conduction in the target material and phase-change cooling, which are not affected by rotation speed, allowing the target to rotate as fast as needed for debris mitigation
3Power
If high pulse-repetition-rate mode is implemented to increase output power, then EUV light output is improved, but target temperature increases beyond acceptable limits
Solution Approach 1:
The cooling system is designed to remove heat continuously and proactively, preventing temperature accumulation before it reaches critical levels. Internal cooling channels are positioned to extract heat at its source, and the system operates in a steady-state regime where heat generation and removal are balanced, enabling sustained high pulse-repetition-rate operation
Solution Approach 2:
The cooling system utilizes phase transitions (such as liquid-to-gas phase change in the cooling medium) to efficiently absorb and remove large amounts of heat from the target. This latent heat absorption mechanism allows the target to withstand high pulse-repetition-rate operation without excessive temperature increase
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 enables a significant increase in EUV light output power and brightness while ensuring effective debris mitigation and maintaining acceptable temperatures, resulting in a compact, commercially viable, and long-lasting EUV light source.
Implementation Method 1
an outer surface of a peripheral part of the rotating target assembly... has a coating with high, more than 0.7, emissivity
Implementation Method 2
heat exchange through the slit gap between a disk of the rotating target assembly and a heat exchanger with liquid cooling
Implementation Method 3
convection air cooling
Implementation Method 4
a gas blowing through the narrow slit gap
Data Source
AI summary
A laser produced plasma (LPP) light source comprises a rotating target assembly supplying a target into an interaction zone with a focused beam of a high-repetition-rate pulsed laser. High effective cooling of the light source is provided by thermal radiation of a peripheral part of the rotating target assembly and through a meander-shaped gap between the rotating target assembly and a fixed heat exchanger with a gas blowing through the slit gap. In an embodiment, a sealing between the vacuum chamber and a shaft of rotating drive unit is provided by a magnetic fluid seal (MFS) with an additional heat exchanger. A heat transfer from the rotating target assembly is provided through the shaft and MFS to additional heat exchanger and by convection air cooling of a counterweight of the rotating target assembly fixed on the shaft. High brightness and high output power of LPP light source are provided.