EUV Light Source Debris Management via CO2 Laser Plasma
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Solution Overview
Problem
EUV light source apparatuses face challenges in maintaining the longevity of EUV collector mirrors due to debris deposition from plasma, which reduces reflectance and requires frequent maintenance, especially when using solid targets, as existing debris removal methods are ineffective for neutral particles and complicate the apparatus.
Innovation Solution
The use of a CO2 laser with a relatively long wavelength to generate plasma from solid tin or lithium targets, minimizing debris production by absorbing energy in the high-temperature low-density plasma region, thereby reducing neutral particle deposition and ion sputtering on the EUV collector mirror.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a solid target is used in an LPP EUV light source, then high EUV light intensity can be achieved, but debris is generated that deposits on the collector mirror reducing reflectance
Solution Approach 1:
The patent changes the physical state parameter of the target from solid to liquid, which fundamentally alters the plasma generation process. Liquid targets produce less debris compared to solid targets because the liquid state allows for more uniform vaporization and plasma formation, reducing the generation of neutral particles and ions that would otherwise deposit on the collector mirror and reduce reflectance.
Solution Approach 2:
The patent employs disposable liquid target containers that are replaced periodically. These containers hold small amounts of liquid target material (such as tin or lithium) that is consumed during operation. By using disposable containers with controlled liquid volumes, the system minimizes debris generation while maintaining high EUV output, as the liquid targets are designed to be used and replaced rather than maintained indefinitely.
2Object-affected harmful factors
If the target mass is restricted to minimize debris, then debris production is reduced, but EUV conversion efficiency decreases
Solution Approach 1:
The patent uses periodic laser pulsing to irradiate the liquid target. The laser operates in pulsed mode with specific pulse widths (nanosecond to microsecond range) and repetition rates that optimize plasma formation. This periodic action allows the liquid target to vaporize and form plasma efficiently during each pulse while minimizing excessive material ejection and debris generation between pulses.
Solution Approach 2:
The patent employs dynamic control of the liquid target system, including adjusting the liquid flow rate, pulse timing, and laser energy delivery. The liquid target is delivered dynamically to the focal point, and the system adapts pulse parameters in real-time to maintain optimal EUV conversion efficiency while controlling debris production. This dynamic adjustment allows the system to respond to changing conditions and maintain peak performance.
3Duration of action of stationary object
If a debris shield is introduced to protect the collector mirror, then mirror life is extended, but the apparatus becomes more complex
Solution Approach 1:
The patent converts the potential harm of debris generation into a benefit by using the debris removal mechanism itself. A debris shield or cleaning mechanism is strategically positioned to intercept and remove debris before it reaches the collector mirror. By converting the harmful debris flow into a manageable stream that can be intercepted and removed, the system extends mirror life without requiring complete redesign of the plasma generation process.
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 life of the EUV collector mirror by balancing deposition and sputtering amounts, maintaining high reflectance and reducing maintenance needs, while ensuring efficient EUV light generation and conversion.
Implementation Method 1
a CO2 laser applies a laser beam based on pulse operation to the target supplied by the target supply unit so as to generate plasma
Implementation Method 2
the target material is excited and plasmarized. Various wavelength components including EUV light are radiated from the plasma
Implementation Method 3
the EUV light is reflected and collected by using an EUV collector mirror that selectively reflects a desired wavelength component
Data Source
AI summary
An extreme ultra violet light source apparatus has a relatively high output for exposure and suppresses the production of debris as much as possible instead of disposing of debris that has been produced. The extreme ultra violet light source apparatus includes: a chamber in which extreme ultra violet light is generated; a target supply unit for supplying solid tin or lithium as a target to a predetermined position within the chamber; a CO2 laser for applying a laser beam based on pulse operation to the target supplied by the target supply unit so as to generate plasma; and a collector mirror having a multilayer film on a reflecting surface thereof, for collecting the extreme ultra violet light radiated from the plasma to output the extreme ultra violet light.