Rotating EUV Light Source for Mask Inspection
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Solution Overview
Problem
Current EUV light sources for lithography systems have high power levels that are excessive for EUV mask inspection, leading to unnecessary complexity and cost, and the use of metal targets in these systems results in contamination due to micro-particle and metal vapor debris.
Innovation Solution
A plasma-based EUV light source system that includes a rotatable, cylindrically-symmetric element coated with a plasma-forming target material within a vacuum chamber, utilizing a drive laser to generate EUV light through plasma formation, with a gas management system to supply plasma-forming material and control systems for precise positioning and focusing, which reduces power requirements and minimizes debris.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high power EUV light sources are used for lithography systems, then sufficient illumination power is achieved, but the power level becomes excessive for mask inspection causing unnecessary complexity and cost
Solution Approach 1:
The patent adjusts the operational parameters of the plasma-based EUV source to achieve moderate power levels suitable for mask inspection. By controlling plasma density, laser pulse energy, and gas flow rates, the system delivers adequate illumination power (sufficient for mask inspection) without the excessive power levels (100W+) required for lithography, thereby reducing system complexity and cost.
2Quantity of substance
If metal targets are used in EUV light sources, then sufficient target material is available for plasma generation, but micro-particle and metal vapor debris is generated causing contamination
Solution Approach 1:
The patent employs an inert gas environment (typically xenon or krypton) in which the plasma is generated. This inert atmosphere prevents the formation of metal vapor and micro-particle debris that would otherwise contaminate the optics. The inert gas serves as the target material for plasma generation, eliminating contamination issues while maintaining sufficient EUV light generation.
3Illumination intensity
If high power EUV sources are designed for lithography, then adequate illumination is provided, but the system produces unneeded complexity when implemented in EUV mask inspection setting
Solution Approach 1:
The patent optimizes the EUV source specifically for the local requirements of mask inspection rather than general lithography applications. By tailoring the plasma generation conditions, optical collection geometry, and power levels to the specific needs of mask inspection (which requires moderate power but high spatial coherence), the system achieves adequate illumination intensity without the unnecessary complexity of a full lithography-grade high-power source.
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 system achieves moderate average power with high brightness in a small source size, reducing contamination and complexity, while maintaining efficient EUV light generation for EUV mask inspection.
Implementation Method 1
a drive laser source configured to generate one or more laser pulses sufficient to generate EUV light via formation of a plasma by excitation of the plasma-forming target material
Implementation Method 2
utilizing a drive laser to generate EUV light through plasma formation
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
An EUV light source includes a rotatable, cylindrically-symmetric element having a surface coated with a plasma-forming target material, a drive laser source configured to generate one or more laser pulses sufficient to generate EUV light via formation of a plasma by excitation of the plasma-forming target material, a set of focusing optics configured to focus the one or more laser pulses onto the surface of the rotatable, cylindrically-symmetric element, a set of collection optics configured to receive EUV light emanated from the generated plasma and further configured to direct the illumination to an intermediate focal point, and a gas management system including a gas supply subsystem configured to supply plasma-forming target material to the surface of the rotatable, cylindrically-symmetric element.