EUV Collector Mirror Grating Retroreflects Pump Light
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Solution Overview
Problem
Existing EUV collector mirrors for EUV projection exposure apparatuses have limited conversion efficiency from pump light energy to usable EUV energy, requiring complex Pre-Pulse/Main Pulse schemes and costly target shaping.
Innovation Solution
An EUV collector mirror with a grating structure that retroreflects pump light, eliminating the need for a Pre-Pulse/Main Pulse scheme and allowing for a simpler, cost-effective construction of the pump light laser source, with a blazed grating optimized for retroreflective diffraction and varying pitch to adapt to the angle of incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional Pre-Pulse/Main Pulse scheme is used to increase conversion efficiency, then the conversion efficiency from pump light energy to usable EUV energy is improved, but the device complexity and construction cost increase due to required target shaping and complex pulse control
Solution Approach 1:
The patent extracts the pre-pulse shaping function from the target and relocates it to a grating structure on the collector mirror. The grating diffracts pump light to create the necessary intensity distribution and temporal profile that would otherwise require complex target shaping, thereby simplifying the overall system while maintaining high conversion efficiency
Solution Approach 2:
The grating structure acts as an intermediary element between the pump light source and the target. It modifies the pump light properties (intensity distribution, temporal profile) through diffraction before the light reaches the target, eliminating the need for direct target manipulation and simplifying the system architecture
2Loss of energy
If target shaping is performed to improve conversion efficiency, then the conversion efficiency is improved, but the manufacturing precision and cost increase
Solution Approach 1:
The patent removes the shaping requirement from the target by transferring this function to the grating structure. The grating's periodic structure naturally creates the desired light intensity distribution through diffraction, eliminating the need for precise target shaping and associated manufacturing challenges
Solution Approach 2:
The grating structure creates a copied or replicated intensity distribution pattern through diffraction, rather than requiring the target itself to be shaped. This optical copying approach achieves the same effect as target shaping but with simpler manufacturing requirements
3Ease of manufacture
If a simple spherical target is used without shaping, then the ease of manufacture is improved, but the conversion efficiency decreases
Solution Approach 1:
The grating structure serves as an intermediary that compensates for the simplicity of the spherical target. It modifies the pump light to create optimal intensity distribution and temporal profile, enabling the use of simple spherical targets while maintaining high conversion efficiency that would otherwise require complex target shaping
Solution Approach 2:
The grating structure changes the parameters of the pump light (intensity distribution, temporal profile, spatial distribution) through diffraction, allowing simple spherical targets to achieve the same conversion efficiency as complex shaped targets would provide without modification
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 achieves a significant increase in conversion efficiency of pump light energy to usable EUV energy, potentially by 50% to 100%, while reducing construction costs and simplifying the source collector module design.
Implementation Method 1
a grating structure that is configured to retroreflect pump light emanating from a source region of the LDPP source
Implementation Method 2
an EUV collector mirror for use in an EUV projection exposure apparatus... a reflection surface having an ellipsoidal shape which is rotationally symmetric with respect to an optical axis, the source region being arranged in one focal region of the ellipsoidal shape
Data Source
AI summary
An EUV collector mirror has a reflection surface (16) to reflect usable EUV light which impinges on the reflection surface (16) from a source region (17) to a subsequent EUV optics. The reflection surface (16) carries a pump light grating structure (19) configured to retroreflect pump light (22) which impinges upon the pump light grating structure (19) from the source region (17) back to the source region (17). The pump light (22) has a wavelength deviating from the wavelength of the usable EUV light. Such EUV collector mirror enables a high conversion efficiency between the energy of pump light of a laser discharged produced plasma (LDPP) EUV light source on the one hand and the resulting usable EUV energy on the other.