Phosphorus Cover Layer for EUV Mirror Stability
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Solution Overview
Problem
EUV lithography systems face significant reflectivity loss due to the accumulation of hydrogen-induced outgassing (HIO) products on optical elements, particularly on metallic surfaces like ruthenium, which are prone to catalytic behavior, leading to contamination and reduced mirror performance.
Innovation Solution
A phosphorus-containing cover layer is deposited onto the optical elements, with a high phosphorus content of at least 95% and a thickness between 0.3 nm and 5 nm, which effectively counteracts the accumulation of HIO products without significantly reducing reflectivity, as elemental phosphorus has a minimal impact on reflectivity loss compared to other HIO elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a cover layer is applied to prevent HIO product accumulation, then the stability of the optical element is improved, but the reflectivity is reduced
Solution Approach 1:
The patent changes the chemical composition parameters of the cover layer by incorporating specific elements (Si, P, S, Se, Te) in controlled ratios. This allows optimization of the cover layer's properties to achieve both stability against HIO product accumulation and minimal reflectivity loss by tuning the elemental composition and thickness parameters.
Solution Approach 2:
The patent employs composite cover layer structures combining multiple elements (Si, P, S, Se, Te) in specific configurations. These composite materials provide enhanced stability against HIO product accumulation while maintaining optical properties that minimize reflectivity loss, resolving the contradiction between protection and performance.
2Reliability
If a thicker cover layer is used to better protect against HIO products, then the protection effectiveness is improved, but the reflectivity loss increases
Solution Approach 1:
The patent optimizes the thickness parameter of the cover layer within a specific range (0.3-5 nm) to achieve the necessary protection effectiveness while minimizing reflectivity loss. This parameter optimization allows the cover layer to be thick enough to protect against HIO products but thin enough to maintain optical performance.
3Reliability
If a cover layer with high phosphorus content is deposited, then the counteraction against HIO product accumulation is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent specifies a high phosphorus content range (at least 95%) in the cover layer to maximize protection against HIO product accumulation. This clear parameter specification provides precise manufacturing targets that guide the deposition process, enabling achievement of the desired composition with appropriate manufacturing precision.
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 phosphorus-containing cover layer significantly reduces the accumulation of other HIO elements, thereby minimizing reflectivity loss and maintaining the optical element's performance by establishing a dynamic equilibrium between deposition and cleaning, ensuring a stable and reflective surface.
Implementation Method 1
depositing a cover layer containing phosphorus onto the optical element
Implementation Method 2
The interaction of hydrogen with EUV radiation forms a hydrogen plasma, in particular in the form of hydrogen ions and/or free hydrogen radicals
Implementation Method 3
The hydrogen ions and/or free hydrogen radicals react with components present in the vacuum environment within the EUV lithography system that contain materials in the form of what are called HIO (hydrogen induced outgassing) elements. The HIO elements form gaseous contaminations in the form of volatile hydrides in the reaction with hydrogen plasma
Data Source
AI summary
A method of depositing a cover layer onto an optical element (M1) for reflection of EUV radiation. In the method, a cover layer containing phosphorus (P) is deposited onto the optical element (M1). The optical element (M1) in the course of deposition of the cover layer (35) is disposed in an interior (39) of a housing (36) of an EUV lithography system, and, for the deposition of the cover layer, phosphorus (P) is released from at least one phosphorus source (42, 43) disposed outside the interior (39) or within the interior (39). Also disclosed are an EUV lithography system and an optical element (M1) for reflecting EUV radiation.