EUV Multilayer Mirror Blister-Resistant Capping
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Solution Overview
Problem
Optical elements used in EUV radiation generation environments face degradation due to contamination and wear, particularly from high energy ions and reactive target materials, leading to reduced reflectivity and blistering of multilayer mirror coatings.
Innovation Solution
A multilayer mirror design with a capping layer comprising an outermost nitride or oxide layer resistant to target material deposition and hydrogen diffusion, combined with spacer and absorber layers made from materials that inhibit hydrogen diffusion and ion penetration, such as nitrides, carbides, and oxides, to enhance EUV reflectance and prevent blistering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multilayer capping layer is used to protect the optical element surface, then reflectivity is improved and surface protection is enhanced, but the capping layer becomes susceptible to hydrogen diffusion and blistering
Solution Approach 1:
The patent applies composite materials by creating a multilayer capping structure with alternating layers of hydrogen-diffusion-resistant materials (such as nitrides, carbides, or borides) and EUV-reflective materials (such as molybdenum or tungsten). This composite structure combines the protective function of hydrogen barrier layers with the optical function of reflective layers, solving the contradiction between surface protection and susceptibility to hydrogen diffusion.
Solution Approach 2:
The capping layer is segmented into multiple thin alternating layers rather than a single continuous layer. Each layer has a specific function: barrier layers resist hydrogen diffusion while reflective layers maintain EUV reflectivity. This segmentation allows the system to simultaneously achieve hydrogen protection and optical performance without blistering.
2Productivity
If the optical element is placed in the vacuum chamber with plasma to collect EUV radiation, then radiation collection efficiency is improved, but the optical element suffers degradation from contamination and wear
Solution Approach 1:
The patent applies preliminary action by depositing the multilayer capping structure on the optical element before it is exposed to the plasma environment. This pre-applied protective coating prevents target material deposition and contamination before they can degrade the underlying optical layers, thereby extending the element's lifetime while maintaining its radiation collection function.
Solution Approach 2:
The protective capping layer uses composite materials combining hydrogen-diffusion-resistant materials (nitrides, carbides, borides) with EUV-reflective materials. This composite structure provides both contamination resistance and optical performance, allowing the optical element to operate longer in the harsh plasma environment without degradation.
3Object-affected harmful factors
If hydrogen gas is introduced into the vacuum chamber for debris mitigation, then protection from target material debris is improved, but hydrogen penetration and diffusion into the coating occurs
Solution Approach 1:
The patent introduces an intermediary layer - the multilayer capping structure with hydrogen-diffusion-resistant materials - that mediates between the hydrogen gas environment and the underlying optical coating. This intermediary barrier allows hydrogen gas to remain in the chamber for debris mitigation while preventing hydrogen atoms from penetrating and diffusing into the sensitive optical layers.
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 extends the lifetime of optical elements by protecting against target material deposition, hydrogen diffusion, and ion penetration, maintaining high EUV reflectance and preventing blistering, thus ensuring effective radiation collection and redirection in harsh plasma environments.
Implementation Method 1
a multilayer structure positioned between the outermost layer and the substrate, the multilayer structure comprising a plurality of bilayers, each of the bilayers comprising a spacer layer including a material resistant to hydrogen diffusion
Implementation Method 2
an absorber layer including a material resistant to ion penetration
Implementation Method 3
a near-normal-incidence mirror (often termed a 'collector mirror' or simply a 'collector') is positioned to collect, direct, and, in some arrangements, focus the radiation
Data Source
AI summary
A multilayer mirror having a cap with a multilayer structure including a top layer and a series of bilayers each having an absorber layer and a spacer layer, where the materials for the top layer, absorber layers, and spacer layers are chosen to resist blistering.