UV Lithography Optical Element Coating for Laser Resistance
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Solution Overview
Problem
Optical elements used in UV lithography face challenges in achieving both good laser resistance and transmission, particularly at wavelengths less than 380 nm, where existing solutions often compromise on one aspect at the expense of the other.
Innovation Solution
A substrate with a coating comprising at least four layers, where a first layer of inorganic fluoride is applied directly on the substrate, followed by alternating layers of inorganic fluoride and oxide-containing compounds, with the most distant layer being of high refractive index oxide-containing material, enhancing both laser resistance and transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer or simple multilayer coating is used, then manufacturing is simpler, but laser resistance and transmission cannot be simultaneously optimized
Solution Approach 1:
The coating is divided into multiple functional layers (first layer with low refractive index inorganic fluoride, second layer with high refractive index inorganic oxide, third layer with low refractive index inorganic fluoride, fourth layer with high refractive index inorganic oxide) to simultaneously achieve antireflection, laser damage resistance, and transmission optimization that cannot be achieved with simpler coatings
Solution Approach 2:
The coating uses composite material structure combining different inorganic fluoride compounds (MgF2, AlF3, LiF, NaF, KF, RbF, CsF, CaF2, SrF2, BaF2, PbF2, ZnF2, HfF4, TiF4, ZrF4, SiF4, GeF4, SnF4, PbClF3, PbBrF3, PbIF3) and inorganic oxide compounds (SiO2, TiO2, ZrO2, HfO2, Al2O3, Ta2O5, Nb2O5, WO3, MoO3, ReO3, Bi2O3, PbO, Pb3O4, Pb2O3, Pb4O5, Pb4O7, Pb5O6, Pb2SiO4, Pb2Si2O5, Pb2SiO2.5, Pb2SiO3, PbSiO3, Pb2SiO3.5, PbSiO4, Pb3Si2O5, Pb3Si2O6, Pb4Si3O10, Pb5Si4O15, Pb6Si4O18, Pb7Si6O21, Pb8Si6O24, Pb9Si6O27, Pb10Si7O30, Pb11Si8O33, Pb12Si9O36, Pb13Si10O39, Pb14Si11O42, Pb15Si12O45, Pb16Si13O48, Pb17Si14O51, Pb18Si15O54, Pb19Si16O57, Pb20Si17O60, Pb21Si18O63, Pb22Si19O66, Pb23Si20O69, Pb24Si21O72, Pb25Si22O75, Pb26Si23O78, Pb27Si24O81, Pb28Si25O84, Pb29Si26O87, Pb30Si27O90, Pb31Si28O93, Pb32Si29O96, Pb33Si30O99, Pb34Si31O102, Pb35Si32O105, Pb36Si33O108, Pb37Si34O111, Pb38Si35O114, Pb39Si36O117, Pb40Si37O120, Pb41Si38O123, Pb42Si39O126, Pb43Si40O129, Pb44Si41O132, Pb45Si42O135, Pb46Si43O138, Pb47Si44O141, Pb48Si45O144, Pb49Si46O147, Pb50Si47O150) with alternating low and high refractive indices to achieve both laser resistance and transmission optimization
2Loss of energy
If high refractive index materials are used to reduce reflection, then transmission improves, but laser resistance decreases due to higher absorption
Solution Approach 1:
Different layers have different local properties: odd-numbered layers (1st, 3rd, 5th, etc.) use low refractive index inorganic fluoride compounds for laser damage resistance, while even-numbered layers (2nd, 4th, 6th, etc.) use high refractive index inorganic oxide compounds for reflection reduction, creating a gradient structure that optimizes both properties at different interfaces
Solution Approach 2:
The alternating low and high refractive index layers act as intermediaries that progressively reduce reflection through multiple interfaces while distributing laser energy absorption across layers with lower individual absorption coefficients, preventing concentrated damage at any single interface
3Reliability
If more layers are added to optimize transmission and laser resistance, then performance improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent provides specific thickness ranges for each layer (first layer: 5-50 nm, second layer: 50-200 nm, third layer: 5-50 nm, fourth layer: 50-200 nm) that can be optimized for different wavelengths and applications, allowing manufacturers to adjust parameters to achieve desired performance while maintaining a manageable four-layer structure
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 configuration provides improved laser resistance and transmission while reducing radiation damage and reflection, extending the lifespan of optical elements in UV lithography, especially at shorter wavelengths.
Implementation Method 1
a coating on the substrate having at least four layers, wherein a first layer comprising an inorganic fluoride compound is arranged on the substrate, a layer comprising an inorganic oxide-containing compound is arranged as a layer the most distant from the substrate, and at least two further layers each comprising an inorganic fluoride compound or an inorganic oxide-containing compound are alternately arranged between the first and the most distant layers
Implementation Method 2
This specific coating proposed here simultaneously results in an antireflective effect and a reduction of potential radiation damage as a result of excessively high laser intensities
Data Source
AI summary
In order to make possible both good laser resistance and good antireflection properties, an optical element, in particular for UV lithography, comprising a substrate and a coating on the substrate having at least four layers, is proposed, whereina first layer comprising a low refractive index inorganic fluoride compound is arranged on the substrate,a layer comprising an inorganic oxide-containing compound is arranged as a layer the most distant from the substrate, andat least two further layers each comprising an inorganic fluoride compound or an inorganic oxide-containing compound are arranged alternately between the first and the most distant layers.