EUV Multilayer Reflectors with Interface Layers for Roughness Control
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Solution Overview
Problem
Extreme ultraviolet lithography systems face challenges with the 'Z-effect' causing non-telecentricity, edge placement errors, and contrast loss due to the phase change and double diffraction of EUV light in multilayer reflective stacks, which require reduction of roughness and improvement in reflectance over a large bandwidth.
Innovation Solution
A multilayer reflective stack comprising alternating layers of specific elements such as Si, B, Al, and Ru, Mo, with interface layers and a capping layer, and an absorber layer to minimize roughness and enhance reflectance, formed using physical vapor deposition techniques like magnetron sputtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a multilayer reflective stack is used to achieve high EUV reflectance, then reflectance is improved, but roughness increases causing the Z-effect and mask 3D effects
Solution Approach 1:
The patent changes the material parameters by using alloys (e.g., Mo-Ru, Si-B) instead of pure elements, and uses nitrides and oxides to modify the optical and physical properties of the layers. This allows achieving high reflectance while controlling roughness growth. The interface layer composition and thickness are also optimized to minimize roughness propagation
Solution Approach 2:
The patent employs composite material structures including alternating layers of different materials (Mo/Si, Ru/Si, Mo-Ru/Si-B) with intermediate interface layers. These composite structures are designed to optimize both reflectance and roughness characteristics, where each material layer contributes specific properties to the overall multilayer system
2Adaptability or versatility
If the multilayer stack depth is increased to improve reflectance bandwidth, then reflectance bandwidth is improved, but the Z-effect increases causing phase change and double diffraction
Solution Approach 1:
The patent optimizes the thickness parameters of individual layers and the overall stack configuration to achieve broad reflectance bandwidth. By carefully controlling layer thicknesses and using materials with appropriate optical constants, the stack maintains high reflectance across a wide wavelength range while limiting the total stack depth to reduce Zeff
Solution Approach 2:
The patent introduces interface layers with specific material properties between the alternating high and low refractive index layers. These interface layers have tailored optical characteristics that locally modify the optical path and reduce the overall Z-effect while maintaining the broadband reflectance property of the multilayer structure
3Manufacturing precision
If interface layers are added to reduce roughness, then surface roughness is improved, but device complexity increases
Solution Approach 1:
The patent introduces interface layers as intermediary structures between the alternating Mo/Si or Ru/Si layers. These interface layers act as mediators that reduce roughness propagation at material boundaries. The interface layers are strategically placed where roughness would otherwise accumulate, serving as buffering zones that maintain overall surface smoothness
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 reduces roughness and enhances EUV reflectance, minimizing the 'Z-effect' and improving lithographic performance by maintaining high reflectivity and bandwidth, thereby addressing the mask 3D effect and other requirements like uniformity and thermal stability.
Implementation Method 1
reflects EUV radiation at unmasked portions by Bragg interference
Implementation Method 2
formed using physical vapor deposition techniques like magnetron sputtering
Implementation Method 3
formed using physical vapor deposition techniques like magnetron sputtering
Data Source
AI summary
Extreme ultraviolet (EUV) mask blanks, production systems therefor, and methods of reducing roughness are disclosed. The EUV mask blanks comprise a multilayer reflective stack on a substrate comprising a plurality of pairs of alternating layers comprising a first layer and a second layer, the first layer including a first element selected from the group consisting of Si, B, Al, Mg, Zr, Ba, Nb, Ti, Gd, Y, and Ca; and the second layer including a second element selected from the group consisting of Ru, Mo, Ta, Sb, Tc, Nb, Ir, Pt, and Pd. Some EUV mask blanks described herein include interface layer between the first layer and the second layer, the interface layer including an interface element selected from the group consisting of Si, B, C, Al, Mo, and Ru.