Composite EUV Reflector Stack for Shadowing and Reflectance
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Solution Overview
Problem
Current multilayer reflectors used in EUV lithography suffer from significant 3D effects (shadowing) and reduced reflectance, leading to pattern placement and line width errors, especially when using Ru—Si multilayer reflectors.
Innovation Solution
A reflective member with a multilayer stack comprising layers of Si, Ru, Nb, and Mo, configured to have a refractive index less than or equal to 0.92 and an absorption coefficient less than or equal to 0.015, which reduces shadowing effects and enhances reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Ru—Si multilayer reflectors are used, then shadowing effects are reduced, but reflectance decreases
Solution Approach 1:
The patent uses a composite multilayer structure combining Ru, Si, Nb, and Mo layers to achieve both reduced shadowing effects and maintained reflectance. The specific stacking sequence and thicknesses of these different materials create a composite reflector that leverages the advantages of each material while mitigating their individual disadvantages.
Solution Approach 2:
The patent optimizes parameters such as layer thicknesses, number of layers, and material composition ratios to achieve the desired balance between shadowing reduction and reflectance maintenance. By carefully controlling these parameters, the reflector achieves superior performance compared to conventional single-material structures.
2Ease of operation
If multilayer reflectors are used in series, then EUV radiation can be directed onto the substrate, but the amount of radiation reaching the substrate decreases
Solution Approach 1:
The patent optimizes the parameters of each multilayer reflector (thickness, material composition, number of layers) to maximize reflectance while minimizing shadowing effects. This ensures that each reflector in the sequence contributes maximally to directing radiation while losing minimal intensity, thereby maintaining overall efficiency through the series of reflectors.
3Manufacturing precision
If the absorber layer thickness is increased, then pattern definition is improved, but 3D effects and shadowing increase
Solution Approach 1:
The patent applies different material properties to different regions and layers. The absorber layer is positioned and dimensioned specifically to provide adequate pattern definition while the multilayer stack above it is configured to minimize shadowing effects. Each layer is optimized for its specific function while working cooperatively with adjacent 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 provides superior reflectance and minimizes 3D effects, improving the accuracy and efficiency of EUV lithography by reducing pattern placement and line width errors.
Implementation Method 1
The thickness of each pair is configured such that there is constructive interference between the radiation reflected at each interface
Implementation Method 2
At each interface between layers, a proportion of radiation travelling through the multilayer reflector is reflected
Implementation Method 3
an absorption coefficient that is less than or equal to 0.015
Data Source
AI summary
A reflective member for use in an EUV lithographic apparatus, the reflective member including a multilayer stack which comprises a plurality of layers arranged in pairs, wherein: each pair comprises a first layer and a second layer; the first layer is formed of a material that comprises Si; and the second layer is formed of a material that comprises at least two selected from: Ru, Nb, and/or Mo, and wherein the second layer is configured to have, for radiation with a wavelength of approximately 13.5 nm, a refractive index that is less than or equal to 0.92 and an absorption coefficient that is less than or equal to 0.015.