Bismuth-Iron Alloy EUV Mask Absorber for 3D Effect Mitigation
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Solution Overview
Problem
Extreme ultraviolet lithography systems face challenges in achieving precise flatness specifications and low tolerance to defects in EUV mask blanks due to the thick absorbing layers, which also cause 3D mask effects and image placement errors.
Innovation Solution
A method of manufacturing EUV mask blanks using a multilayer stack with a capping layer and an absorber layer comprising an alloy of bismuth and iron, which reduces the absorber thickness to mitigate 3D mask effects and improve reflectivity, while maintaining high reflectivity and etch selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick absorbing layer is used in EUV mask blanks, then light absorption is improved, but 3D mask effects and image placement errors increase
Solution Approach 1:
The patent changes the material composition parameter of the absorber layer by using a bismuth-iron alloy instead of traditional single-element absorbers. This material parameter change enables achieving the required light absorption with a thinner layer thickness, thereby reducing 3D mask effects and improving image placement accuracy while maintaining reliable light absorption
Solution Approach 2:
The patent employs a composite material approach by creating an alloy of bismuth and iron for the absorber layer. This composite material combines the high absorption coefficient of bismuth with the etch selectivity and structural stability of iron, enabling thin-layer absorption that mitigates 3D mask effects while maintaining functional performance
2Reliability
If a thick absorbing layer is used in EUV mask blanks, then light absorption is improved, but reflectivity increases
Solution Approach 1:
The patent modifies the material composition parameter to use bismuth-iron alloy, which achieves sufficient light absorption in a thinner layer. This parameter change reduces the overall reflectivity of the mask blank by minimizing the thickness of the absorber layer while maintaining adequate absorption through the alloy's superior absorption coefficient
3Ease of manufacture
If traditional absorber materials are used, then etch selectivity is maintained, but 3D mask effects are exacerbated
Solution Approach 1:
The patent uses a composite bismuth-iron alloy material that combines the etch selectivity properties of iron with the high absorption coefficient of bismuth. This composite enables achieving thin-layer absorption that reduces 3D mask effects while maintaining the etch selectivity needed for manufacturing
Solution Approach 2:
The patent optimizes the local material properties by selecting specific alloy compositions of bismuth and iron. This local quality optimization ensures that the absorber layer has both the etch selectivity required for manufacturing and the absorption characteristics that minimize 3D mask effects when used in thin 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 use of a bismuth-iron alloy absorber layer in EUV mask blanks enhances the reliability and reduces 3D mask effects, achieving improved image placement and overlay accuracy with reduced reflectivity and increased etch selectivity, thus addressing the challenges of defect tolerance and precision in EUV lithography.
Implementation Method 1
a reflective multilayer stack 12 on a substrate 14, which reflects EUV radiation at unmasked portions by Bragg interference
Implementation Method 2
extreme ultraviolet light, which is generally in the 5 to 100 nanometer wavelength range, is strongly absorbed in virtually all materials
Data Source
AI summary
Extreme ultraviolet (EUV) mask blanks, methods for their manufacture and production systems therefor are disclosed. The EUV mask blanks comprise a substrate; a multilayer stack of reflective layers on the substrate; a capping layer on the multilayer stack of reflecting layers; and an absorber layer on the capping layer, the absorber layer made from bismuth and iron.