Boron Nickel Alloy EUV Mask Absorber
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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 boron and nickel, 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
1Object-affected harmful factors
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 parameters of the absorber layer by using a tungsten boride alloy (WBx where 0.7 ≤ x ≤ 1.3) instead of conventional absorber materials. This 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 effective EUV absorption
Solution Approach 2:
The patent employs a composite material approach by creating a tungsten boride alloy absorber layer that combines tungsten and boron elements. This composite material provides superior EUV absorption characteristics per unit thickness compared to conventional absorbers, allowing thinner layers that reduce optical path differences and improve overlay precision
2Manufacturing precision
If the absorber layer thickness is reduced, then 3D mask effects are mitigated, but reflectivity increases
Solution Approach 1:
The patent utilizes parameter changes in the absorber material composition (tungsten boride alloy with controlled boron content) to achieve higher absorption efficiency. This allows the absorber layer to maintain low reflectivity (<2%) even at reduced thickness, because the alloy's intrinsic absorption coefficient is significantly higher than conventional absorber materials
3Manufacturing precision
If a thinner absorber layer is used, then etch selectivity becomes more difficult to maintain, but manufacturing precision improves
Solution Approach 1:
The patent changes the chemical composition parameters of the absorber layer by incorporating boron into tungsten to form tungsten boride alloy. This compositional change provides etch selectivity through the unique chemical properties of the alloy, enabling selective removal of the absorber layer during manufacturing while maintaining thin thickness for improved pattern fidelity
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 boron-nickel alloy absorber layer in EUV mask blanks results in thinner absorber layers with less than 2% reflectivity, reducing 3D mask effects and enhancing the reliability and precision of EUV mask blanks, thereby improving image placement and overlay accuracy.
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
the absorber layer comprising an alloy of boron and nickel... resulting in thinner absorber layers with less than 2% reflectivity
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 boron and nickel.