EUV Mask Blank Alloy Absorber for Overlay Error Reduction
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Solution Overview
Problem
Extreme ultraviolet lithography systems face challenges in reducing overlay errors and three-dimensional mask effects due to the properties of reflective multilayer coatings and absorber layers in EUV mask blanks, which require more precise flatness specifications and tailored absorber layer properties for improved performance.
Innovation Solution
The development of an EUV mask blank with a multilayer stack of reflective layers and a capping layer, featuring an absorber layer composed of an alloy of at least two different absorber materials, which are deposited using physical vapor deposition techniques to enhance reflectivity and etching properties, thereby reducing overlay errors and 3D mask effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If reflective multilayer coatings are used in EUV mask blanks, then reflectivity is improved, but overlay errors and 3D mask effects increase due to flatness specification requirements
Solution Approach 1:
The patent changes the material composition parameter of the absorber layer by using alloys with specific atomic numbers (e.g., bismuth with Z=83, thallium with Z=81, lead with Z=82) to optimize EUV absorption characteristics. This parameter change allows for reduced absorber layer thickness while maintaining absorption efficiency, thereby reducing 3D mask effects and overlay errors while preserving the reflectivity provided by the multilayer coatings.
Solution Approach 2:
The patent employs composite material structures including: (1) multilayer reflective coatings composed of alternating high-Z and low-Z materials (e.g., molybdenum-silicon, germanium-silicon); (2) alloy absorber layers combining multiple elements with different atomic numbers; and (3) capping layers with specific mechanical properties. These composite structures enable simultaneous optimization of reflectivity, absorption, and flatness control to reduce overlay errors.
2Loss of energy
If absorber layer thickness is increased to improve absorption, then absorption efficiency is improved, but 3D mask effects and overlay errors worsen
Solution Approach 1:
The patent utilizes parameter changes by selecting absorber materials with high atomic numbers (bismuth Z=83, thallium Z=81, lead Z=82) that have superior EUV absorption coefficients. This allows the absorber layer thickness to be reduced to 1-10 nm while maintaining high absorption efficiency, thereby minimizing 3D mask effects and overlay errors that would otherwise result from thicker layers.
Solution Approach 2:
The patent applies local quality by creating spatially varying absorber layer structures, including gradient thickness profiles and localized material composition variations. This enables optimized absorption in critical pattern regions while maintaining reduced overall thickness to minimize 3D mask effects, addressing different functional requirements within the same mask structure.
3Ease of manufacture
If conventional absorber materials are used, then ease of manufacture is improved, but etching reliability and absorber layer property tailoring are limited
Solution Approach 1:
The patent employs alloy composite materials combining elements such as bismuth, thallium, lead, and other high-Z elements in specific ratios. These alloys provide both improved etching reliability through controlled chemical reactivity and enhanced absorber properties. The composite nature allows for tailored etch rates and improved pattern fidelity while maintaining manufacturability through established deposition techniques.
Solution Approach 2:
The patent changes the material composition parameters by using alloys with specific atomic number combinations and ratios (e.g., Bi-Tl-Pb systems) to achieve desired etching characteristics. By adjusting the compositional parameters, the etch selectivity and reliability are improved while maintaining compatibility with existing manufacturing processes, thus balancing ease of manufacture with enhanced reliability.
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 solution improves the reflectivity and etching reliability of EUV mask blanks, enabling more precise image placement and reduced overlay errors, while allowing for tailored absorber layer properties to optimize performance in extreme ultraviolet lithography systems.
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
Implementation Method 3
which are deposited using physical vapor deposition techniques
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 an absorber layer on the capping layer, the absorber layer made from an alloy of at least two absorber materials.