Yttrium-Based EUV Pellicle Balancing Transmittance and Stability
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Solution Overview
Problem
Current pellicle materials for extreme ultraviolet lithography, such as polycrystalline silicon (p-Si) or SiN, fail to meet the requirements of high transmittance, thermal stability, mechanical stability, and chemical durability in extreme ultraviolet environments, necessitating improved materials to maintain productivity and mask integrity.
Innovation Solution
A pellicle for extreme ultraviolet lithography utilizing a core layer made of yttrium-based materials like Y-B x , Y-Si x , Y 2 O 3 , or YF 3 , with capping layers and optionally an intermediate layer, providing thermal, mechanical, and chemical stability while maintaining high transmittance of 90% or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polycrystalline silicon (p-Si) or SiN materials are used for pellicle, then the pellicle can be manufactured, but the extreme ultraviolet transmittance is below 90% and thermal, mechanical, and chemical stability are insufficient
Solution Approach 1:
The patent uses a composite structure consisting of a SiN-based base layer and a Mo-based upper layer. The SiN layer provides mechanical strength and chemical durability, while the Mo layer enhances thermal stability and maintains high extreme ultraviolet transmittance. This composite material approach allows the pellicle to simultaneously achieve all required properties that single materials cannot provide alone.
2Area of stationary object
If the pellicle size is increased to 110 mm × 144 mm to cover the mask, then mask coverage is improved, but the mechanical stability under physical movement up to 20G deteriorates
Solution Approach 1:
The composite structure of SiN base layer and Mo upper layer provides enhanced mechanical properties. The SiN layer offers high tensile strength and flexibility, while the Mo layer adds rigidity and resistance to deformation. This combination enables the large-area pellicle to maintain mechanical stability under 20G physical movement conditions.
Solution Approach 2:
The pellicle employs different materials with different properties in different layers. The SiN base layer provides flexibility and tensile strength for large area coverage, while the Mo upper layer provides rigidity and thermal stability. This local differentiation of material properties allows the pellicle to simultaneously achieve large area coverage and mechanical stability.
3Productivity
If the pellicle transmittance is increased to 90% or more to minimize light source loss, then productivity is improved, but the thermal stability under 250W thermal load deteriorates
Solution Approach 1:
The Mo-based upper layer has high reflectivity for extreme ultraviolet light but high thermal conductivity, allowing it to reflect light while dissipating heat effectively. The SiN base layer provides thermal insulation and structural support. This composite structure enables the pellicle to maintain 90% or more transmittance while withstanding 250W thermal load.
4Illumination intensity
If thin film materials such as Mo, Ru, and Zr are used to improve transmittance, then extreme ultraviolet transmittance is improved, but the difficulty of manufacturing and maintaining shape increases
Solution Approach 1:
The patent uses Mo as the upper layer material, which can be deposited as a thin film using conventional sputtering techniques. Mo forms a stable crystalline structure that maintains its shape well, unlike some other high-transmittance materials. The SiN base layer provides a stable substrate that supports the Mo film, making the overall structure easier to manufacture and handle.
Data Source
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AI summary
A pellicle for extreme ultraviolet lithography based on yttrium (Y) and used in a lithography process using extreme ultraviolet rays is disclosed. The pellicle includes a pellicle layer including a core layer formed of an yttrium-based material expressed as Y-M (M is one of B, Si, O, and F).