EUV Mask Blank Trilayer Stack Minimizing Z-Effect
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Solution Overview
Problem
Extreme ultraviolet lithography systems face challenges with the Mask 3D (M3D) effect due to the Z-effect, which causes non-telecentricity, edge placement errors, and contrast loss, especially in high-NA EUV scanners, requiring EUV mask blanks with low Z-effect and high reflectance over a large bandwidth of reflection angles.
Innovation Solution
The development of an EUV mask blank with a multilayer reflective stack comprising a trilayer film structure, including specific elements like silicon, ruthenium, and molybdenum, and interface layers such as silicon nitride, to minimize the Z-effect and enhance reflectance, thereby reducing the M3D effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional multilayer reflective stack is used, then the structure is simple and easy to manufacture, but the Z-effect is high causing M3D effects such as non-telecentricity, edge placement error, and contrast loss
Solution Approach 1:
The reflective stack is segmented into multiple functional layers including Mo/Si bilayers for reflection, Ru/Pt/Ir/Au layers for absorption and protection, and Mo/Nb/W/Mn/Ti layers for structural stability. Each layer serves a specific function to collectively reduce the Z-effect while maintaining manufacturability
Solution Approach 2:
The patent employs composite material structures combining different metal elements (Mo, Si, Ru, Pt, Ir, Au, Nb, W, Mn, Ti) with specific thickness ratios to achieve optimized optical properties. The composite structure creates controlled electron density gradients that minimize the Z-effect while preserving reflectance characteristics
2Illumination intensity
If the multilayer stack is optimized for high reflectance, then reflectance improves but the bandwidth of reflection angle becomes limited
Solution Approach 1:
The patent systematically varies critical parameters including layer thickness (controlling optical path differences), material composition (adjusting electron density and atomic number), and layer sequence to broaden the reflection bandwidth. By tuning these parameters, the stack achieves high reflectance across a wider angular range suitable for high-NA EUV scanners
3Manufacturing precision
If the multilayer stack uses more layers to reduce Z-effect, then M3D effects are minimized but manufacturing complexity and stress control become more difficult
Solution Approach 1:
The patent implements local quality optimization by assigning specific materials to specific positions within the stack based on their inherent properties. Mo/Si layers provide reflection with controlled stress, Ru/Pt/Ir/Au layers provide absorption with minimal stress, and Mo/Nb/W/Mn/Ti layers provide structural support. This localized material assignment achieves precision while managing overall stress
Solution Approach 2:
The patent adjusts layer thickness parameters and material composition ratios to balance stress accumulation across the multilayer structure. By controlling the thickness of each layer and selecting materials with complementary stress characteristics, the stack achieves low net stress that facilitates manufacturing while maintaining the precision needed to minimize M3D effects
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 proposed solution achieves low Z-effect and high reflectance over a broad bandwidth, minimizing M3D effects and improving lithography yield, especially in high-NA EUV scanners, leading to increased throughput and reliability.
Implementation Method 1
reflective multilayer stack 12 on a substrate 14, which reflects EUV radiation at unmasked portions by Bragg interference
Data Source
AI summary
Extreme ultraviolet (EUV) mask blanks, methods of forming EUV mask blanks and production systems therefor are disclosed. The EUV mask blanks comprise a multilayer reflective stack on a substrate. The multilayer reflective stack comprises a trilayer film including a first film, a second film, and a third film. Some EUV mask blanks include an interface layer on one or more of the first film, the second film and the third film. EUV mask blanks described herein have low Zeff and high reflectance over large bandwidth of reflection angle, thereby minimizing the M3D effect, especially for high-NA EUV scanners.