EUV Mask Pellicle Stack for High Transmittance and Thermal Stability
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Solution Overview
Problem
Existing pellicles for EUV lithography masks lack high EUV transmittance, low reflectance, and sufficient mechanical and thermal stability, leading to premature degradation and frequent replacement.
Innovation Solution
A pellicle with a stacked structure of dielectric, semiconductor, and metallic materials, including a core layer, capping layers, an anti-reflection layer, a barrier layer, and a heat emissive layer, optimized to enhance EUV transmittance, reduce reflectance, and improve mechanical strength and thermal properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a pellicle is designed for EUV lithography, then high EUV transmittance is required, but high mechanical strength and low thermal expansion are also needed, creating a material selection conflict
Solution Approach 1:
The pellicle employs a composite structure consisting of a silicon carbide (SiC) core layer providing mechanical strength and thermal stability, combined with molybdenum (Mo) capping layers that provide EUV reflectance control. This multi-material composition allows simultaneous optimization of transmittance, strength, and thermal properties that cannot be achieved with a single material.
Solution Approach 2:
The pellicle is divided into functionally distinct layers: a SiC core layer for mechanical support and thermal stability, and Mo capping layers for EUV optical performance. Each layer is optimized for its specific function, allowing the overall structure to meet multiple conflicting requirements that would be impossible to satisfy with a homogeneous material.
2Illumination intensity
If the pellicle operates under EUV exposure, then high transmittance is needed, but thermal degradation and material diffusion occur prematurely
Solution Approach 1:
The silicon carbide core layer is specifically selected for its low thermal expansion coefficient, which maintains dimensional stability under EUV-induced thermal loading. This prevents thermal degradation and maintains the pellicle's optical and mechanical properties during prolonged exposure to EUV radiation.
Solution Approach 2:
The molybdenum capping layers are applied in advance to prevent material diffusion before it occurs. The Mo layers act as diffusion barriers that preemptively protect the SiC core layer from thermal degradation and material intermixing during EUV exposure, extending the pellicle's operational life.
3Illumination intensity
If molybdenum layers are used for EUV reflectance control, then reflectance is reduced, but Mo diffusion degrades the pellicle performance
Solution Approach 1:
The silicon carbide core layer serves as an intermediary barrier between the molybdenum capping layers, preventing direct contact and diffusion between Mo atoms. This intermediate SiC layer maintains the integrity of the Mo reflectance control layers while protecting against material degradation, allowing both functions to coexist without interference.
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 pellicle achieves EUV transmittance above 85%, reflectance below 0.25%, and extends the life of the pellicle to 80,000 wafers by preventing Mo diffusion and enhancing thermal conductivity.
Implementation Method 1
a barrier layer between the anti-reflection layer and the heat emissive layer to prevent Mo diffusion from the anti-reflection layer to the heat emissive layer
Implementation Method 2
extends the life of the pellicle to 80,000 wafers by preventing Mo diffusion and enhancing thermal conductivity
Implementation Method 3
an anti-reflection layer disposed on the first capping layer
Data Source
AI summary
A pellicle for a reflective photo mask includes a frame, a core layer having a front surface and a rear surface, and disposed over the frame, a first capping layer disposed on the front surface of the core layer, an anti-reflection layer disposed on the first capping layer, a barrier layer disposed on the anti-reflection layer, and a heat emissive layer disposed on the barrier layer.