Aperiodic Multilayer EUV Mask Reflectivity
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Solution Overview
Problem
Conventional EUV lithography masks with periodic multilayer structures suffer from low reflectivity and diffraction imbalance, which are undesirable in extreme ultraviolet lithography processes.
Innovation Solution
The use of an aperiodic multilayer structure in EUV masks, where the thickness of Mo/Si or Mo/Be film pairs gradually or randomly changes within each stack, improving reflectivity and diffraction balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a periodic multilayer structure is used in EUV masks, then the mask structure is simple and easy to manufacture, but the reflectivity is low and diffraction imbalance occurs
Solution Approach 1:
The patent applies local quality by varying the thickness of individual Mo/Si or Mo/Be film pairs within the multilayer structure. Instead of using uniform thickness throughout, specific film pairs have different thicknesses optimized for their local position in the stack, enabling improved reflectivity and diffraction balance while maintaining manufacturing feasibility through sequential deposition processes
2Ease of manufacture
If a periodic multilayer structure is used in EUV masks, then the mask structure is simple and easy to manufacture, but diffraction imbalance occurs
Solution Approach 1:
The patent implements parameter changes by systematically varying the thickness parameter of Mo/Si or Mo/Be film pairs within the multilayer structure. This controlled variation in thickness parameters optimizes the diffraction characteristics and balance without fundamentally changing the manufacturing process, allowing improved optical performance while maintaining ease of manufacture
3Reliability
If film pair thickness is increased in multilayer structure, then reflectivity improves, but manufacturing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the multilayer structure into multiple discrete film pairs, each with independently optimized thickness. This segmentation allows the total reflectivity to be enhanced through cumulative effect of multiple layers while managing complexity by maintaining a regular repeating pattern that simplifies manufacturing control
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 aperiodic multilayer structure enhances reflectivity and reduces diffraction imbalance, leading to improved lithography performance without requiring additional layers or materials, thus addressing the limitations of conventional periodic structures.
Implementation Method 1
The ML structure is configured to reflect radiation
Data Source
AI summary
The present disclosure provides a photolithography mask. The photolithography mask includes a substrate that contains a low thermal expansion material (LTEM). A multilayer (ML) structure is disposed over the substrate. The ML structure is configured to reflect radiation. The ML structure contains a plurality of interleaving film pairs. Each film pair includes a first film and a second film. The first film and the second film have different material compositions. Each film pair has a respective thickness. For at least a subset of the plurality of the film pairs, the respective thicknesses of the film pairs change randomly along a predefined direction.