Pellicle Frame with Hollow Voids for EUV Lithography
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Solution Overview
Problem
EUV lithographic apparatuses face challenges in using pellicles due to thermal stress and material compatibility issues, which affect the reliability and lifespan of pellicle assemblies, especially when using materials other than silicon for the frame and border.
Innovation Solution
A pellicle frame design with volumes devoid of material, allowing the use of alternative materials like aluminum or aluminum nitride, which reduces thermal stress by matching the coefficient of thermal expansion with the pellicle, and incorporates engagement mechanisms to manage thermal expansion and prevent stress buildup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a solid frame structure is used, then the frame provides sufficient stiffness and strength, but the frame weight increases and thermal stress accumulates due to CTE mismatch
Solution Approach 1:
The frame incorporates hollow chambers or voids within its structure, creating a porous or cellular configuration. This reduces the amount of material required, thereby decreasing weight, while the strategic placement and sizing of these voids maintain the necessary stiffness and strength characteristics of the frame.
Solution Approach 2:
The frame structure is divided into multiple segments or sections with internal voids, separating the material into discrete regions. This segmentation allows the frame to achieve lower weight through reduced material volume while maintaining structural integrity through the distributed arrangement of structural elements.
2Strength
If a solid frame structure is used, then the frame provides sufficient stiffness and strength, but the thermal stress increases due to coefficient of thermal expansion mismatch with the pellicle
Solution Approach 1:
The hollow or porous frame structure introduces air or vacuum spaces that can accommodate thermal expansion differences between the frame and pellicle. This reduces the transmission of thermal stress while maintaining the mechanical stiffness required for supporting the pellicle during lithographic operations.
Solution Approach 2:
By segmenting the frame into sections with internal voids, the structure creates thermal isolation zones that reduce the direct thermal coupling between the frame and pellicle. This segmentation allows differential thermal expansion while preserving the overall structural rigidity needed for precise positioning.
3Weight of moving object
If material is removed from the frame to reduce weight, then the frame weight decreases, but the frame stiffness may be compromised
Solution Approach 1:
The frame employs local quality variations where material is selectively removed from non-critical regions while maintaining full material density in areas requiring high stiffness. The hollow chambers are strategically positioned in regions where material removal has minimal impact on overall structural rigidity, allowing weight reduction without compromising frame strength.
Solution Approach 2:
The frame design incorporates three-dimensional hollow chambers or voids that provide structural efficiency by distributing loads across multiple dimensions. This spatial arrangement allows the frame to achieve high stiffness-to-weight ratio by utilizing the geometric efficiency of hollow structures, where the material is positioned to maximize the moment of inertia and resist bending and torsional loads.
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 design reduces thermal stress during fabrication, increases the natural frequency of the pellicle frame, and allows for the use of different materials while maintaining the required stiffness, leading to improved reliability and lifespan of the pellicle assembly.
Implementation Method 1
reduces thermal stress by matching the coefficient of thermal expansion with the pellicle
Data Source
AI summary
A pellicle frame for supporting a pellicle, the frame having a first surface and a second surface opposite the first surface, and a structure provided between the first and the second surfaces, wherein the first and second surfaces and the structure at least partially define at least one volume therebetween that is devoid of the material that forms the frame.