Lithographic Pellicle Flat Adhesive Layer
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Solution Overview
Problem
Conventional lithographic pellicle frames cause deformation and flatness changes in photomasks due to their unevenness and the stress distribution from adhesive layers, which affects the precision of semiconductor device patterning, especially with the increasing demand for shorter wavelengths and finer resolutions.
Innovation Solution
A pellicle frame with an adhesive layer having a flat surface flatness of 15 μm or less is used, which is hardened in a configuration that matches the photomask's flatness, minimizing deformation and stress during affixation, thereby controlling the photomask's flatness change.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pellicle frame with uneven adhesive layer is used to affix the pellicle to the photomask, then the pellicle can be attached for dust protection, but the photomask undergoes deformation and flatness change
Solution Approach 1:
The adhesive layer is prepared in advance with a controlled thickness and flat surface (flatness of 15 μm or less) before the pellicle is affixed to the photomask. This preliminary preparation ensures that when the pellicle is attached, the stress is uniformly distributed, preventing deformation of the photomask while maintaining dust protection functionality
Solution Approach 2:
The invention changes the key parameter of the adhesive layer from an uncontrolled thickness to a controlled thickness with a flatness of 15 μm or less. This parameter change ensures uniform stress distribution during pellicle affixation, preventing photomask deformation while maintaining the dust protection function
2Strength
If pressure is applied to affix the pellicle to the photomask, then the pellicle adheres securely, but stress concentrates on convex portions of the adhesive layer causing photomask deformation
Solution Approach 1:
The invention changes the surface flatness parameter of the adhesive layer to 15 μm or less, which transforms the stress distribution during pressurization from concentrated (on convex portions) to uniform across the entire adhesive layer. This maintains strong adhesion while preventing pattern position deformation
Solution Approach 2:
The flat surface of the adhesive layer preliminarily counteracts the concentrating effect of pressure by providing a uniformly distributed contact surface. This preliminary anti-action prevents the concentration of stress on specific convex portions that would otherwise cause photomask deformation and pattern position shifts
Data Source
AI summary
The present invention is directed to provide a pellicle that can control the deformation of the photomask to a minimum without particular consideration of the flatness of a pellicle frame even in the case where a pellicle is affixed to a photomask for lithography. In the pellicle of the present invention, the pellicle comprises a photomask adhesive for affixing the pellicle to a photomask, the photomask adhesive having a flat surface, wherein the flatness of the surface is no more than 15 μm.