Pellicle Coating Prevents Membrane Separation
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Solution Overview
Problem
The challenge is to design an effective pellicle for large-size photomasks used in flat-panel display manufacturing, which must protect the photomask surface from contamination while maintaining transparency and structural integrity over a large area.
Innovation Solution
A pellicle assembly comprising a frame member affixed to the photomask substrate, a substantially rigid and transparent pellicle membrane, and a coating on its surfaces to prevent separation in case of breakage. The pellicle membrane is spaced from the substrate by a distance of 3 mm to 20 mm and is made of materials like fused silica, ensuring high transparency and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a pellicle membrane is used to protect the photomask surface from contamination, then the photomask is protected from dust and particles, but the pellicle membrane itself may break and separate, causing artifacts on the glass plate
Solution Approach 1:
The patent applies composite materials by combining the pellicle membrane with a coating layer having different mechanical properties. The coating layer is designed with higher strength and elongation at break than the membrane, creating a composite structure where the coating reinforces the membrane without significantly affecting its optical properties. This composite structure prevents membrane breakage and separation while maintaining contamination protection.
Solution Approach 2:
The patent changes the mechanical parameters of the pellicle system by selecting a coating material with specific properties: strength greater than 50 MPa and elongation at break greater than 5%. These parameter changes ensure the coating can withstand mechanical stresses that would otherwise cause membrane failure, while the coating's optical transparency maintains the system's light transmission characteristics.
2Productivity
If the photomask size is increased to manufacture larger flat-panel displays, then production efficiency and product size are improved, but the risk of contamination and structural failure increases
Solution Approach 1:
The patent applies segmentation by dividing the large photomask into a modular assembly consisting of the photomask substrate, pellicle membrane, frame member, and coating layer. This segmented structure allows each component to be optimized independently - the membrane provides contamination protection, the frame provides structural support, and the coating provides reinforcement - while collectively enabling the manufacturing of large-format photomasks without proportionally increasing failure risk.
3Illumination intensity
If the pellicle membrane is made thinner to maintain transparency, then light transmission is improved, but the membrane becomes more susceptible to breakage
Solution Approach 1:
The patent uses composite materials to resolve this contradiction by combining a thin, highly transparent membrane with a reinforcing coating layer. The membrane can be made very thin (e.g., 2-10 μm) to maximize light transmission, while the coating layer (with strength >50 MPa) provides the necessary mechanical reinforcement. The coating is applied in such a way that it reinforces the membrane without significantly affecting optical properties, achieving both high transparency and high strength.
Data Source
AI summary
A pellicle assembly for large-size photomasks including a frame member configured to be affixed to a large-size photomask substrate, a substantially rigid and transparent pellicle membrane affixed to the frame member so as to protect at least a portion of the large-size photomask substrate from contamination during usage, storage and/or transport, and a coating on at least one of top and bottom surfaces of the pellicle membrane that binds the pellicle membrane to prevent separation of pellicle membrane material in the event of breakage.