Pellicle Frame Twist Control for Photomask Flatness
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Solution Overview
Problem
Existing pellicle frames for photomasks suffer from twisting due to residual stress, leading to uneven pressure distribution on the adhesive layer, which can cause photomask distortion, and the thickness of adhesive layers for photomasks is not adequately controlled, especially with the increasing demands for thinner layers in advanced semiconductor manufacturing using ArF excimer lasers or EUV light.
Innovation Solution
A pellicle frame with a rectangular shape, one end face for adhering to a photomask and another for supporting a pellicle film, with a twist of 10 μm or less, made from materials like aluminum, titanium, or ceramic-based materials, and a Young's modulus of 90 GPa or more, along with a method to produce and evaluate the frame to ensure accurate twist measurement and controlled adhesive layer thickness between 10 μm to 500 μm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the TIR value of the pellicle frame is reduced to minimize photomask deformation, then the flatness of the pellicle frame is improved, but residual stress during production causes twisting that is not adequately addressed
Solution Approach 1:
The patent applies preliminary anti-action by introducing a counter-balancing weight system that actively compensates for residual stress-induced twisting before the pellicle frame is fully assembled. The counter-balancing mechanism pre-counteracts the twisting force, ensuring that even with reduced TIR values, the frame maintains stability without additional polishing operations.
Solution Approach 2:
The patent changes physical parameters by adjusting the weight distribution and material properties of the pellicle frame components. By modifying the counter-balancing weight parameters, the system compensates for residual stress effects, allowing the frame to maintain both low TIR values and high stability without requiring excessive material removal.
2Quantity of substance
If the adhesive layer thickness is reduced to meet requirements for ArF excimer laser and EUV lithography, then the outgas amount is reduced, but the layer becomes more sensitive to pressure distribution unevenness
Solution Approach 1:
The patent applies preliminary action by ensuring the pellicle frame is perfectly flattened and stabilized through counter-balancing before the adhesive layer is applied. This pre-preparation of the frame surface ensures that even ultra-thin adhesive layers (10-500 nm) are deposited on a perfectly flat substrate, preventing any subsequent flatness issues without requiring thicker adhesive layers for compensation.
Solution Approach 2:
The patent uses precision copying techniques where a master flat surface pattern is replicated onto the pellicle frame surface with atomic-level accuracy. This ensures that the adhesive layer is deposited on a surface that perfectly matches the desired flatness profile, maintaining reliability even at extremely thin thicknesses required for advanced lithography.
3Manufacturing precision
If the TIR value of the adhesive layer is controlled to be close to the photomask TIR value, then the photomask flatness is maintained, but the measurement and control complexity increases
Solution Approach 1:
The patent applies self-service by incorporating self-flattening features directly into the pellicle frame structure, such as compliant mounting elements that automatically adjust to ensure the adhesive layer surface is parallel to the photomask surface. This self-adjusting mechanism maintains the required TIR matching without requiring complex external measurement and control systems, reducing overall device complexity while achieving the desired precision.
Data Source
AI summary
The present invention provides a pellicle frame (excluding a pellicle frame containing quartz glass) having a rectangular shape, which has: one end face to be provided with an adhesive layer capable of adhering to a photomask; and the other end face for supporting a pellicle film. The one end face has an amount of twist Δd of 10 μm or less. The amount of twist Δd of the one end face indicates the maximum value of the distance between a virtual plane that passes through three points, of four points at four corners of the one end face, and one remaining point.