Pellicle Frame Composite Structure for Flatness
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Solution Overview
Problem
Conventional lithographic pellicle frames made of aluminum alloy have poor flatness, leading to deformation and focal shifts during photomask patterning, especially when affixed with high force, causing irregularities in pattern shape and reducing manufacturing yield.
Innovation Solution
A pellicle frame with a layered structure having different elastic moduli in perpendicular and parallel directions is used, where layers with a small elastic modulus (e.g., 10 GPa) are combined with those having a large elastic modulus (e.g., 50 GPa or greater), with the latter forming the outermost layers to reduce distortion and deformation during handling and affixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a pellicle frame made of aluminum alloy is used, then the frame has sufficient strength, but the flatness is poor leading to deformation during affixation
Solution Approach 1:
The pellicle frame is constructed as a composite structure with an inner frame made of resin material and an outer frame made of aluminum alloy material. The resin inner frame provides excellent flatness (0.1 μm or less) to prevent photomask deformation, while the aluminum alloy outer frame provides sufficient mechanical strength. This composite approach resolves the contradiction between strength and flatness by combining materials with complementary properties.
2Strength
If high affixation force is applied to adhere the pellicle membrane, then the bonding strength is improved, but the pellicle frame deforms causing focal shifts
Solution Approach 1:
The frame is designed with different material properties at different locations: the inner frame region (contacting the photomask) is made of soft resin material with high flatness to prevent deformation under load, while the outer frame is made of hard aluminum alloy for structural strength. This local differentiation allows high affixation force to be applied without causing focal shifts, as the critical inner region maintains its flatness even under load.
3Manufacturing precision
If the pellicle frame is made softer to improve flatness, then deformation is reduced, but the frame strength decreases
Solution Approach 1:
The frame uses a composite structure where the inner frame is made of soft resin material (elastic modulus 1-10 GPa) providing excellent flatness, while the outer frame is made of hard aluminum alloy (elastic modulus 60-80 GPa) providing structural strength. This composite design allows the frame to simultaneously achieve both high flatness and sufficient strength, resolving the contradiction between these two properties.
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
This configuration minimizes pellicle frame distortions and photomask deformation, maintaining the flatness of the photomask and preventing focal shifts, thereby enhancing the quality and yield of semiconductor devices.
Implementation Method 1
the frame has a layered structure having different elastic moduli in perpendicular and parallel directions
Data Source
AI summary
The present invention is directed to reduce pellicle frame distortions due to the tension of a pellicle film and caused during handling, thereby providing an excellent pellicle frame capable of reducing the distortion of a photomask due to a pellicle affixation. In the pellicle frame of the present invention, the frame consists of a plurality of layers of which at least one layer has a different elastic modulus. It is preferable to: make the pellicle frame compositely of a layer having an elastic modulus of 10 GPa or smaller and of a layer having an elastic modulus of 50 GPa or greater; join these layers of the pellicle frame in a direction perpendicular to the pellicle film face; laminate such that layers having a large elastic modulus form the outermost layer; or reverse this lamination structure.