Pellicle Adhesive Layer High-Temperature Peel Strength
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Solution Overview
Problem
Conventional pellicles used in photolithography, especially with EUV light, face challenges in maintaining peel strength at high temperatures, leading to potential peeling off from photomasks, and there is a need for improved reliability across various exposure light sources.
Innovation Solution
A pellicle design with an adhesive layer that meets specific peel strength criteria, including a glass transition temperature range and composition of alkyl (meth) acrylate copolymers with functional groups, to ensure strong adhesion and resistance to high-temperature environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a flexible adhesive layer is used to reduce strain on photomask during attachment, then ease of attachment is improved, but peel strength is reduced when exposed to high-temperature environment
Solution Approach 1:
The adhesive layer's glass transition temperature (Tg) is specifically controlled to be -50°C to 0°C to optimize its mechanical properties. This parameter change ensures the adhesive remains flexible enough for easy attachment while maintaining sufficient peel strength even at elevated temperatures during EUV exposure, resolving the contradiction between ease of attachment and high-temperature reliability
Solution Approach 2:
The adhesive layer is formulated as a copolymer comprising alkyl (meth)acrylate and hydroxyethyl (meth)acrylate in specific ratios (80:20 to 95:5 by mass). This composite material structure combines the flexibility needed for strain reduction with the thermal stability required for high-temperature performance, simultaneously achieving ease of attachment and peel strength retention
2Ease of manufacture
If conventional adhesive materials are used, then ease of manufacture is maintained, but peel strength is insufficient at high temperatures causing pellicle to peel off
Solution Approach 1:
The glass transition temperature (Tg) is precisely controlled within -50°C to 0°C through formulation adjustments. This parameter optimization ensures the adhesive maintains adequate flexibility for manufacturing while achieving sufficient peel strength at high temperatures, preventing pellicle peeling during EUV exposure
Solution Approach 2:
A copolymer adhesive system combining alkyl (meth)acrylate (80-95 parts) with hydroxyethyl (meth)acrylate (5-20 parts) is used. This composite formulation provides both ease of manufacture and high-temperature reliability by balancing flexibility and thermal stability through controlled monomer ratios
3Reliability
If adhesive layer is made stronger to prevent peeling at high temperature, then reliability is improved, but adhesive residue increases
Solution Approach 1:
The glass transition temperature (Tg) is optimized to -50°C to 0°C, which provides the right balance for adhesion strength while enabling clean peeling. This parameter control prevents both peeling during exposure and excessive adhesive residue, achieving reliability without harmful effects
Solution Approach 2:
The copolymer formulation with alkyl (meth)acrylate and hydroxyethyl (meth)acrylate in controlled ratios creates an adhesive that bonds strongly during EUV exposure but peels cleanly afterward. The specific monomer combination provides appropriate cohesive strength while minimizing adhesive residue, resolving the contradiction between reliability and harmful effects
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 pellicle effectively maintains adhesion to photomasks even at high temperatures (up to 60°C), preventing peeling and reducing adhesive residue, while ensuring reliable performance with both EUV and ArF light exposure.
Implementation Method 1
The adhesive layer of the pellicle is likely to absorb scattered EUV light
Implementation Method 2
EUV light is readily absorbed by the photomask. Thus, during exposure with EUV light, the temperature of the photomask is likely to be high
Implementation Method 3
The heat of the photomask is conducted to the pellicle
Implementation Method 4
an adhesive layer provided at another end surface of the pellicle frame
Data Source
AI summary
The present disclosure provides a pellicle that includes: a pellicle frame; a pellicle film supported at one end surface of the pellicle frame; and an adhesive layer provided at another end surface of the pellicle frame, and satisfies the following Equation (1): [A60° C.]≥4.0 gf/mm2 (1). In Equation (1), [A60° C.] represents a first peel strength when the pellicle is used in a test laminated body. The test laminated body is obtained by placing the pellicle on a quartz glass substrate such that the adhesive layer is in contact with a surface of the quartz glass substrate, and maintaining a load on the pellicle under prescribed conditions. The first peel strength represents a load per unit adhesion area, which load is required for peeling the pellicle included in the test laminated body from the quartz glass substrate using a standard universal tester under prescribed conditions.