Onium Salt Acid Diffusion Control in Lithography Resist
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Solution Overview
Problem
Current resist materials for ArF immersion lithography face challenges in achieving high resolution, low mask error factor (MEF), low line width roughness (LWR), and improved depth of focus (DOF), particularly due to acid diffusion issues and defects caused by water droplets during the microfabrication process.
Innovation Solution
A resist composition incorporating a specific onium salt compound with a carboxylic acid sulfonium or iodonium cation, which acts as an acid diffusion controlling agent, is used in conjunction with a polymer and photoacid generator to form a resist pattern with improved resolution, MEF, LWR, and DOF, and is processed using KrF, ArF, EB, or EUV lithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional resist materials are used for ArF immersion lithography, then the lithography process can be performed, but acid diffusion causes degradation of resolution, increased MEF, increased LWR, and reduced DOF
Solution Approach 1:
The patent introduces an onium salt compound as an intermediary substance that mediates between the photoacid generator and the resin. This compound accepts protons from the photoacid generator to form a salt, which then controls acid diffusion by releasing protons gradually. The onium salt acts as a buffer that prevents excessive acid diffusion while maintaining the necessary acid catalysis for pattern formation, thereby resolving the contradiction between achieving high resolution and preventing acid diffusion.
Solution Approach 2:
The patent changes the chemical parameters of the resist system by introducing an onium salt compound with specific structural features (formula 1). This compound has a pKa value that allows it to function as an effective acid diffusion controller. By adjusting the chemical composition and structure of the onium salt, the patent optimizes the acid diffusion characteristics to achieve better resolution and reduced LWR while maintaining DOF.
2Length of moving object
If the pattern size is reduced to achieve finer features, then higher integration density is achieved, but acid diffusion becomes more detrimental and contrast degradation increases
Solution Approach 1:
The onium salt compound serves as a mediator that becomes increasingly important as pattern size decreases. For finer patterns, the intermediary controls the localized acid distribution more effectively, preventing acid from diffusing into adjacent unexposed regions. This maintains the contrast between exposed and unexposed areas even when the distance between features is reduced, enabling higher integration density without sacrificing pattern definition.
3Object-generated harmful factors
If weak acid onium salts are used as diffusion controlling agents, then acid diffusion is suppressed, but resolution, MEF, LWR, and DOF become unsatisfactory in advanced micropatterning
Solution Approach 1:
The patent creates a composite resist system that combines the onium salt compound (formula 1) with specific base resins and photoacid generators. This composite formulation achieves synergistic effects where the onium salt provides acid diffusion control while the other components ensure high resolution and good lithography performance. The composite nature of the resist allows simultaneous optimization of multiple parameters that cannot be achieved with single components.
Solution Approach 2:
The patent optimizes the pKa parameter of the onium salt compound to achieve the right balance between acid diffusion control and lithography performance. By carefully selecting the structural parameters of the onium salt (R1-R5 groups in formula 1), the patent achieves a pKa value that allows sufficient acid diffusion control while maintaining high resolution, low MEF, low LWR, and good DOF in advanced micropatterning applications.
4Manufacturing precision
If ArF immersion lithography is used to achieve higher resolution, then NA can be increased to 1.0 or higher, but defects from water droplets and pattern collapse occur
Solution Approach 1:
The onium salt compound acts as an intermediary that modifies the interaction between the resist and water in immersion lithography. By controlling acid diffusion and reducing the need for excessive water rinsing, the compound minimizes the formation and impact of water droplets on the resist pattern. This intermediary function helps prevent water-related defects while maintaining the high resolution benefits of immersion lithography.
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 resist composition effectively controls acid diffusion, resulting in high-resolution patterns with reduced LWR and improved DOF, enhancing the accuracy of micropatterning and addressing the limitations of existing resist materials.
Implementation Method 1
a photoacid generator... the acid generated therein be limited to exposed regions
Implementation Method 2
the influence of acid diffusion is detrimental to lithography performance
Implementation Method 3
a salt exchange occurs between a weak acid onium salt and a strong acid (sulfonic acid) generated by a PAG upon exposure
Data Source
AI summary
Sulfonium and iodonium salts of nitrogen-containing carboxylic acids are novel. The onium salt functions as an acid diffusion controlling agent in a resist composition, enabling to form a pattern of good profile with high resolution, improved MEF, LWR and DOF.