Negative Resist Composition for Acid Diffusion Control in ArF Lithography
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Solution Overview
Problem
Existing chemically amplified resist compositions face challenges in achieving high resolution, reduced line edge roughness (LER), and forming patterns with high fidelity, particularly in the context of ArF excimer laser lithography, due to uncontrolled acid diffusion and inadequate profile retention.
Innovation Solution
Incorporation of an onium salt consisting of a sulfonic acid anion with an aromatic sulfonic acid structure and a triarylsulfonium cation containing iodine and fluorine as an acid generator, along with a specific base polymer, to control acid diffusion and enhance pattern formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional acid generators are used in chemically amplified resist compositions, then the resist can be exposed and developed, but acid diffusion is uncontrolled leading to poor resolution and high line edge roughness
Solution Approach 1:
The patent introduces a quencher compound as an intermediary substance that mediates between the acid generator and the polymer. The quencher accepts protons from the acid generated during exposure, thereby controlling acid diffusion and preventing excessive spread of the acid catalyst. This intermediary action allows the acid to remain localized at the exposure site, improving resolution while still enabling the desired chemical amplification and crosslinking reactions.
Solution Approach 2:
The patent modifies the chemical parameters of the acid generator system by selecting specific compounds with controlled acid strength and diffusion characteristics. The acid generator is chosen to produce acid with pKa values in a specific range (3-7), and the quencher is selected to have complementary basicity. This parameter control ensures that acid diffusion is limited to a controlled extent, achieving high resolution patterns while maintaining adequate reaction efficiency.
2Strength
If phenolic units are used in negative resist compositions for KrF lithography, then etching resistance is improved, but the composition cannot be used for ArF lithography due to strong absorption at 200 nm
Solution Approach 1:
The patent applies local quality by incorporating phenolic units specifically in the polymer component where etching resistance is needed, while the acid generator and quencher components are selected to be transparent at the ArF wavelength (193 nm). The phenolic units provide localized etching resistance at the resist-substrate interface without affecting the overall light transmission properties of the resist composition at the exposure wavelength.
Solution Approach 2:
The patent creates a composite resist composition combining multiple components with complementary properties: a polymer containing phenolic units for etching resistance, a specifically selected acid generator for controlled acid generation, and a quencher for acid diffusion control. This composite formulation achieves both etching resistance and ArF lithography compatibility by distributing different functions across different components.
3Productivity
If acid diffusion is increased to improve pattern formation, then crosslinking efficiency increases, but resolution deteriorates and line edge roughness increases
Solution Approach 1:
The quencher acts as a spatial mediator that allows acid diffusion only to the extent needed for adequate crosslinking while blocking further diffusion. The quencher is distributed throughout the resist and accepts protons at a controlled rate, ensuring that crosslinking occurs efficiently within the exposed regions without acid spreading into unexposed regions. This mediates between the need for sufficient acid diffusion for crosslinking and the need to limit diffusion for resolution.
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 achieves improved resolution, reduced LER, and forms patterns with high fidelity, including dot patterns with rectangular profiles, by effectively controlling acid diffusion and adhesion to the substrate.
Implementation Method 1
an acid generator which is decomposed to generate an acid upon exposure to light
Implementation Method 2
a crosslinker which causes the polymer to crosslink in the presence of the acid serving as a catalyst
Implementation Method 3
Most often a quencher is added for controlling the diffusion of the acid generated upon light exposure
Data Source
AI summary
An onium salt consisting of a sulfonic acid anion having an aromatic sulfonic acid structure substituted with an aromatic ring-containing hydrocarbyl group and a triarylsulfonium cation containing iodine and fluorine generates an acid having a moderate acidity and limited diffusion. A chemically amplified negative resist composition comprising the onium salt as an acid generator and a polymer is processed by lithography to form a pattern with reduced LER or a dot pattern of rectangular profile.