Topcoat Composition for Immersion Lithography
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Solution Overview
Problem
In immersion lithography, direct contact between the immersion fluid and photoresist layer leads to leaching of photoresist components, causing contamination and affecting the optical properties of the lens, and the use of topcoat layers introduces challenges such as micro-bridging defects and variations in critical dimension and resist profile.
Innovation Solution
Development of new topcoat compositions comprising a first polymer with a reactive nitrogen-containing moiety that produces a basic cleavage product during lithographic processing, along with acid-labile groups and hydrophobic groups, which segregate to form a graded layer reducing photoresist leaching and improving imaging capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a topcoat layer is used to prevent photoresist leaching, then lens contamination is reduced, but micro-bridging defects and critical dimension variation occur
Solution Approach 1:
The topcoat composition uses a copolymer with locally differentiated functional groups: hydrophobic groups (e.g., fluorinated alkyl) at the immersion fluid interface to prevent leaching, and basic nitrogen-containing groups (e.g., carbamate, sulfamate) near the photoresist interface to neutralize acid and prevent micro-bridging. This spatial differentiation of properties resolves the contradiction between contamination prevention and pattern fidelity.
Solution Approach 2:
The invention employs a composite polymer structure combining hydrophobic moieties (for lens protection) and basic nitrogen-containing moieties (for pattern precision) within a single topcoat material. This composite approach enables simultaneous achievement of both contamination prevention and critical dimension control that cannot be achieved with single-function materials.
2Object-affected harmful factors
If topcoat layer thickness is increased to reduce leaching, then photoresist protection improves, but resist profile and imaging quality deteriorate
Solution Approach 1:
The invention changes the chemical parameter of the topcoat by incorporating basic nitrogen-containing groups that can neutralize acid diffusion from the photoresist. This chemical functionality allows the topcoat to effectively prevent leaching at reduced thicknesses, thereby maintaining resist profile quality while improving protection against leaching.
3Object-affected harmful factors
If conventional topcoat materials are used, then lens contamination is prevented, but imaging resolution and process window are limited
Solution Approach 1:
The copolymer structure places hydrophobic groups preferentially at the immersion fluid interface to prevent contamination, while positioning basic nitrogen-containing groups near the photoresist interface to improve imaging resolution by neutralizing acid. This local quality differentiation enables simultaneous achievement of both contamination prevention and enhanced imaging capabilities.
Solution Approach 2:
The topcoat acts as an intermediary layer with dual functionality: its hydrophobic portions mediate between the immersion fluid and photoresist to prevent leaching, while its basic nitrogen-containing portions mediate acid neutralization to improve imaging resolution and expand the process window.
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 topcoat compositions effectively reduce photoresist leaching into the immersion fluid, enhance imaging resolution, and improve pattern formation by creating a tailored interface with the immersion fluid and photoresist, thereby increasing the process window and device yield.
Implementation Method 1
a basic moiety (e.g. moiety with one or more nitrogen atoms) is cleaved (i.e. covalent bond breakage) from the first polymer through reaction of an acid-labile group in the optional presence of an acid generator and optional thermal treatment
Implementation Method 2
the use of self-segregating topcoat compositions to form a graded topcoat layer has been proposed
Data Source
AI summary
Topcoat compositions are provided that are suitably applied above a photoresist composition. Preferred topcoat compositions comprise a first polymer comprising first units comprising a reactive nitrogen-containing moiety spaced from the polymer backbone, wherein the nitrogen-containing moiety produces a basic cleavage product during lithographic processing of the photoresist composition.