Chemically Amplified Resist Composition for EUV Mask Blanks
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Solution Overview
Problem
Current chemically amplified resist compositions for mask blanks face challenges in achieving high resolution, reduced line edge roughness (LER), and improved rectangularity due to uncontrolled acid diffusion and sensitivity issues during electron beam (EB) writing, particularly with the use of low-sensitivity resist materials and the influence of backward scattering in EUV lithography.
Innovation Solution
A chemically amplified positive resist composition is developed, featuring a base polymer with phenolic hydroxy group-containing repeat units and carboxy groups protected by acid labile groups, which minimizes acid diffusion and enhances etching resistance, thereby forming patterns with high resolution and reduced LER, suitable for EUV and EB lithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional chemically amplified resist compositions are used for mask blanks, then the resist can be processed, but acid diffusion is uncontrolled leading to poor resolution and high LER
Solution Approach 1:
The patent introduces a base polymer as an intermediary substance that contains both the acid labile group and the acid generator. This polymer acts as a mediator between the acid generator and the resist film, controlling acid diffusion by incorporating the acid within its structure rather than allowing free diffusion through the resist film.
Solution Approach 2:
The patent uses a composite resist film structure combining a base polymer with acid labile groups and an acid generator. This composite material integrates multiple functions: the base polymer provides structural support and controlled acid release, while the acid generator provides the necessary acid for deprotection, achieving both resolution control and etching resistance.
2Object-affected harmful factors
If low-sensitivity resist materials are used for mask blanks, then backward scattering influence is reduced, but sensitivity to EB radiation becomes insufficient
Solution Approach 1:
The patent changes the chemical composition parameters of the resist material by incorporating specific acid labile groups (such as tert-butyl, t-butoxycarbonyl, or acetal groups) and acid generators in controlled amounts. This parameter optimization allows the resist to maintain low sensitivity to backward scattering while achieving adequate EB radiation sensitivity for pattern formation.
3Object-generated harmful factors
If acid generators generating bulky acids are used, then acid diffusion is controlled, but LER reduction is insufficient
Solution Approach 1:
The patent applies local quality by incorporating acid generators specifically within the base polymer structure at strategic locations. The acid generators are positioned to release acid locally where needed for deprotection, rather than diffusing throughout the entire resist film. This localized acid generation reduces LER by preventing unwanted acid diffusion to adjacent regions.
4Strength
If phenolic hydroxy group-containing repeat units are used in the base polymer, then etching resistance is improved, but solubility in organic solvent may be compromised
Solution Approach 1:
The patent uses a composite polymer structure combining phenolic hydroxy group-containing repeat units (for etching resistance) with other repeat units that provide solubility. The base polymer is formulated as a copolymer or mixture where the phenolic units are present in controlled amounts, balanced with hydrophilic or solvent-compatible segments to maintain adequate solubility in organic solvents like PGMEA.
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 suppresses acid diffusion, achieving high-resolution patterns with improved rectangularity and etch resistance, addressing the limitations of existing resist materials in EUV and EB lithography by optimizing the dissolution rate and pattern fidelity.
Implementation Method 1
a base polymer containing a polymer comprising phenolic hydroxy group-containing repeat units and repeat units having a carboxy group protected with an acid labile group in the form of a tertiary hydrocarbyl group having an electron attractive moiety and/or hydroxy moiety-substituted phenyl group bonded to the tertiary carbon
Implementation Method 2
the diffusion of acid that largely affects the resolution of a resist film... The problem of acid diffusion has been widely studied not only in terms of photomask processing, but also in terms of general resist compositions because the acid diffusion has a significant impact on sensitivity and resolution
Implementation Method 3
High-energy radiation such as UV, deep-UV, EUV or EB is used as the energy source for exposure of these resist compositions
Implementation Method 4
chemically amplified positive resist composition... capable of generating an acid upon exposure
Implementation Method 5
For high resolution and profile retention after etching, it is one important performance factor to maintain the profile of a resist film pattern rectangular independent of the type of substrate
Data Source
AI summary
A photomask blank has a resist film which is obtained by coating a chemically amplified positive resist composition comprising a polymer comprising phenolic hydroxy-containing repeat units and repeat units having a carboxy group which is protected with an acid labile group in the form of a tertiary hydrocarbyl group having an electron attractive moiety and/or hydroxy-substituted phenyl moiety bonded to the tertiary carbon, and an organic solvent. The resist film is processed to form a pattern with a high resolution, reduced LER, improved rectangularity, and pattern fidelity.