Onium Salt Photoacid Generator for ArF Resist
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Solution Overview
Problem
Current resist compositions for ArF lithography face challenges in achieving high resolution and sensitivity while effectively controlling acid diffusion, which leads to degraded contrast and lithographic performance.
Innovation Solution
The development of an onium salt with a ring-condensed structure and an alkanesulfonic acid structure containing a trifluoromethyl group, which enhances solvent solubility, sensitivity, and contrast, and is used as a photoacid generator in a chemically amplified resist composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If perfluorooctanesulfonic acid (PFOS) is used as the photoacid generator, then high sensitivity is achieved, but environmental safety deteriorates due to non-degradability and toxicity
Solution Approach 1:
The patent changes the chemical parameters of the photoacid generator by using perfluorobutanesulfonic acid instead of perfluorooctanesulfonic acid, reducing the carbon chain length from 8 to 4. This parameter change maintains the high sensitivity required for ArF lithography while improving environmental safety and degradability, as the shorter chain makes the molecule more susceptible to environmental degradation.
Solution Approach 2:
The patent adopts a photoacid generator with a shorter carbon chain (perfluorobutanesulfonic acid) that is more environmentally friendly and degradable, replacing the persistent PFOS. This aligns with the principle of using shorter-living, more environmentally benign substances that can be degraded naturally, reducing long-term environmental harm while maintaining functional performance.
2Object-affected harmful factors
If perfluorobutanesulfonic acid is used as the photoacid generator, then environmental safety is improved, but acid diffusion increases leading to degraded resolution
Solution Approach 1:
The patent creates a composite photoacid generator structure combining perfluorobutanesulfonic acid with specific cationic groups (such as triphenylsulfonium or iodonium). This composite approach allows the anion to provide environmental safety while the cationic component contributes to controlled acid generation and reduced diffusion, achieving both environmental and performance goals simultaneously.
Solution Approach 2:
The patent introduces bulky substituent groups (such as triphenylsulfonium cation or iodonium cation with large molecular structures) to localise the photoacid generator. These bulky groups create steric hindrance that restricts the diffusion of the generated acid, thereby maintaining high resolution while using the environmentally friendly perfluorobutanesulfonic acid anion.
3Ease of manufacture
If partially fluorinated alkanesulfonic acid with 2-4 fluorine atoms is used, then synthesis cost is reduced, but solvent solubility deteriorates
Solution Approach 1:
The patent merges the perfluorobutanesulfonic acid anion (providing environmental safety and reasonable cost) with bulky onium cations (providing solvent solubility). This combination allows the system to achieve both cost-effectiveness and adequate solvent solubility, as the cationic component compensates for the reduced fluorine content in the anion.
Solution Approach 2:
The patent develops a composite photoacid generator where the anion is perfluorobutanesulfonic acid (cost-effective and environmentally friendly) and the cation is a bulky onium salt. This composite structure ensures sufficient solvent solubility despite the reduced number of fluorine atoms, by relying on the solubility characteristics of the cationic component.
4Manufacturing precision
If acid diffusion is reduced by lowering bake temperature, then contrast is improved, but sensitivity deteriorates
Solution Approach 1:
The patent changes the chemical parameters of the photoacid generator to have a shorter carbon chain (perfluorobutanesulfonic acid) which inherently reduces acid diffusion. This parameter change allows the system to achieve high contrast at standard bake temperatures without sacrificing sensitivity, as the reduced diffusion is achieved through molecular structure rather than temperature reduction.
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 proposed onium salt-based resist composition exhibits improved lithographic performances, including high sensitivity, excellent contrast, and reduced acid diffusion, thereby preventing pattern collapse during fine pattern formation.
Implementation Method 1
a photoacid generator capable of generating perfluorobutanesulfonic acid by exposure to light
Data Source
AI summary
An onium salt having the following formula (1) is provided. In formula (1), one of R13 and R14 is a group having a partial structure of the following formula (1a). Q1 to Q3 are each independently a hydrogen atom, a fluorine atom, or a C1-C6 fluorinated saturated hydrocarbyl group, provided that, when both of Q1 and Q2 are a hydrogen atom, Q3 is a fluorine atom or a C1-C6 fluorinated saturated hydrocarbyl group, and the total number of fluorine atoms in Q1 to Q3 is 2 or more.