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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

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Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
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Related Experiment Video

Updated: May 31, 2025

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

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Etchant-Free Dry-Developable Extreme Ultraviolet Photoresist Materials Utilizing N-Heterocyclic Carbene-Metal

Dowon Kim1, Jinhwan Byeon1, Jaeboong Ahn1

  • 1Department of Chemistry, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Republic of Korea.

Small (Weinheim an Der Bergstrasse, Germany)
|January 23, 2025
PubMed
Summary

New N-heterocyclic carbene (NHC)-based photoresists enable etchant-free extreme ultraviolet (EUV) lithography. This sustainable, cost-effective approach achieves high-resolution nanopatterns using simple thermal development, overcoming limitations of wet processes.

Keywords:
N‐heterocyclic carbenedry development techniqueextreme ultravioletmetal–organic photoresistsnear‐edge X‐ray absorption fine structure

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Area of Science:

  • Materials Science
  • Nanotechnology
  • Chemical Engineering

Background:

  • Extreme ultraviolet (EUV) lithography faces challenges with pattern collapse in wet processes.
  • Existing dry-development methods often use toxic etchants or specialized equipment.
  • There is a need for sustainable and economical alternatives in nanofabrication.

Purpose of the Study:

  • To synthesize novel, etchant-free, dry-developable EUV photoresists.
  • To investigate the EUV-induced chemical mechanisms in these new photoresists.
  • To demonstrate high-resolution nanopatterning using a simple thermal development process.

Main Methods:

  • Synthesis of N-heterocyclic carbene (NHC)-based metal-ligand complexes for photoresists.
  • Characterization of EUV sensitivity and development processes.
  • Analysis of EUV-induced chemical reactions using advanced spectroscopy (EUV-PES, NEXAFS, XPS) and DFT.
  • Demonstration of nanopatterning with 80 nm resolution.

Main Results:

  • Achieved high EUV sensitivity with half-saturation doses of 8.5 or 27 mJ cm-2.
  • Demonstrated 80 nm resolution using a simple thermal dry development in a standard furnace.
  • Observed line-edge roughness (LER) comparable to conventional wet-developed patterns.
  • Identified branching polymerization initiated by secondary electrons and photoelectrons as the key mechanism for high sensitivity.

Conclusions:

  • NHC metal-organic photoresists provide a sustainable and economical alternative for EUV lithography.
  • The etchant-free, dry-development process eliminates hazardous chemicals and simplifies fabrication.
  • This technology advances nanofabrication by enabling high-resolution patterning through efficient thermal treatment.