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<p>Novolac-based photoresists, widely utilized in <i>i</i>-line and broadband photolithography, rely on diazonaphthoquinone (DNQ) photoactive compounds to enable UV-patterned dissolution via photochemically generated carboxylic acids. While the dissolution mechanism is typically governed by enhanced base solubility following DNQ photolysis and phenolic deprotonation, a counterintuitive decrease in dissolution rate with increasing temperature has been repeatedly observed in an intermediate thermal window—manifesting as a negative activation energy. Previous models have attributed this phenomenon to enhanced photoactive compound–novolac complexation or temperature-induced disruption of phenolate–tetramethylammonium ion pairs. However, these explanations fall short of accounting for additional observations such as surface densification and anion-specific effects. In this study, we uncover a complementary mechanism in which rapid formation of phenolate and carboxylate species leads to hydration-shell collapse and a subsequent densification of the novolac matrix near its glass transition temperature. Through systematic spectroscopic analysis, we propose a unified model that incorporates molecular interactions, ion-pairing dynamics, and polymer network reorganization, providing a comprehensive framework for understanding temperature-dependent dissolution behavior in DNQ/novolac photoresists.</p> Graphical abstract <p>We investigate the mechanism of the dissolution process with negative activation energy of DNQ/novolac photoresists using Fourier-transform infrared spectroscopy. We reveal that rapid anion formation at elevated temperatures induces hydration-shell collapse and matrix densification, suppressing dissolution. This structural transition near the glass transition temperature provides a molecular basis for the observed negative activation energy.</p> <p></p>

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Molecular-scale spectroscopic insights on temperature-induced dissolution inhibition in DNQ/novolac photoresists

  • 期刊论文

  • 发表日期：

    2025年9月10日

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  • Jaehoon Lee,
  • Jihun Noh,
  • Inhee Jeong,
  • Seongmo Kang,
  • Boseok Kang

摘要

Novolac-based photoresists, widely utilized in i-line and broadband photolithography, rely on diazonaphthoquinone (DNQ) photoactive compounds to enable UV-patterned dissolution via photochemically generated carboxylic acids. While the dissolution mechanism is typically governed by enhanced base solubility following DNQ photolysis and phenolic deprotonation, a counterintuitive decrease in dissolution rate with increasing temperature has been repeatedly observed in an intermediate thermal window—manifesting as a negative activation energy. Previous models have attributed this phenomenon to enhanced photoactive compound–novolac complexation or temperature-induced disruption of phenolate–tetramethylammonium ion pairs. However, these explanations fall short of accounting for additional observations such as surface densification and anion-specific effects. In this study, we uncover a complementary mechanism in which rapid formation of phenolate and carboxylate species leads to hydration-shell collapse and a subsequent densification of the novolac matrix near its glass transition temperature. Through systematic spectroscopic analysis, we propose a unified model that incorporates molecular interactions, ion-pairing dynamics, and polymer network reorganization, providing a comprehensive framework for understanding temperature-dependent dissolution behavior in DNQ/novolac photoresists.

Graphical abstract

We investigate the mechanism of the dissolution process with negative activation energy of DNQ/novolac photoresists using Fourier-transform infrared spectroscopy. We reveal that rapid anion formation at elevated temperatures induces hydration-shell collapse and matrix densification, suppressing dissolution. This structural transition near the glass transition temperature provides a molecular basis for the observed negative activation energy.