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<p>Stoichiometric silicon nitride has emerged as a widely used integrated photonic material owing to its high index of refraction, nonlinear optical properties, and broad transparency window spanning visible to mid-IR frequencies. However, silicon nitride is generally more resistant to reactive ion etching than are typical etch masks made of polymer-based resist. This necessitates resist layers that are significantly thicker than the silicon nitride and results in mask patterns which are tall and narrow. These high-aspect-ratio patterns inhibit the plasma transport of reactive ion etching, which leads to difficulties in accurately reproducing dimensions and creating well-defined, vertical waveguide sidewalls. In this work, we overcome these challenges by developing a metallic etch mask deposited via metal lift-off that provides a 30&#xa0;:&#xa0;1 nitride-to-metal etch rate ratio, representing a near 45-fold reduction in the required mask thickness. We demonstrate the validity of this technique by etching microring resonators with near-vertical waveguide sidewalls and intrinsic quality factors of over 1 million. Leveraging the low optical loss of our resonators, we generate optical frequency combs with more than an octave of bandwidth and dual dispersive waves. These results establish metal lift-off as a viable and easy-to-implement technique capable of producing low optical loss waveguides.</p>

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Low-loss silicon nitride Kerr-microresonators fabricated with metallic etch masks via metal lift-off

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月10日

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  • Gabriel M. Colación,
  • Lala Rukh,
  • Franco H. Buck,
  • Tara E. Drake

摘要

Stoichiometric silicon nitride has emerged as a widely used integrated photonic material owing to its high index of refraction, nonlinear optical properties, and broad transparency window spanning visible to mid-IR frequencies. However, silicon nitride is generally more resistant to reactive ion etching than are typical etch masks made of polymer-based resist. This necessitates resist layers that are significantly thicker than the silicon nitride and results in mask patterns which are tall and narrow. These high-aspect-ratio patterns inhibit the plasma transport of reactive ion etching, which leads to difficulties in accurately reproducing dimensions and creating well-defined, vertical waveguide sidewalls. In this work, we overcome these challenges by developing a metallic etch mask deposited via metal lift-off that provides a 30 : 1 nitride-to-metal etch rate ratio, representing a near 45-fold reduction in the required mask thickness. We demonstrate the validity of this technique by etching microring resonators with near-vertical waveguide sidewalls and intrinsic quality factors of over 1 million. Leveraging the low optical loss of our resonators, we generate optical frequency combs with more than an octave of bandwidth and dual dispersive waves. These results establish metal lift-off as a viable and easy-to-implement technique capable of producing low optical loss waveguides.