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1. Metal-Assisted Catalytic Etching (MACE) for Nanofabrication of Semiconductor Powders

   https://doi.org/10.3390/mi12070776  

   Kolasinski, Kurt W. (July 2021, Micromachines)

   null (Ed.)

   Electroless etching of semiconductors has been elevated to an advanced micromachining process by the addition of a structured metal catalyst. Patterning of the catalyst by lithographic techniques facilitated the patterning of crystalline and polycrystalline wafer substrates. Galvanic deposition of metals on semiconductors has a natural tendency to produce nanoparticles rather than flat uniform films. This characteristic makes possible the etching of wafers and particles with arbitrary shape and size. While it has been widely recognized that spontaneous deposition of metal nanoparticles can be used in connection with etching to porosify wafers, it is also possible to produced nanostructured powders. Metal-assisted catalytic etching (MACE) can be controlled to produce (1) etch track pores with shapes and sizes closely related to the shape and size of the metal nanoparticle, (2) hierarchically porosified substrates exhibiting combinations of large etch track pores and mesopores, and (3) nanowires with either solid or mesoporous cores. This review discussed the mechanisms of porosification, processing advances, and the properties of the etch product with special emphasis on the etching of silicon powders. 

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2. Future of plasma etching for microelectronics: Challenges and opportunities

   https://doi.org/10.1116/6.0003579  

   Oehrlein, Gottlieb_S; Brandstadter, Stephan_M; Bruce, Robert_L; Chang, Jane_P; DeMott, Jessica_C; Donnelly, Vincent_M; Dussart, Rémi; Fischer, Andreas; Gottscho, Richard_A; Hamaguchi, Satoshi; et al (June 2024, Journal of Vacuum Science & Technology B)

   Plasma etching is an essential semiconductor manufacturing technology required to enable the current microelectronics industry. Along with lithographic patterning, thin-film formation methods, and others, plasma etching has dynamically evolved to meet the exponentially growing demands of the microelectronics industry that enables modern society. At this time, plasma etching faces a period of unprecedented changes owing to numerous factors, including aggressive transition to three-dimensional (3D) device architectures, process precision approaching atomic-scale critical dimensions, introduction of new materials, fundamental silicon device limits, and parallel evolution of post-CMOS approaches. The vast growth of the microelectronics industry has emphasized its role in addressing major societal challenges, including questions on the sustainability of the associated energy use, semiconductor manufacturing related emissions of greenhouse gases, and others. The goal of this article is to help both define the challenges for plasma etching and point out effective plasma etching technology options that may play essential roles in defining microelectronics manufacturing in the future. The challenges are accompanied by significant new opportunities, including integrating experiments with various computational approaches such as machine learning/artificial intelligence and progress in computational approaches, including the realization of digital twins of physical etch chambers through hybrid/coupled models. These prospects can enable innovative solutions to problems that were not available during the past 50 years of plasma etch development in the microelectronics industry. To elaborate on these perspectives, the present article brings together the views of various experts on the different topics that will shape plasma etching for microelectronics manufacturing of the future. 

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

   Colacion, Gabriel M; Rukh, Lala; Buck, Franco; Drake, Tara E (June 2025, arXivorg)

   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. 

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4. Bilayer metal etch mask strategy for deep diamond etching

   https://doi.org/10.1116/6.0001424  

   Zheng, Yixiong; Muehle, Matthias; Lai, Junyu; Albrecht, John D.; Seo, Jung-Hun (March 2022, Journal of Vacuum Science & Technology B)

   In this study, we demonstrate a tolerant and durable Cr/Ni bilayer metal etch mask that allows us to realize approximately 150:1 etch selectivity to diamond. This result is achieved through the use of a very thin initial Cr layer of <10 nm thickness as part of the bilayer metal mask, which results in five to ten times improved selectivity than thick single metal layer masks or bilayer masks with thicker combinations. A finite element analysis was employed to design and understand the physics and working mechanism of the bilayer metal masks with different thicknesses. Raman spectroscopy and energy-dispersive x-ray spectroscopy on the diamond surface were also performed to investigate the changes in diamond quality before and after the deep diamond etching and found that no noticeable etch damage or defects were formed. Overall, this mask strategy offers a viable way to realize deep diamond etching using a high heat and chemistry tolerant and durable bilayer metal etching mask. It also offers several technological benefits and advantages, including various deposition method options, such as sputtering and physical vapor deposition, that can be used and the total thinness of the bilayer metal mask required given the higher selectivity allows us to realize fine diamond etching or high-aspect ratio etching, which is a critical fabrication process for future power, RF, MEMS, and quantum device applications. 

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5. In situ etching of β -Ga2O3 using tert -butyl chloride in an MOCVD system

   https://doi.org/10.1063/5.0239152  

   Gorsak, Cameron_A; Bowman, Henry_J; Gann, Katie_R; Buontempo, Joshua_T; Smith, Kathleen_T; Tripathi, Pushpanshu; Steele, Jacob; Jena, Debdeep; Schlom, Darrell_G; Xing, Huili_Grace; et al (December 2024, Applied Physics Letters)

   In this study, we investigate in situ etching of β-Ga2O3 in a metalorganic chemical vapor deposition system using tert-butyl chloride (TBCl). We report etching of both heteroepitaxial 2¯01-oriented and homoepitaxial (010)-oriented β-Ga2O3 films over a wide range of substrate temperatures, TBCl molar flows, and reactor pressures. We infer that the likely etchant is HCl (g), formed by the pyrolysis of TBCl in the hydrodynamic boundary layer above the substrate. The temperature dependence of the etch rate reveals two distinct regimes characterized by markedly different apparent activation energies. The extracted apparent activation energies suggest that at temperatures below ∼800 °C, the etch rate is likely limited by desorption of etch products. The relative etch rates of heteroepitaxial 2¯01 and homoepitaxial (010) β-Ga2O3 were observed to scale by the ratio of the surface energies, indicating an anisotropic etch. Relatively smooth post-etch surface morphology was achieved by tuning the etching parameters for (010) homoepitaxial films. 

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