Continued downscaling of semiconductor devices has placed stringent constraints on all aspects of the fabrication process including plasma-assisted anisotropic etching. To address manufacturing challenges associated with atomic-scale control, material selectivity, etch fidelity, and increasingly complex device architectures, reactive ion etching (RIE) is transitioning to plasma-assisted atomic layer etching (ALE). Even though the number of elements used in the semiconductor devices has increased several-fold over the last four decades, SiO₂ and SiN_x remain the most commonly used dielectric materials. In fact, fluorocarbon based, plasma-assisted ALE processes for SiO₂ and SiN_x have already been integrated into semiconductor manufacturing, including etching of self-aligned contacts for advanced transistors. However, several challenges remain in achieving ultrahigh etch selectivity of SiO₂ over SiN_x and vice versa. In this article, first, the authors provide a focused review on selective RIE of SiO₂ over SiN_x and contrast this with ALE. A particular focus is given to the etching mechanism, including the role of the mixing layer composition and thickness at the fluorocarbon-SiO₂ interface, the F-to-C ratio in the fluorocarbon parent gas, H₂ dilution, surface composition on the nonetched SiN_x, ion flux and energy, Ar plasma activation duration in ALE, and chamber memory effects. Second, we discuss the reverse case of selectively etching SiN_x over SiO₂ with careful attention given to the role of novel hydrofluorocarbon gases and dilution of the primary feed gas with other gases such as CH₄ and NO. In the second part of this review, we also discuss how novel surface chemistries are enabled by the introduction of ALE, which include selective (NH₄)₂SiF₆ formation on the SiN_x surface and selective surface prefunctionalization of SiO₂ to enable ultrahigh selectivity. Through this review, the authors hope to provide the readers with an exhaustive knowledge of the selectivity mechanisms for RIE of SiO₂ over SiN_x and vice versa, which provides a basis for developing future highly material-selective ALE processes.

中文翻译：

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SiO2和SiNx的等离子体辅助蚀刻过程中的蚀刻选择性：从反应性离子蚀刻过渡到原子层蚀刻

半导体器件的持续缩小尺寸已经对包括等离子体辅助各向异性蚀刻在内的制造工艺的各个方面施加了严格的限制。为了解决与原子尺度控制，材料选择性，蚀刻保真度和日益复杂的设备架构相关的制造挑战，反应性离子蚀刻（RIE）正在过渡到等离子体辅助原子层蚀刻（ALE）。即使在过去的四十年中半导体器件中使用的元素数量增加了几倍，SiO ₂和SiN _x仍然是最常用的介电材料。实际上，用于SiO ₂和SiN _x的基于碳氟化合物的等离子辅助ALE工艺已经集成到半导体制造中，包括蚀刻先进晶体管的自对准触点。然而，在实现SiO _2相对于SiN _x的超高蚀刻选择性方面仍然存在一些挑战，反之亦然。在本文中，首先，作者针对SiO ₂在SiN _x上的选择性RIE进行了重点综述，并将其与ALE进行了对比。蚀刻机理特别受关注，包括混合层组成和碳氟化合物-SiO ₂界面处的厚度的作用，碳氟化合物母气中的F-C比，H ₂稀释，未蚀刻的表面成分氮化硅_X，离子通量和能量，ALE中Ar的等离子体激活持续时间以及腔室记忆效应。其次，我们讨论了在SiO ₂上选择性刻蚀SiN _x的相反情况，并仔细关注了新型氢氟烃气体的作用以及用其他气体（例如CH ₄和NO）稀释一次进料气体的作用。在本综述的第二部分中，我们还将讨论如何通过引入ALE来实现新颖的表面化学，其中包括在SiN _x表面上形成选择性（NH ₄）₂ SiF ₆以及对SiO _2进行选择性表面预官能化以实现超高选择性。通过这篇综述，作者希望为读者提供有关SiN _x上SiO ₂ RIE的选择性机理的详尽知识，反之亦然，这为开发未来的高材料选择性ALE工艺提供了基础。