Abstract
The fabrication of next-generation semiconductor devices has created a need for low-temperature (≤400 °C) deposition of highly-conformal (>95%) SiO2, SiNx, and SiC films on high-aspect-ratio nanostructures. To enable the growth of these Si-based dielectric films, semiconductor manufacturers are transitioning from chemical vapor deposition to atomic layer deposition (ALD). Currently, SiO2 films deposited using ALD are already being integrated into semiconductor device manufacturing. However, substantial processing challenges remain for the complete integration of SiNx films deposited by ALD, and there are no known processes for ALD of SiC at temperatures that are compatible with semiconductor device manufacturing. In this focused review, the authors look at the status of thermal and plasma-assisted ALD of these three Si-based dielectric films. For SiO2 ALD, since low-temperature processes that deposit high-quality films are known, the authors focus primarily on the identification of surface reaction mechanisms using chlorosilane and aminosilane precursors, as this provides a foundation for the ALD of SiNx and SiC, two material systems where substantial processing challenges still exist. Using an understanding of the surface reaction mechanisms, the authors describe the underlying reasons for the processing challenges during ALD of SiNx and SiC and suggest methodologies for process improvement. While both thermal and plasma-assisted SiNx ALD processes have been reported in the literature, the thermal NH3-based ALD processes require processing temperatures >500 °C and large NH3 doses. On the other hand, plasma-assisted SiNx ALD processes suffer from nonuniform film properties or low conformality when deposited on high-aspect-ratio nanostructures. In the SiNx section, the authors provide a broad overview of the currently known thermal and plasma-assisted SiNx ALD processes using chlorosilane, trisilylamine, and aminosilane precursors, describe the process shortcomings, and review the literature on precursor reaction pathways. The authors close this section with suggestions for improving the film properties and conformality. In the case of SiC, the authors first outline the limitations of previously reported SiC ALD processes and highlight that unlike SiO2 and SiNx plasma-assisted ALD, no straightforward pathway for low-temperature plasma-assisted growth is currently apparent. The authors speculate that low-temperature ALD of SiC may require the design of completely new precursors. Finally, they summarize the progress made in the ALD of C-containing SiNx and SiO2 films, which may provide many of the benefits of SiC ALD in semiconductor manufacturing. In closing, through this review, the authors hope to provide the readers with a comprehensive knowledge of the surface reactions mechanisms during ALD of Si-based dielectrics, which would provide a foundation for future precursor and process development.
Highlights
The miniaturization of microelectronic devices has introduced several processing challenges that need to be overcome for the implementation of advanced architectures at sub-7-nm technology nodes.1,2 In particular, the introduction of FinFET-based transistor devices and the rapid proliferation of 3D NAND memory have created a need for thin filmNote: This paper is part of the 2020 Special Topic Collection on Atomic Layer Deposition (ALD).growth processes capable of depositing materials with a conformality of >95% at temperatures ≤400 °C over high aspect ratio (HAR) nanostructures.3 In the semiconductor industry, two of the most commonly used thin film growth techniques are thermal chemical vapor deposition (CVD) and plasma-assisted CVD
II, we describe the ALD of SiO2, with a particular focus on the surface reaction mechanisms that lead to film growth for chlorosilane, Si alkoxide, and aminosilane Si precursors
While base-catalyzed SiO2 ALD processes that use SiCl4 and H2O precursors are capable of film growth at low temperatures and small precursor exposures, a chlorine-free lowtemperature ALD process would be preferred for many applications, because HCl produced as a by-product is highly corrosive and undergoes further side reactions
Summary
The miniaturization of microelectronic devices has introduced several processing challenges that need to be overcome for the implementation of advanced architectures at sub-7-nm technology nodes. In particular, the introduction of FinFET-based transistor devices and the rapid proliferation of 3D NAND memory have created a need for thin film. To mitigate the shortcomings of CVD processes, and to enable the growth of highly-conformal films at low substrate temperatures, semiconductor manufacturers are turning to atomic layer deposition (ALD) as a potential alternative. The ALD of these three Si-based currently dielectrics represents a substantial segment of the ALD market and will continue to be crucial for the creation of advanced electronic devices in the near future.24 These three Si-based dielectrics have different optical, electronic, and barrier properties, as well as different etch selectivities relative to one another, making them suitable for a wide variety of applications. SiCN can be used in applications typically reserved for SiNx but has the added benefit of a lower dielectric constant.31,33 These low-κ materials can improve the performance of semiconductor devices by reducing resistive-capacitive delays.. We limit the discussion to three applications of ALD in the semiconductor industry: the formation of sidewall spacers in self-aligned
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