Radical-controlled plasma processes

Abstract

In plasmas, a variety of radicals which are defined as electrically neutral radicals in this article are efficiently produced by collisions between electrons and gas molecules. These radicals can subsequently undergo gas phase reactions with solids, liquids and living organisms that result in non-equilibrium surface/interface physicochemical processes. The specific phenomena produced by these reactions remain largely unknown, even though these plasma-based processes could lead to disruptive technological innovations. As an example, in the case of semiconductor microfabrication processes, the density, energy and lifetime of individual radicals, as well as the reaction time constants of these species with various materials should be ascertained. This would allow the identification and control of the effective radical species during processes, such as the high-precision etching and deposition of functional thin films. In addition, the type of reactions occurring between radicals generated in plasmas with liquids or living organisms is still an unexplored area. Establishing a theoretical system for these radical reactions and controlling the associated mechanisms could lead to innovations in the fields of functional devices and materials as well as in the areas of environmental protection, medicine and agriculture/fisheries. Focusing on the non-equilibrium surface/interface physicochemical reactions between radicals and solids occurring in semiconductor plasma processing, this paper describes the formation of nanostructured thin films by top-down mechanisms based on controlled radical production and bottom-up processes involving radical-induced self-organization. As well, this review examines next-generation medical and agricultural applications, such as the selective killing of cancer cells and plant growth promotion and functionalization. These systems result from the interactions of radicals generated in atmospheric-pressure, low-temperature plasmas with liquids, or the interactions of gas or liquid phase radicals with biological species. Finally, the importance of academic research into radical-controlled plasma processes and potential future technologies based on this interdisciplinary field are examined.

Etching Mechanism Based on Hydrogen Fluoride Interactions with Hydrogenated SiN Films Using HF/H2 and CF4/H2 Plasmas

“…Based on the presented results, the following facts can be summarized: (1) In conventional reactive ion etching, it is widely recognized that the etching process of dielectric materials is complex and involves interactions between the film being etched and ions/ radicals. 41 This process is influenced by various factors. When the substrate is exposed to plasma with a high bias voltage, ions are regarded as the primary etchants, exhibiting a higher etching yield for dielectric materials with high bonding energy.…”

“…Simultaneously, in the CF 4 /H 2 plasmas, the CH x F y ions, which act as the primary etchants, can decompose the AFS into SiF 4 and NH 3 or other volatile products, e.g., HCN, via reactive sputtering. Nevertheless, the presence of CH x F y ions and their radicals in the etching processes of SiN using hydrogen-containing fluorocarbon plasmas introduces additional complexity to the reactions, 41 in contrast to the relatively simpler etching process observed in the HF/H 2 plasma. It is plausible that the CH x F y ions have a higher propensity to decompose the AFS phase, supported by XPS, as shown in Figure 4b.…”

Editorial : Reviews of Modern Plasma Physics: Volume 6

“…Topical collection "Plasma Innovation Lecture (PI)" is lecture series of Plasma Innovation Prize laureates and first article is published in 2022 (Hori 2022).…”

Quantitative effect of plasma‐processed multi‐walled carbon nanotubes for mechanical property of in situ polymerized polyurethane composite

“…10,11 In such a plasma, only electrons are at high temperature, while the ions and radicals stay at a much lower temperature, such as in the order of several hundred kelvins. [12][13][14][15] Moreover, plasma functionalization has another advantage over CNT functionalization in that direct functionalization is possible on the CNT surface.…”

“…However, once the nanotubes are exposed to plasma, the opportunity to functionalize CNTs increases because plasma contains a lot of energetic species, 9 especially low‐temperature plasma has an advantage in that the processing temperature could remain low 10,11 . In such a plasma, only electrons are at high temperature, while the ions and radicals stay at a much lower temperature, such as in the order of several hundred kelvins 12–15 . Moreover, plasma functionalization has another advantage over CNT functionalization in that direct functionalization is possible on the CNT surface.…”