New ultrahigh vacuum setup and advanced diagnostic techniques for studying a-Si:H film growth by radical beams

A new ultrahigh vacuum setup is presented which is designed for studying the surface science aspects of a-Si:H film growth using various advanced optical diagnostic techniques. The setup is equipped with plasma and radical sources which produce well-defined radicals beams such that the a-Si:H deposition process can be mimicked. In this paper the initial experiments with respect to deposition of a-Si:H using a hot wire source and etching of a-Si:H by atomic hydrogen are presented. These processes are monitored by real time spectroscopic ellipsometry and the etch yield of Si by atomic hydrogen is quantified to be 0.005±0.002 Si atoms per incoming H atom

Optical diagnostics for high electron density plasmas

Nowadays high electron density plasmas are, beside their fundamental interest, widely used for many applications, e.g., light sources and plasma processing. The well known examples of high electron density plasmas can be found among the class of thermal plasmas as, e.g., the Inductively Coupled Plasma (ICP) and the Wall Stabilized Cascaded Arc (WSCA). Usually the pressure of the plasma is high, i.e., sub atmospheric to atmospheric. Other examples are the plasmas generated in tokamaks for fusion purposes and the recently exploited plasmas for etching and deposition devices such as the Electron Cyclotron Resonance plasmas. For the plasmas mentioned, the electron density is typical in the range of 1018 to 1023 m3, and the electron velocity distribution is close to a Maxwellian velocity distribution

The 2017 Plasma Roadmap: Low temperature plasma science and technology

Journal of Physics D: Applied Physics published the first Plasma Roadmap in 2012 consisting of the individual perspectives of 16 leading experts in the various sub-fields of low temperature plasma science and technology. The 2017 Plasma Roadmap is the first update of a planned series of periodic updates of the Plasma Roadmap. The continuously growing interdisciplinary nature of the low temperature plasma field and its equally broad range of applications are making it increasingly difficult to identify major challenges that encompass all of the many sub-fields and applications. This intellectual diversity is ultimately a strength of the field. The current state of the art for the 19 sub-fields addressed in this roadmap demonstrates the enviable track record of the low temperature plasma field in the development of plasmas as an enabling technology for a vast range of technologies that underpin our modern society. At the same time, the many important scientific and technological challenges shared in this roadmap show that the path forward is not only scientifically rich but has the potential to make wide and far reaching contributions to many societal challenges.I Adamovich et al 2017 J. Phys. D: Appl. Phys. 50 32300

Ion assisted ETP-CVD a-Si:H at well defined ion energies

Hydrogenated amorphous silicon (a-Si:H) was deposited with the Expanding Thermal Plasma-CVD (ETP CVD) method utilizing pulse-shaped substrate biasing to induce controlled ion bombardment during film growth. The films are analyzed with in-situ real time spectroscopic ellispometry, FTIR spectroscopy, as well as reflection-transmission and Fourier transform photocurrent spectroscopy (FTPS) measurements. The aim of this work is to investigate the effect ion bombardment with well defined energy on the roughness evolution of the film and the material properties. We observe two separate energy regimes with material densification and relatively constant defect density below ∼120-130 eV and a constant material density at increasing defect density &gt; 120-130 eV substrate bias. We discuss our results in terms of possible ion - surface atom interactions and relate our observations to reports in literature.</p

High-rate (&gt; 1nm/s) and low-temperature (&lt; 400 °C) deposition of silicon nitride using an N₂/SiH₄ and NH ₃/SiH₄ expanding thermal plasma

High-rate (&gt; 1 nm/s) and low-temperature (50 - 400 °C) deposition of silicon nitride (a-SiNx:H) films has been investigated by the expanding thermal plasma (ETP) technique using SiH4 as Si-containing and N2 or NH3 as N-containing precursor gases. The structural, optical and electrical properties of the a-SiNx:H films have been studied by elastic recoil detection, spectroscopic ellipsometry, infrared spectroscopy, dark conductivity measurements and atomic force microscopy. The film properties of the ETP deposited a-SiNx:H films in this low-temperature range are discussed in terms of deposition rate, atomic composition, UV-VIS optical and IR vibrational properties, conductivity, and surface topography of the films.</p

High-rate (> 1nm/s) and low-temperature (< 400 °C) deposition of silicon nitride using an N2/SiH4 and NH 3/SiH4 expanding thermal plasma

High-rate (> 1 nm/s) and low-temperature (50 - 400 °C) deposition of silicon nitride (a-SiNx:H) films has been investigated by the expanding thermal plasma (ETP) technique using SiH4 as Si-containing and N2 or NH3 as N-containing precursor gases. The structural, optical and electrical properties of the a-SiNx:H films have been studied by elastic recoil detection, spectroscopic ellipsometry, infrared spectroscopy, dark conductivity measurements and atomic force microscopy. The film properties of the ETP deposited a-SiNx:H films in this low-temperature range are discussed in terms of deposition rate, atomic composition, UV-VIS optical and IR vibrational properties, conductivity, and surface topography of the films

High-rate (&gt; 1nm/s) and low-temperature (&lt; 400 °C) deposition of silicon nitride using an N₂/SiH₄ and NH ₃/SiH₄ expanding thermal plasma

High-rate (&gt; 1 nm/s) and low-temperature (50 - 400 °C) deposition of silicon nitride (a-SiNx:H) films has been investigated by the expanding thermal plasma (ETP) technique using SiH4 as Si-containing and N2 or NH3 as N-containing precursor gases. The structural, optical and electrical properties of the a-SiNx:H films have been studied by elastic recoil detection, spectroscopic ellipsometry, infrared spectroscopy, dark conductivity measurements and atomic force microscopy. The film properties of the ETP deposited a-SiNx:H films in this low-temperature range are discussed in terms of deposition rate, atomic composition, UV-VIS optical and IR vibrational properties, conductivity, and surface topography of the films.</p

External rf substrate biasing during a-Si:H film growth using the expanding thermal plasma technique

The interchangeability of ion bombardment and deposition temperature during a-Si:H film growth at high deposition rates (10-42 Å/s) by means of the expanding thermal plasma has been studied. The ion bombardment is generated by applying an external rf bias voltage on the substrate. It is shown that the opto-electronic performance of the a-Si:H films improves considerably when a moderate rf substrate bias voltage (∼20-60 V) is applied, i.e. the photo response increases two orders of magnitude up to 106. Furthermore, it is also revealed that the additional energy supplied to the growth surface by the ion bombardment, makes a reduction of the deposition temperature by ∼100°C possible, while preserving good material properties. On the basis of the results obtained, three effects caused by the rf substrate bias can be distinguished: creation of an additional growth flux, a reduction of the void incorporation, and an increase in the vacancy density.</p

Detailed H(n=2) density measurements in a magnetized hydrogen plasma jet

We present detailed spatial density measurements of H(n = 2), i.e. the first excited state of atomic hydrogen, in a hydrogen plasma expansion that is weakly magnetized. At a specific distance from the source of the expansion a sharp transition from a red light emitting plasma (dominated by H-alpha emission) to a blue light emitting plasma (dominated by H-beta and H-gamma emission) occurs. Molecular processes such as dissociative recombination and processes with negative ions are suspected to be key in the understanding of the distinct emissions observed in the two different plasma regions. The relevance of the presented work is to underline these molecular processes in atomic regimes of hydrogen-containing plasmas. The first excited state density, n = 2, is determined with tunable diode laser absorption spectroscopy on the Balmer-alpha transition to investigate how important molecular processes such as dissociative recombination are in the plasma. The density of n = 2 is 1 x 10(17) m(-3) close to the plasma source and decreases gradually along the plasma column to 10(14) m(-3) at 20 cm from the plasma source exit. The presented results show that the theoretical possibility to generate a stable hydrogen laser in the visible light, i.e. population inversion of n = 3 with respect to n = 2, is not obtained due to the population of n = 2 by dissociative recombination of H-3(+) ions. The presence of molecular processes in the plasma is further evidenced with the use of a collisional radiative model

Population inversion in a magnetized hydrogen plasma expansion as a consequence of the molecular mutual neutralization process

A weakly magnetized expanding hydrogen plasma, created by a cascaded arc, was investigated using optical emission spectroscopy. The emission of the expanding plasma is dominated by H a emission in the first part of the plasma expansion, after which a sharp transition to a blue afterglow is observed. The position of this sharp transition along the expansion axis depends on the magnetic field strength. The blue afterglow emission is associated with population inversion of the electronically excited atomic hydrogen states n = 4 - 6 with respect to n = 3. By comparing the measured densities with the densities using an atomic collisional radiative model, we conclude that atomic recombination processes cannot account for the large population densities observed. Therefore, molecular processes must be important for the formation of excited states and for the occurrence of population inversion. This is further corroborated at the transition from red to blue, where a hollow profile of the excited states n = 4 - 6 in the radial direction is observed. This hollow profile is explained by the molecular mutual neutralization process of H-2(+) with H-, which has a maximum production for excited atomic hydrogen 1 - 2 cm outside the plasma center