Hydrogen Plasma Research Articles

Hydrogen plasma enhanced oxide removal on GaSb planar and nanowire surfaces

Due to its high hole-mobility, GaSb is a highly promising candidate for high-speed p-channels in electronic devices. However, GaSb exhibits a comparably thick native oxide causing detrimental interface defects, which has been proven difficult to remove. Here we present full oxide removal from GaSb surfaces using effective hydrogen plasma cleaning, studied in-situ by synchrotron-based X-ray photoelectron spectroscopy under ultrahigh vacuum (UHV). GaSb nanowires turn out to be cleaned faster and more efficiently than planar substrates. Since the UHV conditions are not scalable for industrial sample processing, H-plasma cleaning is furthermore used as pre-treatment prior to atomic layer deposition (ALD) of a protective high-k layer to demonstrate the use of the cleaning step in a more realistic fabrication situation. We observe a cleaning effect of the H-plasma even in the ALD environment, but we also find residual Ga- and Sb-oxides at the GaSb-high-k interface, which we attribute to re-oxidation of the cleaned surface. Our results indicate that an improved control of the ALD reactor vacuum environment could realize oxide- and defect-free interfaces in GaSb-based electronics.

Production of Nickel by Cold Hydrogen Plasma: Role of Active Oxygen

Production of Nickel by Cold Hydrogen Plasma: Role of Active Oxygen

Defect engineering of hexagonal boron nitride nanosheets via hydrogen plasma irradiation

Atomic defects capable of hosting optically active centers in hexagonal boron nitride (h-BN) demonstrate a rich spin and optoelectronic physics that can be exploited for next-generation nanoelectronics and photonics. The precise controlling of these active defects is thus of particular importance. Here, we demonstrate the modulation of optoelectronic properties of atomically thin h-BN nanosheets (BNNSs) based on defect engineering via hydrogen plasma irradiation. Detailed studies resolve the generation of point defects and oxygen related defects uniformly in h-BN lattice after treated by hydrogen plasma. These tailored defects can lead to stable room-temperature luminescent emissions varying from 440 nm (ca. 2.8 eV) to 580 nm (ca. 2.1 eV) in BNNSs and multiple recombination channels. In addition, we show significant variations in both lattice structure and energy bandgap in BNNSs that can be tuned by the hydrogen plasma treatment. Density functional theory calculations verify the nature of the defect-induced optoelectronic behavior. These results are highly valuable for the fabrication of future two-dimensional semiconducting electronics, optoelectronics, and spintronics.

A 1.5D fluid—Monte Carlo model of a hydrogen helicon plasma

Helicon plasma sources operating with hydrogen or deuterium might be attractive for fusion applications due to their higher power efficiency compared to inductive radiofrequency plasma sources. In recent years, the resonant antenna ion device (RAID) has been investigating the physics of helicon plasmas and the possibility of employing them to produce negative ions for heating neutral beam injectors (HNBs). Herein, we present a fluid Monte Carlo (MC) model that describes plasma species transport in a typical helicon hydrogen plasma discharge. This work is motivated by an interest in better understanding the basic physics of helicon plasma devices operating in hydrogen and, in particular, the volume production of negative ions. This model is based on the synergy between two separate self-consistent approaches: a plasma fluid model that calculates ion transport and an MC model that determines the neutral and rovibrational density profiles of . By introducing the electron density and the temperature profiles measured by Langmuir probes as model constraints, the densities of ion species (, , , ) are computed in a 1.5D (dimensional) geometry. The estimate of the negative ion density profile represents a useful benchmark that is comparable with dedicated diagnostics, such as cavity ring-down spectroscopy and Langmuir probe laser photodetachment. Neutral gas particles (atoms and molecules) are calculated assuming a fixed plasma background. This gas–plasma decoupling is necessary due to the different timescales of plasma (microseconds) and gas kinetics (milliseconds).

Atomistic insights on hydrogen plasma treatment for stabilizing High-k/Si interface

Hydrogen plasma treatment (HPT) is commonly employed to enhance the interface quality of high-k metal-oxide gate stacks in semiconductor, but the plasma process is highly sensitive to variations in process parameters. The modulation of processing conditions to meet the increasing demand for atomic-precision in device feature is severely challenging without a proper understanding of the plasma-facing surface. This study aimed to provide atomistic insights on HPT to improve the quality of high-k metal-oxide/silicon interfaces through a computational approach via molecular dynamics and density functional theory. Hydrogen collision, adsorption, penetration, diffusion and desorption were simulated on the processed surface. Depth-wise distribution of hydrogen, structural evolution of target surface and the resultant charge traps at the interface were captured in the computational model for varying processing conditions, incident atomic energies and substrate temperatures. Notably, a physical correlation between the processing parameters and the interface quality was found; the dangling bond density is directly- (at low E) or inversely proportional (at high E) to the substrate temperature, causing variations in trap defects and stability of the gate stacks. A concrete understanding of the HPT offers a guideline to optimize the process window and development of advanced equipment for practical use.

Confinement properties of L-mode plasmas in ASDEX Upgrade and full-radius predictions of the TGLF transport model

The properties of L-mode confinement have been investigated with a set of dedicated experiments in ASDEX Upgrade and with a related modelling activity with the transport code ASTRA and the quasi-linear turbulent transport model TGLF–SAT2, with boundary conditions at the separatrix. The values at the boundary have been set by the two-point model for the electron temperature, with the ion temperature proportional to the electron temperature by a constant factor, and the electron density set by a constant fraction of the volume averaged density. The influx of neutrals has been set through a feedback procedure which ensures that in the simulation the same particle content as in the experiment is obtained. The sensitivity of the results under considerable variations in the choice of the boundary conditions has been investigated and found to be limited. The predictions of this full-radius modelling set-up have been compared to experimental results covering a scan in electron cyclotron resonance heating (ECRH) power in both hydrogen and deuterium plasmas, a plasma current scan with fixed magnetic field, under both ECRH and neutral beam injection heating, an increase in plasma density with constant ECRH power in hydrogen plasmas, as well as variations of the fraction of electron and ion heating at approximately constant total heating power, as well as a change of main ion from deuterium to hydrogen. The ASTRA-TGLF predictions have been found to reproduce all of the experimentally explored dependences with relatively good accuracy, providing evidence, for the first time to our knowledge, that the main properties of L-mode confinement can be reproduced by conventional full-radius transport modelling with a quasi-linear turbulent transport model. Evidences of largest disagreement, although usually not exceeding the 20%, have been found at high electron heating power, where TGLF underpredicts the electron and particularly the ion thermal stored energies, and in the current dependence of confinement, which, in electron heated conditions, is predicted to be weaker than in the experiment.

Enhancing the Contact between a-IGZO and Metal by Hydrogen Plasma Treatment for a High-Speed Varactor (>30 GHz)

Enhancing the Contact between a-IGZO and Metal by Hydrogen Plasma Treatment for a High-Speed Varactor (>30 GHz)

Qualification of uniform large area multidipolar ECR hydrogen plasma

The design and characterization of a multi-dipolar microwave electron cyclotron resonance (ECR) hydrogen plasma reactor are presented. In this configuration, 16 ECR sources are disposed uniformly along the azimuthal direction at a constant distance from the center of a cylindrical reactor. Several plasma diagnostics have been used to determine key parameters such as neutral species temperature; electron density and temperature; and H+, H2+, and H3+ ion energy distributions. The experimental characterization is supported by electromagnetic and magnetostatic field simulations as well as Particle In-Cell Monte Carlo Collisions simulations to analyze the observed ion energy distribution functions. Especially, we show that both electron density and temperature are spatially uniform, i.e., 1011 cm−3 and 3 eV, respectively. This plasma enables generating ion flux and energy in the ranges 1019–1022 ions m−2 s−1 and few keVs, respectively. The H2+ ion distribution function shows two populations which were attributed to surface effects. These features make this reactor particularly suitable for studying hydrogen plasma surface interaction under controlled conditions.

Characterization of Hydrogen Plasma in an ECR based Large Volume Plasma Chamber

Hydrogen plasma characterization was carried out in a large volume (dia∼ 1.0 m, h∼ 1.0 m) plasma chamber to evaluate the efficacy of production of uniform, large-area H- beam for fusion applications. Up to seven Compact ECR Plasma Sources (CEPS; Indian Patent #301583, Patentee: IIT Delhi) can be mounted on the top dome of the chamber (one in centre and six on a ∼60 cm dia circle). Axially poled permanent ring magnets provide the magnetic field for each CEPS and the total field in the chamber is the combined field of all CEPS. Separate experiments were conducted with: (i) six CEPS with opposite polarity on adjacent magnets, (ii) seven CEPS with identical polarity on all the magnets, and (iii) a single CEPS at the center. In case (ii) the field lines repel while for (i) a cusp field is formed between adjacent sources. For case (iii), one obtains a uniform plasma density over 35 cm radius (n ∼ 4 ϗ 1010 cm-3, Te ∼1-2 eV), ∼ 60 cm downstream (from central source mouth) with 400W power at ∼ 1-3 mTorr pressure, yielding ideal conditions for volume mode H- production over a large area. For case (ii), however, plasma from each source flows along its individual field lines, without forming uniform plasma down-tream. Whereas for case (i), because of cross-talk between adjacent sources, the system became unstable, giving oscillations in plasma formation and microwave reflected power. Hence, it appears that the single CEPS configuration is the most efficacious for large area H- generation.

2.8 kV Avalanche in Vertical GaN PN Diode Utilizing Field Plate on Hydrogen Passivated P-Layer

A novel edge termination method resulting in an avalanche-capable 2.8 kV vertical gallium nitride (GaN) pn diode is reported. A low transition temperature spin-on-glass (SOG) based field plate (FP) was deposited on top of the hydrogen-plasma passivated p GaN layer to achieve better electric field management. The hydrogen plasma treatment along with the field plate offered an edge termination without mesa etch that was able to mitigate the peak electric fields in the diodes. Avalanche was confirmed by the positive temperature coefficient of the breakdown voltage. Without the field plate, the breakdown voltage was recorded between 1.3 to 2.1 kV, without an avalanche behavior. The fabricated diodes exhibited a good rectifying behavior with an on-off ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{9}}$ </tex-math></inline-formula> and a specific resistance of 1.65 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This work demonstrated the avalanche capability with the combination of FP and hydrogen-plasma based termination in GaN vertical pn diodes, showing a high figure-of-merit of 4.8 GW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L–H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.

Electron drag force in EUV induced pulsed hydrogen plasmas

Extreme ultraviolet (EUV) induced pulsed plasma is unique due to its transient characteristics: the plasma switches between non-thermal state (when EUV power is ON at the beginning of the pulse) and thermal state (end of the pulse at ∼20 μs). It is shown that although electron drag force acting on nm size particles in hydrogen plasma is negligible compared to the ion drag force at the beginning of the pulse, however it can be dominant at the end of the pulse and can play important role in particle transport leading to defectivity issues for semiconductor chip production technologies.

Numerical study of different electron density observed in Hydrogen and Deuterium ion source plasmas

Sequences of hydrogen (H) and deuterium (D) experiments have been done by NIFS research and development negative ion source (RNIS) for the deuterium NBI development. In the experiments, the co-extracted electron current with the negative ions and the electron density in the plasma generation region in the D experiment have been around three times higher than that in the H experiment. To explain the difference of the electron density in the RNIS driver region, a zero-dimensional numerical model is developed in the present study. The model only focuses on the isotope effect for vibrationally excited level of electronically grounded state molecules and its relevant cross-sections. The calculation results show that difference of the ionization channel numbers via molecular vibrationally excited states could be a reason to enhance ionization rate in D plasma.

Study of the charged particle flow near the plasma grid in negative ion source

Flows of the charged particles in hydrogen (H) and deuterium (D) plasmas were measured with the single-tip directional Langmuir probe. The flow patterns of positive and negative ions have been constructed from the data by moving the probe near the plasma grid. The positive ion flow from driver to extraction regions showed the different velocity equivalent to the mass difference between H and D. The negative ion flow indicated the surface production of negative ions on the plasma grid, and changed the direction corresponding to the magnitude of the extraction electric field.

Probe measurement of an ECR hydrogen plasma facing the C12A7 electride surface

Plasma parameters of an ECR discharge excited in a compact ion source with a replaceable plasma electrode (PE) were measured with a Langmuir probe. The PE was installed to investigate how an electride PE changes the plasma parameters from those with a Mo PE. The effect upon the plasma parameters in front of the PE due to the material will be elucidated by changing the probe position axially along the beam extraction direction. Analyses of the measured probe characteristics revealed that electride PE has a higher electron density (ne) and lower electron temperature (Te) than the Mo PE. When the PE was biased negatively, the ratio of the positive saturation current (Ii ) to the negative saturation current (Ie +Ih- ) for the electride PE was about 1.6 times of the ratio for the Mo PE.

Duoplasmatron type molecular carbon ion source

An ion source capable of producing molecular ions delivers a beam of impurity dopant for shallow ion implantation of semiconductor device fabrication. Production and transport of low energy molecular ions is indispensable for tabulating fundamental data on plasma-wall interactions that should be used to design a future nuclear fusion reactor. An ion source plasma can produce molecular ions of solid materials by sputtering, while low temperature plasma efficiently transports produced molecular ions to the source extraction hole. A duoplasmatron ion source with the carbon plasma electrode has successfully produced poly-atomic carbon ions up to C6 +. The intermediate electrode has six holes to guide cathode plasma to the carbon anode performing as the plasma electrode. A 1 mm diameter extraction hole is opened at the center of the carbon plasma electrode, where is no direct exposure to the plasma from the cathode region. The ion source maintains a stable discharge with both H2 and Ar as discharge support gas, but works better at lower pressure with Ar. A hydrogen plasma produced molecular ions of hydrocarbons with the mass separated current of C3H5 + with the intensity comparable to other ion species including atomic, diatomic and triatomic hydrogen ions.

Deposition of metal thin films using a hollow cathode hydrogen discharge

Approximately 30 to 40 years ago the group of Stan Vepřek of the University of Zurich described the fabrication of silicon thin films by formation and decomposition of silicon hydride. In their paper they described how pieces of silicon exposed to a low-pressure hydrogen plasma could promote the formation of a volatile silicon hydride. The hydride was then transported to a hot substrate which caused its thermal decomposition and the formation of the silicon film.Hollow cathodes under appropriate experimental conditions can produce a semi-resonant high-density plasma. In a previous study we used such a high-density hydrogen plasma to etch pieces of quartz but under extreme conditions, we observed that rather than etching there was deposition of a thin film of the metal used for the electrode of the hollow cathode.In this paper we describe the etching of the metal (Mo or Ta) lining of a water-cooled cylindrical hollow cathode by a high-density hydrogen plasma. The metal hydride vapour generate in the plasma by chemical sputtering was directed, by the gas flow, to the quartz substrates which were maintained at various temperatures in excess of 573 K. Here the metal hydride was thermal decomposed, and a thin film of the metal was formed. To improve the experimental reproducibility a special substrate heater was constructed such that four quartz substrates could be simultaneously exposed to the metal hydride vapour, but with each substrate at a different temperature: each approximately 30.3 K greater than the neighbouring one. In this way, depositions under identical plasma conditions could be carried out at the same time, but at four different temperatures. We report the deposition rate as a function of the substrate temperature, the hydrogen gas flow and the RF or P-DC plasma power applied to the hollow cathode.

Damping of long wavelength gravitational waves by the intergalactic medium

The problem of radiation by the charged particles of the intergalactic medium (IGM) when a passing gravitational wave (GW) accelerates them is investigated. The largest acceleration (taking a charge from rest to a maximum speed which remains non-relativistic in the rest frame of the unperturbed spacetime) is found to be limited by the curvature of a propagating spherical gravitational wavefront. Interesting physics arises from the ensuing emission of radiation into the warm hot IGM, which to lowest order is a fully ionized hydrogen plasma with a frozen-in magnetic field B. It is found that for a vast majority of propagation directions, the radiation can penetrate the plasma at frequencies below the plasma frequency ω p, provided ω < ω b, where ω b = eB/m e satisfies ω b < ω p for typical IGM conditions. Moreover, the refractive index under such a scenario is n ≫ 1, resulting in an enhanced radiative dissipation of GW energy (relative to the vacuum scenario), which is more severe for electrons if both charge species are in thermal equilibrium and accelerated in the same way. The emission by the electrons then prevails, and is further amplified by coherent addition of amplitudes within the size one wavelength. The conversion of GWs of λ≳ 5 × 1013 cm to electromagnetic waves means such GWs can only propagate a distance ≲1 Gpc before being significantly damped by an IGM B field of ∼10−8 G. The low-frequency GWs targeted by pulsar-timing-arrays will not survive unless the IGM magnetic field is much lower than expected. The mHz frequency GW inspirals targeted by future space based detectors such as the Laser Interferometer Space Antenna remain intact and can be detected.

Combination of micro–macro and spatially hybrid fluid‐kinetic approach for hydrogenic plasma edge neutrals

AbstractA new hybrid fluid‐kinetic approach for the hydrogenic neutrals (atoms and molecules) in the plasma edge is presented. The hybrid approach combines a fully kinetic model for the atoms in the low‐collisional regions near the vessel wall, and for the molecules in the whole plasma edge domain, with a micro–macro approach for atoms originating from recycling at the divertor targets, volumetric recombination, and dissociation of molecules. With the micro–macro approach, the originally scattering‐dominated collision term due to charge‐exchange collisions in the kinetic equation is transformed to an absorption‐dominated term, while a large part of the neutral population is treated through a fluid approach. For JET L‐mode plasmas, the premature termination of Monte Carlo particle trajectories in the hybrid approach leads to a reduction of the CPU time by approximately a factor 3 for a high‐recycling case and by approximately a factor 11 for a partially detached case compared with a simulation with fully kinetic neutrals and the same amount of particles. For coupled fluid plasma – hybrid neutral simulations – the hybrid approach predicts the plasma divertor target profiles with a maximum hybrid‐kinetic discrepancy of approximately 30%.

Effect of hydrogen plasma treatment on the electrical properties for SiC-based power MOSFETs

This study investigates the effects of hydrogen plasma treatment on the leakage current and capacitance characteristics of metal–insulator–semiconductor (MIS) structures on SiC substrate. The H2 plasma treatment resulted in improved breakdown voltage and reduced defect density (Nd) in an atomic-layer-deposited 30 nm-thick Al2O3 (top)/15 nm-thick SiO2 bi-layer dielectric. The breakdown voltage in Al2O3/SiO2 bi-layer dielectric after H2 plasma treatment was improved by about 6.2% (initial 47 V). The value of Nd decreased by about one order in the Al2O3/SiO2 bi-layer dielectric from 2.3 × 1011/cm2 to 3.4 × 1010/cm2 after H2 plasma treatment. Further, the interface trap density (Dit) of Al2O3/SiO2 bi-layer dielectrics was 1.4 × 1012 cm−2·eV−1, and 50% of that of the SiO2 single dielectric film.