H2 Plasma Pretreatment Research Articles

Investigation of atomic layer deposition methods of Al2O3 on n-GaN

In this work, three atomic layer deposition (ALD) approaches are used to deposit an Al2O3 gate insulator on n-GaN for application in vertical GaN power switches: thermal ALD (ThALD), plasma-enhanced ALD (PEALD), and their stacked combination. The latter is a novel method to yield the most ideal insulating layer. Also, the influence of an in situ NH3 or H2 plasma pre-treatment is studied. Planar MIS capacitors are used to investigate the electrical properties and robustness of the gate insulators. In vacuo x-ray photoelectron spectroscopy (XPS) is used to study the changes in chemical composition after every surface treatment. XPS shows that all plasma pre-treatments efficiently remove all carbon contamination from the surface, but only NH3 plasma is observed to additionally remove the native oxide from the n-GaN surface. The water precursor step in the ThALD process does not completely remove the CH3 ligands of the trimethylaluminum precursor step, which might electrically be associated with a reduced forward bias robustness. The O2 plasma step in the PEALD process is associated with the removal of carbon and a tremendous increase of the O content in the GaN surface region. Electrically, this strongly correlates to an enhanced forward bias robustness and an increased forward bias hysteresis, respectively. The ThALD/PEALD stack method mitigates the shortcomings of both ALD processes while maintaining its advantages. Electrical measurements indicate that the stack method alongside NH3 plasma pretreatment provides the best characteristics in terms of hysteresis, threshold voltage, forward bias robustness, and interface trap density of states.

Curing defects in plasma-enhanced atomic layer deposition of Al2O3 by six methods

In this paper, the Al2O3 film was fabricated by plasma-enhanced ALD (PEALD) using trimethylaluminium (TMA, Al(CH3)3) precursor. For curing defects such as hydroxyl (OH), Hydrogen, and Carbon inside Al2O3, six types of treatments combining rapid thermal annealing (RTA) or H2 plasma were applied. The comprehensive electrical characteristics such as C-VG, flat-band voltage (Vfb) were quantitatively analyzed by comparing interface trap density (Dit), oxide trapped charge density (Not), permittivity, and breakdown field. RTA is crucial to reduce Dit, Not by ∼78.2% and ∼86.7%, respectively, and enhance the breakdown field from 9 MV/cm to 14 MV/cm or higher by forming the interfacial layer. However, it was not adequate to prevent the severe Vfb shift and decrease of permittivity. H2 plasma pre-treatment could be a solution for these problems as well as slightly improve the breakdown property. But the widening of Vfb variation was still concerned because the amount of carbon reduced by H2 plasma treatment is not consistent. Thus, a more precise H2 plasma treatment is necessary for reliable threshold voltage distribution.

Conversion of Carbon Dioxide into Chemical Vapor Deposited Graphene with Controllable Number of Layers via Hydrogen Plasma Pre-Treatment.

In this work, we report the conversion of carbon dioxide (CO2) gas into graphene on copper foil by using a thermal chemical vapor deposition (CVD) method assisted by hydrogen (H2) plasma pre-treatment. The synthesized graphene has been characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results show the controllable number of layers (two to six layers) of high-quality graphene by adjusting H2 plasma pre-treatment powers (100–400 W). The number of layers is reduced with increasing H2 plasma pre-treatment powers due to the direct modification of metal catalyst surfaces. Bilayer graphene can be well grown with H2 plasma pre-treatment powers of 400 W while few-layer graphene has been successfully formed under H2 plasma pre-treatment powers ranging from 100 to 300 W. The formation mechanism is highlighted.

Advances of microwave plasma-enhanced chemical vapor deposition in fabrication of carbon nanotubes: a review

Microwave plasma chemical vapor deposition (MPCVD) has received tremendous research interest in fabrication of carbon nanotubes (CNTs) due to its unique advantages of high reactivity, rapid heating, no pollution, good controllability, etc. It would be meaningful to summarize the efforts that have been devoted in this area. Up to now, no such review has been seen in the literature. In this review, a summarization and discussion of the MPCVD devices applied in CNTs fabrication are firstly given, followed by the discussion on effect and affecting mechanisms of H2 plasma pretreatment, nitrogen atoms in the reacting gases and microwave power. Notably, the parameters of as-synthesized CNTs products and the corresponding synthesizing MPCVD conditions are listed out. Finally, the capabilities of MPCVD in facilitating atmospheric-pressure, low-temperature and in situ growth of CNTs are reviewed. This review can give a comprehensive grasp of current progress and understanding of MPCVD in preparation of CNTs and may provide a useful guidance for readers to design their fabricating systems to obtained required CNTs using MPCVD.

Effective suppression of surface leakage currents in T2SL photodetectors with deep and vertical mesa sidewalls via TMA and H2 plasma combined pretreatment

For type-II InAs/GaSb superlattice (T2SL) photodetectors with deep and vertical mesa sidewalls, passivation for suppression of surface leakage currents is facing two key challenges that in the conformal coating of sharp sidewalls and increasing dominance of surface leakage currents as device dimensions shrink. In this work, atomic layer deposited (ALD)-Al2O3 and SiO2 method was employed as conformal passivation for deep and vertical mesa sidewalls. And a stable and high-quality interface between the ALD-Al2O3 and T2SL mesa sidewalls was obtained by the combined pretreatment of trimethylaluminum (TMA) and H2 plasma exposure (Al2O3TH), and thus a significant improvement in electrical performances has been achieved. The electrical performances before and after baking were compared among the Al2O3TH, conventional sulfur plus SiO2 passivated photodiodes. The dark current density of Al2O3TH passivated photodiodes were improved by 81% at 77 K under 0.1 V reverse bias and exhibited no deterioration after 90 °C-4 days baking treatment. Investigation on the effects of TMA and/or H2 plasma pretreatments demonstrates that combined pretreatment of TMA and H2 plasma, rather than TMA or H2 plasma alone, prior to the deposition of ALD-Al2O3 leads to a more thorough elimination of interface native oxides and surface states introduced in mesa process. The innovative application of this effective surface pretreatment technique is very encouraging for the passivation of deep and vertical sidewalls in III-V compound-based devices, such as large-format T2SL infrared detectors.

Adhesion and friction performance of DLC/rubber: The influence of plasma pretreatment

Diamond-like carbon (DLC) films are deposited on rubber surfaces to protect the rubber components, and surface pretreatment of the rubber substrates prior to the film deposition can improve the adhesion between the DLC films and the rubber. Thus, the principal purpose of this work concentrates on determining the effects of argon (Ar), oxygen (O2), nitrogen (N2), and hydrogen (H2) plasma pretreatments on the adhesion and friction performance of the DLC films deposited on rubber (DLC/rubber). The results indicated that the Ar plasma pretreatment promoted the formation of a compact layer on the rubber surface. By contrast, massive fillers were exposed on the rubber surface after oxygen or nitrogen plasma pretreatments. Moreover, the typical micrometer-scale patches divided by random cracks were observed on the surface of DLC/rubber, except for the sample pretreated with oxygen plasma. The adhesion of DLC/rubber was found to strengthen with the removal of weak boundary layers and the generation of free radicals on the rubber surface after plasma pretreatment. The tribo-tests revealed that DLC/rubber with O2, N2, and H2 plasma pretreatments cannot achieve optimal friction performance. Significantly, DLC/rubber with Ar plasma pretreatment exhibited a low and stable friction coefficient of 0.19 and superior wear resistance, which was correlated to the high adhesion, good load-bearing of the rubber surface, and the approximate sine function of the surface profile of the DLC film.

H2 Plazma Ön İşleminden sonra Anodik Oksidasyon Uygulanmış Ti6Al4V Alaşımının Elektrokimyasal Korozyon Davranışının İncelenmesi

H2 Plazma Ön İşleminden sonra Anodik Oksidasyon Uygulanmış Ti6Al4V Alaşımının Elektrokimyasal Korozyon Davranışının İncelenmesi

Inhibiting Metal Oxide Atomic Layer Deposition: Beyond Zinc Oxide.

Atomic layer deposition (ALD) of several metal oxides is selectivity inhibited on alkanethiol self-assembled monolayers (SAMs) on Au, and the eventual nucleation mechanism is investigated. The inhibition ability of the SAM is significantly improved by the in situ H2-plasma pretreatment of the Au substrate prior to the gas-phase deposition of a long-chain alkanethiol, 1-dodecanethiol (DDT). This more rigorous surface preparation inhibits even aggressive oxide ALD precursors, including trimethylaluminum and water, for at least 20 cycles. We study the effect that the ALD precursor purge times, growth temperature, alkanethiol chain length, alkanethiol deposition time, and plasma treatment time have on Al2O3 ALD inhibition. This is the first example of Al2O3 ALD inhibition from a vapor-deposited SAM. The inhibitions of Al2O3, ZnO, and MnO ALD processes are compared, revealing the versatility of this selective surface treatment. Atomic force microscopy and grazing-incidence X-ray fluorescence further reveal insight into the mechanism by which the well-defined surface chemistry of ALD may eventually be circumvented to allow metal oxide nucleation and growth on SAM-modified surfaces.

Improvement in the Grain Growth of Plasma-Treated Nano-Sized ZnO Films and Their Characterization.

The well-aligned ZnO nanorods were rapidly grown on an indium tin oxide (ITO)-coated glass substrate using Al-doped ZnO (AZO) thin film as seed layer by the microwave-assisted hydrothermal chemical route. The optimal growth conditions for the well-aligned ZnO nanorods were obtained by modulating H2 plasma pretreatment time for the seed layer and synthesis time for ZnO nanorods. The H2 plasma effect of the seed layer on the alignment, growth rate and crysallinity of ZnO nanods is also demonstrated. The synthesized ZnO nanorods were annealed in atmosphere of N2, O2 and H2 + N2 mixed gas to improve the related physical characteristics, the ZnO nanorods on grapheme/ITO substrate were also investigated. The results show that the alignment and growth rate of ZnO nanorods depends on the physical characteristics and roughness of the seed layer, which can be improved by H2 plasma pretreatment. The average growth rate of ZnO nanorods synthesized by microwave hydrothermal technique is about 2.2 μm/hr which significantly superior to other conventional techniques. After the appropriate N2 annealing treatment, good quality and well-aligned ZnO nanorods, which are single crystal with stacking defects and pyramid or candle shape, were obtained. A fundamental model of the effect of H2 plasma pretreatment on the surface of seed layer and the growth of ZnO nanorods using a microwave-assisted hydrothermal chemical route is also described.

Flame retardant properties of plasma pre-treated/diamond-like carbon (DLC) coated cotton fabrics

Textiles with superior anti-flammability properties combined with minimal environmental impact are extremely necessary to reduce fire-related issues. In this regard, diamond-like carbon (DLC) coatings on cotton fabrics may represent promising candidates as potential flame-retardant (FR) materials. Herein, superhydrophobic and fire-resistant cotton fabrics were fabricated through a two-step plasma strategy by alternately exposing substrates to H2 and O2 plasma pre-treatments and subsequent DLC deposition. Fourier transform-infrared spectroscopy analysis has revealed that different plasma pre-treatments can impose surface modifications on the chemical structure of cotton, especially in carboxylic and hydroxyl groups, leading to a radical alteration of surface roughness and of the crystalline cellulosic external structure. These changes deeply influenced the growth of DLC thin films and the surface properties of cotton fabric because of the combination of a hierarchical structure and surface chemistry as verified using field emission gun-scanning electron microscopy and water contact angle measurements. The effects of both specific gases used in the pre-treatment step and duration of pre-treatment were analysed and compared using thermogravimetric analyses. The H2-pre-treated DLC cottons exhibited good potential as an FR material, showing improved thermal stability in respect to untreated cotton, as evidenced by increased ignition times. Moreover, vertical burning tests have demonstrated that DLC-cotton systems exhibit enhanced flammability resistance.

매우 작은 크기의 촉매 알갱이를 지지하기 위한 촉매 지지대용 탄소 나노/마이크로 코일의 합성

Carbon coils could be synthesized using C₂H₂/H₂ as source gases and SF? as an incorporated additive gas under thermal chemical vapor deposition system. The Ni layer on the SiO₂ substrate was used as a catalyst for the formation of the carbon coils. The characteristics (formation densities, morphologies, and geometries) of the as-grown carbon coils on the substrate with or without the H₂ plasma pretreatment process were investigated. By the relatively short time (1 minute) H₂ plasma pretreatment on the Ni catalyst layered-substrate prior to the carbon coils synthesis reaction, the dominant formation of the carbon microcoils on the substrate could be achieved. After the relatively long time (30 minutes) H₂ plasma pretreatment process, on the other hand, we could obtain the noble-shaped geometrical nanostructures, namely the formation of the numerous carbon nanocoils along the growth of the carbon microcoils. This noble-shaped geometrical nanostructure seemed to play a promising role as the good catalyst support for holding the very tiny Ni catalyst grains.

The Geometry Variation of As‐Grown Carbon Coils with Ni Layer Thickness and Hydrogen Plasma Pretreatment

Carbon coils could be synthesized using C2H2/H2 as source gases and SF6 as an incorporated additive gas under thermal chemical vapor deposition system. Ni layer on SiO2 substrate was used as a catalyst for the formation of carbon coils. Ni powder was evaporated to form Ni layer on the substrate. The characteristics (formation densities, morphologies, and geometries) of as‐grown carbon coils on the substrate were investigated as a function of the evaporation time for Ni catalyst layer formation. By hydrogen plasma pretreatment prior to carbon coils synthesis reaction, the dominant formation of the nanosized wave‐like geometry of carbon coils could be achieved. The characteristics of as‐grown carbon coils with or without hydrogen plasma pretreatment process were investigated. The cause for the control of the carbon coils geometries from the microsized type to the nanosized wave‐like one by H2 plasma pretreatment was discussed in association with the stress of Ni catalyst layer on the substrate.

Silicon doping effect on SF6/O2 plasma chemical texturing

A SF6/O2 plasma chemical etching is proposed as a process to texture n- and p-doped c-Si (100) by chemical reactivity of active fluorine species, under conditions avoiding ion bombardment and sputtering. Under this chemical etching regime, we found a strong impact of silicon doping on texturing characteristics and effectiveness. Specifically, an anisotropic square-based hillock-like texturing with 6% reflectivity is obtained for n-type Si. Conversely, for p-type Si, H2 plasma pretreatments are necessary to activate the silicon etching and obtain a nanotextured surface with a reflectivity of 16%. Reflectance from textured silicon surfaces is investigated and correlated to the morphology, surface roughness, and dimension of features.

Flexible UV‐Ozone‐Modified Carbon Nanotube Electrodes for Neuronal Recording

Adv. Mater. 2010, 22, 2177–2181 2010 WILEY-VCH Verlag G Neurophysiologists have used sharpened metal electrodes to electrically stimulate neuronal activities to investigate the physiological functions of the brain. Moreover, they employed this electrical stimulation to treat diseases such as Parkinson’s disease, dystonia, and chronic pain. As neurons utilize electrical potential difference between their cell membranes to transmit electrical signals, this particular way of communication enables us to record the neuronal activity extracellularly or intracellularly. For the extracellular recording approach, the electrodes are positioned intimately next to neuron cells to record and to stimulate their electrical activity by capacitive coupling. The coupling efficacy of these electrical recordings or interventions depends significantly on the selectivity, sensitivity, charge-transfer characteristics, long-term chemical stability, and interfacial impedance between electrodes and target tissue. The most common approach to further investigate the functional behavior of neurons, is using Si-based multimicroelectrode probes fabricated by the micro-electromechanical system (MEMS) method to replace the conventional electrodes (Ag/AgCl) in the aspect of device-structure improvement and scaling down device sizes. However, Si-based MEMS electrodes are extremely rigid and cannot be deformed inside the organs; therefore, the recorded positions are easily shifted and the target tissues are consequently damaged when the animals are in motion. This will become an obstacle in future long-term implantation and real-time recording applications. An alternative method is the use of flexible electrodes presented by several groups. The authors utilized soft materials, such as poly(dimethylsiloxane), SU-8 epoxy-based negative photoresist, and polyimides, to fabricate microelectrodes that can deform while being attached to the tissues and that can also be fabricated into small-scale devices using MEMS methods. Not only would rigid Si-based MEMS probes damage target tissues, the reduced electrode size also resulted in a significantly increase in impedance that may degrade recording sensitivity and limit the stimulating current deliverable through an electrode. In order to resolve above issues, the impedance of the electrodemust be as low as possible. Carbon nanotubes (CNTs) exhibit intrinsically large surface areas (700–1000m g ), high electrical conductivity, and intriguing physicochemical properties. Most importantly, CNTs are chemically inert and biocompatible. Based on the above, the promising advantages of flexible substrates and CNTs lead the attempt of fabricating CNTs directly on flexible substrates as microelectrodes for neuronal recording. In this work, the feasibilities of growing CNTs on flexible polyimide substrates at low temperatures (400 8C) by catalyst-assisted chemical vapor deposition (CVD) and utilizing the above devices (see the schematic image in Fig. 1a and the photo in Fig. 1b) as electrodes for extracellularly neuronal recording were investigated. The electrical enhancement (by UV-ozone exposure), biocompatibility (by neuron cell cultures), long-term usage and adhesion, and the detection of action-potential signals on crayfish (using flexible UV-ozone-modified CNTelectrodes) were examined. After a series of process optimizations, the 5-nm Ni-catalyst layer and C2H2 (60 sccm)/H2 (10 sccm) process gases at 5 Torr were found to be the optimum CNT growth parameters in this work. Besides, the Au layer could facilitate CNTgrowth. Figure 1c shows that CNTs have been grown on the polyimide substrate with Au layer, while not on that without Au layer (the inset). The high-resolution transmission electron microscopy (HRTEM) image (Fig. 1d) further confirms the successful syntheses of multi-walled carbon nanotubes (MWCNTs) at 400 8C or even down to 350 8C with H2 plasma pretreatment prior to the CVD processing. As shown in the Supporting Information (Fig. S1a),

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes

Abstract The effect of hydrogen plasma treatment of iron oxide films on the growth and microstructure of carbon nanotubes (CNTs) by microwave plasma enhanced chemical vapor deposition process has been investigated. Microwave plasma was characterized in-situ using optical emission spectrometer. Morphology of the films was examined by scanning electron microscopy. Structural analysis was carried out by high resolution transmission electron microscopy (HRTEM) equipped with energy dispersive X-ray spectroscopy (EDS) and micro-diffraction attachments. It is found that oxide films without H2 plasma pretreatment or treated for lesser time resulted in CNT films with high percentage of carbonaceous particles and with embedded particles/nanorods distributed discontinuously in the cavity of the nanotubes. The embedded particles were found to be of iron carbide (Fe-C) as confirmed by HRTEM, EDS and micro-diffraction analysis. Experimental observations suggested that the iron oxide particles had poor catalytic action for CNT growth and in-situ reduction of oxide clusters to Fe by hydrogen plasma plays a key role in discontinuous filling of the nanotubes by the catalytic particles.

The Influences of H2Plasma Pretreatment on the Growth of Vertically Aligned Carbon Nanotubes by Microwave Plasma Chemical Vapor Deposition

The effects of H2flow rate during plasma pretreatment on synthesizing the multiwalled carbon nanotubes (MWCNTs) by using the microwave plasma chemical vapor deposition are investigated in this study. A H2and CH4gas mixture with a 9:1 ratio was used as a precursor for the synthesis of MWCNT on Ni-coated TaN/Si(100) substrates. The structure and composition of Ni catalyst nanoparticles were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The present findings showed that denser Ni catalyst nanoparticles and more vertically aligned MWCNTs could be effectively achieved at higher flow rates. From Raman results, we found that the intensity ratio of G and D bands (ID/IG) decreases with an increasing flow rate. In addition, TEM results suggest that H2plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles. As a result, the pretreatment plays a crucial role in modifying the obtained MWCNTs structures.

Analysis of Oxidation State of Multilayered Catalyst Thin Films for Carbon Nanotube Growth Using Plasma-Enhanced Chemical Vapor Deposition

We synthesized vertically aligned carbon nanotubes (CNTs) using multilayered catalyst thin films (Fe/Al2O3 and Al2O3/Fe/Al2O3) by RF (13.56 MHz) CH4/H2/Ar plasma-enhanced chemical vapor deposition. Pretreatment of the catalyst is crucial for CNT growth. In this paper, we analyzed the effect of catalyst reduction on CNT growth. Catalyst thin films on substrates were reduced by H2 plasma pretreatment at 550 °C to form nanometer-sized catalyst particles. The multilayered thin films were analyzed; the chemical composition and oxidation state by X-ray photoelectron spectroscopy (XPS) and the surface morphology by scanning electron microscopy (SEM). The Fe 2p peak of the XPS spectra showed that FexOy in the as-deposited catalyst was effectively reduced to Fe by a pretreatment of duration 4 min. Using this catalyst, we obtained CNTs with an average diameter of 10.7 nm and an average length of 5.3 µm. However, pretreatment longer than 4 min resulted in shorter CNTs and the Fe peak was shifted from Fe to Fe3O4. These transitions (Fe2O3→Fe3O4→Fe→Fe3O4) can be explained by the enthalpy of the oxides. This result indicates the presence of an optimum ratio between Fe and FexOy to maximize the CNT lengths.

On the effect of the substrate pretreatment parameters on the composition and structure of plasma deposited SiO2 thin films

The role of the substrate pretreatment using wet and dry cleaning procedures, on SiO2 thin film adhesion, integrity and composition was investigated. The SiO2 depositions were performed in a 27.12 MHz RF plasma reactor and an interelectrode space of 20 mm. The depositions were carried out on different substrates (magnesium, aluminum and c-Si) and at the low temperature of 100 °C. From the wet cleaning methods the use of 5 % HF aqueous solution was found to significantly improve the SiO2 thin film adhesion in all substrates. Even better results were achieved with the application of H2 plasma pretreatment, indicating that the etching during the plasma pretreatment results to better conditions for the film growth and the surface step coverage, especially on non-uniform and rough substrates.

Rapid Thermal Annealing Treatment of Electroplated Cu Films

Cu seed layers for copper electroplating were deposited by magnetron sputtering on silicon wafers using TaN as diffusion barriers between the seed layer and silicon. The Cu seed layer was cleaned with a H2 plasma prior to electroplating the copper film, and the effects of the H2 plasma pretreatment were investigated. After thin copper films were grown by electrodeposition on the copper seed layers which had been cleaned with the H2 plasma, they were then subjected to i) vacuum annealing, ii) rapid thermal annealing (RTA) and iii) rapid thermal nitriding (RTN) at various temperatures over different periods of time. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and resistivity measurements were done to ascertain the optimum heat treatment conditions for obtaining films with minimum resistivity and with smooth, predominantly (111)-oriented surfaces. The as-deposited film had a resistivity of ∼6.3 μΩ-cm and a relatively small intensity ratio of the (111) to the (200) peak. With heat treatment, the resistivity decreased and the (111) peak became dominant. In addition, the surface smoothness of the copper film was improved. The optimal condition (with a resistivity of 1.98 μΩ-cm) is suggested to be rapid thermal nitriding at 400 ◦C.

Enhancement of the film growth rate by promoting iodine adsorption in the catalyst-enhanced chemical vapor deposition of Cu

The effect of H2 plasma pretreatment on the growth rate of films in the catalyst-enhanced chemical vapor deposition of Cu is presented. Cu(I) hexafluoroacetylacetonate-vinyltrimethylsilane [Cu(I)(hfac)(vtms)] and ethyl iodide (C2H5I) were used as a Cu precursor and a chemical source of iodine, respectively. Before adsorbing iodine onto the sputtered Cu seed layer, a pretreatment with H2 plasma promoted the adsorption of iodine. In addition, the Cu film growth rate was almost linearly enhanced with the surface concentration of the iodine adatom. The increment of the surface concentration of the iodine adatom was confirmed by secondary ion mass spectroscopy analysis. The iodine adatoms were not buried during the Cu deposition, but most of them continuously floated out to the film surface. Thus, the iodine on the surface of the Cu seed layer retained its catalytic effect until the film deposition finished. As a result, the H2 plasma pretreatment performed on the Cu seed layer prior to adsorbing iodine enhances the Cu film growth rate and improves the film qualities, such as electrical resistivity and surface smoothness, by promoting iodine adsorption.