Direct Plasma-enhanced Chemical Vapor Deposition Research Articles

Ultrasensitive Biochemical Sensing Platform Enabled by Directly Grown Graphene on Insulator.

To fabricate label-free and rapid-resulting semiconducting biosensor devices incorporating graphene, it is pertinent to directly grow uniform graphene films on technologically important dielectric and semiconducting substrates. However, it has long been intuitively believed that the nonideal disordered structures formed during direct growth, and the resulted inferior electrical properties will inevitably lead to deteriorated sensing performance. Here, graphene biosensor chips are constructed based on direct plasma-enhanced chemical vapor deposition (PECVD) grown graphene on a 4-inch silicon wafer with excellent film uniformity and high yield. To surprise, optimal operations of graphene biosensors permit ultrasensitive detection of SARS-CoV-2 virus nucleocapsid protein with dilutions down to sub-femtomolar concentrations. Such impressive limit of detection (LOD) is comparable to or even outperforms that of the state-of-the-art biosensor devices based on high-quality graphene. Further noise spectral characterizations and analysis confirms that the LOD is limited by molecular diffusion and/or known interference signals such as drift and instability of the sensors, rather than the electrical merits of the graphene devices along. Hence, result sheds light on processing directly grown PECVD graphene into high-performance sensor devices with important economic benefits and social significance.

Direct Plasma‐Enhanced‐Chemical‐Vapor‐Deposition Syntheses of Vertically Oriented Graphene Films on Functional Insulating Substrates for Wide‐Range Applications

AbstractGraphene has inspired wide‐range research interests and practical applications due to its intriguing materials properties and versatile application prospects. Specifically, vertically oriented graphene (VG) constructed by vertically aligned nanosheets emerges as a unique material type, usually achieved through a plasma‐enhanced chemical vapor deposition (PECVD) route. The VG films possess abundant exposed active edges, large surface areas, relatively high electrical conductivity, and excellent thermal property in both in‐plane and out‐of‐plane directions. Direct synthesizing of such VG films on various functional substrates enables their transfer‐free integrations and direct applications in thermal management, sensing, energy storage and conversion, etc. In this review article, it is planned to showcase the recent advances in direct PECVD growth of VG films on some novel functional insulating substrates (e.g., glass, functional ceramics), mainly in terms of improving the electrical conductivity, enhancing the interfacial adhesion, and graphene growth orientation modulation. Meanwhile, the applications of the PECVD‐derived products in various new fields will also be discussed, such as photothermal conversion, switchable windows, light attenuation in photography, transparent heating, and thermal management for high‐power devices. Finally, current challenges and future opportunities will also be presented regarding controllable syntheses of high‐quality VG films and practical application explorations in different fields.

Universal interface and defect engineering dual-strategy for graphene-oxide heterostructures toward promoted Li–S chemistry

Li–S battery is broadly regarded as one of the most promising energy storage systems due to its prominent merits in energy density and theoretical capacity. Nevertheless, existing challenges such as formidable shuttle effect and sluggish redox kinetics hinder its practical application. Herein, we propose a universal interface and defect engineering dual-strategy to design graphene-oxide (G-oxide) hybrids as heterostructured electrocatalysts targeting promoted Li–S chemistry. The employment of direct plasma-enhanced chemical vapor deposition technique allows the in situ formation of graphene over a suite of oxide powders. Benefiting from the creation of heterointerface and carbon/oxygen defects, G-oxide realizes balanced management of polysulfide adsorption, lithium-ion migration and electron transportation, accordingly rendering bi-directional electrocatalysis behaviors for the sulfur conversion. Thus-assembled S/G-oxide cathode affords stable cycling performances even under a sulfur loading of 8.1 mg cm−2 and an electrolyte usage of 4.0 μL mg–1S.

Enhancement for Potential-Induced Degradation Resistance of Crystalline Silicon Solar Cells via Anti-Reflection Coating by Industrial PECVD Methods

The issue of potential-induced degradation (PID) has gained more concerns due to causing the catastrophic failures in photovoltaic (PV) modules. One of the approaches to diminish PID is to modify the anti-reflection coating (ARC) layer upon the front surface of crystalline silicon solar cells. Here, we focus on the modification of ARC films to realize PID-free step-by-step through three delicate experiments. Firstly, the ARC films deposited by direct plasma enhanced chemical vapor deposition (PECVD) and by indirect PECVD were investigated. The results showed that the efficiency degradation of solar cells by indirect PECVD method is up to −33.82%, which is out of the IEC 62804 standard and is significantly more severe than by the direct PECVD method (−0.82%). Next, the performance of PID-resist for the solar cell via indirect PECVD was improved significantly (PID reduced from −31.82% to −2.79%) by a pre-oxidation step, which not only meets the standard but also has higher throughput than direct PECVD. Lastly, we applied a novel PECVD technology, called the pulsed-plasma (PP) PECVD method, to deal with the PID issue. The results of the HF-etching rate test and FTIR measurement indicated the films deposited by PP PECVD have higher potential against PID in consideration of less oxygen content in this film. That demonstrated the film properties were changed by applied a new control of freedom, i.e., PP method. In addition, the 96 h PID result of the integrated PP method was only −2.07%, which was comparable to that of the integrated traditional CP method. In summary, we proposed three effective or potential approaches to eliminate the PID issue, and all approaches satisfied the IEC 62804 standard of less than 5% power loss in PV modules.

In-situ PECVD-enabled graphene-V2O3 hybrid host for lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have been regarded as promising candidates for current energy-storage technologies due to their remarkable advantages in energy density and theoretical capacity. However, one of the daunting challenges remained for advanced Li–S systems thus far deals with the synchronous suppression of polysulfide (LiPS) shuttle and acceleration of redox kinetics. Herein, a cooperative interface bridging adsorptive V2O3 and conductive graphene is constructed in-situ by virtue of direct plasma-enhanced chemical vapor deposition (PECVD), resulting in the design of a novel V2O3-graphene hybrid host to synergize the LiPS entrapment and conversion. The redox kinetics and electrochemical performances of thus-derived cathodes were accordingly enhanced owing to the smooth adsorption-diffusion-conversion of LiPSs even at a sulfur mass loading of 3.7 mg cm–2. Such interfacial engineering offers us a valuable opportunity to gain insight into the comprehensive regulation of LiPS anchoring ability, electrical conductivity and ion diffusive capability in hybrid hosts on suppressing the LiPS shuttle and propelling the redox kinetics. Our devised PECVD route might pave a new route toward the facial and economic design of hetero-phased multi-functional hosts for high-performance Li–S systems.

FORMATION OF NANO STRUCTURES IN RESULT OF HOMOGENOUS NUCLEATION OF CARBON OBTAINED IN THERMAL PLASMA UNDER ATMOSPHERIC PRESSURE

Thermal plasma processing of carbon sources using a plasma jet with high heat capacity is one of the most promising methods for the synthesis of new materials. This paper describes the low-temperature deposition of carbon nanomaterials by remote plasma-enhanced chemical vapor deposition (PECVD) in the absence of catalysts. The remote PECVD process differs from conventional and direct PECVD process in two ways: (a) only a subset of the process reactants and/or diluents are directly plasma excited; and (b) thin film deposition takes place on a substrate that is outside of the plasma glow region. In conventional CVD methods, carbon is produced from the decomposition of carbon sources such as hydrocarbons, carbon monoxide, alcohols, and so on, over a metal catalyst. The unavoidable metal species remaining in carbon nanomaterials would lead to obvious disadvantages for property characterization and application exploration. Despite sustained efforts, it is still an intractable problem to remove metal catalysts completely from carbon nanomaterials samples without introducing defects and contaminations. Good reactor design allowed to overcome problems of chemical and structural purity, and poor process robustness in terms of phase composition of product from run to run. For the synthesis of graphene materials, carbon black, carbon nanotubes, nanowires we used the thermal plasma generator which is a high current divergent anode-channel DC plasma torch. The experiment involved a simultaneous input of hydrocarbons (methane, propane, butane, acetylene) with the plasma forming gas (helium, argon, nitrogen) into the plasma torch, wherein heating and decompositions occurred in the plasma jet and in the region of the arc discharge, followed by condensation of the synthesis product on metallic surfaces. The deposition rate was varied with distance from the plasma. Consumption of carbon source, plasma forming gas and plasma torch power were changed independently from each other. For the experimental conditions the electric power of plasma torch was set up to 40 kW. Regularities of formation of carbon thread-like nanostructures and graphene in the course of hydrocarbons pyrolysis in thermal plasma without participation of catalytic particles were studied by means of electron microscopy, X-ray diffraction, IR-spectrometry and thermogravimetry. Depending on the pyrolytic synthesis parameters, different proportions of crystal carbon and soot may be obtained. It has been demonstrated that the phase composition is varied by hydrocarbons flow rate, plasma forming gas pressure and dc plasma torch power. It has been established through the experiments that carbon nucleation is volumetric and proceeds according to the model of explosive soot formation.

Recent Research Progress of Carbon Nanotube Arrays Prepared by Plasma Enhanced Chemical Vapor Deposition Method

Preparing carbon nanotube (CNT) arrays by plasma enhanced chemical vapor deposition (PECVD) method can dramatically reduce the deposition temperature, which makes it possible for in-situ fabrication of CNT-based nanoelectronic devices. In this paper, up to date research progress of CNT arrays prepared by PECVD method was presented, including radio frequency PECVD, direct current PECVD and microwave PECVD. Then, morphology and quality of CNT arrays were compared. In the end, we analyzed the possible challenges encountered through CNT array preparation by PECVD method at the moment and in the future.

Minority Carrier Recombination Properties of Crystalline Defect on Silicon Surface Induced by Plasma Enhanced Chemical Vapor Deposition

This research investigates the carrier recombination properties of a crystalline defect layer introduced by the plasma enhanced chemical vapor deposition (PECVD) process of amorphous hydrogenated silicon nitride (SiNx) passivation films. A direct PECVD technique was used for SiNx films deposition. A crystalline defect layer existed on the surface of the silicon substrate and is under the SiNx passivation film. The recombination lifetime in this defect layer was obtained by focusing on the thickness of the defect layer and the effective lifetime before and after the defect layer etching. After etching a few nanometer thickness, effective lifetime drastically increased. On the other hands, the carrier recombination center could be electrically inactivated by 600°C annealing after SiNx deposition. According to the depth profile of effective lifetime, it was clarified the high carrier recombination region were concentrated near the surface of silicon substrate.

Direct PECVD growth of vertically erected graphene walls on dielectric substrates as excellent multifunctional electrodes

A novel uniform multi-level matrix of vertically erected graphene walls is directly grown on a dielectric substrate by plasma enhanced chemical vapor deposition (PECVD) at 900 °C without the presence of any catalyst and post-transfer treatment. Such a two-level structure is composed of continuous vertically erected graphene sheets (the second level) on a nanocrystalline graphene film (the first level). A nanocrystalline film is formed in the first stage (<15 min), and the graphene walls initialize on the boundary C sp3 atoms as nucleation centers to grow the erected graphene walls as the second-level component. The microstructure of the graphene walls can be modified by plasma power, growth time and seed layer coating. The unique three-dimensional graphene structure possessed high hydrophobicity (contact angle: 141°), outstanding electron conductivity (sheet resistance: 198 Ω sq−1), and tunable transparency (91.9–38.0% at 550 nm). The three-dimensional structure enables the graphene to act as an excellent electron transport network with high surface area in many aspects. The highly conductive graphene walls were used as the counter electrode of dye-sensitized solar cells (DSSC) with a photovoltaic efficiency of 6.01%, comparable to FTO-based DSSCs (6.10%). This in situ one-step growth indicates the great potential to fabricate excellent electrodes for photovoltaic and electronic applications.

Visible photoluminescence from silicon-incorporated diamond like carbon films synthesized via direct current PECVD technique

Silicon-incorporated diamond like carbon (Si-DLC) films were deposited via DC plasma-enhanced chemical vapor deposition (PECVD) on glass and alumina substrates at a substrate temperature of 473 K. The precursor gas used was acetylene and for silicon incorporation tetraethyl orthosilicate dissolved in methanol was used. Silicon atomic percentage in the films was varied from 0% to 19.3% as measured from energy dispersive X-ray analysis. Fourier transformed infrared spectroscopy studies depicted the presence of Si–C, Si–H and Si–H 2 bonding within the films. The binding energies of C 1s, Si 2s and Si 2p were determined from X-ray photoelectron spectroscopic studies. UV–vis–NIR spectroscopic studies were used to determine the optical gaps as well as the Urbach parameters of the samples. Room temperature photoluminescence study showed a broad peak centered at around 467 nm. Also the peak intensity was found to increase monotonically with Si percentages. The results are discussed in terms of the electronic structure of a-C:H, the doping induced defect states and the enhanced carbon dangling bonds via the formation of more sp 3 hybridized carbon network.

Study of silicon-silicon nitride interface properties on planar (1 0 0), planar (1 1 1) and textured surfaces using deep-level transient spectroscopy

Deep-level transient spectroscopy (DLTS) has been applied to metal–insulator–semiconductor (MIS) capacitors fabricated on planar (1 0 0), planar (1 1 1) orientations and textured n-type silicon wafers. Low frequency direct plasma-enhanced chemical vapour deposition Si–SiNx interface properties with and without plasma NH3 pre-treatment, with and without rapid thermal annealing (RTA) have been investigated. It is shown that three different kinds of defect states are identified at the Si–SiNx interface. For the planar (1 0 0) surface, samples with plasma NH3 pre-treatment plus RTA show the lowest DLTS signals, which suggests the lowest overall interface states density. For planar (1 1 1) Si surfaces, plasma NH3 pre-treatment and RTA yield a small improvement. With the textured surface, the RTA step improves the surface passivation quality further but no obvious impact is found with plasma NH3 pre-treatment. Energy-dependent electron capture cross sections were also measured by small-pulse DLTS. The capture cross sections depend strongly on the energy level and decrease towards the conduction band edge.

Latest innovations in large area web coating technology via plasma enhanced chemical vapor deposition source technology

In this article, the authors discuss the latest results of our development of large area plasma enhanced chemical vapor deposition (PECVD) source technologies for flexible substrates. A significant challenge is the economical application of thin films for use as vapor barriers, transparent conductive oxides, and optical interference thin films. Here at General Plasma the authors have developed two innovative PECVD source technologies that provide an economical alternative to low temperature sputtering technologies and enable some thin film materials not accessible by sputtering. The Penning Discharge Plasma (PDP™) source is designed for high rate direct PECVD deposition on insulating, temperature sensitive web [J. Modocks, Proceedings of the Society of Vacuum Coaters, 2003 (unpublished), p. 187]. This technology has been utilized to deposit SiO2 and SiC:H for barrier applications [V. Shamamian et al. Proceedings of the Flexible Displays and Manufacturing Conferrence, 2006 (unpublished)]. The Plasma Beam Source (PBS™) is a remote plasma source that is more versatile for deposition on not only insulating flexible substrates but also conductive or rigid substrates for deposition of thin films that are sensitive to the high ion bombardment flux inherent to the PDP™ technology. The authors have developed PBS thin film processes in our laboratory for deposition of SiO2, SiC:O, SiN:C, SiN:H, ZnO, FeOx, and Al2O3. [M. A. George, Conference Proceedings of the Association of Industrial Metallizers, Coaters, and Laminators (AIMCAL), 2007 (unpublished)]. The authors discuss the design of the patented sources, plasma physics, and chemistry of the deposited thin films.

Growth mechanism of nanocrystalline silicon at the phase transition and its application in thin film solar cells

Nanocrystalline (or microcrystalline) silicon (nc-Si:H or μc-Si:H) is an absorber material that is crucial for obtaining thin film silicon tandem solar cells with high efficiency. This material is conventionally produced by direct plasma-enhanced chemical vapor deposition (PECVD), which is based on the dissociation of silane (SiH 4) and hydrogen (H 2) in a radiofrequency (rf) plasma. During the last few decades, the plasma deposition parameter regime has been explored intensively, in particular to improve the quality of nc-Si:H and to increase its deposition rate. The desired formation of nanocrystallites occurs under growth conditions close to the transition regime. A technique that is not plasma based is hot-wire CVD (HWCVD), which is based on catalytic decomposition of SiH 4 and dissociation of H 2 gases on a hot filament. Because source gases are catalytically decomposed, the method is often referred to as catalytic CVD (Cat-CVD). The HWCVD technique has been shown to be a viable method for the deposition of silicon-based thin films and solar cells. We discuss the progress at our laboratory. Specifically, recent single junction and multijunction n–i–p-type solar cells are highlighted. Improvements have been achieved by addressing, among others, the morphology of the light-scattering rough surfaces, to avoid cavities and shunting paths, and by studying the structural evolution of the nanocrystalline phase during growth. The obtained solar cells are highly stable against light soaking.

High Electron Mobility (˜150 cm2/Vs) PECVD Nanocrystalline Silicon Top-Gate TFTs at 260 °C

AbstractUndoped nanocrystalline silicon (nc-Si:H) films were prepared by conventional 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) at 260 °C, using highly H2-diluted SiH4 plasma. The nc-Si:H films were evaluated using electrical, structural, and chemical measurements. The optimized nc-Si:H film showed an oxygen concentration (CO) of ˜1.5 X 1017 at./cm3 and a dark conductivity (σD) of ˜10-6 S/cm, while the Raman crystalline volume fraction (XC) was ˜85 %. Top-gate staggered TFTs with a ˜100 nm nc-Si:H channel layer and an amorphous silicon oxide (a-SiOx) as the gate dielectric were fabricated. The TFTs showed a field effect mobility (μFE) of ˜150 cm2/Vs, a threshold voltage (VT) of ˜2 V, a subthreshold slope (S) of ˜0.25 V/dec, and an ON/OFF current ratio more than 106. To the best of our knowledge, the TFT mobility reported here is the highest achieved to date using state-of-the-art nc-Si:H films prepared by direct PECVD.

Nanocomposite Low-k SiCOH Films by Direct PECVD Using Vinyltrimethylsilane

Vinyltrimethylsilane (VTMS) was used as a precursor for the deposition of SiCOH films by direct and remote plasma-enhanced chemical vapor deposition (PECVD). Film property was compared with films prepared with tetramethylsilane (4MS). As-deposited films and the films annealed at 450°C have been characterized. The growth rate decreased with increasing substrate temperature and increased with increasing ratio and plasma power. The dielectric constant was inversely proportional to the relative carbon content and the film deposited with VTMS had higher carbon content. The refractive index of the as-deposited films with VTMS was about 1.46-1.44 and decreased to 1.40 after annealing. The reduction of the refractive index seemed to be due to the lower density and increased porosity of the film. After annealing, the film formed with VTMS showed lower dielectric constant than the film with 4MS. It is believed that a thermally unstable phase in the film was formed more favorably with vinyl groups in VTMS, and the desorption of the unstable phase during postannealing process makes additional nanopores in the film. The SiCOH films from VTMS showed a low dielectric constant of 2.0 at an optimum condition. © 2004 The Electrochemical Society. All rights reserved.

Low-temperature thermal oxide to plasma-enhanced chemical vapor deposition oxide wafer bonding for thin-film transfer application

Low-temperature direct plasma-enhanced chemical vapor deposition (PECVD) oxide to thermal oxide bonding is described. The PECVD oxide is densified at 350 °C and chemical-mechanically polished to obtain reasonably smooth surface for bonding. The PECVD oxide wafer is bonded to the thermal oxide wafer at room temperature after piranha clean that leaves the wafer surfaces hydrophilic. A postbonding anneal at 300 °C completes the bonding. A void-free bonding interface is observed from infrared imaging and the bonding strength is estimated to be 432 mJ/m2. This bonding method can be used in a variety of applications, including three-dimensional integration.

Highest-quality surface passivation of low-resistivity p-type silicon using stoichiometric PECVD silicon nitride

The surface passivation properties of silicon nitride (SiN) films fabricated by high-frequency direct plasma-enhanced chemical vapour deposition (PECVD) on low-resistivity (1 Ω cm) p-type silicon solar cell substrates have been investigated. The process gases used were ammonia and a mixture of silane and nitrogen. In order to find the optimum set of SiN deposition parameters, a large number of carrier lifetime test structures were prepared under different deposition conditions. The optimised deposition parameters resulted in outstandingly low surface recombination velocities (SRVs) below 10 cm/s. Interestingly, we find the lowest SRVs for stoichiometric SiN films, as indicated by a refractive index of 1.9. In former studies similarly low SRVs had only been obtained for silicon-rich SiN films. The fundamentally different passivation behaviour of our SiN films is attributed to the addition of nitrogen to the process gases.

Thick SiOxNy and SiO2 films obtained by PECVD technique at low temperatures

In this work we present the results on the fabrication of thick silicon oxynitride and dioxide films deposited by conventional r.f. direct plasma enhanced chemical vapor deposition (DPECVD), at temperature as low as 320°C and from (N2O+SiH4) gaseous mixtures. The samples were characterized by profile measurements, ellipsometry measurements, etching rate, Fourier transform infrared spectroscopy (FTIR), and by scanning electron microscopy (SEM). The results show that for appropriate N2O/SiH4 flow ratio and SiH4 flow, it is possible to obtain very thick SiO2 and SiOxNy films (up to ∼10 μm) at high deposition rates (∼3 μm/h) and preserving the compositional and structural properties of similar high quality thin films obtained in a previous work (I. Pereyra, M.I. Alayo, J. Non-Cryst. Solids 212 (1997) 225). These thick SiO2 and SiOxNy films, exhibit a very well controlled refractive index, in a short range between ∼1.43 and ∼1.53, which is very attractive to SiO2/SiOxNy based waveguide fabrication. Besides the large thickness, the results show that the films present an etching rate just twice the thermally grown SiO2 rate, therefore lower than the reported values for PECVD SiO2 by other authors (M.S. Haque, H.A. Naseem, W.D. Brown, J. Electrochem. Soc. 142 (1995) 3864). Also etching experiments were performed using reactive ion etching (RIE) equipment on thick silicon oxynitride film grown onto silicon substrates covered by a thick DPECVD SiO2 buffer layer, in order to simulate a waveguide structure (ridge type) fabrication. The results of these tests show that it is possible to define vertical walls in these thick SiOxNy films, which is very important for ridge type waveguides.

High-efficiency polycrystalline silicon film solar cells

High-efficiency polycrystalline silicon film solar cells are fabricated using gettering and low-temperature plasma-enhanced chemical vapor deposition (PECVD) passivation schemes. Thin layers (∼10 nm) of PECVD SiO 2 are used to passivate the emitter of the solar cell, while direct hydrogen rf plasma and PECVD silicon nitride (Si 3N 4) are implemented to provide emitter and bulk passivation of the cells. The combination of Al and POCl 3 gettering is found to be very effective in improving the minority carrier diffusion length of the polycrystalline silicon film wafers and consequently, the efficiency of the solar cells. It is shown in this work that hydrogen rf plasma treatments can significantly improve the solar cell's blue and long wavelength responses when performed through a thin layer of PECVD Si 3N 4. A very high efficiency for Si-supported film of 15.2% on 1 cm 2 area has been achieved using a simple solar cell process with Al/POCl 3 gettering and low-temperature passivation.

High efficiency polycrystalline silicon solar cells using low temperature PECVD process

Conventionally directionally solidified (DS) and silicon film (SF) polycrystalline silicon solar cells are fabricated using gettering and low temperature plasma enhanced chemical vapor deposition (PECVD) passivation. Thin layer (/spl sim/10 nm) of PECVD SiO/sub 2/ is used to passivate the emitter of the solar cell, while direct hydrogen rf plasma and PECVD silicon nitride (Si/sub 3/N/sub 4/) are implemented to provide emitter and bulk passivation. It is found in this work that hydrogen rf plasma can significantly improve the solar cell blue and long wavelength responses when it is performed through a thin layer of PECVD Si/sub 3/N/sub 4/. High efficiency DS and SF polycrystalline silicon solar cells have been achieved using a simple solar cell process with uniform emitter, Al/POCl/sub 3/ gettering, hydrogen rf plasma/PECVD Si/sub 3/N/sub 4/ and PECVD SiO/sub 2/ passivation. On the other hand, a comprehensive experimental study of the characteristics of the PECVD Si/sub 3/N/sub 4/ layer and its role in improving the efficiency of polycrystalline silicon solar cells is carried out in this paper. For the polycrystalline silicon used in this investigation, it is found that the PECVD Si/sub 3/N/sub 4/ layer doesn't provide a sufficient cap for the out diffusion of hydrogen at temperatures higher than 500/spl deg/C. Low temperature (/spl les/400/spl deg/C) annealing of the PECVD Si/sub 3/N/sub 4/ provides efficient hydrogen bulk passivation, while higher temperature annealing relaxes the deposition induced stress and improves mainly the short wavelength (blue) response of the solar cells.