Plasma Enhanced Chemical Vapor Deposition Research Articles

Breakdown voltage and TDDB performance improvement by optimizing the PECVD dielectric film characteristics in MIM capacitors

The dielectric breakdown voltage (BV) and time dependent dielectric breakdown (TDDB) are the most important concerns for device reliability. In this study, the silicon nitride (SiNx) used as metal-insulator-metal (MIM) capacitor dielectric was successfully prepared by a dual-frequency plasma enhanced chemical vapor deposition (PECVD) method. Fourier transform infrared (FTIR) absorption spectra and electrical characterization results suggest that the SiNx film possesses higher dielectric breakdown voltage performance by decreasing SiH4/NH3 gas flow ratio or optimizing the interface layer among multiple layers. Similarly, the TDDB reliability test based on Weibull distribution indicates an increase in failure lifetime of the MIM capacitors by adjusting RF power and NH3 gas flow.

The corrosion and tribological behaviors of DLC film in CO2 saturated NaCl solution with high Cl− concentration

The failure of pipelines during oil and gas exploitation is a pressing issue in the oil and gas industry. The high permeability of chloride ions (Cl−) alters the corrosion morphology of the N80 substrate and diminishes its ability to impede the penetration of corrosive substances. This study aims to deposit DLC films on the inner surface of N80 pipeline using plasma enhanced chemical vapor deposition (PECVD), and investigate the corrosion and friction behavior of DLC films in CO2 saturated NaCl solutions with varying Cl− concentrations. The results indicate that the change in Cl− concentration possess minimal impact on the DLC film. The corrosion current density of DLC films in CO2 saturated NaCl solution with three different Cl− concentrations is one order of magnitude lower than that of the N80 substrate. Moreover, a transfer film can still form in high-concentration CO2-saturated NaCl solutions, reducing wear. DLC film demonstrates exceptional stability, corrosion resistance, and wear resistance, making it an ideal material for safeguarding pipelines during oil and gas exploitation.

Difference in the structure and morphology of CVD diamond films grown on negatively charged and grounded substrate holders: Optical study

Microcrystalline diamond films were grown by plasma-enhanced chemical vapor deposition from a CH4/H2 gas mixture on Si single-crystalline substrates placed on negatively charged and grounded substrate holders. The obtained diamond films had the (100) predominant faceting of microcrystals. The film structure and morphology were analyzed by scanning electron microscopy, photoluminescence, Raman and FTIR spectroscopies. The main physical factor causing the difference in the structure of the diamond films grown on the grounded and charged substrate holders was found to be the flow of low-energy (up to 200 eV) Si+, N2+, H, O ions in the latter holder. These ions predominantly embedded into the structure of the diamond films grown on the charged substrate holder leading to appearance of residual mechanical stress up to 2 GPa. Ion bombardment led to increase in the volume fraction of non-diamond carbon component in the film grain boundaries, decrease in sp3-bonded carbon fraction and reduction of the diamond microcrystals lateral size. Larger amount of grain boundaries in the diamond films grown on the charged substrate holder promoted diffusion of Si atoms from the substrate to the plasma and growing film surface, inducing formation of SiV centers in the diamond microcrystals even in the 150…200 μm thick films. The concentration of Si-related defects was much smaller in the films grown using the grounded substrate holder. These films had substantially smaller volume fraction of graphite-like carbon in the grain boundaries and were more homogeneous.

Development of n-Type, Passivating Nanocrystalline Silicon Oxide Films via Plasma-Enhanced Chemical Vapor Deposition

Nanocrystalline silicon oxide (nc-SiOx:H) is a multipurpose material with varied applications in solar cells as a transparent front contact, intermediate reflector, back reflector layer, and even tunnel layer for passivating contacts, owing to the easy tailoring of its optical properties. In this work, we systematically investigate the influence of the gas mixture (SiH4, CO2, PH3, and H2), RF power, and process pressure on the optical, structural, and passivation properties of thin n-type nc-SiOx:H films prepared in an industrial, high-throughput, plasma-enhanced chemical vapor deposition (PECVD) reactor. We provide a detailed description of the n-type nc-SiOx:H material development using various structural and optical characterization techniques (scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Raman spectroscopy, and spectroscopic ellipsometry) with a focus on the relationship between the material properties and the passivation they provide to n-type c-Si wafers characterized by their effective carrier lifetime (τeff). Furthermore, we also outline the parameters to be kept in mind while developing different n-type nc-SiOx:H layers for different solar cell applications. We report a tunable optical gap (1.8–2.3 eV) for our n-type nc-SiOx:H films as well as excellent passivation properties with a τeff of up to 4.1 ms (implied open-circuit voltage (iVoc)~715 mV) before annealing. Oxygen content plays an important role in determining the crystallinity and hence passivation quality of the deposited nanocrystalline silicon oxide films.

Effect of etchant gases on the structure and properties of carbon nanofibers

The utilization of plasma-enhanced chemical vapor deposition (PECVD) for carbon nanofiber (CNF) growth using NH3 as the etchant gas has been extensively documented. Notably, NH3 serves a dual role by etching excess carbon and providing N heteroatoms. Most studies neglect to address this phenomenon, despite the well-known impact of N-doping on CNF properties. Furthermore, NH3 exhibits specific interactions with C2H2—it not only etches excess carbon, but also suppresses the dissociation of C2H2. The implications of this phenomenon on CNF micro- and macroscale morphology have not been comprehensively investigated. To elucidate the influence of etchant gases on CNF structure and properties, we fabricated two types of CNFs - N-doped CNFs (N-CNF) and undoped CNFs (U-CNF). Both were grown on identical substrates using the same carbon source (C2H2) but different etchants (NH3 and H2). Their microstructure and surface chemistry were analyzed using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Electrochemical properties were investigated using cyclic voltammetry (CV). U-CNFs were found to have a larger population density and a more disordered structure than N-CNFs. N-doping was confirmed in N-CNFs using XPS analysis, which also revealed differences in relative amounts of sp2 C and O functional groups. U-CNFs exhibited distinct electrochemical properties, including smaller pseudocapacitance, larger potential window, slower outer sphere redox (OSR) kinetics, and diminished dopamine sensitivity. Electrochemical differences were rationalized based on CNF structure and surface chemistry, which, in turn, were attributed to how different etchant gases influence the PECVD process.

Influence of the substrate conductivity type on the electroluminescence properties of PP+IN and PIN+N diodes based on amorphous silicon carbide (a-Si1-xCx:H) / crystalline silicon (c-Si) heterostructures

The study of the conduction and light emission mechanisms of PIN diodes based on amorphous silicon-carbide (a-Si1-xCx:H) thin film and crystalline silicon (c-Si) substrates is reported in this work. Using the same low-temperature process (200 °C), PP+IN and PIN+N structures were fabricated on p-type and n-type silicon (Si) substrates, respectively. The plasma enhanced chemical vapor deposition (PECVD) technique was employed for the active layers deposition where two different CH4/SiH4 flow rates ratios of 30 sccm/6 sccm and 30 sccm/1 sccm were used. All structures show red-orange light emission in forward bias (FB). The structures with the active layer deposited with a lower SiH4 flow rate, display light emission with a higher intensity at a lower voltage bias.In addition, we related the current-voltage measurements with different conduction models and the dominant charge transport mechanisms in the PIN structures were proposed. The highest Si content structures were related to Fowler-Nordheim (F-N) tunneling, because of its active layer with lower barrier height. On the other hand, the lowest Si content structures were associated with the Poole-Frenkel (P-F) emission, due to a higher density of defects in localized tail states. The results showed the same conduction and emission mechanisms for the PP+IN and PIN+N diodes with the same active layer, regardless of the conduction type of substrate, proving that it is feasible to use the same process for developing light emission devices on p-type and n-type Si substrates.

Effect of Gas Flow Rate and Ratio on Structure and Properties of Nitrogen-Doped Diamond-like Carbon Films

Diamond-like carbon (DLC) has attracted much attention due to its unique properties such as high chemical inertness, optical transparency, and high biocompatibility. In this study, the total gas flow rate was kept constant, while the ratio of reactive gases was varied to deposit nitrogen-doped diamond-like carbon thin films on glass substrates using radiofrequency plasma-enhanced chemical vapor deposition. The effects of the gas flow ratio on the composition, microstructure, surface morphology, and optical properties of the thin films were investigated through extended deposition times. It was found that with an increase in the nitrogen-to-methane gas flow ratio, the film surface became smoother and more compact. The maximum transmittance in the visible range reached 90%, and the highest and lowest transmittance in the same ultraviolet wavelength region differed by up to 25.62% among several sample groups. The optical bandgap decreased from 3.58 eV to 3.46 eV, contrary to the trend of the sp2 fraction variation. Compared with other studies, this study considered the preparation of nitrogen-doped diamondoids using a chemical vapor deposition method with a lesser total gas flow rate passed into it, which provides practical data reference value for the preparation of N-DLC.

Optical characterization of inhomogeneity of polymer-like thin films arising in the initial phase of plasma-enhanced chemical vapor deposition

In this study, an optical investigation in a wide spectral range of polymer-like (SiOxCyHz) thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) is presented. The primary focus is on assessing the homogeneity of the grown films. Within the PECVD, it is possible to alter the properties of the deposited material by continually adjusting deposition process parameters and hence allow for the growth of inhomogeneous layers. However, as shown in this study, the growth of homogeneous layers could be similarly challenging. This challenge is especially pronounced at the beginning of the deposition process, where it is necessary to consider the influence of the substrate among other factors, as even slight variations in the deposition conditions can lead to the formation of inhomogeneous layers. Several series of polymer-like thin films were deposited onto silicon substrates with the goal of producing homogeneous layers, i.e. all deposition parameters were held constant. These samples were optically characterized with a special interest in homogeneity, especially at the beginning of the growth. It was found that initial inhomogeneous growth is always present. The thickness of the initial inhomogeneous part was found to be surprisingly large.

Tribocorrosion studies on DLC films with silver nanoparticles for prosthesis applications

Metals and their alloys are very important for orthopedic applications, and the basic requirements for a successful implant are chemical stability, mechanical behavior, and biocompatibility in body fluids and tissues. For prosthesis applications, the corrosion resistance of metals is one of the major prerequisites to avoid impairment of the material properties due to degradation. The combined action of corrosion and wear on the material is called tribocorrosion and DLC (Diamond-Like Carbon) films have been extensively studied to increase prosthesis biocompatibility and to protect from corrosion. Additionally, DLC coatings can prevent the prosthesis to release toxic elements due to plastic deformation and corrosion. This paper is about tribocorrosion studies on DLC and DLC-Ag (DLC containing silver nanoparticles) on Ti-6Al-4V substrates. These films were obtained by PECVD (Plasma Enhanced Chemical Vapor Deposition) using hexane as a precursor. The tribocorrosion behavior of uncoated and coated samples was investigated in the reciprocating mode in Ringer’s lactate solution. From the polarization test results, the protective efficiency of the film was calculated. Silver nanoparticles improved the corrosion resistance of the films. The protective efficiency was 15 and 19% for DLC and DLC-Ag films, respectively.

Gas-Phase Fabrication and Photocatalytic Activity of TiO2 and TiO2-CuO Nanoparticulate Thin Films.

CuO-loaded TiO2 nanomaterials have applications in pollutant degradation via photocatalysis. However, the existing methods of fabricating these nanomaterials involve liquid-phase processes, which require several steps and typically generate liquid waste. In this study, TiO2 and TiO2-CuO nanoparticulate thin films were successfully fabricated through a one-step gas-phase approach involving a combination of plasma-enhanced chemical vapor deposition and physical vapor deposition. The resulting films consisted of small, spherical TiO2 nanoparticles with observable CuO on the TiO2 surface. Upon annealing in air, the TiO2 nanoparticles were crystallized, and CuO was completely oxidized. The photocatalytic activity of TiO2-CuO/H2O2, when introduced into the rhodamine 6G degradation system, was substantially enhanced under both ultraviolet and visible light irradiation. Moreover, this study highlights the influence of pH on the photocatalytic activity; TiO2-CuO/H2O2 exhibited the highest photocatalytic activity at pH 13, with a reaction rate constant of 0.99 h-1 cm-2 after 180 min of visible light irradiation. These findings could facilitate the development of nanoparticulate thin films for enhanced pollutant degradation in wastewater treatment.

Revealing the mechanism of interfacial adhesion enhancement between the SiO2 film and the GaAs substrate via plasma pre-treatments

The formation mechanism of a highly adherent silicon dioxide (SiO2) film on gallium arsenide (GaAs) substrate by plasma enhanced chemical vapor deposition (PECVD) is proposed. Ar, N2, and NH3 were used as pre-treatment gas to improve the interfacial adhesion. The interfacial adhesion was measured by the cross-cut tape test. By the measurement of spectroscopic ellipsometry and x-ray photoelectron spectroscopy (XPS), it is revealed that nitrogen plasma pre-treatment had formed a very thin GaN transition layer on the surface, which was responsible for the improvement of interfacial adhesion. XPS depth-profiling further confirmed various pre-treatment gases generate plasma mixtures and form thin film layers with different compositions on the GaAs surface. These layers have a significant impact on the adhesion of the subsequently prepared SiO2 film. The primary mechanism for improving interfacial adhesion is the renovation of the substrate composition via plasma pre-treatment by PECVD, which forms a transition layer of nitrides that eliminates the negative effects of oxides on adhesion. This study reveals the mechanism of interfacial adhesion enhancement between SiO2 film and GaAs substrate, which is of significant importance in fabricating high-performance and reliable semiconductor devices.

Amorphous SiC Thin Films Deposited by Plasma-Enhanced Chemical Vapor Deposition for Passivation in Biomedical Devices.

Amorphous silicon carbide (a-SiC) is a wide-bandgap semiconductor with high robustness and biocompatibility, making it a promising material for applications in biomedical device passivation. a-SiC thin film deposition has been a subject of research for several decades with a variety of approaches investigated to achieve optimal properties for multiple applications, with an emphasis on properties relevant to biomedical devices in the past decade. This review summarizes the results of many optimization studies, identifying strategies that have been used to achieve desirable film properties and discussing the proposed physical interpretations. In addition, divergent results from studies are contrasted, with attempts to reconcile the results, while areas of uncertainty are highlighted.

Evaluation of Potential Occupational Exposure and Release of Nanoparticles in Semiconductor-Manufacturing Environments

Occupational exposure to airborne nanoparticles in semiconductor-manufacturing facilities is of growing concern. Currently, comprehensive information regarding atmospheric concentrations, potential origins, and the physical and chemical properties of nanoparticles in these industrial settings is lacking. This study investigated the occurrence of airborne nanoparticles within a semiconductor-research and -manufacturing facility, during both routine operation and maintenance activities. A Scanning Mobility Particle Sizer was used to monitor size-resolved airborne-nanoparticle number concentrations spanning the range of 6 to 220 nm. Breathing zone filter samples were also collected during maintenance processes and underwent subsequent analyses via Transmission Electron Microscopy and Inductively Coupled Plasma Mass Spectrometry, to discover the size, morphology, and chemical composition of the observed nanoparticles. The findings reveal low levels of airborne nanoparticles during routine operations, but maintenance tasks resulted in substantial concentration surges particularly for plasma-enhanced chemical vapor deposition tools with concentrations up to 11,800 particles/cm3. More than 80% of observed particles were smaller than 30 nm. These smallest particles were predominately composed of metals such as iron, nickel, and copper. Moreover, larger particles above 100 nm were also identified, comprising process-related materials such as silicon and indium. Comparative assessment against established mass-based exposure limits did not yield any exceedances. Current exposure limits do not typically consider size though, and the preponderance of small nanoparticles (<30 nm) would warrant a more size-differentiated exposure-risk assessment.

Key Aspects of p-Type TOPCon on Textured Surface for Silicon Bottom Cells in Tandem Devices

Both-sides TOPCon solar cells are an interesting candidate for a highly efficient and thermally robust Silicon (Si) bottom cell for tandem devices, such as Perovskite-Si solar cells. However, preparation of p-type TOPCon on a textured surface is necessary which is particularly challenging. This work aims to gain a deeper understanding of the limiting factors and thereby optimize the SiOx/poly-Si(p) contact to close the gap to its n-type counterpart. Using symmetrical lifetime samples, we first show that a high level of surface passivation can be achieved using thermally grown interfacial oxides of different thicknesses. The samples strongly benefit from an effective thermal activation of hydrogenation by means of fast-firing. Thus, a recombination current density J0s as low as 23.4 fA/cm² was achieved for p-type TOPCon on textured surface featuring an in situ Boron-doped poly-Si layer prepared by plasma enhanced chemical vapor deposition (PECVD). Moreover, we show that the passivation quality strongly depends on surface morphology. Smoothening the random pyramids’ valleys and – what is more – the tips has a positive impact on the surface passivation.

Plasma-Assisted N2O Oxidation (PANO) in an Industrial Direct Plasma Reactor for TOPCon Production

Plasma-Enhanced Chemical Vapor Deposition (PECVD) is an attractive tool for TOPCon production, as it enables uniformly in situ doped amorphous silicon (a-Si) and dielectric layer depositions with high throughput. However, a lean process requires in situ interfacial oxide growth in the same tool. In this work, we use Plasma-Assisted N2O Oxidation (PANO) in an industrial kHz direct plasma reactor (centrotherm c.PLASMA) to grow the oxide and deposit in situ phosphorus doped a-Si(n) as well as SiNx on asymmetric lifetime samples. Before optimization, the oxide thickness is non uniform on the wafer, and we show that it correlates with the passivation, the contact resistivity, and the doping profile in n-type TOPCon test structures. The passivation seems to benefit more from moderate in-diffusion in the case with PANO than in the case with thermal oxidation. This is probably due to enhanced field-effect passivation compensating for lower chemical passivation, which likely results from plasma-induced damage. After studying the influence of PANO process parameters on the oxide thickness and uniformity, we optimize them to obtain a non-uniformity as low as ±2% and a recombination current density down to 2.3 fA/cm² on planar wafers.

Improved wear and corrosion resistance of alumina alloy by MAO and PECVD

Aluminum alloys, which are vital in various industries, are susceptible to corrosion and wear. Although the micro-arc oxidation (MAO) method addresses these issues, it introduces microporosity, which undermines the integrity of the alloy. In this study, MAO coatings are enriched via plasma-enhanced chemical vapor deposition (PECVD) using hexamethyldisilane, specifically SiCOx and SiOx. The assessment of the mechanical, tribological, and corrosion-resistant characteristics of these composite coatings reveals substantial enhancements in the aluminum alloy properties post-PECVD treatment. Surface morphology observations highlight the reduced pore size and area of the PECVD-coated surfaces, particularly in SiCOx coatings, which are known for their superior gap-filling properties. Scratch tests demonstrate superior adhesion of SiCOx coatings, showed a higher scratch resistance of approximately 17.8 N compared to 15.9 N for SiOx coatings. The wear rate of the SiCOx coating significantly decreased compared to the MAO coating owing to higher hardness, dropping from 3.57 × 10−5 mm3/N·m to 2.04 × 10−5 mm3/N·m. SiCOx-coated surfaces show higher corrosion potential (−0.0078 V) than MAO-only coating (−0.0212 V), indicating enhanced corrosion resistance. These innovative coatings provide an advanced surface treatment strategy and are suitable for a wide range of industrial applications owing to their enhanced surface attributes.

Carbon nanotubes grown by plasma enhanced chemical vapor deposition of acetylene in the presence of water vapor

Carbon nanotubes can be synthesized using various techniques. This work aims to study the experimental process of growing carbon nanotubes via plasma-enhanced chemical vapor deposition (PECVD). Additionally, the study aims to calibrate the reactor and develop a LabVIEW code to introduce water into the process, enabling a water-assisted PECVD procedure. The obtained samples are evaluated through the analysis of SEM images and Raman spectra.

Ultrathin, Transferred Layers of Silicon Oxynitrides as Tunable Biofluid Barriers for Bioresorbable Electronic Systems.

Bio/ecoresorbable electronic systems create unique opportunities in implantable medical devices that serve a need over a finite time period and then disappear naturally to eliminate the need for extraction surgeries. A critical challenge in the development of this type of technology is in materials that can serve as thin, stable barriers to surrounding ground water or biofluids, yet ultimately dissolve completely to benign end products. This paper describes a class of inorganic material (silicon oxynitride, SiON) that can be formed in thin films by plasma-enhanced chemical vapor deposition for this purpose. In vitro studies suggest that SiON and its dissolution products are biocompatible, indicating the potential for its use in implantable devices. A facile process to fabricate flexible, wafer-scale multilayer films bypasses limitations associated with the mechanical fragility of inorganic thin films. Systematic computational, analytical, and experimental studies highlight the essential materials aspects. Demonstrations in wireless light-emitting diodes both in vitro and in vivo illustrate the practical use of these materials strategies. The ability to select degradation rates and water permeability through fine tuning of chemical compositions and thicknesses provides the opportunity to obtain a range of functional lifetimes to meet different application requirements.

Reactivity of the Ethenium Cation (C2H5+) with Ethyne (C2H2): A Combined Experimental and Theoretical Study.

The gas-phase reaction between the ethyl cation (C2H5+) and ethyne (C2H2) is re-investigated by measuring absolute reactive cross sections (CSs) and branching ratios (BRs) as a function of collision energy, in the thermal and hyperthermal energy range, via tandem-guided ion beam mass spectrometry under single collision conditions. Dissociative photoionization of C2H5Br using tuneable VUV radiation in the range 10.5-14.0 eV is employed to generate C2H5+, which has also allowed us to explore the impact of increasing (vibrational) excitation on the reactivity. Reactivity experiments are complemented by theoretical calculations, at the G4 level of theory, of the relative energies and structures of the most relevant stationary points on the reactive potential energy hypersurface (PES) and by mass-analyzed ion kinetic energy (MIKE) spectrometry experiments to probe the metastable decomposition from the [C4H7]+ PES and elucidate the underlying reaction mechanisms. Two main product channels have been identified at a centre-of-mass collision energy of ∼0.1 eV: (a) C3H3++CH4, with BR = 0.76±0.05 and (b) C4H5++H2, with BR = 0.22±0.02. A third channel giving C2H3+ in association with C2H4 is shown to emerge at both high internal excitation of C2H5+ and high collision energies. From CS measurements, energy-dependent total rate constants in the range 4.3×10-11-5.2×10-10 cm3·molecule-1·s-1 have been obtained. Theoretical calculations indicate that both channels stem from a common covalently bound intermediate, CH3CH2CHCH+, from which barrierless and exothermic pathways exist for the production of both cyclic c-C3H3+ and linear H2CCCH+ isomers of the main product channel. For the minor C4H5+ product, two isomers are energetically accessible: the three-member cyclic isomer c-C3H2(CH3)+ and the higher energy linear structure CH2CHCCH2+, but their formation requires multiple isomerization steps and passages via transition states lying only 0.11 eV below the reagents' energy, thus explaining the smaller BR. Results have implications for the modeling of hydrocarbon chemistry in the interstellar medium and the atmospheres of planets and satellites as well as in laboratory plasmas (e.g., plasma-enhanced chemical vapor deposition of carbon nanotubes and diamond-like carbon films).

Enhancement of the Silicon Nanocrystals’ Electronic Structure within a Silicon Carbide Matrix

Using plasma-enhanced chemical vapor deposition (PECVD), a mixed gas of silane (SiH4) and methane (CH4) was diluted with hydrogen (H2) to produce thin films of silicon nanocrystals embedded in a silicon carbide (SiC) matrix. This method prevents the co-deposition of SiH and SiC from high-temperature annealing procedures. This study experimentally explores the improvement of the electronic structure by adjusting two processing parameters according to classical nucleation theory (ratio of SiH4 to CH4 and working gas pressure). The deposited films were examined using ellipsometry spectroscopy, X-ray diffraction, scanning electron microscopy, atomic force microscopy, and photoluminescence to determine grain size, crystal volume fraction, topography, and bond configurations. The results show that increasing the working gas pressure can increase the density of SiC, while increasing the ratio of SiH4 to CH4 can only produce larger grain sizes. This is consistent with how SiC works and grows. Without using a high-temperature annealing procedure, this technique can improve the electrical structure of SiC contained in the SiC matrix formed by PECVD.