Coupled Plasma Chemical Vapor Deposition Research Articles

Strain‐Engineered Unified SiNx Deposition for Device Passivation and Capacitance Dielectric in GaN Monolithic Microwave Integrated Circuit

Silicon nitride (SiNx) is used for device passivation and capacitance dielectric in GaN monolithic microwave integrated circuits. However, this is a conflicting requirement as passivation requires SiNx to cause tensile strain, and capacitance dielectric primarily demands a high breakdown voltage and large dielectric constant for SiNx, leading to a damaged AlGaN surface during deposition. Two independent SiNx depositions under two different conditions (silicon‐ and nitrogen‐rich) are usually carried out to meet both requirements. Herein, a solution for a unified deposition through interfacial strain analysis on an AlGaN/GaN heterostructure grown on 6H‐SiC imposed by thin film silicon nitride (SiNx), deposited using inductively coupled plasma chemical vapor deposition system is proposed. The strain analysis is done using Raman spectroscopy. The surface morphology of the SiNx is studied using atomic force microscopy. The breakdown characteristics are ascertained from measurements on high electron mobility transistors and metal–insulator–metal capacitors.

Parylene-based stretchable neural electrodes with serpentine interconnects

Parylene C has rapidly gained popularity as a flexible and biocompatible material for next generation chronic probes. However, the mechanical strains attributed to the intracranial pressure and micromotion may compromise the longevity and biostability of implanted neural devices. To obtain conformable bioelectronic interfaces, it is essential to incorporate serpentine metal interconnects in flexible neural electrodes to achieve stretchability. In this paper, the influence of straight segments on the mechanical behavior of serpentine-shaped Parylene C probes has been investigated by finite element analysis. The etching performance of Parylene C with different masks are compared and the optimum masking material is the SiO2 film grown at a low temperature by inductively coupled plasma chemical vapor deposition (ICP-CVD). In vitro electrochemical measurements verify excellent electrode function with a low impedance of 13±0.4 kΩ at 1 kHz, which is beneficial for high-resolution neural recording.

Power-efficient programmable integrated multiport photonic interferometer in CMOS-compatible silicon nitride

Silicon nitride (SiN x ) is an appealing waveguide material choice for large-scale, high-performance photonic integrated circuits (PICs) due to its low optical loss. However, SiN x PICs require high electric power to realize optical reconfiguration via the weak thermo-optic effect, which limits their scalability in terms of device density and chip power dissipation. We report a 6-mode programmable interferometer PIC operating at the wavelength of 1550 nm on a CMOS-compatible low-temperature inductance coupled plasma chemical vapor deposition (ICP-CVD) silicon nitride platform. By employing suspended thermo-optic phase shifters, the PIC achieves 2× improvement in compactness and 10× enhancement in power efficiency compared to conventional devices. Reconfigurable 6-dimensional linear transformations are demonstrated including cyclic transformations and arbitrary unitary matrices. This work demonstrates the feasibility of fabricating power-efficient large-scale reconfigurable PICs on the low-temperature ICP-CVD silicon nitride platform.

Transfer-free preparation of flexible strain sensors using high quality VGNs

Recently, flexible mechanically stimulated sensors have attracted widespread attention in the field of wearable devices and soft robotics. Due to the high stretchability, vertical graphene nano-walls (VGNs) become a competitive candidate to be applied in the flexible strain sensors. Herein, by utilizing the inductively coupled plasma chemical vapor deposition (IC-PECVD) method, a transfer-free VGNs-based flexible strain sensors were successfully prepared on fluorphlogopite mica substrate at 600 ℃. The quality of as-grown VGNs were obviously improved by increasing the ratio of H2 to CH4. The directly prepared VGNs on interdigital electrode could improve the interfacial contact between VGNs and interdigital electrode. The results of bending tests show that flexible sensors which VGNs directly grown on the interdigital electrode have good performance. The combination of sleeves and the sensors reveal that the transfer-free flexible strain sensors could perform well in wearable devices.

Spiral-Driven Vertical Conductivity in Nanocrystalline Graphene.

The structure of graphene grown in chemical vapor deposition (CVD) is sensitive to the growth condition, particularly the substrate. The conventional growth of high-quality graphene via the Cu-catalyzed cracking of hydrocarbon species has been extensively studied; however, the direct growth on noncatalytic substrates, for practical applications of graphene such as current Si technologies, remains unexplored. In this study, nanocrystalline graphene (nc-G) spirals are produced on noncatalytic substrates by inductively coupled plasma CVD. The enhanced out-of-plane electrical conductivity is achieved by a spiral-driven continuous current pathway from bottom to top layer. Furthermore, some neighboring nc-G spirals exhibit a homogeneous electrical conductance, which is not common for stacked graphene structure. Klein-edge structure developed at the edge of nc-Gs, which can easily form covalent bonding, is thought to be responsible for the uniform conductance of nc-G aggregates. These results have important implications for practical applications of graphene with vertical conductivity realized through spiral structure.

Effect of Rapid Thermal Annealing on Si-Based Dielectric Films Grown by ICP-CVD.

Silicon nitride, silicon oxide, and silicon oxynitride thin films were deposited on the Si substrate by inductively coupled plasma chemical vapor deposition and annealed at 1100 °C for 3 min in an Ar environment. Silicon nitride and silicon oxide films deposited at ratios of the reactant flow rates of SiH4/N2 = 1.875 and SiH4/N2O = 3, respectively, were Si-rich, while Si excess for the oxynitride film (SiH4/N2/N2O = 3:2:2) was not found. Annealing resulted in a thickness decrease and structural transformation for SiOx and SiNx films. Nanocrystalline phases of Si as well as α- and β-Si3N4 were found in the annealed silicon nitride film. Compared to oxide and nitride films, the oxynitride film is the least susceptible to change during annealing. The relationship between the structure, composition, and optical properties of the Si-based films has been revealed. It has been shown that the calculated optical parameters (refractive index, extinction coefficient) reflect structural peculiarities of the as-deposited and annealed films.

Increased body fluid repellency and electrochemical corrosion resistance of intravascular stent materials by ICP-CVD-based DLC thin-film deposition

Intravascular stents face adhesion- and corrosion-based challenges causing In-stent Restenosis (ISR). This study analyzes the influences of thin-film Diamond-Like-Carbon (DLC) deposition on body fluid repellency and corrosion behavior in Simulated Body Fluid (SBF) at 37 °C for intravascular stent materials. The stent specimens of 316 L and 316 LVM stainless steel, Ti-Alloy, and CoCr-Alloy were coated with DLC thin-films by Inductively Coupled Plasma Chemical Vapor Deposition (ICP-CVD). The repellencies of bare and DLC-coated specimens to body fluids, including the blood, plasma, glycerol, and distilled water (DIW) were analyzed by their Contact Angles (CA). Electrochemical impedance spectroscopy (EIS) and corrosion analysis in simulated body fluid were conducted using a potentiostat system. Bare specimens exhibited hydrophilic behavior with 51° CA for distilled water and lower body fluid repellencies with 69°, 64°, and 57° CAs for total blood, blood plasma, and glycerol, respectively. DLC coating improved blood repellency to 88° CA and hydrophobic feature to 81° CA. The electrochemical corrosion analysis exhibited that ICP-CVD based DLC thin-film deposition increased the electrochemical polarization resistance of BMS specimens from 22.02 kΩ.cm2 to 386.6 kΩ.cm2 for 316 L SS, 408.8 kΩ.cm2 for 316 LVM SS, 1703.0 kΩ.cm2 for CoCr-Alloy, and 1748 kΩ.cm2 for Ti-Alloy. The obtained values reduced the corrosion rate from 447.1 μm/year to 0.241 μm/year and the mass loss rate from 357.1 mg/cm2year to 0.165 mg/cm2year. This study concludes that DLC thin-film structures can lower the risk of ISR by adhesion and corrosion inhibition in BMS specimens, and they have a potential application in fluid-repellent and anti-corrosive drug-free stents.

Synthesis of highly dense and multi-branched carbon nanowalls by two-step growth combining different plasma chemical vapor deposition methods

We report a novel structure of carbon nanowalls (CNWs) synthesized by a two-step growth method using a radical injection plasma-enhanced chemical vapor deposition (RI-PECVD) as combined with a capacitively coupled plasma chemical vapor deposition (CCP-CVD). Scanning electron microscopy (SEM) observation shows that the CNWs grown by this method exhibit a multi-branched morphology with an average wall distance of ∼20 nm and a density of ∼74 wall units/μm2, which is more than 5 times higher than that of CNWs synthesized by the single-step RI-PECVD method. These branched-CNWs are crystalline and comprised of multilayer graphene as confirmed by the Raman and high-resolution transmission electron microscopy (HRTEM) analyses. A static water contact angle of 150° was obtained for the multi-branched CNWs indicating a superhydrophobic property. A possible growth mechanism of the branched-CNWs was also proposed through the investigation of the time-dependent growth from the second step.

Green Reflector with Predicted Chromatic Coordinates

The color reflector with multiple-layer thin film scheme has attracted much attention because of the potential for massive production by wafer-scale deposition and the possibility to integrate with photonics (semiconductor) devices. Here, an angle-insensitive green reflector with a simple multilayer dielectric thin film structure was reported, with predicted chromatic coordinates based on CIE 1931 standard. The SiN/SiO2 multilayer thin film stack, including a special silicon-rich nitride material with ultrahigh refractive index, was grown alternatively by an inductively coupled plasma chemical vapor deposition (ICPCVD) system at a low stage temperature of 80 °C. The green reflector showed a maximum reflectivity of 73% around 561 nm with a full width at half maximum (FWHM) of 87 nm in the visible wavelength range, which contributed significantly to its color appearance. The measurement by an angle-resolved spectrometer under the illumination of p/s-polarized light wave with a variable angle of incidence indicated that the reflectance spectrum blue-shifted slightly with the increasing of incident angle such that the green color could be kept.

Supercontinuum generation in ICP-CVD silicon-rich silicon nitride waveguides

Inductively coupled plasma chemical vapor deposition was used to obtain thin films of siliconrich silicon nitride with a refractive index of 2.44 at optical telecommunications wavelength. The resulting layer was patterned into a 1.6 μm wide waveguide and tested for its nonlinear behavior using a 90-fs all-fiber laser centered at 1630 nm. A significant spectral broadening is demonstrated with a supercontinuum generation from 1300 nm to 1985 nm. Simulations are in fair agreement with the experiments, assuming a nonlinear index of 2 x 10-18 m2/W.

Temperature-modulated synthesis of vertically oriented atomic bilayer graphene nanowalls grown on stainless steel by inductively coupled plasma chemical vapour deposition

It is now clear that growing flat graphene nanostructures from the gas phase on planar substrates is possible. One of the keys to success —particularly in producing a very large specific surface in a reduced space— is the use of 3D carbon nanostructures (i.e., vertical graphene nanowalls, VGNWs) over a planar substrate as a growth template for the deposition of electrochemically active materials (as, for example, transition metal oxides (TMO)). Vertical graphene nanowalls, also known as petal-like, vertical graphene flakes or vertical graphene, can achieve a very large specific surface area of 1100 m2/g, which is comparable to or greater than that of carbon nanotubes —the reference material for its use in high-performance supercapacitors or in other energy-related applications requiring a large active surface area. Vertical graphene nanowalls also exhibit high vertical and in-plane electrical conductivity when grown on metal electrodes, which benefits their use in electrochemical applications. Here, we focus on the growth of VGNWs on flexible stainless-steel substrates (SS310), in principle suitable for applications to electrodes of electrochemical systems (batteries, supercapacitors, catalysts), by inductively coupled plasma chemical vapour deposition (ICP-CVD), from methane as a carbon precursor, in a wide range of temperatures (575 to 900 °C). We will discuss the effect of growth temperature on morphological and structural characteristics of VGNWs based on the results of Raman spectroscopy and field emission scanning electron microscopy (FE-SEM) analysis. Because the nanostructures of graphene nanowalls reported to date are, for the most part, based on multi-layered graphene, here we seek to highlight the effect of temperature on the number of atomic layers of VGNW. In the 700–750 °C range, and under the plasma conditions explored, vertical graphene nanowalls are bilayer, which is foreseen to directly affect the magnitude of the VGNW specific surface.

Low-temperature synthesis of high-quality graphene by controlling the carbon-hydrogen ratio of the precursor

A furnace-free inductively coupled plasma chemical vapor deposition (ICP-PECVD) system, which does not require sample heating, was used to grow graphene at a temperature below 300 °C. This studies have found that under low-temperature PECVD growth conditions, liquid precursors are more suitable for preparing low-temperature graphene precursors than gaseous precursors.​​​​ Hence, benzene is used as a carbon precursor to obtain a sheet resistance of approximately 1.24 kΩ sq−1. In this research, it was discovered that the carbon-hydrogen ratio of the precursor molecule is an important factor while using PECVD to grow graphene. This factor affects the quality of graphene and the sheet resistance value —when the carbon–hydrogen ratio for the precursor molecule is 1:1, graphene has the high quality and lowest sheet resistance; when it is less than 1:2, the graphene that cannot be deposited has the worst quality and sheet resistance. Furthermore, we found that methane, a precursor often used to deposit graphene, will etch graphene under low-temperature conditions, and that acetylene can be used as a precursor to deposit graphene. It was further proven that the carbon–hydrogen ratio of the precursor molecules in the PECVD process caused the reduction in the graphene temperature.

Improved interface and dark current properties of InGaAs photodiodes by high-density N2 plasma and stoichiometric Si3N4 passivation

The interface and dark current properties of mesa-structure In0.83Ga0.17As photodiodes with improved passivation processes are investigated. Inductively coupled plasma chemical vapor deposition (ICPCVD) is used to continuously perform high-density N2 plasma treatment of InGaAs epitaxial material and then SiNx passivation film deposition. The bonding efficiency between Si and N can be effectively improved when close-to-stoichiometric SiNx films are synthesized by precisely controlling the N2 and SiH4 flow rates. Metal-insulator-semiconductor (MIS) capacitors are fabricated to study the interface properties, and C-V analysis shows that the interface state density significantly decreases to 5.3 × 1012 cm−2eV−1. Then, the process is applied to mesa-structure In0.83Ga0.17As photodiodes, and the results show a low dark current density (13 nA/cm2, @ 190 K) and negligible surface current (@ room temperature), indicating the ideal passivation effect. The method of increasing the deposition temperature to promote chemical bonding of SiNx films is studied, and both the interface and dark current properties can be improved. Our work is of important significance to the development of low-noise and large-format InGaAs arrays.

Synthesis, Properties and Aging of ICP-CVD SiCxNy:H Films Formed from Tetramethyldisilazane

Amorphous hydrogenated silicon carbonitride films were synthesized on Si(100), Ge(111), and fused silica substrates using the inductively coupled plasma chemical vapor deposition technique. 1,1,3,3-tetramethyldisilazane (TMDSN) was used as a single-source precursor. The effect of the precursor’s pressure in the initial gas mixture, the substrate temperature, the plasma power, and the flow rate of nitrogen gas as an additional reagent on the film growth rate, element composition, chemical bonding, wettability of film surface, and the optical and mechanical properties of a-SiCxNy:H films was investigated. In situ diagnostic studies of the gas phase have been performed by optical emission spectroscopy during the film deposition process. The long-term stability of films was studied over a period of 375 days. Fourier-transform infrared (FTIR) and X-ray energy dispersive spectroscopy (EDX), and wettability measurements elucidated the oxidation of the SiCxNy:H films deposited using TMDSN + N2 mixture. Films obtained from a mixture with argon had high stability and maintained the stability of element composition after long-term storage in ambient air.

Intrinsic, P-doped and B-doped nanocrystalline silicon thin films grown at room temperature on flexible substrates for photovoltaic applications

Nanocrystalline silicon (nc-Si) thin films in its intrinsic (i-nc-Si), B-doped (p-nc-Si) and P-doped (n-nc-Si) configurations were developed on the flexible substrates at ambient temperature (∼30 °C), using no additional H2 dilution in planar inductively coupled plasma chemical vapour deposition (ICP-CVD) system. A superior crystallinity (∼81%) with electrical conductivity (σD ∼10-7 S cm−1) was achieved for the intrinsic Si thin film by the virtue of the presence of atomic-H in high density within ICP-CVD, which initiates nucleation even at room temperature on the flexible substrates. Substitution of boron (B) dopants at the crystalline Si lattice maintains a high crystallinity (∼80%) and results significantly high electrical conductivity (6 x10-1 S cm−1) in the p-nc-Si thin film. On the contrary, during the growth of n-nc-Si films, a substantial amount of phosphorous (P) dopants, residing at the interstitial position, results in a moderate crystallinity (∼73%) and relatively lesser conductivity (3 x10-1 S cm−1) than the p-nc-Si films. Finally, in the present work i-nc-Si, p-nc-Si and n-nc-Si thin films all are successfully prepared on the flexible substrates at room temperature, with ample crystallinity, wide optical band gap (∼1.9–1.80 eV) and significant electrical conductivity, which appear suitable for the low-cost fabrication of flexible p-i-n solar cells.

Temperature-Modulated Synthesis of Vertically Oriented Atomic Bilayer Graphene Nanowalls Grown on Stainless Steel by Inductively Coupled Plasma Chemical Vapour Deposition

Temperature-Modulated Synthesis of Vertically Oriented Atomic Bilayer Graphene Nanowalls Grown on Stainless Steel by Inductively Coupled Plasma Chemical Vapour Deposition

Fabrication and Characterization of Low-Threshold Single Fundamental Mode VCSELs With Dielectric DBR Mirror

The SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> dielectric film stacks deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) are employed on the top of the oxide-confined vertical-cavity surface-emitting lasers (VCSELs). The reflecting mirror characteristics of the dielectric films are measured with varying numbers of pairs from 4 to 12. The prepared devices have low threshold current of 0.3 mA, single-mode peak power of 1.4 mW at room temperature. The thermal resistance of the device depending on ambient temperature is estimated according to the relationship of wavelength shift and dissipated power, allowing us to extract the actual temperature in active region and the temperature dependence of the output characteristics of the VCSEL. The beam property of the device is characterized by the far field pattern (FFP). Depending on the drive current, the average divergence angles of the output beam estimated from the full-width-half-maximum (FWHM) of the FFP varies between 20.4° and 21.2°. Furthermore, polarization-controlled single mode emission is achieved by introducing a built-in grating into the VCSEL with orthogonal polarization suppression ratio (OPSR) around 19 dB.

Plasma Polymerized SiCOH Films from Octamethylcyclotetrasiloxane by Dual Radio Frequency Inductively Coupled Plasma Chemical Vapor Deposition System.

We have fabricated porous plasma polymerized SiCOH (ppSiCOH) films with low-dielectric constants (low-k, less than 2.9), by applying dual radio frequency plasma in inductively coupled plasma chemical vapor deposition (ICP-CVD) system. We varied the power of the low radio frequency (LF) of 370 kHz from 0 to 65 W, while fixing the power of the radio frequency (RF) of 13.56 MHz. Although the ppSiCOH thin film without LF had the lowest k value, its mechanical strength is not high to stand the subsequent semiconductor processing. As the power of the LF was increased, the densities of ppSiCOH films became high, accordingly high in the hardness and elastic modulus, with quite satisfactory low-k value of 2.87. Especially, the ppSiCOH film, deposited at 35 W, exhibited the highest mechanical strength (hardness: 1.7 GPa, and elastic modulus: 9.7 GPa), which was explained by Fourier transform infrared spectroscopy. Since the low-k material is widely used as an inter-layer dielectric insulator, good mechanical properties are required to withstand chemical mechanical polishing damage. Therefore, we suggest that plasma polymerized process based on the dual frequency can be a good candidate for the deposition of low-k ppSiCOH films with enhanced mechanical strength.

Maintaining superior crystallinity and conductivity in boron-doped nc-Si ultra-thin films by hydrogen plasma treatment

In view of using doped nanocrystalline Si (nc-Si) as the emitter layer in nc-Si/crystalline-Si heterojunction solar cells, a very thin (≤ 50 nm) emitter layer with high conductivity and superior crystallinity is optimum. In the present work, p-nc-Si:H thin film prepared in inductively coupled plasma chemical vapor deposition, without using additional H2-dilution in [SiH4 + B2H6 (1% in H2)]-plasma, retains conductivity ~10−1 S cm−1 and crystallinity ~68% at a low thickness (t) ~50 nm. The charge carrier transport through the heavily doped nc-Si network demonstrates reverse Meyer–Neldel characteristics for t ≥ 50 nm. However, with reduction to t < 50 nm, the evolution of the ultra-nanocrystalline dominated amorphous network, accompanied by accumulation of Si–H–Si platelet-like components in the grain boundary, leads to a drastic reduction in conductivity to 10−4 S cm−1. In this context, the post-deposition and short-time hydrogen plasma treatment (PSHPT) on the as-deposited ultra-thin (t ~30 nm) film becomes instrumental in substantially enhancing the crystallinity from 40% to 69% and increasing conductivity by two orders of magnitude to 10−2 S cm−1. The network modification by PSHPT proceeds via transformation of the surface and sub-surface weak bonds and is significant for the ultra-thin film compared to the thick film, due to retaining a superior surface-to-bulk ratio.

Three-dimensional Si / vertically oriented graphene nanowalls composite for supercapacitor applications

Three-dimensional (3D) carbon nanostructures are promising architectures to improve both specific capacity and power density of electrochemical energy storage systems. Their open structure and porosity provide a large space for active sites and high ion diffusion rates. To further increase their specific capacity, they can be combined with metal oxides. However, this combination often results in the loss of cycling stability and power density. Among the different electrode materials being studied, vertically oriented graphene nanowalls (VG) have recently been put forward as a potential candidate. Here, we report the use of VG covered by Si for increased supercapacitor performance. VG were grown on flexible graphite sheet (FGS) substrate by inductively coupled plasma chemical vapor deposition (ICP-CVD). Furthermore, silicon (Si) was deposited by magnetron sputtering on VG and the electrochemical performance studied in ionic liquid (IL) electrolyte. The incorporation of Si in VG/FGS provides an areal capacitance up to 16.4 mF cm−2, which is a factor 2 and 1.4 greater than that of bare substrate and VG/FGS, respectively. This increase in capacitance does not penalize the cycling stability of Si/VG/GS, which remains outstanding up to 10,000 cycles in IL. In addition, the relaxation time constant decreases from 9.1 to 0.56 ms after Si deposition on VG/FGS.