Inductively Coupled Plasma Chemical Vapor Deposition Research Articles

Non-catalytic direct synthesis of graphene on Si (111) wafers by using inductively-coupled plasma chemical vapor deposition

We employ inductively-coupled plasma chemical vapor deposition for non-catalytic growth of graphene on a Si (111) wafer or glass substrate, which is useful for practical device applications of graphene without transfer processes. At a RF power (P) of 500 W under C2H2 flow, defect-free 3 ∼ 5-layer graphene is grown on Si (111) wafers, but on glass substrate, the layer is thicker and defective, as characterized by Raman spectroscopy and electron microscopy. The graphene is produced on Si (111) for P down to 190 W whereas it is almost not formed on glass for P < 250 W, possibly resulting from the weak catalytic-reaction-like effect on glass. These results are discussed based on possible growth mechanisms.

Fabrication of InGaZnO Nonvolatile Memory Devices at Low Temperature of 150 degrees C for Applications in Flexible Memory Displays and Transparency Coating on Plastic Substrates.

We directly deposited amorphous InGaZnO (a-IGZO) nonvolatile memory (NVM) devices with oxynitride-oxide-dioxide (OOO) stack structures on plastic substrate by a DC pulsed magnetron sputtering and inductively coupled plasma chemical vapor deposition (ICPCVD) system, using a low-temperature of 150 degrees C. The fabricated bottom gate a-IGZO NVM devices have a wide memory window with a low operating voltage during programming and erasing, due to an effective control of the gate dielectrics. In addition, after ten years, the memory device retains a memory window of over 73%, with a programming duration of only 1 ms. Moreover, the a-IGZO films show high optical transmittance of over 85%, and good uniformity with a root mean square (RMS) roughness of 0.26 nm. This film is a promising candidate to achieve flexible displays and transparency on plastic substrates because of the possibility of low-temperature deposition, and the high transparent properties of a-IGZO films. These results demonstrate that the a-IGZO NVM devices obtained at low-temperature have a suitable programming and erasing efficiency for data storage under low-voltage conditions, in combination with excellent charge retention characteristics, and thus show great potential application in flexible memory displays.

Organo‐Functionalization of Silicon Nanocrystals Synthesized by Inductively Coupled Plasma Chemical Vapor Deposition

Octadecyl‐terminated silicon nanocrystals (ODE‐Si NCs) are obtained via a surface‐initiated thermal hydrosilylation reaction on hydride‐terminated Si NCs (HSi NCs). Pristine Si NCs were synthesized at the gram scale by using inductively coupled plasma chemical vapor deposition (ICP‐CVD). The HSi NCs were produced through a chemical etching process with hydrofluoric acid (HF), ethanol (EtOH), and distilled water (d‐H2O). The results obtained from X‐ray diffraction (XRD) and field emission scanning electron microscopy (FE‐SEM) indicate that the synthesized Si NCs obtained via ICP‐CVD have diamond cubic‐structured silicon with a grain size of 10 nm and a densely packed Si NC array consisting of individual NCs. Organo‐functionalized Si NCs, i.e., ODE‐Si NCs, are well soluble in organic solvent whereas pristine Si NCs synthesized through ICP‐CVD are not. The surface chemistry of the ODE‐Si NCs was confirmed via Fourier transform infrared spectroscopy (FT‐IR), proton nuclear magnetic resonance spectroscopy ( 1H‐NMR), and field emission transmission electron microscopy (FE‐TEM). Thereby, these newly synthesized and scalable organo‐functionalized Si NCs are applicable as raw materials for practical use in devices by tuning the surface chemistry with various capping molecules.

Silicon nitride deposition using Inductive Coupled Plasma Chemical Vapor Deposition technique to study optoelectronics behavior for solar cell application

Silicon nitride (Si3N4) is one of the promising dielectric materials for electronic devices, since it has extensive variety of applications in the semiconductor industries such as high speed semiconductor devices, solar cells, etc. This paper is mainly focus on comprehensive study of silicon nitride deposition using ICPCVD (Inductive Coupled Plasma Chemical Vapor Deposition) for potential application in the field of c-Si solar cell and on III–V semiconductor based solar cell. It helps to increases the minority carrier lifetime and reduces the reflectance in c-Si solar cell. Deposition parameters like temperature, power and deposition time have been optimized for getting the nitride layer which will be free from trap states.

Organic/Inorganic Hybrid Materials for Organic Electronic Application

Organic/inorganic stacks were deposited on flexible polycarbonate substrate using inductively coupled plasma chemical vapor deposition (ICP-PECVD) for permeation barrier application. The effects of deposition temperature, RF power, gas flow ratio, deposition pressure on film properties of surface roughness, water vapor transmission rate (WVRT) were investigated. Energy dispersive spectrum (EDS), atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to characterize the film characteristics of the stack layers. It was found that the surface roughness Ra was as low as is 0.25 nm. The WVRT values of the optimum barriers structures were 10-2g/m2 day (1 pair of stacks) and 4.8 x 10-5g/m2 day (4 pair of stacks). This result indicated that the permeation barrier films prepared by ICP-PECVD could be a promising candidate for flexible electronic applications.

Broadband antireflection for a high-index substrate using SiNx/SiO2 by inductively coupled plasma chemical vapour deposition

This paper presents the development of broadband antireflection coating for a high-index substrate such as Si using SiNx/SiO2 by inductively coupled plasma chemical vapour deposition (ICP-CVD). The thin-film design employs a simulated annealing method for a minimal average reflectance over the wavelength range and incidence angles involved, which gives the optimized refractive index and thickness of each layer of the thin-film stack under different layer numbers. Using ICP-CVD, the SiNx material system is optimized by tuning the SiH4/N2 gas ratio. The corresponding thin-film characterization shows the precise refractive index/film thickness control in deposition, and the deposited film also has a low absorption coefficient and smooth surface. The double-layer SiNx/SiO2 coating with the optimized refractive index and thickness for broadband antireflection is demonstrated experimentally. The average reflectance of the Si surface is reduced from ~32% to ~3.17% at normal incidence for a wavelength range from 400 to 1100 nm.

Ultra-low temperature silicon nitride photonic integration platform.

High-quality SiNx films with controllable low stress and low optical loss are deposited at ultra-low temperature (75 °C) using inductively coupled plasma chemical vapor deposition (ICP-CVD). Two kinds of integrated photonic structures have been demonstrated that exemplify its viability as a photonic integration platform. A microcavity consists of two distributed Bragg reflectors (DBR) formed by alternating a total of 49 layers of SiNx and SiO2 with a total thickness of about 11.5 μm is grown without any cracks, confirming the excellent stress control in the process. Microring resonators are also fabricated in as-deposited planar SiNx waveguide layer using electron-beam lithography (EBL) and plasma etching. Average waveguide loss of 0.79 ± 0.22 dB/cm has been achieved in the range of 1550-1600 nm for ring radii larger than 40 μm. The ultra-low temperature grown SiNx with properties of low loss and low stress is therefore a promising photonic integration platform for various photonic integration applications.

Impact of SiNx passivation on the surface properties of InGaAs photo-detectors

We investigate surface passivation effects of SiNx films deposited by inductive coupled plasma chemical vapor deposition (ICPCVD) and plasma enhanced chemical vapor deposition (PECVD) technologies for InAlAs/InGaAs/InP photo-detectors. It is found that ICPCVD deposited SiNx film effectively reduces the densities of the interface states and slow traps near SiNx/InAlAs interface, which realize the small surface recombination velocity and low surface current for InAlAs/InGaAs/InP photo-detectors. By comparing C-V and XPS results, it is suggested that the trap density reduction by ICPCVD technology could be attributed to the disorder suppression on InAlAs surface due to the high density of SiNx film and less processing energy to the InAlAs surface.

Low leakage of In0.83Ga0.17As photodiode with Al2O3/SiNx stacks

Al2O3/SiNx stacks were used as the passivation layer to reduce the dark current of extended wavelength In0.83Ga0.17As photodiodes. The Al2O3 and SiNx layers were deposited sequentially by atomic layer deposition (ALD) and the inductively coupled plasma chemical vapor deposition (ICPCVD), respectively. Compared to the single passivation layer of SiNx deposited by ICPCVD, the Al2O3/SiNx stacks result in a more than 20% lower dark current of the In0.83Ga0.17As photodiodes. The substantial dark current reduction can be attributed to lower defect density at the InGaAs/Al2O3 interface and thus lower surface leakage current.

(Invited) Plasma Processes for Emerging Silicon-Based MEMS, NEMS and Packaging Applications

Plasma processes are important for emerging silicon-based micro-electro-mechanical systems (MEMS), nano-electro-mechanical systems (NEMS) and packaging applications. Typically every device has a customised process flow but synergies can be found as most are produced using a 2.5D approach comprising sequential deposition, lithography and etch cycles. Plasma processes are critical in enabling reproducible dry deposition and etch steps during manufacture. Increasingly they are also being adopted in lithography (nanoimprint) and bonding process steps. Plasma processes can be divided into the following broad families: Chemical vapour deposition (CVD)Atomic layer deposition (ALD)Physical vapour deposition (PVD)Etch (physically-driven)Etch (chemically-driven)Surface functionalisation The merits of each plasma technique and their application to emerging devices are discussed. Plasma-enhanced chemical vapour deposition (PECVD) of dielectrics and silicon is widely used to enable lower temperature processes than conventional low pressure CVD. Adjustment of deposition parameters can tune stress, chemical resistance, optical properties and wear characteristics for different application requirements. At higher temperatures, plasma-assisted nanogrowth of carbon nanotubes and 2D materials (e.g. graphene) are emerging technologies. Conversely, inductively coupled plasma CVD (ICP-CVD) is attracting interest to enable high quality films at lower temperatures. Plasma-assisted ALD enables thin and uniform layers to be grown in a wider range of materials and, similarly, high quality films at lower processing temperatures. Plasma-based PVD processes include sputtering and ion beam deposition. The former is a standard technique for metallisation. Al-based schemes are typical in the silicon IC industry but different metallisations (e.g. Au or Pt-based) may be required for sensors to give HF resistance or long lifetime contacts. Ion beam deposition is often used for complex multilayer stacks. Physically-driven etch processes require ions to provide enough energy to enable a chemical reaction or to physically break bonds at the wafer surface. Conversely, chemically-driven etch processes spontaneously react but require passivation species to obtain directionality (anisotropy). Ion beam etch processes enable non-volatile materials to be physically etched, such as Vanadium Oxide for uncooled infra red detectors. If the substrate is tilted then non-vertical structures, such as blazed gratings, may be realised. Plasmas may be used to clean surfaces or to create specific surface conditions for subsequent steps. This may be to passivate them, increase bond strengths at low temperatures or to subsequently functionalise them – e.g. adding hydrophobic self-assembled monolayers (SAMs) in MEMS microphones or for bio-probes in medical devices. The process step common to the majority of MEMS devices today is the Bosch silicon etch. This uses a repeating sequence of PECVD deposition, physical etch for directional passivation removal and chemical etch that results in a high rate, highly vertical and highly selective silicon etch - although the cyclic nature results in a characteristic sidewall roughness (scalloping). High aspect ratio structures may be realised and the process is not sensitive to crystal orientation (which limits geometries with anisotropic wet etchants). The majority of physical sensing devices are based on sub-70μm depth features. Trends are towards higher aspect ratios for enhanced performance and smaller footprint whilst maintaining throughput. Increasingly, large cavities are also being etched for subsequent chip or wafer scale packaging and sensor structures may comprise multi-wafer stacks with one of more having through wafer etches (300-750μm). With the move to multi-wafer structures interconnect becomes more challenging. Monolithically integrated devices are key to some high volume MEMS applications; however, the most common approach is to use hybrid integration – allowing separate optimisation of readout IC and MEMS devices. Increasingly solutions are moving towards system-in-a-package (SiP) and system-on-a-chip (SoC) solutions. Through silicon vias (TSVs) are emerging as a key technology for this in both the MEMS and IC industries. Aspect ratios are generally limited to 10-15:1 using the Bosch process in production. This is typically followed by dielectric isolation (e.g. TEOS) and barrier / seed metal layers (e.g. by ALD) prior to electroplating for a low via resistance. At the nanoscale, etching becomes more challenging. The Bosch process is less well suited due to finite sidewall scallop size and reduced rate / selectivity. Typically it is not used below 500nm feature sizes although 100nm features have been demonstrated. A continuously passivating process has smooth sidewalls but a lower rate, selectivity and aspect ratio capability at room temperature. Moving to cryogenic temperatures enables the highest rate, selectivity and aspect ratios to be achieved and can realise trench features down to 10nm. Emerging applications in silicon-based MEMS, NEMS and packaging require a diverse range of plasma processes. With no standardised process flow, individual tools need the flexibility to address multiple different process requirements and enable unit cost reductions by running multiple products to achieve higher volumes. Figure 1

Improvement of surface leakage current of 2.6 µm InGaAs photodetectors by using inductive coupled plasma chemical vapor deposition technology

Low surface leakage current is one of the prerequistites to reach the low leakage and high efficiencies of mesa type photodiodes. In this paper, we have studied the surface leakage of 2.6 µm mesa InGaAs p–i–n photodetectors by using two different passivation technologies: inductive coupled plasma chemical vapor deposition (ICPCVD) and plasma enhanced chemical vapor deposition (PECVD). It is found that the total leakage current of the detector with ICPCVD technology is significantly reduced compared to that with PECVD technology due to the decrease of the device’s surface leakage current. A TCAD-based dark current model further reveals that the reduction of the surface leakage current at the low reverse voltage is about two orders of magnitude. As a result, ICPCVD is the promising deposition technology for SiNx passivation layer on mesa InGaAs photodetectors.

Vertically aligned Si nanocrystals embedded in amorphous Si matrix prepared by inductively coupled plasma chemical vapor deposition (ICP-CVD)

Abstract Vertically-aligned nanostructured silicon films are deposited at room temperature on p-type silicon wafers and glass substrates by inductively-coupled, plasma-enhanced chemical vapor deposition (ICPCVD). The nanocrystalline phase is achieved by reducing pressure and increasing RF power. The crystalline volume fraction ( X c ) and the size of the nanocrystals increase with decreasing pressure at constant power. Columnar growth of nc-Si:H films is observed by high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The films exhibit cauliflower-like structures with high porosity that leads to slow but uniform oxidation after exposure to air at room temperature. Films deposited at low pressures exhibit photoluminescence (PL) signals that may be deconvoluted into three distinct Gaussian components: 760–810, 920–935, and 990–1000 nm attributable to the quantum confinement and interface defect states. Hydrogen dilution is manifested in significant enhancement of the PL, but it has little effect on the nanocrystal size and X c .

Silicon-based electrochemical microdevices for silicate detection in seawater

This paper describes the electrochemical characterisation of gold and platinum microdevices mass fabricated using silicon technology. Specific attention was paid to allow in situ electrochemical detection of silicate in seawater. Thus, using a silicon nitride (Si3N4) inorganic passivation layer patterned using Inductively Coupled Plasma Chemical Vapor Deposition (ICP-CVD), coupled with a non-aggressive lift-off based process, different electrodes were isolated electrically: one gold or platinum working electrode named “macroelectrode” (2mm of diameter), four gold or platinum working ultramicroelectrodes (UME) (15μm of diameter), one platinum counter electrode and one silver electrode which can be used as a reference electrode after its chlorination. Their small size and mass fabrication make them very promising for oceanographic applications. As some components of microdevices release silicate and contaminate the solution, after being immersed in seawater, these microdevices were inserted in a specific cell that only puts the electrodes in contact with the seawater solution. Gold has been tested as a possible material for working electrodes but its lack of adherence to the passivation layer in seawater solutions led to non-accurate measurements. On the contrary, passivation layer on platinum electrodes resists to the seawater corrosive medium. The analytical performances of the platinum microdevices has been tested through different silicate calibrations and shows an outstanding accuracy and reproducibility when measurements are performed, especially with the macroelectrodes which showed only 2.8% signal variation after four months of use and a limit of quantification of 0.50μmolL−1 suitable for oceanographic applications.

The 1/f noise characteristics of In0.83Ga0.17As photodiodes with SiNx passivation films fabricated by two different techniques

The 1/f noise characteristics of In0.83Ga0.17As photodiodes have been studied in this work. The surface SiNx passivation films of photodiodes are fabricated by plasma enhanced chemical vapor deposition (PECVD) and inductively coupled plasma chemical vapor deposition (ICPCVD), respectively. The noise measurements are performed at variable reverse bias and temperature for different area diodes. The results show that ICPCVD passivation improves the surface quality and suppresses the 1/f noise significantly compared to PECVD passivation. The 1/f noise has an exponential relationship with reverse bias between 0.1V and 0.5V at room temperature for the diodes passivated by PECVD while it is a power law relationship for the diodes passivated by ICPCVD. As the temperature dropping, the 1/f noise of the diodes passivated by ICPCVD decreases more rapidly at reverse bias 0.1V, which implies the advantage of ICPCVD passivation becomes more conspicuous at the lower temperature. According to the observed geometry dependence, the 1/f noise of the diodes passivated by PECVD dominantly originates from the perimeter, whereas it dominantly originates from the bulk and upper surface for the diodes passivated by ICPCVD.

Self-Aligned Bottom-Gate InGaZnO Thin-Film Transistor with Source and Drain Regions Formed by Selective Deposition of Fluorinated SiNx Passivation

Since the report of an amorphous InGaZnO thin-film transistor (IGZO TFT)[1], many researches have been focused on achieving high performance and high stable oxide TFTs for next generation display. Bottom-gate type with a SiOx etch-stopper have been widely employed for IGZO TFTs. However, one of serious drawbacks of this structure is a large parasitic capacitance of gate-to- drain (CGD) and source (CGS) due to overlap between gate and source/drain (S/D) electrodes. It is known that large parasitic capacitance reduces operation speed of the TFT circuits and induces signal delay of the TFT backplane. Moreover, large CGDof select TFTs in organic light emitting diode (OLED) display strongly influences uniformity of the luminescence of the pixels because the CGD is the main cause of kickback/feedthrough voltage which influences an operation voltage of driving TFTs. Self-aligned (SA) structure is an essential for reducing parasitic capacitance in the TFTs. There are several reports of IGZO homojunction with highly conductive IGZO for source/drain regions which were formed by selective exposure of Ar, H2, or He plasma or ion implantation. [2-4] On the other hand, the IGZO homojunction was demonstrated by hydrogen diffusion from hydrogenated SiNx (SiNx:H) deposited on top of the IGZO.[5] In this paper, we developed the IGZO homojunction with thermally stable S/D regions that was formed by a direct deposition of fluorinated SiNx (SiNx:F) on top of the IGZO. By combining the back-side exposure (BSE) technique and IGZO homojunction formed by the direct deposition of SiNx:F, the SA IGZO TFT are demonstrated.Figure 1(a) and 1(b) show cross sectional views of the SA IGZO TFT with SiOx and SiN:F passivation, respectively. First, Cr gate electrode was formed on a glass substrate. Next, a 150-nm thick SiOx for gate insulator, a 45-nm-thick IGZO for active channel, and a 100-nm-thick SiOx for etch stopper (ES) were deposited. Then, ES layer was aligned by the BSE technique used gate electrode as a mask, and was etched by a dry etching with CF4/O2 plasma. After patterning of the IGZO channel as an active channel, fluorinated SiNx (SiN:F) for passivation was deposited by an inductively-coupled plasma chemical vapour deposition using SiF4+N2 gas mixture as shown in FIg. 1(b). Note that hydrogen-free gas chemistry was used for the SiNx:F deposition. An IGZO TFT with SiOx passivation (deposited by conventional plasma-CVD using SiH4/N2O/N2 gases) was also fabricated for comparison as shown in Fig. 1(a). S/D electrodes were formed by ITO via contact holes. It is noted that there is no overlap region between gate and S/D electrodes. The TFT properties were measured after post fabrication annealing at 300 ºC in N2 for 1h.Figure 1(c) and 1(d) show transfer characteristics of the IGZO TFTs with SiOx and SiNx:F passivation, respectively. On current of the IGZO TFT with SiOx passivation was suppressed due to series resistance of the S/D region. This result indicates that ES dry etching with CF4/O2 plasma did not contribute to form highly conductive S/D region. In contrast, the TFT with SiNx:F passivation exhibited good electrical properties with the field effect mobility of ~10 cm2/Vs. The bottom-gate SA IGZO TFT with homojunction can be achieved by a direct deposition of SiNx:F on the S/D regions.Authors would like to thank Tokyo Electron Co., Ltd. for their supports and useful discussion regarding the SiNx:F films. This work is supported in part by JSPS KAKENHI Grant No. 23560408. [Ref]1) Nomura et al., Nature 432, 488 (2004)2) J.-S. Park et al., Appl. Phys. Lett. 90, 262106 (2007)3) H. Jeong et al., Appl. Phys. Lett. 104, 022115 (2014)4) R. Chen et al., IEEE Elec. Dev. Lett., 33, 1150 (2012)5) A. Sato et al, Appl. Phys. Lett. 94, 133502 (2009)

Inductively coupled plasma chemical vapor deposition silicon nitride for passivation of In0.83Ga0.17As photodiodes

Silicon nitride films (SiNx) deposited by ICPCVD (inductively coupled plasma chemical vapor deposition) at lower temperature (75°C) are investigated on extended wavelength In0.83Ga0.17As photodiodes. Compared to SiNx films (330°C) grown by PECVD (plasma enhanced chemical vapor deposition), the low-temperature-deposited SiNx films grown by ICPCVD have a better effect on decreasing the dark current of In0.83Ga0.17As photodiodes. Area- and perimeter-dependent leakage current were separated by test arrays with different area photosensitive elements. The results indicate that the perimeter-dependent leakage current is obviously decreased for the devices passivated by ICPCVD. The analysis of activation energy indicates that the area-dependent leakage current is dominated by diffusion and generation-recombination mechanisms at reverse bias of 0.1–0.5V and temperature of 260–300K for both ICPCVD and PECVD processes. At reverse bias of 0.1–0.5V and temperature of 200–300K the perimeter-dependent leakage current is dominated by surface recombination current mechanism for ICPCVD, while it is dominated by ohmic current and surface recombination current mechanisms for PECVD. The cause of the reduction of perimeter-dependent leakage current for ICPCVD may derive from its better restraint of ohmic current.

Neural Network Modeling of Deposition Rate Characteristics of Low Temperature Silicon Nitride Deposited by Inner Two Parallel Coil Inductively Coupled Plasma Chemical Vapor Deposition

In this study, a neural network model for silicon nitride (SiN) deposition process is proposed. SiN thin films were deposited by a direct inner two parallel inductively coupled plasma chemical vapor deposition (ICPCVD) system that can control the activated radical and charged species in plasma. This system can produce SiN thin films at low temperature for flexible displays. The input parameters considered for deposition conditions were the N2 gas flow rate, NH3 gas flow rate, and substrate temperature. These were varied within the ranges of 0-20 sccm, 0-20 sccm, and 100-300 degrees C, respectively. For those of input parameters and the output of deposition rate, we developed a back propagation neural network model with a pre-processor. It is shown that the model accuracy and learning speed of the proposed model are better than those of a conventional neural network model. In the experiments conducted, it was found that the deposition rate increased as the flow rates of ammonia (NH3) and nitrogen (N2) increased up to a certain amount. On the contrary, when the flow rates of NH3 and N2 went over a certain amount, the deposition rate decreased. It was also found that an increase in temperature resulted in an increase in the deposition rate.

A-IGZO TFTs With Inductively Coupled Plasma Chemical Vapor Deposited ${\rm SiO}_{x}$ Gate Dielectric

In this brief, amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) are fabricated at . Inductively coupled plasma chemical vapor deposition (ICP-CVD) is used to grow SiOx gate dielectric of the a-IGZO TFTs. The fabricated devices exhibit a high saturation mobility of 26.85 cm2/V·s, a steep subthreshold swing of 0.145 V/decade, and an ON/OFF current ratio of 2.3×107. Atomic force microscope and scanning electron microscope images show that the surface characteristics of the ICP-CVD SiOx gate dielectric are much superior to those of the conventional plasma-enhanced CVD SiOx. It is suggested that the superior surface characteristics of the ICP-CVD SiOx are the main origin of the high performance of the a-IGZO TFTs with the ICP-CVD SiOx gate dielectric.

Electrical properties of organic field effect transistors with thin graphite/metal electrode directly grown by ICP-CVD at low temperatures

The high contact resistance of organic thin film transistors (OTFTs), due to the work function difference between metal electrode and organic channel, seriously decreases the electrical properties. Graphene electrode could reduce the contact resistance and improve the electrical performance of OTFTs. However, the high chemical vapor deposition (CVD) temperature (900–1000 °C) limits the available OTFT substrate in the case of direct graphene growth on S/D metal electrodes. Furthermore, the application of a transferred graphene electrode induces significant problems due to the transfer process. In this work, thin graphite sheet was directly grown on a metal electrode by the inductively coupled plasma-chemical vapor deposition (ICP-CVD) method at as low temperature as 400, 500 °C. We show that OFETs with thin graphite sheet/metal, grown at 400, 500 °C, exhibit much lower contact resistance than OFETs with metal-only electrode.

Graphene Formation on Ni/SiO2/Si Substrate Using Carbon Atoms Activated by Inductively-Coupled Plasma Chemical Vapor Deposition

Graphene has been synthesized on 100- and 300-nm-thick Ni/<TEX>$SiO_2$</TEX>/Si substrates with <TEX>$CH_4$</TEX> gas (1 SCCM) diluted in mixed gases of 10% <TEX>$H_2$</TEX> and 90% Ar (99 SCCM) at <TEX>$900^{\circ}C$</TEX> by using inductively-coupled plasma chemical vapor deposition (ICP-CVD). The film morphology of 100-nm-thick Ni changed to islands on <TEX>$SiO_2$</TEX>/Si substrate after heat treatment at <TEX>$900^{\circ}C$</TEX> for 2 min because of grain growth, whereas 300-nm-thick Ni still maintained a film morphology. Interestingly, suspended graphene was formed among Ni islands on 100-nm-thick Ni/<TEX>$SiO_2$</TEX>/Si substrate for the very short growth of 1 sec. In addition, the size of the graphene domains was much larger than that of Ni grains of 300-nm-thick Ni/<TEX>$SiO_2$</TEX>/Si substrate. These results suggest that graphene growth is strongly governed by the direct formation of graphene on the Ni surface due to reactive carbon radicals highly activated by ICP, rather than to well-known carbon precipitation from carbon-containing Ni. The D peak intensity of the Raman spectrum of graphene on 300-nm-thick Ni/<TEX>$SiO_2$</TEX>/Si was negligible, suggesting that high-quality graphene was formed. The 2D to G peak intensity ratio and the full-width at half maximum of the 2D peak were approximately 2.6 and <TEX>$47cm^{-1}$</TEX>, respectively. The several-layer graphene showed a low sheet resistance value of <TEX>$718{\Omega}/sq$</TEX> and a high light transmittance of 87% at 550 nm.