Papers by Keyword: PECVD

Abstract: The amorphous silicon (a-Si) grown by plasma enhanced chemical vapor deposition (PECVD) has been widely applied in advanced semiconductor devices. However, it still suffers from the bubble defects when the deposition temperature goes above 450 °C. In this work, we have investigated the influence of underlying materials on the formation of bubbles of a-Si. The a-Si was deposited on different dielectric substrates, including silicon nitrides (SiN) and silicon dioxide (SiO₂), using PECVD technique at a substrate temperature of 500 °C. A large number of bubbles of the a-Si has been observed on the thermal ALD deposited SiN underlayer, and some of them even burst. In contrast, no bubble defects were observed at the a-Si grown on PECVD SiN and PECVD SiO₂ films. Such deviation may be attributed to the quality of the underlying material, which induces the H/H₂ diffusion during the growth of a-Si and results in bubbles. A solution based on the model has been used to suppress the formation of such bubbles. An inserting layer of SiO₂ was introduced in between SiN and a-Si to improve the density of the lower layer material and the adhesion between the two materials. As a result, there is no bubble defects at the surface of a-Si observed using optical microscope. Our work reveals the mechanism of the formation of bubble defects and paves a new method to eliminate the bubbles defects and to form high-quality a-Si, which shows potential in the manufacture of semiconductor devices.

Abstract: We present the improvement of SiO₂/4H-SiC interface quality and high field-effect (FE) mobility (µ_FE) in 4H-SiC MOSFETs. This is achieved by introducing a nitrous oxide (N₂O) plasma in-situ pre-treatment before gate stack formation using plasma enhanced chemical vapour deposition (PECVD) oxide followed by a post deposition anneal (PDA) in diluted N₂O for times ranging from 30 to 120 minutes thereby creating an ultra-thin thermally grown SiO₂ layer at the SiO₂/4H-SiC interface. MOS capacitors with SiO₂ deposited on in-situ pre-treated SiC surfaces had a lower density of interface traps (D_IT) for all PDA durations, compared with devices having untreated PECVD oxides or control devices with 30 nm thermally grown oxide. After PDA for 90 minutes, a minimum D_IT value of 1.2×10¹¹ cm^-2·eV^-1 was measured. A peak µ_FE value reaching 94 cm²/(V·s) was measured in n-channel planar MOSFETs fabricated with PECVD oxide on in-situ pre-treated devices, which significantly exceeds a maximum µ_FE of 6 cm²/(V·s) in control devices.

Abstract: At present, the preparation of conductive and corrosion-resistant carbon coatings by plasma-assisted chemical vapor deposition (PECVD) has received extensive research. In this paper, the acetylene plasma model was established by using the Particle in Cell/Monte Carlo method (PIC/MCC) to study the influence of different electrode voltages on the composition and particle energy of deposited particles, and explore the corresponding relationship between acetylene gas and deposited particles. The results show that increasing the electrode voltage can reduce the density of acetylene particles in the plasma, increase the ionization rate of acetylene, and reduce the particle density of C₂ and CH groups. The energies of C₂H₂ and CH particles increase with the increase of voltage, while the energies of C₂ and H particles are basically stable and not affected by the voltage. Keywords: PECVD, PIC/MCC, carbon film, electrode voltage, acetylene plasma, deposition particles.

Abstract: This work aims to optimize Plasma-Enhanced Chemical Vapour Deposition (PECVD) amorphous hydrogenated silicon carbide (a-SiC:H) as a conformal passivation layer for invasive microelectrode array (MEA) neural interface applications. By carefully tuning the PECVD deposition parameters, the composition, structure, electrical, and mechanical properties of the films can be optimized for high resistivity, low stress, and great resistance to chemical attack. This optimization will eventually allow a-SiC:H to be used as an ideal insulation, passivation and protection layer for thin and biocompatible all-SiC neural interfaces.

Abstract: In photovoltaic system the major challenge is the cost reduction of the solar cell module to compete with those of conventional energy sources. Evolution of solar photovoltaic comprises of several generations through the last sixty years. The first generation solar cells were based on single crystal silicon and bulk polycrystalline Si wafers. The single crystal silicon solar cell has high material cost and the fabrication also requires very high energy. The second generation solar cells were based on thin film fabrication technology. Due to low temperature manufacturing process and less material requirement, remarkable cost reduction was achieved in these solar cells. Among all the thin film technologies amorphous silicon thin film solar cell is in most advanced stage of development and is commercially available. However, an inherent problem of light induced degradation in amorphous silicon hinders the higher efficiency in this kind of cell. The third generation silicon solar cells are based on nano-crystalline and nano-porous materials. Hydrogenated nanocrystalline silicon (nc-Si:H) is becoming a promising material as an absorber layer of solar cell due to its high stability with high V_oc. It is also suggested that the cause of high stability and less degradation of certain nc-Si:H films may be due to the improvement of medium range order (MRO) of the films. During the last ten years, organic, polymer, dye sensitized and perovskites materials are also attract much attention of the photovoltaic researchers as the low budget next generation PV material worldwide. Although most important challenge for those organic solar cells in practical applications is the stability issue. In this work nc-Si:H films are successfully deposited at a high deposition rate using a high pressure and a high power by Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF PECVD) technique. The transmission electron microscopy (TEM) studies show the formations of distinct nano-sized grains in the amorphous tissue with sharp crystalline orientations. Light induced degradation of photoconductivity of nc-Si:H materials have been studied. Single junction solar cells and solar module were successfully fabricated using nanocrystalline silicon as absorber layer. The optimum cell is 7.1 % efficient initially. Improvement in efficiency can be achieved by optimizing the doped layer/interface and using Ag back contact.

Abstract: One promising method for growing carbon-based materials, especially for electronics and optoelectronics application, is PECVD (Plasma Enhanced Chemical Vapor Deposition). In addition to the large-area thin film obtained, this method also requires relatively lower growth temperature. By modifying the PECVD reactor through the application of Hot-Wire Cell (HWC) placed between two electrodes (called In Plasma, IP), and plasma generator frequency of 70 MHz which is categorized as Very High Frequency (VHF), graphene flakes have been successfully grown by using methane (CH₄) gas as precursor at pressure 300 mTorr and substrate temperature of 275°C on corning glass substrate. This result indicates that this method is potentially to grow graphene at lower temperature by adjusting several growth parameters, especially temperature of hot wire cell that plays important role in the deposition process. It should be noted that important factor that greatly determined the successful of graphene flakes growth was the use of metal catalyst in the form of very thin film. In this research, silver was used as metal catalyst which was prepared by evaporation method and then annealed at 600°C for 30-60 minutes.

Abstract: Thin films of mixed amorphous/ microcrystalline-phases have been researched during the last decade, for manufacturing silicon solar cells. In this work the Plasma Enhanced Chemical Vapor Deposition PECVD process parameters; namely dilution ratios and substrate temperature, were controlled to build i-layer at low dilution ratios with moderate substrate temperatures. In this work an intrinsic layer was deposited on Indium Tin Oxide ITO glass by PECVD technique, with different dilution ratios of silane in hydrogen to study the transition from amorphous to microcrystalline phase. The Si:H thin film was evaluated by field emission scanning electron microscopy, x-ray diffraction and atomic force microscopy. The structural transition between a-Si:H to μc-Si:H achieved at dilution ratio 13.3 and substrate temperature 250°C with surface roughness 22.5 nm.

Abstract: In this paper, the deposition and the electrical characterization of hydrogenated amorphous silicon germanium (a-Si_xGe_y:H) thin films were performed by plasma enhanced chemical vapour deposition (PECVD) at low temperature with different flow ratios of SiH₄/GeH₄. The temperature coefficient of resistance (TCR) and temperature dependence of conductivity were measured to study the influence of deposition parameter. The resistance uniformity were also investigated. The result showed that the film presented high TCR values of around 3.5%K^-1 and moderate conductivity value of 1.47×10^-3 (Ω•cm)^-1 respectively at room temperature, while the non-uniformity below 5% which indicated the high resistance uniformity in films.

Abstract: Secondary cells, which are the core storage media of energy storage systems (ESS), and carbon nanowalls (CNWs), which are expected to improve the performance of supercapacitors while being used as their electrodes, were investigated in this study. CNWs were directly grown on the substrate, and the substrate was a Si wafer with a nickel layer deposited on top of it. The nickel layer was deposited with the RF-magnetron sputtering method using a 4-inch Ni target. The CNWs were grown on the prepared substrate using microwave plasma-enhanced chemical vapor deposition (PECVD). The substrate temperature was changed from 550 to 800°C by 50°C increments to identify the growth characteristics according to the growth temperature. The surficial and cross-sectional images according to the temperature were analyzed using a field emission scanning electron microscope (FE-SEM). It was confirmed that the density of the CNWs increased along with the temperature. Especially, it was confirmed that the density increased dramatically at 750°C or higher.

Abstract: 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.