Plasma-enhanced Chemical Vapor Deposition System Research Articles

Optimization of Light Emission from Silicon Nanocrystals Grown by PECVD

AbstractLight emission from Si nanocrystals ( SiNCs ) embedded in Si oxide was studied in this work. SiNCs were fabricated by annealing a Si-rich oxide ( SRO ) deposited by a plasma-enhanced chemical vapor deposition ( PECVD ) system. The gas flow ratio between SiH4 and N2O of a precursor gas was changed by varying a N2O gas flow rate and the annealing temperature was varied from 800 to 1100°C. The highest PL intensity was obtained with a N2O flow rate of 125sccm, a SiH4 flow rate of 1400sccm and annealing temperature of 900°C. The PL wavelength was also controlled by N2O gas flow rate and annealing temperature, with blue shifting to the visible wavelengths for increasing N2O flow rate and decreasing annealing temperature. In addition, forming gas ( 4% H2 ) anneal for 1 hour, which is a common method to passivate Si surface, at 500°C to SiNCs was used to further enhance the emission intensity. To approach emission at shorter wavelength, the Si oxide with SiNCs / SiO2 multi layer structure ( MLS ) was also fabricated by similar methods. The SiO2 layer was used as a diffusion barrier to extra Si on vertical direction during the annealing process. Such a barrier can effectively reduce the diameter of SiNCs and shift the emission peak to shorter wavelength. A blue shift from PL was clearly observed as the thickness of Si oxide layer with SiNCs in MLS reduces. Finally, the PIN light emitting diode which consisted of n-type poly-Si / Si oxide with SiNCs / p-type poly-Si structure was also fabricated to study the electroluminescence ( EL ) of SiNCs. The current under the forward bias was about 10 times higher than under the reverse bias. The carrier injection mechanism assumed that Poole-Frenkel type conduction or hopping conduction dominates under a low electric field and Fowler-Nordheim tunneling dominates under a high electric field. EL was obtained with a forward bias voltage of around 6V and EL emission efficiency was proportional to the current density.

Hybrid radio-frequency/direct-current plasma-enhanced chemical vapor deposition system for deposition on inner surfaces of polyethylene terephthalate bottles

A hybrid radio-frequency (rf)/direct-current (dc) system has been developed to control the biasing effects during deposition of diamondlike carbon (DLC) films onto the inner wall of polyethylene terephthalate (PET) bottles. An additional dc bias is coupled to the rf electrode to produce the effect of equivalent rf self-biasing. This allows more flexible control of the deposition of the DLC films which are intended to improve the gas barrier characteristics. The experimental results demonstrate that the additional dc bias improves the adhesion strength between the DLC film and PET, although the enhancement in the gas barrier properties is not significantly larger compared to the one without dc bias. The apparatus and methodology have practical importance in the food and beverage industry.

Room-temperature photoluminescence in erbium-doped deuterated amorphous carbon prepared by low-temperature MO-PECVD

We report on a novel optical thin film material, erbium-doped deuterated amorphous carbon, fabricated directly on silicon substrate at room-temperature via controlled thermal evaporation of a Metal-Organic compound in a Plasma-Enhanced Chemical Vapour Deposition (MO-PECVD) system. High erbium concentrations (up to 2.3 at.%) and room-temperature photoluminescence at 1.54 microm are successfully demonstrated. Concentration quenching due to erbium clustering is reduced by adopting an appropriate MO precursor-Er(tmhd)(3). Another quenching mechanism, caused by non-radiative C-H and O-H vibrational transitions, is shown for the first time to be significantly reduced by deuteration instead of hydrogenation of amorphous carbon. Our results suggest that erbium-doped deuterated amorphous carbon is a promising new class of photonic material for silicon-compatible optoelectronics applications in the technologically important 1.5microm wavelength region.

Very low surface recombination velocity on p-type c-Si by high-rate plasma-deposited aluminum oxide

Aluminum oxide layers can provide excellent passivation for lowly and highly doped p-type silicon surfaces. Fixed negative charges induce an accumulation layer at the p-type silicon interface, resulting in very effective field-effect passivation. This paper presents highly negatively charged (Qox=−2.1×1012 cm−2) aluminum oxide layers produced using an inline plasma-enhanced chemical vapor deposition system, leading to very low effective recombination velocities (∼10 cm s−1) on low-resistivity p-type substrates. A minimum static deposition rate (100 nm min−1) at least one order of magnitude higher than atomic layer deposition was achieved on a large carrier surfaces (∼1 m2) without significantly reducing the resultant passivation quality.

Radio frequency bias power effects on silicon nitride film deposited in SiH4-NH3 using a plasma-enhanced chemical vapor deposition

Silicon nitride films were deposited at room temperature in a plasma-enhanced chemical vapor deposition system. Ion energy and ion energy flux were measured with an ion energy analysis system. The effects of the radio frequency bias power on the ion energy distribution, deposition rate, refractive index, and surface roughness were examined along with the correlations between the ion energy diagnostics and film properties. The bias power varied from 30 W to 90 W. The surface roughness measured by atomic force microscopy was detailed in terms of the mean surface roughness and major pixel density. The deposition rate increased from 271 A/min to 308 A/min, increasing the bias power and correlation with the ion energy. Particularly, the refractive index increased with a decrease in the bias power. This is a unique feature resulting from the room-temperature deposition of silicon nitride film controlled in terms of the bias power. Moreover, the large variation from 1.94 to 2.49 facilitates the control of the refractive index as a function of the bias power. Strong dependency of the refractive index on the ion energy flux was also identified.

Effect of Annealing on the Optical and Chemical Bonding Properties of Hydrogenated Amorphous Carbon and Hydrogenated Amorphous Carbon Nitride Thin Films

Hydrogenated amorphous carbon (a-C:H) and hydrogenated amorphous carbon nitride (a-CNx:H) films were prepared in a custom-built radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system with a parallel-plate configuration. Pure methane and a gas mixture of methane and nitrogen were used as gas sources to obtain these films. The films were characterized using Fourier transform infrared and optical transmission spectroscopy techniques. The incorporation of nitrogen and the effect of annealing (100–500 °C) on the film properties were studied. The films were determined to be thermally stable up to 300 °C. Upon annealing above 300 °C, the thickness and refractive index of both a-C:H and a-CNx:H films increase while the optical energy gap E04 decreases. These effects were more pronounced in a-CNx:H. From the IR spectra, these changes are considered to be due to the decreases in nitrogen and hydrogen concentrations in the films which result in their structural modification.

Electrical characteristics of MIS capacitors with multi-stack thermal-agglomerating Ge nanocrystals in SiO 2/SiN x dielectrics

Metal–insulator–semiconductor (MIS) capacitors, having 1-, 2-, or 3-layer Ge nanocrystals (NCs) in SiO 2/SiN x dielectrics for charge storage application have been fabricated and characterized. Multi-stack Ge NCs were fabricated by thermal-annealing the amorphous SiGeO/SiN x multilayers deposited with a plasma-enhanced chemical vapor deposition (PECVD) system. Micro-Raman spectra and images of transmission electron microscopy (TEM) demonstrated the presence of Ge NCs after annealing. More holes trapping and storage than electrons were exhibited in capacitance–voltage ( C– V) hysteresis curves at room temperature. Increasing the number of layer for Ge NCs in SiO 2/SiN x dielectrics from 1 through 2 to 3 improved the memory window from 0.3 through 0.5 to 2.3 V as obtained by C– V hysteresis curves. The current density–voltage ( J– V) curves of MIS capacitors exhibited the multi-peak form at the higher negative voltages due to the transient displacement current from the substrate to the Ge NCs.

Controllable fabrication of carbon nanotubes on catalysts derived from PS- b-P2VP block copolymer template and in situ synthesis of carbon nanotubes/Au nanoparticles composite materials

Highly ordered iron oxide nanoparticles with controlled size and spacing over a large surface area were prepared with polystyrene- block-poly(2-vinyl pyridine) (PS- b-P2VP) diblock copolymer template, the obtained nanoparticles could be used as catalysts for CNTs growth in a plasma-enhanced chemical vapor deposition (PECVD) system. This route offers the capability of controlling the density of CNTs on the substrate by altering the growing time, and aligned CNTs grew vertically onto the substrates with a pre-coating of aluminium oxide (Al 2O 3) layer. In addition, Au nanoparticles were successfully attached to the sidewall of deposited CNTs through in situ synthetic method.

Improved quality of polycrystalline diamond grown by two-stage growth in microwave plasma chemical vapor deposition

The quality of polycrystalline diamond films grown by chemical vapor deposition is dependent on the growth time, pressure, carbon-to-hydrogen ratio, bias, and nucleation mechanism involved. In this study, reaction gases, methane (CH 4) and hydrogen (H 2), were used to grow polycrystalline diamond on a p-type (111) silicon substrate with a microwave plasma-enhanced chemical vapor deposition system. In addition to the conventional etching, bias-enhanced nucleation, and growth steps, the growth step was further divided into two stages. The first stage (Growth I) was carried out at low pressure and the second (Growth II) was carried out at high pressure. Results clearly indicate that the use of the Growth I stage can considerably improve the quality of the diamond film. In the Growth I stage, well-faceted grains with lower contents of graphite and carbide, and fewer defects are obtained. Therefore, the conductivity is drastically decreased by nearly two orders of magnitude and the diamond film exhibits the semi-insulating characteristics of intrinsic diamond. The improvement is caused solely by the addition of the low-pressure Growth I stage. Application of bias in the Growth I and/or Growth II stages can only degrade the synthesized polycrystalline diamond film.

Low-Temperature Growth of Multiwalled Carbon Nanotubes by Surface-Wave Plasma-Enhanced Chemical Vapor Deposition Using Catalyst Nanoparticles

Carbon nanotubes (CNTs) have been grown by surface-wave plasma-enhanced chemical vapor deposition (CVD) using size-classified Co nanoparticles at low temperatures. A mesh grid is used in the remote plasma-enhanced CVD system for the suppression of ion bombardment damage from plasma. The control of the electric field distribution using a mesh grid with a narrower opening is effective for the CNT growth. Multiwalled CNTs are obtained at a low temperature of 400 °C under low ion-density conditions. No significant difference in the microscopic structure of the CNTs grown at temperatures between 400 and 500 °C is observed.

Initial nucleation and growth of in-plane solid-liquid-solid silicon nanowires catalyzed by indium

We report a systematic investigation of the initial nucleation and growth of in-plane solid-liquid-solid (IPSLS) silicon nanowires (SiNWs), catalyzed by indium (In) drops prepared in situ by a ${\text{H}}_{2}$ plasma superficial reduction of indium tin oxide in a plasma-enhanced chemical-vapor deposition system. A supersaturation of Si atoms in the In catalyst drop is first established by the absorption of the hydrogenated amorphous silicon (a-Si:H) layer coating the catalyst drops. The initial nucleation of Si seeds in the catalyst drop is found to happen preferentially along the catalyst bottom edge and the lateral growth of SiNW is actually triggered by the largest Si seed that tilts the catalyst drop into the opposite direction to form new absorption edge with nearby a-Si:H layer. We show that the ratio of the a-Si:H layer thickness to the catalyst diameter is a key controlling factor for achieving a high-growth activation rate of the lateral IPSLS-SiNWs.

Electron emission studies of CNTs grown on Ti and Ni containing amorphous carbon nanocomposite films

Carbon nanotubes (CNTs) were grown successfully on the as-deposited dual metal (Ti and Ni) embedded films using a radio frequency plasma-enhanced chemical vapor deposition system. The microstructure of CNTs grown on the dual metal films proved to be heavily dependent on the percentages of metals included, varying both in size and in density. Electron emission tests carried out on the films with CNTs grown showed that the threshold field was dependent on the surface morphology of the CNTs, with the lowest threshold field at 3.5 V/μm from 2.5% Ti/Ni film with CNTs. The field enhancement factor, β, of the emitting tips was also calculated from the Fowler–Nordheim plots, where CNTs from the 2.5% Ti/Ni film gave the highest field enhancement factor. However, it was observed that films with a single metal of either Ti or Ni did not manage to grow CNTs, possibly due to a lack of catalyst centres at the surface of the films. It was believed that the Ni nanoclusters acted as catalysts centres giving a rather uniform but randomly orientated type of CNTs. Results obtained pointed that the fabricated nanocomposite material could be a possible choice for cold cathode emitters and the Ti/Ni mixture could be an effective composite for controlling the CNT density.

Fundamental Study of CNTs Fabrication for Charge Storable Electrode using RF-PECVD System

Plasma enhanced chemical vapor deposition (PECVD) is commonly used for Carbon nanotubes (CNTs) fabrication, and the process can easily be applied to industrial production lines. In this works, we developed novel magnetized radio frequency PECVD system for one line process of CNTs fabrication for charge storable electrode application. The system incorporates aspects of physical and chemical vapor deposition using capacitive coupled RF plasma and magnetic confinement coils. Using this magnetized RF-PECVD system, we firstly deposited Fe layer (about 200[nm]) on Si substrate by sputter method at the temperature of 300[℃] and hence prepared CNTs on the Fe catalyst layer and investigated fundamental properties by scanning electron microscopy (SEM) and Raman spectroscopy (RS). High-density, aligned CNTs can be grown on Fe/Si substrates at the temperature of 600[℃] or less.

Controlling the Shape of a Carbon Nanotube by Using the ReactionChamber Pressure

We report the effects of the reaction chamber pressure on the shape and the structure of verticallyaligned carbon nanotubes (CNT) grown on a Ni catalyst by using dc plasmaenhanced chemical vapor deposition system. By controlling the pressure of the reaction chamber We were able to alter the shape and the crytallinity of CNTs. With increasing the chamber pressure, the length was rapidly reduced from 4.5 /μm to 800 nm, but the crytallinity was strongly enhanced. As the reaction chamber pressure decreases, the tips of the CNTs were observed to change from a hemispherical tip with one conical Ni particle to a distorted the tip with more than one tiny Ni particle which means that the formation of Ni conglomerates does not only occur during the pretreatment process but also continues during the CNT growth process. These results have further clarified the role of the reactive etching ions in the growth of CNTs. Author

A comparison of silicon oxide and nitride as host matrices on the photoluminescence from Er3+ ions

This paper compares the properties of silicon oxide and nitride as host matrices for Er ions. Erbium-doped silicon nitride films were deposited by a plasma-enhanced chemical-vapour deposition system. After deposition, the films were implanted with Er3+ at different doses. Er-doped thermal grown silicon oxide films were prepared at the same time as references. Photoluminescence features of Er3+ were inspected systematically. It is found that silicon nitride films are suitable for high concentration doping and the thermal quenching effect is not severe. However, a very high annealing temperature up to 1200 °C is needed to optically activate Er3+, which may be the main obstacle to impede the application of Er-doped silicon nitride.

Continuous Synthesis of Carbon Nanotubes Using a Plasma-Enhanced Chemical Vapor Deposition System at Atmospheric Pressure

Continuous synthesis of carbon nanotubes (CNTs) without replenishment of catalyst was investigated using a plasma-enhanced chemical vapor deposition system at atmospheric pressure for the first time. CNTs were successfully grown in a continuous manner on an iron-catalyzed substrate up to a height of 750 µm by two cycle of continuous growth. In the first growth step, the height of the CNT forest was 427 µm under the optimum synthesis conditions. The high-density Fe nanoparticles remained on the surface after the first growth step, although the density was slightly reduced. The second growth step was performed after harvesting the grown CNTs mechanically. The height of the CNTs obtained in the second growth step was 320 µm, which is 100 µm shorter than that of the CNTs obtained in the first growth step. By the same procedure, the third growth step was carried out. Unlike the results of the first two growth steps, the CNT forest was sparsely formed with a height of less than 30 µm, suggesting that the catalytic material was used up during the second growth step. The results show that a 20-nm-thick catalytic material was consumed for the growth of CNTs up to a height of 750 µm. This study opens up the possibility of continuous synthesis of CNTs and mass production at low cost for industrial applications.

Deposition of Hard and Adherent Diamond-Like Carbon Films Inside Steel Tubes Using a Pulsed-DC Discharge

A new, low cost, pulsed-DC plasma-enhanced chemical vapor deposition system that uses a bipolar, pulsed power supply was designed and tested to evaluate its capacity to produce quality diamond-like carbon films on the inner surface of steel tubes. The main focus of the study was to attain films with low friction coefficients, low total stress, a high degree of hardness, and very good adherence to the inner surface of long metallic tubes at a reasonable growth rate. In order to enhance the diamond-like carbon coating adhesion to metallic surfaces, four steps were used: (1) argon ion sputtering; (2) plasma nitriding; (3) a thin amorphous silicon interlayer deposition, using silane as the precursor gas; and (4) diamond-like carbon film deposition using methane atmosphere. This paper presents various test results as functions of the methane gas pressure and of the coaxial metal anode diameter, where the pulsed-DC voltage constant is kept constant. The influence of the coaxial metal anode diameter and of the methane gas pressure is also demonstrated. The results obtained showed the possibilities of using these DLC coatings for reduced friction and to harden inner surface of the steel tubes.

Boron-doped silicon film as a recombination layer in the tunnel junction of a tandem solar cell

Boron-doped hydrogenated silicon films with different gaseous doping ratios (B2H6/SiH4) were deposited in a plasma-enhanced chemical vapor deposition (PECVD) system. The microstructure of the films was investigated by atomic force microscopy (AFM) and Raman scattering spectroscopy. The electrical properties of the films were characterized by their room temperature electrical conductivity (σ) and the activation energy (Ea). The results show that with an increasing gaseous doping ratio, the silicon films transfer from a microcrystalline to an amorphous phase, and corresponding changes in the electrical properties were observed. The thin boron-doped silicon layers were fabricated as recombination layers in tunnel junctions. The measurements of the I–V characteristics and the transparency spectra of the junctions indicate that the best gaseous doping ratio of the recombination layer is 0.04, and the film deposited under that condition is amorphous silicon with a small amount of crystallites embedded in it. The junction with such a recombination layer has a small resistance, a nearly ohmic contact, and a negligible optical absorption.

Infrared laser-based monitoring of the silane dissociation during deposition of silicon thin films

The silane dissociation efficiency, or depletion fraction, is an important plasma parameter by means of which the film growth rate and the amorphous-to-microcrystalline silicon transition regime can be monitored in situ. In this letter we implement a homebuilt quantum cascade laser-based absorption spectrometer to measure the silane dissociation efficiency in an industrial plasma-enhanced chemical vapor deposition system. This infrared laser-based diagnostic technique is compact, sensitive, and nonintrusive. Its resolution is good enough to resolve Doppler-broadened rotovibrational absorption lines of silane. The latter feature various absorption strengths, thereby enabling depletion measurements over a wide range of process conditions.

A New Gate Dielectric for Highly Stable Amorphous-Silicon Thin-Film Transistors With $\sim\!\! \hbox{1.5-cm}^{2}/\hbox{V} \cdot \hbox{s}$ Electron Field-Effect Mobility

Hydrogenated amorphous-silicon (a-Si:H) thin-film transistors (TFTs) in the bottom-gate back-channel-cut geometry were made with a homogeneous SiO2-silicone hybrid as the gate dielectric. The dielectric is deposited in a plasma-enhanced chemical vapor deposition (PE-CVD) system at nominal room temperature, and the a-Si:H channel and n+ source/drain layers are deposited by PE-CVD at 150degC. The threshold voltage VT is ~3V, the subthreshold slope is S ~ 290 mV/decade, the electron field-effect mobility is mu~1.5 cm2/Vldrs, and the on/off current ratio is ~107. The threshold-voltage shift DeltaVT under high-field gate bias is approximately one-half of that in conventional a-Si:H/SiNx TFTs fabricated at 300degC . These results suggest that the SiO2-silicone hybrid material may become the gate dielectric of choice for a-Si:H TFT applications that require high transconductance and high stability.