Reactive Gas Flow Rate Research Articles

Plasma‐Enhanced Chemical Vapor Deposition of Silicon Dioxide Deposited at Low Temperatures

Thin silicon dioxide films are commonly used as insulating layers in metal‐insulator structures, such as integrated circuits and multichip modules. These films are either thermally grown or deposited by thermal or plasma‐enhanced chemical vapor deposition (PECVD). The advantage of PECVD is that lower deposition temperatures can be used avoiding defect formation, diffusion, and degradation of the metal layer. However, the low deposition temperature of the PECVD process has a negative effect on the quality of the silicon dioxide. Oxides produced at low temperatures contain more silanol and water impurities and are more porous than those deposited at higher temperatures. The deposition parameters, including substrate temperature, RF power, pressure, and reactant gas flow rate, affect the silanol and water concentration. The substrate temperature has the largest effect on the silanol concentration of the oxide. Using a large RF power, high pressure, and low nitrous oxide to silane ratio will minimize the silanol concentration at a given temperature. This will minimize the dielectric constant and maximize the etch resistance of the oxide produced.

The influence of process parameters on the properties of chromium-nitrogen coating by d.c. reactive sputtering at room temperature

A chromium-nitrogen coating (10 μm thick) was successfully applied to the contact surfaces of line matrix printer heads by d.c. reactive sputtering for the prevention of mechanical degradation caused by impact wear. The coating was deposited at room temperature where the substrate was maintained below 93°C (200°F) during the sputtering. A microgrit blasting process was used for the surface preparation. The effect of chamber pressure, bias voltage and reactive gas flow rate on the resulting coating properties was studied. The hardness, morphology and adhesion of the coatings were examined. With the optimal settings of the process parameters, the chromium-nitrogen coating can withstand more than 5000 h of continuous printing without any evidence of degradation.

Kinetics of Reduction of Composite Pellets Containing Iron Ore and Carbon

The effects of temperature, pellet type, inert and reactive gas flowrate, and external atmosphere on the reduction rates of composite pellets containing iron ore and coal or coke were investigated in the temperature range 900–1200°C. Two different pellets were reduced in N2 atmosphere. Experiments were also conducted for one of the pellets in CO and in CO2 atmospheres. The conversions were obtained by the fraction of oxygen removed from the pellets, calculated from gas analysis. It was observed that with increasing temperature, decreasing the N2 flowrate and utilizing CO atmospheres, the reaction rate increased. The Boudouard reaction is likely to control the solid reduction for both pellets, at the temperatures investigated. A well-known kinetics equation successfully represented most of the experimental data and allowed the evaluation of the rate constants. The pre-exponential factors and activation energies were determined by the Arrhenius equation. Résumé Les effets de la température, du type de boulette, du débit des gaz inerte ou réactif et de l'atmosphère extérieure ont été analysés afin de mesurer les taux de réduction de boulettes composites contenant du minerai de fer et du charbon/coke. L'intervalle de température étudié était 900–1200°C. Deux boulettes différentes ont été réduites sous atmosphère azotée alors qu'un seul type de boulette a été soumis à des atmosphéres de CO et de CO2, Les conversions ont été obtenues par un calcul issu de l'analyse gazeuse de l'oxygène originant de la boulette. Il a été observé que le taux de réaction augmente avec une augmentation de la température, une baisse du débit d'azote et l'utilisation d'une atmosphère de CO. La réaction de Boudouard semble contrôler la réduction solide pour les deux types de boulette aux températures étudiées. Une équation cinétique bien connue représente la plupart des données expérimentales et permet l'évaluation des constantes de taux de réaction. Les facteurs pré-exponentiels et les énergies d'activation ont été trouvés au moyen d'une loi d'Arrhénius.

低圧CVDによるTiO<SUB>2</SUB>薄膜の形成過程の<I>In-Situ</I>エリプソメトリー解析

The formation process of a TiO2 thin film on a Si(100) substrate by low-pressure CVD with tetraisopropyl titanate (TPT) has been studied by in-situ ellipsometry. Changes in the growth rate and the refractive index of the film obtained from ellipsometry were examined as a function of the substrate temperature, the vaporization temperature of TPT, and the flow rate of O2 reactant gas. The formation process of the film at the substrate temperatures below 569 K can be divided into two regions; the initial region corresponding to the nucleation of TiO2 and the steady state region corresponding to the growth of the TiO2 layer after coalescence of the nuclei. The initial region was undistinguishable at the substrate temperatures higher than 600 K. The growth rate in the steady state region increased with increasing substrate temperature and the refractive index decreased. At a constant substrate temperature of 695 K, both the growth rate and the refractive index increased with increasing vaporization temperature of TPT. A Raman spectroscopic analysis indicated that the film has an anatase structure. An infrared spectroscopic analysis suggested that the more ordered anatase is formed with the higher substrate temperature.

Characteristics of hollow cathode discharge plasma and its application for the reactive ion plating of TiN and TiC

A hollow cathode discharge (HCD) plasma source was developed and its characteristics were investigated as the evaporation and ionization source for the reactive ion plating of titanium. There is a proper pressure range for ion plating process ∼1×10−2 mbar for the maximum electron density. Titanium nitride and titanium carbide films have been prepared by the HCD plasma enhanced reactive ion plating. The dependence of the electron density and temperature of plasma on the vessel pressure was examined. The interfacial region of the titanium-coated SUS-304 and the high-speed steel substrates were analyzed by the Auger electron spectroscopy depth profiling to identify the effects of the ion bombardment. It was shown that the parameters such as the substrate bias voltage and reactive gas flow rate influenced the film properties such as the crystal orientation, color tone, deposition rate, grain size, and hardness.

Modeling of time-dependent process changes and hysteresis in Ti-O2 reactive sputtering

Understanding the mechanisms of reactive sputtering is thought to be crucial to obtain a better process control and widen applications of reactive sputtering. A model simulating reactive gas mass balance changes in reactive sputtering is described. The model is based on physical mechanisms involved in target and wall gettering behavior. This enables calculation of time-dependent condition changes that occur until the process reaches a steady state, without assuming how the process reaches a steady state. Another important feature of the model is that hysteresis curves are obtained as a result of the calculation of time-dependent target condition changes. This approach to obtain hysteresis curves is more similar to an actual reactive sputtering process. The proposed model clearly displays changes in target coverage, sputtered flux, and reactive gas partial pressure during compound-layer formation and sputter etching processes as a function of elapsed time. Effects of reactive gas flow rate, pumping speed, and sputtering current on compound-layer formation and sputter etching are also discussed. Hysteresis curves are yielded as a result of compound-layer formation and sputter etching calculations. The obtained curves are in accord with experimental results. Further, the dependence of hysteresis on pumping speed, sputtering current, and the difference of sputtering yields between metallic and compound-covered targets was investigated, resulting in showing a good agreement to that obtained experimentally. Mechanisms of hysteresis formation are also discussed on the basis of obtained results. It is concluded that hysteresis is formed because of the difference of gettering capacity before and after the target surface condition transition.

Synthesis of Silicon Carbide–Silicon Nitride Composite Ultrafine Particles Using a Carbon Dioxide Laser

The synthesis and the structure of silicon carbide‐silicon nitride (SiC─Si3N4) composite ultrafine particles have been studied. SiC─Si3N4 composite ultrafine particles were prepared by irradiating a SiH4, C2H4, and NH3 gas mixture with a CO2 laser at atmospheric pressure. The composition of composite powders changed with the reactant gas flow rate. The carbon and nitrogen content of the powder could be controlled in a wide range from 0 to 30 wt%. The composite powder, which contained 25.3 wt%. carbon and 5.8 wt% nitrogen, had a (β‐SiC structure. As the nitrogen con‐ tent increased, SiC decreased and amorphous phase, Si3N4, Si appeared. The results of XPS and lattice constant measurements suggested that Si, C, and N atoms were intimately mixed in the composite particles.

Fine silicon powder synthesis by the laser induced reaction

Fine silicon particles were produced by a continuous wave CO 2 laser driven reaction of SiH 4. X-ray diffraction patterns of silicon particles produced indicated that particles with a highly crystalline structure could be obtained through high power laser beam irradiation. The size distribution was measured by the photo-extinction sedimentation method. The mean size of the particles was 50-200 nm depending on the operating conditions, laser power density, the reactant gas pressure and the reactant gas flow rate. The size distributions obeyed a log-normal relation and the geometric standard deviation was 1.7-1.9. The mean size increased with increasing laser power density, gas pressure and flow rate of SiH 4. The increase of the mean size was influenced by collision and coalescence between the particles.

Deposition of TiN films with titanium interlayer on low carbon steel by reactive r.f. magnetron sputtering

TiN coatings with a titanium interlayer were deposited on low carbon steel by reactive r.f. magnetron sputtering. The preliminary titanium interlayer began to react with oxygen, carbon and nitrogen during sputtering as the substrate temperature was increased. The adhesive strength as estimated by the pull-off test was found to be raised when a titanium interlayer was present. The orientations of the deposited TiN films depended on the reactive gas flow rate and the substrate temperature. It appeared that a (111) TiN film could endure greater stress as a result of lattice misfit. It was also found that the film structure tended to be polycrystalline and consequently it is suggested that with such films the interfacial stress is lowered and so good adhesion can be achieved.

Dry etching in low frequency plasma system

Low frequency dry etching process of SiO2 on GaAs substrates was investigated with different etch gases. The etch rate depends on the flow rate of reactive gases, the applied pressure, the applied rf power density and the polarity of the DC bias connected to the rf electrodes.

Interactions of Cold Radiofrequency Plasma with Solid Wood I. Nitrogen Permeability along the Grain

Abstract Exposure of 1.5 cm diameter × 1.2 cm long white fir and Douglas-fir heart-and sapwood samples to the action of cold radiofrequency oxygen, nitrogen, and helium plasmas strongly increased wood permeability to nitrogen flow along the grain. Oxygen was most effective, followed by nitrogen and helium. While an increase in radiofrequency energy level increased the effect, the opposite was true for an increase in reactant gas flow rate. With white fir the rate of permeability increase was higher at the beginning of the plasma treatment. This was attributed to differing ablation rates of cellulose, hemicelluloses, and lignin. No significant time difference in the rate of permeability increase was observed with Douglas-fir. Extractives suppressed the plasmainduced permeability increase; thus extraction with water and ethanol, followed by oxygen plasma treatment increased permeability of Douglas-fir heartwood 32 times, while plasma treatment of the unextracted Douglas-fir increased permeability only 8 tim...

Interfacial studies of chemical-vapor-infiltrated ceramic matrix composites

The objective of this program was to investigate the fiber-matrix interfacial chemistry in chemical-vapor-infiltrated SiC matrix composites utilizing NICALON SiC and Nextel 400 mullite fibers and how this interface influences composite properties such as strength, toughness and environmental stability. The SiC matrix was deposited using three different reactants: methyldichlorosilane, methyltrichlorosilane and dimethyldichlorosilane. It was found that by varying the reactant gas flow rates, the ratio of carrier gas to reactant gas, the type of carrier gas (hydrogen or argon), the flushing gas used in the reactor prior to deposition (hydrogen or argon) or the type of silane reactant gas used, the composition of the deposited SiC could be varied from very silicon rich (75 at.%) to carbon rich (60%) to almost pure carbon. Stoichiometric SiC was found to bond very strongly to both NICALON and Nextel fibers, resulting in a weak and brittle composite. A thin carbon interfacial layer deposited either deliberately by the decomposition of methane or inadvertently by the introduction of argon into the reactor prior to silane flow resulted in a weakly bonded fiber-matrix interface and strong and tough composites. However, composites with this type of interface were not oxidatively stable. Preliminary results point to the use of a carbon-rich SiC (mixture of carbon plus SiC) interfacial zone to achieve a relatively weak, crack-deflecting fiber-matrix bond but also exhibiting oxidative stability.

Deposition Mechanism of Tungsten Silicide Films by Low Pressure CVD

ABSTRACTWSix thin films were deposited on SiO2/Si substrates by Low Pressure Chemical Vapor Deposition (LPCVD) using WF6 and SiH4 gases. The deposition mechanism has been studied by measuring the thickness, resistivity and composition of the films by varying deposition temperature and gas flow rate at a constant total reactant gas pressure. Below 300°C, the surface chemical reaction was the rate-limiting process and the deposition rate increased exponentially with temperature having a thermal activation energy of 3.2 kcal/mol. Meanwhile, above 300°C the reaction was governed by the mass transfer step in the gas. The deposition rate in this range is insensitive to the deposition temperature but shows dependence of the flow rate of reactant gases. AES and RBS analyses were performed to determine the stoichiometry of WSix thin film. The Si content in film gradually increased as the deposition temperature increased. The resistivity of as-deposited WSix film has dependence on both deposition temperature and Si/W ratio, and exponentially increased with a moderate slope. However, temperature insensitive behavior of resistivity appeared in the mass transfer controlled region. Such resistivity changes with temperature were discussed with the Si/W ratio and the microstructure of films.

Time-dependent simulation modelling of reactivesputtering

A time-dependent simulation model of reactive sputtering is proposed. The model deals with time-dependent poisoning of the target surface and hysteresis phenomena. The model is based on the calculation of the time-dependent change in gettering pumping speed and target poisoning speed, yielding the time-dependent change in target coverage and reactive gas partial pressure. By calculating the equilibrium values of the time-dependent change over a range of reactive gas flow rates, hysteresis effects of target coverage and reactive gas partial pressure are investigated as a function of the gas flow rate. The hysteresis results obtained suggest that with the time-dependent model it is possible to evaluate the effect of pumping speed on the transition points and width of hysteresis curves. As compared with experimentally investigated results it is found that the model explains mechanisms of reactive sputtering qualitively.

ハイドライドＶＰＥ法によるＧａＮの成長及びその諸特性

Gallium nitride (GaN) epitaxial layers are grown on oe-Al203 (0001) substrates, by using a hydride vapor-phase-epitaxy method. Surface morphology, crystal structures and electrical properties of the films are investigated in respect of the growth conditions. Surface morphology of the films depends upon the growth temperature and the ratio of the reactive gas flow rates. Relalively smooth surface is obtained when the NH3 flow ratio is large, and its electrical properties are also good. The optical band gap of the films with smooth and transparent surface is about 3.4eV.

The effect of target-substrate coupling on reactive direct current magnetron sputtering

Summary From a consideration of the reactive gas flow rates and of the reactive gas partial pressure a criterion for process stability in reactive direct current magnetron sputtering is derived. By a discussion of this stability criterion the methods of self-stabilization and stabilization through high pump speed are deduced. If the gas discharge is considered as a getter pump with a reactive gas pressure dependent pumping rate S Dis ( p R ), the stability criterion includes a term — d S Dis /d p R which describes the degiee of target-to-substrate coupling (TSC). From this the method of stabilization through reduction of TSC, i.e. through decoupling, is deduced. The relationship of process stability, TSC and film properties is discussed and exemplified by the system CrSi-O 2 . Coating of large areas and plasma-assisted deposition call for strong TSC, which may be contradictory to the stability criterion. An active closed-loop control circuit, e.g. using the plasma emission intensity signal (PEM control), has to be employed for process stabilization.

Synthesis of silicon carbide powders by a CW CO2 laser

Ultrafine SiC ceramic powders have been produced by irradiating silane and acetylene mixtures with a CW CO 2 laser. The work is mainly concerned with the evaluation of the parameters affecting the material production efficiency: laser power and laser intensity, pressure in the reaction chamber, reactant and carrier gas flow rates. The characterization of the produced material refers to particle composition, size and shape and crystalline structure. Sintering tests have been made in order to evaluate the performances of laser-produced ceramic powders. Preliminary measurements aimed at the evaluation of the feasibility of process scaling-up have been also carried out.

Film stress-related vacancy supersaturation in silicon under low-pressure chemical vapor deposited silicon nitride films

The effect of stress in silicon nitride films, deposited by the low-pressure chemical vapor deposition process, on the point defect concentrations in silicon has been studied. The stress level in the nitride film is varied by controlling the ratio of flow rates of reactant gases R=fSiH2Cl2/fNH3, from 1/6 to 6. The stress in the nitride film is tensile and its magnitude increases with decreasing R. During anneals at 1100 °C in Ar with a high stress in the nitride, phosphorus diffusion in silicon is retarded, antimony diffusion is enhanced, and extrinsic stacking faults shrink faster than with a low stress. These results suggest that a vacancy supersaturation and a self-interstitial undersaturation exist under the nitride and that the deviation from the equilibrium point defect concentrations are closely related to the stress level in the silicon nitride film. From the phosphorus junction profiles with varying shape width, an effective vacancy diffusivity of 3×10−10 cm2/s has been obtained.

Influence of process parameters on the composition and the electrical properties of thin-plasma-nitrided oxides

We studied the influence of process parameters on the composition and the electrical properties of thin SiO2 films nitrided in a plasma reactor of a novel design. The process parameters investigated include pressure, temperature, reactant gas species and flow rate, plasma frequency and power, and process duration. The structure and morphology of these films were examined by cross-sectional transmission electron microscopy. Their composition was analyzed using Auger electron spectroscopy, secondary ion mass spectroscopy, and etch rate measurements. Metal–oxide–semiconductors capacitors were fabricated and electrically characterized by C–V, time-dependent breakdown, and charge trapping measurements. Our results show that more nitrogen is incorporated in films treated in a NH3 plasma than in a N2 plasma. Yet, the latter films present better electrical properties. Compositional variations between different films are not sufficient by themselves to explain their electrical properties. It appears that the effect of ion bombardment in the plasma plays an important role. By properly optimizing process parameters, the charge to breakdown of nitrided films can be enhanced over that of SiO2. This improvement is ascribed to a lower electron trapping rate.

The effects of deposition variables on deposition rate in the chemical vapour deposition of silicon nitride

Amorphous Si 3N 4 was deposited by a chemical vapour deposition technique using an SiCl 4, NH 43 and H 2 gaseous mixture onto a silicon single crystal. The effects of deposition time, substrate temperature, gas flow rate, system pressure and partial pressure of reactant gases on the deposition rate were investigated. The metal-insulator-semiconductor (MIS) structure was fabricated by evaporating gold on Si 3N 4 to measure the charges stored in the interface between the insulator and silicon. The charges were determined for different deposition temperatures from capacitance-voltage plots. The experimental results indicate that the growth of Si 3N 4 is a thermally activated process in this experimental condition. It is calculated that the apparent activation energy is about 33 kcal mol -1 below the deposition temperature of 1100 °C. The homogeneous reactions in the gas phase are promoted when the total pressure is increased. At pressures above 300 Torr, deposition rates are decreased because the reactant gases are depleted because of the homogeneous reaction. The charges stored in the MIS structure are found to be larger at lower deposition temperatures.