Variation Of Deposition Rate Research Articles

Plasma‐Assisted Chemical Vapor Deposition and Characterization of Boron Nitride Films

Boron nitride films were deposited in a single‐wafer plasma enhanced chemical vapor deposition (PECVD) system using two different reactant gas chemistries: (i) dilute diborane (1% in nitrogen), nitrogen and ammonia; (ii) borazine, and nitrogen as precursor materials. Variations of deposition rates, thickness uniformities, refractive indexes, wet and plasma dry etch rates, film stress, and electrical properties were studied as a function of the corresponding deposition parameters. Several analytical methods such as Fourier transform infrared spectroscopy, x‐ray photoelectron spectroscopy, nuclear reaction analysis, elastic recoil detection analysis, scanning and transmission electron microscopy were used to study the deposited films. Electrical properties were measured using metal‐insulator‐metal and metal‐insulator‐semiconductor structures. The stable boron nitride films do not react with water vapor showing dielectric constant values between 4.0 and 4.7. These good insulators also show promising characteristics for potential applications in high‐performance ultralarge scale integration fabrication.

Temperature fluctuations during the deposition of InSb films

High-quality InSb films must be grown through the melting-solidification process. A fluctuation of the film temperature, especially in the early stages of the evaporation process gives rise to this melting-solidification process. The shape of the temperature fluctuation curves can be explained by the variation of deposition rate during the evaporation process. It was found that the fluctuation of the film temperature was closely related to the maximum value of the deposition rate. The optimum fluctuation curve of film temperature was established by selecting a suitable value of the maximum deposition rate. The maximum deposition rate of around 50 Hz/s gives the optimum fluctuation curve, which causes a large area of black spots. The effectiveness of the sensing position of the substrate temperature on the fluctuation of film temperature is also investigated.

A possible mechanism for the recrystallization of InSb film on mica substrates

The recrystallization of InSb films while growing through the melting–solidification process was investigated in detail. A great fluctuation of the film temperature was seen in some cases of the growing film, especially in the early stage of the evaporation process. This fluctuation of the film temperature gives rise to the melting–solidification process. In this work, two distinct types of temperature fluctuations were observed. It was found that the shape of the temperature fluctuation curves can be reasonably explained by the variation of deposition rate in such a way that a higher deposition rate at the early stage of evaporation yields higher temperature fluctuations. The deposition rate was also found to depend on the preheating time of source, hence the optimum deposition rate was easily obtained by varying this time. The optimum substrate temperature and preheating time for high quality InSb films were 260 °C and 180 s, respectively. The present method greatly improves the reproducibility of preparing high quality InSb thin film.

Kinetics of ion beam deposition of carbon at room temperature

Growth rates of carbon films grown by ion beam deposition using methane gas were measured in situ as a function of deposition conditions. The methane pressure dependence of the growth rate was used to measure the cross-section for charge exchange. Variations in deposition rate per incident energetic particle found for each ion energy were related to ion current density. It was found that rates of growth per incident energetic specie were (i) largest for the smallest current densities, (ii) decreased monotonically with increasing current density, and (iii) were consistently larger than can be explained by deposition directly from the energetic flux alone. These observations were interpreted in terms of irradiation-induced surface interactions which promote chemisorption of methane physisorbed from the ambient atmosphere.

SiC membranes for x-ray masks produced by laser ablation deposition

Laser ablation deposition is used for the first time to fabricate SiC membranes for x-ray lithography. The process has the unique advantage of producing in a very simple manner purely stoichiometric (1:1) SiC films free of hydrogen. The variation of deposition rate with laser energy and intensity, the uniformity and quality of the films produced as well as an estimate of the energy of the neutrals and of the ions involved in the deposition are presented. SiC membranes of 1 in. diam have been successfully fabricated after anisotropic etching of the silicon substrate in a KOH solution. They present an optical transparency of 40% at 633 nm.

Droplet entrainment and deposition in horizontal annular flow

Local measurements of droplet fluxes, in the core of horizontal annular flow, are employed in order to calculate the liquid concentration distribution as well as the circumferential variation of deposition rate. A relatively simple model is proposed for predicting the above quantities. Terms representing fluxes due to turbulent diffusion and gravitational settling are used in the model. An additional parameter a is introduced and is considered to represent a combination of fluxes; i.e. the net upward flux of droplets responding to turbulence and the flux of droplets that gain high inertia upon atomization. An interpretation is given of average deposition (or atomization) rates obtained from the data, by using detailed information on film thickness properties and by recognizing that only films with a local thickness greater than a critical value can contribute to atomization. The development of a physically realistic correlation for the mean deposition rate is explored.

CVD of Silicon Carbide on Structural Fibers: Microstructure and Composition

AbstractStructural fibers are currently being considered as reinforcements for intermetallic and ceramic materials. Some of these fibers, however, are easily degraded in a high temperature oxidative environment. Therefore, coatings are needed to protect the fibers from environmental attack.Silicon carbide (SiC) was chemically vapor deposited (CVD) on Textron's SCS6 fibers. Fiber temperatures ranging from 1350 to 1500 °C were studied. Silane (SiH4) and propane (C3H8.) were used for the source gases and different concentrations of these source gases were studied. Deposition rates were determined for each group of fibers at different temperatures. Less variation in deposition rates were observed for the dilute source gas experiments than the concentrated source gas experiments. A careful analysis was performed on the stoichiometry of the CVD SiC-coating using electron microprobe. Microstructures for the different conditions were compared. At 1350°C, the microstructures were similar;however, at higher temperatures, the microstructure for the more concentrated source gas group were porous and columnar in comparison to the cross sections taken from the same area for the dilute source gas group.

Sediment dispersal and accumulation on the continental margin of the Gulf of Lions: sedimentary budget

An integrated study of particle transport, deposition and storage was carried out over the continental margin of the Gulf of Lions (northwestern Mediterranean Sea). The dispersal system of fine-grained sediment is discussed and a sedimentary budget of sediment transfer and accumulation is established. Sediment cores were collected from the continental shelf and slope, along the ECOMARGE—I transect. Accumulation rates were measured using radiochemical techniques. Sediment traps were deployed, from 1985 to 1986, at two sites: on the continental shelf (27 m) and in the Lacaze-Duthiers Canyon (645 m). This study revealed that the most important sedimentary processes on this margin are high seasonal variability of lithogenic particle fluxes and lateral advection. The major fluctuations are related to storm events, to an increase in river discharge and the intensity of the regional current. Flux gradients increase exponentially toward the bottom, in shallow and deep water. However, in the deeper traps at the two sites annual lithogenic fluxes decrease seaward, from 25 to 3.5 g m −2 day −1. Across this margin, sediment accumulation rates ranged from 2.9 g m −2 day −1, on the middle of the prodeltaic area, to 0.16 g m −2 day −1 at 645 m in the canyon. Smectite was found to be a natural tracer for characterizing an annual cycle of sediment input, deposition, resuspension and shelf-slope exchange processes. At the shelf site, two intra-annual cycles of sedimentation and erosion of the surface sediments were recognized. Comparison between trap deposition rates and bottom sediment accumulation rates implies that the prodelta area acts as a zone of storage (11%) for the silty material and as a temporary sink for fine-grained sediment, that is eroded from the area in winter. In the canyon, variations in deposition rates, smectite content, and grain size are related to morphological features and the various modes of transport that control sedimentation. The discontinuity in the flux gradient between surface and deep layers, and the discrepancy between long-term accumulation rates based on 14C dating and trap deposition rates suggest that fluxes in the deeper layer in the canyon are in fact essentially controlled by settling from the intermediate nepheloid layers detached from the shelf break and by along-bottom transport; also that resuspension has a longterm impact on the entire canyon maintenance. On the other hand, comparing near-bottom trap 210Pb fluxes to the fluxes required to support the excess 210Pb inventories in the sediments leads to the conclusion that much (70%) of the particulate flux passes through the canyon to the deep sea on this short time scale (< 100 years).

A-Si:H Deposition from SiH4 and Si2H6 rf-Discharges: Pressure and Temperature Dependence of Film Growth in Relation to α-γ Discharge Transition

We present an interpretation of the pressure and temperature dependence of the growth kinetics of hydrogenated amorphous silicon (a-Si:H) in SiH4 and Si2H6 rf-glow discharges. At constant rf power, the a-Si:H deposition rate increases drastically at a given pressure depending on the nature of the gas and on the wall temperature. The threshold nature of this transition is attributed to the onset of an electron avalanche due to ion-induced secondary electron emission and ionization in the plasma sheaths close to the electrodes. We analyze the effect of various plasma parameters governing this α-γ discharge transition in terms of equivalent circuit of the discharge and power dissipation mechanisms. The ratio of a-Si:H deposition rates from SiH4 and Si2H6 rf discharges at the same rf power and flow rate is strongly dependent on the pressure because the α-γ transition occurs at a lower pressure for Si2H6 than for SiH4. The transition is shifted to higher pressures as the temperature increases primarily because of the reduction of gas density, which explains contradicting results in the literature on the influence of temperature on a-Si:H deposition rate. At a given rf power and substrate temperature, the optical, structural and electrical film properties are correlated with the variation of deposition rate as a function of SiH4 or Si2H6 pressure.

Convective Transport in Silicon Epitaxial Deposition in a Barrel Reactor

Much of the silicon epitaxial deposition done in the semiconductor industry is done in infrared heated barrel reactors. Measurements of deposited epitaxial layer thickness distributions summarized in this paper give an indication of the variations in deposition rate that typically occur within these reactors. To gain insight into the causes of these variations, an experimental apparatus was constructed and used to investigate the gas flow patterns. The flow measurements revealed a strong recirculation pattern driven by the momentum supplied by the flow through the inlet nozzles. Effects of gas flow rate and nozzle aiming on the flow pattern were determined. Cholesteric liquid crystal films were used to gain additional insights into how the flow patterns affect the transport of silicon to the surface. The flow and heat‐transfer measurements were related to the measurements of deposited layer thickness.

Syn-sedimentary and burial related deformation in the Middle Jurassic non-marine formations of the Yorkshire Basin

Summary The non-marine formations of the middle Jurassic Ravenscar Group consist of channel sandstone bodies set in interbedded mudstones, silts and thin sheet sandstones. These rocks contain syn-sedimentary and burial related deformation structures. Frequent discharge fluctuations are deduced to have enhanced inherent river bank instability and with occasional tectonic movements produced a wide range of bank collapse structures. These had a low preservation potential and are observed at various stages of erosion. Several faults associated with channel sandstones can be related neither to tectonic activity nor to bank collapse. They may be explained as compensation structures formed during differential compaction of the sandstones and adjacent mudstones. Differential compaction structures form on a smaller scale around plant material, early diagenetic nodules and sandstone dykes. Continued sedimentation on the alluvial plain, together with differential compaction, produces a positive topography over channel sandstones. This effect was reduced by variations in deposition rate and facies. Laterally continuous beds deposited on this topography form gentle folds that are exaggerated by differential compaction during burial. Although most of the deformation seen in the Ravenscar Group is related to alluvial processes or sediment burial, some is connected to syn-sedimentary tectonic activity.

The temporal and spatial variations in the aerial deposition of metals for a residential area adjacent to a motorway

Part of a study into the pathways utilised by heavy metal pollutants during their passage through a small residential catchment involved collecting data on aerial deposition. Vandalism to the network of deposit cannisters necessitated adoption of a novel approach for the determination of mean deposition rates. The paper discusses the relationship between temporal variations in deposition rate and meteorological parameters, and comments on spatial variations across the catchment.

Pressure effects in planar magnetron sputter deposition

Argon pressure during magnetron sputtering affects coating uniformity, deposition rate, and target bias under constant current conditions as well as coating microstructure, stress level, and chemical composition. This paper reports the results of an investigation into the effects of argon pressure on coating uniformity, deposition rate, and target bias. The experimental results indicate that both coating thickness uniformity and deposition rate improve with decreasing argon pressure. A diffusion model predicts the variation of deposition rate with argon pressure, in qualitative agreement with experimental data. For pressures greater than 10 mTorr, the deposition rate varies inversely with pressure. The unexpected decrease in uniformity with increasing pressure is explained by comparing a model diffusion ‘‘kernel’’ with the cosine distribution. The width of the diffusion kernel is less than the width of the cosine distribution.

Room temperature glow discharge deposition of silicon oxides from SiH4 and N2O

Room temperature plasma deposition of silicon dioxide from silane and nitrous oxide has been described. Depositions were made using a capacitively coupled magnetically enhanced glow discharge system. Near stoichiometric SiO2 was deposited at N2O/SiH4 flow ratios from 11:1 to 2.3:1. Mass spectroscopic analyses of the plasma during the deposition suggest that the SiO2 forming reaction takes place between oxygen from decomposition of N2O and silane. MS data also show that the decomposition rates of N2O and and SiH4 in the glow discharge differ as a function of power with N2O decomposing at a lower rate. As a result, in a magnetically enhanced glow discharge where there are power density variations throughout the system, there will be corresponding variations in deposition rate and deposit properties.

Monitoring roadside lead deposition by sampling vegetation — Some problems of interpretation

Analysis of samples of roadside vegetation has often been used as a means of investigating the pattern of lead deposition in relation to such factors as traffic density. Longer term monitoring presents a number of difficulties: differing Pb retention capacities of different kinds of plant material, seasonal and spatial variation in vegetation density, height, live/dead ratio and longevity. Seasonal variation of deposition rates and possibly deposition routes are apparently superimposed on these variables. The problems of interpretation are discussed in the light of experience of a 3-year sampling programme.

Heavy metal uptake in transplanted and in situ yarrow (Achillea millefolium) and epiphytic cryptogams at rural, urban and industrial localities in Denmark

Yarrow (Achillea millefolium L.) and 3 cryptogamic epiphytes were collected from and transplanted to 10 various locations in Denmark. The spatial and temporal variation in Pb and Cd concentrations of yarrow leaves and the cryptogams were determined. The physical structure of the plant parts, the mobility differences between the metals and the atmospheric fallout of metals at the growing site were believed to be important for the metal uptake. It was concluded, that yarrow leaves give a measure of the relative variation in deposition rates to surface of higher plants when collected at the end of a growth season, and that the geographic variation was revealed with similar accuracy by yarrow and the cryptogams.

CHANNEL SHOALING PREDICTION: A METHOD AND APPLICATION

Due to concerns of possible shoaling problems, an extensive field survey program was carried out at the site of the proposed Cerrejon coal port on the Caribbean coast of northeast Colombia. The program yielded considerable data on winds, waves, currents, and sediment factors. Techniques for the primary measurement of sedimentation-related tendency included dredged test pits, scour crosses, and suspended sediment samplers. The port plan includes dredging a 4.6 kilometer long channel varying from 12 to 21 meters in depth. In order to assess the magnitude of maintenance dredging and related problems, a method was developed for incorporating the sediment response measurements into predictions of the areal and seasonal distributions of bed load and suspended sediment deposition. Offshore test pits were monitored for rate of filling and character of the material being deposited. Suspended sediment samplers were similarly observed and also provided data on concentration versus depth. The procedure which was developed for analysis and interpretation of the data included extrapolation of suspended sediment data to the seabed, investigation of correlations between wind activity and deposition rates, application of test pit data to a channel of larger dimensions, and testing of hypotheses regarding transport mechanisms. The procedure concluded that average annual shoaling would be approximately 300,000 m and predicted areal and seasonal variation of deposition rates.

10Be dating of North Pacific sediment cores up to 2.5 million years B.P.

The10Be method of dating of marine sediment cores is applied to five North Pacific cores. Assuming a constant10Be precipitation rate and varying sedimentation rates with time during the past 2.5 m.y. dating confirms to that obtained from paleomagnetic stratigraphy. The10Be concentration variations with depth in the cores are primarily due to changes in sediment dilution and do not reflect cosmic ray intensity or global climate variations. The limits of10Be deposition rate variation in the investigated cores are less than ± 10% for periods of (2–7) × 105 years and less than ±30% for periods of 1 × 105 years. The data set gives a half-life of10Be is 1.50 × 106 years. The latitudinal effect of10Be concentrations and10Be/9Be ratios relates to a frequency of particulate matter occurrence (detrital and biological particles) in the oceans and to oceanic circulation.

Observation of Gas Bubbles in Vapor-Deposited Gold Films

Voids or gas hubbies have been observed in sputtered and evaporated gold films, following post deposition annealing. Small voids have also been observed in gold films after electromigration (EM). AS few voids are visible before annealing or prior to EM, it was concluded that these processes are responsible for the principal mechanism for void formation. We have made a further study on the formation of voids or gas bubbles in as-deposited as well as annealed gold films which are prepared by vapor deposition. It is demonstrated that a large number of voids (&lt; 50 Å) are, in fact, present in gold films prior to annealing or EM.Single-crystal gold films were grown epitaxially by vapor deposition onto KC1 substrates held at 250°C in an ion-pump vacuum of 1 x 10-5 Torr. In order to obtain a variation in deposition rate within a single sample, deposits were made through a mask separated from the substrate, resulting in significant shadowing.

Reflectance and optical constants of evaporated ruthenium in the vacuum ultraviolet from 300 to 2000 Å*

The reflectance and optical constants of evaporated ruthenium films were measured in the wavelength region from 300 to 2000 Å. The films were evaporated by electron bombardment in an ion-titanium-pumped vacuum system and were typically deposited at a rate of about 40 Å/s onto glass and super-polished fused-quartz substrates which were at 40 and 300 °C. Variation of deposition rate from 1 to 80 Å/s had very little effect on their reflectance. The optical constants were determined from reflectance measurements made at several angles of incidence. Reflectance losses during extended exposure to air were rather small, indicating that, if oxide films form at room temperature, they are very thin. Films made on substrates at 300°C had slightly higher reflectances than those made at 40°C. Owing to interference effects, semitransparent films 150 to 200 Å thick showed higher reflectances than opaque films at wavelengths in the region of 584 Å. At wavelengths near 2000 Å, films 300 Å thick had highest reflectances. Ruthenium films prepared under optimum conditions had reflectances of 26% at 584 Å.