Decrease In Deposition Rate Research Articles

Allotaxy in the Ni–Si system

Allotaxy is a special method to grow epitaxial heterostructures. An important role in this process is the distribution of the crystallites of the compound AB X in the matrix A. This study concerns the first step of allotaxy in the Ni–Si system, that is, the preparation of the precipitate distribution. To investigate the influence of the deposition conditions on the growth and arrangement of the precipitates the substrate temperature as well as the deposition rate have been varied. RBS measurements revealed the redistribution of the deposited Ni already during the deposition process resulting in precipitate coarsening. This effect increases with increasing substrate temperature and decreasing deposition rate. A strong diffusion of Ni atoms towards the sample surface has been observed. The TEM analysis shows that oriented cubic NiSi 2 is grown. Under appropriate deposition conditions self-assembling of the NiSi 2 precipitates has been observed.

Lateral variability of overbank sedimentation on a Devon flood plain

Deployment of sediment traps over a 12-month period has enabled investigation of the lateral variability of overbank deposition rates and particle size composition of deposited sediment across a frequently inundated flood plain section of the River Culm, southeast Devon, UK. Although a general exponential decrease in deposition rate and grain size with distance from the channel occurs, significant deviations from these trends are associated with the microtopography of the flood plain and secondary flow routes and, in particular, with ditches. The coarsest material and the greatest variability in deposition rates occur within a few metres of the channel. Similar trends are evident for mean particle size, percentage silt and clay, arithmetic sorting and skewness. These parameters also display substantial variation at the distal margins of the flood plain due to the presence of drainage ditches.

The influence of magnetron configuration on ion current density and deposition rate in a dual unbalanced magnetron sputtering system

A series of experiments were carried out to investigate the influence of magnetron configuration on the performance of a dual unbalanced magnetron system. The rig was operated in the closed-field (CF), mirrored-field (MF) and, for comparison, single unbalanced magnetron (UBMS) configurations. The performance of the rig was assessed in tenns of the substrate ion current density, I s , deposition rate, R, and the ion-to-atom ratio incident at the substrate, J i /J a . R was not significantly influenced by magnetron configuration. Also, for all configurations. R decreased with increasing substrate-to-target separation, d s-t , in a relationship of the form R=a(d s-t ) b , where b-2. I s also decreased with increasing d s-t . However, I s values were 2-3 times lower, and the rate of decrease of I s with increasing d s-t was greater, when operating in the MF, or UBMS mode, compared to the CF mode. Values of b in the relationship I s =a(d s-t ) b were -0.26, -0.53 and -0.59 for the CF. UBMS and MF modes, respectively. An important finding of this study is that, although both deposition rate and ion current density decrease with increasing separation, because the rate of change with separation is different in each case, the ion-to-atom ratio actually increases with increasing separation. For example, operating in the CF mode. J i /J a was found to increase from 1.25 to 3.0 when d s-t as increased from 80 to 150 mm.

Run by run advanced process control of metal sputter deposition

Metal sputter deposition processes for semiconductor manufacturing are characterized by a decrease in deposition rate from run to run as the sputter target degrades. The goal is to maintain a desired deposition thickness from wafer to wafer and lot to lot. Run by run (RbR) model-based process control (MBPC) has been applied to metal sputter deposition processes at Texas Instruments. RbR MBPC, based on the exponentially weighted moving-average filter, provides the ability to track and compensate for process drifts without a priori assumptions on their magnitude or consistency (from sputter target to sputter target or collimator to collimator). The application of RbR MBPC resulted in an improved C/sub pk/ of 44% for aluminum sputter deposition, while reducing the number of lot-based monitor wafers by a factor of three. The application of RbR MBPC to the titanium sputter deposition process eliminated look-ahead test runs and reduced the number of monitor wafers by a factor of three. At the same time, C/sub pk/ was improved by 10% with the application of RbR MBPC.

Computer modeling as a tool to predict deposition rate and film composition in the reactive sputtering process

Reactive sputtering is a widely used technique to deposit oxides, nitrides, etc. A serious drawback of this technique, however, is the drastic decrease in deposition rate that almost always occurs when depositing compound films as compared to depositing pure metal film. In many cases it is possible to overcome this problem by operating the process in the narrow critical processing region between metallic and compound mode sputtering. In this processing region, however, the composition of the deposited compound thin film is extremely sensitive to the processing conditions. It is, therefore, very interesting to investigate the sensitivity of different processing parameters on the overall processing behavior. Computer modeling can be used as a tool to increase the understanding of this complex process. We will show that such results can be used to illustrate the individual effects of the major involved processing parameters. It also serves to assist in the work of process optimization. The relationship between target poisoning, argon current density, deposition rate, reactive gas supply, partial pressure, total pressure, and film composition have been carefully examined. In particular, we will point out a serious limitation that may arise during high rate multielement reactive sputter deposition. The effect of different reactivity of the involved elements may cause that one of the elements during deposition will not be fully oxidized.

Characterization of Low-Temperature PECVD Silicon Dioxide Films

AbstractSilicon dioxide (SiOx, x ≤ 2) films were plasma-deposited at a pressure of 1 Torr and low substrate temperature (≤ 300°C) by N20/lSiH4 flow. Deposition rates in the range 20–50 nm/min were achieved at 20 W rf source power. Deep level transient spectroscopy showed that no significant defect levels were introduced in the Si substrates at this low source power. The effects of flowrate ratio, R, of N2O/SiH4 and substrate temperature on film properties were determined using ex-situ spectroscopic ellipsometry, prism coupler, Rutherford backscattering spectroscopy (RBS), secondary ion mass spectrometry (SIMS), Fourier transform infrared spectroscopy (FTIR) and chemical etching (P-etch). Near-stoichiometric oxide layers were obtained for R ≥ 1, and a decrease in deposition rate with increasing R was observed. The increase in refractive index for R ≤ 1 has been correlated to compositional changes in the thin films. Complementary results were obtained from FFIR and P-etch measurements. Nitrogen was present in the films deposited using R = 4.4, for which the depostion rate showed an Arrhenius-like relationship to substrate temperature. No OH-related bands were observed in our films.

Percolation and Continuation Thickness of Ag Films on the Initial Growth Stage

Growth of vapor-deposited Ag films by the coalescence process in the post-nucleation stage is discussed. During and after deposition, the amplitude V of surface acoustic waves (SAW) propagated on the piezoelectric substrate through the films deposited on it, and the electric sheet resistivity of the films, Rsq, were measured. The microstructures of films with various thicknesses d were examined with a scanning electron microscope. As a result, it was found that (1) the thickness dp at which V reaches a minimum value corresponds to the critical thickness at which the islands of a film begin to percolate, (2) the thickness dc at which 1/Rsq begins to be proportional to the film thickness corresponds to the critical thickness at which the film becomes two-dimensionally continuous, (3) dp and dc become larger with decreasing deposition rate, and (4) in the early coalescence stage (d<dp), the microstructural change progresses, increasing the average inter-island spacing. From these results, we can conclude that a higher deposition rate is necessary to suppress the microstructural change of islands and to allow fabrication of continuous ultra-thin films.

Particle deposition on a rotating disk in application to vapor deposition process (VAD)

Vapor Axial Deposition (VAD), one of optical fiber preform fabrication processes, is performed by deposition of submicron-size silica particles that are synthesized by combustion of raw chemical materials. In this study, flow field is assumed to be a forced uniform flow perpendicularly impinging on a rotating disk. Similarity solutions obtained in our previous study are utilized to solve the particle transport equation. The particles are approximated to be in a polydisperse state that satisfies a lognormal size distribution. A moment model is used in order to predict distributions of particle number density and size simultaneously. Deposition of the particles on the disk is examined considering convection, Brownian diffusion, thermophoresis, and coagulation with variations of the forced flow velocity and the disk rotating velocity. The deposition rate and the efficiency directly increase as the flow velocity increases, resulting from that the increase of the forced flow velocity causes thinner thermal and diffusion boundary layer thicknesses and thus causes the increase of thermophoretic drift and Brownian diffusion of the particles toward the disk. However, the increase of the disk rotating speed does not result in the direct increase of the deposition rate and the deposition efficiency. Slower flow velocity causes extension of the time scale for coagulation and thus yields larger mean particle size and its geometric standard deviation at the deposition surface. In the case of coagulation starting farther from the deposition surface, coagulation effects increases, resulting in the increase of the particle size and the decrease of the deposition rate at the surface.

Excimer Laser Ablation of Silicon at High Temperature

AbstractPulsed laser ablation of granulated Si target was carried out at 1200 °C in an Ar atmosphere. Multishot ablated target surface forms intensity dependent features, including porous, skeleton, and columnar structures. Very long columnar structures were observed when the angle of the target surface with respect to the direction of the laser beam was small. Evidence on preferable remove of smaller particles has been observed. Formation of the columnar structures started from the biggest particles at the surface and grew deeper, straight in the laser beam direction, by consuming the removed Si species from the deep channel between columns. The Si species ablated off the granulated Si target deposited as Si nanowires or nanoparticles down stream of the Ar flow. Significant decrease in the deposition rate of Si nanostructures has been observed upon the formation of the columnar structures at the target surface.

Investigations of the surface chemistry of silicon substrates etched in a rf-biased inductively coupled fluorocarbon plasma using Fourier-transform infrared ellipsometry

In situ Fourier-transform infrared (FTIR) ellipsometry has been performed on silicon substrates processed in a rf-biased transformer coupled plasma reactor. Plasmas in CHF3, CF4, C2F6, and C4F8 have been used. The reaction layer, which is present on the surface of the silicon wafer during the plasma process, has been analyzed in detail, addressing both chemical composition and thickness. The absolute reliability (expressed in terms of thickness) of the results is of the order of 0.01 nm, which corresponds to 3% of a monolayer. The instabilities of a silicon surface, which have been observed under specific conditions, can be of the order of tens of percents of a monolayer, which clearly illustrates the advantage of using a real in situ technique like FTIR ellipsometry over quasi in situ techniques like x-ray photoemission spectroscopy and Auger electron spectroscopy. For CHF3 plasmas it has been found that, if the bias increases to moderate levels (30–50 V), the fluorocarbon film deposition rate decreases and the silicon etching reaction rate increases. The reaction layer changes from a thick, predominantly CFx polymerlike film to a thin, carbon dominated layer of plasma and etching products showing vibrational absorptions of SiFx, C–C, and CF2. Increasing the bias voltage in a CHF3 plasma has a similar effect as increasing the F/C ratio of the feed gas.

The effect of coating grain size on the selective oxidation behaviour of Ni-Cr-Al alloy

Arnell showed that the grain size of sputter-deposited Cu coatings decrease with the decreasing deposition rate following a linear relation. Therefore, different deposition parameters may produce coatings with different grain size. In the present program, the authors used the unbalanced magnetron sputtering technique to produce a series Ni-Cr-Al alloy coatings on Ni-Cr-Al substrates. The general compositions of the alloys are Ni-20Cr-XAl where X = 1,2,3, and 5 (weight percent). During deposition, the Ar pressure was varied in order to control the deposition rates. The present report is concentrated on the effect of coating grain size on the oxidation behavior of 78Ni-20Cr-2Al.

Effect of the pressure on the chemical vapor deposition of copper from copper hexafluoroacetylacetonate trimethylvinylsilane

The effects of the deposition pressure on the deposition rate and the properties of the copper film prepared by chemical vapor deposition were studied. Copper films were deposited on titanium nitride (TiN) substrates in a low-pressure warm-wall reactor using copper(I) hexafluoroacetylacetonate trimethylvinylsilane, Cu(hfac)(tmvs), as the precursor. The deposition temperature was varied between 160°C and 220°C, and the deposition pressure was varied in the range 0.25–1.0 Torr. The deposition rate decreased with total pressure in the low-temperature region limited by surface reaction, whereas the rates were constant in the high-temperature region limited by mass transport. The decrease of deposition rate in the region limited by surface reaction is thought to be due to the by-product inhibition. The transition temperatures of the kinetic region and the surface morphology coincided with each other. In addition, both of them increased with the total pressure of the reactor. The surface roughness and resistivity decreased with total pressure, and showed rapid increase with deposition temperature. The effect of the partial pressure of the precursor on the deposition rate was also investigated.

Influence of oxygen on the nucleation and growth of diamond films

The addition of oxygen to a diluted methane/hydrogen gas mixture (2% CH 4 in H 2) activated by a microwave discharge during diamond film deposition has been studied. We have observed that oxygen addition at very low concentrations (< 2%) to the methane/hydrogen gas mixture makes the nucleation of diamond crystals more difficult, by causing a sharp decrease in the deposition rate of the diamond film. For increasing oxygen concentrations, in the [O 2] = 0.25 – 1% range, the diamond and graphite deposition rates remain nearly constant, showing a slight decrease in the graphite deposition rate for [O 2] = 1%. By contrast, for higher oxygen concentrations (1% < [O 2] < 2.5%) thinner films of a high quality are deposited (diamond content > 84%). These facts have been explained by an abrupt change in the chemical processes when the oxygen is fed to the CH 4 + H 2 mixture, even in a small concentration. We assume that the role of the atomic oxygen is two-fold: (i) formation of OH radicals, which etch the diamond and graphite phases at high rates, and (ii) direct etching of the initial carbon layer formed during the nucleation stage, producing CO molecules. However, for [O 2] ≥ 2.5% the carbon etching rate (for all the phases) is so high that no continuous film can be deposited. In this paper we present the relative variation of the formation, in the 0–2.5% oxygen range, for both the diamond and non-diamond phases, as determined by Raman spectroscopy and scanning electron microscopy. The results have been related to the changes in the plasma composition (mainly the OH, O and CO species), as detected by optical emission spectroscopy and mass spectrometry.

An improvement of surface smoothness and lattice match of CeO 2 buffer layers on R-sapphire processed by MOCVD

Epitaxial thin films of CeO 2 and Ce 1− x R x O 2− y (R=Y, Nd; x=0–0.32) on R-sapphire were prepared by band flash evaporation MOCVD. It was demonstrated that the smoothness of the films can be improved by a decrease of deposition rate and by post deposition annealing at 1000 °C. The lattice match of buffer layers with R-Al 2O 3 and YBa 2Cu 3O 7−δ was improved by doping of ceria yttrium and neodymium correspondingly. A bilayer structure Ce 0.7Nd 0.3O 2− y /Ce 0.68Y 0.32O 2 − y /R-Al 2O 3 is proposed as potential substrate material for YBa 2Cu 3O 7 − 6 deposition.

Single source deposition of Me-C:H films using metal-organic precursors

Abstract The deposition mechanisms of Fe-C:H films from a plasma-activated chemical vapour deposition from metal-organic precursors (PAMOCVD) were investigated by feeding a ferrocene plasma with additional hydrogen. While the deposition rate decreases continously from 36 μm h −1 for low hydrogen flow down to 8 μm h −1 for 50 seem hydrogen flow (1 seem ferrocene), the iron content in the film increases in a steplike behaviour from 9 at% to 15 at% at a hydrogen flow between 20 and 30 seem. The decrease of the deposition rate is due to an etching of the film by atomic hydrogen while the film composition is influenced by a change in the plasma gas chemistry. This change was investigated by quadrupole mass spectroscopy (QMS). We detected a steplike change of iron-containing and iron-free fragments leading to a reduction of iron-free radicals and therefore to an increase in the iron content of the film.

Optical properties of polycrystalline silicon thin films deposited by single-wafer chemical vapor deposition

The ellipsometric study of polycrystalline silicon films deposited using a single wafer rapid thermal chemical vapor deposition reactor under varying conditions of temperature and doping is presented. In particular, using spectroscopic ellipsometry in the visible spectral range, we determined the thickness of the films and the structural changes as a function of the deposition temperature. A different film structure, from amorphous to polycrystalline, has been found for the different deposition temperatures. A shift to lower values of the transition temperature which marks the structural change and a decrease in the deposition rate as the doping level is increased are observed. Moreover, from the ellipsometric results the optical functions of the different samples were evaluated.

Scots pine needle injuries at subarctic industrial sites

Injuries to needles of Scots pines (Pinus sylvestris L.) growing in nutrient-poor soils on the Kola Peninsula collected in April 1991 were studied on a gradient of increasing distances (10 – 115 km) from the Monchegorsk nickel smelter, Russia, which emits SO2, Ni and Cu. The condition of the mesophyll cells was quantified from needles of the two latest age classes using a light and an electron microscope. The damage to the ultrastructure consisted of multistress symptoms caused by excess sulphur, heavy metals, frost, acidic precipitation and ozone. Injuries were most commonly manifested in the form of dark, irregularly shaped chloroplasts with protrusions and light thylakoids and plastoglobuli. These symptoms gradually disappeared with increasing distance and decreasing deposition rate. Concentrations of sulphur, copper and nickel decreased towards more distant sites where normal levels of the latter two elements were reached. Sulphur concentrations remained above background throughout the distance gradient. In the closest plots to the smelter area, cell collapse under the stomata and epidermis related to acute SO2 and heavy metal effects was found, whereas further away symptoms were more diverse, pointing towards the effects of ozone, acidic deposition and thereby decreased frost tolerance. The additive multistress symptoms were clearly seen in the area up to 40 km from the smelter where needle Cu concentration was above 110 ppm, Ni concentration above 39 ppm and S concentration above 1343 ppm.

Structure and mechanical properties of hard amorphous carbon-nitrogen films obtained by plasma decomposition of methane-ammonia mixtures

Hard amorphous hydrogenated carbon-nitrogen films (a-C(N):H) were deposited by rf plasma decomposition of methane-ammonia mixtures onto silicon substrates. The incorporation of nitrogen increases with the partial pressure of ammonia. On the other hand, the deposition rate decreases. The samples were characterized by a a combination of analytical techniques: MeV ion beam techniques (RBS,NRA and ERDA), SIMS, AFM, EELS, infrared absorption and Raman spectroscopy. The Vickers hardness and the internal stress of the films were also determined. Infrared results indicate that the nitrogen is incorporated into the amorphous network mainly as terminating groups at the expense of C-H radicals. EELS and Raman results show that the incorporation of nitrogen induces a progressive graphitization of the films. The incorporation of up to 11 at% nitrogen reduces the internal stress of the films by a factor of two without significant modification of the film hardness.

Investigation of Pt/Ti Bottom Electrodes for Pb(Zr,Ti)O 3 Films

Pt films, as bottom electrodes for PZT capacitors, were deposited on Ti/SiO2/Si substrates using DC magnetron sputtering under various deposition conditions. The effects of post-annealing on surface morphology, element diffusion, microstructure and structural phase of the Pt films were investigated. The structure and electrical properties of PZT films deposited on Pt/Ti/SiO2/Si electrodes were also studied. As the deposition temperature of the Pt film increases and the deposition rate decreases, the film becomes dense so that Ti out-diffusion and film deformation are suppressed. The out-diffused Ti faciliates the formation of nucleation sites for perovskite PZT films. However, excess Ti out-diffusion not only decreases the total capacitance of the PZT films due to formation of an interfacial layer having a low dielectric constant but also degrades the leakage current characteristics of the PZT films due to deformation of the Pt electrode.

Hydrogenated Carbon-Nitrogen Films Obtained by Pecvd using Acetylene and Nitrogen as Precursor Gases

ABSTRACTAmorphous hydrogenated carbon-nitrogen films were deposited by plasma enhanced chemical vapor deposition (PECVD) using acetylene-nitrogen mixtures. The atomic composition and density of the films were determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERDA). Raman and Infrared spectroscopies monitored their structure. The addition of nitrogen gas to the deposition atmosphere resulted in a decrease in the film deposition rate. The increase of the nitrogen content is accompanied by the reduction of the carbon content. The IR absorption spectra show an increase intensity of the C=N Raman band and the N-H and CsN stretching bands. On the other hand, the IR results show a decrease in the intensity of the C-H stretching band. Raman results suggest an increase with the nitrogen content of the fraction of carbon atoms in a sp2 state of hybridization with the nitrogen content. The internal compressive stress has been measured by the determination of the bending of the substrate; a reduction of up to 50 % has been observed depending on the nitrogen content.