Decrease In Deposition Rate Research Articles

Signal performance of DC-SQUIDs with respect to YBCO thin film deposition rate

The signal performances of YBa 2Cu 3O 7− δ (YBCO) direct current superconducting quantum interference devices (DC-SQUIDs) have been investigated as a function of the thin film structure affected by the growth process. YBCO thin films of 200 nm thicknesses were deposited by DC magnetron sputtering using different deposition rates between 1.0 nm/min and 2.0 nm/min onto 24° bicrystal SrTiO 3 (STO) substrates. The thin film samples were subsequently analyzed by XRD and AFM in order to determine their crystalline structures and surface morphologies respectively. The 67 pH directly coupled DC-SQUIDs with 4 μm-wide bicrystal Josephson junctions were fabricated, and characterized with respect to their device performances. The variations in the critical current ( I c), the voltage modulation depth (Δ V) and the noise performance of DC-SQUIDs were reported. The SQUIDs having relatively low deposition rate of 1.0 nm/min was observed to have larger voltage modulation depth as well as higher critical current than that of the samples having larger rate of 2.0 nm/min. The better noise performances were observed as the film deposition rate decreases. The results were associated with the thin film structure and the SQUID characteristics.

Effect of Charge Density on the Taylor Cone in Electrospinning

A detailed understanding of charge density and its origins during the electrospinning process is desirable for developing new electrospinnable polymer-solvent systems and ensuring mathematical models of the process are accurate. In this work, two different approaches were taken to alter the charge density in order to measure its effect on the Taylor cone, mass deposition rate and initial jet diameter. It was found that an increase in charge density results in a decrease in the mass deposition rate and initial jet diameter. A theory is proposed for this behaviour in that an increase in charge density leads to the tip of the Taylor cone forming a smaller radius of curvature resulting in the concentration of electric stresses at the tip. This leads to the electrostatic forces drawing the initial jet from a smaller effective area or “virtual orifice”.

EFFECT OF CHARGE DENSITY ON THE TAYLOR CONE IN ELECTROSPINNING

A detailed understanding of charge density and its origins during the electrospinning process is desirable for developing new electrospinnable polymer-solvent systems and ensuring mathematical models of the process are accurate. In this work, two different approaches were taken to alter the charge density in order to measure its effect on the Taylor cone, mass deposition rate and initial jet diameter. It was found that an increase in charge density results in a decrease in the mass deposition rate and initial jet diameter. A theory is proposed for this behaviour in that an increase in charge density leads to the tip of the Taylor cone forming a smaller radius of curvature resulting in the concentration of electric stresses at the tip. This leads to the electrostatic forces drawing the initial jet from a smaller effective area or "virtual orifice".

Stability of a-C:N:H Layers Deposited by RF Plasma Enhanced CVD

A series of amorphous hydrogenated carbon layers doped with nitrogen (a-C:N:H) was deposited on Si (001). The synthesis was performed from gaseous N2/CH4 mixture using PE CVD (RF CVD technique; 13,56 MHz). An influence of the processing conditions on layer-growth rate was analysed. Thickness of the layers deposited during 1 hour at various temperatures, pressures and RF powers were taken as a basis. It has been proved that the substrate temperature is a key parameter for the layer formation. Temperature rise results in the deposition rate decrease. This unfavourable effect may be reduced by application of increased gas pressure and/or higher plasma RF generator power. At optimal conditions (46 oC; 0,8 Tr; 60 W) the deposition rate reaches up to 600 nm/hour. FT-IR spectra of the layers were measured within 1250 - 4000 cm-1 and discussed with regard to the atomic structure. The intensities of the characteristic absorption bands were compared. The results show that the layers have various N/C ratios according to the applied processing conditions.

Low Temperature Si Homoepitaxy by a Reactive CVD with a SiH4/F2 Mixture

AbstractSingle crystalline Si thin films on insulating substrates (SOI) have a variety of potential applications to such as high mobility TFT and to high efficiency and low cost solar cells. Since the SOI is limited to a thin layer, it is needed to develop a low temperature epitaxial growth technology to form active layers thicker than several micorns at low temperatures. The purpose of this study is to develop a deposition technique of single crystalline Si thin films by a reactive CVD method [1] at temperatures less than 600○C utilizing gas-phase reaction (SiH4, F2). Deposition of Si films was performed on a single crystalline Si (100) wafer. Substrate-temperature was varied between 100 and 700○C, reaction-pressure 1 and 500mTorr, flow-rate between SiH4/F2 = 1/1 and 1/3, and the geometry of the substrate and the gas-outlet were optimized. First, it was found that deposition rate was sensitive to the distance between the gas-outlet and the substrate and to the total pressure. For four different combinations of pressures, 250 and 500 mTorr and distances, 50 and 150 mm. The deposition took place only for the combination of 500 mTorr and 50 mm, and otherwise the deposition rate was significantly lower or etching of Si wafer was observed. The deposition rate for gas flow ratio, SiH4/F2 of 1/1 was 1.7 nm/s at a substrate-temperature of 400○C, while for higher F2 flow rate ratio, SiH4/F2 = 1/2 and 1/3, the deposition rates were 8.3×10-3 nm/s and etching, respectively. Raman measurements show that crystallinity depends on the substrate-temperature; broad amorphous signal appears at 300, microcrystalline signal at 300 and 500○C and sharp crystalline at 400○C. RHEED observation shows a halo-pattern of amorphous-Si at 200○C, a mixed pattern of streak and spot without 2×1 superstructure at 300○C, a 2×1 streak-pattern at 400○C and a spot-pattern at 500○C. The reason of the narrow temperature window for epitaxial layer is a characteristic feature of low temperature epitaxy as reported before [2]. It is noteworthy the deposition rate of epitaxy obtained in this work is quite high, 1.7 nm/s even at 400○C. These observations are ascribed to the gas phase reaction between SiH4 and F2 and successive surface reactions. The SiH4 and F2 cause an exothermic reaction in the gaseous phases to generate radicals such as SiHx, H and F. The SiHx acts as a film precursor and others act as etchant. Under the conditions which radical density ratio SiHx/F increases, therefore, the deposition rate decreases or etching occurs. The material properties also will be discussed in relation to the growth mechanism. [1]J. Hanna et al., J. Non-Crst. Solids 114 (1989) 172-174 [2]T. Kitagawa, M. Kondo et al, Appl. Surf. Sci. 159-160 (2000) 30-34

Reactive magnetron sputtering of CuInS 2 absorbers for thin film solar cells: Problems and prospects

We have investigated the reactive magnetron sputtering process from copper and indium targets in Ar/H 2S sputtering atmospheres for the deposition of CuInS 2 absorber films. This large area deposition method is in principle suited for the preparation of absorbers of good electronic quality. One of our best CuInS 2 cells exhibits an efficiency of 11.4% and an open circuit voltage of 745 mV, the highest reported value for CuInS 2 cells. However, it was found that the reproducibility of the photovoltaic layer properties is low. By analyzing the different defects in the films, it was found that the main defects are microscopic pin holes and crevices, which lead to short circuits. The intrinsic electronic quality of the magnetron sputtered CuInS 2 films is excellent, proven by room temperature photoluminescence spectroscopy. The occurrence of short circuits depends decisively on the film morphology, which is determined by the copper-to-indium ratio during the deposition. Even for constant external deposition parameters this ratio changes over the life time of the targets, mainly caused by a significant decrease of the indium deposition rate. For a stable CuInS 2 film deposition process an in situ control of the Cu/In ratio and the film morphology is advisable.

Organic–inorganic behaviour of HMDSO films plasma-polymerized at atmospheric pressure

Abstract Recently, plasma-polymerization at atmospheric pressure has become a promising technology due to its reduced equipment costs and its possibility of in-line processing. This paper focuses on plasma deposition by an atmospheric pressure dielectric barrier discharge (DBD) using hexamethyldisiloxane (HMDSO) as gaseous precursor. HMDSO plasma-polymerized films are deposited onto polyethylene terephthalate (PET) films using argon and different argon/air mixtures as carrier gases. The chemical and physical properties of the obtained coatings are discussed using contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Contact angle and FTIR results show that the composition of the gas phase and the chemical structure of the obtained coatings are clearly correlated. When pure argon is used as working gas, the film is polymeric with a structure close to [(CH3)2–Si–O]n. However, with increasing air content, a gradual change is observed from organic polydimethylsiloxane-like coatings to inorganic, quartz-like deposits. AFM results clearly indicate that with increasing air content, the deposition rate decreases, while the surface of the deposited films becomes rougher. From this point of view, the capability of controlling both chemical and physical properties of the plasma-polymerized films by varying operation conditions opens interesting perspectives.

DC마그네트론 스퍼터링법으로 PET 기판위에 저온 증착한 ITO박막의 비저항과 굽힘 저항성에 대한 RF인가의 영향

Indium tin oxide (ITO) films were deposited on PET substrate by RF superimposed DC magnetron sputtering using ITO (doped with 10 wt% SnO2) target. Substrate temperature was maintained below 75 o C without intentionally substrate heating during the deposition. The discharge voltage of DC power supply was decreased from 280 V to 100 V when superimposed RF power was increased from 0 W to 150 W. The electrical properties of the ITO films were improved with increasing of superimposed RF power. In the result of cyclic bending test, relatively high mechanical property was obtained for the ITO film deposited with RF power of 75 W under DC current of 0.75 A which could be attributed to the decrease of internal stress caused by decrease in both deposition rate and plasma impedance.

Evaluation of the barrier capability of Zr–Si films with different substrate temperature for Cu metallization

Barrier capability of Zr–Si diffusion barriers in Cu metallization has been investigated. Amorphous Zr–Si diffusion barriers were deposited on the Si substrates by RF reactive magnetron sputtering under various substrate temperatures. An increase in substrate temperature results in a slightly decreased deposition rate together with an increase in mass density. An increase in substrate temperature also results in grain growth as deduced from field emission scanning electron microscopy (FE-SEM) micrographs. X-ray diffraction (XRD) spectra and Auger electron spectroscopy (AES) depth profiles for Cu/Zr–Si(RT)/Si and Cu/Zr–Si(300 °C)/Si samples subjected to anneal at various temperatures show that the thermal stability was strongly correlated with the deposition temperature (consequently different density and chemical composition etc.) of the Zr–Si barrier layers. ZrSi(300 °C) with higher mass density make the Cu/Zr–Si(300 °C)/Si sample more stable. The appearance of Cu 3Si in the Cu/Zr–Si/Si sample is attributed to the failure mechanism which may be associated with the diffusion of Cu and Si via the grain boundaries of the Zr–Si barriers.

Deposition of thick TiAlN coatings on 2024 Al/SiCp substrate by Arc ion plating

Aluminum-matrix composites with particulate SiC ceramic reinforcements (Al/SiC(p)) have received much attention for space and aircraft propulsion applications. It is imperative to deposit thick hard coatings on these composites for protection. TiAlN coatings with a Ti interlayer were deposited by arc ion plating (AlP) on 2024 Al/SiC(p) substrates at various nitrogen flow rates. It was found that when the nitrogen flow rate is increased from 100 sccm to 250 sccm, the deposition rate decreases, the coating hardness increases and the adhesion strength decreases. Based on the above results and the principle of gradient materials. the thick gradient TiAlN coatings with a Ti interlayer were successfully deposited on a 2024 Al/SiC(p) substrate to a thickness of 60 pm by continuously increasing the nitrogen flow rate during deposition. Such an achievement can be attributed to the gradient distribution of elements, hardness, and stresses across the coating thickness. (C) 2008 Elsevier B.V. All rights reserved.

Electrophoretic deposition of natural hydroxyapatite on medical grade 316L stainless steel

Natural hydroxyapatite has been electrophoretically deposited on medical grade 316L stainless steel. The suspension consisted of isopropyl alcohol and polyethylenimine. The substrates were 16 × 6 × 4 mm in dimension. Deposition was achieved on the cathode at 30, 60, and 90 V in 1 to 5 min at constant voltage. After deposition the samples were dried at room temperature for 24 h and deposition weight, roughness, and thickness of the coatings were measured. The coated samples were sintered in a vacuum furnace at 800 °C for 1 h. The surface morphology of the samples was studied by a scanning electron microscope, and phase purity of the coating material was investigated by XRD. The sample coated at 60 V and 3 min led to an adherent, continuous, and crack-free coating. The coating efficiency and thickness increased with increasing deposition time while the slope of the curves decreased which showed a decrease in deposition rate. Also, the current density decreased and yielded to saturation at the constant applied voltage during electrophoretic deposition. Quantitative analysis of the coatings after sintering showed some partial decomposition of natural hydroxyapatite to tricalcium phosphate. Additionally, the experimental results were also compared extensively with the theoretical proposed expressions.

Application of droplet‐free metal ion source to formation of gas barrier thin films

AbstractThis paper reports on application of droplet‐free aluminum ion sources for formation of gas barrier coating of PTFE polymer sheets. Addition of oxygen to the ion source was also made in order to obtain transparent coating films of alumina. Optimized conditions on the oxygen addition allowed the transparent almina films to be formed without a significant decrease in deposition rate. Square‐wave‐modulated bias voltages were also applied to the sheet with the film in order to control the incident ion bombarding energy, and was much effective for improvement of gas barrier performance. However such a bias effect was obtained only under a discharge condition that the aluminum ions were efficiently produced. The alumina films had less bias effect than the aluminum films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Controlling the Assembly of Nanocrystalline ZnO Films by a Transient Amorphous Phase in Solution

The chronological sequence of the precipitation and crystallization of Zn species in methanol solutions containing poly(vinyl pyrrolidone) (PVP) was studied with dynamic light scattering, electron microscopy, and chemical analysis and correlated with the film formation on substrates. It was found that the polymer inhibited uncontrolled precipitation of ZnO and promoted the formation of smooth ZnO films on substrates. The reaction solution was quenched from 60 °C to room temperature after different periods of time. It could be shown that amorphous needle-like particles formed in the first place. This intermediate and metastable phase dissolved, and aggregated ZnO nanocrystals formed concurrently, whereby the transformation rate was determined by the PVP concentration. The formation of high-quality ZnO films, with respect to uniformity and low surface roughness, on substrate surfaces modified by self-assembled monolayers was strongly related to the presence of the intermediate amorphous phase in solution. Uncontrolled crystallization at low PVP concentrations resulted in defective and rough deposits. Very high PVP concentrations resulted in rapid aggregation of the zinc oxide nanocrystals in solution and a strongly decreased deposition rate. Control of the reaction conditions through intermediate amorphous phases commonly occurs in biomineralization processes. The employment of this mechanism could facilitate the development of novel chemical bath deposition processes of artificial nanostructured materials.

The characteristics of the plasma in a powder sputtering rig

The powder sputtering rig was specifically designed for the sputtering of loosely packed blended powder targets. The rig incorporates a single unbalanced magnetron with an additional unpowered dummy magnetron used only to provide a closed magnetic field. Sputtering took place mainly in the pulsed direct current (DC) mode, with continuous DC operation also investigated for comparison purposes. The variations in substrate self-bias potential and substrate ion current with substrate-target separation and target current were studied for varying magnetron configurations. The voltage waveforms at the targets were diagnosed, and the effect of pulse parameters on the deposition rate was investigated. The term ‘dead time’ has been introduced to explain, in part, the observed decrease in deposition rate with increasing pulse frequency. To demonstrate the advantages of the powder rig, the structure and properties of aluminium-doped zinc oxide coatings deposited under various magnetron configurations and power delivery modes were compared. The results showed that the closed-field configuration and the use of the pulsed DC power supply were two essential factors in this system, which produced defect free, dense columnar coatings with good electrical and optical properties.

Mediation of room temperature ferromagnetism in Co-doped SnO2 nanocrystalline films by structural defects

Co-doped SnO2 nanocrystalline films have been fabricated by magnetron sputtering to investigate the effects of structural defects on mediating ferromagnetism in this system. X-ray photoelectron spectroscopy analysis reveals that Co element is incorporated into SnO2 lattice and is in 2+ oxidation state in all samples. High-resolution transmission electron microscopy observation indicates that along the film growth direction, Sn1−xCoxO2 films change from amorphous structure to columnar grain except for the film deposited at room temperature. With the decrease of film thickness, deposition rate, and deposition temperature, a relative proportion of structural defects in films increases, resulting in an enhancement of the saturated magnetic moment of Sn1−xCoxO2 film. Bound magnetic polaron mechanism is adopted to explain the mediation effect of structural defects on ferromagnetism in this system.

Towards multiscale modeling of Si nanocrystals LPCVD deposition on SiO 2: From ab initio calculations to reactor scale simulations

A modeling study is presented involving calculations at continuum and atomistic (DFT, Density Functional Theory) levels so as to better understand mechanisms leading to silicon nanocrystals (NC) nucleation and growth on SiO 2 silicon dioxide surface, by Low Pressure Chemical Vapor Deposition (LPCVD) from silane SiH 4. Calculations at the industrial reactor scale show that a promising way to improve reproducibility and uniformity of NC deposition at short term could be to increase deposition time by highly diluting silane in a carrier gas. This dilution leads to a decrease of silane deposition rate and to a marked increase of the contribution to deposition of unsaturated species such as silylene SiH 2. This result gives importance to our DFT calculations since they reveal that only silylene (and probably other unsaturated species) are involved in the very first steps of nucleation i.e. silicon chemisorption on silanol Si–OH or siloxane Si–O–Si bonds present on SiO 2 substrates. Saturated molecules such as silane could only contribute to NC growth, i.e. chemisorption on already deposited silicon bonds, since their decomposition activation barriers on SiO 2 surface are as high as 3 eV.

Effect of substrate bias voltages on the diffusion barrier properties of Zr–N films in Cu metallization

Zr–N diffusion barriers were deposited on the Si substrates by rf reactive magnetron sputtering under various substrate bias voltages. Cu films were subsequently sputtered onto the Zr–N films by dc pulse magnetron sputtering without breaking vacuum. The Cu/Zr–N/Si specimens were then annealed up to 650 °C in N 2 ambient for an hour. The effects of deposition bias on growth rate, film resistivity, microstructure, and diffusion barrier properties of Zr–N films were investigated. An increase in negative substrate bias resulted in a decrease in deposition rate together with a decrease in resistivity. It was found that the sheet resistances of Cu/Zr–N(−200 V)/Si contact system were lower than those of Cu/Zr–N(−50 V)/Si specimens after annealing at 650 °C. Cu/Zr–N(−200 V)/Si contact systems showed better thermal stability so that the Cu 3Si phase could not be detected.

Surface Morphology of Magnetron Sputtered TiO2 Films

This article reports on investigation of the correlations between the process parameters, structure, and surface morphology of sputtered TiO2 films prepared by magnetron sputtering. It has been found that the increase in the partial pressure of oxygen results in (i) the decrease of TiO2 film deposition rate and (ii) strong changes in its structure. The structure of ∼1 µm thick TiO2 films gradually changes from rutile through mixture of rutile + anatase to anatase with increasing at pT = 0.75 Pa. The same evolution of structure is observed when a TiO2 film is sputtered at a constant value of and the film thickness h increases. Increase in total working pressure leads to suppression of rutile structure. Maximum surface roughness was observed for films sputtered in the transition mode of sputtering.

Transport of Escherichia coli in saturated porous media: Dual mode deposition and intra-population heterogeneity

Because of heterogeneity among members of a bacteria population, deposition rates of bacteria may decrease upon the distance bacteria are transported in an aquifer. Such deposition rate decreases may result in retained bacteria concentrations, which decrease hyper-exponentially as a function of transport distance, and may therefore significantly affect the transport of colloids in aquifers. We investigated the occurrence of hyper-exponential deposition of Escherichia coli, an important indicator for fecal contamination, and the causes for such behavior. In a series of column experiments with glass beads of various sizes, we found that attachment of E. coli decreased hyper-exponentially, or, on logarithmic scale in a bimodal way, as a function of the transported distance from the column inlet. From data fitting of the retained bacteria concentration profiles, the sticking efficiency of 40% of the E. coli population was high ( α=1), while the sticking efficiency of 60% was low ( α=0.01). From the E. coli total population, an E. coli subpopulation consisting of slow attachers could be isolated by means of column passage. In subsequent column experiments this subpopulation attached less than the E. coli total population, consisting of both slow and fast attachers. We concluded that the main driver for the observed dual mode deposition was heterogeneity among members of the bacteria population. Intra-population may result in some microbes traveling surprisingly high distances in the subsurface. Extending the colloid filtration theory with intra-population variability may provide a valuable framework for assessing the transport of bacteria in aquifers.

Influence of substrate bias on the structure and properties of ZrN films deposited by cathodic vacuum arc

ZrN films were deposited by cathodic vacuum arc (CVA) technique in N 2 atmosphere at low temperature with different substrate bias. The ZrN films deposited are atomically smooth. The influence of substrate bias at the wide range (0 to −500 V) on the deposition rate, surface morphology, crystal structure, internal stress, and mechanical properties of the ZrN films were systematically investigated. Increasing substrate bias results in the decrease of deposition rate and the increase of surface roughness. It was found that there is a strong correlation between the substrate bias, film structure and properties. At the bias of 0 V, ZrN films characterize with random orientation, low surface roughness, small grain size. With the increase of bias, the structure changes from random orientation to (1 1 1) preferred orientation and then to (2 2 0) orientation. As substrate bias increases to about −150 V, the internal stress, hardness and Young's modulus increase to maximum. A further increase of bias results in the gradual decrease to lower level.