AVS2001 Session TF-ThP: Thin Film Deposition/Carbon-Containing Films Poster Session
Thursday, November 1, 2001 5:30 PM in Room 134/135
Thursday Afternoon
Time Period ThP Sessions | Topic TF Sessions | Time Periods | Topics | AVS2001 Schedule
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TF-ThP-1 Substrate Response During Dual Bipolar Pulsed Sputtering
P.J. Kelly, J. O'Brien (University of Salford, U.K.); J.W. Bradley (UMIST, U.K.); P.S. Henderson (University of Salford, U.K.); R. Hall (Advanced Energy Industries UK Ltd.) Dual bipolar pulsed sputtering is a highly successful technique for the deposition of dielectric materials. Operating in the mid-frequency range (20-350kHz), each magnetron acts alternately as an anode and a cathode. With the polarity of each magnetron alternating in this manner, target cleanliness is maintained, anode surfaces are preserved, and long term process stability is achieved. Asymmetric bipolar pulsed DC power supplies are commonly used to drive this process. In such instances, the target voltage during each pulse-off period typically reverses to approximately 10% of the nominal pulse-on voltage, i.e., if the pulse-on voltage is –400V, then the pulse-off voltage will be approximately +40V. However, as pulse frequencies are increased, particularly to in excess of 150kHz, target voltage waveforms increasingly depart from this idealised "square wave" behaviour. Very significant voltage overshoots are observed in each direction during each half of the pulse cycle. In particular, large positive overshoots are observed at the beginning of each pulse-off period. For example, at a pulse frequency of 350kHz, the target voltage can reach a peak value of +500V. Monitoring of the substrate I-V waveforms during operation has revealed that similar transient "spikes" also occur here. As a result, there is a short burst of high energy ions incident at the substrate during each "spikes", and since two targets are in use, these transients occur at twice the pulse frequency. Clearly, such bursts of high energy bombardment could have a significant influence on the growing film. Consequently, an investigation into the complex processes occurring at the substrate during dual bipolar pulsed sputtering has been carried out. A model is proposed to account for the observed phenomena, and the impact on film properties is considered. |
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TF-ThP-2 Modified HFCVD System for Diamond Coatings on Dental Burrs
H. Stein, W. Ahmed, C.A. Rego, N. Ali (Manchester Metropolitan University, U.K.) Chemical vapour deposited diamond films grown in a modified hot filament reactor using filament metals such as tantalum and tungsten have been optmised. The non-planar e.g. a small dental burrs or small metal abrading device was used as a substrate. The filament in hot filament chemical vapour deposition "HFCVD" plays an essential role in creating the gas phase species that enable and influence the diamond growth. The modification of HFCVD was such that the coiled filament was fixed vertically within the vacuum deposition chamber as opposed to horizontal position as used in conventional HFCVD systems. The dental burrs were placed within the coiled filament during deposition and this was the distinctive feature of the system. The substrate varied from 0.5mm to 1.25mm in diameter and were as long as 20mm. The as-grown diamond films were found to be polycrystalline, uniform and the film coverage was good. A preferential diamond (111) surface morphology has been obtained which is srongly dependent on diamond growth paramaters, including substrate and filament position in the reactor. Raman spectroscopy and scanning electron microscopy measurements confrimed the good quality of the obtained diamond films. |
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TF-ThP-3 High Rate Deposition of Thick CrNx Films by Unbalanced Magnetron Sputtering
K.H. Nam, J.H. Bin, J.G. Han (Sungkyunkwan University, Korea) The high rate deposition processes such as high current arc, laser arc, hollow cathode discharge ion plating and magnetron sputtering method have been developed for cost effective industrial applications. Especially magnetron sputtering is emerging a very efficient method for high rate deposition of dense thin films. In previous works, we have synthesized CrNx films by magnetron sputtering. The deposition rate was reached to be about 0.6µ/min. and the microhardness was evaluated up to 2200kg/mm2. And then phase and microstructure were controlled by change of N2 partial pressure and pulsed DC bias. In this study, high rate deposition of thick CrNx films was carried out by magnetron sputtering for the special application such as piston ring employed in automobile engine. For the high rate deposition of CrNx films with thickness of 30µ, residual stress in films was controlled by various N2 partial pressure, target power density and bias in processing. The microstructure was analyzed by X-ray Diffraction(XRD) and Scanning Electron Microscopy(SEM) and mechanical properties were evaluated by microhardness test, residual stress and adhesion tests. |
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TF-ThP-4 Comparison of Poly-Si Films Deposited by UHVCVD and LPCVD and Its Application for Thin Film Transistors
D.Z. Peng, H.W. Zan (National Chiao Tung University, Taiwan); T.C. Chang (National Sun Yat-Sen University, Taiwan); C.Y. Chang, P.S. Shih (National Chiao Tung University, Taiwan) The ultra high vacuum chemical vapor deposition (UHV/CVD) system can deposite poly-Si film without any laser or furnace annealing at lower temperature (550C). The uniformity of threshold voltage and mobility is superior to that deposited by low pressure chemical vapor deposition (LPCVD) system. The threshold voltage and mobility deviation for UHV/CVD are 0.16V, 10%, respectively and 0.23V, 21% for LPCVD system. However, due to the deposition in polycrystalline phase for UHV/CVD, the film surface is rough and results in low field effect mobility (27 cm2/VS, after plasma passivation, p-type device) compared to that (103 cm2/V-s, after plasma passivation, p-type device) obtained by low pressure chemical vapor deposition (LPCVD) using disilane (si2H6) in amorphous phase followed by solid phase crystallization (SPC). It can be shown that poly-Si film thickness will influence the leakage current. In this thesis, NH3, N2 and N2O were used to passivate the devices. They have obvious improvement on device performance after plasma passivation, in addition, NH3 passivation will result in the smallest leakage currrent and highest on/off current ratio. However, N2O needs a longer passivation time compared to the other two. After passivation, the devices show a poor stress endurance compared to unpassivated devices. |
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TF-ThP-5 Oxygen Partial Pressure Effect on the Properties of the Novel Semiconducting Alloy CuxCd1-xTe Grown by rf Sputtering
J. Santos-Cruz, G. Torres-Delgado, O. Jiménez-Sandoval, R. Castanedo-Pérez (Cinvestav-IPN, Unidad Querétaro, Mexico); B.S. Chao (Energy Conversion Devices, Inc.); P. García-Jiménez, S. Jiménez-Sandoval (Cinvestav-IPN, Unidad Querétaro, Mexico) High quality thin films of the novel semiconductor alloy CuxCd1-xTe have been succesfully grown by rf sputtering from a single target made of a mixture of high purity Cu and CdTe powders.1 Micro Raman experiments carried out on the Cu powder particles showed the existence of a CuO overlayer. However, the presence of such oxide, or of oxygen molecules, have not been detected as important components in the films. The role that oxygen plays during the growth and properties of the CuxCd1-xTe films is unknown to date. In this work we report the results of a study about the effects of incorporating controlled amounts of oxygen during the growth of CuxCd1-xTe thin films, on their crystalline structure, composition, and optical and transport properties. This study was carried out in a two-target sputtering system, in which one target is made of Cu and the other of CdTe. The native oxide on the Cu target surface was removed previously by presputtering for a few minutes before opening the deposition shutters. The controlled incorporation of oxygen into the chamber was achieved by using an electronic mass flow controller and the elemental composition profiles obtained by Auger spectroscopy. |
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TF-ThP-6 Reactive Dual Magnetron Sputtering Technology for Oxide Dielectric Film Deposition
S. Xu (HIVAC Technology(GROUP) CO. LTD, P.R. China); X. Hou (Tsinghua University, P.R. China); C. Fan (HIVAC Technology(GROUP) CO. LTD, P.R. China); L. Zhao, L. Cha (Tsinghua University, P.R. China) A study on oxide dielectric film deposition by medium frequency (MF) reactive dual magnetron sputtering (DMS) is reported in this paper. A continuous system for large-area deposition by DMS has been developed more than two years ago. The operation state of the DMS depends on the hysteresis curve of the target voltage with respect to the reactive gas (O2) flow rate. The process was controlled by adjusting O2 flow based on the target voltage in the closed-loop. Possible mechanism of physical and chemical processes on the target/substrate surface has been discussed. Based on the detailed experimental studies, criteria of the operation point according to the hysteresis were summarized. It was shown that magnetic field profile, distance between the two targets, structure of the shield, arrangement of the pipes for reactive gas supply and direction of the O2 flow have strong influence on the time constant and film quality as well as the precision and stability of the feedback closed-loop. Characteristics of deposited SiO2, Al2O3 and TiO2 films have been evaluated, including thickness, uniformity, surface topography, crystal structure, stoichiometric composition, refractive index and transmittance, etc. Long term operation confirmed that uniform, dense and amorphous optical film could be deposited rapidly and stably. |
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TF-ThP-7 Copper Metallization for ULSI Using 90°-bend Magnetic Filtered Cathodic Arc Evaporation Plasma System
J.-H. Lin, U.-S. Chen, W.-J. Hsieh, H.C. Shih (National Tsing Hua University, Taiwan) The cathodic arc evaporation plasma generated the highest plasma density compared with other PVD systems, but is known to be contaminated with macroparticles. In order to produce high quality defect-free copper films, a 90X-bend magnetic filter is suitable for ULSI interconnects metallization application. Macroparticle contamination has been alleviated by magnetic filter, the copper ions in the fully ionized copper plasma were accelerated and deposited on the wafer with a negative pulsed bias voltage. The fully ionized copper plasma flux was highly directionally deposited on the patterned and blank wafers, the filling of trenches/vias as narrow as 0.2 µm, with an aspect ratio as high as 7, FESEM and TEM images showed conformable copper step coverage ability. Both XRD and SEM/EBSD spectra showed that the FCAE-deposited copper film has an obvious Cu(111) preferred orientation. The result of this process as made, by scratch tests, showed that higher substrate bias and 50% pulse bias duty cycle can effectively enhance the adhesion strength of copper film on TaN layer. |
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TF-ThP-8 Velocities and Ionization Degree of Vapor Stream Produced from Evaporation Source using Porous Rod by Electron Beam Heating
H.M. Ohba, T. Shibata (Japan Atomic Energy Research Institute) A metal vapor was produced by electron beam heating with high thermal efficiency using a hearth liner and a porous rod for copper and cerium. While the top surface of the porous rod was heated by electron beam, the molten evaporation material surrounding the rod was transferred to the top surface by capillarity; then the atomic vapor stream was produced from the top surface. The ionization degree and the vapor velocities were measured with Langmuir probes, and a microbalance or laser induced fluorescence. The vapor characteristics were compared by evaporation from the bare water-cooled copper crucible. The ionization degree in the metal vapor is proportional to the electron beam current of the electron gun. In the case of evaporation from the porous rod, so a large amount of vapor flux can be produced at low electron beam current that the degree of ionization of metal vapor in the vicinity of the source is very low. The velocities of vapor produced from the porous rod were lower than that from the bare crucib le even at high vapor flux. The lower velocity for the porous rod was explained as follows. The excitation and ionization energies of the atoms evaporated by electron impact are converted to the kinetic energy of the vapor atoms by atom-atom collision. In the case of the porous rod, the rate of electron impact ionization of the evaporated atoms is lower than that of the bare crucible. |
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TF-ThP-9 Effects of Plasma Exposure on Structural and Optical Properties of TiO2 Films Deposited by Facing Targets Sputtering
T. Takahashi, H. Nakabayashi, N. Sasai, K. Masugata (Toyama University, Japan) In sputtered films, it is very important to investigate the influence of plasma exposure to the substrate because the properties of films strongly depend on the plasma state. So, in this study, TiO2 films have been deposited at different substrate positions using the facing targets sputtering which can easily vary the degree of plasma exposure. The plasma was confined sufficiently between two Ti targets faced each other. The substrates were placed at a certain distance from the middle of a straight line connecting the centers of the targets' planes. TiO2 films with thickness of about 2-3 µm were reactively deposited on glass-slide substrates. The crystal structure, and optical properties of films were measured using a X-ray diffractometry and a Raman spectroscopy, and a spectrophotometer, respectively. The A(101), A(200), A(112) and A(220) peaks were observed from the X-ray diffraction patterns, where A shows an anatase of TiO2. With increasing plasma exposure, X-ray peak intensities IP of A(101) and A(200) gradually decreased, and IP of A(112) and A(220) gradually increased, respectively. IP significantly depended on the substrate position in this study. Moreover, A(220) peak was significantly higher than others and the TiO2 crystallites became larger with an increase of plasma exposure. TiO2 films also showed anatase from the Raman spectra with Raman shift of 145 cm-1. With decreasing plasma exposure, the changes in the optical transmittance spectra of TiO2 films were very small at the wavelength of 350-900 nm. However, the transmittance spectra significantly depended on the wavelength with increasing plasma exposure. The transmittance monotonically decreased with decreasing wavelength in the range of 700 to 350 nm. Consequently, it was found that crystal structure and optical properties of TiO2 films were strongly affected to plasma exposure during deposition. |
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TF-ThP-10 High Rate Deposition of TiO2, TiN, and TiO2/TiN/TiO2 Thin Films Using New High Power Magnetron Sputtering Source and Comparison with Its Optical Characteristics
M.J. Jung, H.Y. Lee, Y.-S. Sin, J.G. Han, J.-H. Boo (Sungkyunkwan University, Korea) Thin films of TiO2, TiN and TiO2/TiN/TiO2 were deposited on glass substrates at a temperature below 200 °C using a newly developed pulsed DC magnetron sputtering source with high power (20 - 150 W/cm 2) and unbalanced magnetron. Titanium metal target (4-inch diameter, 99.9% purity) was mounted onto the sputtering sources, and oxygen and nitrogen were used as reactive gases and argon as working gas. Highly oriented, crack-free, stoichiometric polycrystalline TiO2(101) and TiN(100) thin films were successfully grown on glass surfaces at 200 °C. In the case of the TiO2 deposition, a thin film with high transmittance (90%) in the visible range was obtained while the TiN films showed very high reflectance (70%) in the infrared region. In this study, however, we found that the transmittance and reflectance are strongly influenced by the film thickness and the film surface roughness. For comparison, a multilayer film of TiO2/TiN/TiO2 was also deposited on glass substrates under the same growth condition as for TiO2 and TiN thin films based on computer simulation results. Quite good optical properties can be obtained for the as-grown multilayer films. The most excellent values of transmittance (85%) and reflectance (80%) were found for a thin film with TiO2 (380 nm)/TiN (20 nm) /TiO2 (440 nm)/glass structure. The high IR reflection indicates that the as-grown multilayer film can be applied for heat mirrors. |
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TF-ThP-11 Deposition of Dielectric Films by Photo Chemical Vapor Deposition using Vacuum Ultraviolet Xe2 Excimer Lamp from Tetraethoxysilane
N. Horii, A. Inouye, H. Nishibata (Fukui National College of Technology, Japan); K. Okimura (Tokai University, Japan) Dielectric films have deposited by photo-chemical vapor deposition (CVD) using Xe2 excimer lamp as a vacuum ultraviolet light source. Tetraethoxysilane was used as a silicon source. The goal of the research was to obtain insulation films for between layers in LSI fabrication and plasma free environment for sensitive substrate at low temperature. First, photo-chemical dissociation process of TEOS in the gas phase was investigated by in-situ mass spectrometry. We have found that TEOS was dissociated by VUV irradiation while releasing alkyl groups such as CxHy (x=1-2,y=2-5). Moreover, almost all Si-O bonds of TEOS were not broken at the energy of Xe2 excimer light. These are main reaction of the forming precursors for film deposition in the photo CVD process. A structure of films was investigated by FTIR analysis. The film prepared from TEOS at room temperature was SiOxCx like film having large amount of CH groups, however, Si-OH bonds was not included. Investigation of a stability of the films in ambient air was obtained undesirable results such as the Si-OH bonds increased and the film thickness decreased by the day. In order to improve a stability of the films we have irradiated VUV light to deposited films at room temperature. The result from the technique was effective for reducing unstable CH groups contained in the films and obtaining a good chemical and physical stability. |
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TF-ThP-12 Bahaviours of Energetic Oxygen Particles in the Reactive Sputtering of Zr Target in Oxygen Atmosphere
K. Tominaga, T. Kikuma, K. Kusaka, T. Hanabusa (The University of Tokushima, Japan) ZrO2 films were deposited in oxygen atmosphere with conventional planar magnetron sputtering system. In a sputtering of oxide target, energetic negative oxygen ions and energetic neutral oxygen atoms are bombarding the film. Then energetic oxygen ion s are generated in cathodefall in front of an oxide target. Precauser of the energetic neutral atoms is the negative oxygen ions that are accelerated in the cathode fall. These energetic particles bombard depositing oxide film and degrade film qualities s uch as internal stress, insulative characteristics. However, these energetic particles in a reactive sputtering is not so clear, especially in cases of materials such as Zr that is active with oxygen. We investigated the degree of the energetic oxygen particles in ZrO2 deposition and the generation mechanism of the energetic oxygen particles. Strong energetic oxygen ions generated in the sputtering of the Zr oxide target in O2 atmosphere were ascribed to the strong oxidization at the Zr surface. The energetic negative oxygen ions were detected using a probe constructed here. At the same time, the photoemission intensity from the sputtered Zr atoms was observed in order to monitor the target surface oxidization. The results show that the Zr targe t is very active with the oxidization of the target surface and drastically oxidized in a metal mode sputtering. The strong negative oxygen ions in an oxide mode sputtering are due to the generation of thick Zr-oxide layer on the Zr target. At the same time, films were prepared by the two sputtering modes and the relation the film properties and the energetic oxygen ions were investigated. |
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TF-ThP-13 In-situ Fabrication of Polycrystalline Thin Film Cathodes for Secondary Thin Film Batteries using Radio Frequency Sputter Deposition
K.-F. Chiu, F.C. Hsu, M.K. Wu, T.-P. Perng (National Tsing Hua University, Taiwan) In situ deposition of polycrystalline LiNi0.8Co0.2O2 thin films was performed using radio frequency magnetron sputter deposition on indium tin oxide substrates. Different substrate temperatures, upto 500 oC, were applied during deposition. The films deposited at elevated temperature exhibited a strong preferred orientation (or texture). It was found that varying the substrate temperature resulted in changing in film texturing. As the substrate temperature increased, the film structure changed from non-crystalline to polycrystalline with enhanced preferred orientation. The film texture was examined using X-ray diffraction (XRD) method. The surface morphology was observed using optical microscope and scanning electron microscope. The compositions of the targets and films were characterized by an inductively coupled plasma spectroscopy method (ICP) and were found to be identical. The change of texturing was interpreted by volume strain energy and surface energy minimization. Textured polycrystalline thin films can be deposited by controlling the deposition temperature. The technique was also used to deposit polycrystalline LiCoO2, LiNiO2 and LiMn2O4 thin films, and similar results were obtained. |
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TF-ThP-14 Effects of Deposition Parameters and Physical Properties of Thin NiO Films on Gas Sensing Characteristics
I. Hotovy (Slovak University of Technology Bratislava, Slovakia); L. Spiess (Technical University of Ilmenau, Germany); P. Siciliano, S. Capone (IME-CNR Lecce, Italy) Our research has been focused on the preparation and characterization of NiO thin films deposited by reactive magnetron sputtering. Small gas sensors on alumina substrate with different NiO thin films were fabricated and then were investigated their physical and sensing properties for application to nitrogen oxide. In order to apply NiO thin films to the nitrogen oxide gas sensor, NiO thin films (2000 Å) were prepared by dc reactive magnetron sputtering from a nickel metal target in an Ar+ O2 mixed atmosphere in two sputtering modes. Details about the deposition of NiO have been reported in previous papers.1 The oxygen content in the gas mixture varied from 20 to 60 %. The films deposited in the metal-sputtering mode resulted in a polycrystalline (fcc) NiO phase with nearly stoichiometric composition. On the contrary, the films prepared in the oxide-sputtering mode were amorphous and oxygen rich. The post-annealing (500degreeoC) of as-deposited NiO thin films changes amorphous to the (fcc) NiO phase for samples prepared in oxide-sputtering mode. TEM observations revealed a dense fine-grained structure with the grain size in the range 40-100 Å. AFM showed that the surface morphology NiO films could be modified by the process parameters as the oxygen content and the pumping speed. SEM observation and EDX analyses revealed uniform morphology and homogenous dispersion of NiO, Pt and Al2O3 phases. We have investigated the sensitivity (Ig/Io) versus operating temperature of NiO films when a concentration varied from 1 to 10 ppm of NO2. |
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TF-ThP-16 Computer Modeling of Thin Metal Films for Advanced Devices
L He (San Jose State University) Computer simulation for semiconductor devices and process is becoming more and more important due to the high cost of device fabrication and processing. In recent years, semiconductor optoelectronic device has undergone explosive growth. This growth has fueled a vast expansion of device modeling and simulation. Low temperature (LT) process on metal thin film has been proven effective to increase Schottky barrier height and reduce film resistivity in recent study. For the potential application of LT process in advanced semiconductor devices, a computer simulation program is developed. The computer simulation focus on microstructure and electric properties of the thin metal films. Metal-semiconductor-metal (MSM) photodetectors are widely used in the optoelectronic integrated circuit receivers because of their compatibility with the preamplifier for their planar integration scheme, the minimum number of processing steps, high performance, and low cost. InGaAs/InP is chosen for long wavelength application. In this work, analysis based on the results of computer simulation is presented. The Ag/InGaAs/InP contact formed by LT process showed that the Schottky barrier height is as high as 0.64eV. This value is more than double of the barrier height when processed in room temperature. It is believed that the LT process could greatly enhance the performance of a MSM photodetector. The device simulation includes RC time simulation, frequency response, and efficiency analysis. |
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TF-ThP-18 Structural Stability of Amorphous Al78W22 Thin Films Below Crystallization Temperature
N. Radic (Rudjer Boskovic Institute, Croatia); J. Ivkov (Institute of Physics, Croatia); A. Tonejc (Faculty of Sciences, Croatia); T. Car (Rudjer Boskovic Institute, Croatia) In this work the structural stability of Al78W22 amorphous thin films upon isochronal and isothermal heating below crystallization temperature (about 840 K) is reported. The amorphous Al78W22 films were prepared by a magnetron co-deposition onto alumina ceramic, sapphire, and glass substrates, held at four temperatures: LN2, RT, 200 degC, and 400 degC, respectively. Their stability was investigated by a continuous in situ electric resistance measurements during a two kinds of thermal treatment: a) A cycle of isochronous heating of the as-deposited sample up to 790 K, isothermal annealing at that temperature for 6 hrs, followed by cooling to room temperature. A strong irreversible variation of the film electrical resistivity is observed upon first heating. It is less pronounced at higher heating rates, presumably due to the competition between the relaxation of amorphous structure and temperature dependence of the resistivity. Deposition onto substrates held at high temperatures also strongly reduces the amount of resistivity variation. b) Isothermal annealing at high subcrystallization temperatures (803, 813, and 823 K) for several tens of hours resulted in a partial phase transformation of the amorphous alloy into the intermetallic Al4W compound. The Johnson-Mehl-Avrami model analysis of the phase transformation kinetics yields the Avrami coefficent close to 1, suggesting a nucleation as a crystallization mechanism. The above results show that the amorphous Al78W22 films require an initial annealing in order to attain the structural stability against heating, which is then retained in a marked degree even during a prolonged heating at the high subcrystallization temperatures. |
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TF-ThP-19 Composite Ti/C:H Films and Their Potential Application
H. Biederman, D. Slavinska, H. Boldyreva, S. Gretchany (Charles University, Czech Republic); S. Kvasnica (Boltzmann Inst. for Biomedical Microtechnology and Vienna Univ. of Tech., Austria); W. Fallmann (Vienna University of Technology, Austria); L. Bacakova, V. Stary (Academy of Sciences of the Czech Republic) Titanium containing carbonaceous thin films have been examined for some time because of their tribological properties1-4 and because of the prospect of their biomedical applications.5,6 Composite Ti/CH films reveal hardness Hv up to 35 GPa and coeficient of friction below 0.3 for Ti concentrations below 40 at % The presence of Ti in C:H matrix causes cellular reactions of bone marrow cells. Therefore Ti/C:H hard coating can be applied for bone implants. Composite Ti/CH films were deposited using an unbalanced dc planar magnetron equiped with Ti target operating in Ar/n-hexane or Ar/methane mixtures. Deposition process is described in relation to composition and structure as well as basic electrical, optical properties and hardness of the films. XPS analysis of the film surface revealed considerable oxidation and static contact angle of a water droplet ranged from 68 to 85 deg. The potential application of these films for bone implants has been assessed. |
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TF-ThP-20 The Effect of Substrate Bias and Nitrogen Incorporation on the Diamond-like Carbon Film Depositions by 90°-bend Magnetic Filtered Cathodic Arc Evaporation Plasma
W.-J. Hsieh, J.-H. Lin, P.-S. Shih, X.-W. Liu, H.C. Shih (National Tsing Hua University, Taiwan) The properties of nitrogen incorporated diamond-like carbon (DLC) films were deposited on silicon (111) wafers by a 90°-bend Magnetic filtered cathodic Arc Evaporation Plasma system. The structure and properties have been studied by TEM/EELS, Raman spectra, Vickers hardness, RBS, and SIMS spectra. For the DLC depositions using highly ionized energetic plasma, carbon ions with varying energies can form different types of carbon bonding in the films. The energies can be controlled by applying a variable bias to the substrate. It has been reported that the DLC films have the highest hardness with a substrate pulsed bias between -100V to -150V, and the maximum sp3 bonding content can be obtained at a pulsed bias of -150V (duty cycle:50%) is up to 85% as measured by TEM/EELS. The DLC films have a higher hardness when the content of sp3 bonds have a higher fraction of sp3 bonding contents. The hardness seems to be related to the Raman I(D)/I(G) ratio. It also founds that nitrogen content increases with increasing substrate bias and the deposition temperature on DLC films. However, the deposition above 400°C causes a sudden loss of sp3 bonding. The maximum incorporation of nitrogen to the DLC films was measured up to 15%(N) by SIMS as well as RBS. |
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TF-ThP-21 DLC Thin Films Characterized by AES, XPS and EELS
E.C. Samano, G. Soto, L. Cota (CCMC-UNAM, Mexico) DLC films have been grown by laser ablating a graphite target in a UHV system. Two kinds of depositions are processed depending on the experimental conditions, a HOPG film and a DLC film. A relationship of the film microstructure with laser power density and substrate conditions was observed. The films are in situ monitored and characterized during the first stages of the deposition process by means of surface spectroscopic techniques, such as AES, XPS and EELS. The film microstructure is confirmed by SEM. Clear evidence of a SiC interface of two monolayers thick was clearly observed to form due to the reaction of the first carbon species impinging on the substrate surface. |
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TF-ThP-22 Physical Properties of Nitrogen Doped Diamond-Like Amorphous Carbon Films Deposited by Supermagnetron Plasma CVD
H. Kinoshita, N. Otaka (Shizuoka University, Japan) Diamond-like amorphous carbon films doped with nitrogen (DAC:N) were formed using a supermagnetron plasma chemical vapor deposition (CVD) method.1 The electrical conductive DAC:N films were studied for the fabrication of high performance field emitters. DAC:N films were deposited on Si and glass wafers intermittently using i-C4H10/N2 repetitive plasma CVD. CVD duration was selected to be 40sec or 60sec, and several layers were deposited repetitively to form one film. Physical properties such as deposition rate, hardness, resistivity and optical band gap were measured at lower-electrode temperature of 100 °C as a function of upper- and lower-electrode rf powers (200W/200W-1kW/1kW) and N2 concentration (0-80%). With increase of rf powers supplied to two electrodes, resistivity, hardness and optical band gap decreased monotonously. Refractive index, however, was almost constant to 2.0-2.1. With increase of N2 concentration at rf powers of 1kW/1kW, deposition rate, hardness, resistivity and optical band gap decreased monotonously. With increase of plasma CVD duration from 40sec to 60sec, resistivity decreased to 0.032Ωcm and optical band gap decreased to 0.02eV, at N2 concentration of 80%. FT-IR spectroscopy measurements revealed that, with increase of N2 concentration, absorption peak intensities of NH single and CN triple bonds increased and that of CH single bond decreased.
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TF-ThP-23 Fabrication of Diamond Photocathode of Transmissive Type
K. Kato, K. Ito, M. Hiramatsu, M. Nawata (Meijo University, Japan); C.H. Lau, A. Bennett, J. Foord (University of Oxford, UK); R. Jackman (University College London, UK) Diamond is attractive as a "visible-blind" photocathode material for UV imaging, in view of its wide band gap and optical absorption properties, electrical transport characteristics and chemical stability. Under the negative electron affinity (NEA) condition, when the photon energy is higher than the band gap, the electrons are excited to the conduction band as a result of UV absorption, transported to the surface and then escape into vacuum. In order to realise the efficient diamond photocathode, it is n ecessary to optimise the optical absorption coefficient, the electron diffusion length in the bulk, and the surface escape probability. An investigation of these parameters is the purpose of the current work. Two types of diamond photocathode have been fabricated, for conventional reflective mode (UV photons and electrons interact with the same surface) and, for the first time, the more demanding trasnsmissive mode operation (electrons emitted from the opposite surface to the incoming UV light). The efficiencies of these two designs are compared and discussed in terms of the fundamental optical and electronic properties of the diamond films. In addition, we have investigated systematically the influence of a variety of surface treatments upon the photo-emissive properties of diamond photocathode, with differing levels of hydrogenation and oxidation. As a result of oxygen surface treatment, a drastic decrease in the photocurrent was observed. The use of the alkali metals, caesium and potassium in conjunction with various oxidation treatments is therefore explored in order to stabilise high quantum photo yield. |
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TF-ThP-24 Fabrication of Carbon Whisker Film Using RF Plasma CVD
K. Ito, K. Kato, M. Hiramatsu, M. Nawata (Meijo University, Japan); M. Hori (Nagoya University, Japan); C.H. Lau, J. Foord (University of Oxford, UK) In the case of film formation by utilizing the plasma enhanced chemical vapor deposition (PECVD) method, it is desirable to supply selectively reactive species suitable for the film growth onto the substrate. Previously we demonstrated the successful formation of diamond crystals using a unique PECVD system, which has the parallel-plate capacitively coupled radio-frequency (rf, 13.56 MHz) discharge plasma assisted by the hydrogen radical source using the remote microwave (2.45 GHz) discharge plasma.1 In the present work, by using this system with a mixture of C2F6 and H2, carbon films with whisker array were successfully formed on Si (100) substrate at C2F6/H2=0.3/13 Pa, rf power of 100W, microwave power of 100W, and substrate temperature of 600 °C. Deposited films were characterized by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Although fluorocarbon gas was used as a source gas, fluorine was not detected in the deposited film from the XPS analysis. Surface morphology was changed from pyramids to whiskers according to the deposition conditions. Field emission characteristics have been investigated for the fabricated carbon film with whisker array. The V-I characteristics revealed a current density of 750 µmA/cm2 at an applied field of 60 V/µmm. Corresponding Fowler-Nordheim plot was well fitted by the straight line, indicating that the field emission property can be explained by a tunneling mechanism. |
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TF-ThP-26 Effect of Ar Addition on Microstructure and Composition of Nitrogen Containing Carbon Films Prepared by Hot Filament CVD
Y. Watanabe, A. Yamazaki, N. Kitazawa, Y. Nakamura (National Defense Academy, Japan) Nitrogen containing amorphous carbon (a-CNx) films were synthesized on Si (100) substrates by hot filament chemical vapor deposition method using a carbon filament, which supplies carbon and heat. Deposition was performed in low pressure atmosphere of pure nitrogen and a gas mixture of nitrogen and argon. Effects of argon addition on film microstructures and composition were studied by changing the argon fraction under the total pressure of 100 Pa. The film microstructure was observed by field-emission scanning electron microscope (FE-SEM) and the composition was analyzed by X-ray photoelectron spectroscopy (XPS). FE-SEM observations reveal that films prepared in pure nitrogen atmosphere show a columnar structure, while the films change to tapered structure with argon addition. Spectra of XPS show that the films were composed of carbon and nitrogen, and no contamination was observed except a small amount of oxygen. It is also found that the nitrogen concentration in films increases in dependence on argon partial pressure. |