Papers

ICMCTF2002 Session C2-1: Film Properties/Structure/Deposition Process Relationships

Wednesday, April 24, 2002 8:30 AM in Room Sunset

Wednesday Morning

Start	Invited?	Item
8:30 AM		C2-1-1 Investigation on TiO_x Coatings Produced using Variable Magnetic Field Magnetrons in Dual Bipolar Pulsing Mode. J. O'Brien (University of Salford, United Kingdom); V. Bellido-Gonzalez (Gencoa Ltd, United Kingdom) Investigations have been made into the effect of the degree of balance and field strength in a dual magnetron system on the properties of titania coatings. Magnetic field configuration and strength were varied with the aid of Gencoa Vtech variable magnetrons, which allow in-situ variation of magnetic field via the independent linear positioning of the inner and outer arrays of magnets. This allows field variations from nearly balanced to highly unbalanced and a simultaneous or independent variation of the field strength, which may be set prior to or during the deposition process. TiO_x films were deposited using the dual bipolar pulsed cathode process as this is well proven for its ability to enable arc-free, stable, long-term deposition. Anode and substrate temperatures have been measured and suggestions are given for possible mechanisms that lead to differences in these temperatures. In addition, coating properties such as optical, mechanical and structural properties have been analysed as well as photocatalytic behaviour, and consideration is given to the underlying reasons for the variation observed. Furthermore, studies have included assessment of relative deposition rates and uniformity over the full substrate area, along with any variations in coating properties over this area, and these findings are also reported.
8:50 AM		C2-1-2 Hetero-Epitaxial Growth and Optical Properties of LaF₃ on CaF₂ Y. Taki, K. Muramatsu (Nikon Corporation, Japan) Lanthanum fluoride (LaF₃) is a primary candidate of high refractive index materials available for optical interference multilayers in deep ultraviolet (DUV) and vacuum ultraviolet (VUV) regions. In this study, we have found the hetero-epitaxial growth of LaF₃ onto the (111) orientation surface of CaF₂ at low temperatures from 250°C to almost room temperature and improved optical transparency of LaF₃ films in a VUV region with this hetero-epitaxial growth. LaF₃ films were fabricated on CaF₂ single crystal substrates by vacuum evaporation (VE) and magnetron sputtering. In the VE process, substrates were heated with radiation in advance and substrate temperature was maintained at 250°C during film deposition. In the magnetron sputtering process, in contrast, substrates were not heated prior to film deposition but at room temperature when the film deposition started. LaF₃ films were characterized with XRD, EPMA, XPS, SIMS, SEM and DUV-VUV spectroscopy. LaF₃ films prepared by both VE and sputtering grow hetero-epitaxially onto CaF₂ substrates. [00l] of LaF₃ is parallel with [111] of CaF₂. CaF₂ has a cubic lattice named fluorite-type (Fm3m). In sight of a (111) face, Ca (or F) atoms lie on apexes of equilateral triangles. A triangle layer of Ca only stacks alternately with a triangle layer of F only. LaF₃, on the other hand, has a hexagonal lattice (P-3c1 or P6₃/mmc). A side in a basal plain is nearly twice as long as a side in a triangle mentioned above. Overall LaF₃ films consist of accurately stoichiometric composition. The film surfaces, however, are partially hydroxidized and oxidized. Therefore, VUV light is much more absorbed at near surface area of the films than the film insides. It is significant for LaF₃ film deposition to make a dense film structure with the epitaxial growth and reduce surface area exposed to the air.
9:10 AM		C2-1-3 Optical Constants and Roughness Study of DC Magnetron Sputtered Iridium Films L. Yan, J.A. Woollam (University of Nebraska-Lincoln) The accuracy of optical constants of partially transparent thin films often depends on having accurate optical constants for the substrate. These must be known over the entire spectral range of interest. As the spectral range of thin film applications continues to widen, so does the need for well-characterized substrates. Durable, corrosion-free, reproducible iridium (Ir) thin films with smooth surfaces and good adhesion to substrates are of considerable interest. Due to its unique properties, Ir is currently being considered by NASA as a substrate (optically thick Ir on ultra-smooth fused silica) for the study of contamination layers deposited in the space environment. Extremely smooth thin films of iridium have been deposited in this work onto super-polished fused silica substrates, using DC magnetron sputtering in an argon plasma. The influence of gas pressure, deposition time, and other parameters, on film microstructure have been investigated by optical microscopy, atomic force microscopy, x-ray diffraction, and energy dispersive x-ray analysis. Moreover, Ir film optical constants were determined using variable angle spectroscopic ellipsometry, over the entire spectral range from vacuum ultraviolet to middle infrared (140 nm-33 µm). Based on the fact that the film surface roughnesses were so low and the films themselves were optically thick, the optical constants determined for these films are therefore expected to be those of Ir bulk metals, minimally affected by surface or microstructure. In addition, effects of oxygen plasma irradiation on Ir film optical constants were investigated, using an electron cyclotron resonance (ECR) plasma source to simulate the low earth orbital (LEO) environment. This work is supported by NASA Glenn Research Center, Grant NAG3-2219.
9:30 AM		C2-1-4 Metallization of Ceramic Vacuum Chambers for SNS Ring Injection Kicker Magnets P. He, H.C. Hseuh, R.J. Todd (Brookhaven National Laboratory) Ceramic chambers are used in the pulsed kicker magnets for the injection of H⁺ into the accumulator ring of the Spallation Neutron Source (SNS). There are two reasons for using ceramic chambers in kickers: (1) to avoid shielding of a fast-changing external magnetic field by metallic chamber walls; and (2) to reduce heating due to eddy currents. The inner surfaces of the ceramic chambers will be coated with a conductive layer, possibly titanium(Ti) or copper(Cu) with a titanium nitride(TiN) overlayer, to reduce the beam coupling impedance and provide passage for beam image current. This paper describes the development of sputtering method for the 0.85m long 17cm inner diameter ceramic chambers. Coatings of Ti, Cu and TiN with thicknesses up to 35µm were produced by means of DC magnetron sputtering. The difficulties of coating an insulator were addressed with the introduction of an anode trap. Films with good adhesion, uniform longitudinal thickness, and surface conductivity were produced.
9:50 AM		C2-1-5 Sputter Deposition of Silicon-Oxide Optical Coatings A.F. Jankowski, J.P. Hayes (Lawrence Livermore National Laboratory) Fused silica and Si-O_x coatings are of interest for use under high flux conditions of laser light. Si-O_x coatings are sputter deposited from silicon and fused quartz targets using planar magnetrons operated in the rf mode with a variable working-gas mixture of Argon-Oxygen. A series of 2-4 µm thick coatings are prepared on optically flat, fused quartz substrates. Analysis of surface curvature measurements by ellipsometry reveals the deposition process conditions that minimize residual stress. Compressive stress levels that exceed 1.5 GPa can be reduced to less than 0.4 GPa when the working gas pressure is reduced. Characterization by x-ray photoelectron spectroscopy indicates that both the fused quartz and silicon targets can be used to sputter deposit coatings with the chemical bonding features of the fused-quartz substrate material, i.e. a 2p binding energy of 103 eV. From these findings, we demonstrate deposition of Si-O_x optical coatings that are thicker than 10 µm.
10:10 AM		C2-1-6 Zirconia and Zirconium Silicate Thin Films Deposited by Magnetron Sputtering D. Kuo, C. Chien (National Dong Hwa University, Taiwan, ROC) Amorphous zirconia and zirconium silicate thin films prepared on glass and silicon substrates by magnetron sputtering. Two sputtering targets were used: ZrO₂ and ZrSiO₄. These films were studied by choosing different substrate temperatures and rf growth powers. Dielectric properties and mechanical performance, e.g. hardness, internal stress and adhesion. Optical properties, e.g. refractive index and optical transmittance, were also measured. Zirconium silicate films had higher growth rate, better adnerance, higher hardness, lower internal stress and stable dielectric properties. Dielectric properties of zirconia films, instead, were controlled by the processing.
10:30 AM		C2-1-7 Properties of Nickel Oxide Thin Films Deposited by Reactive Magnetron Sputtering Y.-M. Lu (Kung Shan University of Technology, Taiwan, ROC) The NiO films were deposited by RF reactive magnetron sputtering from Ni and NiO targets in a mixture of oxygen and argon onto heated Si and Corning 7059 substrates.The process parameters investigated were the target power,the O₂/Ar ratio,sputtering gas pressure and the substrate temperature and their influence was studied on the film properties such as O/Ni atomic ratio,crystallographic structure,preferred orientation,transpancy and resistivity.The deposition rate increased as a function of the RF power but decreased with increasing substrate temperature,O₂/Ar ratio and sputtering gas pressure.The NiO films showed only the (200) diffraction peak in the XRD pattern.Such a textured growth is apparently characteristic for rocksalt-type oxide,since the surface energy of (200)is the lowest as compared with other crystal planes.The O/Ni ratio of the thin films decreased as the substrate temperature was increased.The O/Ni ratio was between 1.87 and 1.80.The transmission of undoped NiO films show a strong dependence on the O₂/Ar ratio.With increasing 02/Ar ratio,the transmittance decayed.The films resistivity increasing with increasing substrate temperature.The conduction in nickel oxide is due to the presence of Nisuber +3 ions.These ions formed by the appearance of NiO nickel vacancies and can be forther confirmed by XPS data in this study.
10:50 AM		C2-1-8 Effect of Frequency and Pulse Width on the Properties of DLC Films Prepared by FCVA Together with Substrate Pulse Biasing D. Sheeja, B.K. Tay, L. Yu (Nanyang Technological University, Singapore) An investigation has been carried out to study the effect of frequency and pulse width on deposition rate, intrinsic stress, morphological and micro-structural behaviour as well as surface energy of Diamond-Like Carbon (DLC) films prepared by Filtered Cathodic Vacuum Arc (FCVA) technique together with substrate pulse biasing. It is observed that the deposition rate increases with both increasing frequency and pulse width until it reaches to steady values at around 200 Hz and 25 micro-sec. The intrinsic stress in the films decreases with increasing frequency and reaches to a steady minimum value of 1 GPa at around 200 Hz. However, the variation of stress with pulse width is found to be less significant. The morphological study shows that the film tends to become rougher, when it is prepared at higher frequencies. The micro-structural evaluation of the film using visible Raman spectroscopy shows that the intensity ratio of D-peak to G-peak (ID/IG) increases with increasing frequency. It is also observed that the G-peak width (FWHM) and the stress display linear correlation. The dependence of frequency and pulse width on the surface energy is also studied.
11:10 AM		C2-1-9 Influence of rf Substrate Bias on SiO₂ Films Prepared by ECR-PECVD Zhaoxing Ren, Shuhua Xu (Chinese Academy of Science, China) The SiO₂-based planar lightwave circuit (PLC) is one of the most important devices for optical fiber communication systems. To achieve a good match with an optical fiber network, SiO₂-based PLCa are required for low loss and they must have the same core refractive index as those of an optical fiber. So SiO₂ film is one of the most important materials used in optoelectronic devices. Due to its high quality and low depositing temperature for planar optical waveguide, silicon dioxide films was prepared on crystalline silicon substrate by 2.45-GHz microwave electron cyclotron resonance plasma enhanced chemical vapor deposition. A 13.56 MHz rf power is applied to the substrate holder through a match network. The effect of RF bias on the properties of SiO₂ film has been studied. X-ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, atomic force microscopy and three-dimensional space morphology picture of scanning tunneling microscope were used to investigate the properties of deposited films. The experimental results show that the stress, the sputtering, the microstructure, and the stoichiometry of the films are greatly influenced by changing the parameters of RF substrate bias to control ion bombardardment energy.
11:30 AM		C2-1-10 Thin Films of Copper : Aluminum Alloy by Electron Beam Evaporation Technique: Effect of Substrate Temperature on Electrical and Optical Properties S. Srinivasan, B. Ullash Kumar, A. Subrahmanyam (Indian Institute of Technology, India) The recent investigations on Oxide thin films of copper : aluminum alloys show p-type conductivity and transparency in the visible region [1]. It is stated that these oxides has Delafossite structure which is believed to be responsible for the p-type conduction. The conduction mechanism in these oxide films is yet to be understood. As a first step towards the understanding of these Oxides thin films, present investigation reports the electrical and optical properties of Copper : Aluminum alloy thin films. Electron beam evaporation technique is employed to prepare these films. The starting material is the copper (Cu) : aluminum (Al) alloy of concentration 80:20 by wt%. The alloy is prepared in an arc melting furnace in the presence of argon gas. The films are prepared by varying the substrate temperature in the range : 25-200^oC. All other growth parameters: electron beam voltage (3.4 KV), beam current (60 mA), substrate to source distance (10 cm), base pressure of the vacuum chamber (2 x 10^â€“5milli Bar) have been kept constant through out the investigation. The thickness of the films is 300 nm as seen by a digital thickness monitor(in situ). With increasing substrate temperature, it is found that (i) the crystalline nature of the films increases (as shown by X-ray diffraction), (ii) the resisitivity of the film (measured at room temperature 25^oC) increases from 8.4 x 10^-5ohm cm at 25^oC to 1.8 x 10^-3 ohm cm at 150^oC and (iii) the optical transmission of these films increases. The dependance of the electrical conductivity on temperature of measurement is being studied. These data are being analyzed for an understanding of the electrical and optical behavior of these thin films. [1] H.Kawazoe,H.Yanagi, K.Ueda and H.Hosono Mat.Res.Bull vol 25, pp 28 (2000).
11:50 AM		C2-1-11 Effect of Oxide Growth Temperature on the Electrical Performance of Extremely Thin ( ~3 nm) Oxides of Silicon V.K Bhat, K.N. Bhat, A. Subrahmanyam (Indian Institute of Technology, India) Extremely thin (~3 nm) oxides of silicon are required for the ultra large scale integration (ULSI) applications such as submicron MOS transistors and 1 G-bit DRAMs. Hence the growth and characterization of the extremely thin oxides with good electrical properties became the subject of intensive study. The requirement for extremely thin oxide with good electrical performance places stringent demands on the oxidation techniques used to grow these oxides. In the present work, extremely thin (~3nm) oxides of silicon are grown by using wet oxidation in the temperature range 600-900^oC. The capacitance-voltage, current-voltage and charge trapping characteristics are used to study the electrical properties of these thin oxides. The results show that the electrical performance of the extremely thin oxide improves with the increase in the oxide growth temperature.