Film Properties/Structure/Deposition Process Relationships

Wednesday, May 2, 2001 1:30 PM in Room Sunset

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1:30 PM C2-2-1 In-Situ Stress Measurements of Thin Films
N.S. Sirotkina (University of Salford, United Kingdom); R. Valizadeh, J.S. Colligon (Manchester Metropolitan University, United Kingdom)
Stress measurement methods based on the curvature of the substrate are described and the relation between stress in thin film coatings and curvature of the substrate is analysed. Different formulae for the relation between stress and curvature have been investigated. It is shown that, within certain guidelines, the modified Stoney equation gives sufficiently accurate stress values. Models which include the effects of ion bombardment are also reviewed. Thin films of Ta2O5 and SiO2 at different O2 partial pressure with both Ar and Xe as sputtering gases were synthesised on double side polished silicon and glass substrates at room temperature using the dual ion beam sputtering technique. Optical properties and the stress evolution for stoichiometric films were investigated as a function of pre-cleaning procedures, target to substrate angle and concurrent ion bombardment at 200-600 eV with ion/atom arrival ratios ranging from 0.5 to 2. The stress in thin films of SiO2 and Ta2O5 was measured in-situ during deposition using the laser reflection method for a polished Si (100) substrate in the form of cantilever beam. In order to obtain the stress evolution as a function of film thickness, measurements were taken before deposition and after subsequent frequent intervals. The stress in the thin film was evaluated using the modified Stoney formula. Film thickness and composition were measured ex-situ using Rutherford Backscattering Spectroscopy. Optical properties of the films were investigated using ellipsometry and ultraviolet spectrophotometry. It has been shown that the stress is independent of the surface treatment, deposition interval and film thickness and is in the range of 650-970 MPa for SiO2 and 230-580 MPa for Ta2O5 films. The stress is dependent on concurrent ion bombardment conditions. The value of the refractive index is in the range of 2.0-2.15 for Ta2O5 films and 1.42-1.52 for SiO2 films.
1:50 PM C2-2-2 Graded Cermet Selective Coatings Based on Aluminium Deposited by Magnetron Sputtering Technology
C. Nunes (Instituto Nacional de Engenharia e Tecnologia Industrial, Portugal); V. Teixeira, A. Monteiro, A Peixoto (Universidade do Minho, Portugal)
Selective solar absorber surfaces are of great importance especially for efficient solar photothermal conversion at high temperatures. Selective cermet thin films were produced by D.C. magnetron sputtering of metallic aluminium - molybdenium target at constant substrate temperature, target current and substrate bias. These films are graded cermet basically with a cermet layer rich in metal, Cermet layer with less metal fraction than the first one and the last only ceramic layer (the antireflection layer). The ceramic and metallic components of the cermets were deposited in a sublayer system consisting in alternating metallic and nitride (or oxide) sublayers. In order to change the metal volume fraction the thickness of the sub-layers is changed. The effect of metallic fraction and number of sub-layers in optical properties of the films were studied and good results were obtained. The optimum film selectivity achieved was a solar absorptance of 94% and a thermal emittance of 4% at 82ÂșC. While the metallic component was deposited by D.C. non-reactive sputtering, the ceramic component is deposit by D.C. reactive sputtering in an atmosphere of Argon and Nitrogen or Argon and Oxygen depending if is wanted Nitride or Oxide in ceramic layer respectively. The film thickness and microstructure were studied by scanning electron microscopy (SEM). The surface microtopography was analyzed by atomic force microscopy (AFM).
2:10 PM C2-2-3 ZnS Sol-Gel Deposited Films: The Characteristics of the Sulphidation Process
Y. Lydon-Kavanagh (I T Carlow, Ireland); D.C. Cameron (Dublin City University, Ireland)
Zinc sulphide is a wide-gap semiconductor which when doped is an efficient luminescent phosphor. Zinc sulphide films have been produced by a process where a zinc oxide film is deposited by a sol-gel technique and then converted to zinc sulphide by annealing in a sulphur containing atmosphere. The films so produced have a polycrystalline wurtzite structure and have been previously shown to be able to form part of an electroluminescent device @footnote1@. This paper reports the results of investigations into the sulphidation process whereby O is replaced by S in the zinc compound. The structural evolution of the films and the changes in compositional profiles have been observed as a function of the annealing conditions. The rates of diffusion of S and O and the rates of exchange between them have been estimated from these. The possible physical processes underlying these phenomena are discussed. @FootnoteText@ [1] W. Tang and D. C. Cameron, Thin Solid Films 280 (1996) 221 .
2:50 PM C2-2-5 Significant Structure and Property Variations on Si-C-N Films Via the Wet Etching Treatment of the Si Substrate
H.L. Chang, ChengTzu Kuo (National Chiao Tung University, Taiwan)
The Si-C-N thin films have been synthesized on Si wafer substrate by a microwave plasma chemical vapor deposition (MPCVD) system with CH@sub 4@ and N@sub 2@ as the source gases and with or without additional Si source. The Si substrates were mechanically polished or chemically etched with HF-KIO@sub 3@-H@sub 2@O solutions to different surface roughness before film depositions. Effects of the substrate pretreatments on surface morphology, compositions, crystal structure, field emission and mechanical properties of the films will be examined. The preliminary results show that the atomic N/C ratios of the Si-C-N films can be varied from 0.25 ~ 0.67, depending on the etching time of the Si substrate. The deposition rates and the peak intensities of cathodoluminescence (CL) spectra of the films are significantly higher for the substrates, which are chemically etched. The emission current density at field strength of 2 V/cm can go up to 1.3 mA/cm@super 2@, which is much higher than the reported values in the literature. The results also indicate that the maximum field emission occurs at a range of surface roughness. Effect of composition, nucleation rate and surface roughness on field emission, band structure and mechanical properties of the films will be discussed.
3:10 PM C2-2-6 Optical , Electrical and Compositional Studies of Silicon Nitride Thin Films
K.C. Mohite, S.T. Pawar, M.G. Takwale (Pune University, India)
Silicon Nitride films are widely used in very large scale integrated circuits, thin film transistors and solar cell applications.The mechanical hardness and chemical inertness of Silicon Nitride have made it a valuable material for use in sensors. Silicon Nitride thin films were deposited on silicon and glass substrates by electron beam evaporation technique. The emmition current, deposition time and substrate temperature were varied at suitable values. The effect of these parameters on optical,electrical and compositional properties of the films was investigated. Films were characterised by using FTIR,UV,ellipsometry,AES and XPS techniques.
3:30 PM C2-2-7 Poster C Summary Session
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