Showing papers on "Sputtering published in 1979"

Ion‐beam deposition of thin films of ferroelectric lead zirconate titanate (PZT)

Abstract: Lead zirconate titanate is a solid solution with nominal composition Pb(ZrxTi1−x)O3. Ferroelectric thin films of this material have been successfully deposited by a focused ion‐beam sputtering technique in an O2 atmosphere. These films were characterized according to composition, crystal structure, and dielectric and ferroelectric properties. The effects of deposition temperature, heat treatment after deposition, and substrate and target material were investigated. The composition of the films was within 1 at.% of the composition of the multicomponent PZT target for substrate temperatures up to 200 °C. The Pb concentration decreased for substrate temperatures above 200 °C. Films deposited at substrate temperatures below 250 °C were microcrystalline. At 300 °C, the pyrochlore phase was obtained. Films with the ferroelectric perovskite structure were deposited above 400 °C, which is the lowest deposition temperature ever reported for this phase. O2 losses during postdeposition annealing resulted in a collap...

Reactive sputtering of carbon and carbide targets in nitrogen

Abstract: Paracyanogenlike films – (CN)n– are prepared by reactive rf sputtering of carbon in nitrogen. The material is deposited on quartz, silicon, metals, sapphire, and mica from 20° to 450°C. Above 450°C, there is no film accumulation on the substrates. The sputtering process yields a deposition rate greater than ten times the best known commercial method for paracyanogen film preparation. Also described are the results of sputtering carbide targets i.e. HfC, TiC, SiC, in the presence of nitrogen. Due to the stability of the C≡N bond, for example, stoichiometric Si3N4 films unexpectedly were deposited from a SiC target sputtered in N2. Similar results are described for HfC and TiC targets.

Influence of atomic mixing and preferential sputtering on depth profiles and interfaces

Abstract: Atomic mixing and preferential sputtering impose a depth resolution limit on the use of sputter sectioning to measure the composition of metal–semiconductor interfaces. Experimental evidence obtained with the Pt–Si system is used to demonstrate ion‐induced atomic mixing and then its effect on sputter etching and depth profiling. Starting with discrete layer structures, a relatively low ion dose (≳3×1013 cm−2) first produced a mixed surface layer with thickness comparable to the ion range. Higher ion doses then result in successive sputter etching and continual atomic mixing over a constant surface layer thickness. A model is developed that is based on a sputter removal (including preferential sputtering) of atoms at the surface and a uniform mixing of atoms over a constant thickness. The model predicts the influences of atomic mixing and preferential sputtering on the depth profiling of thin‐film structures and interfaces.

Reactive ion etching of silicon

Abstract: Reactive ion etching of silicon substrates in a plasma containing chlorinated species does not result in undercut of a permanent mask. When the silicon is very highly doped it behaves as a different material and undercut has been observed. This phenomenon will be discussed. For use in chlorinated plasmas, there is a choice of nonerodible masks that sputter slowly but will not be redeposited on the substrate surface. Both CCl4/Ar and Cl2/Ar plasmas will be described. The variation in etch rate of silicon with rf power, frequency, reactant concentration, reactant flow rate, gas presure, crystal orientation, and batch size will be presented. The possibilities of polymer formation and surface roughening will be discussed.

Mass effects on angular distribution of sputtered atoms

Abstract: Sputtering metal targets at low ion energies (Hg or Ar at less than 300 eV) under normal ion incidence causes the lighter atoms (lighter isotopes or lighter elements of alloys) to be preferentially ejected in a direction normal to the target surface. Experimental results are shown for several elements and alloys at various bombardment energies. The amount of enrichment of the lighter species normal to the target surface decreases quite rapidly with increasing ion energy. The phenomenon is a result of reflective collisions because lighter atoms can be backscattered from heavier ones underneath but not vice versa. The effect provides an explanation of why solar-wind-exposed lunar material is enriched in the heavier isotopes, since sputtered lower-mass elements have a higher chance of achieving the lunar escape velocity.

Electrical properties of RF sputtering systems

Abstract: A theory is developed that gives a relatively complete electrical characterization of rf sputtering systems. Three types of systems are analyzed: tuned substrate, driven substrate, and controlled area ratio of electrode (CARE) systems. The theory is applicable to any of these systems that do not use magnetic fields to confine the plasma. Given the input rf power and voltage at the target, and any other parameters that can be specified as independent variables (e.g., pressure, substrate drive voltage, tuning impedance, and system geometry), the theory provides explicit values for all dc and rf electrical parameters of the system. The dc bias developed ut the substrate is explained and related to the resputtering energy. In addition, an approximate calculation is presented for the ion density in the plasma; this calculation allows a semiquantitative estimate of the rf voltage developed at the target for a given value of rf input power. It also shows the influence of pressure and frequency on rf sputtering system operation. Comparisons are made with real rf sputtering systems; these show that the theory is quite successful in predicting the operation of these systems. In addition, a much better understanding is achieved of some of the complex electrical phenomena encountered in these systems. The theory should prove useful both for new system design and for diagnostic work on existing equipment.

Preparation and properties of CuInS2 thin films produced by exposing sputtered Cu‐In films to an H2S atmosphere

Abstract: CuInS2 thin films have been made from copper, indium, and hydrogen sulfide gas using a two‐step technique which involves exposing Cu‐In films produced by sputtering pure copper and pure indium to H2S gas diluted with argon. X‐ray diffraction, Auger electron spectroscopy, optical transmission, and electrical measurements were used to identify and characterize the CuInS2. The resulting films were all p type with resistivity in the range 0.1–500 Ω cm and showed a preferred orientation of the (112) plane parallel to the substrate.

Method of producing a microstructured surface and the article produced thereby

Abstract: A method is disclosed for producing a micro structure on the surface of an article. The method comprises the steps of depositing a discontinuous coating of a material exhibiting a low rate of sputter etching on a substrate exhibiting a higher rate of sputter etching and differentially sputter etching the composite surface to produce a topography of pyramid-like micropedestals random in height and separation. The articles produced by this method are characterized by both the microstructured surface and by the detectable presence of the material exhibiting the lower rate of sputter etching. The microstructured surface results in the articles having uniform antireflecting properties over a large range of angles of incident light and over an extremely broad range of wavelengths, in which the antireflecting characteristic is obtained without an attendant increase in diffuse scattering. Also, the microstructured surface results in the articles being characterized by a high degree of adherence, such that the treated surface may be considered to be "primed", thereby enabling the application of highly adherent coatings or layers thereon.

Stress induced anisotropy in amorphous Gd‐Fe and Tb‐Fe sputtered films

Abstract: The perpendicular anisotropy caused by the internal planar stress due to the substrate constraint in Gd‐Fe and Tb‐Fe sputtered films was investigated. The internal planar stress σ in these films is found to be very sensitive to preparation conditions, especially to the argon pressure during sputtering, PAr. Stress is compressive for low PAr and tensile for high PAr. The contribution of the stress to the total perpendicular anisotropy varies depending on PAr. Measurement of the anisotropy change before and after the removal of the substrate reveals that the predominant part of the perpendicular anisotropy originates from the internal stress due to the substrate constraint for Tb‐Fe films with a composition of around 30 at.%Tb, where the magnetostriction is extraordinarily large.

Energy and fluence dependence of the sputtering yield of silicon bombarded with argon and xenon

Abstract: Using the quartz oscillator technique, we have measured the sputtering yield of silicon bombarded with 10–140‐keV argon and 10–540‐keV xenon, respectively. Considerable effort has been devoted to achieving high‐purity silicon films with smooth surfaces and to calibrating the microbalance. In situ combination of the quartz oscillator technique with Rutherford backscattering allowed a quantitative determination of the fluence dependence of the sputtering yield. Measurements with xenon at 140 and 270 keV showed that the sputtering yield of silicon increases by about 25% due to loading of the target with projectile atoms. A simple estimate indicates that the yield enhancement is caused, to a large extent, by the increase in nuclear‐energy deposition resulting from the accumulation of the heavy projectiles in silicon. The measured steady‐state sputtering yields are in satisfactory agreement with results achieved by other experimental techniques. Discrepancies with results derived by other authors applying the ...

Textured silicon: A selective absorber for solar thermal conversion

Abstract: We have used reactive sputter etching to texture the surface of Si wafers. The texturing was in the form of pillars whose diameters and spacing were small compared with the useful solar wavelengths and whose heights were comparable with or larger than these wavelengths. The normal and hemispherical reflectances of textured wafers were measured. The solar absorptance was found to be 0.99 for wavelengths below 1.0 μm. Because of the sharp drop in absorptance for photon energies less than the energy gap, the overall solar absorptance was about 0.85. The calculated thermal emittance was about 0.25 and was primarily due to multiphoton absorption processes normally observed in thick Si crystals. Much smaller values of thermal emittance would be obtained from thin textured films.

Nonlinear sputtering effects in thin metal films

Abstract: The sputtering yields of Ag, Au, and Pt have been measured for monatomic and polyatomic ions of P, As, Sb, and Bi over the energy range 15–135 keV. Very lare enhancements of the sputtering yields over those predicted by linear cascade theory have been observed. These enhancements appear to be consistent with a strong contribution resulting from the near‐surface region of the impact area and that the complete collision cascade, even for high energy densities, plays a lesser and possibly minor role. It is also shown that the enhancements can in no way be explained based upon a thermal model in which the localized high‐temperature zone is responsible for an evaporation component.

The Sputtering Mechanism for Low-Energy Light Ions

Abstract: The computer simulation program MARLOWE which follows the trajectories of energetic ions and recoiling target atoms in solids has been used to calculate sputtering yields for low energy (0.1–10keV) light ions (H, D, T,4He). Recoil energy densities were calculated for comparison with analytical theories. The sputtering yields obtained for amorphous Fe agree within a factor of two with experimentally measured values for polycrystalline stainless steel, while the calculated yields for protons on amorphous molybdenum are more than twice the experimental values on polycrystalline material. The calculations show that in the parameter range investigated, ions backscattered in the solid contribute a major part to sputtering. This result confirms earlier calculations of the threshold energy for sputtering which are in agreement with recent measurements.

Computer simulation of low-energy sputtering in the binary collision approximation

Abstract: The sputtering of amorphous Cu targets by low-energy atoms has been investigated in the binary collision approximation using the computer program MARLOWE. Particular attention was given to the influence of the surface binding model on the results. Calculations were made of the dependence of the sputtering yield on the incident particle direction, energy, and mass. Angular-, energy-, and yield-distributions of the ejected atoms were evaluated. Comparisons with experimental results on polycrystalline targets show that the planar surface binding model is to be preferred over the isotropic surface binding model, especially with regard to the angular- and energy-distributions. Calculated yields are in reasonable agreement with experiment at energies below about 1 keV, but deviate at higher energies, apparently because of crystal correlation effects that are neglected in the amorphous model.

Kinetics of decomposition of amorphous hydrogenated silicon films

Abstract: The decomposition kinetics of amorphous hydrogenated silicon films have been studied by thermomanometric analysis at constant heating rate. rf and dc‐biased rf glow‐discharge films, as well as films deposited by reactive sputtering, have been analyzed and the results used to determine the thermodynamic parameters characterizing the activation barriers for decomposition of the =SiH2 and ≡SiH centers. Conclusions regarding the structure of these films are presented on the basis of kinetic evidence and parallel infrared absorption studies.

Thin-film semiconductor NO x sensor

Abstract: A thin-film semiconductor NO x sensor has been fabricated by reactive RF sputtering from a tin target. The gas detection is based on monitoring the sensor resistance change caused by NO x chemisorption on the sensor surface. The sensor is highly sensitive and selective toward detecting NO x in air. The chemical composition of the film was investigated by AES and ESCA. A simple chemisorption model is presented to explain the observed phenomena.

Method for producing an inhomogeneous film for selective reflection/transmission of solar radiation

Abstract: A sputtered thin film coating characterized by a stepwise and/or variable refractive index as a function of film depth. By means of an in-line assembly of planar magnetrons, each magnetron essentially isolated from the others but for a region of sputtering overlap, select materials and combinations of said materials with reactive gases can be continuously deposited upon a dynamic substrate whereby to obtain pre-determined refractive index gradients. Substrates coated with an inhomogeneous thin film exhibit superior non-spectral reflective characteristics particularly desirable for architectural designs and applications.

Sputtered hydrogenated amorphous silicon

Abstract: Hydrogenated a-Si, whose properties can be modified by impurity doping, can be produced either by decomposition of silane or by reactive sputtering of Si in an argon-hydrogen plasma. This article reviews advances made during the past few years in the preparation and characterization of films produced by the second method. The basic deposition conditions are summarized. The conclusions of analytical studies (photo-emission, infrared spectroscopy, and volumetric measurements of evolved gases), regarding the amount of hydrogen and its bonding configuration in the network, are outlined. The optical, carrier transport, photoconductivity and photoluminescence properties as a function of hydrogen content and doping are described. Electron drift mobilities, deduced from steady state and transient photoconductivity are presented. The transport and recombination properties are discussed with existing models of amorphous semiconductors, and are found to be consistent with atomic relaxations, i.e. polaronic effects.

Sputtering process model of deposition rate

Abstract: A model of the sputtering process has been developed that predicts the deposition rate of a sputtering system with parallel-plate geometry. By using data for sputtering yield vs voltage obtained from an ion-beam sputtering system, the model applies a new theory for computing the backscatter of the sputtered material, and, from the results, predicts deposition rates. The model also considers the effects of charge exchange in the sheaths, and of re-emission of sputtered material at the substrate. The model is valid for magnetic, tuned substrate, driven substrate, and controlled area ratio diode systems. Comparison with observed deposition rates shows good agreement for clean systems. An experimental APL program that uses the model has been written.