Sputter-deposited Thin Films Research Articles

Effect of E × B electron drift and plasma discharge in dc magnetron sputtering plasma

Study of electron drift velocity caused by E × B motion is done with the help of a Mach probe in a dc cylindrical magnetron sputtering system at different plasma discharge parameters like discharge voltage, gas pressure and applied magnetic field strength. The interplay of the electron drift with the different discharge parameters has been investigated. Strong radial variation of the electron drift velocity is observed and is found to be maximum near the cathode and it decreases slowly with the increase of radial distance from the cathode. The sheath electric field, E measured experimentally from potential profile curve using an emissive probe is contributed to the observed radial variation of the electron drift velocity. The measured values of the drift velocities are also compared with the values from the conventional theory using the experimental values of electric and magnetic fields. This study of the drift velocity variation is helpful in providing a useful insight for determining the discharge conditions and parameters for sputter deposition of thin film.

Microstructure of sputter-deposited noble metal-incorporated oxide thin films patterned by means of laser interference

ABSTRACTLaser interference patterning-induced microstructural modifications have been investigated in two noble metal-incorporated oxide thin film systems: Pd0.25Pt0.75Ox and gold-incorporated yttria-stabilized zirconia - Au-YSZ. Transmission electron microscopy was used to investigate the influence of the laser treatment on the microstructure of the samples. In the case of Pd0.25Pt0.75Ox, the formation of a nanocomposite arrangement resulted from the precipitation of metal nanograins in the oxide matrix triggered by laser irradiation. In Au-YSZ, the starting microstructure consisted of gold nanograins embedded in a YSZ matrix. A noticeable growth and coalescence of gold nanograins occurred near the surface in the region of maximum interference. Simultaneously, a foamy morphology, mostly consisting of gold crystals, was formed at the film surface. In contrast to thermal annealing, the laser treatment proposed here is a fast procedure to partially relocate gold at the film surface and provide a local solid lubrication.

Chemistry, phase formation, and catalytic activity of thin palladium-containing oxide films synthesized by plasma-assisted physical vapor deposition

The chemistry, microstructure, and catalytic activity of thin films incorporating palladium were studied using scanning and transmission electron microscopies, X-ray diffraction, spectrophotometry, 4-point probe and catalytic tests. The films were synthesized using pulsed filtered cathodic arc and magnetron sputter deposition, i.e. techniques far from thermodynamic equilibrium. Catalytic particles were formed by thermally cycling thin films of the Pd–Pt–O system. The evolution and phase formation in such films as a function of temperature were discussed in terms of the stability of PdO and PtO2 in air. The catalytic efficiency was found to be strongly affected by the chemical composition, with oxidized palladium definitely playing a major role in the combustion of methane. Reactive sputter deposition of thin films in the Pd–Zr–Y–O system allowed us forming microstructures ranging from nanocrystalline zirconia to palladium nanoparticles embedded in a (Zr,Y)4Pd2O matrix. The sequence of phase formation is put in relation to simple thermodynamic considerations.

Direct current magnetron sputter-deposited ZnO thin films

Zinc oxide (ZnO) is a very promising electronic material for emerging transparent large-area electronic applications including thin-film sensors, transistors and solar cells. We fabricated ZnO thin films by employing direct current (DC) magnetron sputtering deposition technique. ZnO films with different thicknesses ranging from 150nm to 750nm were deposited on glass substrates. The deposition pressure and the substrate temperature were varied from 12mTorr to 25mTorr, and from room temperature to 450°C, respectively. The influence of the film thickness, deposition pressure and the substrate temperature on structural and optical properties of the ZnO films was investigated using atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectrometer. The experimental results reveal that the film thickness, deposition pressure and the substrate temperature play significant role in the structural formation and the optical properties of the deposited ZnO thin films.

AlN-based sputter-deposited shear mode thin film bulk acoustic resonator (FBAR) for biosensor applications — A review

A new type of biosensor device is here presented which is fabricated using the same processes used for the fabrication of integrated electrical circuits to enable tighter integration and further sensor/biosensor miniaturization. The device is a so-called thin film bulk acoustic resonator (FBAR) operating in shear mode. Here specifically AlN-based shear mode FBAR is addressed but also an overview of the shear mode FBAR development in general is presented. Developments are reported of a low temperature reactive sputtering process for growing wurtzite–AlN thin films with a close to homogenous c-axis inclination over a 4″ substrate wafer. This process enabled fabrication of shear mode FBAR sensors. The sensor operation is described along with how the design parameters influence its performance. Specifically, sensitivity amplification utilizing low acoustic impedance layers in the FBAR structure is demonstrated and explained. The resolution of the AlN shear mode FBAR sensor is demonstrated to already be comparable with the conventional quartz crystal microbalance (QCM) sensor, suggesting that shear mode FBAR may be a competitive and low cost alternative to QCM.

ChemInform Abstract: Corrosion Mechanism of Sputter-Deposited TbFe Thin Films in Aqueous Environment.

This paper reports on the corrosion mechanism of sputter-deposited TbFe thin films for magneto-optical recording material that was investigated using electrochemical methods in aqueous environment with and without Cl{sup {minus}} ions. TbFe thin films with varying composition prepared by an ion beam sputtering method were used as specimens. TbFe tape alloys made by the rapid quench method of melting alloys were also used for comparison. In an acid buffer solution without Cl{sup {minus}} ions, the corrosion rate of the TbFe thin films and tape alloys decreased with increasing Tb content. In this solution, passive films composed of Tb oxide or hydroxide were formed on both the TbFe thin films and tapes and the selective dissolution of Fe through the passive films occurred. In neutral solutions with Cl{sup {minus}} ions, pitting corrosion occurred on both the TbFe thin films and tapes. The stoichiometric dissolution of the substrate at pitted sites and the selective dissolution through the passive films at nonpitted sites take place in these solutions.

Pressure-dependent transition from atoms to nanoparticles in magnetron sputtering: Effect onWSi2film roughness and stress

We report on the transition between two regimes from several-atom clusters to much larger nanoparticles in Ar magnetron sputter deposition of WSi2, and the effect of nanoparticles on the properties of amorphous thin films and multilayers. Sputter deposition of thin films is monitored by in situ x-ray scattering, including x-ray reflectivity and grazing incidence small angle x-ray scattering. The results show an abrupt transition at an Ar background pressure Pc; the transition is associated with the threshold for energetic particle thermalization, which is known to scale as the product of the Ar pressure and the working distance between the magnetron source and the substrate surface. Below Pc smooth films are produced, while above Pc roughness increases abruptly, consistent with a model in which particles aggregate in the deposition flux before reaching the growth surface. The results from WSi2 films are correlated with in situ measurement of stress in WSi2/Si multilayers, which exhibits a corresponding transition from compressive to tensile stress at Pc. The tensile stress is attributed to coalescence of nanoparticles and the elimination of nano-voids.

Thermal expansion coefficients and composition of sputter-deposited silicon oxynitride thin films

Modern technology is heavily reliant on silicon dioxide and silicon nitride thin films. These films have many electronic and optical applications, and in some cases silicon oxynitride films of intermediate composition are desirable. We have systematically deposited several SiOxNy films by magnetron sputter deposition and thoroughly investigated their composition with Rutherford backscattering spectrometry and optical measurements. The as-deposited stress in these thin films was also measured and all were found to be compressive.Temperature-dependent stress measurements up to 450 °C were then used to extract the biaxial modulus and coefficient of thermal expansion for each SiOxNy. The SiO2-like films exhibit negative thermal expansion, which is consistent with a strong but porous structure. Increasing the nitrogen content results in the thermal expansion coefficient increasing towards values reported elsewhere for Si3N4.

Studies on the properties of sputter-deposited Sc-doped ZnO thin film

Structural, optical and electrical properties of Sc-doped ZnO films grown by RF magnetron sputtering at room temperature were investigated. The deposition pressure was varied from 0.3 to 2.0 Pa. XRD spectra indicated that the (1 0 0) peak of the film decreased as the deposition pressure decreased and the (1 1 0) peak showed the highest intensity at the pressure of 0.3 Pa. Compared with (1 0 0) and (1 1 0) peaks, the intensity of (0 0 2) peak was relatively weak. The morphology of the films is related to the deposition pressure. The stress in the film was investigated. The film with resistivity as low as 7.7×10 −2 Ω cm has been obtained at 0.8 Pa. The average transmittance of these films was about 90% in the wavelength range 400–800 nm, but decreased in the short wavelength region due to light scattering.

Crystallization and high temperature shape memory behavior of sputter-deposited NiMnCoIn thin films

Amorphous Ni50Mn38Co6In6 films of 20 μm in thickness are fabricated using dc magnetron sputtering technique. Ex situ annealing studies demonstrate the crystallization at elevated temperature, and the retention of L10 martensite at room temperature. In situ annealing inside a transmission electron microscope reveals the crystallization process as well as the transformation to B2 austenite at elevated temperatures. Differential scanning calorimetry studies show the crystallization activation energy of ∼239 kJ/mol, a reversible martensitic phase transformation temperature of ∼350 °C, and a hysteresis of ∼75 °C.

Growth and characterization of (Pb,La)(Zr,Ti)O 3 thin film epilayers on SrTiO 3-buffered Si(001)

Ferroelectric Pb 0.92La 0.08Zr 0.4Ti 0.6O 3 (PLZT) thin films were deposited on SrTiO 3-buffered Si(001) substrate by on-axis radio frequency magnetron sputtering. X-ray diffraction analysis revealed epitaxial growth of monocrystalline PLZT films, with an (001) rocking curve full width at half maximum of ∼ 0.3°. φ-scans showed 45° in-plane orientation of the perovskite unit cell relative to that of silicon. The elemental composition of the thin film heterostructure was examined by Auger sputter depth profiling measurements. The recorded profiles suggest that the SrTiO 3 buffer layer serves not only as a template for epitaxial growth, but also as a barrier suppressing Pb–Si interdiffusion between the PLZT layer and the Si substrate. The surface roughness of the PLZT layer was measured at ∼ 4 nm for films with ∼ 500 nm thickness. Wavelength dispersions for the refractive index ( n) and the extinction coefficient ( k) were obtained from spectroscopic ellipsometry measurements, with n ∼ 2.48 at the main communication wavelength λ = 1550 nm and k < 0.001 for λ > 650 nm. Recorded polarization vs. electric field loops for the PLZT epilayer, with a SrRuO 3 electrode layer interposed between PLZT and SrTiO 3, showed a remnant polarization P r ≈ 40 µC/cm 2 and coercive field E c ≈ 100 kV/cm. These findings suggest that the sputter-deposited PLZT thin films retain the functional properties critical to ferroelectric and electro-optic device applications, also when integrated on a semiconductor substrate.

Influence of plasma pressure on the growth characteristics and ferroelectric properties of sputter-deposited PZT thin films

PZT thin films of thickness (320–1040) nm were synthesized on Si/SiO 2/Ti/Pt multilayered substrates by radio frequency magnetron sputtering. The influence of plasma pressure in the range of (0.24–4.9) Pa, during deposition, on the structural, electrical and ferroelectric properties of the PZT films was systematically studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and cross-sectional transmission electron microscopy (XTEM) were employed for structural study. Nano-probe Energy Dispersive (EDX) line scanning was employed to investigate the elemental distribution across the film-bottom electrode interface. I– V characteristics and polarization–electric field ( P– E) hysteresis loop of the films were measured. The study reveals that the plasma pressure has a strong influence on the evolution and texture of the ferroelectric perovskite phase and microstructure of the films. At an optimum plasma pressure of 4.1 Pa, PZT films are grown with 93% perovskite phase with (1 1 1) preferred orientation and uniform granular microstructure. These films show a saturation polarization of 67 μC/cm 2, remnant polarization of 30 μC/cm 2 and coercive field of 28 kV/cm which, according to the literature, seem to be suitable for device applications. Transmission electron microscopy (TEM) study shows that at a plasma pressure of 4.1 Pa, the PZT/bottom Pt interface is sharp and no amorphous interlayer is formed at the interface. At a higher plasma pressure of 4.9 Pa, poor I– V and P– E hysteresis loop are observed which are interpreted as due to an amorphous interlayer at the film-bottom electrode interface which is possibly enriched in Pb, Zr, O and Pt.

Effects of Hydrogen in Working Gas on Valence States of Oxygen in Sputter-Deposited Indium Tin Oxide Thin Films

X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy-elastic recoil detection analysis (RBS-ERDA) revealed that hydrogen in working gas for dc-plasma sputter deposition resided in indium tin oxide (ITO) films and generated the O(-) state seen as the suboxide-like O 1s peak in XPS. Growth of the suboxide-like O 1s peak was parallel with an increase of the resided hydrogen quantified by RBS-ERDA. The first-principles band structure calculation revealed that the electronic structure of In(2)O(3) crystal was realized typically for the most conductive as-deposited film grown in the gas containing hydrogen of 1%. The as-deposited film grown in the gas containing hydrogen of more than 1% exhibited rather high density but low mobility of carriers and showed the electronic structure above 4 eV originated from the O(-) state due to the resided hydrogen in addition to that of the most conducting one. Both well preserved In(2)O(3) band structure and proper concentration of the O(2-) vacancy are indispensable for achieving the highest conductivity; however, the O(-) state lowers efficiency of the carrier doping using the O(2-) vacancy in the lattice and increases density of the ionized scattering center for the carriers.

Utilization of Water Vapor for Sputter Deposition of Thin Films

Utilization of Water Vapor for Sputter Deposition of Thin Films

Direct formation of a water oxidation catalyst from thin-film cobalt

A cobalt-based water oxidation catalyst may be grown from sputter-deposited thin films (800 nm thick) of cobalt metal on a non-conductive glass substrate. Chemical composition and function of the catalyst prepared in this manner are similar to that for catalyst films prepared by electrodeposition of the catalyst from aqueous solutions of Co2+ salts. The method permits water oxidation catalysis to be established from protective barrier layers on materials that otherwise experience corrosion under the aqueous oxidative conditions.

(100) Oriented Sputter-deposited Pt Thin Films on MgO/Fe Composite Bilayers using SiO2/Si substrates With Addition of O2 During Pt Sputtering

AbstractPerovskite type oxide thin films have attracted a lot of attention, because they are essential materials which will be used for various electric devices such as ferroelectric random access memory (FeRAM) and tunable filter devices. When the materials are used for such capacitive devices, bottom electrode layers for oxide films are very important, since they significantly affect the crystallinity of the oxide films. Platinum (Pt) is one of the well known bottom electrode materials used for the oxide thin films. Pt provides also better nucleation sites for such perovskite materials due to small lattice misfit. Since dielectric properties of ferroelectric films are originated from the displacement of ions in a crystal along the c-axis direction, c-axis oriented ferroelectric thin films are required to attain better dielectric properties. (100) oriented Pt layers are required to attain c-axis oriented perovskite type ferroelectric films. In our previous report, we succeeded in preparing (100)-oriented Pt thin films with thickness of 20 nm on SiO2/Si substrate at substrate temperature Ts above 400 °C using MgO (100) buffer layers which deposited on Fe (100) seed layers. However, the growth of Pt(111) texture appeared when the thickness was increased from 20 nm to 100 nm, since (100) texture has relatively higher surface energy than (111) closely packed texture for Pt surface. It suggested that surface energy of the films changed during the deposition. In order to keep the surface energy, addition of O2 gas was performed during Pt deposition. Pt thin films with (100) preferred orientation with thickness above 100 nm were deposited on the (100) oriented MgO layer prepared on very thin seed Fe layers deposited on SiO2/Si substrates at Ts of 500 °C by facing-targets sputtering. It was also succeeded to attain (100) oriented perovskite oxide layer when they were deposited on the Pt(100)/Mg(100)/Fe/SiO2/Si underlayer.

Effect of Ion-implantation on Forming and Resistive Switching Response of NiO Thin-Films

AbstractThe forming voltage and set/reset response of sputter-deposited NiO thin films is studied as a function of implant fluence for samples implanted with Ni and O ions. The forming voltage of the films is shown to decrease with increasing ion fluence and to scale with the damage production rate of the different ions. In contrast, the set/reset response of the films was largely unaffected by the ion-implantation. These results are discussed in terms of the filamentary model of conduction and the thermochemical model of resistive switching.

Microstructure Analysis and Optimization of Sputter-Deposited Zinc Oxide Thin Films Used in Low-Emissivity Coatings for Energy Efficient Windows

Microstructure Analysis and Optimization of Sputter-Deposited Zinc Oxide Thin Films Used in Low-Emissivity Coatings for Energy Efficient Windows

Surface morphology evolution during sputter deposition of thin films – lattice Monte Carlo simulations

The growth of uniform thin films on foreign substrates is impeded by several morphological instabilities. Hill-and-valley structures are formed and enhanced during sputter deposition where surface height perturbations have an opportunity to grow to large amplitudes. We show via kinetic Monte Carlo (kMC) simulations that while surface roughness can be partially controlled by changing growth conditions, such as substrate temperature, the diffusion of particles over step edges plays a very important role in determining both surface roughness and the density of the films. Our kMC simulations provide a way to evaluate the strength of surface instabilities during sputter deposition of thin films.

Photo-degradation activity of sputter-deposited nitrogen-doped titania thin films

Various approaches have been reported during the last decade to enhance the photo-catalytic and super-hydrophilic characteristics of the intrinsic TiO 2 materials. Results on the photo-degradation activity of RF-sputtered nitrogen-doped titania thin films are presented here with respect to two environmental pollutants in gas- and liquid phases, as a function of dopant concentration. This study was accomplished by monitoring the time dependence of pollutant concentration in contact with the films, both under UV and solar light illumination. The synergic effects of surface morphology, crystalline and electronic structure of the materials are discussed in relation with the observed experimental facts. The results presented here show a close correlation between the oxidative power of the films and their previously reported wettability features.