ICMCTF2009 Session B1-2: Sputtering Coatings and Technologies

Wednesday, April 29, 2009 1:30 PM in Room Golden West

Wednesday Afternoon

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1:30 PM B1-2-1 Development of Multi-Element Nitride/Oxide Coatings
F.-S. Shieu, D.-C. Tsai, R.-S. Yu (National Chung Hsing University, Taiwan)
Multi-element/high entropy alloys have emerged as a new class of high temperature materials over the years. Unlike conventional alloys with only one or two major components, multi-element alloys usually contain more than three principal elements of equal fraction. One of the distinct characteristics of the high entropy alloys is that the tensile strength of the alloys increases with temperature. The crystal structure of the alloys also exhibits a simple form, such as body-centered cubic, face-centered cubic, and hexagonal closed-packed. Research on the properties and microstructure of multi-element alloy thin films prepared by magnetron sputtering has been carried out intensively in recent years. An overview of the current research on nitride/oxide thin films of the multi-element alloys that contain Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zr, Nb, Mo, and Ta, is given. Attempt is made to correlate among deposition parameters, microstructure, and mechanical properties of the multi-element nitride/oxide films either from literature or our experiments.
2:10 PM B1-2-3 Preferential Sputtering of Oxides and Target Design for Stable Reactive Magnetron Deposition of Oxides
T. Kubart, T. Nyberg, S. Berg (Uppsala University, Sweden)

In reactive magnetron sputtering, hysteresis effect often limits the deposition rate and achievable compositions of the coatings. Hysteresis is of particular concern in the deposition of oxides due to the large difference between metal and compound sputtering yields and the high reactivity of oxygen.

In this work we have focused on the understanding of sputtering from different oxides. The overall aim is to avoid hysteresis and increase the deposition rate. High sputtering rate has previously been observed from TiOx target. This was attributed to the sputter reduction of TiO2 to lower oxides which have substantially higher sputtering yields. To investigate this effect for other materials, a study of sputtering from metal and oxide targets of Al, Ti, V, Nb, and Ta has been carried out. Sputtering was performed by means of RF magnetron reactive sputtering and x-ray photoelectron spectroscopy (XPS) with ion beam sputtering. The evolution of the surface composition during ion bombardment, as measured by XPS, was related to the corresponding hysteresis behaviour in reactive sputtering. Computer modelling of the sputtering process using the Tridyn code was employed in order to describe the preferential sputtering effects and extract the values of surface binding energy

Preferential sputtering could be described using Tridyn. The results have shown an anomalous behaviour of Ti oxide which differs from all the other materials. Even though the formation of lower oxides and preferential sputtering was observed for other oxides as well, the rate increase was substantially lower. Mixed targets consisting of a metal and its compound have been suggested as an alternative to ceramic targets for high rate stable reactive sputter deposition.

2:30 PM B1-2-4 Low Temperature Deposition of Anatase TiO2 Film by Dual Magnetron Sputtering
J. Sicha, P. Baroch, M. Meissner, R. Cerstvy, J. Musil (University of West Bohemia, Czech Republic)
A formation of thin crystalline photoactive TiO2 films at low deposition temperatures belongs to important topics whose solution would open wide utilization of TiO2 films on plastics and as a functional barrier coating in microelectronics. To reach this goal, the surface temperature during the deposition must not exceed 150°C and at these low temperatures crystalline films must be formed. For this purpose, a pulsed dual magnetron sputtering system operated at high repetition frequencies and at interruptive deposition mode was proposed. To reduce maximum surface temperature of the substrate and deposited film, the deposition process was periodically interrupted. The deposition process consisted of 1 to 7 deposition cycles with a 60 min pause between each cycle. It was found that the interruption of the deposition process reduced maximum surface temperature, however had no influence on the final crystallographic structure of the TiO2 films of the same thickness. Likewise, no significant differences in the photocatalytic activity and hydrophilicity of anatase TiO2 films were observed. The photoactive nanocrystalline TiO2 anatase film can be deposited at the surface temperature Tsurf below 130°C and at a relatively high deposition rate aD ~ 10 nm/min. Results indicate that i) the formation of crystalline TiO2 films with the anatase phase requires a certain amount of energy to be delivered to the growing film independently on the surface temperature and ii) the energy deliver to the growing TiO2 film by bombarding ions has a dominant effect on its nanocrystalization. The structure, optical and photocatalytic performance of TiO2 films are reported in detail.
2:50 PM B1-2-5 Photocatalysis and Phase Transformation of Oxygen-Deficient Carbon-Containing Titania Films
C.C. Lin, Y.S. Wang, P.W. Chou, M.S. Wong (National Dong Hwa University, Taiwan)
A series of pure and carbon containing titania films of varying oxygen content were prepared by either sputtering or evaporation by increasing the oxygen flow rate during film deposition. The films were annealed at different temperatures from 300 to 800℃ to study the effect of carbon and oxygen content on the phase transformation of titania films and their photocatalysis. The results indicated that the phase of the as-deposited films with increasing oxygen flow changed from amorphous, rutile, mixed phase of rutile and anatase, and finally anatase. Upon annealing the films deposited at higher oxygen flow maintained anatase with improved crystallinity up to 800℃, while the films deposited at lower oxygen flow transform to rutile phase at low temperature at 300℃ and maintained rutile phase with improved crystallinity with increasing temperature. The photocatalytic performance is strongly related to the content and quality of anatase phase in the films. The more conte nt and the better crystallinity of anatase in the films, the better the phtocatalytic degradation of methylene blue.
3:10 PM B1-2-6 Nucleation and Crystal Growth Behavior of α-Alumina by Reactive Magnetron Sputtering
H. Tamagaki, Y. Ikari (Kobe Steel, Ltd., Japan); H. Fujii, K. Yamamoto (Kobe Steel Ltd., Japan); T. Kohara (Kohara Ltd., Japan)

Alumina as top-coat of hard coatings is considered as the best material for oxidation-resistance and heat-resistance layer for cutting tools. Particularly, α-alumina with the corundum structure is considered as the best because of its thermal stability compared with the other crystal structures of alumina. Previously, the authors demonstrated the successful deposition of α-Alumina by a reactive magnetron sputtering at temperature around 750°C in a production scale PVD system, by using oxidization layer of CrN or TiAlN as under layer of Alumina.

In this work, the nucleation and crystal growth behaviors of PVD-Alumina were studies. The films were deposited form the metallic aluminum target in Ar and O2 mixture at the substrate temperature from 600 to 750°C on various kind of substrates and under layer, including Si wafers, Cemented Carbide, CrN, TiAlN etc. The proper process windows for the successful growth of α crystallin e was found on the temperature as well as the deposition rate. Under the optimized conditions around 750°C, the formation of single phase α-Alumina with good crystallinity was confirmed on CrN under layer and some other substrates. However, even at the identical deposition conditions, only γ phase was found on some of the substrates such as Si wafers. In the paper, the effects of the substrates and under layers on the crystal growth of α phase will be demonstrated, and possible growth mechanism of α-Alumina will be discussed.

3:30 PM B1-2-7 Low-Temperature Deposition of Alpha Alumina by Physical Vapor Deposition without a Chrome Template Layer
A. Barito (University of Arkansas); H.H. Abu-Safe (Lebanese American University, Lebanon); D.E. Spearot, M.H. Gordon (University of Arkansas)

Alpha alumina has many chemical and mechanical properties that make it an ideal candidate for cutting tool coatings and bio-medical applications. In previous work, we have deposited low-temperature (480C) alpha-alumina with a chrome template layer, and low-temperature (480C) mixed-phase alumina coatings without a chrome template layer using an AC inverted cylindrical magnetron sputtering system. SEM analysis indicated films that were predominantly alpha-phased, and TEM demonstrated pure alpha phase in some samples.

In this work we report on the systematic deposition of alumina films as a function of power (4-6kW), pressure (2-8mTorr), substrate bias (DC and pulsed), and oxygen partial pressure (35-75%). 39 total runs were performed and several substrates were used (glass, silicon, stainless steel, and a titanium alloy). Analysis of each film included XRD, SEM and AFM. Preliminary results indicate that pure alpha films are favorable at 5-6kW, 50% oxygen partia l pressure, pulsed bias, and 2mTorr. In general, pure aluminum films are observed at lower oxygen partial pressures. At lower powers, little alpha alumina is observed as the energy at the substrate is too low. Indicating noticeable pressure dependence, films deposited at lower pressure (2mTorr) tend to exhibit phases fairly independent of power and oxygen partial pressure. Initial evidence suggests that the deposited films have a weak dependence on substrate bias.

3:50 PM B1-2-8 RF Sputtered Piezoelectric Zinc Oxide Layers for Microfluidic Applications
K.F. Wätje, A. Wixforth (University of Augsburg, Germany)

Surface acoustic waves (SAWs) on piezoelectric substrates find widespread applications for high frequency signal processing applications. Recently, SAW induced acoustic streaming for agitation and actuation of smallest volumes of fluids has attracted considerable attention in the field of microfluidics. Apart from single crystal substrates like LiNbO3, low-cost, high quality alternatives are required for on-chip biosensor applications.

Here, we investigate high performance piezoelectric ZnO films produced by radio frequency magnetron sputtering on different host substrates.

We use Rutherford backscattering spectroscopy (RBS) and elastic recoil detection analysis (ERDA) to analyze the composition of the ZnO layers. Structural characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrates preferential c-axis orientation and an excellent microstructure of our ZnO thin fil ms.

The influence of process conditions such as pressure and temperature are discussed as well as the applicability of different crystalline and non-crystalline substrates considering the advantages and disadvantages for the envisioned applications. We find high coupling factors (close to single crystals). These allow for efficient mixing as required for any microfluidic application. The effects of post annealing, film thickness, roughness, residual stress and resistivity are studied in terms of these properties.

4:10 PM B1-2-9 Phase Transition and Mechanical Properties of Zr(N,O) Thin Films on AISI 304 Stainless Steel
J.H. Huang, T.C. Lin, G.P. Yu (National Tsing Hua University at Hsinchu, Taiwan)
Nanocrystalline Zr(N,O) thin films were deposited on 304 stainless steel substrates using unbalanced magnetron sputtering (UBMS) system. The purpose of this study was to investigate the phase transition and the accompanied mechanical properties of the Zr(N,O) thin films deposited on AISI 304 stainless steel by varying oxygen flow rate (ranging from 0 to 2 sccm). The oxygen contents of the thin films determined using X-ray Photoelectron Spectroscopy (XPS) increased significantly with increasing oxygen flow rate. From the observation of X-ray Diffraction (XRD), the dominant phases in the films were in a sequence of fcc-ZrN, c-Zr2ON2, and m-ZrO2 with increasing oxygen flow rate. The characteristics of the films can be divided into three zones: Zone I (ZrN), Zone II (Zr2ON2) and Zone III (m-ZrO2). Modified XRD sin2ψ method was used to respectively measure the residual stresses of ZrN, Zr2ON2 and m-ZrO2 phases. The residual stress in ZrN was relieved as the oxygen content increased. Zr2ON2 and m-ZrO2 were found to be low residual stress phases. The hardness of the Zr(N,O) films decreased with increasing the oxygen content due to the formation of the soft oxide phase. AES analysis showed that there existed a ZrO2 interlayer between the Zr(N,O) film and the substrate for those samples deposited using O2/N2 mixing gas. Contact angle was used as an index to assess the wettability of the film on substrate, which was associated with adhesion of the film. The contact angle was calculated from the measured surface energies of the related materials. The results indicated the poor wettability between ZrO2 and SS304, which was correlated to the film spallation in salt spray tests.
4:30 PM B1-2-10 Preparation of Artificial BiFeO3/SrTiO3 Superlattices by rf Sputtering
S.-J. Chiu, G.P. Yu, J.H. Huang (National Tsing Hua University, Taiwan); H.-Y. Lee (National Synchrotron Radiation Research Center, Taiwan)
Artificial superlattice structures consisting of multiferroic BiFeO3 and paraelectric SrTiO3 sublayers have been successfully grown on a SrTiO3 substrate with rf magnetron sputtering. X-ray reflectivity and high-resolution diffraction measurements were employed to characterize the microstructure of these films. A symmetric sublayer structure, with the designed thickness of a sublayer varied in a range from 2.5 nm to 10 nm and the total thickness of the superlattices was fixed at 100 nm, was adopted. By changing the stacking periodicity, we introduced the several of interfacial strain in superlattice. The effect of strain resulted from difference of lattice constant of BiFeO3/SrTiO3 was investigated on the microstructures. The X-ray reflectivity curve showed the formation of superlattice structure and increasing of roughness with stacking period decreased, which are consisted with the measurements of atomic force microscopy (AFM). Increasing surface roughness of the superlattice may be resulted from the grain growth of BiFeO3/SrTiO3 superlattice by increase of periodic rotation of targets during deposition. The epitaxial relation between the BiFeO3 and SrTiO3 layers in the superlattice is examined by the in-plane orientation with respect to the major axes of the SrTiO3 substrate. The results clearly show the four-fold symmetry of BiFeO3 sublayer, and it confirmed the pseudocubic structure of the BiFeO3. The analysis of crystal truncation rod spectra showed higher elongation of BiFeO3 sublayer along [0 0 L] by the heteroepitaxial strain when stacking period of BiFeO3/SrTiO3 superlattice increased. The ferroelectric properties of BiFeO3/SrTiO3 superlattice could be improved by adjusting deposition conditions.
4:50 PM B1-2-11 PVD Module for High Quality AC Reactive Sputtering of Oxide and Nitride Thin Films
V.V. Felmetsger, P.N. Laptev, S.M. Tanner (Tegal Corporation)

Various electronics and surface engineering applications require deposition of thin dielectric films having certain functional characteristics. In recent years, remarkable progress has been achieved in developing new techniques for reactive sputtering. In this paper, we discuss design features and application capabilities of the S-Gun magnetron for ac (40 kHz) reactive sputtering.

Due to its dual target arrangement, the ac powered S-Gun is uniquely able to realize reactive sputtering processes free of parasitic arcing and disappearing anode effects thus enabling formation of high quality silicon oxide, aluminum oxide, aluminum nitride and other dielectric films with deposition rates up to 100 nm/min. The process module is equipped with a stress adjustment unit to reduce compressive stress in the films by controllably suppressing the flux of charged particles to the substrate by redistributing the discharge current between the targets and the internal shields of the magnetron. If film has excessive tensile stress, deposition with rf substrate bias allows reducing stress to near zero level.

The key advantages of the deposition technique we developed are the following:

- Reliable, arcless reactive sputtering at ambient and elevated temperatures;

- Precise adjustment and high run to run repeatability of the film thickness and uniformity;

- Formation of well-textured and, if required, crystal oriented films;

- Enhancement of the film adhesion using energy of accelerated neutrals and ion-assisted condensation;

- Effective stress control to produce films with either compressive, or near-zero, or tensile stresses.

In the paper, we also discuss some examples of the S-Gun reactive sputter technologies, particularly, deposition of highly c-axis oriented AlN films with low intrinsic stress at relatively low temperature (below 300°C).

5:10 PM B1-2-12 Adhesion Improvement of Reactive RF-Sputtered Zirconium Nitride Films on WC Substrate
A. Rizzo, M.A. Signore, L. Mirenghi, L. Tapfer, D. Valerini (ENEA, UTS FIM, CR Brindisi, Italy); U. Galietti (DIMEG – Politecnico of Bari, Italy); D. Altamura (University of Lecce, Italy)
Thin films and coatings are used for a variety of purposes over a large variety of applications. According to the projected function, adequate adhesion to the underlying substrate is of fundamental importance. In this work the attention is focused on the adhesion of sputtered ZrN films on WC–wt.10 % Co substrate tuning different parameters: the assistance bias applied during the growth of the nitride (in the range −5 to 20 V), the implanted N ions flux during substrate surface treatment, the addition of TiN layers in different coating configurations. The structure and morphology of the obtained coatings were analyzed using atomic force microscopy (AFM) and x-ray diffraction (XRD) while elemental composition was deduced from x-ray photoelectron spectroscopy (XPS). It was found that the substrate bias strongly influenced the residual oxygen (impurities) incorporation that decreases until a trivial value for positive bias. A structural switch from (200) to (111) has be en detected increasing the bias voltage. The gradient composition layer formed by implantation improves the bond in the coating-substrate interface. The presence of TiN layers in the coating structure improves the adhesion decreasing the thermal and the intrinsic strain. These investigated properties have been correlated to the films adhesion studied by scratch test and to the wear resistance carried out by pin-on-disc tribometer. The maximum critical load is about 70 N and the wear rate is about 2.23*10-6mm3/Nm.
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