Shozo Inoue

Oxidation behavior of (Ti1 − xAlx)N films perpared by r.f. reactive sputtering

Abstract (Ti, Al)N films have drawn much attention as alternatives for TiN coatings, which are oxidized easily in air above 500 °C. We have investigated the effect of Al content on the oxidation resistance of (Ti 1 − x Al x )N films prepared by r.f. reactive sputtering. (Ti 1 − x Al x N films (O ≤ x ≤ 0.55) were deposited onto fused quartz substrates by r.f. reactive sputtering. Composite targets with five kinds of Al-to-Ti area ratio were used. The sputtering gas was Ar (purity, 5 N) and N 2 (5 N). The flow rate of Ar and N 2 gas was kept constant at 0.8 and 1.2 sccm, respectively, resulting in a sputtering pressure of 0.4 Pa. The r.f. power was 300 W for all experiments. Substrates were not intentionally heated during deposition. The deposited films (thickness, 300 nm) were annealed in air at 600 ∼ 900 °C and then subjected to X-ray diffractometer and Auger depth profiling. The as-deposited (Ti 1 − x Al x )N films had the same crystal structure as TiN (NaCl type). Al atoms seemed to substitute for Ti in lattice sites. The preferential orientation of the films changed with the Al content of the film, x . Oxide layers of the films grew during annealing and became thicker as the annealing temperature increased. The thickness of the oxide layer grown on the film surface decreased with increasing Al content in the film. For high Al content films an Al-rich oxide layer was grown on the surface, which seemed to prevent further oxidation. All of the films, however, were oxidized by 900 °C annealing, even if the Al content was increased up to 0.55.

In-situ observations of crack nucleation and growth during stress corrosion by scanning vibrating electrode technique

Abstract A scanning vibrating electrode technique (SVET) was applied to make in-situ observations of stress corrosion cracking (SCC) in type 304 steel single crystals exposed to a 2.5 kmol m −3 H 2 SO 4 +0.4 kmol m −3 NaCl solution at room temperature. The three-dimensional (3-D) plots of corrosion current density during SCC can be successfully displayed with the SVET. Under the applied stress conditions of yield strength and above, the anodic current is observed locally at the site of crack nucleation along the mechanically induced slip-steps. Following the crack nucleation, the anodic current peaks disappear with the crack growth on {110} planes, regardless of the test condition. It is, therefore, concluded that the SVET can be applied to make in-situ observations of crack nucleation and growth during stress corrosion.

Electrochemical evaluation of pinhole defects in TiN films prepared by r.f. reactive sputtering

Abstract TiN films were deposited onto stainless steels by r.f. reactive sputtering and they contained more or less pinhole defects. The area ratio of pinhole defects was evaluated potentiodynamically with the ratio of critical passivation current density of TiN-coated and non-coated specimen in a deaerated 0.5 kmol/m3H2SO4 + 0.05 kmol/m3KSCN solution. The result coincided well with the true defect area ratio based on the optical micrographs before and after polarized anodically. Such electrochemical method was concluded to be a reliable evaluation technique for the pinhole defects of corrosion-resistible coating.

Effect of partial pressure on the internal stress and the crystallographic structure of r.f. reactive sputtered Ti-N films

The influence of nitrogen partial pressure (P N2 ) and argon partial pressure (P Ar ) on internal stress, crystallographic structure, and resistivity have been investigated for reactively sputtered Ti-N films in order to get some insight into the influence of deposition parameters. Ti-N films were deposited onto glass substrates by r.f. reactive magnetron sputtering using a plasma emission monitoring control system. The r.f. power applied was kept constant at 300 W during deposition, and the substrate temperature was room temperature. When P Ar is 0.4 Pa and P N2 is I × 10 -3 Pa or higher, films deposited become single phase of TiN, although preferential orientations of films change with P N2 . Ti-N films deposited at a P N2 of 2-6 X 10 -3 Pa become a gold color, and the resistivity becomes minimum. The internal stress of deposited Ti-N films changes as a function of both argon and nitrogen partial pressure, and films deposited at a low P Ar tend to have high compressive stress. The internal stress is also related to preferred orientation of films. Films having the (001) preferential orientation show higher compressive stress than those having the (111) preferred orientation.

Focused Ion Beam Induced Surface Damage Effect on the Mechanical Properties of Silicon Nanowires

In this paper, the effect of surface damage induced by focused ion beam (FIB) fabrication on the mechanical properties of silicon (Si) nanowires (NWs) was investigated. Uniaxial tensile testing of the NWs was performed using a reusable on-chip tensile test device with 1000 pairs of comb structures working as an electrostatic force actuator, a capacitive displacement sensor, and a force sensor. Si NWs were made from silicon-on-nothing (SON) membranes that were produced by deep reactive ion etching hole fabrication and ultrahigh vacuum annealing. Micro probe manipulation and film deposition functions in a FIB system were used to bond SON membranes to the devices sample stage and then to directly fabricate Si NWs on the device. All the NWs showed brittle fracture in ambient air. The Youngs modulus of 57 nm-wide NW was 107.4 GPa, which was increased to 144.2 GPa with increasing the width to 221 nm. The fracture strength ranged from 3.9 GPa to 7.3 GPa. By assuming the thickness of FIB-induced damage layer, the Youngs modulus of the layer was estimated to be 96.2 GPa, which was in good agreement with the literature value for amorphous Si.

Ti-Ni SMA film actuated Si cantilever beams for MEMS probe card

We present a new MEMS probe card, which is composed of silicon (Si) cantilever beams actuated by titanium-nickel (Ti-Ni) shape memory alloy (SMA) films. Since Ti-Ni film can yield a higher work output per unit volume, the Ti-Ni film-actuated Si cantilever beam has the potential as a MEMS probe card to generate a large contact force between a probe and electrode pad. The cantilever beam produces a contact force by not only cantilever bending in contact but also the shape memory effect (SME) of Ti-Ni film arising from Joules heating. The SME of the Ti-Ni film containing Ti atom of 50.5% to 53.2% can generate an additional contact force of 200 /spl mu/N on average on applying an electric power of 500 mW to the film. The Ti-Ni film-actuated Si cantilever beam could be a key element for a successful MEMS probe card with larger contact force and smaller size.

Preparation of compositionally gradient Ti-TiN films by r.f. reactive sputtering

The r.f. reactive sputtering of a Ti target in a mixed gas of Ar and N2 was used to fabricate compositionally gradient films consisting of Ti and TiN phases. In this paper, two methods are described to form the compositionally gradient Ti-TiN films. The first uses the N2 flow-to-total flow ratio (FN2Ftotal) control method, and the other is the r.f. power control method. The compositionally gradient Ti-TiN films were deposited onto microscope glass slides. The substrate was at room temperature. The crystallographic structure, the composition and the morphology of the deposited films were characterized by X-ray diffractometry, Auger electron spectroscopy and scanning electron microscopy, respectively. Both the FN2Ftotal and r.f. power control method can be used to grow compositionally gradient films. It was demonstrated that the deposited film has a structure with a non-oriented TiN layer on a c-axis perpendicular Ti layer. The morphology of the films is independent of the deposition method. It is also shown that optical emission spectroscopy and mass spectroscopy are useful tools to monitor the growth of these films.

Structure and composition of (Ti, Al)N films prepared by r.f. planar magnetron sputtering using a composite target

(Ti, Al) alloy nitride films have drawn much attention because of their excellent oxidation resistance. The purpose of this paper is to investigate the structure, morphology and composition of the (TixAl1 − x)Ny films prepared by r.f. reactive sputtering using a composite target where the area ratio of Ti to Al is unity. Nitrogen flow to total nitrogen and argon flow ratio (Fn2Ftotal) is used as a parameter. The partial pressures of these gases that resulted were monitored by their optical emission in the glow discharge. The crystallographic structure of deposited films were divided into three groups by the Fn2Ftotal that was used in their preparation. The first group (Fn2Ftotal = 0) is a Ti and Al metal mixed structure. The second group (0.1 ≤FN2Ftotal<0.4) has an amorphous structure. The last group (FN2Ftotal≥ 0.4) has the wurtzite structure. Under all conditions, the composition of the films was richer in Al than the target area ratio of Ti to Al, as would be expected from their sputtering yields. This ratio changes with admission of nitrogen because of selective poisoning (the formation of nitrides on the sputtering target). The plot of composition ratio CTiCAl vs. FN2Ftotal showed the local minimum at about FN2Ftotal = 0.3. The ratio of Ti to Al emission intensity, IT1IAl, from optical measurements shows excellent agreement with CTiCAl. It is concluded that the optical emission signal is very useful for the composition control during deposition, both of the materials being sputtered and of the residual atmosphere.

Self-Propagating Explosive Reactions in Nanostructured AL/NI Multilayer Films Asalocalized Heat Process Technique Formems

This paper describes a novel local heating technique for MEMS soldering and bonding technologies. Nanostructured aluminum/nickel (Al/Ni) multilayer films show self-propagating exothermic reactions, driven by a reduction in atomic bond energy. In this work, we demonstrate the validity of the Al/Ni reactive films as a heat source in manufacturing MEMS solder packages. Dual-source DC magnetron sputtering was employed to deposit the alternative layers of Al and Ni under controlling their thicknesses. By inducing spark, the Al/Ni multilayer film that generates heat enough to melt Au-Sn solder films is ignited, thereby having succeeded in fabrication of Au-Sn film-bonded MEMS elements. The local heating technique using Al/Ni multilayer film’s exothermic reactions is expected to have the great potential as soldering technologies in MEMS.

TiN films prepared by unbalanced planar magnetron sputtering under control of photoemission of Ti

Abstract TiN films have been prepared by unbalanced planar magnetron sputtering, where the flux of sputtered Ti atoms was maintained constant by adjusting N2 gas flow during sputtering. At a set point of 75% of the Ti signal in pure Ar gas, the film resistivity has a minimum, the film stress becomes a minimum and the appearance is most gold-like. With an increase in ion bombardment, the internal stress increases, whereas the film resistivity decreases. These results confirm that stoichiometric TiN films are prepared at the set point of 75%, where the target surface is not fully covered by TiN. The energetic ions appear to improve the properties of the TiN films.