Tsuneaki Kamei

Hybrid IC Structures Using Solder Reflow Technology

A study of hybrid ICs produced by solder refiow technology was carried out to achieve optimum miniaturization and substantial cost reduction. Thin-film resistor and capacitor network (R-C) chips and silicon integrated circuit (SIC) chips are mounted on a multilayered thick-film conductor substrate and connected to the substrate by solder joining. The chips are first supported by solder bumps, and then they are self-aligned by the surface tension of the solder through the reflow process. This process results in a joint that compensates for the deviation and undulation of the substrates. Mechanical supports and electrical contacts of hybrid ICs are accomplished through a single reflow process. These hybrid ICs have proven to be completely satisfactory and reliable.

Properties of high resistivity Cr-Si-O thin-film resistor

Several Cr-Si-O thin films with a resistivity of 5-10 m Omega -cm were studied as candidates for high-resistance stable resistors. The films were prepared by reactive sputtering with an Ar+O/sub 2/ gas mixture. It was found that the specific resistivity increases with increased oxygen content in the film, and that the high oxygen content in the film suppresses the formation of CrSi upon thermal treatment up to 673 K. The films are resistant to oxidation when thermally treated in an oxygen-containing environment, and are thus suitable for high-temperature operation in air. The resistance of Cr-Si-O thin films can change with time during high-temperature operation (e.g. in a thermal printing head application) due to the formation of the silicide, annealing effects in the film and the electromigration of components of the film materials. The optimum oxygen content for stabilizing the thin film under high-temperature conditions and high electric current density was determined.<<ETX>>

Aluminum sputtering with intermittent pulse bias application

dc aluminum bias‐sputter deposition was studied to develop a process which better fits the requirements of very large scale integration applications such as improvements in the step coverage, control of film stress, and hillock formation. Intermittent negative bias voltage pulses were applied with a cycle period of 1 ms during the deposition of an aluminum film. The pulse has two voltage levels: Vd (deep) and Vs (shallow). The duty factor was defined as the ratio of time during which the bias voltage is Vd to the cycle period. It was found that a Vd greater than −115 V was needed to attain an appreciable improvement in the step coverage. For a duty factor of 15%, a maximum was found in the peak intensity ratio I(111)/I(200) with x‐ray diffractometry at Vd=−120 V. Minima for the film stress at room temperature and the hillock formation density after annealing at 475 °C for 30 min in nitrogen were found to occur in the bias voltage region mentioned.

High rate deposition of MoSi2 films by selective co-sputtering☆

Abstract A new sputtering method has been developed to achieve the high rate deposition of refractory metal silicide films. This method employs a planar magnetron sputtering cathode with two coaxially wound electromagnet coils in a magnetic yoke and a target plate of multiring structure composed of silicon and molybdenum target pieces. The diameter of the glow ring can be changed by controlling the magnetomotive forces in the two electromagnet coils. The target consisted of a centre silicon disc and molybdenum and silicon target rings which concentrically surround the centre silicon disc. The glow ring diameter was controlled so that each of the target pieces was selectively sputtered. The amount of sputtered silicon and molybdenum was adjusted to obtain a film of the required thickness and composition on the substrate. Distributions of the composition and the film thickness of 37±0.5 wt.% Si and ±2% respectively were obtained over a 4 in wafer. The film was annealed at 1000°C for 30 min. A sheet resistance of about 2.3 Ω/□ was obtained for a film 300 nm thick with an average deposition rate of 95 nm min -1.

Properties of anodic oxide films prepared on nitrogen-doped tantalum films

Abstract Capacitors prepared from thin films of tantalum nitride, which has an h.c.p. structure, show various excellent electrical properties. TaN capacitors, in particular, exhibit great endurance to heat treatment and have no polarity in their anodic and cathodic leakage currents. The structure of these anodic films, their dielectric properties and their electrical conduction characteristics were studied. An anodic film formed on a nitrogen-doped tantalum film was shown to consist of two layers by analysis using the chemical etching method and by Auger electron spectroscopy. The first layer, which is situated at the oxide-electrolyte interface, has a high density and includes very little nitrogen. The second layer is porous and contains excess nitrogen.

Thin-Film Capacitors Made from TaN Films

Thin-film capacitors were prepared from sputtered tantalum nitride thin films (TaN capacitors). The dielectric was formed by anodic oxidation and the counterelectrode was deposited by evaporation of nichrome-gold. The TaN capacitors excelled the usual TM capacitors in various properties. The temperature coefficient of capacitance was 129 ppm/°C and the dissipation factor was 0.0014 at 1 kHz. In addition, TaN capacitors showed high endurance to heat treatment. The capacitance change was only -0.02 percent after 350°C heat treatment for 2 minutes. Reliability tests were performed which indicated a failure rate of 0.1 FIT at 40°C, 6 V. The capacitance change was within ±0.4 percent after 3000 hours at 125°C. The TaN capacitors were applied to make highly stable and highly precise filter circuits such as multifrequency receivers for touch tone telephones now in commercial use.