Toshiro Kajiwara

Structure modification of radio frequency sputtered LaB6 thin films by internal stress

Thin films of LaB6 are prepared by a radio frequency (rf) magnetron sputtering technique. The effect of sputtering conditions on the film properties of internal stress and crystalline orientation are investigated. The film deposited at low pressures (<1 Pa) has a strong compressive stress as high as 109 Pa. As the pressure of Ar discharge gas decreases, the internal stress becomes greater and the preferred orientation is transformed in the sequence: (100)→(110)→(111). This behavior can be explained as an energetically favorable structure of LaB6 film by taking both the surface energy and the strain energy into account. An application of a negative bias (−20 V) to substrates results in a greater stress, so that the (110) and (111) orientation becomes more preferential.

Adhesion measurement of thin films on glass substrates

Abstract Adhesion measurements of thin films deposited on glass substrates were carried out using a modified scratch tester. Films were scratched by a diamond stylus and the critical loads required to peel off the films were determined. The effect of the stylus hardness and of the film thickness on adhesion measurement are discussed.

Mechanical and electrical properties of rf sputtered LaB6 thin films on glass substrates

Abstract LaB 6 films from 2000 to 5000 A thick were prepared on glass substrates by rf magnetron sputtering. The effects of Ar discharge gas pressure from 5.3 to 5.3 × 10 −2 Pa on the structural, electrical and mechanical properties of the films were examined. The structural characteristics were analyzed by X-ray diffraction and emission spectrochemical technique (ICP). The electrical film resistivity was measured using a four-point probe technique. The internal stress and adhesion of films were determined by the bending-plate method and the microtribometer, respectively. The deposition process of rf magnetron sputtering was studied by a quadrupole mass filter system. The results indicated that an increase in Ar gas pressure in sputtering depositions increased the atomic ratio B/La in LaB films. The most preferable Ar gas pressure for stoichiometric LaB 6 formation was found to 10 −1 Pa and it was also suitable for producing high quality films as electrodes. The main crystalline orientation of the sputtered LaB 6 films was (100) which is the orientation of lower work function (2.4–2.5 eV) in LaB 6 crystals.

Internal stress and adhesion of r.f.-sputtered MgO films on glass substrates☆

Magnesium oxide films from 50 nm to 1 μm thick were prepared on glass substrates by an r.f. magnetron sputtering technique. The effects of the introduction of oxygen in the sputtering gas and the substrate bias on the internal stress and the film adhesion were studied. The tribological characteristics were examined with a new scratch tester (microtribometer). Sputtering in 100% Ar yielded films of strong compressive internal stress and weak cohesion, i.e. the films were scratched into small pieces at light loads. As the concentration of oxygen in the sputtering gas was increased, the internal stress was relieved and the adhesion strength increased. Flaky fragments of broken films were observed. By contrast, a negative substrate bias resulted in a strongly compressive internal stress. Although the film structure became homogeneous, it was not possible to obtain thick films without crack generation.

LaBx thin films prepared by magnetron sputtering

LaBx (x = 0–6) thin films were prepared by magnetron sputtering using a LaB6 target and Ar discharge gas. The composition of the films was investigated by the ICP method. It has been found that the composition strongly depended on the Ar discharge gas pressure. The film composition was mostly stoichiometric (x = 6) at low Ar pressures while the value of x decreased with increasing pressure. This nonstoichiometry is interpreted in terms of collision scattering of sputtered particles from the target by Monte Carlo simulation. The Ar pressure change induces the change of the crystal orientation of the films and this change is related with the work function of the film. The most appropriate Ar pressure for the preparation of the films used as electrodes is discussed.