K. Y. Ahn

Formation of an amorphous Rh‐Si alloy by interfacial reaction between amorphous Si and crystalline Rh thin films

Interfacial reaction in bilayers of amorphous Si and crystalline Rh thin films has been studied by transmission electron diffraction and microscopy. In a bilayer of ∼190‐A amorphous Si and ∼60‐A polycrystalline Rh films, we have observed the formation of an amorphous Rh‐Si alloy film upon thermal annealing at 300 °C. The amorphous alloy film crystallizes into the RhSi phase at 400 °C. On the other hand, no amorphous alloy formation was observed upon annealing a bilayer of ∼150‐A amorphous Si and ∼100‐A polycrystalline Rh films; instead, they react at 300 °C to form Rh2Si, followed by the formation of RhSi or a mixture of RhSi and Rh5Si3 around 400 °C.

Investigation of Tin films reactively sputtered using a sputter gun

Abstract TiN films were prepared by reactive sputtering of titanium in a gas mixture of argon and nitrogen using a sputter gun. The properties of the sputtered films were investigated with Rutherford backscattering spectrometry, electrical resistivity and optical reflectivity measurements, X-ray diffractometry and transmission electron microscopy. For a given input power to the sputter gun the film properties depend on the gas composition, the bias voltage applied to the substrates and oxygen contamination during sputtering. In addition, it was found that powering the sputter gun with r.f. causes an iron contamination in the films by material sputtered off the plasma confinement shield. This contamination is very much reduced when d.c. is employed to power the sputter gun.

Magnetic properties and domain structures in narrow NiFe stripes

The coercivity of narrow stripes of 81 percent Ni-19 percent Fe films has been found to increase rapidly, by up to an order of magnitude, as the stripe width decreases and approaches 1 μm. Furthermore, the coercivity increases with decreasing film thickness as it does in sheet films, but in the stripes the changes in coercivity with film thickness are much larger than in sheet films. For example, in stripes of 2 μm × 100 μm, H c increases from 10 Oe to 35 Oe as the thickness decreases from 1800 A to 300 A. The increase in coercivity with decreasing stripe width may be explained by a buckling of the magnetization perpendicular to the length of the stripe. This buckling process was made visible by decoration of domain walls with Ferrofluid, and is shown to lead to the formation of walls perpendicular to the stripe. These walls do not move, but block reverse domains from propagating down the stripe. In the narrowest stripes (2 μm) fields larger than 100 Oe are required to collapse the 360° wall segments which eventually form. A theoretical model for this buckling process is given which shows that a minimum in energy occurs when the stripe buckles with a buckling wavelength approximately equal to the width of the stripe. These findings suggest that, as structures of NiFe like those in magnetic bubble devices and in magnetic recording heads are made smaller, coercivity and dispersion will rise significantly, leading in many cases to undesirable magnetic behavior.

Relationship Between Stoichiometry and Properties of EuO Films

The preparation of EuO films by co‐evaporation of Eu and Eu2O3 has been studied. The two most important parameters to control are the ratio r=Eu/Eu2O3 and the background pressure. The latter should be in the 10−6‐Torr range, and only by starting with high density (>95%) Eu2O3 is it possible to maintain this. As r increases from 0.8 to 1.4 we observe the following: (1) A large increase in Tc is observed from 51° to 117°K; (2) the absorption a increases from 0.85×105/cm to 1.6×105/cm and the peak shifts toward the red (from 5900 to 6000 A); (3) the longitudinal Faraday rotation 2φ (with 25° incident angle at 6328 A) increases from 0.9×105 deg/cm to a maximum of 3.7×105 deg/cm, followed by a slight decrease; and (4) Hc (10°K) decreases sharply from 140 Oe to a minimum of 43 Oe for r=0.94, followed by a slight increase. The best films which were single‐phase stoichiometric EuO, with bulk‐like properties, are obtained with r=0.94. These have well‐defined x‐ray diffraction patterns with lattice constants a0=5.14 A, Tc of 71°K, and the normal Faraday rotation (at 20°K with H=20 kOe) of 8.5×105 deg/cm. In films with r>0.9 the increase of Tc is attributed to the presence of Eu‐metal which contributes conduction electrons to enhance the Eu2+–Eu2+ interaction. For r 95%) Eu2O3 is it possible to maintain this. As r increases from 0.8 to 1.4 we observe the following: (1) A large increase in Tc is observed from 51° to 117°K; (2) the absorption a increases from 0.85×105/cm to 1.6×105/cm and the peak shifts toward the red (from 5900 to 6000 A); (3) the longitudinal Faraday rotation 2φ (with 25° incident angle at 6328 A) increases from 0.9×105 deg/cm to a maximum of 3.7×105 deg/cm, followed by a slight decrease; and (4) Hc (10°K) decreases sharply from 140 Oe to a minimum of 43 Oe for r=0.94, followed by a slight increase. The best films which were single‐phase stoichiometric EuO, with bulk‐like properties, are obtained with r=0.94. These have well‐defined x‐ray diffraction patterns with lattice constants a0=5.1...

Preparation and properties of EuO films

Films of EuO have been vacuum deposited by three techniques: electron beam heating of bulk EuO, simultaneous deposition of Eu and Eu 2 O 3 , and evaporation of Eu in a partial pressure of oxygen. X-ray measurements show the structure of these films to be essentially the same as bulk EuO. The Faraday rotation of EuO films was measured at 5° K for wavelengths between 0.5μ and 1.2μ. The largest specific Faraday rotation occurs at a wavelength of 0.66μ and is 5 × 105degrees per cm, which is one of the highest values yet reported for any material. From magneto-optical measurements and force balance measurements, various magnetic properties of these films have been determined and compared with bulk EuO. Magnetic moment, susceptibility, and squareness of EuO films do not differ greatly from bulk. The coercive force, however, is several times bulk value, and appears to be related to stress in the films.

Magnetic and Magneto‐optic Properties of EuO Films Doped with Trivalent Rare‐Earth Oxide

The ferromagnetic Curie temperature of EuO films has been increased by selective doping with trivalent rare‐earth oxides. The electrical resistivity, which depends upon the temperature and has a broad peak at ≈100°K, decreases markedly to ≈10−1 Ω·cm with doping. A typical ferromagnetic Curie temperature, determined from magneto‐optic measurements in zero applied field, is ∼135°K. Maximum longitudinal Faraday rotation occurs at 0.65 μ with a specific rotation of +1×105 deg/cm for an incidence angle of 20 deg. At 0.84 μ the Faraday rotation reverses sign and reaches a negative maximum at 0.93 μ. The longitudinal Kerr rotation also has two maxima at 0.58 μ and 0.83 μ with double rotations of ≈4°. The transverse Kerr effect depends on the wavelength in the same manner and has maximum values of +0.4 and −0.3, respectively. There is a strong optical absorption band centered at 0.6 μ (at 300°K) with α≈1.2×105 cm−1 which shifts toward longer wavelengths at lower temperatures accompanied by a small decrease in α. ...

Thermal stability and electrical conduction behavior of coevaporated WSi2±x thin films

The thermal stability of coevaporated amorphous WSi2±x(x≂±0.2) thin films from room temperature to 1000 °C has been studied by in situ resistivity measurements and hot‐stage transmission‐electron microscopy. During continuous heating two consecutive phase transformations were observed to occur via nucleation and growth processes. The first which occurs at ∼420 °C is the crystallization of the amorphous film to a metastable, semiconducting hexagonal phase WSi2. The second which occurs at ∼620 °C is the transformation of the hexagonal phase to the thermodynamically stable, metallic, tetragonal phase of WSi2. The hexagonal phase is characterized by an acicular morphology and its formation is associated with a drastic increase in resistivity. The crystallites (grains) of the stable tetragonal phase are equiaxed and their formation is associated with a rapid decrease in resistivity. In order to achieve a low value of resistivity, ∼70 μΩ cm at room temperature, the tetragonal phase must be annealed to the neigh...

A comparison of tungsten film deposition techniques for very large scale integration technology

Abstract Tungsten films have long been considered as a metallization candidate for integrated circuits because of their relatively low electrical resistivity, freedom from electromigration and mid-range work function. Initial work in the early 1970s employed electron gun evaporation at high substrate temperatures in order to improved adhesion, to lower resistivity and to control the high stress present in refractory metal films. Planar diode sputtering was not widely used because of radiation damage caused by the high target voltage and the slow deposition rate. Progress in magnetically enhanced plasma technology led to the development of magnetron sputtering, and this resulted in a higher deposition rate at much lower ion energies. The high stress ever present in refractory metal films has almost been eliminated by the use of a high sputtering pressure. By contrast with evaporation, films with reasonably low resistivity in the range 10–11 μΩ cm can be routinely deposited by magnetron sputtering onto unheated substrates with excellent adhesion and reproducibilty. Successful application of magnetron-sputtered tungsten films in metal/oxide/semiconductor (MOS) devices was reported recently. In the meantime new applications of tungsten films prepared by chemical vapor deposition in very large scale integration technology are emerging. The selective tungsten deposition process, in which the desired film grows on silicon and other metals and alloys, but not on oxides and nitrides, appears to be very attractive for contact metallization in MOS devices because of the process simplicity, although there seem to be some problems associated with this process: encroachment and tunneling. The same selective tungsten films are also ideally suited to via-hole filling, contact metallization and upper level wiring. The non-selective chemically vapor- deposited tungsten films may also find applications in upper-level wiring because of their resistance to electromigration.

Bubble to T-I bar coupling in amorphous film small bubble devices

In GdCoMo amorphous film bubble devices the drive field required for device operation has been found to be linearly dependent on the saturation magnetization of the bubble material over the range from 350 to 1200G. The devices studied were 8000 bit storage chips employing electron-beam-fabricated T-bars, Y-bars, and chevrons of 1μm linewidth. The bubble domain diameter and film thickness were approximately 2μm in all devices. The linear increase in drive field with 4πM s is found to be related with the energy required to move a bubble from one permalloy pattern to another across a gap. On the other hand, the field required to overcome coercivity in the movement of a bubble without leaving a single permalloy T-bar is found to be independent of variations in 4πM s of the bubble material.

Magnetic domain structures in multilayered NiFe films

The coercivity of NiFe (80/20) films can be lowered by laminating several layers with nonmagnetic spacers. A reduction by a factor of 10 can be achieved with a simple bi‐layer, regardless of spacer material, provided the spacer thickness is below a critical value. No further reduction is found for multilayers. Two peaks of Hc near thicknesses of 250A and 1000A for single layer films, associated with changes in domain structure, are suppressed by lamination. After a minimum spacer thickness (S) of 10–15A, the domain walls in the separate layers no longer coincide but track closely, their separation depending on S. With S?100A the layers switch independently, giving rise to multiple values of Hc.