Kaizo Kuwahara

Internal stress in aluminium oxide, titanium carbide and copper films obtained by planar magnetron sputtering

Abstract Internal stresses in sputter-deposited aluminium oxide, titanium carbide and copper films were measured. Aluminium oxide and titanium carbide films developed compressive stresses whereas copper films exhibited tensile stresses. Their magnitudes and signs were found to be in good agreement with those of the thermal stresses estimated from the constants and deposition temperatures of the materials. It is suggested that an atomic peening is one of the verifiable mechanisms whereby the compressive component of the stresses is induced in these films.

Resistivity anisotropy of nickel films induced by oblique incidence sputter deposition

Abstract The effect of incidence angle on resistivity anisotropy in sputter-deposited thin (around 50 nm) film is studied. The resistivity anisotropy of nickel films is found to change sensitively with incidence angle similar to that found in vapour-deposited Ni-Fe films at oblique incidence. Thin copper films, by contrast, show no appreciable resistivity anisotropy. It is concluded that the anisotropy of nickel films is attributable to the fact that the atoms have a dominant direction (parallel to the target axis) among the various directions of incidence and to the low surface diffusivity of nickel atoms.

Resistivity Anisotropy in Oblique Incidence Evaporated Films

The resistance change along a ring, prepared by photoetching a thin flat film evaporated on a glass substrate, is analized and the resistivity anisotropy is separated from the effect of thickness gradient. It is found that in thin films of 84.5% Ni-Fe the resistivity anisotropy coefficient β, defined as β=(ρ//-ρ⊥)/(ρ//+ρ⊥) (ρ//: resistivity in the film plane parallel to the plane of incidence, ρ⊥: resistivity perpendicular to the plane of incidence), increases with the angle of incidence, makes a maximum at 70° and then decreases to a negative value. This behaviour is very similar to that of the magnetic uniaxial anisotropy constant except that it is already negative at 70°. In the case of thin films of Cu, there is no appreciable change in β at low angles of incidence, only a decrease being observed at high angles of incidence above 60°.

Internal stress in sputter-deposited Al2O3 films

Abstract The internal stress in Al2O3 films (0.1–10 μm thick) sputter deposited onto cemented carbide, high speed steel and glass substrates was measured as a function of substrate temperature during the deposition. With all the films, the stress was found to be compressive. This indicates that the thermal stress caused by the difference in thermal expansion between the deposit and the substrate has a minor effect compared with that of the intrinsic film stress (compressive). In the films grown on high speed steels the compressive stress was found to increase very rapidly with increasing substrate temperature, probably owing to thermal stress. The dependence of the stress on film thickness and substrate material as well as the difference in the magnitude of the stress between films obtained by conventional and planar magnetron sputtering are discussed.

Adhesion evaluation of r.f.-sputtered aluminium oxide and titanium carbide thick films from grown carbide tools

Abstract Attempts were made using two novel techniques to evaluate the adhesion of thick (about 5 μm) aluminium oxide and titanium carbide films sputter deposited onto cemented carbide tools. The first method is to apply an indentation on the coated surface with a Vickers microindenter, and the film-peeling pattern around the indentation in then taken to be a measure of the film adhesion. The second method is to compress the film/substrate system parallel to the film surface until the film is peeled off, and the compressive stress necessary to peel off the film gives a measure of the adhesion. These two methods yielded satisfactory information on the magnitude of the film adhesion. With the use of these techniques it was found that the adhesion of aluminium oxide and titanium carbide films to carbide tools is increased with increase of the substrate temperature (at least up to 500°C) in the initial stage of sputter deposition. This temperature dependence was found to be in good agreement with that of the tool life obtained in an actual machine cutting test using the coated carbide tools.

Microstructure of permalloy and copper films obtained by vapor deposition at various incidence angles

Abstract Transmission electron microscopy (TEM) was used to study the microstructure of Permalloy and copper films vapor deposited at various incidence angles (0–85°). A TEM examination showed that Permalloy films contain a well-defined columnar microstructure which consists of an array of columnar grains surrounded by a network of void regions. Furthermore, the columnar structure was found to vary sensitively with increasing incidence angles. The pronounced change in the columnar structure for different incidence angles indicated that the columnar structure was formed by a self-shadowing process and that very little structural relaxation had occurred in the Permalloy films during film formation. By contrast, in copper films a columnar structure was not observed and the incidence angle effect was also negligibly small. In this case the columnar structure formation was apparently prevented by a large amount of structural relaxation during film formation. The extent of this relaxation in these Permalloy and copper films was found to correlate with the magnitude of surface diffusivity of a condensing metal.

Adhesion Measurement on Thin Evaporated Films

Methods to evaluate the adhesion of thin evaporated films to their substrate were devised. One was to pull down and the other to twist off a rod whose bottom was cemented with epoxy to the film. The critical force or torque to strip off the film from the substrate was taken as a measure of the adhesion. It was important to maintain adequate temperature and humidity [16 °C (61°F) and below 60 percent] during the cementing and measurement, to assure the high adhesion of the cement and the reproducibility of the result. The adhesion of thin films of aluminum, silver, and copper to substrates of mild steel and glass was studied, along with the adhesion of epoxy and other cements. It was found that the critical force and torque were proportional not to the 3rd power as expected but rather to the 2.5 ∼ 2.9th power of the rod diameter. In the case of thin films, the dispersion of the measured values was very large. The dispersion and also the ratio of tensile to shear adhesive strength increased rapidly with the decrease in adhesion. This is contrary to the effects of the small dispersion, the independence of the dispersion, and the ratio on the adhesion in the case of cement itself. Also mentioned is an experiment on the fracture of brittle substrates such as silicon wafers which sometimes happened during the measurement.

Relaxation of elastoresistance in thin metal films

Abstract The change in the resistance of thin evaporated metal films in response to a step strain has been studied. Among the several metal films examined, aluminium and bismuth films exhibited remarkable relaxation, with a time constant of about 1 min at room temperature for a thickness of around 1000 A. In the case of aluminium films, the time constant was found to decrease with increase of deposition temperature, thickness, annealing period and annealing temperature. In the case of bismuth films, such a clear tendency to decrease was not observed, at least for films thinner than 2 μm. It is suggestef that the resistance relaxation is related to the unusually large stress-strain relaxation which is known to exist in bismuth films. The thickness dependence of the gauge factors of both films is also illustrated.

Magnetoresistance Investigation of RIS-II Films

The magnetoresistance effect of RIS-II films of Permalloy was studied and the results were expressed as an empirical formula. This formula describes the hysteresis loops as well as torque measurements. A model composed of three layers was proposed for RIS-II films, and experimental results obtained by Wilts were explained. The validity of the model was supported by a drastic change in magnetic characteristics when the surface of RIS-II films was etched off slightly.

Adhesion Failure of PVD Films Caused by Repeated Bending of Substrates

A method to evaluate the adhesion of PVD films was devised. Bi, Al and SiO films of various thicknesses were thermally evaporated onto copper or mild steel substrates. The substrate was subjected to repeated plastic bending. The adhesion failure life (bending cycles until the film-peeling) was taken as a measure of the adhesion. It was found that this method gave a result analogous to that obtained from the conventional method using adhesives. It was further confirmed that this method was applicable when the adhesion was so strong that the conventional method failed.