Deformation mechanisms of Al films on oxidized Si wafers

Abstract

The mechanism for plastic deformation of 0.5 μm thick, 0.5 μm grain-size evaporated Al films on oxidized Si wafers has been studied using wafer curvature measurements over a temperature range from room temperature to 500 °C. Extensive evidence for both morphology changes and plastic deformation was obtained. Transmission electron microscopy confirmed the occurrence of grain growth, and stress changes attributed to recrystallization were observed. Deformation under tension could be explained by dislocation glide according to the kinetics observed in bulk Al at the same temperatures, stresses, and grain sizes. The kinetics of deformation under compression were investigated at 400 °C and were completely different from those under tension. This is either due to a difference in the deformation mechanism or to the occurrence of work softening.

Dislocation Plasticity in Thin Metal Films

“…Under such conditions, the physical mechanism of plastic deformation is expected to be the thermally activated motion of dislocations past lattice obstacles, as it is for bulk samples of these materials, but with values of flow stress reflecting the special conditions that prevail in small-scale structures. This expectation was reflected in the early work of Flinn et al 4 and Volkert et al 8 on Al and Cu films, and it has been confirmed through direct observations by Kobrinsky and Thompson, 18 as noted earlier. The theory of thermally activated glide of dislocations in fcc metals has its origins in statistical mechanics, but its implementation in continuum plasticity theory is largely empirical.…”

“…In this case, stress can be imposed on the film by changing the temperature of the system. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The constraint of the substrate implies that the generated thermal strain is essentially offset by the generation of some combination of elastic and plastic strain in the film. If is the equi-biaxial stress in the film, and p is the equi-biaxial plastic strain, then rates of change are related by /M ϩ p ϩ (␣ film Ϫ ␣ sub )Ṫ 0,…”

“…However, this picture is incomplete, as the film stress relaxes quite substantially when temperature is held at a constant value; this tendency is more pronounced at the higher end of the temperature range being considered here. 8,18 Therefore, the rate of temperature change has an influence on the stress-temperature dependence observed, and the time-dependence of the plastic deformation needs also to be taken into account for a complete description. Furthermore, it has been discussed that the stress-temperature evolution is also influenced by strain-hardening or a Bauschinger effect 14,20,21 as the film is plastically strained, despite the fact that the imposed plastic strains of about 0.5% are rather small.…”

Mechanical and electrical performance of thermally stable Au–ZnO films

“…The heating segment of all the curves follow approximately the same slope (M heating ) until initial yielding, indicating the elastic modulus is independent of ZnO concentration as would be expected in these dilute solutions. After the initial elastic portion of the heating curve, the stress slowly levels out as the temperature increases, indicating the start of plasticity brought on by diffusion-based creep, dislocation motion, grain growth, or phase transformations [37][38][39], most likely a mixture of multiple mechanisms depending on the stress and temperature state [40][41][42]. The stress at the onset of plasticity (r min ) is unique for each film and is indicative of the strength of the film, with increasing strength for increasing ZnO content.…”

Externally constrained plastic flow in miniaturized metallic structures: A continuum-based approach to thin films, lines, and joints

“…Models taking into consideration of specific aspects of diffusional flow pertaining to the columnar grain structure have also been reported [57,72,[206][207][208]. The rate equations, in various formats with different levels of complexity, have been applied to investigate a wide variety of time-dependent mechanical response of polycrystalline blanket films bonded to stiff substrates [50,55,57,58,61,62,65,69,70,72,[209][210][211][212][213].…”