The 1/f noise in three types of aluminum lines has been investigated in the temperature range 140-510 K. The types are one long single crystal, a chain of short single crystals ͑''bamboo''͒, and a polycrystal. In the lines of the first two types the 1/f noise power is significantly lower than in the polycrystalline specimens. The temperature dependence of the noise power in the polycrystalline lines shows a plateau between 370 and 415 K, corresponding to activation energies 0.9-1.0 eV. Both types of monocrystalline lines have equal noise power with a peak around 340 K, corresponding to an activation energy of about 0.8 eV. In the polycrystalline lines the dominant contribution to 1/f noise appears to be the thermally activated motion of atoms in grain boundaries. The measurements on the monocrystalline lines reveal the existence of at least one further contribution to 1/f noise in metals, presumably associated with the thermally activated diffusion of atoms along dislocations.
The electromigration damage in polycrystalline AlSiCu lines caused by dc current densities of the order of magnitude 1010 Am 2 at 500 K has been investigated by long-time high-resolution ac noise measurements over a wide range of temperatures. A multiple-probe setup allowed us to monitor the electrical resistance increase along the line and to show that sudden enhancements of the noise power and the resistance occurred in the same line segment. The peak in the distribution function N(E) of the activation energies E for the defect motion responsible for 1/f noise was found to shift from E 0 = 0.7 eV with Gaussian width AE = 0.1 eV in the undamaged samples to E 0 = 1.0 eV and AE = 0.2 eV in the damaged samples. The latter values are compatible with the Cu diffusivity along intermediate-misfit grain boundaries in Al, indicating that the damage process depends not only on the composition but also on the microstructure of the lines. It is proposed that electromigration causes Cu atoms to drift towards and get trapped in grain boundaries, that their thermally activated motion in the boundaries contributes substantially to the 1/f noise, and that eventually the Cu atoms assemble on the anode side of the sample. The dependence of the diffusivity on the grain-boundary mismatch may cause flux divergencies at boundary junctions and thus lead to void formation.
The relation between electromigration and microstracture for three types of Al lines with different microstructures has been studied. The lines were made by recrystallization of Al in a SiO2 groove pattern. They were either truly bamboo with grains of on average 3 μm long or distorted (i.e. with dislocations) single-crystals. In addition, conventional, polycrystalline Al lines with grains of on average 230 nm were made. The lines were lifetime-tested (200 °C,j=2, 5 and 8 MA/cm2) and subjected to 1/f noise measurements (from 200 to 500 K).The bamboo and single-crystalline Al lines showed the same, although weak, 1/f noise. This observation demonstrates that other mechanisms than thermal motion of atoms at grain boundaries can cause noise. It is suggested that dislocations are the sources for noise in our samples. The measured activation energy (0.8 eV) is in agreement with the activation energy for pipe diffusion along dislocation lines.The lifetime-tests showed significantly higher times to failure for the single-crystalline and bamboo lines as compared to polycrystalline lines. Preliminary results indicate slightly higher lifetimes for the bamboo than for the single-crystalline lines. It is concluded that interface diffusion is the main mechanism for electromigration in truly bamboo or single-crystalline lines. Our measurements demonstrated that dislocations are important in the formation of 1/f noise and interfaces in the formation of electromigration damage.
The relation between electromigration and microstructure for three types of Al lines with different microstructures has been studied. The lines were made by recrystallization of Al in a SiO2 groove pattern. They were either truly bamboo with grains of on average 3 μm long or distorted (i.e. with dislocations) single-crystals. In addition, conventional, polycrystalline Al lines with grains of on average 230 nm were made. The lines were lifetime-tested (200 °C,j=2, 5 and 8 MA/cm2) and subjected to l/f noise measurements (from 200 to 500 K).The bamboo and single-crystalline Al lines showed the same, although weak, 1/ƒ noise. This observation demonstrates that other mechanisms than thermal motion of atoms at grain boundaries can cause noise. It is suggested that dislocations are the sources for noise in our samples. The measured activation energy (0.8 eV) is in agreement with the activation energy for pipe diffusion along dislocation lines.The lifetime-tests showed significantly higher times to failure for the single-crystalline and bamboo lines as compared to polycrystalline lines. Preliminary results indicate slightly higher lifetimes for the bamboo than for the single-crystalline lines. It is concluded that interface diffusion is the main mechanism for electromigration in truly bamboo or single-crystalline lines. Our measurements demonstrated that dislocations are important in the formation of l/ƒ noise and interfaces in the formation of electromigration damage.
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