Electromigration and 1/f Noise in Single-Crystalline, Bamboo and Polycrystalline Al Lines

Abstract

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.

Probing nanocrystalline grain dynamics in nanodevices

“…Previously, we have observed profound universal conductance fluctuations (UCFs) in single RuO2 nanowires at low temperatures, suggesting the existence of a large number of vibrant (atomic) TLSs (26). A significant portion of the atomic TLSs should reside at or nearby grain boundaries (11,12), which in turn may lead to weak nanograin bonding. Thus, the existence of granular TLSs can be expected.…”

“…Microscopically, a soft grain boundary reflects a weak bonding strength between grain-boundary atoms (11,12). Previously, it was found in both in-situ HRTEM and molecular dynamics simulation studies of polycrystalline metal films that nanograin rotations (8,13,14) and boundary sliding (6,9) can occur in specimens under stress.…”