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

Abstract

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.

1/fnoise in mono- and polycrystalline aluminum

“…The microstructure of the lines was characterized thoroughly by transmission electron microscopy ͑TEM͒ and scanning electron microscopy ͑SEM͒, as well as by backscattering Kikuchi diffraction ͑BKD͒. [11][12][13] The last-mentioned technique allows one to determine the crystallographic orientations locally. 14 Figure 1 depicts TEM micrographs ͑bright field͒ of the recrystallized lines.…”

“…TEM on other samples confirmed the complete absence of polycrystalline segments. 13 The polycrystalline lines had an average grain size of 230 nm ͑Fig. 2͒.…”