1/f² Noise and Electromigration in Al-Cu Interconnects

Abstract

Electromigration in Al-1.5%Cu interconnects was studied using a direct current (d.c.) induced 1/f2 noise spectrum. The interconnects were fabricated with a multi-step sputter deposition process, with deposition temperatures of 25°C, 300° C, and 475°C. The resulting microstructures were analyzed using SEM and TEM, and grain size distribution parameters were measured. The minimum temperature at which 1/f2 noise could be detected was found to depend on the deposition temperature; for the 25°C, 300°C, and 475°C depositions the lowest temperature at which 1/f2 noise could be measured was 190°C, 220°C, and 265°C, respectively. The activation energy of 1/f2 noise was measured and compared with the electromigration activation energy. The noise activation energy was found to depend on deposition temperature; 0.56 eV, 0.64 eV, and 0.96 eV for the 25°C, 300°C, and 475° C depositions, respectively. SEM analysis of the samples after measurement show initial stages of void and hillock formation. Corresponding electromigration activation energies, 0.56 eV, 0.69 eV, and 1.04 eV were also dependent on deposition temperature. Noise measurements of interconnects made prior to electromigration testing were highly correlated with the electromigration failure times.

Noise as Diagnostic Tool for Quality and Reliability of MEMS

“…Vandamme [3] lists three factors that increase the 1/f noise, namely crystal defects being created by ions or protons, current constrictions and interfaces, and decreasing minority carrier lifetime. 1/f 2 is used to study the lifetime of various compounds [44][45][46] Mechanical noise Thermomechanical noise [9] Effects of atomic and molecular vibrations on small structures…”