Microstructure Evolution of Al-1.5% Cu Alloy as a Function of Resistance Change Due to Isothermal DC Stressing

Abstract

AbstractThis paper investigates Cu segregation and void morphology along AlCu alloy metal lines as a function of resistance change resulting from isothermal DC stressing at 225°C and a current density of J=2×106 A/cm2. The Al-1.5wt.%Cu alloy was deposited via DC magnetron sputtering onto a Si substrate at 525°C with a 1500Å TiW barrier layer. NIST test structures (length = 800µm, thickness = 1.2µm, width = 5 and 10 µm) were utilized in this study. BPSG was used as the insulation layer between Si substrate and conductor. The surface passivation layer was composed of Si3N4/PSG. Various failure criteria were selected to explore the correlation between Cu segregation and void morphology along the metal line and the relative percent resistance change (ΔR/R). The log-normal plots, mean-times-to-failure, and sigmas at each ΔR/R ( -−%, 2%, 5%, 10%, 20%, 100%, 250%) were plotted and listed. The microstructural evolution in terms of void morphology was monitored using SEM. SEM-EDS was used to analyze the Cu concentrations along metal lines tested at various %ΔR criteria.