Temperature-Dependent Activation Energy Of Electromigration In Cu/Porous Low-K Interconnects

In this paper, it was reported that the Time-to-Failure (TTF) of electromigration (EM) in Cu/porous low-k interconnects deviated from the classical Black's Equation at 250-350 degrees C due to moisture invasion. The EM activation energy (E-a) was 1.003 eV at above 300 degrees C, whereas the apparent value reduced to be negative below 300 degrees C, being accompanied by significantly narrowed TTF distribution. The corresponding change in the failure mode was distinctly revealed, which indicated that the oxidation of Ta-based liner due to moisture invasion through the porous low-k contributed significantly and modestly to the EM failure below and above 300 degrees C. The mechanism of the liner oxidation was interpreted with the theory of field-assisted cation migration, which suggested the steep slowdown of the oxidation from 275 to 300 degrees C could be ascribed to the substantial decrease in the moisture concentration at the low-k/Ta oxide interface, most probably owing to significant suppression of adsorption and surface diffusion of chemisorbed moisture in the nanoporous low-k. The inconsistent EM behaviors at the lower and higher temperatures were thus interpreted by the competition of intrinsic and extrinsic EM controlled separately by Cu diffusion along the Cu/SiN-based cap layer interface and the moisture-damaged Cu/Ta interface. Published by AIP Publishing.