Contact-electromigration-induced leakage failure in aluminum-silicon to silicon contacts

Abstract

Si migration is observed in AI-Si contacts to both n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> silicon. Etch pits axe found near the leading edges of the more positively biased contacts. Leakage failure is observed in n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> contacts, but despite the Si migration, no junction leakage increase is measurable in Al-Si to p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> Si contacts. In n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> contacts, the leakage mean time to failure (MTF) is found to have an activation energy of 0.83 eV and be inversely proportional to the current density at the leading edge of the contacts. A current crowding parameter and an effective current are defined which enable the prediction of MTF with contact and technology scaling. In a typical case, current crowding is so severe that at constant current, changes in contact length have little effect on MTF.