Excellent Reliability of Xtacking™ Bonding Interface

Abstract

Xtacking™ is a novel 3D (three-dimensional) NAND flash architecture, in which memory cells and peripheral circuits are bonded by millions of pairs of small-pitch metal vias. Consequently, its bonding interface reliability attracts great interest. In this paper, we conducted reliability test of Xtacking™ bonding interface in both test structure level and product level. In test structure level reliability test, the bonding layer showed stable electrical properties and bonding interface after ultra-long time thermal or humidity stress (e.g., 7000hrs), which is much longer than common industry requirement (e.g., 1000hrs). Furthermore, the double cantilever beam test following long time temperature cycling and package level electromigration test also demonstrated good strength and stability of bonding interface. In product level reliability test, no function failure or scanning acoustic microscope image abnormality was observed after thermal or humidity stress, which further proves the excellent reliability of the bonding interface in actual product. Thus Xtacking ™ architecture achieved robust and reliable bonding interface with millions of pairs of small-pitch metal vias.