Rapid unidirectional growth of electronic micro-intermetallic interconnects with prismatic grains

Abstract

As conventional solder interconnects continuously downsize to less than 20 μm in three-dimensional integrated circuits, the rapid fabrication of reliable micro-intermetallic interconnects in chip stacking has become a critical concern. A temperature gradient (TG) process was investigated to fabricate micro-intermetallic interconnect. The results showed that the resulting interconnect consists of single prismatic Cu₆Sn₅ grains surrounded by Sn solder within only 7 min, which is nearly 7 times faster than the conventional SLID process. The contained Cu₆Sn₅ grains and Sn grains exhibited highly preferred orientations, indicating a unidirectional formation of the interconnect and thereby achieving controllable properties. The mechanisms of this unidirectional growth were elucidated and experimentally verified. The properties were examined to demonstrate desirable features including high mechanical strength and low electronic resistance. Furthermore, the soft Sn solder surrounding Cu₆Sn₅ grains may enhance the interconnects resistance against brittle fracture under mechanical shock conditions. The TG process and resulting oriented micro-intermetallic interconnects offer a promising solution for next-generation chip stacking.