Micropillar mechanics of Sn-based intermetallic compounds

Abstract

The semiconductor industry is exploring a new scheme called “More-than- Moore” to overcome the high cost and difficulty of smaller node fabrications when facing the end of Moore’s law. For this purpose, the three-dimensional integrated circuit (3D IC) architecture is favored by most major semiconductor companies. The stacking of chips in 3D IC architecture with design of microbumps and through silicon vias (TSVs) allows integration of heterogeneous function within a single chip for enhancing performance with small form factor by increasing I/O density, shortening interconnect distance. Due to this reduction in solder volume, it is anticipated that Sn-based solder in microbumps will be totally converted into intermetallics (IMCs) during the assembly or the operation of further process. Sn-based IMCs therefore dominate the properties of microbump and become potential candidates of structural materials. The mechanical behaviors of IMCs and the preferred types of IMC become questions of importance. This chapter focuses on the micromechanical behaviors of single-crystalline Cu6Sn5 and Ni3Sn4 by micropillar compression. The failure mode of single-crystalline Cu6Sn5 and Ni3Sn4 are cleavage, but they both performed strain bursts as a result of dislocation gliding with certain slip system before failure. They are not as brittle as people thought and have adequate mechanical properties. For Cu6Sn5, grains with the c-axis aligned with the load direction have better mechanical properties. The compound Ni3Sn4 can withstand more than 4% strain along the slip system, (100)[010]. Compared to Cu6Sn5, Ni3Sn4 has better mechanical performance as well as toughness and should be more favorable to be adopted as structure materials of 3D IC microbumps.