Glycerol Vapor Assisted Cu Direct Bonding: Implications for 3D Semiconductor Packaging

Abstract

As the scaling down of semiconductor devices reaches its physical limits, 3D stacking packaging technology is emerging as a new miniaturization solution. Among the various 3D packaging technologies, Cu direct bonding is widely adopted due to copper's excellent electrical conductivity and the absence of intermetallic compounds for solder bumps. Since copper readily undergoes oxidation, technologies that prevent Cu surface oxidation during Cu direct bonding are essential. However, current research suggests that the methods require additional pretreatment processes, which demand high costs. In this study, a Cu direct bonding method utilizing glycerol vapor is developed to effectively streamline the pretreatment steps. The potential of glycerol as a reducing agent and antioxidant for Cu is demonstrated using a silicon die sample with a size of 10  ×  10 mm², verified through the X-ray photoelectron spectroscopy. The Cu direct bonding for 3D semiconductor packaging is successfully performed under glycerol vapor atmosphere, without any plasma pretreatment. The cross-section of the bonded specimens is examined by scanning electron microscopy, and mechanical reliability is assessed by die shear testing.