Investigation on how nanostructured silicon surfaces impact reactive bonding between silicon-silicon and silicon-low-temperature cofired ceramics

This study investigates the use of reactive multilayer (RML) systems as a localized heat source for bonding materials and chips, utilizing randomly structured silicon substrates to replace traditional metallization and solder layers. Two types of silicon surfaces-silicon "grass" (SiG) created by deep reactive ion etching and oxidized black silicon (obSi) produced through reactive ion etching followed by thermal oxidation-were coated with 5 μm thick Al/Ni RML stacks (Λ = 50 nm). These substrates were bonded at 10 MPa to (i) Si/Ti–Au/Sn and (ii) LTCC/AgPd substrates, both with and without Sn–Ag–Cu solder layers. Prior to bonding, scanning electron microscopy (SEM) and image analysis were used to examine surface structure and RML adhesion. After bonding, the joint microstructure was analyzed, and tensile strength was measured. Results show that obSi structures consistently supported self-propagating exothermic reactions, causing localized Sn melting and forming partial reactive bonds with tensile strengths up to ~2 MPa. In contrast, shorter SiG samples fully reacted but showed poor adhesion, while bonds with longer SiG structures relied on mechanical interlocking without self-propagating reactions. Bonds involving LTCC substrates were inconsistent and unsuitable for tensile testing. Failure analysis revealed fractures within silicon and at the bond interfaces, highlighting challenges in adhesion and material compatibility. This work provides important insights into RML-driven bonding processes for heterogeneous integration in microelectronics and microsystem packaging.