Minimizing the process temperatures during bonding is essential for the heterogeneous integration of substrates on wafer level. It reduces the thermomechanical stress in the interface and thereby increases the reliability of the bond.
Reactive bonding is an innovative technology to provide the energy required to form a stable bond without heating of the whole substrates. Instead, a self-propagating exothermic reaction causes localized heating close to the bond interface, enabling an overall binding temperature of the substrate with less than 50°C. Thereby, the integrated reactive multilayer system (iRMS) acts as energy source. The iRMS consist of alternating multilayers of reactive material, deposited by magnetron sputtering. During the binding process, an short initiation impulse causes diffusion between the single layers, leading to the formation of an alloy while releasing energy as well. The reaction front propagates through the whole iRMS with a high velocity of several meters per second, providing the heat energy to join the substrates. This heat energy is used to surface-fuse a metal layer atop the bonding partner, such as aluminum, copper or gold in order to create a mechanically strong, hermetically sealed and depending on the iRMS electrically conductive bond interface. Due the high reaction velocity, the substrates can be joined with in less than a second.
A cleanroom preparation line, including characterization equipment for the processing of 4” up to 8” substrates is available at Fraunhofer ENAS for wafer-level reactive bonding.