Strength and Fracture of Silicon Wafers Reactively Bonded by Al/Ni Rapid Heating

Al/Ni exothermic reaction, wafer bonding, four-point bending test, fracture strength We describe the strength and fracture of Si wafers instantaneously bonded by exothermic reaction in an Al/Ni multilayer film.The Al/Ni multilayer film deposited by dual-source direct current (DC) sputtering is used as a heat source for the solder bonding of Si wafers.To reduce the numbers of voids and microcracks produced at the solder-reacted NiAl interface and the reacted NiAl layer, respectively, Al/Ni multilayer films are modified.By depositing the Al/Ni multilayer film with Ni layers on the top and bottom surfaces onto the base-side Si wafer, the number of voids at the base-side solder and reacted NiAl interface is reduced.Using a selfstanding Al/Ni multilayer sheet with Ni layers on both sides reduces the number of microcracks introduced into the reacted NiAl layer.After dicing the bonded wafer to make a miniature rod having the bonded section, a four-point bending test is conducted.The improvements of the bonded section provide high fracture strength.The mechanical test determines the weakest portion of the bonded section.The effectiveness of modifying the Al/Ni reactive-bonding conditions is discussed, based on observations of fractured samples and results of energydispersive X-ray (EDX) analysis.