Effect of interfacial structure on peel strength between Cu and AlN bonded with a Mg–Ti co-deposited film

Abstract

Eliminating electrochemical migration of Ag is effective for improving the long-term reliability of power modules for high-voltage applications. In this work, a Cu plate was bonded onto an AlN substrate via Mg–Ti co-deposited films with three different compositions as Ag-free bonding materials between 800 and 950 °C for 0.5 h. The interfacial structures and the peel strength between the Cu and AlN were investigated by using the Surface And Interfacial Cutting Analysis System (SAICAS). Cu was bonded onto AlN through a TiN layer consisting of TiN particles and a Cu-containing grain boundary phase. All fractures at the Cu/AlN interface were observed to occur between the TiN layer and AlN after the SAICAS test. The peel strength at the Cu/AlN interface, which was independent of the thickness of the TiN layer, increased exponentially with increasing bonding temperature. Cu-containing phases, such as grain boundary phases and segregation phases between TiN particles and AlN, were present at the TiN layer/AlN interface. Mg and O were segregated at the interface, which had a high peel strength between the Cu-containing phase and AlN, while at the signal peak position of Mg, a plateau was observed in the Al concentration distribution between the Cu-containing phase and TiN particle. The peel strength of the Cu-containing phase/AlN interface, which increased as the O concentration in the Mg-containing segregation layer increased, dominated that of the TiN layer/AlN interface.