When manufacturing semiconductor devices, various joining materials are used to join a semiconductor element and a lead frame and the like (support member). When joining a power semiconductor, an LSI, and the like, which are operated at a high temperature of 150° C. or higher, among the semiconductor devices, high-melting-point lead solder is used as a joining material. In recent years, a demand for an operation at a high temperature of 175° C. or higher has been increased due to large capacity and space saving of a semiconductor element. Accordingly, at a joining portion formed from a high melting point solder layer, heat resistance and thermal conductivity become insufficient, and thus it is difficult to secure connection reliability. On the other hand, a joining material, which does not contain lead, is demanded in accordance with strengthening of RoHS regulations.
Joining of a semiconductor element by using a material other than lead solder has been examined. For example, Patent Literature 1 suggests a technology of forming a sintered silver layer by sintering silver nanoparticles at a low temperature. It is known that the sintered silver has high connection reliability with respect to a power cycle.
A technology of forming a sintered copper layer by sintering copper particles as another material is also suggested. For example, Patent Literature 2 discloses copper paste for joining which includes a cupric oxide particles and a reducing agent as a joining material for joining a semiconductor element and an electrode. In addition, Patent Literature 3 discloses a joining material that includes copper nano particles, and copper micro particles, copper sub-micro particles, or both of the copper micro particles and the copper sub-micro particles.