Wafer bonding method

A wafer bonding method comprising:

• providing a first wafer and a second wafer, the first wafer having a first metal layer and a first insulating layer at a first surface thereof, the second wafer having a second metal layer and a second insulating layer at a first surface thereof, and the first metal layer and the second metal layer comprising a same metal material;
• performing a pretreatment on one or both of the first wafer and the second wafer to form a compound of the metal material at a surface or surfaces of the one or both of the first metal layer and the second metal layer;
• bonding the first wafer and the second wafer in a manner that the first metal layer and the second metal layer face each other;
• and
• performing a treatment on the first wafer and the second wafer which are bonded, to convert the compound of the metal material into whiskers of the metal material.