US Patent 9412629 Wafer bonding for 3D device packaging fabrication

An apparatus and method bond a first wafer to a second wafer. The apparatus includes a first pressure application device configured to apply pressure at a central region of the first wafer in a direction toward the second wafer to initiate a bonding process between the first wafer and the second wafer. The apparatus also includes one or more second pressure application devices configured to apply pressure between the central region and an outer edge of the first wafer to complete the bonding process. The one or more second pressure application devices apply pressure on the first wafer after the first pressure application device has initiated the bonding process and while the first pressure application device continues to apply pressure at the central region. A controller controls the first pressure application device and the one or more second pressure application devices.