A method includes performing a cleaning process on a first surface of a first wafer, and performing a surface activation process on the first surface. The surface activation process is selected from the group consisting of: a plasma surface activation process comprising generating a plasma from a process gas, wherein ions in the plasma are removed using a filter, and wherein a remaining uncharged part of the plasma is used to treat the first surface; a laser surface activation process using a laser beam; an acid surface activation process using an acid; and an alkali surface activation process using an alkali. After the surface activation process, a rinsing process is performed on the first surface. The first surface of the first wafer is bonded to a second surface of a second wafer.

A method includes performing a cleaning process on a first surface of a first wafer, and performing a surface activation process on the first surface. The surface activation process is selected from the group consisting of: a plasma surface activation process comprising generating a plasma from a process gas, wherein ions in the plasma are removed using a filter, and wherein a remaining uncharged part of the plasma is used to treat the first surface; a laser surface activation process using a laser beam; an acid surface activation process using an acid; and an alkali surface activation process using an alkali. After the surface activation process, a rinsing process is performed on the first surface. The first surface of the first wafer is bonded to a second surface of a second wafer.