Surface activation and direct bonding of semiconductor wafers

An apparatus for surface activation treatment of a substrate 101 comprises first and second electrodes 102, 103 for generating a plasma, and a substrate mount disposed perpendicular to the electrodes 102, 103. The electrodes 102, 103 define a plasma generation region 100 which is separated from the substrate mount. At least one of the electrodes 102, 103 has perforations which allow active neutral species generated in the plasma to diffuse on to substrate 101 to treat the substrate surface whilst restraining charged species of the plasma. A method of pre-bonding treatment of one or more substrates 101 comprises exposing the surface of the one or more substrates 101 to active neutral species created locally by non-equilibrium electrical discharges. The apparatus and methods disclosed reduce substrate surface damage by using indirect plasma exposure