PLASMA PROCESSING APPARATUS, WAFER TO WAFER BONDING SYSTEM AND WAFER TO WAFER BONDING METHOD

A plasma processing apparatus includes a load lock chamber switchable between an atmospheric pressure state and a vacuum pressure state, and a substrate processing apparatus configured to transfer a substrate to and from the load lock chamber and to perform a plasma process on a surface of the substrate in a plasma chamber under a vacuum atmosphere. The substrate processing apparatus includes a substrate stage disposed within the plasma chamber and configured to support the substrate, a plasma gas supply configured to supply a plasma gas into the plasma chamber, a steam supply configured to supply a water vapor into the plasma chamber, and a plasma generator configured to generate a plasma in the plasma chamber.