A processing system is disclosed, having a process chamber that houses a substrate for exposure of a surface of the substrate to a travelling electromagnetic (EM) wave. The processing system also includes an EM wave transmission antenna configured to launch the travelling EM wave into the process chamber for the travelling EM wave to propagate in a direction substantially parallel to the surface of the substrate. The processing system also includes a power coupling system configured to supply EM energy into the EM wave transmission antenna to generate the travelling EM wave at a prescribed output power and in a prescribed EM wave mode during treatment of the substrate. The processing system also includes an EM wave receiving antenna configured to absorb the travelling EM wave after propagation through the process chamber.