Slotted waveguide structure for generating plasma discharges

摘要

A waveguide structure has at least one shaped slot machined in the wall of the waveguide. The slot is configured such that a high voltage is generated across the slot when the waveguide is suitably excited with high-power microwaves. The strong electric fields generated in the region of the slot can be used to produce a non-equilibrium plasma discharge in a working gas introduced in the vicinity of the slot. Various substrates can be translated past the slot and exposed to the plasma species generated by the microwave discharge. The slotted waveguide structure is designed to operate as a traveling wave structure with microwave energy uniformly dissipated along the length of the slot. Several methods are disclosed for providing uniform power dissipation. These methods include changing the dimensions of the waveguide, altering the position and shape of the wall slot, coupling power into the waveguide by means of auxiliary sources, and using an auxiliary ground plane. The auxiliary ground plane can also serve as a secondary electrode for the application of a low-frequency voltage for the enhancement of high-pressure operation. Altering the background gas pressure, gas composition, gas flow rate, and gas flow pattern provide additional ways to affect the plasma discharge. The structure can be designed to operate over the pressure range of about 10 Torr to atmospheric pressure (i.e., about 760 Torr) using a wide variety of gases and gas mixtures.