Resonant excitation method and apparatus for generating plasmas

Abstract

Two methods and corresponding electrode designs are provided for the generation of a plasma, for example, at or about one atmosphere. Using these methods, various webs, films and three-dimensional objects are beneficially treated in a reduced amount of time. A first method utilizes a repetitive, asymmetric voltage pulse to generate a plasma discharge between two electrodes. An asymmetric voltage pulse is used to generate a discharge in which a substrate can be exposed predominately to either positive or negative plasma species depending on the voltage polarity used. A second method uses the gap capacitance of an electrode pair and an external inductor in shunt to form a resonant LC circuit. The circuit is driven by a high power radio frequency source operating at 1 to 30 MHz to generate a uniform discharge between the electrode pair. Both methods have temperature controlled discharge surfaces with supply gas temperature, humidity and flow rate control. The gas flow is typically sufficient to cause a turbulent flow field in the discharge region where materials are treated. Electrode pairs implement these methods and include a metal faced electrode and a dielectric covered electrode, one or both of which have a series of holes extending through the electrode face for supply gas flow. The second of the above-described methods will also operate with paired, metal faced electrodes, but under more restricted operating conditions.