Radio frequency plasma method for uniform surface processing of RF cavities and other three-dimensional structures

#This application claims priority to U.S. Provisional Application Ser. No. 61/982,017, filed on Apr. 21, 2014, the entirety of which is incorporated herein by reference.

#The invention relates generally to a method for plasma etching of surfaces and more specifically to a method for efficient plasma etching of surfaces inside three-dimensional structures.

#Generally, in reactive ion etching processes, an electric field plays a fundamental role. The chemistry in many discharges is affected strongly by the ion flux and energy distribution in the sheath and at the surface of walls and electrodes, which are in turn determined by the sheath electric field. Using measurements of electric fields in plasmas to provide a direct insight into the physics of discharges can be experimentally demanding. Moreover, the control of the electric field based on measurements is almost impossible to establish by feedback mechanisms. Therefore, the electric field in the sheath has to be controlled by external parameters, such as radiofrequency power and frequency combined with d.c. bias, radiofrequency circuit parameters, electrode dimensions and shape, pressure and composition of gas mixture. In order to control the electric field in the sheath with an external parameter, a link between one or more external parameters and a particular component of the electric field must be established.

#These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims, and accompanying drawings where:

#FIG. 1: is a photograph of an RF plasma etching system according to various embodiments;

#FIG. 2: is a photograph of ring samples with the diameter of the outer electrode;

#It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.

#The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention as well as to the examples included therein. All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the term “about” may include numbers that are rounded to the nearest significant figure.

#Various embodiments of the invention describe methods and apparatus to etch, to purify, and to passivate a large-area Niobium (Nb) or other contaminated metallic surfaces using a cylindrical radiofrequency discharge in a gas mixture composed of specified amounts of argon (Ar), chlorine (Cl2), helium (He), and oxygen (O2). A radio frequency discharge can be generated between two coaxial full or segmented cylindrical electrodes in the capacitively-coupled regime, whereby the exposed inner surface of the outer electrode is being treated. U.S. Provisional Application Ser. No. 61/880,415, titled, “Efficient Plasma Etching of Surfaces Inside Three Dimensional Structures,” filed Sep. 20, 2013, which is hereby incorporated by reference in its entirety, describes the use of a smooth central driven electrode in an asymmetric RF discharge with the processed surface acting as the grounded electrode, which can be treated at external room temperature.