Experimental investigation of mini-microwave plasma sources

Abstract

Summary form only given. In the past, the challenge in microwave plasma research was to develop techniques that provide high ion and free radical densities uniformly, over large and ever increasing process areas. Scale-up was usually an important issue when considering industrial applications. Thus, the creation of very small microwave plasmas-on the order of a few millimeters-was rarely investigated. However, the recent interest in development of systems on a chip, MEMs and their related micro system applications, has suggested the possibility of numerous applications for mini and micro plasma sources. Accordingly, this investigation is devoted to the development and the understanding of the behavior of very small microwave plasmas. We have constructed a microwave plasma system that creates and allows for the experimental investigation of millimeter size plasmas. Plasmas are generated across a wide range of input parameters, including pressure variation from one millitorr to one atmosphere, input power from one Watt to one hundred Watts, microwave frequency from 2.45 to 15 Gigahertz, and a variety of gas mixtures (e.g. hydrogen, methane, argon, nitrogen). The system construction allows for quick reconfiguration of the microwave reactor, such that different probe shapes and sizes can be used to effect plasma formation, size, and stability. Plasma density, size, shape, ignition, and emission spectra are monitored during each experiment to characterize the mini plasmas over the input parameter space. The experimental results will identify the experimental operating regime necessary to excite and maintain stable, high density, millimeter scale microwave plasma sources for micro system applications and will also identify the important figures of performance, such as electron temperature vs. power, absorbed power densities (Watts per cubic centimeter), plasma densities per Watt, etc.