The Miniaturized Inductively Coupled Plasma Source And Its Characteristics

As a plasma source is scaled down, some unique characteristics of the plasma appear such as high gas temperature, high plasma density, etc. The development of Miniaturized Plasma Sources have extended their applications in many fields, such as gas analysers, ion thrusters, sterilizers, plasma displays, UV light source, etc. Among numerous Mini-plasma Sources, much attention of miniaturized inductively coupled plasma source has been paid due to easy fabrication, low cost, etc.A kind of miniaturized inductively coupled plasma sources (mICP) has been presented in this paper. The antenna with certain turns depending on the driving frequency, is winded around a quartz tube with a outside diameter of 8mm and inside diameter of 6mm, argon plasma with a low pressure can be excited as rf signal with a certain input power applied on the antenna. Characteristics for the miniaturized inductively coupled plasma with different driving frequency of 13.56MHz, 27.12MHz and 40.68MHz, respectively, are investigated by using Langmuir probe and optical emission spectroscopy (OES) techniques.From experimental measurements of Langmuir probe, it can be found that, due to enhancing power coupling coefficiency, the increase of rf input power and/or driving frequency causes the enhancement of plasma power absorption, hence leads to a rise in ion density and a drop in electron temperature in bulk plasma. Due to the rise of collisional between electron and neutral particles, the increasing pressure of Ar also improves the rf power absorption and is favor of increasing ion density. However, further increase of Ar pressure will lead to the drop in the electron/ion energy diffusion coefficient, thus cause the plasma density to be saturated. Due to strong confinement of ambipolar field and electromagnetic field, plasma density and electron temperature remain basically unchanged along the axis of plasma, only a slight drop in ion density occurs at low driving frequency. The gas temperature of mICP has been measured by using gas traced OES. It is found that, due to electron induced heating, rather than ion induced one, the gas temperature increases with rf input power and total pressure. In addition, the higher driving frequency helps to the increase in gas temperature in the plasma. Electron excitation temperature is increased by raising gas pressure, rf input power or dirving frequency, a drop in gas temperature and a constant in electron excitation temperature are also found away from the discharge region along the axis of plasma.