Calorimetric Probes for Energy Flux Measurements in Process Plasmas

Abstract

This chapter gives an overview of the method of calorimetric probes which are used for characterizing the interaction between low-temperature plasmas and substrates in materials processing. Although the focus is on low-temperature non-equilibrium plasmas most of the concepts can also be transferred to thermal plasmas or are in fact adopted from fusion research. An introductory section showing the importance and complexity of plasma wall interactions is followed by a section providing an overview and comparison of various probe concepts, which have been developed in the last decades. Special focus is on the type of probes which are similar to the probes used by J.A. Thornton (In fact, Thornton was not the first, to use this type of probe. From his work from 1978 [1], one can follow the citations back to the work of Jackson in 1969, who used equation (6.7) for the determination of the power dissipated by a copper block located at substrate position in a sputtering discharge [2]) who was one of the pioneers connecting plasma characteristics with resulting surface properties. Thereafter, a short section gives a basic overview of the different contributions to the total energy influx and which are of importance for the plasma wall interaction. The last section shows different examples of applications of calorimetric probes. It demonstrates the applicability and flexibility of these types of probes for characterization of different low-temperature plasmas. The examples mainly focus on complex plasmas, where the variety of the involved processes also causes a specific plasma wall interaction. Such complex situations can be found in systems where reactive gases or gas mixtures, nano or micro particles (dust), magnetic fields or large surface to volume ratios are involved.