Diagnostic techniques for plasma reactor temperature and species determination in advanced materials processing

Abstract

Although plasma techniques continue to emerge as one of the more efficient means for processing advanced materials, the technology transfer, including optimization and scaleup, of plasma systems (both thermal and non-equilibrium) is hindered by a lack of understanding of the basic mechanisms which govern the plasma process. Understanding the plasma chemical reactions that occur in these reactors depends on the ability to accurately determine the plasma gas temperature and species concentration distributions. Concentration gradient measurements in turn yield information on the homogeneous/heterogeneous nature of the reactions, chemical kinetic constants, and mass transport coefficients. Detailed knowledge of the temperature and reaction rates is also essential to the success of any detailed modeling effort. Laser/optical diagnostic techniques have the capability to provide much of this crucial information. Many of these optical techniques are non-intrusive, species specific and yield excellent spatial and temporal resolution. Optical in-situ measurements, in contrast to measurements using conventional sampling probe techniques, provide valuable information on the presence of excited species (e.g., hydrogen atom concentration in the diamond deposition process) as well as the deviation from local thermodynamic equilibrium in the case of high temperature gas flows generated by plasma sources. This paper includes discussion of both optical/laser techniques and representative conventional probe techniques. Approximate temperature limitations, advantages, and disadvantages of representative temperature and species measurement techniques are summarized. A recent example of the complementary use of laser diagnostic techniques in plasma reactors for advanced material processing is presented. © 1994, Walter de Gruyter. All rights reserved.