Kinetic and Diagnostic Studies of Molecular Plasmas Using Laser Absorption Techniques

Abstract

Listen

Translate article

AbstractWithin the last decade, mid-infrared absorption spectroscopy between 3 and 20 μm – known as infrared laser absorption spectroscopy (IRLAS) and based on tunable semiconductor lasers, namely lead salt diode lasers, often called tunable diode lasers (TDLs), and quantum cascade lasers (QCLs) – has progressed considerably as a powerful diagnostic technique for in situ studies of the fundamental physics and chemistry of molecular plasmas. The increasing interest in processing plasmas containing hydrocarbons, fluorocarbons, and organosilicon compounds has led to further applications of IRLAS because most of these compounds and their decomposition products are infrared active. IRLAS provides a means of determining the absolute concentrations of the ground states of stable and transient molecular species, which is of particular importance for the investigation of reaction kinetics. Information about gas temperature and population densities can also be derived from IRLAS measurements. A variety of free radicals and molecular ions have been detected, especially using TDLs. Since plasmas with molecular feed gases are used in many applications such as thin film deposition, semiconductor processing, surface activation and cleaning, and materials and waste treatment, this has stimulated the adaptation of infrared spectroscopic techniques to industrial requirements. The recent development of QCLs offers an attractive new option for the monitoring and control of industrial plasma processes as well as for highly time-resolved studies on the kinetics of plasma processes. The aim of the present contribution is threefold (1) to review recent achievements in our understanding of molecular phenomena in plasmas including interactions with solid surfaces, (2) to report on selected studies of the spectroscopic properties and kinetic behavior of radicals, and (3) to review new applications of QCLs and to describe the current status of advanced instrumentation for QCLAS in the midinfrared.KeywordsTransition Dipole MomentFundamental BandTunable Diode Laser Absorption SpectroscopyExternal Light SourceIntegrate Cavity Output SpectroscopyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.