Plasmas: diagnostic techniques

Various plasma diagnostic techniques have been used to study the SiH discharges and results have helped in the understanding of the growth kinetics. These processes can be categorized as r-f discharge electron kinetics, plasma chemistry including transport, and surface deposition kinetics. 

In order to relate material properties with plasma properties, several plasma diagnostic techniques are used. The main techniques for the characterization of silane-hydrogen deposition plasmas are optical spectroscopy, electrostatic probes, mass spectrometry, and ellipsometry [117, 286]. Optical emission spectroscopy (OES) is a noninvasive technique and has been developed for identification of Si, SiH, Si+, and species in the plasma. Active spectroscopy, such as laser induced fluorescence (LIF), also allows for the detection of radicals in the plasma. Mass spectrometry enables the study of ion and radical chemistry in the discharge, either ex situ or in situ. The Langmuir probe technique is simple and very suitable for measuring plasma characteristics in nonreactive plasmas. In case of silane plasma it can be used, but it is difficult. Ellipsometry is used to follow the deposition process in situ. 

Knowledge on the plasma species can be obtained by the use of plasma diagnostics techniques, such as optical emission spectroscopy (OES) and mass spectroscopy (MS). Both techniques are able to probe atomic and molecular, neutral or ionized species present in plasmas. OES is based on measuring the light emission spectrum that arises from the relaxation of plasma species in excited energy states. MS, on the other hand, is generally based on the measurement of mass spectra of ground state species. 

A brief description of the key plasma diagnostic techniques, which have been especially useful in delineating the gas phase processes in fluorocarbon plasmas, will be given followed by an extensive discussion of plasma etching and polymerization mechanisms. 

Hieftje G. M. (1992) Plasma diagnostic techniques for understanding and control, Spectrochim Acta, Part B 47 3-25. 

The most direct need for plasma diagnostic techniques results from the determination of the etch end point for a given process. In addition, plasma diagnostic techniques are used for process monitoring and provide information on the types of species present in a plasma etching, the concentration, and the energy content. Laser interferometry (or reflectance) and optical emission spectroscopy (OES) are two commonly used techniques for EPD and require only an appropriate optical window attached to the chamber. They are easily implemented to obtain information about etching plasmas [1]. 

Diagnostic techniques that involve natural emissions are appHcable to plasmas of all sizes and temperatures and clearly do not perturb the plasma conditions. These are especially useful for the small, high temperature plasmas employed in inertial fusion energy research, but are also finding increased use in understanding the glow discharges so widely used commercially. 

Optical spectroscopies. These techniques are the least intrusive in situ plasma diagnostic methods. The most commonly used techniques are emission spectroscopy, absorption spectroscopy, laser-induced fluorescence. 

Optical diagnostic techniques are convenient and popular for alkali metal plasmas, because the strong and well-understood emission lines and continua can be easily observed in the visible and near-visible region. 

Plasmas The similarity between electrochemical and low-temperature plasma systems is emphasized in describing charge transfer at interfaces, materials degradation, mathematical modeling, deposition and etching, and diagnostic techniques. 

Diagnostic techniques must also be developed for characterizing plasma-surface interactions. Four important areas have been identified (16) ... 

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