Plasma properties

Processing variables that affect the properties of the thermal CVD material include the precursor vapors being used, substrate temperature, precursor vapor temperature gradient above substrate, gas flow pattern and velocity, gas composition and pressure, vapor saturation above substrate, diffusion rate through the boundary layer, substrate material, and impurities in the gases. Eor PECVD, plasma uniformity, plasma properties such as ion and electron temperature and densities, and concurrent energetic particle bombardment during deposition are also important. 

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. 

In the ASTER deposition system, experiments have been carried out in which the excitation frequency was varied between 13.56 and 65 MHz [169]. The other process conditions were kept constant at a power of 10 W, a pressure of 0.16 mbar, gas flows of 30 seem SiHa and 30 seem H2, and a substrate temperature of 250°C. As in Section 1.6.2.3, plasma properties that are deduced from lED measurements are compared with material properties in Figure 63. The lEDs of SiH at four frequencies are shown in Figure 64. 

The interaction of real metal plates is in fact far more complicated than what is derived assuming ideal infinite conductance. See B. W. Ninham and J. Daicic, "Lifshitz theory of Casimir forces at finite temperature," Phys. Rev. A, 57, 1870-80 (1998), for an instructive essay that includes the effects of finite temperature, finite conductance, and electron-plasma properties. The nub of the matter is that the Casimir result is strictly correct only at zero temperature. 

The choice of wall materials also influences the plasma properties, since eroded wall materials penetrate as impurities into the main plasma even as far as to the plasma center. There are two aspects which limit the presence of impurities in the confined plasma ... 

Because of the different nature of these data, they are not accessed in the same manner as other numerical data. In this case, the user can specify a desired electron temperature and density. The interface will then interpolate on the data to obtain plasma properties such as ionization balance, average charge, and radiated power at the required plasma parameters. The data are displayed in tabular and graphical form. These data are available for the elements neon, silicon, argon, titanium, and iron over a range of electron temperatures and densities of interest for fusion plasmas. 

The ta-C and a-C films are produced experimentally using a variety of PVD methods such as sputtering, laser ablation and filtered cathodic vacuum arc (FCVA) technique among which the FCVA technique attracts more attention due to high ionization yield which leads to easy control on plasma properties, high surface quality and high deposition rate which promotes this technique for different industrial applications [1]. 

The dc plasma jet described for example by Margoshes and Scribner [367] is a current-carrying plasma. This also applies to the disk stabilized arc according to Riemann [352], where the form of the plasma is stabilized by using several disks with radial gas introduction keeping the plasma form stable under different sample loads and the influence of the plasma composition on the plasma properties low. However, the plasma described by Kranz [368] is a transferred plasma. 

Obtained in Low-Temperature Plasma Properties Mixture of amorphous material, a- and p-form, 2% elementary Si, specific surface area 60 mVg, average diameter 30 nm [2506],... 

Kg. 4. Representation of the parameter space in plasma etching. The key internal plasma properties (middle) are the bridge between externally controlled variables (top) and the figures of merit (bottom). 

Equivalent circuits are used to determine important plasma properties (such as electron density, sheath thickness, etc.) from measurements of the current-voltage... 

Furthermore, clusters (i.e., aggregates of atoms or molecules) and particulates (i.e., small particles of solid) are also formed. The particulates thus formed may contaminate the base surface, influence plasma properties and structure, or have other undesirable consequences (Kushner, 1994). Furthermore, interactions of these particulates or of dust particles otherwise present are important to plasma properties and behavior therefore, they are a subject of extensive current research (Chutjian, 1999). 

For the understanding of plasma properties and for the control of a plasma reactor, it is important to detect electrons, ions, and other active species present in a plasma and to measure their densities. To this end, various methods have been developed, including measurements of radicals by absorption spectroscopy (Anderson et al, 1999) or optical-emission spectroscopy, measurements of electron densities and electric fields by probes, and measurements of ions by mass spectrometry (Matsuda et al, 1983 Robertson et al, 1983). In particular, neutral and nonemitting radicals (for instance, radicals in the electronic ground state) are expected to be abundantly present in a nonequilibrium plasma and have become measurable recently (Sugai et al., 1995 Cosby, 1993 Mi and Bonham, 1998 Motlagh and Moore, 1998). 

The application of quasi-equilibrium statistics and thermodynamics to plasma-chemical systems requires a clear understanding and distinction between the concepts of complete thermodynamic equilibrium (CTE) and local thermodynamic equilibrium (LTE). CTE is related to uniform plasma, in which chemical equilibrium and all plasma properties are unambiguous functions of temperature. This temperature is supposed to be homogeneous and the same for all degrees of freedom, all components, and all possible reactions. In particular, the following five equilibrium statistical distributions should take place for the same temperature T ... 

Finding out the thermodynamic plasma properties first reqtrires a statistical calcrrlation of partition functiorrs (Pathria, 1996). The partition function g of an eqtrilibritrm particle system at temperatrrre T can be expressed as a statistical sirm over states 5 of the particle with energies and statistical weights gs ... 

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