Discharge parameter

The ID fluid discharge model has been applied to the ASTER deposition system (see Section 1.2.4). The deposition reactor has an inner volume of 10 1 and an inner diameter of 20 cm. The upper electrode is grounded (see Fig. 4a), and the powered electrode is located 2.7 cm lower. Other typical silane-hydrogen discharge parameters are summarized in Table IV. 

For one specific set of discharge parameters, in a comparison between the hybrid approach and a full PIC/MC method, the spectra and the ion densities of the hybrid model showed some deviations from those of the full particle simulation. Nevertheless, due to its computational advantages, the hybrid model is appropri-... 

The form of deposited polymer usually depends on the discharge condition (16,21-23). In region I and II, most deposited polymers were cracked or powder like films whose colour was yellow or dark brown, but continuous films were also obtained in the small discharge current and low pressure region. In region III, a transparent or a yellow film was obtained in the relatively wide discharge parameter range. 

All the work just mentioned is rather empirical and there is no general theory of chemical reactions under plasma conditions. The reason for this is, quite obviously, that the ordinary theoretical tools of the chemist, — chemical thermodynamics and Arrhenius-type kinetics - are only applicable to systems near thermodynamic and thermal equilibrium respectively. However, the plasma is far away from thermodynamic equilibrium, and the energy distribution is quite different from the Boltzmann distribution. As a consequence, the chemical reactions can be theoretically considered only as a multichannel transport process between various energy levels of educts and products with a nonequilibrium population20,21. Such a treatment is extremely complicated and - because of the lack of data on the rate constants of elementary processes — is only very rarely feasible at all. Recent calculations of discharge parameters of molecular gas lasers may be recalled as an illustration of the theoretical and the experimental labor required in such a treatment22,23. ... 

The use of low pressure plasma for chemical transport was proposed by Haupt-man in 196542. Since then, this idea has been developed in a series of papers28,30-35 It was shown that relatively simple chemical transport experiments under plasma conditions can reveal the fundamental nature of the dependence of the steady state composition of the plasma on the discharge parameters. Transport experiments in open (gas flow) systems yield information on the amount of solid A(s) which is chemically diluted in the gas phase due to the formation of the volatile compounds [e.g. C(g) — see Eq. (1)]. 

In order to determine the influence of various discharge processes on laser characteristics, gas temperature, electron density, and average electron energy were taken as independent modeling parameters [8]. In reality this cannot be achieved under ordinary dc discharge conditions. However, by using this approach it is possible clearly to identify the discharge parameters that have major influence on laser performance characteristics. 

N Hershkowitz, In Plasma Diagnostics Discharge Parameters and Chemistry, O. Auciello, D.L. Flamm (Eds.), Plasma-Materials Interaction Series, Academic Press, San Diego, 1989, p. 113. 

Figure 9.9 Sputtering on the discharge parameter W/p the aluminum sputtering is measured by the deposition onto the thickness monitor sensor in the glow discharge of argon, flow rate (cm sTP /min) , 2.3 O, 5.6 A, 12.4 A, 23.3. Adapted from Ref. 15.

Figure 9.10 Discharge parameter of CH4 glow discharge the amount of aluminum deposited is determined by XPS.

Figure 35.1 depicts the dependence of the deposition rate on the discharge parameter WjFM. The figure is essentially the same as Figure 8.3 and, if plotted using D.R./ FM, the same as Figure 8.4. Such a plot is necessary to identify the domain of LCVD, namely, the energy-deficient domain or monomer-deficient domain. Based on this figure, 2.6GJ/kg (energy-deficient domain) and 21.8GJ/kg (monomer-deficient domain) were selected for analysis of coating characteristics.

Milton D. M. P., Hutton R. C. and Ronan G. A. (1992) Optimization of discharge parameters for the analysis of high-purity silicon wafers by magnetic sector glow discharge mass... 

Hexamethylcyclotrisilazane and hexamethylcyclotrisiloxane were purified by rectification in vacuum following which their purity was tested by gas chromatography. Plasma polymerizations were carried out in an electrode system described previously ( ). Thin film were deposited in a 20 kHz glow discharge on the surface of stainless steel electrodes or on gold or silicon electrodes in the case of thin layers intended for further studies of electrical properties. All polymerizations were carried out at constant discharge parameters current density j = 1 mA/cm2, discharge duration t = 30 sec, monomer vapour pressure p = 0.3 Torr. 

Too often in the literature the details of a device used in a kinetic study are only vaguely recorded. Discharge parameters, common to all devices, need to be identified and measured in the course of such studies. In this way the results of various investigators can be properly compared and used to advantage in the selection of a device for chemical processing. Phelps (11) has discussed some parameters of particular importance. However, to date very little correlation of these parameters against chemical reaction results in discharges has been reported. 

The precise form of f(E) for molecular gases remains controversial (see References 10, 20, and 25) but there is increasing evidence that the Maxwellian form is a useful approximation (see References 24, 29, 52, 53, 55, 57, 61, 92 and 93). It follows that XK is a function of X/n which, in principle, is an unrestricted parameter alternatively, it may be preferred to discuss XK and related rate coefficients discussed below in terms of E. For many reactions QXK is characterized by a major maximum for some value of the electron energy now denoted by EQimax consequently, it may be expected in such cases that the overlap with E1/2/(E) is small for E << or >> EQ>maa , that is that aXK passes through a maximum when considered as a function of X/n or E. This is relevant to the selection of discharge parameters to effect a particular reaction at a conveniently rapid rate. 

This is a useful formula for estimating the maximum attainable value of tjxk and the indications from experiment are that this formula has a wide validity. A correspondingly simple procedure for estimating the discharge parameters that are associated with the attainment of r xximax is, however, lacking. 

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