The temperature of a substrate, while the covering is drawing on it’s surface, страница 20

MS Excel automatically defines a kind of a curve on the initial data (shaped lines in figure 5.19). It is necessary to determine the algebraic function, describing the received curve (continuous lines) as much authentically as possible. MS Excel allows to choose for approximation the following kinds of dependence: linear, logarithmic, polynomial, sedate. After construction of five various approximated curves (lines of a trend) it turned out, that a curve of the logarithmic function the most authentically describes the dependence, the size of reliability of approximation makes 0.95 … 0.99 (for the dispersions coefficients of various materials). Thus, algebraic functions of dependence of the dispersion coefficients for various materials are received. Results are tabulated 5.7.

Figure 5.19 Construction of graphic dependences of the dispersion coefficients of the titan (▲) and copper (■) on bombardment by ions of argon.

Table 5.7 Results of approximation of the data on the dispersion coefficients of various materials

Thus, as a result of approximation the equations describing dependence of the dispersion coefficient from energy of bombarding ions are received. A general view of the equation is

,                                                (5.21)

where          у – the dispersion coefficient, х – energy of bombarding ions,

a и b – coefficients.

Similar approximation allows to speed up process of definition of the dispersion coefficient of the cathode material using the set of initial data.

6. The analysis of angular distribution of the sputtered particles

To determine the function of distribution of the sputtered atoms of the cathode - target on the surface of the substrate and as consequence of it a thermal mode of the substrate, we shall analyse in the given section, what corners and what law of dispersion of the target atoms at bombardment by ions of working gas in magnetron sputtering systems takes place.

Studying of angular distributions of the particles sprayed from polycrystalline surfaces by beams of ions of different weights and energies, falling on a target under various corners, represents extremely big interest for understanding of the mechanism of the dispersion process - the mechanism of the energy transfer of an ion to atom of the target.

First such researches have been executed by Zeeliger and Zommermejier [74], treating a silver target with rays by ions of argon with energy about 10 keV. Measurements have shown, that angular distribution of the sprayed particles is described by Knudsen’s «cosine law» irrespective of a hade of ions on the target. During long time this result was the proof of the truth of the evaporation theory. For the first time universality of Zeeliger and Zommermejier’s conclusion has been subjected to doubt as a result of Verner’s experiments [43.] Verner has found, that the sprayed particles are let out mainly in some certain directions at bombardment of monocrystals. To establish, in what limits the angular distributions deviate the cosine law in case of polycrystalline targets, Verner and coll. [43] irradiated targets from Ni, Pt, Mo, Fe  with ions Hg + of low energies (100-1000 eV). The results received by them for ion energies 250, 500 and 1000 eV are shown on fig. 6.1 In the form of polar diagrams. At this image the areas limited to various polar curves, are proportional to factors of dispersion. Forms of separate polar curves testify that there are significant deviations from the cosine law. In comparison with distribution under the cosine law the greater number of particles is sprayed in the directions parallel to the surface of the target, and smaller number - in the direction of the normal to the surface of the target (Verner has named such distribution "undercosine"). Such effect is more strongly pronounced in case of targets from Mo and Fe, than in case of targets from Ni and Pt (face-centered cubic lattice). Further, on the basis of fig. 6.1 it is possible to draw an interesting conclusion, that in process of increasing of ion energy angular distribution of the sprayed particles approach to distribution under the cosine law. The researches executed at much bigger energies of ions (for example by Roll and coll. [69] at 20 keV, by Kobich and coll. [13] at 17 keV, by Kaminsky [40] at 800 keV), show, that when increasing of ion energy distributions pass from "undecosine" to "overcosine", i.e.