Magnetic field argon plasma

In another approach to reduce the energy spread of ions produced in the plasma source and remove polyatomic interferences, a hexapole collision cell (see also Chapter 2) is placed in front of the magnetic field. Argon, helium, or hydrogen gas is introduced into the cell, where ions from the plasma collide with the gas. Interaction between ions and the gas causes the ions to lose kinetic energy and polyatomic species formed in the plasma are decomposed as a result of ion-molecule collisions and/or, in the case of H2, chemical reactions. The collision cell will attenuate most interferences by several orders of magnitude. 

Figure 14.21 Drop of voltage as a function of magnetic field strength in argon magnetron glow discharge plasmas.

Figures 14.22 and 14.23 show the sputter deposition rates of copper from the copper electrode surfaces in argon plasmas at pressures of 30 and 60 mtorr as a function of discharge power. The deposition rate increased with increasing magnetic field strength and discharge power. No appreciable deposition of copper was observed in the argon plasma at a pressure of 30 mtorr for a maximal parallel magnetic component of less than 100 G.

Figure 14.22 Rate of sputter deposition of copper as a function of discharge power in argon plasmas (30 mtorr) with various magnetic fields.

In contrast to argon plasma, in which the sputtering of metal from the electrode is the primary process, the deposition of polymeric materials via plasma polymerization predominantly takes place in methane plasma. In such a polymer-forming plasma, the sputter deposition of electrode materials is considered as a secondary process, and the extent of the sputtering of metal depends on the plasma polymerization conditions, the nature of the electrode material, and the magnetic field strength. 

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