ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
In recent years a number of workers have observed, using laser light-scattering methods, contamination particles suspended in rf process plasmas. Some recent studies show that the regions occupied by the particles appear finite and well defined, e.g., a ring. In this paper, a tuned Langmuir probe has been used to measure the plasma potential of these regions. Five cases are considered, where a case is distinguished by a disk of material A placed upon a larger diameter disk of material B, which in turn is placed upon an aluminum electrode driven by the rf power. It is consistently found that the regions occupied by particles are at a larger potential than the surrounding or ambient plasma. These regions are electrostatic traps. It is found that the incremental increase in potential as well as the geometry of the trap is dependent on materials A and B. For example, the trap configurations found are: case 1, silicon on graphite: ring and disk traps; case 2, silicon on silicon: ring trap; case 3, 304 stainless steel on silicon: disk trap; case 4, aluminum on silicon: bowl-shaped trap; case 5, silicon on aluminum: T-shaped or mushroom-shaped trap. Case 5 also contains a ring-shaped antitrap, i.e., a region where the potential is less than the ambient potential. The scenario proposed is that traps are system generated and depend on the design of the tool and the electrode. Particles subsequently flow into the traps. Particles may distort the trap boundaries as the density of trapped particles increases. However, particles do not determine the basic configuration (e.g., disk) of a trap, nor do they determine the plasma potentials within the trap or the surrounding ambient plasma region. In nearly all cases the trap and antitrap regions appear to be bounded by a double layer. Measurements of the plasma-sheath interface show that it generally follows the topography of the driven electrode. Explanations are presented for many of the observed phenomena.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.351865
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