Calculation of crater profiles on a flat cathode in a direct current glow discharge

A three-dimensional hybrid set of models (Monte Carlo and fluid models) for the different plasma species in a glow discharge is used to calculate crater profiles on a flat cathode in the VG9000 direct current glow discharge cell. The characteristic crater profiles found experimentally are at least qualitatively predicted by the modeling work: (i) the crater is deeper at the edges than in the center (called the ''crater edge effect''), (ii) the crater walls are not completely steep, (iii) the crater bottom can be concave, convex or flat, and (iv) there is a rim outside the crater profile due to redeposition of material. The crater edge effect is the most pronounced feature in the calculated profiles, and arises from the anodic front plate at 0.5 mm from the cathode surface. As this effect impairs depth resolution in depth-profiling, some modifications to the cell geometry are proposed, which are expected to eliminate or minimize this effect. (C) 1997 Elsevier Science B.V.