Sheath expansion in two-dimensional cartesian and cylindrical targets

The transient sheath expansion induced by a voltage pulse applied to two-dimensional targets is simulated numerically with a fluid model. Non-linear sheath expansion due to sheath overlapping in a small cylindrical bore with a finite depth is presented. The sheath expansion inside the bore is enhanced by the initially nonuniform plasma distribution. The angular distribution of the ions impinging on the target surface and the nonuniformity of the incident ion dose are calculated for a cylindrical bore target. A dip of the dose profile, seen earlier for square targets, appears at convex corners of the target. This dip is a numerical artifact, not a real physical phenomenon, mainly caused by false diffusion (numerical diffusion) and inaccurate estimation of the electric field on the corner. By re-orientation of the numerical mesh to suppress false diffusion, the dip effect can be eliminated effectively in the square target case