Interior surface plasma immersion ion implantation of a small oval tube

We use a two-dimensional particle-in-cell model to investigate ions dynamics implanted into the inner sidewall of an oval tube target during a high voltage pulse in plasma immersion ion implantation. Our study shows that the potential structure in the plasma sheath adjacent to the surface of the oval tube acts as two cylindrical divergent potential lenses with different focal lengths which principal axes along the major and minor axes on the elliptical cross-section respectively. The focusing properties of the two potential lenses results in non-uniform total incident ion dose distribution along the inner elliptical arc surface of the oval tube, an ion dose peak between the vertices of the major and minor axes of the elliptical arc surface and nearer the vertex of the major is observed. It is notable that non-uniform ion dose distribution is obtained at any time during the whole implantation process from the beginning of the implantation until all ions exhausted. The calculation of the cross-correlation of the ion dose distributions at different time shows that the ion dose distribution along the surface remains unchanged.

► We model interior surface PIII of an oval tube using 2D particle-in-cell.
► Ion focusing is proposed to explain the non-uniform ion dose distribution.
► The shape of ion dose distribution remains unchanged with time.