Determination of ion incidence angles in plasma immersion ion implantation by means of a hollow multi-aperture target

Abstract

In plasma immersion ion implantation, ions are accelerated from a spherical cathode sheath edge which surrounds the target. On a non-spherical target, a distribution of angles of ion incidence can be expected. In order to determine the angles of ion incidence, a hollow cylindrical target with an upper cover plate with small drill holes was used. Ions enter the target through these apertures and impinge onto the inner bottom which is covered with cellulose. The organic material is blackened as a consequence of ion bombardment. The position of the black spots is determined by the position of the aperture with respect to the cellulose bottom and by the angle under which the ions enter the aperture, i.e. the angle of ion incidence on the plate. By measuring the position of the spots, the angles of incidence can be calculated. The obtained data show that in the center of the cylindrical target the ions impinge at right angles, whereas in the outer parts smaller angles of incidence are found. The distribution of angles is a function of the process parameters such as pulse length and pulse voltage.