Apparatus for obtaining dose uniformity in plasma doping (PLAD) ion implantation processes

DETAILED DESCRIPTION A PLAsma Doping (PLAD) ion implantation apparatus is described for obtaining dose uniformity radially across the surface of an ion implantation target wherein the target is disposed upon an electrode, this target preferrably has an edge extending thereover.
This apparatus employs a separately biasable concentric structure(s) disposed around the electrode in close proximity to the target, preferrably beneath the extended edge of the target.
This separately biasable concentric structure(s) is independently yet adjustably biased concurrently with the biasing of the electrode in order to adjust the shape of a plasma electric field induced near the target implantation surface thereby providing a substantially uniform PLAD dose distribution across the target.
By preferrably disposing such concentric structure(s) beneath the extended edge of the target, the risk of target sputter contamination is diminished.
Applying separate bias to the concentric structure(s) alters the shape of the electric field near the target by changing the effective shape of the cathode and thereby altering the plasma environment e.
g.
the plasma sheath thickness.
Means for accomplishing the biasing of the concentric structure(s) simultaneously with the biasing of the electrode include: voltage dividing the output of a single high voltage pulser, or utilizing correspondingly separate pulsers.
Either of which provides means for adjustable bias variation between the electrode and the structure(s) which thereby controls dose uniformity during PLAD ion implantation of the target surface.