RF ion source for low energy ion implantation — beam profile control of a large-area ion source using 500-MHz discharge

In order to fabricate ULSI devices on large wafers up to 300 mm in diameter, an ion implantation system that can transport a high-current ion beam with low energy and suppress the charge-up on the wafer is necessary. Both problems come from the space charge effect; to solve them it is convenient to use a large-area ribbon-beam ion source, because it leads a low current density and low charge-up on the wafer. However, handling of the large-area beam is not easy and beam profile control on the wafer is even more difficult. This article is concerned with a method for controlling the beam profile of the large-area ribbon-beam ion source in RF plasma production. As the size of the ion-source chamber is comparable to the RF wavelength, then the ion-beam profile can be controlled by adjusting the size of the variable windows into the chamber for the RF wave. Accordingly, less than 2% spread in uniformity of the large-area ion beam is achieved.