Dose perturbation by wafer charging during ion implantation

It was found that the dose uniformity of bare wafers in simultaneous arsenic ion implantation into thickly oxidized silicon wafers and bare silicon wafers varies according to the loading combination of wafers. The implantation was executed using a batch-process machine with a wafer loading disk in which a slit is cut to measure beam current during ion implantation. When an oxide wafer was loaded next to the slit with a beam irradiating the oxide wafer just after the slit, disk transverse motion was slowed, which subjected the middle band region of every bare wafer to a high dose. When an oxide wafer was loaded next to a bare wafer with the beam irradiating the oxide wafer just after the bare wafer, part of the bare wafer adjacent to the oxide wafer was subjected to a low dose. It was experimentally clarified that the bare wafer dose variation is caused by the beam blow-up due to the charging of the oxide wafer