Applications of Magnetic Scanning to High Current Implantation

Abstract

High current ion implantation systems employing beams of 75As+ at 10 mA or more at energies of the order of 100 keV depend upon electron space charge neutralization to preserve the ion optical quality of the beam during transport from the source to the wafer implant location. Time varying magnetic fields have been used to deflect these beams over lateral dimensions up to 300 mm at frequencies of the order of 0.1 Hz, without affecting low energy electrons trapped in the potential well of the beam, and without significant modification of the ion beam shape. Hybrid magnetic-mechanical scanning of high current ion beams has been shown to be capable of averaging the implanted dose with uniformities as good as 2σ < 1% across 100 mm diameter silicon wafers mounted on an 0.8 meter disc rotating in vacuum at 1000 r.p.m. The physical basis of angle corrected hybrid magnetic-mechanical scanning is analyzed leading to a calculated relationship for the deflection (X) dependent on the scanner magnetic field (Bs). This functional dependence X = f(Bs) has also been measured using the disc as a rotating beam profile monitor. From the measured dependence, implant dose uniformity across a long scan can be obtained as shown by sheet resistance maps of ion implanted wafers. The dependence of dose uniformity on the number of scans has also been evaluated, and data is presented illustrating uniformity 2σ < 2% can be achieved using a single scan across the wafer.