Local penetrating proton beam transmutation doping method for silicon

摘要

Efficient transmutation doping of silicon through the bombardment of silicon wafers by a beam of protons is described. A key feature of the invention is that the protons are required to have an energy of at least 4 MeV to overcome the Coulomb barrier, thereby achieving practical utility . When this is done, transmutationally formed phosphorus in concentrations as high as 1016 atoms per cc. are formed from proton beams having a fluence as low as 1019 protons per square cm. As a byproduct of the process sulfur is also formed in a practical concentration range of about 1013 atoms per cc. This is readily removed by annealing at temperatures of the order of 700 DEG C. Because of the high energy of the protons, several silicon wafers may be processed simultaneously. As expected, the additional phosphorus is uniformly deposited throughout the entire thickness of a wafer. Masks, either freestanding or contact, may also be used in order to limit the transmuted regions to particular desired areas.