Angled ion implantation for selective doping

摘要

A method of implanting dopants within an exposed first active region on a semiconductor substrate of a semiconductor wafer without doping an exposed second active region of the semiconductor substrate. A barrier wall is formed adjacent to the second active region and projects from the semiconductor substrate to a height above the second active region. A minimal angle relative to an axis perpendicular to the semiconductor substrate is determined at which doping ions directed at the semiconductor substrate must travel so that the barrier wall blocks the doping ions from contacting the second active region. The doping ions are used to bombard the semiconductor substrate at an angle at least as large as the minimal angle previously determined. As a result, the doping ions contact the first active region but do not substantially contact the second active region. The width of the second active region can be formed as greater than that of the first active. In one embodiment, a buried channel of a MOS device is created, the doping concentration of which is profiled so as to optimize both the threshold voltage thereof and the depth to the beginning of the buried channel ( gamma J).