Shallow p⁺ junction formation by a reverse-type dopant preamorphization scheme

Device grade ultrashallow p+ junctions have been fabricated by a novel ion implantation scheme. The novelty of the method is in using antimony to amorphize silicon prior to a low-energy boron implantation. Antimony satisfies a combination of two requirements lacking from all previously applied preamorphization schemes. First, due to the heavy mass of antimony, amorphization of silicon is achieved with a minimal amount of implantation damage. Second, and most important, antimony is a dopant of an opposite type than boron. Because of this, the inevitable implant tail of the preamorphizing species serves to confine the depth of the p layer. The optimized conditions for the application of this scheme have been determined. Junctions below 100 nm in depth, with less than 200 Ω/ sheet resistance and junction leakage of 10 nA/cm2, have been achieved. The electrical results have been correlated with the residual defect structure observed by cross-sectional transmission electron microscopy.