Defects and leakage currents in BF₂‐implanted preamorphized silicon

High‐dose silicon implants have been used to preamorphize the surface of single‐crystal silicon prior to the implantation of low‐energy BF₂. The preamorphization results in shallow junction formation with minimal channeling of the boron, but high concentrations of electrically active defects are formed, leading to excessive reverse bias leakage currents. Measurements of leakage current and deep‐level defects indicated that two distinct types of electrically active defects were important: those associated with what are probably complexes or clusters of point defects located near the far end of the range of the implanted silicon, and those associated with extended defects (loops) at the edge of the regrown amorphous region. The former defects were deep‐level donors present in high concentrations (>10¹⁷ cm⁻³) after regrowth of the amorphous layer at 600 or 700 °C and resulted in leakage currents >10⁻⁴ A/cm². These centers could be annealed out at 800 °C reducing the leakage current to values between 5×10⁻⁸ and 2×10⁻⁵ A/cm² depending upon the relative locations of the extended defects and the metallurgical junction. Measurements and modeling have shown that the location of the band of extended defects is critical in controlling the leakage current and that it will need to be a few hundred angstroms shallower than the junction itself for the associated generation current to be fully suppressed.