SHALLOW BORON JUNCTIONS AND PREAMORPHIZATION FOR DEEP SUBMICRON SILICON TECHNOLOGY

In this study, shallow p+-n junction diodes were formed by implanting BF2+ ions into single-crystal silicon or silicon preamorphized by eith er Si or Ge implantation. BF2+ implantation at energies of 20 or 25 ke V and a dose of 1 X 10(15) cm-2 was followed by furnace annealing at 6 00-degrees-C in nitrogen ambient. Most samples received a further nitr ogen-ambient anneal at 850-degrees-C, with various periods of time. Se condary ion mass spectroscopy was used to measure the B profiles. Cros s-sectional transmission electron microscopy was used to study the amo rphous layers and the defects remaining after annealing. Electrical ch aracterization of the diodes is described. In preamorphized samples, t he residual defect density decreases, and the defect band located at t he original amorphous-crystalline interface becomes sharper, as the ma ss of the amorphizing ion species is increased. Ideal low-leakage shal low junctions can be made following either Si or Ge preamorphization a nd furnace annealing, without removing all the defects induced by prea morphization. This is achieved by containing the implanted B profile c ompletely within the amorphous layer, and by containing the defect ban d completely within the final biased junction. However, even without a preamorphization step, ideal low-leakage shallow junctions were obtai ned after BF2+ implantation and 600-degrees-C furnace annealing. This suggests that preamorphization may not ultimately be needed for practi cal engineering of shallow junctions.