Optimization of advanced PMOS junctions using Ge, B and F co-implants

Abstract

The main challenges for PMOS ultra shallow junction formation remain the transient enhanced diffusion (TED) and the solid solubility limit of boron in silicon. It has been demonstrated that low energy boron implantation and spike annealing are key in meeting the 90nm technology node ITRS requirements. To meet the 65nm technology requirements many studies have used fluorine co-implantation with boron and Si+ or Ge+ pre-amorphization (PAI) and spike annealing. Although using BF2+ can be attractive for its high throughput, self-amorphization and the presence of fluorine, many studies have shown that the fluorine successfully reduce TED, its energy needs to be well optimized with respect to the boron’s, therefore BF2+ does not present the right fluorine/boron energy ratio for the optimum junction formation. In this work we optimize the fluorine energy for boron energies down to 200eV. We show the dependence of optimized junction on Ge+ energies of 2keV and 20keV. We also demonstrate that the fluorine dose needs to be carefully optimized, otherwise a reverse effect can be observed.