Very shallow p+-n junctions and subquarter micron gate p-channel MOSFETs

Fabricating shallow p⁺-n junctions by low energy BF₂ implantation, especially using furnace annealing, requires preamorphous implantation of crystalline silicon to eliminate the boron channeling and the suppression of diffusion in heat cycles. A preimplantation technique is presented that uses fluorine to influence the electric characteristics of p-channel MOSFETs. Using heat cycling of 850°C for 10 min, a junction depth of 80 nm and sheet resistance of 400 Ω was achieved. The boron profile after annealing is close to a bell shape, like the profile obtained by boron-only implantation. Lowering preimplantation energy is found to increase the excess vacancy density in the region of high boron concentration and increases diffusion there