Phosphorus diffusion into silicon after vapor phase surface adsorption of phosphine

Shallow phosphorus doping of silicon was carried out by using a damage-free two-step doping process. Phosphorus was deposited on to the silicon surface by self-limited dissociative adsorption of phosphine from the gas phase. Diffusion and activation of the phosphorus was performed by succeeding conventional rapid thermal lamp annealing in a low pressure oxygen atmosphere. Different deposition and annealing conditions, as well as the influence of the oxide coverage were investigated. The sheet resistance, the oxide thickness, and the phosphorus concentration were analysed by four point probe measurements, ellipsometry, and secondary ion mass spectroscopy (SIMS), respectively. Annealing at different temperatures above 850 °C for 10 s resulted in junction depths of 55 nm to 126 nm with sheet resistances of 1150 to 620 Ω/sq., respectively. The SIMS measurements revealed a Gaussian doping profile and a peak of the phosphorus concentration close to the surface of the as-doped samples while the piled-up phosphorus almost disappeared with the oxide removal in an HF-dip. The trapped phosphorus appeared to be inactive as inferred from comparison of the sheet resistance measurements and calculations of the sheet resistance from the profiles. The phosphorus movement and activation are assumed to be due to detrapping—as it is also observed in the reverse dose loss effect of annealed implanted samples—and oxidation enhanced diffusion.