High-temperature phosphorus ion doping of silicon

Abstract

P + 100 keV ions have been implanted into p-Si (100) at target temperatures T i = 600–1100 ° C. The properties of doped layers were studied by Hall measurements and SIMS. The electrical activation of phosphorus has been shown to occur mainly in the 700–900 ° C temperature region coinciding with activation temperatures during post-implantation anneal of nonamorphized silicon layers. At T i = 900 ° C the concentration of free electrons increases linearly with dose up to φ ≃ 10 15 cm −2, and then saturates at a level one order of magnitude lower than the phosphorus solubility limit. Additional anneals at 1000 ° C and SIMS measurements did not reveal nonactive phosphorus in layers at T i ⩾ 900 ° C. It has been found that the highest level of doping is determined by the radiation-enhanced diffusion of phosphorus to the surface followed by its evaporation into vacuum. Radiation-enhanced diffusion is shown to exhibit itself at T i ⩾ 750 ° C (for T i< 750 ° C the deep penetration of phosphorus is due to channeling) and to remain, unlike proton enhancement, a temperature dependent function at T i > 800 ° C. The temperature dependence has been explained by the anneal of stable defects introduced by relatively heavy P + ions. The diffusion coefficient of phosphorus has been found to exhibit a reciprocal temperature dependence with 900 < T i < 1100 ° C range due to the lifetime decrease of diffusion enhancing excess point defects.