Atomic-layer doping in Si by alternately supplied PH 3 and SiH 4

Abstract

Atomic-layer doping of P in Si epitaxial growth by alternately supplied PH 3 and SiH 4 was investigated using ultraclean low-pressure chemical vapor deposition. Three atomic layers of P adsorbed on Si(100) are formed by PH 3 exposure at a partial pressure of 0.26 Pa at 450°C. By subsequent SiH 4 exposure at 220 Pa at 450°C, Si is epitaxially grown on the P-adsorbed surface. Furthermore, by 12-cycles of exposure to PH 3 at 300–450°C and SiH 4 at 450°C followed by 20-nm thick capping Si deposition, the multi-layer P-doped epitaxial Si films of average P concentrations of ∼10 21 cm −3 are formed. The resistivity of the film is as low as 2.4×10 −4 Ω cm. By annealing the sample at 550°C and above, it is found that the resistivity increases and the surface may become rough, which may be due to formation of SiP precipitates at 550°C and above. These results suggest that the epitaxial growth of very low-resistive Si is achieved only at a very low-temperature such as 450°C.