LOW-TEMPERATURE GROWTH OF SILICON-BORON LAYER AS SOLID DIFFUSION SOURCE FOR POLYSILICON CONTACTED P(+)-N SHALLOW JUNCTION

Abstract

A new material, Si-B, is proposed as a solid diffusion source for fabrication of poly-Si contacted p(+)-n shallow junctions, The junction depth of the Si-B source diode has been measured and compared with that of a BF2+-implanted poly-Si source diode, It was found that the Si-B source diode had a much shallower junction and was less sensitive to thermal budget than the BF2+ source diode, This was attributed to the smaller surface concentration and diffusivity of boron in the silicon in Si-B source diodes. Regarding electrical characteristics of diodes with a junction depth over 500 Angstrom, a forward ideality factor of better than 1.01 over 8 decades and a reverse-current density lower than 0.5 nA/cm(2) at -5 V were obtained, As the junction depth shrank to 300 Angstrom, the ideality factor and reverse current density of diodes increased slightly to 1.05 and 1.16 nA/cm(2), respectively, These results demonstrated that a uniform ultrashallow p(+)-n junction can be obtained by using a thin Si-B layer as a diffusion source.