Examination of impurities in ISE SOI material

Summary form only given. The detection of impurities in isolated silicon epitaxy (ISE) SOI material has reached the resolution limit of most conventional techniques. This is illustrated by EDS and secondary ion mass spectroscopy (SIMS) spectra which show transition-metal impurities and shallow-level impurities to be generally less than 10¹⁶/cm³. Heavy-ion backscattering spectroscopy (HIBS) is a sensitive technique which can be used to determine the type and concentration of remaining impurities. The technique has been applied to several substrate sources, the initial insulating layer, the polysilicon layer, the capping layer, and a complete ISE SOI structure which has been recrystallized. Results show that the pre-ISE SOI polysilicon layer is extremely pure. The recrystallized layers also remain very pure, with trace levels of impurity less than 10¹¹/cm² in the isolated silicon layer after ISE processing. The effect of various substrate types and substrate cleaning on the ultimate ISE purity is examined, and further improvement of the latter in ISE SOI is expected