METHOD FOR NEUTRON-TRANSMUTATION DOPING OF SILICON Russian patent published in 2002 - IPC

FIELD: electronic and electrical industries; industrial silicon doping in fast reactors for manufacturing semiconductor devices. SUBSTANCE: method includes cyclic irradiation of container holding silicon ingot with pulsating neutron flux delivered at definite time intervals between pulses (so-called dose-and-time schedule) in nuclear reactor channel with originally known and varying with time distribution of neutron flux density through height, check-up of neutron fluence in container averaged through ingot length; novelty is disposition of several check silicon disks in container, periodic interruption of irradiation process, removal of container, annealing of check disks, and measurement of electrophysical parameters of one of them. Irradiation and measurements are repeated until desired electrophysical parameters of silicon are attained; next irradiation time is found from formula t_act = (t₁+t_i); t_i = 0.7t_o - first irradiation cycle; t_i = (f_o-f_i)/ϕ_t(ir) - next irradiation cycles, where t_act is actual irradiation time of silicon ingots in cyclic irradiation, s; t₁ is irradiation time of silicon ingots during first irradiation cycle, s; t_i is irradiation time of silicon ingots during i-th irradiation cycle, s; t₀ is theoretically calculated irradiation time of silicon ingots to build up design fluence, s; f_o is design irradiation fluence to attain desired electrophysical parameters of silicon, cm^-2; f_i is fluence built up by silicon ingots during i-th irradiation cycle, cm^-2; f_t(ir) is thermal neutron flux density as measured prior to initiating neutron irradiation of silicon and used for calculating t_o(n/cm²s^-1). Proposed method for producing phosphate- doped single-crystalline silicon improves quality of silicon radiation- doped to low resistivity ratings, that is, to reduced spread in its resistivity and provides for retaining single-crystalline structure of ingot. EFFECT: reduced internal mechanical stresses and enhanced lifetime at majority charge carriers. 2 cl, 2 dwg, 2 tbl