Efficient Neutron Irradiation Procedure for Uniform Dopant Distributions in Silicon Doping

Neutron transmutation doping (NTD) is one of the several techniques used for n-type doping with good homogeneity. NTD performances were investigated in this work within a project funded by the Academy of Scientific Research and Technology (ASRT), Egypt, for the "production of doped Silicon Wafers for Solar Panels and Basic Electronics," 2015-2018. The Egypt second research reactor (ETRR-2) has two irradiation positions for silicon doping using NTD. The two positions can accommodate silicon ingots with large diameters up to six inches. One crucial parameter that affects the quality of the product is the distribution of the dopant in the irradiated ingot. The irradiation facility provides the option of rotating the sample during irradiation for flattening the radial distribution of the dopant. Since the neutron flux is not flat along the irradiation position due to leakage and the effect of control rods, the generated dopant will be not flat along the axial direction. To overcome this problem, this paper proposed an irradiation procedure to smooth the dopant distribution along the axial direction. Such procedure can be applied for NTD facilities that has not an acceptable axial neutron flux distribution in silicon doping process. The procedure is based on loading the irradiation position by two ingots staked end to end and, at the middle of the irradiation duration, the two ingots swap their places. This strategy was verified by MCNP5 calculations and experimentally.