Study of the effect of neutron damage on anodic oxidation of monocristalline silicon solar cells for the purpose of determining phosphorus concentration depth profile using neutron activation analysis

Neutron activation analysis for the determination of phosphorus concentration depth profile in monocristalline silicon solar cells, requires known thicknesses of silicon oxide grown on the irradiated silicon sample by anodic oxidation. These are then etched by an HF solution which is measured for the β radioactivity of P32. The thickness of silicon oxide formed by anodic oxidation is known by establishing the linear calibration curve giving the thickness versus the voltage used. Neutron damage on silicon samples modify their resistivity and consequently the thicknesses of silicon oxide formed by anodic oxidation will vary according to the resistivity of irradiated silicon samples. To study this effect, samples were irradiated at different neutron doses in a 1 MW nuclear research reactor at a position where the thermal neutron flux is in the order of 1013 n cm−2 s−1. For each dose, the resistivity of the irradiated silicon samples was measured using the four points probe method; for the doses considered a linear relationship between neutron dose and resistivity has been observed. The samples where then treated by anodic oxidisation to establish the calibration curve (thickness of silicon oxide versus voltage) for each dose and the thicknesses were measured by Rutherford backscattering with a Van de Graaf accelerator and α particles of 2 MeV. Finally, the oxide growing rate (Å/V) was determined versus the neutron fast fluence.