Industrial Czochralski n-type Silicon Wafers: Gettering Effectiveness and Possible Bulk Limiting Defects

An assessment of the bulk material quality of industrial Czochralski (Cz) grown phosphorus-doped n-type silicon (Si) wafers along an ingot is reported. The minority charge carrier lifetimes of the Cz-Si wafer bulk before and after phosphorous (POCl₃) diffusion gettering are assessed, by applying room-temperature superacid surface passivation to avoid any additional gettering or hydrogenation effect. A substantial increase in the bulk lifetime of all of the n-type Cz-Si wafers along the ingot is observed, indicating the effectiveness of a gettering step for such wafers and the presence of getterable metallic impurities in these wafers. By experimentally monitoring the lifetime changes upon a gettering anneal and simulating the gettering kinetics based on different metal diffusivities, iron is identified to be a limiting defect, at least for the wafers from the tail part of the ingot. A dissolved iron concentration of (8±2) x 10¹¹cm^-3 is estimated from the bulk lifetimes of the tail wafers. This lifetime kinetics approach is also a demonstration of a new method to identify iron, or other getterable metals with moderate diffusivities such as chromium, in n-type silicon wafers.