Applications of Photoluminescence Imaging to Dopant and Carrier Concentration Measurements of Silicon Wafers

Abstract

Abstract-Photoluminescence-based imaging is most commonly used to measure the excess minority carrier density and its corresponding lifetime. By using appropriate surface treatments, this high-resolution imaging technique can also be used for majority carrier concentration determination. The mechanism involves effectively pinning the minority excess carrier density, resulting in a dependence of the photoluminescence intensity on only the majority carrier density. Three suitable surface preparation methods are introduced in this paper: aluminum sputtering, deionized water etching, and mechanical abrasion. Spatially resolved dopant density images determined using this technique are consistent with the images obtained by a well-established technique based on free carrier infrared emission. Three applications of the technique are also presented in this paper, which include imaging of oxygenrelated thermal donors, radial dopant density analysis, and the study of donor-related recombination active defects. These applications demonstrate the usefulness of the technique in characterizing silicon materials for photovoltaics.

Light-induced activation and deactivation of bulk defects in boron-doped float-zone silicon

“…The observed characteristic pattern of PL intensity exhibits fine striations along the wafer diameter that resemble the oscillations of dopant concentrations observed by Lim et al 23 and similar measurements we have performed. However, the contrasts in PL intensity exceed typical N dop variations and thus indicate that the defect concentration distribution exhibits similar striations.…”

“…7(b) resembles patterns observed in PLbased dopant concentration imaging of FZ wafers (e.g., in Ref. 23). However, the observed distribution cannot be caused by mere doping concentration striations, as proven by two features shown in Figs.…”

“…Therefore, we conclude that the concentration N t of activated or formed defects responsible for the observed LID is not radially homogeneous but shows fine striations in a characteristic pattern. The fascinating resemblance of this defect distribution pattern to the doping striations found by Lim et al 23 indicates that the concentration of the defect in question is related either to quantities affected by the same mechanism causing dopant concentration striations or to doping concentration itself. In the latter case, the observed DI PL could be a superposition of DN dop and DN t .…”

“…In numbers, e.g., observed striations in I PL of 5% would require variations of N dop of 6.5%, whereas 4.0% variation in s eff could cause the same effect. Radial doping concentration variations in p-type FZ material are rather in a <5% range, 23 and thus the observed PL intensity variations of up to 10% are unlikely to be caused purely by doping variation. (2) As shown in Fig.…”

Quantitative Surface Recombination Imaging of Single Side Processed Silicon Wafers Obtained by Photoluminescence Modeling

“…Extending on previous work [19,20], we use a highly recombining rear surface, which is both low-effort to experimentally realize (bare / metalized) [21] and provides a well-defined boundary condition to facilitate accurate modeling. The high rear-surface recombination rate leads to a strong asymmetry in the carrier profile, which makes the PL signal less sensitive to bulk recombination and reduces the effective diffusion length.…”