Diffusion length mapping

Fig. 10.5 Diffusion length maps characteristic of certain sources of contamination. Each dot corresponds to one measurement, with dark regions representing areas of high diffusion length, (a) Concentric rings indicate oxygen precipitates caused by a high oxygen level...

Defects in a SCR, which is present under reverse bias, can be tested in a similar way. Figure 10.6 c shows the same wafer as in Fig. 10.6 e after removal of the oxide and under cathodic polarization in the dark. Hydrogen bubbles caused by the dark current now decorate nickel silicide precipitates that short-circuit the SCR. Nickel precipitates are known to increase the dark current of a p-type Si electrode under reverse bias by orders of magnitude [Wa4]. If the bias is increased the copper silicide precipitates also become visible, as shown in Fig. 10.6 d. This method, like defect etching (Fig. 10.4f), is only sensitive to precipitated metals. Metals that stay in solution, like iron, do not show up in defect mapping and have to be determined by other methods, for example diffusion length mapping. 

Upper left Electrolytic double cell for diffusion length mapping of 200 mm silicon wafers using the ELYMAT technique, as discussed in Section 10.3. After [21]. 

V. Lehmann and H. Foil, Minority carrier diffusion length mapping in silicon wafers using a Si-electrolyte-contact, I. Electrochem. Soc. 135, 2831, 1988. 

Engelter, S., et al.. Infarct volume on apparent diffusion coefficient maps correlates with length of stay and outcome after middle cerebral artery stroke. Cerebrovasc Dis, 2003. 15(3) p. 188-91. 

Fig. 1. The MR Toolkit MR techniques yield infonnation about chemical and physical processes over length scales of A to cm. Imaging pulse sequences may be integrated with spectroscopy and molecular diffusion measurements providing maps of chemical composition and molecular transport phenomena at spatial resolutions of 30-500 pm.

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