How far will metallic impurities diffuse (in silicon) during oxidation? More spe

Question

How far will metallic impurities diffuse (in silicon) during oxidation? More specifically, estimate the distance iron (Fe) and aluminum (Al) atoms would diffuse for a 1000 °C oxidation for one hour.

Use equation x = 2Dt your estimate.

Some diffusivity data of various impurities in silicon are shown

1x10 Co Fe Na He cr K. Li Cu 1x10 1x10 Au Pt 1x10 Ag o 1x10 C 3 1x10 13 F Sb- As 1x10 15 Sn 1x10 Ge 1x10 19 1x10 1x10 3 1x10 600 700 800 900 1,000 1,100 1,200 1,300 Temperature (c) Figure 1.23: Diffusivities of selected impurities in silicon versus temperature

Explanation / Answer

From the given graph, at 100oC

D=10-6 for Fe atom

D=10-12 for Al atom

distance Fe=2(Dt)1/2=2(10-6*60*60)1/2=0.12 cm

distance Al=2(10-12*60*60)1/2=12*10-5 cm

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