Iron Precipitates in Si Integrated Circuits

Iron is a major contaminant in integrated circuits because there is a lot of steel in contact with the wafers or with materials needed to process a wafer.
Iron atoms diffuse as interstitials; they are rather mobile. Since the solubility at low temperatures is low, there is a strong tendency for agglomeration. The small iron silicide precipitates in turn serve as nucleation centers for large defects, especially the huge oxidation induced stacking faults.
An iron concentration of well below 1 ppb thus may enough to kill all integrated circuits in the thus "contaminated" part of a wafer.
FeSi precipitates
The defects shown are almost certainly FeSi2 precipitates, which often occur in "needle-shape". Some stacking fault and dislocation dipole components may also be involved. These needles are already very large; the defects labelled "H" may be a smaller needle.

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go to 6.3.2 Examples and Case Studies for Dislocations

go to 6.3.3 Stacking Faults and Other Defects

go to Impurity Diffusion in Si

go to Oxidation Induced Stacking Faults in Silicon

© H. Föll (Defects - Script)