|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.
|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.
6.3.2 Examples and Case Studies for Dislocations
6.3.3 Stacking Faults and Other Defects
Impurity Diffusion in Si
Oxidation Induced Stacking Faults in Silicon
© H. Föll (Defects - Script)