Wafer warpage behavior during a local oxidation of silicon isolation process was investigated. Anisotropic etching of the front side nitride produced unbalanced stress states between front and back side nitride films, and caused a large wafer warpage. The maximum warpage was observed after field oxidation due to a wedge-effect of field oxide on the front side. Plastic deformation was shown to occur when the maximum warpage after field oxidation exceeded a critical value, although the warpage dramatically decreased after nitride stripping.
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