A much higher leakage current, a lower breakdown effective field, a poorer charge-to-breakdown, and worse stress-induced leakage current are observed in ultrathin 30 Angstrom oxides even at a low Cu contamination of 10 ppb. The strong degradation of the ultrathin gate oxide integrity can be explained by the tunneling barrier lowering and the increased interface trap tunneling due to the presence of Cu in the oxide and at the oxide-Si interface.