Dual gate oxide integrity improvement by implementing nitrogen implantation technology

Dual gate oxide layers were implemented in 0.15 μm Mask ROM device. Two predominant approaches were carried out to achieve a combination of thin and thick gate oxides. One was the conventional, growth-etching-growth, process and another one was oxidation on wafers with pre-gate-oxide nitrogen implantation. The retardation rate of oxidation was dependent on the nitrogen implant dosage but independent on implant energy. For thin gate oxide, device performance by using nitrogen implantation prior to gate oxide demonstrated better thickness uniformity and breakdown voltage than that by using conventional approach. Furthermore, directly formed thick gate oxide achieved better thickness uniformity and breakdown voltage than that of the grow-etching-grow process.