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Abstract

A process for forming a nitrogen enriched ultra thin gate oxide is described. The nitrogen enrichment increases the dielectric constant of the gate oxide thereby decreasing it's effective oxide thickness. This in turn enhances the performance of MOSFET devices formed thereon. The nitrogen enrichment is accomplished by first enriching the surface of a silicon wafer with nitrogen by implanting nitrogen atoms into the silicon through a sacrificial screen oxide. After fixing the nitrogen by annealing, a nitrogen enriched gate oxide is thermally grown. Additional nitrogen is then infused into the gate oxide by remote plasma nitridation. This two step nitrogen enrichment process increases the dielectric constant of the gate oxide by a significant amount, approaching that of silicon nitride which not only decreases it's effective thickness with respect to gate capacitance, but also lowers device leakage by suppressing hot carrier injection over device drain regions. In addition, because the initial silicon surface is nitrogen rich, the thermal oxidation rate is reduced. The reduction of oxidation rate improves process control by making the oxidation time and temperature more manageable. A further benefit nitrogen of enrichment of the gate oxide is improvement of the durability of the gate oxide when used as an etch stop during polysilicon gate patterning.

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