Diffusion of implanted nitrogen in silicon

Growth of thinner gate oxides and their thickness control is one of many challenges in scaling technologies today. Nitrogen implantation can be used to control gate oxide thicknesses. This article reports a study on the fundamental behavior of nitrogen diffusion in silicon. Nitrogen was implanted as N2+ at a dose of 5×1013 ions/cm2 at 40 and 200 keV through a 50 Å screen oxide into Czochralski silicon wafers. Furnace anneals at a range of temperatures from 650 to 1050 °C have revealed anomalous diffusion behavior. For the 40 keV implants, nitrogen diffuses very rapidly and segregates at the silicon/silicon-oxide interface. Qualitative modeling of this behavior is also discussed in terms of the time taken to create a mobile nitrogen interstitial through the kickout, Frenkel pair, and the dissociative mechanisms.