Rapid thermal oxidation of silicon in N2O between 800 and 1200 °C: Incorporated nitrogen and interfacial roughness

Abstract

Oxynitrides can suppress the diffusion of boron from the polycrystalline silicon gate electrode to the channel region of an ultralarge scale integrated device, and are therefore important potential substrates for thin SiO₂ gates. Direct oxynitridation of Si in N₂O is a simple and manufacturable N incorporation scheme. We have used rapid thermal oxidation to grow O₂‐ and N₂O‐oxides of technological importance (∼10 nm thick) in the temperature range 800–1200 °C. Accurate measurements of the N content of the N₂O‐oxides were made using nuclear reaction analysis. N content increases linearly with oxidation temperature, but is in general small. A 1000 °C N₂O‐oxide contains about 7×10¹⁴ N/cm², or the equivalent of about one monolayer of N on Si (100). Nonetheless, this small amount of N can retard boron penetration through the dielectric by two orders of magnitude as compared to O₂‐oxides. The N is contained in a Si‐O‐N phase within about 1.5 nm of the Si/SiO₂ interface, and can be pushed away from the interface by O₂‐reoxidation. We have measured Si/SiO₂ interfacial roughness by x‐ray reflectometry, and found that it decreases with increasing oxidation temperature for both O₂‐ and N₂O‐oxides, although the N₂O‐oxides are smoother. The enhanced smoothness of N₂O‐oxides is greater the greater the N content. N₂O‐oxides are promising candidates for thin ultralarge scale integrated circuit gate dielectrics.