Cathodoluminescence spectroscopy of nitrided SiO2–Si interfaces

Abstract

We use cathodoluminescence spectroscopy (CLS) to investigate the electronic states of ultrathin gate dielectrics with nitrided SiO2–Si interfaces, known to improve reliability in advanced complementary metal–oxide–semiconductor devices. The 5 nm thick films investigated were: (i) as-deposited (at 300 °C) structures, (ii) 400 °C hydrogen anneal, (iii) 900 °C rapid thermal anneal (RTA), and (iv) a combination of both anneals. CLS emission energies and intensities versus excitation energy were essentially unchanged for the as-deposited interface compared to non-nitrided plasma-processed interfaces. In the near-infrared, features appear at 0.8 and 1.0 eV, with the 1.0 eV peak Si substrate intensity increasing with increasing depth. From depth variation measurements at higher photon energy, a 3.4 eV peak is also shown to arise from the Si substrate, and a 2.7 eV feature is shown to come from the interface region. After hydrogenation, the CLS is essentially the same as for non-nitrided interfaces, except for an increase in the relative intensity of a broad background luminescence ranging from 1.5 to 2.5 eV. However, the RTA and the combination of the RTA and hydrogenation do not completely suppress emission near 2.0 eV feature as for non-nitrided interfaces. From the behavior of the CLS features, we are able to clearly distinguish between interfacial defects and substrate features, which are significantly reduced by the combined RTA/hydrogen anneal, and features that are not reduced by the annealing procedures.