An experimental study of SiOxNy/Si interfaces prepared by rapid thermal processing evidence for two groups of interface states

Abstract

Three types of MIS capacitors are prepared by rapid thermal processing of n-Si: rapid thermal oxidation (RTO), rapid thermal oxidation followed by rapid thermal nitridation (RTN) in N2O, and rapid thermal oxynitridation in N2O (RTON) at temperatures of 1100 to 1150°C. The resulting densities of interface states above the midgap are reconstructed from measurements of charge transient spectroscopy (QDLTS) and the feedback charge C–V method (FCM) of Mego. The midgap-level density is assessed from quasistatic C–V measurements, while the related surface generation velocities can be deduced from the well-known C–t method of Zerbst. The QDLTS and FCM data point to a superior SiOxNy/Si interface quality after the two-step (RTO + RTN) processing. Contrary to this, a minimum density of the midgap levels is found in devices prepared by the RTON procedure. The surface generation velocity of minority carriers (holes) seems to be insensitive to the type of processing, being in the 10−4 ms−1 range. The resolved two branches of interface states may be of different origin and are to be treated separately. Finally, in the samples prepared by the RTON a discrete trap level at Ec – Et ≈︁ 0.34 eV with a capture cross section of 1.6 × 10−15 cm2 can be resolved, in addition to the two branches of interface states distributed in energy.