The Early Oxynitridation Stages of Hydrogen-Terminated Single-Crystalline Silicon in N 2 O Ambient

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The Early Oxynitridation Stages of Hydrogen-Terminated Single-Crystalline Silicon in N2O Ambient G. F. Cerofolini, M. Camalleri, G. G. Condorelli1, I. L. FragalĂ 1, C. Galati, S. Lorenti, L. Renna, O. Viscuso STMicroelectronics, Stradale Primosole 50, 95100 Catania CT, Italy 1 Department of Chemistry, University of Catania, 95100 Catania CT, Italy ABSTRACT Oxynitridation of hydrogen-terminated silicon with N2O has been studied by x-ray photoemission spectroscopy. Our analysis has given evidence that the broad N(1s) peak at 398.3 eV usually reported in the literature is preceded by the formation of a very narrow peak at 397.3 eV, attributed to the moiety Si3N in which nitrogen is only marginally oxidized, and two other peaks (previously never reported) at 400.0 eV and 401.5 eV, attributed to the moieties Si2NOSi and SiNO, respectively. INTRODUCTION Nitrous oxide N2O has become in recent years a chemical of fundamental importance in integrated-circuit processing. It is used not only as a reactant in chemical-vapor-deposition of SiO2 from SiH4, but also to substitute hydrogen as a passivating agent of Si-SiO2 interface defects (thus improving their stability against degradation under hot-electron bombardment) and as an oxidizing agent for the preparation of thin (1-10 nm thick) SiO2 films. Oxidation Due to its enormous technological relevance, silicon oxidation in O2 has been one of the most studied processes. For sufficiently thick oxides (say, for thickness xox in the 10-102 nm length scale) silicon oxidation kinetics are well described by a linear-parabolic law first proposed by Deal and Grove [1]. When xox is reduced below the 10 nm length scale, the linear-parabolic law no longer describe the oxide growth: for xox > 1 nm the kinetics are adequately describes by a time-logarithm law [2] and the interface does not behave as predicted by the Deal-Grove model [3], while in the subnanometer length scale new phenomena (like layer-by-layer growth [4] or time-logarithm oscillations [5,6]) are observed. The kinetics of silicon oxidation by N2O have been studied by Koyama et al. [7]. They showed that, similarly to what happens in O2 or H2O ambients, the oxidation kinetics in N2O obey a linear-parabolic law. Koyama et al. did not study however the very early stages of oxidation, leaving unexplored the growth kinetics in the region below 3 nm, which seems anyway to be described by a time-logarithm law [8]. Nitridation The nitridation of thermally grown SiO2 has become in recent years a key technological step in flash-memory processing, because of its ability to improve the resistance of the Si-SiO2 interface against hot-electron damage [9]. P6.4.1

According to the nitriding agents (NH3, N2O or NO), reaction conditions, or SiO2 growth conditions, nitridation results in different nitrogen bonding configurations and in-depth concentration profiles. In all cases, however, nitrogen has a distribution covering a narrow region extending from the interface into the SiO2 for 1-2 nm. Extended XPS (x-ray photoemission spectroscopy) ana

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