On the thermal re-oxidation of silicon oxynitride
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E3.17.1
On the thermal re-oxidation of silicon oxynitride Arturo Morales-Acevedo and G. Francisco Pérez-Sánchez Centro de Investigación y de Estudios Avanzados del IPN Electrical Engineering Department Av. IPN No. 2508, 07360 México, D. F. e-mail: [email protected] ABSTRACT We propose a two layer model to describe the growth of silicon oxide (SiO2) during the thermal re-oxidation (O2) of silicon oxynitride (SiOx:N) thin films previously deposited on silicon. Based on this model, the activation energy for the diffusion coefficient of oxygen through the oxynitride layer was determined. The value observed (3.67 eV) is much higher than the activation energy for oxygen diffusion in SiO2 due to the small concentration of nitrogen in the oxynitride film. INTRODUCTION Nitrogen incorporation during the thermal oxynitridation of silicon, either in nitrous oxide (N2O) or nitric oxide (NO) ambient, provide silicon oxynitride (SiOx:N) thin films. In the first case (N2O ambient), the nitrogen concentration is relatively low, of the order of 5×1014 atoms/cm3, which is equivalent to one mono-layer of nitrogen in the SiO2 volume. In addition, it has been observed that nitrogen tends to pile up close to the insulator-silicon interface forming stable silicon-nitrogen bonds that possibly inhibit the diffusion of the oxynitridating species causing a very low growth rate [1-4]. Okada et. al [5] deposited silicon oxyinitrides with different molar concentrations of N2O mixed with Argon, and by Secondary Ion Mass Spectroscopy (SIMS) they determined the nitrogen concentration profiles for each deposition condition. Then, the films were oxidized in O2 at 900º C. They found that the incorporated nitrogen inhibit the oxide growth since a lower growth rate was observed for those layers that contained higher nitrogen concentrations at the oxynitride/silicon interface. The growth rate seems to change inversely with the nitrogen atomic concentration in the oxynitride film. In addition, they showed that oxygen is transported through the oxynitride layer and reacts with silicon at the silicon surface. Further studies have revealed that the nitrogen concentration peak does not stay at the silicon oxynitride interface during the re-oxidation process in O2, but it moves away from this interface while spreading within the layer [6]. Saks et. al. [7], on the other hand, observed a similar motion of the nitrogen peak during the re-oxidation but the height remains unaltered suggesting that nitrogen does not react with oxygen during this process. In this paper we take into account the above observations and establish a simple two layer model in order to describe the growth phenomenology during the re-oxidation of silicon oxynitride films previously deposited on silicon at high temperature in a conventional furnace. With the help of such a model we adjust experimental results in order to determine the activation energy for the diffusion of oxygen through the oxynitride film.
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Fig. 1. Schematics of the System used for the N2O oxid
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