 precursors related to positive trapped charge [Lena-83], [Chu-90], [Devi-94], [Pail95-c]. If we consider this mechanism, the simplest resolution of Fick's equation allows us to calculate the profile of O interstitials in the silicon substrate: (103) where: X is the abscissa in silicon taken from the Si/SiO2 interface t is the anneal time (in this simple model, ramping up and down temperature histories are not taken into account) is the concentration of O in the oxide adjacent to the interface ( 5. 1022 cm-3), k being the solubility segregation coefficient derived from (1). Dsj is the diffusion coefficient for O interstitials in Si, modeled as: (104) DSi = 0.17 exp(-2.54eV/kT) In order to evaluate the validity of these assumptions, one must first compare the density of traps revealed by irradiation and the quantity of the out-diffused oxygen. Let Nox be the density of oxygen vacancy in the oxide (cm-2 due to high temperature anneals. Let Voxy be the voltage shift developed at the MOS interface by the "oxygen vacancies", in the case where they were all charged positively: (105) Voxy = - q Nox / Cox The calculated out-diffused concentration of oxygen is shown in fig. 64. Figure 64. Quantity of exo- (10 12 cm 2 Furnace 30min diffused oxygen. RTA 10s Anneal Temperature (C) To that purpose, we have simply strictly followed the calculation process pointed out [Warr-94], but applied to various RTA and furnace anneals conditions. The authors first calculate the out- diffused oxygen profile Nox (cm-3): III-75 (106) where XSiO2 is the abscissa taken from the Si/SiO2 interface, and: (107) Dsi=0.17exp(-2.54eV/kT) (108) Dox=2.6exp(-4.7eV/kT) are the diffusivities (cm².s-1 in silicon and oxide respectively. Then the integration of the profile over XSiO2 gives Nox at a given time. One supposes that cooling down is instantaneous and does not cause oxygen back-diffusion into SiO2. Although the model is simple, this physical process can explain the difference between the two types of annealing. The model accounts for the two exper