sed on dry oxide. At that point, it might be noted that in fig. 61 the slope seems to be influenced by the entire process, SO that it is likely that this simple parameter could depend also on many other features related to the process sequences. On a macroscopic scale, implied intrinsic properties are the mechanical constant (rheological) of SiO2 and Si (coefficients of dilatation, elastic modules of Young and Poisson, viscosity of SiO2). On the microscopic scale, the consequence of stress fields and flows have to be the generation of defects and strained bonds in the silica and at interface, which would be only partially annealed during the processing. Despite the ability of these theories of the 70s and 80s to explain remarkably well the range of value of the threshold in the temperature and the activation energy, they fundamentally fail to describe the involved microscopic mechanisms at the level of atomic bonds. Another reasoning has therefore been researched by authors in the last 10 years [Warr-94, Devi-95, (and Mathiot), Flam-95, Kak-89], based on the contrary on microscopic mechanisms of chemical nature such as the diffusion and the solubility of oxygen in the silicon. 6.4.2. INTERPRETATION IN TERM OF EXO-DIFFUSION OF OXYGEN Observe first of all that the layer of silicon oxide is confined between two layers of Si (substrate or polysilicon gate). This model is based on the observation that the solubility limit of oxygen interstitials at elevated temperature is not negligible: (102) [0]" =1.53102 -1.03 eV / kT) and therefore, an effect of "gettering" can exist due to Fick's law of diffusion for oxygen surface concentration at the Si/SiO2 interface. Silicon substrate being very thick, a certain amount of III-74 oxygen can penetrate more or less deeply into it, basically leaving oxygen vacancies in the oxide in a quantity determined by the temperature and the duration of the anneal. This should result in the build-up of oxygen vacancies on the silicon dioxide side of the interface, which are one of the defect