meter. To explain these phenomena mixing the temperature and the duration of anneals, one has researched key-parameters of the SiO2 material, that would allow us to understand the build-up of defects from the mechanics of layers. The first proposed parameters have been the constants of dilatation, Si and SiO2 elastic modulus and the viscosity of SiO2 [Eern-76]. This is the viscoelastic theory. The observation of effects linked to the thermal processing duration is coherent with characteristic time constants of the SiO2 flow [Eern-76, Lera-89a]. These time constants vary from some tens of seconds to several minutes for temperatures usually employed in anneals. More, the increase of the threshold of temperature observed for the RTA could be explained by the fact that in this case, the duration of anneal can become inferior to the characteristic time of the viscous flow, for temperatures under 975°C. The figure 63 shows the Arrhenius plot of the results obtained in [Flam-95b], compiled with results of [Win-85] and [Lera-89a] (to see also [Schw-88]). III-73 RTA anneal Furnace anneal After Ref. [3] 1000/T (K) Figure 63. Arrhenius plot of VT after 1 Mrad(SiO2), versus the anneal temperature for NMOS transistor [Flam-95b]. We notice that the slope is similar for the three sets of data (nearly 3 eV). This slope, representative of energy of creation of defects is similar and independent of the type of anneals (either furnace or RTA). More, as processing (oxidation ovens, atmospheres of anneal, temperature, thickness of oxide, nature of the gate, etc.) and conditions of anneal (for example duration of the anneal), employed in the 70s [Eern-76], in the 80s [Wino-85] and in the 90s in this study [Flam-95] are very different, this suggests that this energy of creation could be an intrinsic property of the material SiO2, which tends to support the viscoelastic theory. However, it is noticeable that other activation energies (more exactly, enthalpy), has been reported, e.g. 1.5 eV only [Conl-97], but on a very simple process ba