 models have been proposed to explain the generation of interface states: Some authors suggest that hydrogen intervenes in the form of an ion [McLe-80] or neutral atom [Gris-85]. Others [Lai-83] associate this creation as a consequence of the detrapping of holes, which release energy when they reach the Si/SiO2 interface and "plunge" into the silicon valence band. These mechanisms, in principle, have as a common origin the localization of carriers of electronic charge at a chemical bond. This can be understood if one considers that there is a parallel with what can be observed in gases and organic insulators (cf. radiolysis). The role of hydrogen has been suggested by [Reve-77], [Swen-78] and [McLe-80]. The main identified mechanism is the liberation of species linked to hydrogen, such as H° or H+ Such mechanisms have been studied by [Brow-83, Brow-85, Gris-88], and confirmed by more recent authors ([Boes-88] and [Saks-89, Saks-90, Saks-91, Mrst-91, Stah-93]). The figure 67, from [Gris-88], gives a complete picture of the known or suggested electrical and chemical radiation- induced processes in the hydrogen model of interface-trap formation. Based on this picture, data have been interpreted by H+ drift, being the likely rate-limiting step in a two-stage process [Saks- 89]. Based on these results, [Shan-90] proposed a hole-trapping/hydrogen transport (HT)2 model-involving hole trapping and subsequent near-interfacial H+ release, transport, and reaction at the interface-as a possible explanation of Vit buildup in polysilicon- and metal-gate transistors. Anyway, these model are difficult to quantify, because of the difficulty to measure the amount of hydrogen present and the various forms it can take. This, along with the exact model of hydrogen drift or diffusion, is up to now a great obstacle of numerical implementation in codes, whereas the modeling of hole trapping is much more advanced. The concern of modeling in the surface oxide of bipolar transistors may incite evolution in this domain [Witz- 98] (see next 