] in the case of implanted oxides. Only numerical calculation of trapping, self-consistent with the Poisson equation, can adequately describe this second-order effect, and the reader is invited to refer to the section "Numerical Modeling". 3.13. SIMPLE METHOD TO EVALUATE THE HARDNESS FACTOR OF A MOS PROCESS FOR THE TRAPPING OF HOLES The sensitivity of a given oxide + interface system is measured by the fraction of trapped holes as compared to the quantity of holes that have escaped the initial recombination. If one considers only the interfacial trapping, the problem is greatly simplified since it suffices to evaluate the relationship between the quantity of trapped holes (cross-section notions are applicable) and the III-42 quantity of holes that cross the interface by escaping the trapping. The hardening of the oxide consists in this case to reduce this quantity of trapped holes at the interface. 3.13.1. SIMPLIFIED FORMULA the following, assume that the two Vit and Vot components have been separated by one of the standard methods. We make the additional assumptions or requirements: - There is negligible apparent quantity of trapped electrons. - The NMOS transistor is positively biased during irradiation with not too much space charge effect (EGS>1 MV/cm during irradiation, and Vt / tox< 1 V/10nm). The consequence of these on hole trapping effects is the negative drift of MOS threshold voltages. In the low dose regime, we generalize the simple formula we have derived from the uniform and the interface distribution of traps: with: .N trapping coefficient (N = surface density) Xh/tox position of charge distribution centroid 36 V/ / krad(SiO2) or 0.36 V/kA 2 / krad(SiO2) or 36 mV/nm2/Mrad(SiO2) fh(E) = function of charge collection at the trapping location Y(E) = function of non-recombination It can be recalled that this type of analysis has been proposed from 70s by Freeman and Holmes- Siedle (coefficients "F=R.A.D" [Free-78]). It has been extended by [McGa-80] and [Benedetto] (introducing coefficients ft, fy). Th