LPIO (EA 3254), Faculté des Sciences de Nantes, 2 rue de la Houssinière, 44322 Nantes Cedex 03, France
CEA, Le Ripault, BP 16, 37260 Monts, France
The scanning electron microscope mirror (SEMM) method is considered as a suitable approach for the characterisation of the charge trapping ability of insulators. However, the interpretation of the experimental results is far from being obvious. The aim of this paper is to give some new insights in this problem. Our description of the mirror plots is conventionally based on a multipole analysis of the charge distribution and on the radius of curvature approximation. This approach indicates that the trend of the plots is mainly controlled by the quadrupole contribution. This clearly illustrates the non- uniqueness of the interpretation since different trapped charge distributions, but with nearly equal quadrupole terms, can produce rather similar mirror plots. To make the problem unambiguous, a semi-ellipsoidal shell model is used to account for the implanted space charge. Within this model, we propose a simple method to get the mean density of trapped charge ρ 0. Our Monte Carlo simulations of the charge implantation phase show that ρ 0 can strongly differ from the density of traps N T. The reasons for these deviations are discussed for a significant set of values of N T and of the primary energy E p.
(Received June 3 2002)
(Accepted July 31 2002)
(Online publication October 1 2002)