Prediction and limitation of polymer degradation in Environmental SEM

Polymer materials degradation is a well-known limitation to their characterization in SEM. In this paper authors present an additional possibility for polymer imaging offered by the Environmental SEM applied to the PMMA with micrometric relief. As shown by the so-called double-scan procedure, increasing the pressure enables to delay the degradation of the polymer surface. To evaluate quantitatively this observation, the classical formula to calculate the electron dose is adapted to ESEM characteristic. It is shown first that pressure enables to decrease the electron dose and all that takes place as if the skirt electrons do not participate in the irradiation. Secondly this procedure allows to obtain the critical dose of topographic degradation, applied to the PMMA with micrometric relief DC was found to be 1.31±0.28 C m−2. Finally it becomes then possible, knowing the DC for a given sample, to evaluate the limit of investigation without topographic surface degradation: for example, the maximal field of view (linked to the magnification) depending on the other parameters.