About the role of the various types of secondary electrons (SE1; SE2; SE3) on the performance of LVSEM

The relative weight, δΒ, of the yield of secondary electrons, SE2, induced by the backscattered electrons, BSE, with respect to that, δP, of secondary electrons, SE1, induced by the primary electrons, PE, is deduced from simple theoretical considerations. At primary energies E0 larger than EM (where the total SE yield δ = δP + δB is maximum), the dominant role of the backscattering events is established. It is illustrated in SEM by a direct comparison of the contrast between SE images and BSE images obtained at E0 ∼ 5 keV and E0 ∼ 15 keV on a stratified specimen. At energies E0 less than EM, the dominant role of SE1 electrons with respect to SE2 (and SE3) is established. It is illustrated by the better practical resolution of diamond images obtained with an in‐lens detection in low voltage SEM E0 ∼ 0.2–1 keV range compared with that obtained with a lateral detector. The present contribution illustrates the improved performance of LVSEM in terms of contrast and of practical resolution as well as the importance of variable voltage methods for subsurface imaging. The common opinion that the practical lateral resolution is given by the incident spot diameter is also reconsidered in LVSEM.