Local field effects on voltage contrast in the scanning electron microscope

Abstract

The local field effects on voltage contrast in the scanning electron microscope (SEM) mean that local fields generated by a non-uniform potential distribution on specimen surface cause a variation in the secondary electron (SE) detector current. It causes some errors in the voltage measurement. The authors present a theory to calculate the SE detector current in the presence of the local fields. In the calculation, they assume that the field distribution above the specimen surface (metal electrodes with 8 mu m width and 12 mu m separation) is two-dimensional. Analysed models are a conventional SEM detector system (model A), a retarding-field energy analyser with an extraction field (model B) and a high-resolution energy analyser with an extraction field (model C). The results show that the local field effects could not be neglected even in models B and C with strong extraction fields. The calculated values of local field effects in models A and B agree well with the experimental ones. The dependence of local field effects on the electrode geometry is equivalent to that on the extraction field, though this dependency is not so strong.

Quantitative secondary electron energy filtering in a scanning electron microscope and its applications

“…Both experimental data and theoretical models exist in the literature [14,15]. A numerical fit to the experimental SE energy distribution measured by Kollath [14] for several metals was approximated to be…”

“…2). A plot of W versus y, otherwise known as the acceptance diagram, can be used to illustrate the area of the acceptable parameters (W, y) and thus the detector response [15] as shown schematically in Fig. 5…”

Feasibility study of the application of voltage contrast to printed circuit board

“…The right electrode (Pin 2) is grounded and the left one (Pin 1) is biased at either À10 or +10 V. The bottom of the PCB board is also grounded, and the inter-line Cu pad is floating. An extraction field of 4 V/mm is applied to the top of the vacuum to simulate the electron detector, as reported by Nakamae et al [5]. The simulation is performed by employing commercially available finite element modeling software ANSYS (version 5.6).…”

“…A number of scientific efforts have been made to improve the quality of the voltage contrast implemented in a SEM, such as floating the ground level of a device [3], using a planar grid retarding field spectrometer [4], etc. It is believed that the local electric field [5,6], passivation [7], and specimen geometry [4,8] will affect the observation of voltage contrast.…”

Carbon Nanotube Electron Sources: From Electron Beams to Energy Conversion and Optophononics

“…The combined effect of secondary and field-emission is also possible through electron-stimulated field-emission [32,33], where electrons strike the tip of a nanoscale emitter under a strong applied field, leading to highly enhanced emission of further electrons. An applied electric field can also affect the emission and trajectories of secondary electrons emitted from a cathode, enabling voltage-contrast imaging in electron microscopy [34][35][36]. Finally, it is only natural to expect that more than two stimuli can also be employed, as in combining several of field, light, heat, and primary energetic particles all at once, to induce electron emission.…”