Improving Passive Voltage Contrast with Positive Stage Bias in Scanning Electron Microscopy

Passive voltage contrast (PVC) is a method to investigate the surface conductivity of semiconductors using scanning electron microscopy (SEM). When a sample surface is irradiated with primary electrons, a difference in voltage contrast can be observed owing to the electron conductivity of the material. The PVC method is generally used for semiconductor failure analysis. However, it is difficult to determine the optimal conditions necessary for observing PVC, such as the accelerating voltage, probe current, and type of objective lens. This is because the energy cut-off for the secondary electrons indicating PVC was not known thus far. In a recent study, we used an electron energy spectrometer mounted on an Auger electron spectrometer to measure the energy of the secondary electrons indicative of PVC and consequently determined the optimal conditions for PVC imaging of a semiconductor device. We found that high-quality PVC images were obtained for secondary electrons with energies higher than 4 eV. Therefore, in this study, we performed using an SEM with a positive stage bias and a high-efficiency detector consisting of a semi-in-lens objective lens to detect such electrons.