Charge Modeling for Metal Layer on Insulating Substrate

Abstract

A charging model for magnification variation in the observation of a metal pattern on an insulating substrate using a scanning electron microscope is proposed. To calculate the time evolution of charging, we replace electron trajectory with current. Negative charging of the metal layer is observed and is caused by the current from the anode, which is set above the sample, to the metal layer. The origin of the current is tertiary electrons produced by backscattered electrons colliding with the anode. By controlling tertiary-electron trajectories through the application of bias voltage to the anode, the magnification variation can be reduced to almost zero.

A systematic investigation of the charging effect in scanning electron microscopy for metal nanostructures on insulating substrates

“…The build‐up of negative charge in the sample is seen as a systematic shrinkage effect, manifesting itself as a demagnified image (Okai et al ., ). Positive sample charging would result in an overmagnified image, evident as an ‘expansion effect’.…”

“…The primary electrons and emitted SEs are deflected causing magnification variations, image drift and abnormal contrast (Cazaux, ; Jbara et al ., ; Fakhfakh et al ., ; Okai et al ., ; Okai & Sohda, ). Trapped primary electrons contribute to negative charging, whereas the emission of SEs and BSEs give rise to positive charging of the sample (Cazaux, ).…”

“…The characterization of insulating materials is a well‐known challenge in SEM (Cazaux, ; Joy & Joy, ; Thong et al ., ; Ose et al ., ; Goldstein et al ., ; Okai et al ., ; Okai & Sohda, ). Insulating samples do not provide a path to ground and therefore accumulate charge.…”

“…Insulating samples do not provide a path to ground and therefore accumulate charge. As a result of the accumulated charge, the path of the incident and emitted electrons are deflected, evident as image distortions (Jbara et al ., ; Okai et al ., ; Okai & Sohda, ).…”

Study on Image Drift Induced by Charging during Observation by Scanning Electron Microscope

“…Since these phenomena degrade the accuracy of SEM observation, they have been extensively studied by experiment and simulation. [1][2][3][4][5][6][7][8][9] Image-contrast variation is caused by a change in the efficiency of detecting emitted electrons during observation owing to the sample charging. It has been observed when a metal-insulator mixed sample [1][2][3] or SiO 2 lines on silicon 4,5) is inspected.…”