Study on Thermal Effect on the SEM Contrast of a Nanorod in a Fast Scanning Mode

Abstract

Modern scanning electron imaging (SEM) frequently adopts the multi-frame stacking technique to minimize the vibration and drift but ignores the electron beam-induced thermal effect (called thermal effect hereafter for short) during the stacking. This study investigates the thermal effect on SEM contrast in multi-frame stacking mode for two systems, namely one gold nanorod (Au-NR) and one silicon nanorod (Si-NR) on a Si substrate through a Monte-Carlo approach (In short, Au/Si and Si/Si systems). The primary focus of this investigation was to explore the correlation between two distinct types of signals, namely secondary electrons (SE) and backscattering electrons (BSE), in relation to the number of frames. It was observed that the SEM contrast exhibited sensitivity to the frame. The stacking process generally led to a reduction in SE contrast and an increase in BSE contrast compared to the scenario without thermal effects. This is attributed to higher heat accumulation within the solid as more frames are stacked, resulting in electrons from NRs acquiring extra energy and consequently causing a deep penetration depth that inhibits most SEs from being emitted. However, it helps BSEs to emit because there is more conversion of low-energy Ses into BSE signals with assistance from the extra energy. Furthermore, it was found that the thermal effect had less impact on cases involving a large primary electron (PE) beam energy. This is mainly because the larger initial energy causes the smaller relative variation in electron energy. Details of the explanation of the mechanism behind these results were given systematically by the electron-solid interaction theory. This study advances our comprehension and clarification of the physical mechanism underlying electron-beam-induced deposition, thereby enhancing process control, performance, and reliability.