扫描电镜样品表面残留电位均匀化的机理研究/Mechanism Study of Surface-Potential Initialization for a S

2018-09-04 05:45:54

表面 potential surface 电位 SEM



扫描电子显微镜(SEM)样品受到电子束照射后,其表面由于电荷积累产生分布不均匀的残留电位。残留电位影响二次电子产生的信号从而干扰电位衬度和带电衬度,甚至引起异常衬度效应,降低了SEM的观测精度。因此,去除积累电荷、消除表面残留电位对于样品的重复观测和带电衬度的研究有着重要的意义。本文在分析了残留电位对SEM衬度的影响后,针对利用低电压电子束持续扫描照射使表面电位均匀化的实验结果,建立了表面电位随电子束扫描时电荷在样品表面附近积累而变化的模型,并对其表面电位均匀化工作机理进行了数值模拟。结果表明,在不同表面电位条件下出射二次电子返回表面的比例不同是引起表面电位均匀化的主要因素;一次电子、返回表面的二次电子和空穴三者的共同作用使得在低于平衡电位的区域空穴被积累而电位上升,在高于平衡电位的区域电子被积累而电位下降;表面电荷差异因而逐渐减小,表面电位趋向于均匀的正平衡电位。

The charge accumulation near the sample surface will produce remained non-uniform potential after e-beam irradiation in a SEM.
This remained potential can disturb the voltage and charging
contrast and even cause the abnormal contrast. Therefore, it is important for the reproducible observation and study of charging contrast to initialize the surface potential, i.e. erase the accumulated charge. The influence of the remained potential on
SEM image contrast is analyzed firstly. For the experimental results of initializing the remained potential by low voltage e-beam scanning, a numerical model is built to calculate the surface potential varying with the charge accumulation near the insulator surface during the scanning irradiation process. The computed results show the proportion of the secondary electrons returning to the surface changes with the surface potential. The potential rises at the area in which the remained potential is less than the steady-state voltage and
decreases at the higher potential area because of the effect of the primary electrons, secondary electrons that returned to the surface and the holes. The differences of the surface potentials are lowered with the scanning time and the surface-potential initialization can
be realized.