Background: Line-edge roughness (LER) is often measured from top-down critical dimension scanning electron microscope (CD-SEM) images. The true three-dimensional roughness profile of the sidewall is typically ignored in such analyses. Aim: We study the response of a CD-SEM to sidewall roughness (SWR) by simulation. Approach: We generate random rough lines and spaces, where the SWR is modeled by a known power spectral density. We then obtain corresponding CD-SEM images using a Monte Carlo electron scattering simulator. We find the measured LER from these images and compare it to the known input roughness. Results: For isolated lines, the SEM measures the outermost extrusion of the rough sidewall. The result is that the measured LER is up to a factor of 2 less than the true on-wafer roughness. The effect can be modeled by making a top-down projection of the rough edge. Our model for isolated lines works fairly well for a dense grating of lines and spaces as long as the trench width exceeds the line height. Conclusions: In order to obtain and compare accurate LER values, the projection effect of SWR needs to be taken into account.

中文翻译：

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在扫描电子显微镜图像中了解三维侧壁粗糙度对观察到的线边缘粗糙度的影响

背景：线边缘粗糙度（LER）通常是通过自上而下的临界尺寸扫描电子显微镜（CD-SEM）图像测量的。在这种分析中，通常会忽略侧壁的真实三维粗糙度轮廓。目的：我们通过仿真研究了CD-SEM对侧壁粗糙度（SWR）的响应。方法：我们生成随机的粗线和空格，其中SWR由已知的功率谱密度建模。然后，我们使用蒙特卡洛电子散射模拟器获得相应的CD-SEM图像。我们从这些图像中找到测得的LER，并将其与已知的输入粗糙度进行比较。结果：对于隔离线，SEM会测量粗糙侧壁的最外层挤压。结果是，所测得的LER比晶片上的真实粗糙度小2倍。可以通过对粗糙边缘进行自顶向下的投影来对效果进行建模。只要沟槽的宽度超过线的高度，我们的隔离线模型对于密集的线和空间光栅就可以很好地工作。结论：为了获得和比较准确的LER值，需要考虑SWR的投影效果。