Scanning electron microscopy (SEM) is a practical tool to determine the dimensions of nanometer-scale features. Conventional width measurements use arbitrary criteria, e.g., a 50 % threshold crossing, to assign feature boundaries in the measured SEM intensity profile. To estimate the errors associated with such a procedure, we have simulated secondary electron signals from a suite of line shapes consisting of 30 nm tall silicon lines with varying width, sidewall angle, and corner rounding. Four different inelastic scattering models were employed in Monte Carlo simulations of electron transport to compute secondary electron image intensity profiles for each of the shapes. The 4 models were combinations of dielectric function theory with either the single-pole approximation (SPA) or the full Penn algorithm (FPA), and either with or without Auger electron emission. Feature widths were determined either by the conventional threshold method or by the model-based library (MBL) method, which is a fit of the simulated profiles to the reference model (FPA + Auger). On the basis of these comparisons we estimate the error in the measured width of such features by the conventional procedure to be as much as several nanometers. A 1 nm difference in the size of, e.g., a nominally 10 nm transistor gate would substantially alter its electronic properties. Thus, the conventional measurements do not meet the contemporary requirements of the semiconductor industry. In contrast, MBL measurements employing models with varying accuracy differed one from another by less than 1 nm. Thus, a MBL measurement is preferable in the nanoscale domain.

中文翻译：

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通过扫描电子显微镜轮廓对图案线宽度进行传统测量与基于模型的测量


扫描电子显微镜 (SEM) 是确定纳米级特征尺寸的实用工具。传统的宽度测量使用任意标准，例如50%阈值交叉，以在测量的SEM强度分布中分配特征边界。为了估计与此类过程相关的误差，我们模拟了来自一组线形状的二次电子信号，这些线形状由具有不同宽度、侧壁角度和圆角的 30 nm 高硅线组成。在电子传输的蒙特卡罗模拟中采用了四种不同的非弹性散射模型来计算每种形状的二次电子图像强度分布。这 4 个模型是介电函数理论与单极近似 (SPA) 或完整 Penn 算法 (FPA) 的组合，并且有或没有俄歇电子发射。特征宽度通过传统阈值方法或基于模型的库（MBL）方法确定，该方法是模拟轮廓与参考模型（FPA + Auger）的拟合。根据这些比较，我们估计通过传统程序测量的此类特征的宽度误差高达几纳米。例如，标称 10 nm 晶体管栅极的 1 nm 尺寸差异将显着改变其电子特性。因此，传统的测量方法不能满足当今半导体工业的要求。相比之下，采用不同精度模型的 MBL 测量结果之间的差异不到 1 nm。因此，MBL 测量在纳米级领域是优选的。