Abstract. In the microelectronics industry, most of the dimensional metrology relies on critical dimension (CD) estimation. These measurements are mainly performed by critical dimension scanning electron microscopy, because it is a very fast, mainly nondestructive method and enables direct measurements on wafers. To measure CDs, the distance is estimated between the edges of the observed pattern on an SEM image. As the CD becomes smaller and smaller, the needs for more reliable metrology techniques emerge. In order to obtain more meaningful and reproducible CD measurements regardless of the pattern type (line, space, contact, hole, etc.), one needs to perform a CD measurement at a known and constant height due to a methodology that determines the topographic shape of the pattern from SEM images. An SEM capable of bending the electron beam (up to 12 deg in our case) allows images to be caught at different angles, giving access to more information. From the analysis of such images, pattern height and sidewall angles can be determined using geometric considerations. Understanding interaction between three-dimensional (3-D) shapes, pattern materials, and the electron beam becomes essential to correlate topography information. A preliminary work based on Monte–Carlo simulations was conducted using JMONSEL, a software developed by the National Institute of Standards and Technology. With this analysis, it is possible to determine theoretical trends for different topographies and beam tilt conditions. Due to the effects highlighted by simulations, the processing of the tilted beam SEM images will be presented, as well as the method used to create a mathematical model allowing topographic reconstruction from these images. Finally some reconstruction using this model will be shown and compared to reference measurements. The overall flow used to process images is presented. First, images are transformed into grayscale profiles. After a smoothing procedure, positional descriptors are computed for specific profile derivatives values. Then, from these descriptors coming from two images of the same pattern taken at different tilt angles, we use a low-complexity linear model in order to obtain the geometrical parameters of the structure. This model is created and initially calibrated using JMONSEL simulations and then recalibrated on real silicon patterns. We demonstrate that the use of real SEM images coming from real silicon patterns with our model leads to results that are coherent with conventional 3-D measurements techniques taken as reference. Moreover, we are able to make reliable reconstructions on patterns of various heights with a single calibrated model. Our batch of experiment shows a three-sigma standard deviation of 10 nm on the estimated height for heights ranging from 50 nm to more than 200 nm. Based on simulations, we are able to reconstruct the corner rounding (CR) from SEM images. However, because our wafer has no CR variability, measurements still need to be assessed on real wafer.

中文翻译：

---

倾斜光束扫描电子显微镜，微电子行业的 3-D 计量

摘要。在微电子行业中，大多数尺寸计量依赖于临界尺寸 (CD) 估计。这些测量主要通过临界尺寸扫描电子显微镜进行，因为它是一种非常快速、主要是非破坏性的方法，并且可以对晶圆进行直接测量。为了测量 CD，估计 SEM 图像上观察到的图案边缘之间的距离。随着 CD 变得越来越小，对更可靠的计量技术的需求出现了。为了获得更有意义和可重复的 CD 测量，而不受图案类型（线、空间、接触、孔等）的影响，由于确定地形形状的方法，需要在已知且恒定的高度执行 CD 测量SEM 图像中的图案。能够弯曲电子束（在我们的例子中高达 12 度）的 SEM 允许以不同的角度捕捉图像，从而获得更多信息。通过对此类图像的分析，可以使用几何考虑确定图案高度和侧壁角度。了解三维 (3-D) 形状、图案材料和电子束之间的相互作用对于关联形貌信息至关重要。使用美国国家标准与技术研究院开发的软件 JMONSEL 进行了基于蒙特卡罗模拟的初步工作。通过这种分析，可以确定不同拓扑和光束倾斜条件的理论趋势。由于模拟突出的效果，将介绍倾斜光束 SEM 图像的处理，以及用于创建允许从这些图像进行地形重建的数学模型的方法。最后，将显示使用该模型进行的一些重建，并与参考测量值进行比较。介绍了用于处理图像的整体流程。首先，图像被转换为​​灰度配置文件。在平滑过程之后，计算特定轮廓导数值的位置描述符。然后，从这些来自以不同倾斜角度拍摄的相同图案的两个图像的描述符中，我们使用低复杂度的线性模型来获得结构的几何参数。该模型是使用 JMONSEL 仿真创建和初始校准的，然后在真实硅图案上重新校准。我们证明，在我们的模型中使用来自真实硅图案的真实 SEM 图像会产生与作为参考的传统 3-D 测量技术相一致的结果。此外，我们能够使用单个校准模型对各种高度的图案进行可靠的重建。我们的这批实验表明，对于从 50 nm 到超过 200 nm 的高度，估计高度的 3 σ 标准偏差为 10 nm。基于模拟，我们能够从 SEM 图像中重建圆角 (CR)。然而，由于我们的晶圆没有 CR 可变性，因此仍需要在真实晶圆上评估测量结果。我们能够使用单个校准模型对各种高度的图案进行可靠的重建。我们的这批实验表明，对于从 50 nm 到超过 200 nm 的高度，估计高度的 3 σ 标准偏差为 10 nm。基于模拟，我们能够从 SEM 图像中重建圆角 (CR)。然而，由于我们的晶圆没有 CR 可变性，因此仍需要在真实晶圆上评估测量结果。我们能够使用单个校准模型对各种高度的图案进行可靠的重建。我们的这批实验表明，对于从 50 nm 到超过 200 nm 的高度，估计高度的 3 σ 标准偏差为 10 nm。基于模拟，我们能够从 SEM 图像中重建圆角 (CR)。然而，由于我们的晶圆没有 CR 可变性，因此仍需要在真实晶圆上评估测量结果。