Sidewall sensing in critical dimension atomic force microscopes (CD-AFMs) usually involves continuous lateral dithering of the tip or the use of a control algorithm and fast response piezo actuator to position the tip in a manner that resembles touch-triggering of coordinate measuring machine (CMM) probes. All methods of tip position control, however, induce an effective tip width that may deviate from the actual geometrical tip width. Understanding the influence and dependence of the effective tip width on the dither settings and lateral stiffness of the tip can improve the measurement accuracy and uncertainty estimation for CD-AFM measurements. Since CD-AFM typically uses tips that range from 15 nm to 850 nm in geometrical width, the behavior of effective tip width throughout this range should be understood. The National Institute of Standards and Technology (NIST) has been investigating the dependence of effective tip width on the dither settings and lateral stiffness of the tip, as well as the possibility of material effects due to sample composition. For tip widths of 130 nm and lower, which also have lower lateral stiffness, the response of the effective tip width to lateral dither is greater than for larger tips. However, we have concluded that these effects will not generally result in a residual bias, provided that the tip calibration and sample measurement are performed under the same conditions. To validate that our prior conclusions about the dependence of effective tip width on lateral stiffness are valid for large CD-tips, we recently performed experiments using a very large non-CD tip with an etched plateau of approximately 2 μm width. The effective lateral stiffness of these tips is at least 20 times greater than typical CD-AFM tips, and these results supported our prior conclusions about the expected behavior for larger tips. The bottom-line importance of these latest observations is that we can now reasonably conclude that a dither slope of 3 nm/V is the baseline response due to the induced motion of the cantilever base.

中文翻译：

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CD-AFM度量学中的横向笔尖控制效果：大笔尖限制。

临界尺寸原子力显微镜（CD-AFM）中的侧壁感测通常涉及尖端的连续横向抖动或使用控制算法和快速响应压电致动器以类似于坐标测量机的触摸触发的方式来定位尖端（ CMM）探针。但是，所有的刀尖位置控制方法都会产生有效的刀尖宽度，而有效的刀尖宽度可能会偏离实际的几何形状的刀尖宽度。了解有效尖端宽度对抖动设置和尖端横向刚度的影响和依赖性可以提高CD-AFM测量的测量精度和不确定性估计。由于CD-AFM通常使用的尖端的几何宽度范围为15 nm至850 nm，因此应了解在此范围内有效尖端宽度的行为。美国国家标准技术研究院（NIST）一直在研究有效笔尖宽度对抖动设置和笔尖横向刚度的依赖性，以及由于样品成分而产生材料影响的可能性。对于130 nm及以下的针尖宽度（也具有较低的侧向刚度），有效针尖宽度对横向抖动的响应大于大针尖。但是，我们得出的结论是，只要在相同条件下进行笔尖校准和样品测量，这些影响通常不会导致残留偏差。为了验证我们有关有效尖端宽度对横向刚度的依赖性的先前结论对于大型CD尖端有效，我们最近使用非常大的非CD尖端进行了实验，该非CD尖端的蚀刻平台宽度约为2μm。这些尖端的有效侧向刚度至少是典型CD-AFM尖端的20倍，这些结果支持了我们先前关于较大尖端的预期性能的结论。这些最新发现的底线重要性在于，我们现在可以合理地得出以下结论：由于悬臂基座的感应运动，抖动斜率为3 nm / V是基线响应。