Dixson Ronald G, Orji Ndubuisi G, Goldband Ryan S
National Institute of Standards and Technology, 100 Bureau Drive Gaithersburg, MD 20899-8212, Phone number: 301-975-4399.
National Institute of Standards and Technology, 100 Bureau Drive Gaithersburg, MD 20899-8212, Phone number: 301-975-3475.
J Micro Nanolithogr MEMS MOEMS. 2016 Jan 25;15(1). doi: doi:10.1117/1.JMM.15.1.014003.
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.
临界尺寸原子力显微镜（CD-AFM）中的侧壁传感通常涉及探针的连续横向抖动，或者使用控制算法和快速响应压电致动器来定位探针，其方式类似于坐标测量机（CMM）探针的触发式测量。然而，所有的探针位置控制方法都会产生一个有效探针宽度，该宽度可能与实际的几何探针宽度有所偏差。了解有效探针宽度对抖动设置和探针横向刚度的影响及依赖性，有助于提高CD-AFM测量的精度和不确定度估计。由于CD-AFM通常使用几何宽度在15纳米至850纳米范围内的探针，因此应了解在此范围内有效探针宽度的行为。美国国家标准与技术研究院（NIST）一直在研究有效探针宽度对抖动设置和探针横向刚度的依赖性，以及样品成分可能产生的材料效应。对于宽度为130纳米及以下、横向刚度也较低的探针，有效探针宽度对横向抖动的响应比大尺寸探针更为显著。不过，我们得出的结论是，只要在相同条件下进行探针校准和样品测量，这些影响通常不会导致残留偏差。为了验证我们之前关于有效探针宽度对横向刚度依赖性的结论对于大尺寸CD探针是否有效，我们最近使用了一个蚀刻平台宽度约为2微米的非常大的非CD探针进行了实验。这些探针的有效横向刚度至少比典型的CD-AFM探针大20倍，实验结果支持了我们之前关于大尺寸探针预期行为的结论。这些最新观察结果的关键要点在于，我们现在可以合理地得出结论，由于悬臂基座的诱导运动，3纳米/伏的抖动斜率是基线响应。
