双探针原子力显微镜视觉对准系统

传统的原子力显微镜（AFM）受针尖形状和放置方式的影响很难测量线条的宽度和两个侧壁的形状，故本文提出采用双探针对顶测量方案来消除AFM针尖形状对测量结果的影响。介绍了一种基于机器视觉的双探针原子力显微镜对准系统，该系统将两个探针接触到一起，实现了双探针在三维方向上的对准。系统采用具有亚微米级分辨率的镜头，配合高分辨率的CCD来获得探针的清晰图像，用于在水平和垂直两个方向实时监控双探针的运动情况。采用基于石英音叉式的自传感自调节的原子力探针，无需外加光学探测系统，缩小了系统体积，避免了杂散光对视觉对准系统的干扰。最后对针尖进行了亚像素边缘提取，精确地获取了探针之间的相对位置，实现了亚微米级的双探针对准（1 μm以内）。该结论由探针之间距离与幅度/相位曲线得到了验证。

Vision alignment system for AFM with dual probes

When a traditional Atomic Force Microscope (AFM) is used to measure the critical dimension (CD) of a line, the line width and the shape of two side-walls are difficult to be measured due to the probe shape and positioning. Therefore, this paper proposes a AFM with dual probes to eliminate the effect of probe shapes on measuring results. A alignment system based on machine vision for the AFM with dual probes was introduced, the system contacted the two probes each other to implement the alignment of the two probes in 3D directions. A lens with sub-micron resolution was used in the system to match a high resolution CCD to obtain the clear images and to acquire the movement states of two probes in both horizontal and vertical directions. Furthermore, the novel self-sensing and self-actuating probe based on a quartz tuning fork combined was used for dynamic mode AFM to simplify the system, by which it not needed the external optical detection system, and its dimension was shortened and the affect come from stray light was eliminated. Finally, by extracting sub pixel edge of the tips, the related position between two probes was obtained accurately and the alignment of two probes in sub micron(within 1 μm)was implemented. The results were verified by the distance between two probes and amplitude/phase curves.