基于原子力显微镜的薄膜原位压痕力学性能研究

In Situ Nanoindentation Mechanical Property of Films by Atomic Force Microscope

基于原子力显微镜(AFM)和扫描电子显微镜(SEM)建立了一套原位纳米压痕测试系统。该系统可以实现控制带有金刚石(Cube corner)压头的AFM微悬臂梁对样品进行压入实验,并得到载荷-位移曲线,同时可以对压痕过程进行原位SEM实时观察。发展了一种基于AFM微悬臂梁加载和原位SEM压痕图像分析的力学性能测试方法,通过测量压入最大载荷和原位SEM测量压痕残余面积得到塑性薄膜的硬度和弹性模量。利用此方法对磁控溅射硅衬底上纳米晶银薄膜进行了压痕实验,并与Nanoindenter G200型纳米压痕仪实验进行对比研究。结果表明,原位AFM压痕方法具有高的载荷和位移分辨率,可以实现纳牛至微牛级的压痕实验,通过测量压痕面积得到塑性薄膜的硬度值,减小了使用Oliver-pharr方法中软膜硬基底上凸起(Pile-up)效应的影响,计算结果也具有好的测试精度和可靠性。

An in situ nanoindentation test system was established by combining atomic force microscope（AFM） and scan electron microscope（SEM）. This system enabled the indentation experiment using the AFM cantilever with Cube corner diamond indenter, and acquired the curve of load versus displacement. The experimental process can be observed in real time by in situ SEM simultaneously. A mechanical property testing method, based on the AFM cantilever loading curve and the in situ SEM indentation of images analysis, was well developed. The hardness and elastic model of the plastic thin film were obtained by measuring the maximum loading during the indentation and the residual area of the indentation by measuring SEM image. This method was demonstrated by conducting the indentation experiment on the sliver film deposited on the Si substrate using magnetron sputtering. Furthermore, the experiment conducted by the Nanoindenter G200 was presented here for comparison. The results show that the in situ AFM indentation possesses higher resolution of loading and displacement, and can achieve the indentation experiment scaled from n N to m N of the applied load. The hardness of the plastic thin film can be obtained by measuring the residual area of indentation. The pile-up effect of the soft film deposited on the hard substrate, which exists in the Oliver-pharr method, can be reduced by SEM image analyses of residual area and the calculation has a higher testing accuracy and reliability as well.