Development of In-Situ Surface Observation System with an Atomic Resolution under Tensile Stress by Atomic Force Microscope

为了在微纳米机械系统中解释薄膜的表面变形和裂纹扩展机制，研制了一种新的原子分辨拉应力下的表面原位观测系统。可同时测定材料的杨氏模数等力学性能。该观测系统由片上拉伸测试系统和商品化原子力显微镜(AFM)组成。该片上测试系统的特点是带有平板弹簧的静态加载机构和15×15×0.5 mm的单晶硅测试芯片。特别注意了抑制振动对具有原子分辨率的表面图像的影响。在不同拉伸应变下均可观察到云母表面的原子图像，直至断裂发生。沉积在硅片上的TiN薄膜的裂纹扩展和杨氏模量也可以用…来描述该系统由片上拉伸测试装置和商品化的原子力显微镜系统组成。为了改进片上拉伸测试装置的部件和整个单元，应特别注意以下几点：(A)选择具有足够刚性的不锈钢材料和每个部件的尺寸设计，(B)在系统周围设置气密室，(C)在系统和气密室的适当点下插入橡胶板。(2)即使在2.37%的拉伸应变下，挠度信号中的周期性噪声也会消失，直到可以观察到与云母表面原子分辨率相同的图像。因此，首次研制了一种新的具有原子分辨率的拉应力下的云母表面原位观测系统。(3)当应变连续增加到4.08%时，云母的表面图像发生突变。可以看出，在保持六保持转动对称性的情况下，基面的晶格参数是标准常数0.52 nm的两倍。在张应力释放后，图像恢复到原来的状态。这种突如其来的图像变化也显示了重复性。对于这一有趣的现象，我们无法解释。(4)在应变为1.56%时，TiN薄膜在垂直于拉应力的方向上观察到了第一个裂纹。结果表明，随着应变的增加，裂纹长度增大，裂纹数目增加。有趣的是，还可以澄清的是，在TiN的情况下，裂纹几乎彼此相等的距离发生。可以认为，裂纹形态的周期性与应力体的波动稳定性有关。横截面轮廓呈矩形，裂纹深度与膜层厚度相对应。可以认为，薄膜与硅衬底界面的分层影响了TiN薄膜中裂纹的扩展。(5)TiN薄膜中裂纹的形成与衬底材料和厚度有关。较少

A new in-situ surface observation system under tensile stress with an atomic resolution has been developed for the purpose of the explanation of the deformation of the surface and the crack growth mechanism for thin films in the micro- and nano-mechanical systems. The mechanical properties such as Young's modulus can be determined at the same time. This observation system consists of the on-chip tensile testing system and a commercialized atomic force microscope (AFM). The on-chip testing system is characterized by a static loading mechanism with a flat spring and a test chip of single-crystal silicon of 15×15×0.5 mm. Particular attention has been paid to the suppression of the vibration which effects on images of the surface with an atomic resolution. Atomic images of the surface of mica can be observed under various tensile strains till the occurrence of the fracture. The growth of the cracks and Young's modulus for TiN thin film deposited on silicon (100) specimen can be also clarif … More ied.(1) The system was consisted of a on-chip tensile testing device and a commercialized AFM system. In order to improve the part of the on-chip tensile testing device and the whole unit, special attentions for the fetal vibration should be paid to the points as follows : (a) the selection of the stainless steel material with enough stiffness and the design of the dimension for each part, (b) an air tight chamber around the system and (c) insertion of rubber plates under the appropriate points of the system and air tight chamber.(2) The periodic noise in the deflection signal disappears even under tensile strain of 2.37% until the same image with an atomic resolution of mica surface could be observed. Therefore, a new in-situ surface observation system under tensile stress with an atomic resolution has been first developed.(3) When the strain was continuously added up to 4.08%, the surface image of the mica suddenly changed. It can be seen that the lattice parameter of the basal plane has become twice times as long as the standard constant of 0.52 nm as the six hold rotational symmetry was maintained. After the tensile stress was released, the image returned to its original one. This abrupt image change also showed reproducibility. We couldn't clarify the reason of this interesting phenomenon.(4) The first crack of TiN film was observed in the vertical direction to the tensile stress at the strain of 1.56%. It could be seen that the crack length grows and the number of the crack increase with increasing the strain. Interestingly, it could be also clarified that the cracks occurs almost at equal distances each other in the case of TiN. It could be considered that the periodicity of the cracking pattern is attributed to the wave stability of stressed solid. The cross section profile showed the rectangular shape and the depth of the crack corresponds to the thickness of the film. It could be considered that the delamination of the film at the interface between the film and the silicon substrate affected the growth of the cracks in TiN film.(5) The formation of the cracks in TiN thin films depended on the substrate material and the thickness. Less