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

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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