Study of Elastic Anharmonicity in Mo Thin Films

薄膜比其体材料具有更大的残余应力。本计画的目的是从弹性非谐性的观点来探讨薄膜弹性模量的差异。在实验上，钼薄膜溅射沉积在硅衬底上。研究了不同沉积条件下Mo薄膜的弹性性能。沉积参数包括衬底温度和目标功率。用激光曲率测量系统测量残余应力。通过X射线衍射仪测量残余应变。弹性模量和硬度通过纳米压痕测试仪测量。主要结果如下：（1）在所有沉积条件下，Mo薄膜均处于压应力状态。残余应力随衬底温度和靶功率的增加而减小。这种趋势归因于表面扩散率的温度依赖性和沉积原子的动能的靶功率依赖性。（2）压应力和应变分别为0.4- 1.2GPa和0.2- 0.6%。测得的残余应力为体应力的2倍，为0.4-0.6GPa。另一方面，硬度和杨氏模量没有表现出任何依赖于沉积条件，并大致相同的散装value.These结果表明，薄膜中的残余应力和应变可以在很大程度上受到沉积条件的影响，并可能采取比散装更大的值。与此相反，在应力和应变的观测范围内，弹性非谐性可以忽略不计。

Thin films have a larger residual stress than their bulk materials. The purpose of this project was to investigate a possible difference in the elastic moduli in thin films from the view poin of elastic anharmonicity. Experimentally, Mo thin films were sputter deposited on silicon substrates. The elastic properties of Mo thin films were studied for various deposition conditions. Deposition parameters included substrate temperature and a target power. Residual stress was measured by a laser curvature-measuring system. Residual strain was measured by a X-ray diffractometer. Elastic modulus and hardness were measured by a nano-indentation tester. The major obtained results were the following :(1)Mo thin films were under a compressive stress state for all deposition conditions. Residual stress were found to decrease with increasing substrate temperature and a target power. This tendency was attributed to the temperature dependence of the surface diffusivity and to the target power dependence of the kinetic energy of the deposited atoms.(2)Compressive stress and strain were found to be in a range of 0.4-1.2 GPa and 0.2-0.6%, respectively. The observed residual stress was twice as much as that of the bulk value of 0.4-0.6GPa. On the other hand, hardness and Young's modulus did not show any dependence on the deposition conditions and were approximately the same as the bulk values.These results indicate that residual stress and strain in thin films can be substantially affected by the deposition conditions and may take larger values than the bulk. In contrast, in the observed range of stress and strain, elastic anharmonicity can be neglected.