Microscopic Characterization of Temperature Effect on Tensile Fracture of Nano-films Via Molecular Dynamics Simulation

• Main Authors: Jian-Hui Lee, 李建輝
• Other Authors: Steven Hsin-Yi Lai
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/23645366740461704719

碩士 === 國立成功大學 === 機械工程學系碩博士班 === 95 === Thin film is widely applied to the process of connecting the conducting lines in ultra large integration circuit. With the demand of the component becoming slight, multi-layered, highly dense, high speed operating and the product cost, and the effects of stress-migration and electro-migration, how to promote operation speed is a pending topic to solve. In recent years, the filmic materials are gradually changed to copper to replace aluminum. Because the research result of the property of nano-scale copper thin film is not clear, it is an important topic worth exploring in depth. And in tradition, the experiments still used trial and error to test the film mechanical properties repeatedly, the steps took lots of time and did not have economic benefits, and the effective length was hard to measure directly in stretching, residual stress releasing caused folding when cutting film, it was unable to observe the transient destructive action inside the materials et cetera. For those reasons, there still exist technical difficulties. For research of designing and manufacturing, the mechanical property of its materials is an extremely important factor concerning the performance of the entire structure, reliability and working life. Therefore, we need a simple, correct and rapid testing technology. In this article, we will establish a stretching theory and simulating system about nano-scale copper thin film to evaluate and predict the parameter of thin film effectively for researching the relations of the stress, the strength of structure and the evolution of dislocation. In research of designing and manufacturing, it can be an important reference in choosing film material to increase product qualities and shorten researching time. In this paper, submicroscopic method is employed to carry out three dimensional molecular dynamics theory and simulations of the mechanical properties of rectangular cross-section copper thin film. This proposed approach is utilized to elucidate the stress behavior, the deformation mechanism and the elastic-plastic fracture materials during the tension test of the nano-scale copper thin film. First, the copper atom should obey the Morse potential function, and we calculate it by using the potential to deduce spatial differentials. The Gear fifth order predictor-corrector method is adopted to calculate the positions of atoms, while the arithmetic method of local interactions by Velet's neighbor lists and cut-off are used to analyze the interactions among molecules in numerical calculation. That can promote the simulating speed efficiently and monitor the state of systemic atoms in equilibrium at any time. Then we can execute the simulation of structural tensile strength to get the mechanical properties and transient behavior in order to analyze. Furthermore, we can control the temperature, the scale and the strain-rate factors of simulating system to research how structural parameters affect the mechanical properties and failure mechanics. Finally, we compare the simulating results and references (or experimental datum) with each other to predict the practicability and accuracy of the theory and the simulating system to be the base of the model improvement and correction. In this article, in the tensile test simulation of nano-scale copper thin film, we discovered in the state of different systemic temperature (5 K to 1200 K ) and strain-rate (2×108 sec-1). If the systemic strain value is zero, the existing stress is not zero. At this moment pre-stress will rise to 0.8 GPa. Then, we discuss the relationship between the systemic temperature and the stress curve quassation. Taking this result to compare with references, we can find this phenomenon also occurs in different materials. So in nano-scale, the size and the surface effect is not allowed to be neglected. This result shows different conspicuous phenomenon between nano-scale and large-scale. And then, we discuss the relations of the yield stress, the yield strain, the elasticity modulus and the resilience modulus. Then, gray theory is used to fit and predict the curve, we will discover the average residual error is 1 to 2 % between the fitting and predicting curves and we see the error is extremely small. By this cure, we can understand the relations of the esilience, the material toughness and the ductility. Finally, we discuss the crystal structure rotation, Lüders bands, the multiple glide dislocation and the energy behavior. The method can improve sufficiently the fact that the investigations of the physical phenomenon are only carried out by theories and experiments. Therefore, this research proposed another method to test nano-scale copper thin film. This study of mechanical and fracture properties of thin film will be helpful to the strength prediction, the material choice and reference design of nano-electromechanical system. The method can also be used to provide a clear direction for further design studies.