铜薄膜内微孔对其力学性能影响及开裂行为研究

研究了铜薄膜内微孔对其力学性能影响及开裂行为,采用磁控溅射工艺制备聚酰亚胺柔性基板上铜薄膜,通过扫描电镜(SEM)对铜薄膜表面形貌表征、EDS能谱分析及SEM原位拉伸观察实验,得出磁控溅射工艺制备出超薄铜薄膜多为柱状晶结构,且带有微米级孔洞.并测得不同孔隙率铜薄膜载荷与位移增量的变化,由相关公式求出应力-应变关系;分析了不同孔径微孔的上下边缘沿晶开裂,微裂纹萌生、扩展的行为.结果表明:磁控溅射工艺在聚酰亚胺柔性基板上制备的微米级铜薄膜受拉伸时微孔沿晶开裂形成初始微裂纹,孔径≤4μm微孔处局部应力偏低,未能使微裂纹沿晶界改变方向继续扩展,微裂纹受到抑制;在较高的局部应力下,孔径>10μm微孔裂纹继续沿新的晶界方向扩展,与其他微孔裂纹连通;孔隙率越高,多孔微裂纹连通几率越高,薄膜力学性能就越差,且铜薄膜开裂可能性也越高.

The mechanical properties and cracking behavior of copper film containing micro pores

The effect of micro pores on the mechanical properties and cracking behavior of copper thin films was studied. Copper thin films were prepared on Polyimide Flexible substrate by magnetron sputtering. Scanning electron microscopy ( SEM ) and EDS energy spectrum analysis were used to characterize the surface morphology and compositions of copper films, and found that the ultra-thin copper films are mostly columnar crystal structures with micron size pores. SEM in-situ tensile test was used to measure the load and displacement increment of copper film with different porosity. The stress-strain relation is calculated by the correlation equation. The behavior of crack initiation and propagation in the upper and the lower edge of the pores with different pore sizes was analyzed. The results show that the micro cracks of micro copper films prepared by the magnetron sputtering process on the polyimide flexible substrateare formed along the surface of the micro pores. When the diameter of the pore is less than 4 μm, the local stress is low, and cannot make the micro crack develop along the grain boundary and continue to expand. When the diameter of the pore is more than 10μm,however, the micro crack continue to expand along the boundary and is connected with other micro cracks. Higher porosity results in the higher probability of connectivity of porous micro cracks, and thus worse mechanical properties and higher possibility of cracking of copper films.