The Thermodynamic Modeling And Study Of Air-gap/Cu Interconnect Structure By Finite Element Analysis

As devices continue to shrink proportionally, the ultra-Low-K dielectric materials with the relative dielectric constant less than 2.0 have become a research hotspot. Under such context, the material with minimum K value - air (k=1) has received serious attention. The introduction of air-gaps between copper wires can effectively reduce the equivalent dielectric constant Keff, but the mechanical stability of interconnect structure is also facing challenges. During the manufacturing process with temperature variations, thermal stress will be generated owing to differences between materials'thermodynamic properties and cause lots of threats, such as material deformation, cracks, delamination and other defects. Some serious damages will directly make the system invalidated. Study of the trend of thermal stress in manufacturing process, namely, thermal stress history, will help us to learn the impact of thermal stress on the system and find out appropriate solutions for improvement. In this paper, ANSYS finite element thermal analysis was used, through studying two kinds of mainstream process for manufacturing the air-gap/Cu interconnect structure, CVD deposition method and thermal decomposition of the sacrificial layer method ,to simulate the thermal stress history on the copper wire and compare two methods'pros and cons. In the end, it was found that after a series of thermal stress circularly acted on the interconnect structure, many materials had large deformation in various degree, which will largely affect the structure's mechanical stability and even cause damage. Besides, interconnect structure design has become a key bottleneck of enhancing the system architecture's mechanical stability. Therefore, further improvement requires optimization of the structural design and use of more proper dielectric.