Effect of Microstructure and Dielectric Materials on Stress-Induced Damages in Damascene Cu/Low-k Interconnects

Abstract

The line width dependence of stress in damascene Cu was examined experimentally as well as with a numerical simulation. The measured hydrostatic stress was found to increase with increasing line width. The larger stress in an interconnect with large dimension is attributed to the larger grain size, which induce higher growth stress in addition to thermomechanical stress. A stress model based on microstructure was constructed and the contribution of the growth and thermal stress of the damascene lines were quantified using finite element analysis. It was found that the stress of the via is lower than that of wide lines when both the growth stress and thermal stress were considered. This stress gradient between via and line, which is the driving force of vacancy diffusion, is larger when the low-k with lower stiffness and higher thermal expansion is used for dielectric layer. For this reason, the Cu/low-k can be more vulnerable to stress-induced voiding.

Reliability of Copper Interconnects: Stress-Induced Voids

“…Hence, grain growth will occur in the Cu. Grain growth eliminates excess free space in the Cu, resulting in excess vacancies and shrinkage of the metal lines (8). If grain growth occurs before cap layer deposition, the vacancies can diffuse to the surface and are annihilated.…”

Modeling the Impact of Layout Variation on Process Stress in Cu/Low k Interconnects

“…At typical process temperatures, low k dielectrics can also be characterized using linear elastic relations [2,6]. The thermal and mechanical properties of these materials are taken from [6]. The thermal and mechanical properties of these materials are taken from [6].…”

“…Recent study has shown that the grain growth stress is very anisotropic and has strong size dependence at small dimensions due to the difference in grain boundary elimination [6]. The thermal expansions are isotropic for typical materials in interconnects.…”