Stress Analysis of Tungsten Deposition in a 3D Trench Mold With Regard to Initial Nuclei Shape

Tungsten has been commonly used for fine interconnects due to its good gap-filling characteristics in 3D molds, such as trench patterns. However, tungsten shows high deposition stress. This causes mold distortion because tungsten has low ad-atom mobility, and diffusion-driven relaxation does not occur. To reduce tungsten’s deposition stress, the shape of the nuclei can be controlled, which is an effective way to suppress the mechanical deformation caused by the formation of a grain boundary between free surfaces during the coalescence stage. In this study, elliptical tungsten nuclei with various aspect ratios, which suppress coalescence in the early stage of deposition, were proposed to reduce the deposition stress. Stress was calculated using the finite element method (FEM) in the range of 0.5 to 8 radius ratios of the tungsten nuclei. The bending of the trench mold was calculated due to tungsten stress and additional coalescence between films during the filling process. As a result, the wider the elliptical nucleus was, the lower the film stress, and mold bending between line patterns was also reduced. The defects in the depth and width of the periodic trench influenced the mold bending in the early growth stage and the stage of coalescence between films, respectively.