Influence of Line-Width on Microstructure and Texture of Damascene Copper Interconnects

Abstract

The structure, texture and grain boundary character distribution in the copper interconnects, for ten different line-widths varying from 0.35 to 100 μm, were investigated. Field Emission Gun-SEM orientation imaging microscopy was used in the investigation. The shape of the grains changed with increasing line-widths. The frequency of occurrence of more than one grain along the width and grain size increased with increasing line-width. The mean grain size was found to be 0.2 μm in the smallest lines with width 0.35 μm and as high as 2.5 μm in the 100 μm lines which were the largest in width. The grain size distribution was skew-symmetric with an inclination towards smaller size. The (111) pole figures, inverse pole figures and the area fraction of the grain boundaries with different misorientation angles were computed for all the line-widths. The 0.4 and 0.5 μm lines had stronger {111} component in the direction transverse to the trenches. The intensity of the component increased with decreasing width. The 0.35 μm lines, which were narrowest in width had two {111} components with <110> direction parallel to transverse and longitudinal directions. The higher line-widths had predominantly (111) fiber texture though presence of {111}<110> could also be identified. Number fraction of the grain boundaries with misorientation angle between 55-62° was maximum in all line-widths. The ∑3 and ∑9 coincidence site lattice (CSL) boundaries were present in significant number in all the investigated lines. Presence of twins running along the width could be easily identified in the submicron lines.