Grain structure analysis and effect on electromigration reliability in nanoscale Cu interconnects

Abstract

Articles you may be interested in Grain structure analysis and effect on electromigration reliability in nanoscale Cu interconnects Appl. Simulation of the effects of grain structure and grain growth on electromigration and the reliability of interconnects Abstract. This paper combined experiments and simulation to investigate the grain size and cap layer effects on electromigration (EM) reliability of Cu interconnects. First the statistical distribution of EM lifetime and failure modes were examined for in laid Cu interconnects of large and small grain structures with two different cap layers of SiCN vs. CoWP. The CoWP cap was found to significantly improve the EM lifetime due to the suppression of the interfacial mass transport as a result of strengthening of the Cu/cap interface bonding. In addition, the grain size was observed to affect the EM reliability significantly, particularly for the CoWP capped structures. Resistance traces and failure analysis revealed two distinct failure modes: mode I with voids formed near the cathode via corner and mode II with voids formed in the trench several microns away from the cathode via. It was found that large grain size and strong cap interface reduced the mass transport rate and the void diffusion in the Cu line, leading to a longer EM lifetime and a higher proportion of mode II failures. A statistical simulation of EM lifetimes was also applied to Cu interconnects with grain structures generated by the Monte Carlo method. The simulation results for different grain sizes and cap interfaces are in good agreement with the experimental observations.

Modeling the copper microstructure and elastic anisotropy and studying its impact on reliability in nanoscale interconnects

“…A bamboo polycrystalline structure is observed in metal lines with a lognormal grain size distribution (Cao et al 2014;Rizzolo 2014;Meyer et al 2005. A typical observance that grains are smaller at the bottom and larger at the top of the trench as been made from experiments (Cao et al 2013;Karmarkar et al 2012;B. Li et al 2014).…”

“…A clear dependance between the copper microstructure in nanoscale interconnects, void formation kinetics, and electromigration statistics has been established through experiments (Cao et al 2013). A significant difference in the electromigration failure lifetime as a function of grain size was observed, large grain structures had 14x higher lifetime compared to small grain structure.…”

“…The remaining 30% grains had other orientations. Whereas, (Cao et al 2013;Cao et al 2014) have observed a preferred orientation of (110) along the trench normal and (111) along the trench width in 70 nm patterned copper lines. This difference in preferred orientation could possibly be due to different processing conditions.…”

Electron Diffraction and Crystal Orientation Phase Mapping Under Scanning Transmission Electron Microscopy

“…This research group has extensively used this D-STEM technique, applying it to a wide range of nanostructured materials, like downscaling nanoscale Cu interconnects used in the semiconductor industry, where this technique, in combination with precession microscopy, was determinant in the acquisition of quantitative local texture information in damascene copper interconnects (1.8 μm-45 nm in width) with a spatial resolution of less than 5 nm. Their results revealed strong variations in texture and grain boundary distribution of the copper lines upon downscaling, observations that have been very useful for the semiconductor industry [10][11][12]. This D-STEM technique has also been used by this research group to study lithium-rich layered oxide materials used as cathode materials in Li-ion batteries [13,14].…”

Lattice degradation by moving voids during reversible electromigration

“…Clearly, the grain structure, surface orientation, wire crystallinity, and possible containment strongly influence the material transport. [12][13][14][15][16][17][18][19][20][21][22][23] This leads to the question: How reversible is the EM driven mass transport, especially if one considers the microstructure?…”