Due to their promising mechanical and electrical properties, carbon nanotubes (CNTs) have the potential to be employed in many nano/microelectronic applications e.g., through silicon vias (TSVs), interconnects, transistors, etc. In particular, use of CNT bun dles inside annular cylinders of copper (Cu) as TSV is proposed in this study. To evaluate mechanical integrity o f CNT-Cu composite material, a molecular dynamics (MD) simula tion o f the interface between CNT and Cu is conducted. Different arrangements of single wall carbon nanotubes (SWCNTs) have been studied at inteiface of a Cu slab. Pullout forces have been applied to a SWCNT while Cu is spatially fixed. This study is repeated for several different cases where multiple CNT strands are interfaced with Cu slab. The results show similar behavior of the pull-out-displacement curves. After pull-out force reaches a maximum value, it oscillates around an average force with descending ampli tude until the strandls is/are completely pulled-out. A linear relationship between pull out forces and the number of CNT strands was observed. Second order interaction effect was found to be negligible when multiple layers of CNTs were studied at the inteiface of Cu. C-Cu van der Waals (vdW) interaction was found to be much stronger than C-C vdW's interactions. Embedded length has no significance on the average pull-out force. However, the amplitude of oscillations increases as the length of CNTs increases. As expected when one end of CNT strand was fixed, owing to its extraordinary strength, large amount of force was required to pull it out. Finally, an analytical relationship is proposed to determine the inteifacial shear strength between Cu and CNT bundle.

Carbon Nanotubes (CNTs) and Carbon Nanofibers (CNFs) exhibit high ampacity, the key property needed for next-generation interconnects, at miniaturized scales. Copper (Cu), the current state-of-the-art material used in interconnects, faces reliability issues at further miniaturized scales. This is due to high current density causing electromigration of Cu atoms. Therefore, CNTs and CNF were proposed to replace Cu in next-generation microelectronics. Using standalone CNT or CNF structures is very challenging and achieving the same properties as an individual CNT or CNF is difficult. The difficulty arises because the electrical properties of a grown forest depend on characteristics of the forest including self-alignment, density and mechanical stability. Thus, in this study, Cu is used to densify self-aligned CNTs and CNFs so that the mechanical stability and high density can be achieved. Parameters that impact the quality of the final Cu-CNT composite layer including the CNT qualities and fabrication techniques, CNT underlayer effect and different Cu deposition techniques are investigated. Different Cu deposition techniques on the as-grown CNTs are also experimented including electroplating, electroless plating and physical vapor deposition (PVD). The experiments show that although CNFs were successfully coated with Cu using electroless plating, CNTs are found to be fragile and are dissolved during the process of electroless plating. Furthermore, it was found that CNTs cannot act as seed layer for Cu. Other underlayer material such as Ti and TiN were found difficult to work with due to several reasons. Ti and TiN were not found a good material to grow vertically aligned CNTs using CVD. However, PECVD combined with TiN underlayer was successful in obtaining vertically aligned CNTs, although with a much slower growth rate compared to CNTs grown on Al 2 O 3 underlayer. However, TiN was not successful in terms of electroplating.

Due to their superior mechanical and electrical properties, multiwalled carbon nanotubes (MWCNTs) have the potential to be used in many nano-/micro-electronic applications, e.g., through silicon vias (TSVs), interconnects, transistors, etc. In particular, use of MWCNT bundles inside annular cylinders of copper (Cu) as TSV is proposed in this study. However, the significant difference in scale makes it difficult to evaluate the interfacial mechanical integrity. Cohesive zone models (CZM) are typically used at large scale to determine the mechanical adherence at the interface. However, at molecular level, no routine technique is available. Molecular dynamic (MD) simulations is used to determine the stresses that are required to separate MWCNTs from a copper slab and generate normal stress–displacement curves for CZM. Only van der Waals (vdW) interaction is considered for MWCNT/Cu interface. A displacement controlled loading was applied in a direction perpendicular to MWCNT's axis in different cases with different number of walls and at different temperatures and CZM is obtained for each case. Furthermore, their effect on the CZM key parameters (normal cohesive strength (σmax) and the corresponding displacement (δn) has been studied. By increasing the number of the walls of the MWCNT, σmax was found to nonlinearly decrease. Displacement at maximum stress, δn, showed a nonlinear decrease as well with increasing the number of walls. Temperature effect on the stress–displacement curves was studied. When temperature was increased beyond 1 K, no relationship was found between the maximum normal stress and temperature. Likewise, the displacement at maximum load did not show any dependency to temperature.

Carbon nanotube (CNT)/copper (Cu) composite material is proposed to replace Cu-based through-silicon vias (TSVs) in micro-electronic packages. The proposed material is believed to offer extraordinary mechanical and electrical properties and the presence of CNTs in Cu is believed to overcome issues associated with miniaturization of Cu interconnects, such as electromigration. This study introduces a multi-scale modeling of the proposed TSV in order to evaluate its mechanical integrity under mechanical and thermo-mechanical loading conditions. Molecular dynamics (MD) simulation was used to determine CNT/Cu interface adhesion properties. A cohesive zone model (CZM) was found to be most appropriate to model the interface adhesion, and CZM parameters at the nanoscale were determined using MD simulation. CZM parameters were then used in the finite element analysis in order to understand the mechanical and thermo-mechanical behavior of composite TSV at micro-scale. From the results, CNT/Cu separation does not take place prior to plastic deformation of Cu in bending, and separation does not take place when standard thermal cycling is applied. Further investigation is recommended in order to alleviate the increased plastic deformation in Cu at the CNT/Cu interface in both loading conditions.

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