# A Short Review of Through-Silicon via (TSV) Interconnects: Metrology and Analysis
## 3 TSV Reliability
### Thermal Management  
The generation of excessive heat within a confined region inherently gives rise to a more substantial temperature elevation, thereby causing potential performance degradation and, in severe instances, physical harm to the circuit. In a 3D-IC chip stack, where one end is typically allocated for electrical interconnections, only a singular end can be utilized for effective heat dissipation. Consequently, the options for heat dissipation may be constrained, particularly within the middle section of the stack [45]. Thermal management is a critical aspect of 3D ICs that has a significant impact on their performance and reliability. In 3D-ICs, two primary mechanisms are used for thermal management, namely thermal junctions and thermally conductive pillars. The purpose of thermal junctions is to collect heat from various regions of the IC. On the other hand, thermally conductive pillars are utilized to dissipate heat from the substrate. Their role is comparable to that of through-silicon vias (TSVs). It is essential to consider copper TSVs in the thermal management of 3D-ICs as an effective vertical heat dissipation pathway in stacked ICs. This entails optimizing their distribution and stacking while also considering the associated reliability risks. To elaborate further, thermal junctions and thermally conductive pillars play crucial roles in mitigating the effects of heat on 3D ICs. Thermal junctions are typically formed by connecting multiple layers of a 3D IC through metal lines, thereby facilitating heat transfer between different areas of the IC. On the other hand, thermally conductive pillars are vertical interconnects that traverse the entire thickness of a 3D IC. These pillars are responsible for dissipating heat from the IC's substrate, which is essential for maintaining optimal operating temperatures. Several research efforts have concluded that the top surface temperature of Si wafers containing Cu-TSVs is higher than that of Si wafers without Cu-TSVs as the heating power increases. This phenomenon is attributed to the preferential heat transfer through a Cu TSV in the vertical direction caused by the high thermal conductivity of Cu, which implies that a Cu TSV is an efficient vertical heat dissipation path [36; 46]. This also poses several challenges for the reliability of the TSV. Copper TSVs are increasingly being recognized as a promising solution for thermal management in 3D-ICs due to their excellent thermal conductivity properties. By providing an efficient vertical heat dissipation pathway, they can significantly reduce the temperature gradients within stacked ICs, leading to improved performance and reliability. Moreover, copper has excellent mechanical and electrical properties that make it a popular filler material for TSV structures, back-end-of-line (BEOL), and micro-solder blocks. This is because copper is highly compatible with current microelectronics manufacturing pro cesses, including integration with front-of-line (FEOL). However, the design of reliable copper TSVs remains a significant challenge. Optimizing the distribution and stacking of TSVs is critical to ensure effective heat dissipation while minimizing thermal stresses that can arise during operation. Additionally, the thermal expansion coefficient of copper differs from that of silicon, which can cause significant stress and deformation during the manufacturing and operation of TSVs. As a result, it is essential to design TSVs with appropriate dimensions and spacing to minimize the thermal stress and deformation that can occur during operation. Another important consideration when designing copper TSVs is their impact on the performance of the IC. The introduction of TSVs leads to increased parasitic capacitance and resistance, which have a negative impact on signal integrity and power consumption. Therefore, optimizing the design of TSVs to minimize their impact on the IC's electrical performance is critical [7].