Through-silicon via (TSV), as a key technology for realizing interconnections in three-dimensional integrated circuits (3D ICs), critically depends on the integrity of its sidewall interfaces to maintain optimal leakage characteristics. This study conducted temperature cycling experiments, incorporating leakage current I-V testing, microstructural observations, and EDS elemental analysis to evaluate the effects of temperature cycling on the integrity of TSV sidewall interfaces and the leakage mechanisms in the insulation layer. The results indicate that, as the number of temperature cycles increases, the alternating cyclic loads progressively degrade the integrity of the TSV barrier layer, transitioning from an intact interface to the formation of micro-voids and micro-cracks. This results in a significant increase in leakage current. When through-thickness cracks appear at the interface, a sudden decrease in leakage current occurs. The TSV failure mode shifts from thermally induced leakage to mechanical cracking. The leakage mechanism of the insulation layer transitions from the Schottky emission mechanism (Cycle ≤ 60) to a combination of Schottky emission and Poole-Frenkel emission mechanisms (Cycle ≥ 90), and this shift becomes more pronounced under high electric field conditions. Further analysis of TSV interface integrity reveals that thermomechanical stress induced by temperature cycling generates defects at the interface between the TSV copper fill and the barrier layer. As thermally induced defects accumulate, the barrier height of the insulation layer continuously decreases, making it easier for electrons in the metal to overcome the Schottky barrier under thermal and electric field excitation, thereby forming leakage currents. Moreover, these defects facilitate the diffusion of copper atoms into the insulation layer, resulting in the formation of localized high electric field regions. These high-field regions in the insulation layer increase electron emission rates through the Poole-Frenkel emission mechanism, creating leakage paths. Therefore, copper diffusion emerges as one of the primary causes of dielectric performance degradation in the insulation layer.