Yuqi Lin

Cu electroplating is one of the most expensive, complex and critical steps in fabricating through-glass vias (TGVs), which serve as the core component of 2.5D or 3D integration. This paper presents a simplified 2D via electroplating model to systematically investigate the influences of electrolyte additive, current density, and via geometry on plating performance in terms of via filling profile and Cu thickness. Under a fixed accelerator concentration of 0.1 mol/m³, plating performance for both blind- and through-vias initially improves but subsequently deteriorates with increasing suppressor concentration. Notably, the through-via filling mode dramatically transitions from super-conformal to sub-conformal, achieving a maximum throwing power (TP) of 135.74%. A gradual growth in current density from 0.1 to 0.3 amps/dm² (ASD) leads to deteriorating plating quality for both via types, with the through-via TP dropping to 95.56%. In addition, sub-conformal filling occurs in U-shaped, V-shaped, and X-shaped blind-vias if single-sided plating is employed. However, after shifting them to a through configuration with double-sided plating, complete filling can be realized across all cases. These findings offer a theoretical foundation and practical guidance for enhancing the depositing rate and minimizing/eliminating internal void for the Cu electroplating of TGVs.

Metasurface holograms, with the capability to manipulate spatial light amplitudes and phases, are considered next-generation solutions for holographic imaging. However, conventional fabrication approaches for meta-atoms are heavily dependent on electron-beam lithography (EBL), a technique known for its expensive and time-consuming nature. In this paper, a polarization-insensitive metasurface hologram is proposed using a cost-effective and rapid nanoimprinting method with titanium dioxide (TiO₂) nanoparticle loaded polymer (NLP). Based on a simulation, it has been found that, despite a reduction in the aspect ratio of meta-atoms of nearly 20%, which is beneficial to silicon master etching, NLP filling, and the mold release processes, imaging efficiency can go up to 54% at wavelength of 532 nm. In addition, it demonstrates acceptable imaging quality at wavelengths of 473 and 671 nm. Moreover, the influence of fabrication errors and nanoimprinting material degradation in terms of residual layer thickness, meta-atom loss or fracture, thermal-induced dimensional variation, non-uniform distribution of TiO₂ particles, etc., on the performance is investigated. The simulation results indicate that the proposed device exhibits a high tolerance to these defects, proving its applicability and robustness in practice.