Investigations into electroless copper seed layer deposition in through-glass vias based 3D packaging

Abstract Electroless copper seed layer uniformity is a critical requirement for reliable through-glass via (TGV) metallization. In this work, electroless Cu deposition in tapered vias with an aspect ratio of ∼4 is investigated using a combined numerical and experimental approach. A two-dimensional axisymmetric finite-element model incorporating species diffusion, surface reaction kinetics, and moving-boundary mesh deformation was used to simulate Cu thickness evolution along via sidewalls during electroless deposition at 30 °C for 1200 s. The simulated Cu thickness varies from ∼450 nm near the via entrance and exit regions to ∼250 nm at intermediate depths. Cross-sectional scanning electron microscopy analysis of electroless Cu deposited in silicon through-holes processed under identical conditions shows corresponding thickness values of ∼400 nm near the top and bottom regions and ∼200 nm at the mid-depth. Electroless Cu films deposited for 20 min exhibit continuous coverage with a sheet resistance of ∼0.24 Ω/□, a peel adhesion strength of ∼2.65 N cm −1 , and a tensile residual stress of ∼33.5 MPa for an average thickness of ∼200 nm. Electrical continuity of glass-based redistribution lines (RDL) test vehicles was shown by fabricating a test vehicle using electroless Cu followed by Cu electrodeposition. A linear current-voltage behavior across the TGV-RDL network was demonstrated with measured electrical resistance of ∼1.09 Ω.