Abstract
The crystallographic microstructure between the electroplated Cu fillings and the substrate in a stacked-via structure and its electrical/mechanical characteristics were systematically investigated using a focused ion beam (FIB), electron backscatter diffraction (EBSD), a probe station with an ohmmeter, a quick via pull (QVP) test, and a 3D-optical microscope. A two-stage Cu electrodeposition process with various plating current densities at the early stage (j(1) = 0.3, 0.5, 1.0, or 2.0 A/dm(2)) and a fixed plating current density at the subsequent stage (j(2) = 2.0 A/dm(2)) was utilized to fill a daisy-chain blind-hole (BH) structure. The Cu crystal coherency between electroplated Cu fillings and substrate can be significantly improved with the j(1) minimization, which efficiently enhances the electrical/mechanical characteristics of the stacked-via structure. The strong dependence of the Cu crystal coherency on j(1) can be ascribed to a slow discharge rate of Cu ions at a low plating current density, allowing the Cu nuclei to laterally extend and epitaxially grow with a crystalline substrate. Therefore, the Cu crystal modification via j(1) adjustment can greatly promote the packaging reliabilities of a stacked-via structure.
NSTL
Elsevier