Influence of Macroscale Dimension on the Electrocrystallization of Cu Pad and Redistributed Layer in Advanced Packaging

Abstract

Copper with equiaxed grains (EG Cu), copper with columnar nanotwinned grains (C‐NT Cu), and copper with mixed equiaxed and columnar grains (MG Cu) are electroplated on pads and redistributed layers (RDLs) with different dimensions. When the diameters of pads increase from 40 to 105 μm, the flatness of pads decreases from 34.5% to 24.0%. The flatness gradually deteriorates from 16.5% to 34.4% with the increase of RDL width from 8 to 20 μm. In contrast, the flatness of C‐NT Cu and MG Cu fluctuates between 1% and 5%, showing a weak correlation on the dimension. In terms of microstructure, the EG Cu and MG Cu has a weak correlation with size change, and the grain orientation shows a randomness. However, the (111) texture component of C‐NT Cu differs greatly with different dimensions, especially in transition layer. The (111) texture component changes from 9.6% to 38.1% for ϕ 40–105 μm pad and from 14.3% to 18.9% for 8–20 μm‐wide RDL. The study reveals the significant size effect on the deposited profile and microstructure of electrodeposited copper materials, which should give insights of the materials design in advanced packaging technology.