Trade-Off Between Surface Roughness and Crystallographic Orientation in Copper Electrodeposition via High-Concentration Gelatin

TL;DR

This study explores how gelatin affects copper electrodeposition, balancing surface smoothness and crystal orientation for better 5G/6G materials.

Contribution

The paper introduces a kinetic framework for understanding the trade-off between surface roughness and crystallographic orientation in copper electrodeposition.

Findings

High-concentration gelatin reduces surface roughness from ~449.5 nm to ~81.3 nm via steric hindrance.

Gelatin-induced suppression causes texture randomization, inhibiting (111)-preferred crystal growth.

A ternary MPS + PEG + Cl− system increases roughness due to competitive adsorption.

Abstract

High-frequency 5G/6G communications demand copper foils combining sub-micron surface roughness (Rz < 0.6 μm) to minimize the skin effect with (111)-preferred orientation (for electromigration resistance), a balance challenging to achieve in conventional electrodeposition. This study quantifies the synergistic mechanism of a systematic series of additive formulations—from unary sodium 3-mercapto-1-propanesulfonate (MPS) to a quaternary MPS + polyethylene glycol (PEG) + Cl− + gelatin (GEL) formulation—using electrochemical and microstructural analyses. While the ternary MPS + PEG + Cl− system induced severe surface roughening (Rq = 449.5 nm) due to competitive adsorption, the introduction of high-concentration gelatin induced a kinetic bifurcation. It established a distinct “High-N/Low-D” regime—characterized by a 104-fold reduction in diffusion coupled with a 103-fold enhancement in nucleation, effectively suppressing the growth, reducing roughness from ~449.5 nm to ~81.3 nm via robust steric hindrance. However, this isotropic suppression simultaneously inhibited preferential crystal growth, leading to texture randomization. These findings kinetically quantify the intrinsic trade-off between extreme surface planarization and crystallographic orientation, providing a theoretical framework for designing high-performance interconnect materials.

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