Scaling analysis of electrodeposited copper and the influence of a modified polysaccharide on surface roughness

Abstract

The influence of a commercially available modified polysaccharide (HydroStar®, Chemstar Chemical Products) on the roughness of short-term and small-scale copper electrodeposits was investigated using Atomic Force Microscopy (AFM), linear scan profilometry and scaling analysis. Copper was deposited on a 316L stainless steel cathode at 40 °C and 300 A m⁻² from an electrolyte containing 40 g L⁻¹ Cu²⁺, 170 g L⁻¹ H₂SO₄, 1.5 g L⁻¹ Fe³⁺, 15 mg L⁻¹ Cl⁻ and either 0, 10, 50 or 100 mg L⁻¹ of HydroStar. Copper deposits produced between 15 and 25 min were imaged using AFM and 2D linear scan profilometry was used to gather surface features of copper samples produced in the range of 120 and 240 min. Scaling analysis was applied to quantify the surface characteristics of limiting roughness (δ) and critical length (L_C) from which δ/L_C was computed and related to the aspect ratio of surface features. All copper deposits showed a general rise in δ and L_C with deposition time but the growth rates decreased when HydroStar was included in the electrolyte indicating that the additive lowers the vertical height of surface features as well as their widths. Furthermore, copper deposits were more consistently produced in the presence of HydroStar and, for a given value of limiting roughness, had surface features with wider base than those created in the absence of the additive. The results show that the modified polysaccharide acts to create smooth copper deposits by generating surface features with lower aspect ratios.