Abstract
Abstract Cobalt is a promising material for electronic interconnections in the post-Moore law period. However, the vertical cobalt pillar is not fully compatible with the current electroplating-involved manufacturing process due to hydrogen evolution at the cathode and poor throwing power of the products. In this article, electrodeposition with multiple organic additives was employed to realize the fabrication of cobalt pillars. Electrochemical measurements were used to investigate the depolarization of 3-mercapto-1-propane sulfonate sulfonic acid (MPS) and the polarization of the polyvinylpyrrolidone (PVP) during cobalt electrodeposition. Notably, the competitive adsorption between MPS and PVP was verified and discussed in cobalt electrodeposition. In order to understand the adsorption and functional groups of the additives, quantum chemical calculations were performed to simulate the distribution of electrostatic potential and molecular orbital energy of the additives. Accordingly, the thiol group of MPS and the amide group of PVP were speculated to be the molecular adsorption sites in cobalt electrodeposition. The mechanism including three stages was proposed for cobalt pillar electrodeposition in solution with MPS and PVP. The electrodeposition of practical cobalt pillars with a depth of 50 µm and diameters of 60, 80, and 100 µm was successfully achieved by electroplating experiments, thereby promoting the application of metal cobalt for electronic packaging.
Highlights
With the booming development in the miniaturization of electronic products in the 5G era, the system-in-package technology and chip interconnection have reached the scale of a single micron in recent years [1,2]
mercapto-1-propane sulfonate sulfonic acid (MPS) and PVP as additives exhibit the function of acceleration and inhibition during cobalt electrodeposition, respectively
They undergo competitive adsorption behavior in cobalt electrodeposition and some adsorption sites of MPS are replaced by PVP
Summary
With the booming development in the miniaturization of electronic products in the 5G era, the system-in-package technology and chip interconnection have reached the scale of a single micron in recent years [1,2]. As a good candidate of alternative metal in the post-Moore law period, cobalt exhibits several advantages such as the low electron mean free path and low thermal expansion coefficient [15,16]. In this way, it is reasonable to assume that the cobalt structures from the compatible electroplating process will promote the productivity and reliability of cobalt formation. In the cobalt pillar electrodeposition, the growth of cobalt along the wall of the hole is faster than that in the middle, leading to the overgrowth outside of the hole without enough cobalt deposition in the middle It is well-known that organic additives can effectively improve the quality of electroplating, especially in coating uniformity and filling completeness. Cobalt pillar electrodeposition was successfully carried out in solution with MPS and PVP by galvanostatic electrodeposition
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