Wires used in most electronic devices are formed through copper electrodeposition. This technique has been specifically employed in constructing the interconnects of large-scale printed circuit boards and integrated circuits. However, successful electrodeposition requires effective control of the process and properties of deposited copper, which depends on various process parameters, including current density and temperature. Additionally, the composition of the electroplating baths and additives used in the process do influence not only the behavior of copper electrodeposition but also the crystal orientation, resistivity, and surface morphology of the resulting electrodeposited copper. Therefore, it is necessary to develop effective tools for studying and understanding the various factors influencing the copper electroplating process.
Classical Hull cells have been used to study different factors influencing deposited copper as functions of other electroplating parameters such as current density. However, their irreproducible and limited solution agitating compromises their further applications. Consequently, the enhancement of mass transfer in Hull cells has been extensively studied both theoretically and experimentally. An example is developing the hydrodynamic electroplating test cell (HETC) with improved structural features to enhance well-defined hydrodynamics and controllable mass transfer conditions. However, despite its many advantages, it exhibits a narrow current density transfer along the cathode, thus limiting its practical applications. This problem has been solved by further modifying the HETC structure to form modified-HETC (M-HETC).
The electrodeposition process also involves using additives that exhibit several effects on the resulting copper deposits, depending on their applications. However, there are limited studies on the effective use of additives through Hull cells and modified Hull cells. Additionally, electroplating test cells have been widely used to monitor industrial plating bath operations and developing plating electrolyte compositions. On this account, Dr. Tsung-Wei Zeng from Feng Chia University and Dr. Shi-Chern Yen from National Taiwan University from Taiwan studied the effects of gelatin on the morphology of electroplated copper deposits under various current densities using M-HETC. Their research work is currently published in the International Journal of Electrochemical Science.
In this approach, the proposed and utilized M-HECT was an electroplating test cell capable of providing reproducible and stable flow field as well as controllable mass transfer. In a single electroplating experiment, the authors obtained electrochemically deposited copper with enhanced thickness uniformity over different current densities. The effects of gelatin were more adverse at low current density and were characterized by a decrease in the surface roughness, many protrusions, and increased surface uniformity. The positive results were also attributed to the controllable mass transfer and reproducible and stable flow field induced by the modified HECT.
In a nutshell, the authors used modified HECT to evaluate the effects of an additive and current density in the electroplating bath on the electrodeposition of copper. The results demonstrated the effectiveness of the modified HECT as an efficient tool for quality control and research development applications. It allowed the study of various parameters such as surface profile as a function of different parameters, including current density and the plating bath composition. The modified HECT is a time-efficient tool appropriate for studying a range of key factors influencing surface morphology and other properties of the electrodeposited copper. In a statement to Advances in Engineering, the authors said their findings would expand the applications of M-HECT in various research and industrial activities involving electrodeposition of various metals. They also added “The successful electrodeposition in the copper interconnects is quite important to the yield of fabrication and the reliability of the electronic devices. The proposed electroplating cell was developed and can be an efficient tool for studying the key parameters for the fabrication of copper interconnects”.
Zeng, T., & Yen, S. (2021). Effects of Gelatin on Electroplated Copper Through the Use of a Modified-Hydrodynamic Electroplating Test Cell. International Journal of Electrochemical Science, 16, 210214.