New precision electroforming process for the simultaneous improvement of thickness uniformity and microstructure homogeneity of wafer-scale nanotwinned copper arrays. (April 2023)

• Record Type: Journal Article
• Authors: Zhan, Xiaofei; Shen, Chunjian; Zhu, Zengwei; Zhu, Di
• Is Part Of: International journal of machine tools & manufacture. Volume 187(2023)
• Publication Date: 2023-04
• Subjects: Nanotwinned copper -- Precision electroforming -- Thickness uniformity -- Microstructure homogeneity -- Auxiliary cathode -- Pulse reverse current; Machine-tools -- Periodicals; Manufacturing processes -- Periodicals; Machines-outils -- Périodiques; Fabrication -- Périodiques; Electronic journals; 621.902
• DOI: 10.1016/j.ijmachtools.2023.104006
• Languages: English
• ISSNs: 0890-6955

Abstract

Abstract: Nanotwinned (nt) Cu has received much attention because of its superior mechanical and electrical properties, but only a few production processes can yield nt-Cu parts with uniform thickness and a homogeneous microstructure on the wafer scale. To solve this problem, a new precision electroforming process is proposed that combines auxiliary cathodes with pulse reverse current (PRC) electroforming, which provides a synergistic effect to increase the homogeneity of the thickness and a nanoscale twin structure. As a practical example of the proposed process, 4-inch nt-Cu lamina arrays were fabricated and numerically modeled to probe into the synergistic mechanisms. The intrinsic correlations among the array element spacing, current waveform, and main forms of thickness nonuniformity were determined. In addition, the effects of the processing parameters on the microstructural evolution and microhardness of the nt-Cu arrays were analyzed. The results indicated that such a significant improvement in thickness uniformity and microstructure homogeneity were due to the auxiliary-cathode/PRC combination, which enables maximization of the PRC leveling efficiency by inducing a uniform current distribution; this effectively ensures that the microstructures are uniform across all laminae on the wafer scale. Additionally, thick nt-Cu deposited on the current-crowding regions was preferentially stripped during the application of reverse current. This alleviates the adverse effects of the current redistribution resulting from the auxiliary cathode on the thickness uniformity of the laminae and offers additional possibilities for homogeneous growth of nt-Cu. The new precision electroforming process has significant potential to produce wafer-scale components with uniform thickness and specific microstructures. Graphical abstract: Image 1 Highlights: A new precision electroforming process based on the combination of auxiliary cathode and pulse reverse current is proposed. The process can fabricate wafer-scale array components with uniform thickness and homogeneous microstructures. Numerical simulation and experimental studies highlighted the synergistic mechanisms controlling the thickness and microstructure. The process maximizes the leveling efficiency while minimizing the current-redistribution problems caused by the auxiliary cathode. The relationship between processing parameters, thickness distribution, microstructure, and microhardness were established.