Optimization of copper electroplating process applied for microfabrication on flexible polyethylene terephthalate substrate

Nguyen Ngan Le, Thi Cam Hue Phan, Anh Duy Le, Thi My Dung Dang and Mau Chien Dang

Abstract

Electroplating is an important step in microfabrication in order to increase thickness of undersized parts up to a few micrometers with a low-cost, fast method that is easy to carry out, especially for metals such as copper, nickel, and silver. This important step promotes the development of the fabrication technology of electronic devices on a flexible substrate, also known as flexible electronic devices. Nevertheless, this technology has some disadvantages such as low surface uniformity and high resistivity. In this paper, parameters of copper electroplating were studied, such as the ratio of copper (II) sulfate (CuSO₄) concentration to sulfuric acid (H₂SO₄) concentration and electroplating current density, in order to obtain low resistivity and high surface uniformity of the copper layer. Samples were characterized by scanning electron microscopy (SEM), four-point probe, and surface profiler. The results showed that the sample resistivity could be controlled from about 2.0 to about 3.5 μΩ  cm, and the lowest obtained resistivity was 1.899 μΩ  cm. In addition, surface uniformity of the electroplated copper layer was also acceptable. The thickness of the copper layer was about 10 μm with an error of about 0.5 μm. The most suitable conditions for the electroplating process were CuSO₄ concentration of 0.4 mol l⁻¹, H₂SO₄ concentration of 1.0 mol l⁻¹, and low electroplating current density of 10–20 mA cm⁻². All experiments were performed on a flexible polyethylene terephthalate (PET) substrate