Abstract
Plating on GaAs devices is almost always gold. Gold has many advantageous properties for electronic components. Gold plates well, have high electrical conductivity, are resistant to oxidation, and are ductile.In the first stage of our project, we used plating gold to be Metal 1 and Metal 2 in PHEMT process. In order to get good roughness, uniformity and desired target, the aim of this study is to find the important parameters of plating operation. It is well known that plating flow rate and current density are the essential parameters of plating process. However, from this study, we found that the most important parameter affect roughness and uniformity is current density. In addition, we have achieved target by making sure real plating area and correcting plating current. Subsequently, the uniformity and roughness became worth with increased current density while the plating flow rate affected only the uniformity. When the plating flow rate increased, the uniformity was improved. In addition, we have taken step against watermark by using Descum treatment (the kind of plasma cleaning) before plating.In the second stage of our project, the gold surface was investigated by ESCA after the process of Descum. We found the Au-O compound was produced in the surface of Au and this compound was reduced with the time increased at room temperature. It is interested that the sheet resistance of Au-surface was increased significantly initially and decreased to the original value (before the process of Descum) with the time increased. In addition, the time required for the restoration of the sheet resistance was reduced with the temperature increased.