Picosecond Ultrasonics Applications on Electroplated Cu Process

The manufacturing of electronic devices has transitioned from aluminum-connection to copper-connection because of copper's low electrical resistivity and excellent electromigration resistance. Accurate thickness measurement of copper (Cu) film is critical in electroplating process control. Picosecond Ultrasonics (PULSE™ Technology) has been widely used in thin metal film metrology because it possesses the advantage of being rapid, non-contact, and non-destructive. In this paper, we demonstrate that Picosecond Ultrasonics has excellent repeatability and stability in electroplating (ECP) Cu thickness measurement applications. Additionally, PULSE Technology shows that probe reflectivity has a high correlation with surface roughness. This could be used as an indicator to monitor the process stability during thickness measurement. Edge bevel removal (EBR) area in top metal plays a key role in wafer die yield and the EBR width which should be controlled in a tight range. PULSE Technology can also be used to detect the EBR boundary with line-scan measurements and feedback to the EBR process when there is remaining metal within the removal area, helping to avoid defects at wafer edge.