Study on the electrochemical deposition behavior and blind hole filling behavior of Cobalt under the regulation of hexamethylenetetramine as a leveling agent

Abstract

The metal cobalt is expected to be the next generation of interconnect materials due to its shorter average free path of electrons and greater resistance to electromigration. Additives especially the leveling agents are key regulatory factors for achieving a bottom-up dense superfilling of interconnect metals in the electroplating process. Here the hexamethylenetetramine (HMTA) with methylene structure was chosen as a leveling agent to study the deposition behavior and the blind hole filling behavior of cobalt. The electrochemical analysis showed that the HMTA exhibits an evident inhibition ability on the deposition of cobalt. Moreover, this inhibitory ability has a significant dependence on the rotational speed of the solution and a greater inhibitory effect on the deposition of cobalt occurs at high rotational speeds.The simulation indicates that such a strong inhibition ability on the deposition of cobalt sourced from the preferred adsorption of the leveling agent on the cobalt surface by the nucleophilic active site provided by the methylene structure of HMTA. Such preferential adsorption behavior was further confirmed by the captured vibration peaks of CN and CH bonds associated with the HMTA from the in-situ electrochemical surface enhanced Raman spectroscopy. Under the action of this leveling agent, the metal cobalt exhibits the expected bottom-up growth behavior in blind holes of Printed circuit board (PCB) The addition of HMTA is also beneficial for obtaining a flat and dense coating with preferred growth of (100) crystal planes. These results indicate that the HMTA is a potential effective leveling agent for the cobalt interconnects processes.