Cobalt subtractive etch for advanced interconnects

The modern IC process consists of a 13-layer metallization stack. Critical dimensions are 30-40 nm at the M0- M2 metal layers and due to barrier resistance and electromigration reasons, copper is not the perfect choice nowadays. There are two main alternatives to copper on M0-M2 layers: cobalt and ruthenium. Return to the subtractive scheme could be a powerful solution for future interconnects although the dry etching process of the metal is required for it. In this paper, different approaches to plasma etching of cobalt are studied. CO- and halogen-containing plasmas were considered. It seems that etching in CO-based plasma is inefficient. The rate was only 2 nm/min in a wide temperature range. The low-temperature (60°C) process of the cobalt etching in BCl3/Ar plasma was developed. The etching rate for the process was 50 nm/min. All of the considered processes are found to be aggressive toward the mask.