Theory of Co-Adsorption and Its Application to Copper Superfilling

The advanced scaling in microelectronic devices requires filling of smaller and smaller copper lines without the introduction of voids and defects. Electrochemical deposition is the process of choice as it ensures a bottom-up, void-free copper growth, so-called superfilling. The present work focuses on the mechanism of superfilling based on additive co-adsorption principles. These principles describe the formation of a complex and reversible adsorption layer of two interacting surface active substances [1]. While positive interaction causes enhanced adsorption and increased surface coverage, negative interaction results in inhibited adsorption and lower surface coverage (Figure 1). The co-adsorption theory is adopted to explain the functioning of plating additives which is presumed to be the key for superfilling. Electrochemical measurements and partial fill experiments under production-like conditions are carried out to study the effects of bath additives in sub-100 nm structures. It is shown that superfilling is a result of the synergetic adsorption behavior of two organic additives, accelerator and suppressor, and a balancing between additive accumulation and copper deposition rate. During copper deposition both additives accelerator and suppressor accumulate near the growing surface. Due to diffusion limitations inside narrow features, a higher additive concentration evolves compared to blank surface areas. If the deposition proceeds at a high rate, the different additive concentrations inside and outside small features can be used to achieve superfilling (Figure 2).

References

[1]        B. B. Damaskin, V. A. Safonov, O. A. Baturina, and N. V. Safonov, J. Electroanal. Chem., 550–551, 3 (2003).