Impact of introducing CuSiN self-aligned barriers in advanced copper interconnects

Self-aligned barriers have been widely investigated in the replacement of standard PECVD dielectric liners to decrease coupling capacitance. As an alternative to CVD or electroless approaches, a two step process based on the modification of the Cu surface is proposed. This technique consists first in enriching Cu surface with Si atoms followed by a nitridation step to complete the so called CuSiN self-aligned barrier. In this paper, the silicidation mechanism is described and the crucial role of the nitridation step is demonstrated in terms of barrier stability under electrical stress. CuSiN efficiency against Cu diffusion and oxidation is also evidenced. Compared to a standard SiCN barrier, CuSiN self-aligned barriers revealed a gain of at least 3 decades in time-dependent dielectric breakdown lifetime and up to 7% decrease in intra-level coupling capacitance.