Advanced BEOL Interconnects

Feasibility of single damascene Cu BEOL nanowires with TaN/Ta barrier (i.e. omitting a CVD-Co liner) was studied. Successful Cu gap-fill in 36 nm pitch trenches demonstrated 30% line resistance (Line-R) reduction vs. leading-edge Cu with conventional TaN/Co liner. This was attributed to larger Cu volume fraction and 15% lower intrinsic Cu resistivity. In order to assess the Line-R crossover point, comparable Ru nanowires were estimated through analysis of electron scattering components, based on Rs of blanket Ru films. The calculation predicts Line-R of subtractive-etched Ru lines (larger grains) crosses conventional Cu with TaN/Co liner at 12 nm linewidth, but never crosses Cu with TaN/Ta liner. Analysis of electron scattering components shows the resistivity of Ru lines will be dominated by grain boundary scattering, suggesting that the key for subtractive-etched Ru wires crossing over Cu would be innovations that enhance grain growth of blanket Ru films.