W versus Co--Al as Gate Fill-Metal for Aggressively Scaled Replacement High-k/Metal Gate Devices for (Sub-)22 nm Technology Nodes

In this work we provide a comprehensive evaluation of a novel, low-resistance Co–Al alloy vs W to fill aggressively scaled gates with high aspect-ratios [gate height (Hgate) ~50–60 nm, gate length (Lgate) ≥20–25 nm]. We demonstrate that, with careful liner/barrier materials selection and tuning, well-behaved devices are obtained, showing: tight gate resistance (Rgate) distributions down to Lgate~20 nm, low threshold voltage (VT) values, comparable DC and bias temperature instability (BTI) behavior, and improved RF response. The impact of fill-metals intrinsic stress, including the presence of occasional voids in narrow W-gates, on devices fabrication and performance is also explored.