The Impact of Silicon Concentration on the Reliability of Tungsten Silicide

A new reliability mechanism is identified for W-Si resistor metal (RM). EM (Electromigration) risk is significantly increased in W-Si RM with high silicon concentration, as excessive silicon is found migrating from anode to cathode. The silicon migration was confirmed by physical failure analysis. The failure mode is silicon accumulation and extrusion, causing contact barrier separation from contact silicide at the cathode. Similar to conventional EM, we can model RM EM by temperature and current density. The activation energy and current exponent were extracted with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Ea = 1.2\text{eV}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$n = 2.1$</tex> , respectively. The short-length effect was also observed. The key parameter, threshold product <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$( {jL} )c = 200\mathrm{A}/\text{cm}$</tex> , was derived from experimental data on various RM lengths. Lastly, we showed high silicon concentration can degrade EM performance and the silicon migration in RM can cause circuit instability due to the significant changes in TCR (Temperature Coefficient of Resistance) and R0 (Resistance at Room Temperature) by EM stress.