Robust self-assembled monolayer as diffusion barrier for copper metallization

Excellent results on copper (Cu) diffusion barrier characteristics of a self-assembled monolayer (SAM) of 2-(diphenylphosphino)ethyltriethoxy-silane are reported. The thickness and roughness of the SAM were determined by grazing incidence x-ray reflectometry as 1.7 and 0.3 nm, respectively. To evaluate Cu diffusion barrier performance of the SAM, Cu/SiO2/Si and Cu/SAM/SiO2/Si metal-oxide-semiconductor capacitors were prepared to measure their lifetimes under the 2 MV/cm electric bias at 498–548 K. The mean times to failure obtained from the Weibull plots of time to failures were 33.6, 9.24, 4.57, and 2.03 h at 498, 523, 533 and 548 K, respectively. These values show that the barrier characteristic of the SAM of 1.7 nm in thickness is comparable to that of physical-vapor-deposited Ta film of 20 nm in thickness. The estimated lifetime of the SAM barrier at the device operation temperature of 392 K is longer than 10 yr.