Highly stable HoScO 3 with different thicknesses as the Cu diffusion barrier on Si is prepared and characterized. The ultrathin (3 nm) HoScO 3 barrier scheme is stable after 50 h annealing at 400°C, while its electrical resistivity shows no noticeable increase after annealing at 600°C for 1 h. Both the 5 and 10 nm thick barrier schemes are stable up to 700°C according to the resistivity result. Transmission electron microscopy and Auger electron spectroscopy reveal that the ultrathin amorphous barrier is uniformly present at the interface after annealing at high temperatures. The results indicate that the 3 nm thick HoScO 3 is an effective diffusion barrier for copper metallization. © 2010 The Electrochemical Society.