The properties of self-formed diffusion barrier layer in Cu(Cr) alloy

• Cu(Cr) alloys were studied as candidates for highly reliable interconnects materials.
• A 7 nm Cr rich layer can be obtained at the interface after annealing at 450 °C.
• No inter-diffusion and reaction occur between Cu(Cr) alloy layer and SiO2 layer.
• The resistivity of Cu(Cr) films is about 6.9 μΩ cm after annealing at 550 °C.

The properties of Cu(Cr) alloy films were measured to evaluate its potential application as self-formed diffusion barrier in copper interconnect. Pure Cu and Cu(4.5 at%Cr) alloy films were deposited on SiO2/Si substrates using magnetron sputtering and subsequently annealed in vacuum (2 × 10−4 Pa) at the temperature of 350°C–550 °C. After annealing, the film properties were examined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and four-point probe (FPP) method. The results indicate that there was no intermetallic compound (copper–silicide) detected at the interface after annealing. A 7 nm Cr rich layer was self-formed at the interface between Cu(Cr) and SiO2/Si after annealing which acted as a thermally stable barrier against the diffusion of Cu into SiO2. The resistivity of the films decreased with increasing the annealing temperature. After annealing at 550 °C for 1 h, the resistivity of the studied alloy films was 6.9 μΩ cm, which is comparable to that of Cu films (5.17 μΩ cm). These evidences suggest that Cu(Cr) films with excellent thermal stability and low sheet resistance would become a promising material for future advanced barrierless Cu interconnects.