Experimental study of multilayer SiCN barrier film in 45/40 nm technological node and beyond

• SiCN with high dielectric constant is decreased from 5.3 to 3.8 by introducing C2H4.
• Bilayer SiCN5.3/SiCN3.8 suffers adhesion and capacitance is improved.
• Tri-layer SiCN5.3/SiCN3.8/SiCN5.3 is used to improve interfacial adhesion.

With feature size of device scaled down 45 nm technological node and beyond, the backend of the line (BEOL) faces too many problems such as resistance–capacitance (RC) delay, crosstalk noise, and power consumption. In order to improve RC delay, the SiCN dielectric constant had to further decrease through introducing C2H4 gas to increase its carbon content. The SiCNkI (k ~ 5.3) and SiCNkII (k ~ 3.8) were characterized by spectroscopic ellipsometer, fourier transform infrared spectroscopy (FTIR), Rutherford backscattering spectrometry–hydrogen forward scattering (RBS–HFS), X-ray reflectivity (XRR), Hg probe, four point bending (4-PB) test, scanning electron microscope (SEM), and transmission electron microscope (TEM). Results indicated that the hardness and modulus and density of the SiCNkII were lower than that of the SiCNkI. RBS–HFS and FTIR examination indicated that SiCNkII barrier film had high carbon content and terminating CH3 group to cause low cross-linking and density of dielectric films resulting in large volume. 4-PB test combined with transmission electron microscope (TEM) examination demonstrated that the crack occurred in the interface between SiCNkII film/SiCNkI bilayer barrier film and low k film. After adding SiCNkI barrier film, no crack was found using SiCNkI/SiCNkII film/SiCNkI tri-layer barrier film. In addition, the capacitance and RC reduction ratios were improved to about 7–8% using the SiCNkII/SiCNkI bilayer barrier film.