Leakage and breakdown mechanisms of Cu comb capacitors with bilayer-structured α-SiCN/α-SiC Cu-cap barriers

This work investigates the leakage and breakdown mechanisms in copper (Cu) comb capacitors with carbon-doped low-k plasmaenhanced chemical vapor deposited organosilicate glass (OSG; k = 3) as the intermetal dielectric and an alpha-SiCN (k = 5)/alpha-SiC (k = 4) bilayer-structured dielectric film as the Cu-cap barrier. The leakage mechanism between Cu lines is dependent on the thickness ratio of the alpha-SiCN/alpha-SiC bilayer barrier. Using an alpha-SiCN/alpha-SiC bilayer barrier of 40 nm/10 nm or 30 nm/20 nm bilayer thickness, the increased leakage current (Frenkel-Poole emission) between Cu lines is attributed to the large number of interfacial defects, such as cracks, voids, traps or dangling bonds at the alpha-SiC/OSG interface, which are generated by the larger tensile force of the thicker alpha-SiC film. The Cu comb capacitor with an a-SiCN (50 nm)/alpha-SiC (2 nm) bilayer barrier exhibits a much smaller leakage current. The breakdown field and time-dependent dielectric breakdown lifetime of the Cu comb capacitor reveal little dependence on the thickness ratio of the alpha-SiCN/alpha-SiC bilayer barrier, and the observed breakdown of the Cu comb capacitor is presumably due to dielectric breakdown of the bulk OSG layer.