Fundamental studies of copper diffusion barriers
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Copper diffusion barriers are necessary to contain copper within microelectronics interconnect wiring, preventing copper diffusion to the underlying silicon transistors. Both conducting and insulating copper diffusion barriers are used to encapsulate copper wiring, with low resistivity and dielectric constant of the barriers, respectively, critical to minimizing the time-delay contributions. TaCxNy films deposited from pentakis(dimethylamino)tantalum and methane were studied. Thermal chemical vapor deposition (CVD) at 365 °C resulted in films with resistivity > 6000 µΩ·cm due to high-resistivity Ta3N5. Plasma-enhanced CVD films using no methane had the lowest resistivity within this study of 440 µΩ·cm. The incorporation of carbon using CH4 increasing the resistivity due to preferential formation of graphitic- vs. carbidic-carbon. TaCxNy films as thin as 4 nm were found to be effective copper diffusion barriers. BCxNy films deposited by CVD using dimethylamine borane with ammonia and/or ethylene were characterized. Amorphous films could be deposited with k less than 4 at 360 °C, with hardness and modulus of 8.7 GPa and 71.3 GPa, respectively. BCxNy adhered strongly to dielectric films (> 10 J/m2 ). BCxNy adhesion to copper surfaces varied with surface pretreatment and generally ranged from 1.65 to 5.59 J/m2 , with one set of samples snapping (strong adhesion). Adhesion increased with carbon content, x, on oxidized copper surfaces. Adhesion to metallic copper was improved by the π- bonding character of the B-N bond. The barrier effectiveness was evaluated using bias-temperature stress testing. BC0.90N0.08 (k of 3.8) deposited using ethylene was the most promising boron-based film, having leakage current of 1.12×10-8 A/cm2 at 0.5 MV/cm and comparable barrier performance to SiC0.76N0.44. BCxNy barrier performance appeared to improve with lower boron content, fewer B-B bonds, and increased B-C bonds.