Silicon carbide (SiC) films are often used to seal the highly porous ultra low-k polymers prior to the deposition of a Tantalum (Ta) diffusion barrier layer. However, hydrogen can not be eliminated because SiC films are fabricated by PECVD processes, which sometimes causes Ta layers to become an ineffective diffusion barrier against copper (Cu) diffusion. Through large scale ab initio molecular dynamic simulations, we show that such degradation is due to hydrogen atoms diffusing into the Ta layers and preventing Ta from forming crystalline dense films. These loose amorphous layers allow Cu atoms to diffuse into crevices. However, further simulations show that nitrogen addition to SiC thin films will strongly enhance the barrier effects of the Ta layers even in the presence of a high percentage of hydrogen. We predict that SixCyNz thin film is an excellent candidate to replace SiC.

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