Low-k a-SiCO:H films as diffusion barriers for advanced interconnects

•a-SiCO:H films were deposited by PE-CVD using OMCTS as a precursor.•The effect of process parameters on film characteristics was investigated.•An a-SiCO:H film of 30 nm with a dielectric constant of 3.4 is a copper barrier.•For the same film, moisture barrier properties are doubtful.

Scaling of the copper interconnect structures requires dielectric barrier materials with a gradually lower dielectric constant that still have adequate copper and moisture barrier properties. In this work, we study the PE-CVD deposition of a-SiCO:H films using octamethyl cyclotetrasiloxane (OMCTS) as a precursor, targeting a dielectric constant of 3.5 or below. The effect of process parameters on film characteristics and chemical bonding structure was investigated. Copper and moisture barrier properties were studied for a selection of films. For an a-SiCO:H film with a dielectric constant as low as 3.4, the intrinsic TDDB lifetime at 1 MV/cm exceeds the 10 years specification, meaning that it is a copper barrier, at a thickness of 30 nm. A Young’s modulus of 14.8 ± 0.8 GPa was measured, and a hardness of 1.8 ± 0.1 GPa. The plasma etch selectivity to a commercial porous a-SiCO:H film with dielectric constant of 2.5 is 1:2.3. However, moisture barrier properties are doubtful, as was shown by 2 different evaluation methods based on spectroscopic ellipsometry.

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