A plasma-enhanced chemical vapor deposition (PECVD) was developed for the growth of highly conformal carbon-doped silicon nitride (SiCN) films with enhanced barrier properties drawing on tunable carbon contents, k-values, and wet etch rates (WER). Trisilylamine (TSA) was used as the main precursor and hexane was used as a hydrocarbon-containing additive precursor for carbon doping. At low deposition temperatures <= 400 C-degrees, we show that this PECVD process leads to the formation of SiCN films with good conformality of approximately 91% over high aspect ratio trench nanostructures (4.2:1) with a growth rate of similar to 2.5 ((A)over circle/cycle). In particular, the role of TSA and hexane precursors on the film growth mechanism and the k-values, and WER in the composite structures has been explored. The precursors were introduced pulse-wise into the reaction chamber while plasma was excited. The WER of the film was evaluated in a buffered hydrofluoric acid etchant. The k-value and carbon concentration varied depending on the TSA/hexane supply time in the ranges of 7-4.5 and around 6-40%, respectively. Analysis showed that the hexane precursor improved the WER of deposited SiCN films by more than a factor of 100 compared to when only TSA was used. The SiCN film with a thickness of 5.0 nm exhibited excellent prevention of moisture diffusion into the device. Furthermore, the step coverage was improved to equivalent conformality of the plasma-enhanced atomic layer deposition (PEALD) by modifying the supply method of the Si and carbon precursors and the moisture barrier property was secured with thicknesses of < 10 nm. In particular, the Si and carbon precursors are biased to maximize the process margin and control the film characteristics, where tuning can be easily implemented.