We have studied the effect of H dilution on silicon nitride films deposited by the hot-wire chemical vapor deposition (HWCVD) technique using SiH4, NH3, and H2 gases. We found that H dilution significantly enhances the properties at silicon nitride films. The N content in the film increases by more than 2 times compared to the film without dilution, based on FTIR measurements. As a result, we can achieve high-quality a-SiNx:H films at low substrate temperature using a much lower gas ratio of NH3/SiH4(∼1) compared to a ratio of about 100 for conventional deposition by HWCVD. We also found that dilution decreases the H content in the films. More importantly, diluted SiNx films are conformal. Scanning electron microscopy measurements show a nearly 100% surface coverage over a sharp object. Electric breakdown measurement shows a well-insulated film with more then a few MV/cm for the breakdown field.