Coverage properties of SiNx films prepared by catalytic chemical vapor deposition on trenched substrates below 90 degrees C were investigated by using SiH4, NE3 and H-2 as source gases. The aspect ratio was changed between 0.35 and 3.4. Conformal step coverage was obtained when the aspect ratio was less than unity, but the coverage property was degraded with the increase in the aspect ratio. SiNx films on the side walls of the trenches were found to have low etch-resistance by an aqueous solution of HF compared with those on the top and bottom of the trenches. Thermal radiation from the heated catalyzer should be the cause of this difference. Coverage properties at the concave corners of the trenches were improved by increasing the H-2 flow rate. This improvement may be ascribed to the local heating of the substrate surfaces by H atoms. (c) 2007 Elsevier B.V. All rights reserved.