Silicon nitride films have been deposited at 50 degrees C using a high-density plasma (HDP) chemical vapor deposition (CVD). Electron cyclotron resonance (ECR) plasma has been employed as a HDP source. The electrical properties of resulting low-temperature silicon nitrides have been previously evaluated. X-ray photoelectron spectroscopy shows that chemical bonding structure of this low-temperature ECR nitride is very comparable to that of 250 degrees C industry-deposited plasma-enhanced CVD (PECVD) nitride. IR absorption data indicate that the low-temperature ECR nitride has more Si-H bonds and less N-H bonds than the high-temperature PECVD nitrides. These ECR films display robustness to buffered oxide etch attack with etch rates that are 20-50 % of a 250 degrees C-deposited PECVD nitride. ECR-nitride aged for 17 months has the leakage current of <5 x 10(-9) A/cm(2) and electrically breaks down at 5.7 MV/cm. It is suggested that these low-temperature ECR nitrides can be very suitable for encapsulation, passivation, and barrier layers.