Amorphous Si oxynitride (a-SiOxNy) films were deposited at 300 degreesC using a plasma-enhanced chemical vapor deposition technique, by varying the NH3 flow rate, [NH3] Under fixed SiH, and O-2 flow rates to control the x- and y-values. The characteristics of defects were investigated vis--vis structural and bonding properties. These films were 'stoichiometric', including no or less homobonds. As [NH3] increases, the x- and y-values decreased and increased, respectively, and a relationship of 2x+ 3y = 4.14 (+/-0.02) was found. With increasing [NH3], the deposition rate increased, but the defect density and the stress can be decreased.