Silicon dioxide films have been deposited by plasma-enhanced chemical vapor deposition at low substrate temperature (50 degreesC) in a parallel-plate reactor using hexamethyldisilazane (HMDS), diluted in He, and O-2 as Si and O precursors. The effect of the O-2/(HMDS+He) flow rate ratio on the oxide properties has been investigated in the range of 0.05-1.25 by means of deposition rate, wet etching rate, secondary ion mass spectrometry, thermally stimulated luminescence, and high frequency capacitance-voltage measurements. Both the deposition rate and the etching rate increase by increasing the O-2/(HMDS+He) flow rate ratio and reach a constant value at flow rate ratios higher than 0.6. The strong increase and saturation in the deposition rate can be attributed to the impinging oxide atoms flux and to the consumption of silyl radicals at the deposition surface, respectively. The Si/SiO2 interface state density and the positive fixed charge density are in the range 1X10(11)-1X10(12)eV(-1)cm(-2) and 6X10(11)-1.5X10(12)Ccm(-2), respectively. These concentrations are comparable with literature data concerning SiO2 films obtained by plasma enhanced chemical vapor deposition at temperatures higher than 200 degreesC using other Si precursors. Moreover, the interface state density decreases while the fixed oxide charge increases by increasing the O-2/(HMDS+He) flow rate ratio. A correlation has been found between defects monitored by thermally stimulated luminescence and fixed oxide charges. From a comparison with secondary ion mass spectrometry results, the fixed oxide charges can be preliminarily attributed to intrinsic defects.