The effect of the additional ac-bias voltage applied to the substrate on the characteristics of the SiOX deposited using modified remote-type atmospheric pressure plasma at room temperature was investigated for the gas mixture of hexamethyldisilazane/O-2/He/Ar. The addition and increase of ac-bias voltage not only increased the deposition rate but also improved the characteristics of the deposited SiOX. With the increase of ac-bias voltage to the substrate, the oxygen percentage in the film increased while the carbon percentage is decreased by increasing Si-O-Si bonding and by decreasing the impurity such as -(CH3)(X) in the deposited film. In addition, the hardness and the surface smoothness of the deposited film were also increased with the increase of the ac biasing. The improvement of the film properties was related to the ion bombardment effect in addition to the increased gas dissociation by the additional power absorption, which was caused by the ac biasing of the substrate. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3530792] All rights reserved.