Semiconductor devices are fabricated using a plasma process with a non-silane gas that includes deuterium, and which may result in improved device reliability and/or other improved device operational characteristics. One such method can include forming a gate oxide layer on a transistor region, which is defined on a substrate, and forming a gate electrode on the gate oxide layer. An etch stop layer is formed on the gate oxide layer and the gate electrode. A plasma process is performed on the interface between the gate oxide layer and the substrate using a non-silane treatment gas including deuterium. An interlayer dielectric layer is formed on the etch stop layer. A bottom metal line is formed on the interlayer dielectric layer.