High quality dielectric layers may be achieved without introducing excessive impurities when a semiconductor device is manufactured by a method that includes forming a lower wire layer on a structure above a semiconductor substrate, forming a silicon rich oxide layer having a refractive index of 0.45-1.55 on the lower wire layer and the structure, implanting carbon and oxygen (e.g., CO2) into the silicon rich oxide (SRO) layer, and forming an organosilicate glass layer by heat-treating the implanted SRO layer.