Provided are methods of forming a semiconductor device. The methods include providing a first precursor and a substitute gas into a reaction chamber having a substrate therein, the first precursor having a first substituent and further providing a second precursor into the reaction chamber. Either the first precursor or the second precursor includes a metal element and the other includes a silicon element, at least one of the first substituents of the first precursor are substituted with the substitute gas, the first precursor substituted with the substitute gas is adsorbed onto the substrate, and the second precursor is reacted with the adsorbed first precursor.