A semiconductor device may be manufactured by employing an ashing process for removing a photoresist in a process chamber, wherein the ashing process comprises: removing the photoresist for a first predetermined process time by flowing one or more oxygen and nitrogen source gases into the process chamber at first predetermined pressure, power, and temperature conditions; removing a surface portion of a polymer (e.g., from a previous etching process) for a second predetermined process time by flowing a mixture of one or more water source gases (e.g., H2O) and a fluorocarbon (e.g., CF4) into the process chamber at second predetermined pressure, power, and temperature conditions; and removing remaining photoresist for a third predetermined process time by flowing an oxygen source gas (e.g., O2) gas into the process chamber at third predetermined pressure, power, and temperature conditions.