Method of forming a conductor in a fluoride silicate glass (FSG) layer

A fluoride silicate glass (FSG) layer, comprising a plasma enhanced oxide layer (PEOX layer) on a surface of the FSG layer, is positioned on a substrate of a semiconductor wafer. An etching tank, employed as a plug hole or a trench, is formed in the FSG layer. A first plasma ashing process, using oxygen or a gas mixture of nitride and hydrogen as a reacting gas, is then performed to remove fluorine atoms for a predetermined thickness of a surface of the etching tank. A wet cleaning process is performed thereafter. By performing a second plasma ashing process, using oxygen or a gas mixture of nitride and hydrogen as a reacting gas, residual fluorine atoms are removed for the predetermined thickness of the surface of the etching tank. Finally, the etching tank is filled with a conductive material so as to form a conductor.