Methods of cleaning a processing chamber of semiconductor device fabrication equipment are highly effective in removing polymers produced as a by-product of a fabrication process from surfaces in a processing chamber. The cleaning process uses a plasma etchant produced from cleaning gas including an O-based gas and at least one gas selected from the group consisting of an F-based gas and a Cl-based gas. The polymer is dissolved in-situ using the plasma etchant. Thus, frequency at which PM (preventative maintenance) of the equipment must be performed is minimized, and the method contributes to maximizing the yield and quality of the semiconductor devices.