We have studied the effects of halogenizingHgBa2CaCu2O6+&dgr;(Hg-1212) thin films and have found that the addition of chlorine/fluorine significantly enhances (1) the reproducibility and stability of Hg-1212 thin films, (2) the phase purity of Hg-1212 to over 90&percent;, and (3) the magnetic critical current density(Jc,mag)both at zero field and in-field. A possible mechanism of preventing contamination of precursor materials by chlorine/fluorine doping is proposed. ©1998 American Institute of Physics.