A new technique has been developed to introduce very refractory materials into an electron cyclotron resonance ion source by fluorinating them with SF6 plasma, and we succeeded in generating multiply charged ions of B, Mo, Nb, W, and Ta. A metallic sample is set inside the plasma chamber with SF6 plasma, in which the metallic fluoride is generated with sufficiently high vapor pressure by a chemical reaction between fluorine and the metal. The gaseous metallic fluoride is decomposed into fluorine and metal, which are ionized by the SF6 plasma. Generally, ion sources are corroded by gases of fluorine and fluoride, but utilization of SF6 gas reduces the corrosion and allows stable operation for a long time. © 1998 American Institute of Physics.