Experimental studies of the etching of platinum have been performed with a photoresist mask in Ar/Cl-2 plasmas. The etch rate of platinum decreased with addition of Cl-2, showing no enhancement of etching by Cl-2 addition. Moreover, the etch rate of platinum was found to be independent of substrate temperature in pure Cl-2 plasmas. These results indicated that the platinum etching with chlorine-containing plasmas is proceeded mainly by physical sputtering due to incident ions, not by chemical reactions that produce volatile etch products. Thus, in platinum etching with Ar/Cl-2 plasmas, the redeposition of nonvolatile etch products was observed to occur on sidewalls of the photoresist mask and platinum pattern; in this situation the etched profiles of platinum were tapered outwardly, because the redeposited films acted as etching masks for platinum. The thickness of deposited films on sidewalls increased with increasing Cl-2 concentration, but they were found to be removed by wet treatment with HCl solutions. It was further demonstrated that by optimizing the Cl-2 concentration, platinum could be etched without redeposition residues on sidewalls, although the etched profiles still remained outwardly tapered.