Platinum thin films have been successfully patterned without fence residues using an Ar/O-2 helicon wave plasma. Photoresist and silicon oxide masks were also studied for comparison. The etch rate of the TiN mask decreases, but the etch slope increases with an increase of the oxygen concentration in the Ar/O-2 gas mixture. An etch rate of about 670 Angstrom/min was obtained by operating at 4 mTorr with an Ar/O-2 flow rate of 32/8 seem. The etch selectivity is enhanced with the addition of oxygen to Ar, and a high Pt-to-TiN selectivity of above 14 could be obtained. X-ray photoelectron spectroscopy and Auger electron spectroscopy indicated that a thick TiO2 layer could be formed on the TiN mask in the Ar/O-2 plasma. The high etch selectivity of platinum to TiN may be attributed to the presence of a TiO2 layer of similar to 60 Angstrom thickness on the TiN surface. A high etch selectivity and fence-free Pt etching with sidewall angles of similar to 70 degrees could be achieved using a thin TiN hard mask without a postwet cleaning.