Argon/oxygen based chemically assisted ion-beam etching has been investigated for the patterning of stacked capacitor platinum electrodes at ground rules of 200 nm and below. Titanium nitride and bilayers of titanium on top of titanium nitride were used as hard mask layers in the patterning of the platinum. The ion-beam platinum etch process relies on physical sputtering by Ar ions with oxygen being added to the chamber during the etch to provide passivation of the Ti or TiN hard mask material. Pt:Ti etch selectivities of up to 20 have been achieved on blanket wafer samples. Sidewall profile angles greater than 80 degrees (measured from the horizontal) were obtained for tightly spaced platinum features with a pitch of 350 nm using a multiple-angle ion-beam etch process. The uniformity of the etch process across 200 mm diam blanket oxide wafers was measured to be 3.5% (3 sigma value).