In micropatterning down to 0.1 mum class devices, photolithography requires highly accurate microfabrication of chrome (Cr) reticle masks. In this paper we report the vertical chrome etching using electron beam (EB) resist masks in downstream chlorine plasmas, where the resist damage during etching can be suppressed because of the reduced electron density through negative ion production. Though the Cr etch rare in pure Cl-2 downstream plasmas was only 15 Angstrom /min, slight oxygen addition of 1% resulted in a great increase of Cr etch rates as large as 20 times, while resist etch rates increased only twice. Though isotropic Cr etching reactions with chlorine and oxygen radicals caused undercut features, appropriate substrate biasing allows vertical patterning of 0.2 mum wide lines and spaces due to sidewall protection by redeposition of by-products from etched Cr and resists.