Patent ID: 7413992

Claim:
A method for etching a layer formed on a substrate, comprising: providing a substrate into a plasma processing chamber, the substrate having a metal silicide layer formed thereon and a patterned mask defined over the metal silicide layer, wherein the metal silicide layer is part of a gate stack; supplying an etching gas mixture of a fluorine-containing gas, a chlorine-containing gas, a nitrogen-containing gas, and an oxygen-containing gas to the plasma processing chamber, wherein a ratio of the nitrogen-containing gas to the fluorine-containing gas is between about 6 to about 10, a ratio of the fluorine-containing gas to the chlorine-containing gas being between about 0.5 to about 1.5 and a ratio of the fluorine-containing gas to the oxygen-containing gas being between about 5 to about 7; and generating a plasma in the plasma processing chamber using the supplied etching gas mixture to etch the metal silicide layer in regions not covered by the patterned mask, an RF power between about 200 watts to about 1000 watts being provided to generate the plasma, an RF bias power supply providing the substrate with a direct current (DC) bias voltage between about 100 volts to about 300 volts, wherein the DC bias voltage is used to control direction and energy of ion bombardment toward the substrate, the patterned mask defining dense regions and isolated regions, wherein the generated plasma is configured to remove the metal silicide layer in the dense regions and the isolated regions at a reduced etch rate micro-loading to reduce gate oxide punch through of the gate stack.