Method of etching a trench in a silicon-containing dielectric material

1. Field of the Invention Disclosed herein is a method of etching a trench in a silicon-containing dielectric material, in the absence of a trench etch-stop layer, where the silicon-containing dielectric material has a dielectric constant of about 4 or less. The method comprises exposing the dielectric material to a plasma generated from a source gas comprising a fluorine-containing etchant gas and an additive gas selected from the group consisting of carbon monoxide (CO), argon, and combinations thereof. A volumetric flow ratio of the additive gas to the fluorine-containing etchant gas is within the range of about 1.25:1 to about 20:1 (more typically, about 2.5:1 to about 20:1), depending on the particular fluorine-containing etchant gas used. The method provides good control over critical dimensions and etch profile during trench etching. Also disclosed herein is a method of forming a dual damascene structure, without the need for an intermediate etch stop layer.