Methods are disclosed for forming trench or via cavities in a single damascene interconnect structure, comprising etching a dielectric layer to form a cavity there and to expose an underlying etch-stop layer, and etching the exposed etch-stop layer to extend the cavity and to expose a conductive feature in an existing interconnect structure, wherein etching the portion of the dielectric layer and etching the exposed portion of the etch-stop layer are performed concurrently with substantially no intervening processing steps therebetween. Also disclosed are methods of forming a via cavity in a dual damascene interconnect structure, comprising forming an etch-stop layer over an existing interconnect structure, forming a dielectric layer over the etch-stop layer, etching a portion of the dielectric layer to form a via cavity in the dielectric layer and to expose a portion of the etch-stop layer, and etching the etch-stop layer to extend the via cavity, where the dielectric layer is covered during etching of the etch-stop layer.