Methods of etching metals in semiconductor devices

A method, comprising:

• forming a first metal layer over a via in a first interlayer dielectric (ILD) layer disposed over a semiconductor substrate;
• forming a second metal layer over the first ILD, wherein the second metal layer includes a second metal different from the first metal;
• forming a third metal layer over the second metal layer, wherein the third metal layer includes a third metal different from the second metal;
• forming a patterned hard mask layer over the third metal layer;
• performing a first dry etching process using a first etchant to the third metal layer through the patterned hard mask layer, thereby forming a conductive feature adjacent to a trench, wherein the trench exposes a portion of the second metal layer;
• performing a second dry etching process to the second metal layer through the patterned hard mask layer using a second etchant different from the first etchant;
• and
• performing a wet etching process to remove the patterned hard mask layer, thereby extending the trench to expose a portion of the first ILD layer.

A semiconductor structure, comprising:

• a via contact disposed in a first interlayer dielectric (ILD) layer, wherein the via contact includes a first etch-stop layer (ESL) disposed over a via bulk layer;
• a second ESL disposed over the via contact, wherein the second ESL includes a first metal, and wherein the first and the second ESLs have different compositions;
• a conductive line disposed over the second ESL, wherein the conductive line includes a second metal different from the first metal;
• and
• a second ILD layer disposed over the first ILD layer, wherein the second ILD layer directly contact sidewalls of the conductive line and the second ESL.