Method for using ultra thin ruthenium metal hard mask for etching profile control

A method of processing a substrate, comprising:

• forming a multi-layer hard mask stack comprising at least a first metal hard mask layer and a second metal hard mask layer underlying the first metal hard mask layer, the second metal hard mask layer being a ruthenium metal hard mask layer comprising ruthenium, the multi-layer hard mask stack formed overlying over one or more underlying layers on the substrate, the one or more underlying layers comprising a dielectric hard mask;
• etching the multi-layer hard mask stack to provide a patterned ruthenium metal hard mask layer to expose portions of the one or more underlying layers, by using a first etch process to etch the first metal hard mask layer and a second etch process to etch the ruthenium metal hard mask layer, the first etch process and the second etch process being different, additional patterned layers not being formed above the multi-layer hard mask between performing the first etch process and performing the second etch process;
• and
• etching the exposed portions of the one or more underlying layers using the patterned ruthenium metal hard mask layer as a mask to protect unexposed portions of the one or more underlying layers, etching the exposed portions of the one or more underlying layers comprising etching portions of the dielectric hard mask layer.