Etching method for preparing a stepped structure

A method for forming a stepped structure on a substrate, comprising:

• preparing a multi-layer film stack on a substrate having alternating layers of differing composition, wherein said alternating layers of differing composition include one or more layers of a first composition and one or more layers of a second composition;
• preparing a mask layer on said multi-layer film stack and forming a mask pattern in said mask layer to expose a portion of said one or more layers of said first composition;
• and
• preparing a stepped structure having one or more steps using a process sequence comprising the following:
• transferring said mask pattern to said one or more layers of said first composition to form a first layer pattern in said one or more layers of said first composition using a first etch process and stopping on said one or more layers of said second composition,
• trimming said mask pattern to expose another portion of said one or more layers of said first composition using a mask trim process, and
• following said trimming, transferring said first layer pattern to said one or more layers of said second composition using a second etch process and stopping on said one or more layers of said first composition.