Undercut-free patterned aluminum nitride structure and methods for forming the same

A method of patterning a microstructure, comprising:

• forming a layer stack including at least one metal layer and interlayer dielectric material layers over a substrate, wherein the interlayer dielectric material layers comprise an aluminum nitride layer overlying a topmost metal layer of the at least one metal layer;
• forming a continuous aluminum oxide-containing layer over the aluminum nitride layer;
• forming a dielectric spacer layer over the continuous aluminum oxide-containing layer;
• forming at least one contact via cavity extending through the dielectric spacer layer, the continuous aluminum oxide-containing layer, and the aluminum nitride layer, wherein a respective one of the at least one metal layer is physically exposed underneath each of the at least one contact via cavity;
• and
• forming at least one contact via structure in the at least one contact via cavity, wherein each of the at least one contact via structure comprises a respective top portion that is vertically spaced from the interlayer dielectric material layers by an aluminum oxide-containing layer.

A method of patterning a microstructure, comprising:

• forming metal layers vertically spaced by aluminum nitride layers over a substrate;
• converting a surface portion of a topmost aluminum nitride layer among the aluminum nitride layers into a continuous aluminum oxide-containing layer by oxidizing the surface portion;
• forming a dielectric spacer layer over the continuous aluminum-oxide containing layer;
• forming contact via cavities extending through the dielectric spacer layer and down to a respective one of the metal layers using etch processes;
• and
• forming contact via structures in the contact via cavities, wherein at least one of the contact via structures provide electrical connected between at least two metal layers that are vertically spaced from the substrate by different vertical spacings.