Diffusion layer for magnetic tunnel junctions

A method, comprising:

• forming an interconnect layer over a substrate, wherein forming the interconnect layer comprises:
• forming an interlayer dielectric (ILD) layer over the substrate;
• and
• forming a via structure with a barrier layer and a metal fill layer within the ILD layer;
• forming a capping layer comprising a first portion in the metal fill layer and surrounded by the barrier layer and a second portion protruding above top surfaces of the barrier layer and the ILD layer;
• and
• forming a magnetic tunnel junction (MTJ) structure surrounding the second portion of the capping layer.

A method, comprising:

• forming a first interconnect layer over a substrate, wherein forming the first interconnect layer comprises forming a first conductive structure with a first conductive material;
• forming a second interconnect layer over the first interconnect layer, comprising:
• a second conductive structure with a second conductive material that is different from the first conductive material and is in contact with the first conductive material, and
• forming a barrier layer with a metal layer and a doped metal nitride layer;
• and
• forming a magnetic tunnel junction (MTJ) structure on the second conductive structure.