Top electrode coupling in a magnetoresistive device using an etch stop layer

A method of manufacturing a magnetoresistive device, comprising:

• depositing a lower layer of conductive material on a substrate;
• depositing a plurality of layers corresponding to a magnetoresistive stack over the lower layer of conductive material;
• depositing an upper layer of conductive material over the plurality of layers corresponding to the magnetoresistive stack;
• depositing a layer of hard mask over the upper layer of conductive material;
• etching the layer of hard mask to form a patterned hard mask;
• etching the upper layer of conductive material to form a top electrode;
• etching the plurality of layers corresponding to the magnetoresistive stack to form the magnetoresistive stack;
• depositing a layer of silicon nitride over exposed portions of the patterned hard mask, the top electrode, the magnetoresistive stack, and the lower layer of conductive material;
• depositing a first layer of silicon dioxide over the layer of silicon nitride;
• forming a patterned layer of photoresist over the first layer of silicon dioxide;
• forming a bottom electrode from the lower layer of conductive material, wherein forming the bottom electrode includes removal of portions of the layer of silicon nitride, portions of the first layer of silicon dioxide, and portions of the lower layer of conductive material that are not covered by the layer patterned layer of photoresist, wherein forming the bottom electrode results in a partially formed device having remaining portions of the first layer of silicon dioxide and the layer of silicon nitride over a remaining portion of the lower layer of conductive material, wherein the remaining portion of the lower layer of conductive material corresponds to the bottom electrode;
• depositing a second layer of silicon dioxide over the partially formed device and portions of the substrate not covered by the partially formed device;
• performing a polishing step to expose the top electrode, wherein the polishing includes removing (i) portions of the first and second layers of silicon dioxide, (ii) portions of the layer of silicon nitride on a top surface and sidewalls of the patterned hard mask, and (iii) the patterned hard mask;
• depositing a third layer of silicon dioxide over (i) the top electrode as exposed, (ii) exposed portions of the first and second layers of silicon dioxide, and (iii) exposed portions of the layer of silicon nitride;
• and
• forming a via through the third layer of silicon dioxide to expose at least a top portion of the top electrode within the via, wherein forming the via further comprises etching the first layer of silicon dioxide and the second layer of silicon dioxide below the top portion of the top electrode using an etching chemistry selective with respect to silicon nitride such that portions of the layer of silicon nitride remaining after the polishing step act as an etch stop such that the portions of the layer of silicon nitride remaining after the polishing step are not removed and act as a barrier to further etching during the formation of the via.