Underlayer for high performance magnetic tunneling junction MRAM
View Patent ↗An MRAM structure is disclosed in which the bottom electrode has an amorphous TaN capping layer to consistently provide smooth and dense growth for AFM, pinned, tunnel barrier, and free layers in an overlying MTJ. Unlike a conventional Ta capping layer, TaN is oxidation resistant and has high resistivity to avoid shunting of a sense current caused by redeposition of the capping layer on the sidewalls of the tunnel barrier layer. Alternatively, the α-TaN layer is the seed layer in the MTJ. Furthermore, the seed layer may be a composite layer comprised of a NiCr, NiFe, or NiFeCr layer on the α-TaN layer. An α-TaN capping layer or seed layer can also be used in a TMR read head. An MTJ formed on an α-TaN capping layer has a high MR ratio, high Vb, and a RA similar to results obtained from MTJs based on an optimized Ta capping layer.
1. A method of forming an MRAM structure on a substrate, comprising:
(a) forming a bottom electrode that is comprised of a seed layer on a substrate, a Ru, Rh, or Ir conductive layer on the seed layer, and an α-TaN capping layer on the conductive layer wherein the capping layer forms a planar film;
(b) forming an MTJ element comprised of a pinned layer/tunnel barrier/free layer stack and having a top surface, bottom surface, and sidewalls, said bottom surface contacts a top surface of said capping layer in the bottom electrode; and
(c) forming a top electrode on the top surface of the MTJ element.
2. The method of claim 1 wherein the α-TaN capping layer has a thickness of about 50 to 400 Angstroms and a nitrogen content between about 25 and 35 atomic %.
3. The method of claim 2 wherein said α-TaN capping layer is formed by a reactive sputtering process with a nitrogen containing plasma.