Magnetic tunnel junction patterning using Ta/TaN as hard mask
View Patent ↗An MTJ MRAM cell is formed by using a reactive ion etch (RIE) to pattern an MTJ stack on which there has been formed a bilayer Ta/TaN hard mask. The hard mask is formed by patterning a masking layer that has been formed by depositing a layer of TaN over a layer of Ta on the MTJ stack. After the stack is patterned, the TaN layer serves at least two advantageous purposes: 1) it protects the Ta layer from oxidation during the etching of the stack and 2) it serves as a surface having excellent adhesion properties for a subsequently deposited dielectric layer.
1. A patterned MRAM MTJ cell comprising:
an MTJ stack, said stack including an upper ferromagnetic free layer, a lower ferromagnetic pinned layer and a tunneling barrier layer formed therebetween;
a single bilayer capping and masking layer formed on said upper ferromagnetic free layer of said MTJ stack, said single bilayer comprising:
a capping layer of Ta formed to a thickness between 200 and 400 angstroms on said ferromagnetic free layer, said Ta layer being substantially free of oxidation;
a masking layer of TaN formed to a thickness between 100 and 200 angstroms on top of said layer of Ta; wherein
said single bilayer capping and masking layer are patterned and
said MTJ stack is conformally patterned by said patterned single bilayer capping and masking layer and wherein said TaN layer protects said Ta capping layer and provides improved adhesion to contiguous dielectric materials; whereby
a layer of dielectric material formed surrounding said MTJ cell is rendered smooth and coplanar and well bonded to an upper surface of said TaN layer as a result of said improved adhesion properties.
2. The MRAM cell of claim 1 wherein said layer of dielectric material is a layer of SiN, SiO 2 , F-doped SiOx, C-doped SiO 2 and their laminated combinations and said layer of dielectric material is rendered smooth and coplanar, with no loss of adhesion, by a process of CMP.