Negative electron-beam resist hard mask ion beam etching process for the fabrication of nanoscale magnetic tunnel junctions

Abstract

The authors have demonstrated fabrication of 30 nm diameter perpendicular anisotropy magnetic tunnel junctions (MTJs) using negative electron-beam resist (NER) as the ion beam etching (IBE) hard mask. The NER pillar of 30 nm diameter and 105 nm thickness was fabricated by electron-beam lithography. The redeposition of the MTJ etching debris generated during the IBE on the outer surface of the NER pillar increased the lateral etch resistance of the resist polymer, allowing the edge profile to remain constant for the duration of the MTJ etching, resulting in a vertical MTJ sidewall profile. A multistep IBE (repetition of 45° primary etching and 30° secondary etching) was conducted to reduce the MTJ sidewall redeposition while reducing mechanical damage. The measurement results showed a tunnel magneto-resistance ratio of 22% at 30 nm junction diameter.

High-Density Physical Random Number Generator Using Spin Signals in Multidomain Ferromagnetic Layer

“…The p-MTJ layers, deposited by UHV sputtering (ULVAC, Inc.), use TiN(500)/Ta(30)/Ru(100)/Co-Pd multilayer(52) (thicknesses in angstroms) as the bottom electrode and the free layer, CoFeB(11)/MgO(8)/CoFeB (12), as the (001)oriented MgO tunnel barrier layer and CoFeTb(300)/ Ru(100)/Ti(50) as the pinned layer and top electrode. After arrays of 30 nm, dot-pattern, 100 nm thickness hard mask were created by 80 kV electron beam lithography (Nano-Beam, nB3) in NER (propylene glycol monomethyl ether acetate compound); an ion beam etching (IBE) process was performed by tilting the rotating sample stage with a beam supply voltage of 700 V and an acceleration supply voltage of 100 V [18,19]. After IBE, the MTJ pillar dimensions and etching characteristics were measured using a scanning electron microscope (SEM) and a high-resolution transmission electron microscope (HR-TEM).…”

Temperature dependent nucleation and propagation of domain walls in a sub-100 nm perpendicularly magnetized Co/Ni multilayer

“…7 Nanopillar devices with a lateral size deep below 50 nm have recently been demonstrated. 8,9 Due to the large magnetostatic coupling between the perpendicularly magnetized free and polarizing layers, patterned devices smaller than 100 nm in diameter may not exhibit two remanent states in zero applied field. However, the polarizer may be replaced by a perpendicularly magnetized synthetic antiferromagnet composite to reduce this coupling and render the free layer bistable at zero field.…”