Multi-step ion beam etching of sub-30 nm magnetic tunnel junctions for reducing leakage and MgO barrier damage

Abstract

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

“…Although the redeposition layer was useful for the side protection of the NER, it must be removed since it may render the MgO tunnel barrier useless by creating a short between the pinned layer and the free layer. This suggested that a multistep ion beam etching, 14 repeating a high angle primary etching step followed by a secondary lower angle etching step, was needed. As shown in Fig.…”

“…But it shows after-corrosion and oxidation problems. Ion beam etching (IBE) 14,15 has also been used for magnetic material etching which also has many problems, such as sidewall redeposition, mechanical etch damage, and low selectivity. Despite these problems for MTJ pattering, the deposition and etch back technique employing a hard mask layer to increase selectivity during processing is widely used.…”

“…Here, we utilized a layer of negative electron-beam resist (NER) 14 to act as the etch mask to overcome hard mask pattering issues and allow untapered etched side wall profiles. By using the nanopattern-defining NER as the hard mask, the need for an additional hard mask layer was removed, reducing overall required etch depth.…”

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).…”

Progress and prospects in nanoscale dry processes: How can we control atomic layer reactions?

“…The etching of metals also has the problem of the redeposition of etching by-products. 12,[188][189][190][191][192][193][194][195][196][197] In self-limiting formation, another difficulty arises for intermetallic compounds or alloys such as CoFe, NiFe, CrFe, and PtMn. Simply, in etching processes for compounds such as high-k materials, dichalcogenides, GaAs, GaP, and GaN, it is difficult to maintain the surface stoichiometry during and after the etching.…”