A novel metallic complex reaction etching for transition metal and magnetic material by low-temperature and damage-free neutral beam process for non-volatile MRAM device applications

Abstract

A new oxidation reaction at ultralow temperature (-30ºC) by bombardment of O 2 neutral beam can be enhanced at the extremely low activation energy, which can efficiently form a thin oxide film of all transition metal, such as platinum and ruthenium. Meanwhile, a novel neutral beam enhanced chemical etching for transition metals and magnetic materials was proposed without chemical and physical damages at ultralow temperature through Metallic Complex Reaction process. Highly anisotropic etching profile without both any sidewall re-deposition and damages on magnetic properties could be achieved just with a pure chemical reaction between ethanol and metallic oxide with low kinetic energy by neutral beam for the first time. This new etching technology has been considered as a breakthrough technology to develop next generation MRAM devices. IntroductionMagnetic random access memory (MRAM), which can offer similar performance to that of DRAM, higher density than SRAM, and faster speed and longer write endurance with nonvolatility than flash memory, might be suitable for replacement of numerous volatile and nonvolatile semiconductor memories that are currently in use. The etching technology of magnetic tunnel junction (MTJ) stack, which is composed of magnetic materials (nickel-iron alloy (NiFe), cobalt-iron alloy (CoFe) etc.) and transition metals (ruthenium (Ru), platinum (Pt), tantalum (Ta) etc.), is the serious problem to limit the miniaturization of MRAM devices. Several methods have been applied as shown in Table I. Halogen-gas-based reactive ion etching (RIE) require a high temperature (>200°C) due to low vapor pressure, which causes thermal damages to magnetic properties, as well as post-corrosion generation. Conversely, the ion milling was limited by the several problems, such as miniaturization, sidewall re-deposition and physical sputtering damages due to the high energy [1][2][3].In this study, to overcome these processing problems, a damage-free and low temperature (-30°C) neutral beam etching technology [4, 5] without any halogen gases has been proposed for etching transition metals and magnetic materials through our newly proposed Metallic Complex Reaction process. Experimental Figure 1 shows a neutral beam enhanced chemical etching apparatus. Oxygen (O 2 ) and/or argon (Ar) gases are introduced into the plasma chamber, which excited by an inductively couples plasma (ICP) source, and then accelerated Ar + or O 2 + pass through the silicon aperture, and Ar, O 2 neutral beams are efficiently formed by maintaining the kinetic energy without any charge built-up. Then, the ethanol (C 2 H 5 OH or EtOH) gas directly injected into the process chamber without any dissociation in plasmas and directly absorbed on the material surface. Finally, the etching of these materials was investigated by combination of surface oxidation and Metallic Complex Reaction due to bombardment of Ar+O 2 neutral beams. Results and discussionsAs Ta was widely used in MRAM as electrode, Ta etching was investigated through Metallic Complex...

A Neutral Beam Process for Controlling Surface Defect Generation and Chemical Reactions at the Atomic Layer

“…Figure 8 shows the reaction energies and etching shapes obtained in the oxidation and complexing reactions of transition metals such as Ta, Ru and Pt. 23 The oxidation and complexing reactions even went ahead even for Pt, which is normally difficult to oxidize, and since ideal shapes were formed matching the shape of the mask, this verifies that the proposed neutral beam process can bring about oxidation and complexing reactions. We also found that the oxidation and complexing reactions used in neutral beam etching caused absolutely no deterioration of the magnetic properties observed in plasma etching.…”

“…This paper introduces the application of sub-10-nm structure fabrication technology and its application to devices, [11][12][13][14][15][18][19][20][21] a low-k film deposition technique based on the control of polymerization reactions at the atomic level, 22 and an etching technique for magnetic materials and transition metals that controls the oxidation and complexing reactions at the atomic layer level. 23…”

“…Also, since a high substrate temperature is needed to evaporate the reaction products, the thermal history causes the magnetic properties to deteriorate. 23 On the other hand, in ion milling methods using physical sputtering with argon ions, these materials have poor selectivity relative to the mask, and sputtered atoms become attached to the side walls of the etched side walls so that detailed processing is difficult to achieve in the first place. To resolve these problems, the authors have proposed a method that can bring about chemical reactions at low temperatures with good efficiency.…”

“…To resolve these problems, the authors have proposed a method that can bring about chemical reactions at low temperatures with good efficiency. This method uses atomic layer oxidation and complexing reactions 23,24 that are completely different from the conventional chemical reactions. According to a computational science analysis, neutral beam processing can bring about surface reactions at the ideal atomic layer level.…”

“…We also found that the oxidation and complexing reactions used in neutral beam etching caused absolutely no deterioration of the magnetic properties observed in plasma etching. 23…”