Magnetic random access memory (MRAM) has made a prominent progress in memory performance and has brought a bright prospect for the next generation nonvolatile memory technologies due to its excellent advantages. Dry etching process of magnetic thin film is one of the important issues for the magnetic devices such as magnetic tunneling junctions (MTJs) based MRAM. MTJs which are the basic elements of MRAM can be used as bits for information storage. CoFeB is a well-known soft ferromagnetic material, of particular interest for magnetic tunnel junctions (MTJs) and other devices based on tunneling magneto-resistance (TMR), such as spin-transfer-torque MRAM. One particular example is the CoFeB–MgO–CoFeB system, which has already been integrated in MRAM. In all of these applications, understanding and control over the etching properties of CoFeB is crucial. Recently, transferring the pattern by using an Ar⁺ ion milling is a commonly used, although the redeposition of sputter etch products on the sidewalls and the low etch rate are main disadvantages of this method. Other method, which reported the etch rates higher than 50 Å/s for magnetic multilayer structures using Cl₂/Ar plasmas, is also proposed. However, the chlorinated etch residues on the sidewalls of the etched features tend to severely corrode the magnetic material. To prevent corrosion of MTJ layer, the etching of MTJ layer using organic-based gases such as CO/NH₃, CH₃OH, etc. are actively investigated currently.

In this work, MTJ materials such as CoFeB, MgO, etc. were etched using various gas mixtures which can be expected to form volatile metallo-organic compounds and the results were compared with those etched using Cl₂-based gas mixture. As one of the gas mixtures, gas mixtures of carbon monoxide (CO) and ammonia (NH₃) were used as etching gases to form carbonyl volatiles, and the etched features of CoFeB thin films under by Ta cap-material were observed with transmission electron microscopy. The etch results showed the enhanced etch rates higher than 3 times by using a gas mixture of CO/NH₃ compared to that etched by pure CO or NH₃ possibly indicating the formation of products composed of carbonyl volatiles. The composition of etched sidewall was less damaged compared with that etched with Cl₂-based gas. The characteristics of etched MTJs were also compared to the MTJs etched by the other method such as neutral beam etching, etc.