Plasma etching processes for spin electronic devices
Recently, R&D in Spinelectronics, a domain that merges magnetism and electronics, have developed very promising applications in the field of magnetic memories (MRAM). A complete expertise of the patterning and integration of magnetic materials needs to be developed at the same level of the CMOS technology in order to bring spintronics devices into mass production.
Data in MRAM are not stored as electric charge or current flows, but by magnetic storage elements. The elements are formed from two ferromagnetic plates, each of which can hold a magnetic field, separated by a thin insulating layer. The development of MRAM devices requires the optimization of the fabrication process, which is very hallenging since the core device is composed of a great number of different thin magnetic layers with a 1nm thick insulating layer in between.
So far, the etching of magnetic materials has been performed using Ion Beam Etching techniques. However, this type of etching, based on pure sputtering, is non uniform and non selective and generates significant slopes in the final device rendering critical dimension control very difficult. Moreover, severe metal deposition is observed on the sidewalls of the structures, often generating shorts between the different parts of the magnetic devices. Going to traditional plasma etching techniques could be very beneficial to the development of spintronic based devices. Indeed, plasma etching processes lead in principle to more volatile etch by-products than Ion beam etching, limiting the amount of metal based products re-deposited on the sidewalls of the structures. The LTM etch team dedicates its 200 mm etch cluster tool equipped with powerful characterization techniques of the plasma and plasma surface/interactions (XPS, optical emission , mass spectrometry..) to study the etching of complex stacks of magnetic materials. Various plasma chemistries are investigated in order to minimize the metal etch products deposition on the sidewalls (such as CO/NH3 based chemistries) and the assistance of temperature during the plasma process on the product volatility is also be evaluated. Other chemistries using methanol are also investigated since this type of chemistry can also lead to the formation of etch by-products that can be easily rinsed.
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