Viable chemical approach for patterning nanoscale magnetoresistive random access memory

Abstract

A reactive ion etching process with alternating Cl2 and H2 exposures has been shown to chemically etch CoFe film that is an integral component in magnetoresistive random access memory (MRAM). Starting with systematic thermodynamic calculations assessing various chemistries and reaction pathways leading to the highest possible vapor pressure of the etch products reactions, the potential chemical combinations were verified by etch rate investigation and surface chemistry analysis in plasma treated CoFe films. An ∼20% enhancement in etch rate was observed with the alternating use of Cl2 and H2 plasmas, in comparison with the use of only Cl2 plasma. This chemical combination was effective in removing metal chloride layers, thus maintaining the desired magnetic properties of the CoFe films. Scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy showed visually and spectroscopically that the metal chloride layers generated by Cl2 plasma were eliminated with H2 plasma to yield a clean etch profile. This work suggests that the selected chemistries can be used to etch magnetic metal alloys with a smooth etch profile and this general strategy can be applied to design chemically based etch processes to enable the fabrication of highly integrated nanoscale MRAM devices.

Molecular mechanisms of atomic layer etching of cobalt with sequential exposure to molecular chlorine and diketones

“…In fact, the variation of cobalt removal rates from several angstroms to several nanometers per cycle has been reported. 4 Despite practical knowledge and potential process optimization success, the mechanism of the process remains largely unknown.…”

Surface chemistry of thermal dry etching of cobalt thin films using hexafluoroacetylacetone (hfacH)

“…Previously, an efficient ALE method has been demonstrated by applying halogen and hydrogen plasma to etch CoFe alloy films [17]. It was discovered that the combination of Cl 2 and H 2 plasma can etch CoFe alloy at a reasonable rate (up to 4.2 nm/min) and can preserve its magnetic properties.…”

“…Since the target of the current investigation is the half-cycle of the ALE process, instead of utilizing plasma methods for surface oxidation, as reported previously [17,19], this study simply utilized cobalt films whose surface are covered by oxide, as the starting point. The overall mechanisms of ALE can be very complicated and they can certainly depend on the surface morphology, cleanliness, and etching conditions.…”

Suboxide/subnitride formation on Ta masks during magnetic material etching by reactive plasmas

“…Also, for magnetic metals, there have been various attempts to devise efficient RIE processes for their smallscale patterning. For example, etching of magnetic materials by Cl 2 based plasmas has been proposed, [5][6][7][8] but under typical conditions of chlorine etching of magnetic materials, metal chlorides are not volatile and corrosion occurs on etched metal surfaces.…”