Sunday, November 8, 2015: 3:30 PM
251D (Salt Palace Convention Center)
As advanced memory devices begin to dictate the adoption of complex magnetic and multiferroic materials, overcoming the challenge of achieving high-fidelity patterning for these multifunctional films becomes imperative. Physics- and chemistry-based modeling affords tremendous understanding of elementary reaction mechanisms in plasma patterning; however, the parameters necessary for kinetic modeling are sometimes difficult to obtain experimentally for novel multifunctional compounds. Developing a comprehensive framework for selecting viable chemistries in plasma patterning of magnetic metals has the potential to reduce the time and cost associated with design of experiments.
In this work, a generalized methodology, combining thermodynamic assessment of various etching chemistries and kinetic verification of etching efficacy, is proposed. To screen various chemistries, reactions between the dominant vapor phase/condensed species at various partial pressures of reactants are first considered. The volatility of etch product is determined to aid the selection of viable etch chemistry. Magnetic tunnel junction (MTJ) based MRAM (Magnetic Random Access Memory) was used as a case study to address the challenge of patterning constituent materials of multilayers. Ar ion beam milling was a traditional method in patterning MRAM devices; however, sidewall re-deposition results in electrical shorts as the features become smaller with higher aspect ratios. Selected metals (Fe, Co, Pt) and their alloys within the MRAM were studied by the generalized approach. To validate the thermodynamic calculation, films were patterned using a modified reactive ion etch process of halogen discharge with subsequent H2 plasma exposure. To further improve selectivity to mask materials, a separate novel method of Ar ion beam assisted chemical etch (IBACE) was then investigated.
The etch rate of Fe, Co, and Pt were enhanced 40%, 25%, and 20% respectively with secondary H2 chemistry. X-ray photoelectron spectroscopy (XPS) suggested chemical removal of non-volatile metal chlorides by H2 plasma. Moreover, characterization through superconducting quantum interference device (SQUID) proved that coercive field strength of magnetic alloy after Cl2 plasma can be recovered by additional H2 plasma exposure from 63.6 to 20.9 Oe. Etching of metals and alloys was further examined in organic solution by mass spectroscopy to verify formation of organometallic complexes predicted by thermodynamics. IBACE, a vacuum-compatible process was developed and proven to be effective in patterning magnetic metal stacks.