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M2001-0043 Process for Formation and use of Amorphous Tantalum Oxynitride Hard mask for Patterning Tunnel Junction Structures Disclosure Number: IPCOM000016681D
Original Publication Date: 2003-Jul-09
Included in the Prior Art Database: 2003-Jul-09
Document File: 4 page(s) / 60K

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Formation of an amorphous TaON hard mask for patterning of magnetic tunnel junctions for MRAM devices. The hard mask is formed by anodization of the TaN cap layer of a magnetic tunnel junction stack

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  M2001-0043 Process for Formation and use of Amorphous Tantalum Oxynitride Hard mask for Patterning Tunnel Junction Structures

      The patterning of magnetic random access memory (MRAM) devices usually requires the use of a hard mask for good definition of the submicron patterned magnetic tunnel junction (MTJ) structures. Depending on the integration scheme, either an electrically conducting or insulating material is chosen for the hard mask. The top Cu write line then makes contact to the conducting hard mask remaining on top of the patterned stack, or the hard mask material is subsequently etched to make direct contact of the Cu with the stack cap layer We propose the use of an insulating hard mask material, tantalum oxynitride (TaON), for etching the MTJ stack. The TaON hard mask layer is formed by a simple anodic oxidation process of the as-grown top TaN layer of the MTJ stack, leading to reduced stress. This also avoids the use of an additional vacuum deposition process for the hard mask. Since the TaON is amorphous, it is expected to provide better pattern definition than polycrystalline hard mask materials. In addition, it can be etched using fluorine-based chemistry instead of the more corrosive chemistry needed for some alternative hard mask materials.

    Two proposed integration schemes using the TaON hard mask are shown in Fig. 1 and Fig. 2. The precursor of the hard mask material, TaN with a thickness of about 500Å, is deposited as part of the MTJ stack. In the next step, part of the TaN is anodized to convert it to TaON. Anodization involves oxidation of the TaN layer in an electrolyte. Ta and TaN are typically anodized in aqueous based electrolyes. A common electrolyte used is 0.01% citric acid that has a pH 3.5 and a resistivity of 8000 ohm cm. The counter electrode used is a Pt plated Ti material and act in this case as the cathode. The incorporation of N into the precursor film has been shown to increase the thermal stability of the a...