Dry Etching of MRAM Structures
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Dry Etching of MRAM Structures S.J. Pearton(1), H. Cho(1), K.B. Jung(2), J.R. Childress(2), F. Sharifi(3) and J. Marburger(3) (1)
Department of Materials Science and Engineering University of Florida, Gainesville, FL 32611 (2)
IBM Almaden Research Center San Jose, CA 95120 (3)
Department of Physics University of Florida, Gainesville, FL 32611 ABSTRACT A wide variety of GMR and CMR materials have been patterned by high density plasma etching in both corrosive (Cl2-based) and non-corrosive (CO/NH3) plasma chemistries. The former produce much higher etch rates but require careful in-situ or ex-situ, post-etch cleaning to prevent corrosion of the metallic multilayers. The former may have application for shallow etching of NiFe-based structures, but there is little chemical contribution to the etch mechanism and mask erosion can be a problem. The magnetic performance of patterned MRAM elements is stable over long periods (>1 year) after etching in Cl2 plasmas, provided a suitable cleaning protocol is followed. It is also clear that high ion energies during patterning of magnetic materials can have a significant influence on their coercivity. The effects of ion energy, ion flux and process temperature are discussed. INTRODUCTION As bit densities continue to increase in magnetic random access memories (MRAM) and read/write heads for data storage, there has been increasing need for plasma etching processes which can produce high resolution pattern transfer into these magnetic device structures.[1-8] Due to the fact that the component materials used in these magnetic multilayers (e.g. NiFe-based Giant Magneto Resistive (GMR) materials) form relatively involatile reaction products which cannot be removed readily from the surface in conventional dry etching techniques such as ion milling and reactive ion etching, high resolution pattern transfer has only been realized in high density plasmas. Furthermore a problem often encountered with ion milling techniques is redeposition onto the sidewall of the features being patterned, leading to degradation of the magnetic performance of the device. [9-12] In this paper we summarize plasma chemistries for dry etching of magnetic multilayers (including GMR, CMR and Heusler materials), post-etch cleaning methods and magnetic and structural stability over an extended period. EXPERIMENTAL Full MRAM structures (shown in Figure 1) with total thickness ~2500Å (80Å NiFeCo/10Å CoFe/35Å Cu/15Å CoFe/8-Å NiFeCo/200Å Ta/750Å TaN/800Å CrSi) and with additional 2000Å thick SiO2 masks, and single layers of Ni0.8Fe0.2, Ni0.8Fe0.13Co0.13Co0.07, TaN and CrSi were deposited on Si (100) substrates by dc magnetron sputtering from composite targets. Typical thicknesses of the single layer structures were 3000-5000Å and they were
F10.2.1
masked with Apiezon wax for etch rate measurements. In addition NiMnSb Heusler alloy samples were grown by magnetron sputtering and LaCaMnO3 and PrBaCuMnO3 layers were deposited by pulsed laser deposition. 3000Å SiO2
ETCHED REGION
800Å CrSi 550Å TaN 200Å Ta 80Å NiFe (C
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