Thermochemical Stability of IrO_2 Bottom Electrodes in Direct-Liquid-Injection Metalorganic Chemical Vapor Deposition of Pb(Zr,Ti)O_3 Films

摘要

The IrO_2 film has been regarded as a leading candidate bottom electrode of ferroelectric capacitors in ferroelectric random access memories (FRAMs). We have addressed a new issue on the thermochemical stability of IrO_2 bottom electrodes during the growth of Pb(Zr,Ti)O_3 (PZT) ferroelectric films on such electrode using direct liquid injection metalorganic chemical vapor deposition (DLI-MOCVD). The IrO_2 electrode thermally dissociated at elevated temperatures in vacuum ambient at a low oxygen pressure. It was also reduced by carbon and hydrogen dissociated from the solvent in liquid solution. The reduction of IrO_2 by the solvent was more pronounced at lower temperatures, which is attributed to the longer residence time of solvent molecules on the IrO_2 surface at lower temperatures. The reduction of IrO_2 was also induced by the metal elements Zr and Ti in metalorganic precursors because they have higher chemical affinities with oxygen than Ir. The reduction by Zr and Ti metal elements was more pronounced at higher temperatures. The use of thin Pt interlayers is a promising solution for the prevention of the reduction of IrO_2 electrode during the growth of PZT films.