Atomic Layer Deposition of Nanocrystalline-As-Deposited (GeTe)x(Sb2Te3)1-x Films for Endurable Phase Change Memory

This paper introduces a new atomic layer deposition process for highly conformal, nanocrystalline-as-deposited GeTe-Sb2Te3 pseudobinary film growth at a deposition temperature of 130 degrees C. The process utilizes Ge(II)-amidoguanidinate ((GeN)-N-II(CH3)(2)[((NPr)-Pr-i)(2)CN(CH3)(2)]), Te(Si(CH3)(3))(2), and Sb(OC2H5)(3) with an NH3 coreagent. The alternative GeTe and Sb2Te3 subcycles produced various film compositions, all consistent with the GeTe-Sb2Te3 tie lines, owing to the stoichiometric reactions between the precursors without involvement of undesirable side reactions. The density of the nanocrystalline Ge2Sb2Te5 (GST225) films was 6.2 g.cm(-3), similar to the density of the bulk crystalline material. The crystallization behaviors indicated that the distribution of the constituent elements of the GST225 films was highly uniform at the atomic level, as opposed to the case of the low-temperature (100 degrees C)-deposited films. The cubic to hexagonal transition at 350 degrees C upon postannealing produced (0001) hexagonal planes highly aligned along the substrate. The demonstration of the phase change memory device achieved high cycling endurance (>10(7)). Considering that further scaling and optimization of the cell design can improve the electrical performance, the nanocrystalline GST films introduced herein can provide potential utilities in the large-capacity three-dimensional vertical-type phase change memory.