Developing Precursor Chemistry for Atomic Layer Deposition of High-Density, Conformal GeTe Films for Phase-Change Memory

Atomic layer deposition (ALD) of phase-change materials has been suggested as the most feasible technique for the construction of high-aspect-ratio architectures required for ultrahigh-density phase-change random access memory (PcRAM). The recent advances in the ALD technique have established the foundations for the formation of conformal Ge−Te or Ge−Sb−Te films, but their electrical performance as a phase-change memory device has been rarely reported, especially with prolonged cycles. This study introduced Ge(II)−amido guanidinate (Ge(guan)NMe₂ (guan = (ⁱPrN)₂CNMe₂, Me = CH₃)) as a new ALD Ge precursor that was compatible with the high ALD temperature of up to 170 °C, which was necessary for achieving the high-density and stoichiometric as-deposited GeTe thin films. The films were deposited in an amorphous state. Coinjection of NH₃ gas with the Te precursor (Te(SiMe₃)₂) was essential to initiate the feasible ALD reaction with the new Ge(II) precursor. Ab initio calculation proposed plausible exergonic chemical reaction pathways where NH₃ actively participated in the dissociation of both −SiMe₃ and guanidinate ligands from Te and Ge precursors, respectively. The ALD process showed self-limiting growth behavior and produced highly uniform and conformal morphologies. Low impurity levels (<5%) and a low crystallization temperature (180 °C) were observed for the samples deposited at 170 °C. The prototypical memory device showed a current− voltage curve with a voltage snapback region followed by switching to a low resistance state. Over 10⁴ cycling endurance was achieved for the 170 °C grown GeTe film, whereas inferior endurance (<10³) was observed for the low-temperature-grown GeTe.