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.