Thermo-desorption measurements during N-doped Ge-rich Ge₂Sb₂Te₅ crystallization

Abstract

Ge-rich Ge2Sb2Te5 (GGST) is considered as one of the best candidates for industrial phase change memory production. GGST memory cells are generally embedded with Si or Ti nitride layers to prevent oxidation, as it leads to an undesired decrease of the GGST crystallization temperature. Furthermore, GGST films are usually doped with elements such as N, C, O, or Bi, aiming to delay GGST crystallization during the fabrication process as well as during memory cell operation. In this work, ultrahigh vacuum thermal desorption spectroscopy (TDS) was performed during isochronal annealing of a N-doped GGST film covered by a 10 nm-thick TiNx layer. Desorption is observed before GGST crystallization, but the comparison between TDS and in situ X-ray diffraction (XRD) measurements shows that the main desorption peak, observed between 653 K and 703 K, occurs after GGST full crystallization. The most prominent desorbing species are Ar, N2, H2, and H. These results show that the TiNx polycrystalline layer cannot prevent N atoms from leaving the GGST layer during annealing, suggesting a progressive change of the N-doped GGST chemical composition during thermal annealing and crystallization.

Exploring the evolution of mass density and thickness of N-doped Ge-rich GeSbTe during multistep crystallization

“…Despite the fact that, as a general rule, one can expect to measure an average electron density using XRR, these inclusions in the GGSTN layer possess closed interfaces that could lead to more complex interactions with reflected X-rays from flat interfaces, misleading XRR interpretations. A second possibility could be linked to N diffusion from the nitride layers into the GGSTN layer 21 . If N atoms are incorporated on interstitial sites in the crystalline grains in the GGSTN layer, the density of the layer could increase without significant change of its thickness.…”