R&D: Thermo-Desorption Measurements During N-Doped Ge-rich Ge2Sb2Te5 Crystallization

Nanotechnology has published an article written by J Remondina, A Portavoce, M Bertoglio, Aix-Marseille University/CNRS, IM2NP, Faculté des Sciences de Saint-Jérôme case 142, F-13397 Marseille, France, G Roland, Aix-Marseille University/CNRS, IM2NP, Faculté des Sciences de Saint-Jérôme case 142, F-13397 Marseille, France, and STMicroelectronics, 850 Rue Jean Monnet, F-38920 Crolles, France, E Petroni, STMicroelectronics, TR&D, Agrate Brianza, Italy, D Benoit, Y Le Friec, F Lorut, STMicroelectronics, 850 Rue Jean Monnet, F-38920 Crolles, France, and M Putero, Aix-Marseille University/CNRS, IM2NP, Faculté des Sciences de Saint-Jérôme case 142, F-13397 Marseille, France.

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 TiN_x layer. Desorption is observed before GGST crystallization, but the comparison between TDS and in situ x-ray diffraction 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 TiN_x 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.“