Effects of surface oxidation on the crystallization characteristics of Ge-rich Ge-Sb-Te alloys thin films

Marta Agati (1) , Clément Gay (1) , Daniel Benoit (2) , Alain Claverie (3)

1 CEMES - Centre d'élaboration de matériaux et d'études structurales
2 ST-CROLLES - STMicroelectronics [Crolles]
3 CEMES-MEM - Matériaux et dispositifs pour l'Electronique et le Magnétisme

We have studied the effect of surface oxidation on the crystallization of Ge-rich Ge-Sb-Te materials, promising for Phase Change Memories working at high temperatures (>350°C). For this, we have compared the structural and chemical characteristics of films left exposed to air with those shown by TiN-encapsulated films. The effect of air exposure is to lower the temperature at which the onset of crystallization starts by 50-60°C. Instead of homogeneous nucleation observed in encapsulated films, crystallization proceeds from the surface towards the bulk of the film and results in a massive redistribution of the chemical elements, forming Ge grains which grow until Ge concentration is low enough to allow the Ge2Sb2Te5 cubic phase to nucleate. In the air-exposed films, Ge crystallization preferentially occurs at the film surface while the Ge2Sb2Te5 grains develop later, at higher temperature, and deeper in the film. Our results strongly suggest that "seeds" are formed in or below the oxide during the early stage of annealing, promoting the heterogeneous nucleation of the Ge cubic phase at a lower temperature than observed in encapsulated films. These seeds necessarily involve oxygen and we speculate that crystalline Sb2O3 nuclei formed in the surface layer during annealing play this role.

Mots clés: Phase Change Materials; Ge-Sb-Te; oxidation; crystallization; surface engineering; transmission electron microscopy

Domaines: Science des matériaux [cond-mat.mtrl-sci]; Micro et nanotechnologies/Microélectronique

Marta Agati, Clément Gay, Daniel Benoit, Alain Claverie. Effects of surface oxidation on the crystallization characteristics of Ge-rich Ge-Sb-Te alloys thin films. Applied Surface Science, 2020, 518, pp.146227. ⟨10.1016/j.apsusc.2020.146227⟩. ⟨hal-03015408⟩