Growth mechanism of Ge2Sb2Te5 thin films by atomic layer deposition supercycles of GeTe and SbTe

The film with a composition close to Ge₂Sb₂Te₅ was fabricated by the supercycle atomic layer deposition (ALD) of GeTe and SbTe, followed by tellurization annealing. Supercycle processes are widely used for thin film deposition of multicomponent materials and often exhibit non-ideal growth behavior. Since only in situ analysis can reveal the substrate-dependent growth behavior, we used in situ quartz crystal microbalance (QCM) to study the growth mechanism during ALD supercycle processes at 85 °C. GeTe grown on SbTe was more Te-deficient than continuously grown GeTe film. As a result, more Te-deficient Ge-Sb-Te films were formed than expected. By annealing in a Te ambient at 250 °C, the Te-deficient Ge-Sb-Te film was converted to the Ge_0.23Sb_0.23Te_0.54 close to Ge₂Sb₂Te₅ film, which had a high density equivalent to 95 % of the FCC structure of Ge₂Sb₂Te₅. The film showed excellent conformality and uniform composition in a trench pattern, suggesting a uniform crystallization temperature of 118 °C at all locations.