Abstract 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 rocksalt 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.

中文翻译：

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表面氧化对富锗Ge-Sb-Te合金薄膜结晶特性的影响

摘要 我们研究了表面氧化对富锗 Ge-Sb-Te 材料结晶的影响，有望用于在高温 (>350 °C) 下工作的相变存储器。为此，我们将暴露在空气中的薄膜的结构和化学特性与 TiN 封装薄膜的结构和化学特性进行了比较。暴露在空气中的作用是将开始结晶的温度降低 50–60 °C。与在封装薄膜中观察到的均匀成核不同，结晶从表面向薄膜主体进行，导致化学元素的大量重新分布，形成 Ge 晶粒，该晶粒生长直到 Ge 浓度足够低以允许 Ge2Sb2Te5 岩盐相成核. 在空气曝光的胶片中，Ge 结晶优先发生在薄膜表面，而 Ge2Sb2Te5 晶粒在较高温度下发育较晚，并且在薄膜中更深。我们的结果强烈表明，在退火的早期阶段，在氧化物内部或下方形成了“种子”，在比封装薄膜中观察到的温度更低的温度下促进了 Ge 立方相的异质成核。这些种子必然涉及氧，我们推测退火过程中在表面层中形成的结晶 Sb2O3 核起到了这个作用。