Nanomechanical morphology of amorphous, transition, and crystalline domains in phase change memory thin films
Nanomechanical morphology of amorphous, transition, and crystalline domains in phase change memory thin films
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DOI：
10.1016/j.apsusc.2014.06.135
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发表时间：
2014-06
影响因子：
6.7
通讯作者：
J. Bosse;I. Grishin;B. Huey;O. Kolosov
中科院分区：
文献类型：
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作者：
J. Bosse;I. Grishin;B. Huey;O. Kolosov
在寻找可以与传统随机存取存储器相抗衡的相变材料(PCM)时，需要对非晶态到晶态的相变有完全的了解。对于著名的Ge2Sb2Te5(GST)和GeTe(GT)硫系化合物，分别表现出形核和生长主导的结晶动力学，本工作探索了50 nm薄膜中非晶相和晶相的纳米机械形态。将这些相变材料样品置于横跨结晶温度的横向温度梯度，可以进行详细的形态研究。对产生的非晶区、过渡区和结晶区的表面和深度相关分析是通过浅角截面实现的，这是唯一利用束出口Ar离子抛光实现的。为了分辨不同的相结构，用超声力显微镜(UFM)同时观察到非晶相和晶相之间的相对硬度差异，自由膜表面的非晶相和晶相的相对硬度差分别为14%和20%。对于GST和GT，成核优先发生在PCM-衬底和自由膜界面，而精细的亚表面结构与溅射方向有关。以这种方式结合表面和横截面的纳米机械映射允许以纳米级的横向和深度分辨率对微结构和缺陷进行3D分析，适用于需要检测弹性模数或硬度的细微变化的广泛的材料表征研究。
In the search for phase change materials (PCM) that may rival traditional random access memory, a complete understanding of the amorphous to crystalline phase transition is required. For the well-known Ge2Sb2Te5(GST) and GeTe (GT) chalcogenides, which display nucleation and growth dominated crystallization kinetics, respectively, this work explores the nanomechanical morphology of amorphous and crystalline phases in 50 nm thin films. Subjecting these PCM specimens to a lateral thermal gradient spanning the crystallization temperature allows for a detailed morphological investigation. Surface and depth-dependent analyses of the resulting amorphous, transition and crystalline regions are achieved with shallow angle cross-sections, uniquely implemented with beam exit Ar ion polishing. To resolve the distinct phases, ultrasonic force microscopy (UFM) with simultaneous topography is implemented revealing a relative stiffness contrast between the amorphous and crystalline phases of 14% for the free film surface and 20% for the cross-sectioned surface. Nucleation is observed to occur preferentially at the PCM-substrate and free film interface for both GST and GT, while fine subsurface structures are found to be sputtering direction dependent. Combining surface and cross-section nanomechanical mapping in this manner allows 3D analysis of microstructure and defects with nanoscale lateral and depth resolution, applicable to a wide range of materials characterization studies where the detection of subtle variations in elastic modulus or stiffness are required.