Chalcogenide-based phase change memory devices have recently garnered significant interest due to their potential scalability beyond that of conventional DRAM and Flash memory technologies.[1] Due to the stringent demands imposed by the scaling roadmap, it is becoming increasingly important to understand the effects of processing on the crystallization properties of the material since it is known that there is an etch-induced material modification layer resulting from patterning.[2] In this work, we examine chemical and structural effects of processing on the crystallization properties of nitrogen doped Ge2Sb2Te5 using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), time resolved laser reflectivity and time resolved X-ray diffraction (XRD). The laser reflectivity results indicate that upon exposure to various etch and ash chemistries the (re)crystallization speed is significantly reduced. Time resolved XRD data further show that the transition temperature from the rocksalt to the hexagonal phase is increased from 400 ºC to ~ 500 ºC. From depth profiled XPS and XAS measurements, we attribute this increase in crystallization time (and increase in transition temperature) to the selective removal and/or oxidization of numerous elemental species (N, Ge, Sb, Te) which alters the local bonding environment and which may result in the formation of additional phases. The relevance of these effects and their ability to potentially alter device performance will also be discussed.

 

[1] Y.C. Chen, C.T. Rettner, S. Raoux et al., IEDM Tech. Dig., p. S30P3, 2006.

[2] E. A. Joseph, T. D. Happ, S.-H. Chen, S. Raoux, et al., Symp. VLSI-Technology Systems and Applications, 2008. pg 142-143, 2008