Amorphization of Crystalline Phase Change Material by Ion Implantation
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1251-H02-06
Amorphization of Crystalline Phase Change Material by Ion Implantation Simone Raoux1,2, Guy M. Cohen2, Robert M. Shelby3, Huai-Yu Cheng1,4, and Jean L. Jordan Sweet2 1
IBM/Macronix PCRAM Joint Project IBM T. J. Watson Research Center, P. O. Box 218, Yorktown Heights, New York 10598, USA 3 IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA 4 Macronix Emerging Central Lab., Macronix International Co. Ltd., 16 Li-Hsin Rd. Science Park, Hsinchu, Taiwan, ROC 2
ABSTRACT Germanium ion implantation at an energy of 30 keV was used as a different method to re-amorphize thin films of crystalline phase change material Ge2Sb2Te5 (GST). It was found that rather low doses of 5x1013 cm-2 were sufficient to re-amorphize GST. Amorphization was determined by X-ray diffraction (XRD) as well as reflectivity measurements. Re-crystallization characteristics of ion-implantation-amorphized samples was studied using time-resolved XRD. It showed that samples re-crystallize at an increased crystallization temperature with increasing dose compared to as-deposited material. A static laser tester was applied to measure the crystallization times of material that was (1) as–deposited amorphous; (2) crystallized by annealing and re-amorphized by melt-quenching using a laser pulse; and (3) crystallized by annealing and re-amorphized by ion implantation. It was found that as-deposited amorphous and high-dose ion implanted samples had longer crystallization times while melt-quenched amorphous and low-dose ion implanted samples had shorter crystallization times.
INTRODUCTION Phase change materials are the core component in re-writable optical storage technology and phase change random access memory (PCRAM) technology [1]. They exist in amorphous and crystalline phases that have very different optical and electrical properties, and these differences in properties are used to store information. In optical storage the difference in reflectivity (about 30 %) is used [2] while in PCRAM the orders of magnitude difference in resistivity is applied [3]. Many of the phase change properties such as crystallization temperature and crystallization time depend on the structure and history of the phase change material. In many cases the phase change material is deposited by sputter deposition, which will lead to amorphous thin films if deposition is performed at room temperature, or polycrystalline films if deposition is done at elevated temperature above the crystallization temperature. Single-crystalline material, on the other hand, can be obtained if films are deposited epitaxially [4], if phase change material is grown as nanowires [5-7], or is synthesized by solution-based chemistry in nanoparticle form [8]. The structure of the amorphous phase and its thermal history also
has a large influence on crystallization properties [9]. The properties of the amorphous phase can vary greatly depending on the way it was formed and treated (by deposition at room temperature, by melt-quenching, treated thermally or by ion bombardment) [9-
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