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Crystallization Kinetics of Sputter-Deposited Amorphous Aginsbte Films Walter K

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Crystallization Kinetics of Sputter-Deposited Amorphous Aginsbte Films Walter K Crystallization kinetics of sputter-deposited amorphous AgInSbTe films Walter K. Njoroge and Matthias Wuttig Citation: Journal of Applied Physics 90, 3816 (2001); doi: 10.1063/1.1405141 View online: http://dx.doi.org/10.1063/1.1405141 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/90/8?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Improved phase-change characteristics of Zn-doped amorphous Sb7Te3 films for high-speed and low-power phase change memory Appl. Phys. Lett. 103, 031914 (2013); 10.1063/1.4816062 Studies on melt-quenched AgInSbTe system AIP Conf. Proc. 1512, 38 (2013); 10.1063/1.4790899 Crystallization and high temperature shape memory behavior of sputter-deposited NiMnCoIn thin films Appl. Phys. Lett. 96, 173102 (2010); 10.1063/1.3407670 Study on the crystallization by an electrical resistance measurement in Ge 2 Sb 2 Te 5 and N-doped Ge 2 Sb 2 Te 5 films J. Appl. Phys. 102, 113507 (2007); 10.1063/1.2818104 Atomic force microscopy measurements of crystal nucleation and growth rates in thin films of amorphous Te alloys Appl. Phys. Lett. 84, 5240 (2004); 10.1063/1.1764591 Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 41.89.10.241 On: Wed, 15 Jun 2016 08:40:52 JOURNAL OF APPLIED PHYSICS VOLUME 90, NUMBER 8 15 OCTOBER 2001 Crystallization kinetics of sputter-deposited amorphous AgInSbTe films Walter K. Njoroge I. Physikalisches Institut der RWTH Aachen, D-52056 Aachen, Germany and Department of Physics, Kenyatta University, P.O. Box 43844 Nairobi, Kenya Matthias Wuttiga) I. Physikalisches Institut der RWTH Aachen, D-52056 Aachen, Germany and ISG3, Forschungszentrum Ju¨lich, D-52428 Ju¨lich, Germany ͑Received 20 March 2001; accepted for publication 26 July 2001͒ AgInSbTe films have recently attracted considerable interest as advanced materials for phase change recording. For this application the determination of crystallization kinetics is of crucial importance. In this work the temperature dependence of structural and electrical properties of sputtered AgInSbTe films has been determined. Temperature dependent measurements of the electrical resistance have been employed to study the kinetics of structural changes of these films. Upon annealing a major resistivity drop is observed at around 160 °C which can be attributed to a structural change as corroborated by x-ray diffraction. X-ray diffraction shows an amorphous phase for as-deposited films, while crystalline films with hexagonal structure (aϭ4283 Å, cϭ16 995 Å͒ are obtained upon annealing above 160 °C. By applying Kissinger’s method, an activation energy of 3.03Ϯ0.17 eV is obtained for the crystallization. X-ray reflection measurements reveal a density increase of 5.2%Ϯ0.2% and a thickness decrease of 5.5%Ϯ0.2% upon crystallization. © 2001 American Institute of Physics. ͓DOI: 10.1063/1.1405141͔ I. INTRODUCTION changes of Ag0.08In0.13Sb0.49Te0.30 . Structural properties of vanadium doped AgInSbTe films have also been reported by Materials which can be stabilized in two different physi- Duc et al.14 and Tominaga et al.11,15 cal states that exhibit significantly different optical properties The determination of crystallization kinetics and the un- have attracted much interest in recent years due to their po- derlying mechanisms is of crucial importance for the perfor- tential application in phase change media technology. These mance of the material. In addition, it provides useful infor- materials are used as the memory device in rewritable phase mation to improve the switching behavior and enables a 1–3 change optical disks. The key attributes for promising re- higher rate of data transfer and the development of new ma- writable storage media include high-speed writing and eras- terials with superior properties. In this work we report on the ing, adequate number of overwrite cycles, stable marks, suf- temperature dependence of structural and electrical proper- ficiently high signal-to-noise ratio, and good recording ties of sputtered AgInSbTe films. Temperature dependent 4 sensitivity. Currently applied phase change media are measurements of the electrical resistance have been em- mainly based on two families of phase change materials, ployed to study the kinetics of structural changes of these namely ternary Ge:Sb:Te alloys or quaternary Ag:In:Sb:Te films. X-ray reflectivity measurements ͑XRR͒ are used to alloys. Several ternary stoichiometric alloys formed with determine the temperature dependence of thickness, rough- 5 compositions along the GeTe–Sb2Te3 line have been iden- ness and the density of the films. The temperature depen- tified as possible candidates for use in erasable disks. Among dence of the film structure is determined by x-ray diffraction these alloys are GeSb4Te7 , GeSb2Te4 and Ge2Sb2Te5 . Most ͑XRD͒. In the next section, the experimental procedures are 6–10 studies have been focused on Ge2Sb2Te5 due to its ex- discussed while the results are presented and discussed in the cellent properties regarding the reflectivity change between third section. A short summary is presented in Sec. IV. the amorphous and crystalline state, its cyclability of record- ing and erasing, and also its durability at room temperature. Recently, in order to improve the stability of amorphous II. EXPERIMENTAL PROCEDURES marks at high temperature and also to increase the density of AgInSbTe films with thickness between 40 and 200 nm the marks, a new alloy has been developed based on 11 were deposited on glass or silicon substrates at room tem- AgInSbTe. A high density of 12 GB capacity and a high perature by dc magnetron sputtering. The composition of the data-transfer rate of 30 Mbps corresponding to that of a sputtered film was determined by energy dispersive x-ray DVD-ROM have been reported using an AgInSbTe phase 12 analysis to Ag5In6Sb59Te30 . The background pressure of the change material. Despite the technological use of this ma- sputter system was 2ϫ10Ϫ7 mbar. An Ar pressure of 7.5 terial, very little information has been reported on its prop- ϫ Ϫ3 13 10 mbar and a power of 100 W were used to deposit the erties. Iwasaki et al. have reported on the structural films. The resulting growth rate was determined to be 0.5 nm/s. XRR measurements were performed to determine the a͒Electronic mail: [email protected] thickness, roughness and the density of the films while XRD 0021-8979/2001/90(8)/3816/6/$18.003816 © 2001 American Institute of Physics Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 41.89.10.241 On: Wed, 15 Jun 2016 08:40:52 J. Appl. Phys., Vol. 90, No. 8, 15 October 2001 W. K. Njoroge and M. Wuttig 3817 FIG. 1. Temperature dependence of the sheet resistance Rs for a 100 nm thin film ͑heating rate (dT/dt)ϭ3 K/min͒. The dotted line denotes the transition temperature Tc . measurements were used to determine the structure. These measurements were carried out using a Philips X’pert mate- rials research diffractometer ͑MRD͒ system. The system is equipped with a knife edge which is placed above the sample surface when measuring XRR of films deposited on slightly curved substrates. The divergence of the x-ray beam was set to 1/64° and a detector slit of 0.1 mm was used for XRR FIG. 2. X-ray diffraction scans of 200 nm AgInSbTe films on a glass sub- measurements. A grazing angle geometry (␪ϭ0.75°) was strate after annealing at different temperatures. All measurements were per- ␪ ͑ ͒ ͑ ͒ preferred for XRD measurement since this arrangement im- formed under a grazing angle of 0.75° a as-deposited sample. b An- nealed at 200 °C for 5 h. ͑c͒ Annealed at 250 °C for 5 h. ͑d͒ Annealed at proves the signal-to-noise ratio for very thin films. Films of 300 °C for 5 h. 45 and 200 nm were used for XRR and XRD characteriza- tion, respectively. All measurements were performed at room temperature. due to a transformation in physical state, the structure of The sheet resistance was measured with a four-point various films has been analyzed after annealing them at dif- probe setup following the procedure proposed by van der ferent temperatures in argon ambient. Pauw.16 The setup allows us to monitor the sheet resistance upon annealing in argon ambient. The sample temperature B. Film structure dependence on temperature was measured by a NiCr–Ni thermocouple. Figure 2 shows XRD scans performed on samples an- nealed isothermally at different temperatures. In each case, a III. RESULTS AND DISCUSSION 200 nm thin film was annealed for 5 h. Figure 2͑a͒ shows the XRD pattern of the as-deposited sample. The two broad A. Resistance dependence on temperature peaks confirm a disordered phase for the as-deposited Figure 1 displays a typical dependence of the sheet re- AgInSbTe films. Figures 2͑b͒–2͑d͒ show XRD patterns of sistance Rs upon the temperature of a 100 nm thin film ob- samples annealed at 200, 250 and 300 °C, respectively. Dif- tained using a heating rate of 3 K/min. As-deposited films fraction peaks, indicative for a crystalline phase, are ob- have a sheet resistance of 6 M⍀/ᮀ which corresponds to a served in all three patterns. This confirms that the resistivity ␳ ⍀ resistivity of 60 cm. A continuous decrease in sheet re- drop at Tc is caused by the phase transition from an amor- sistance upon annealing is observed below a temperature Tc phous to a crystalline phase. The three diffraction patterns where a sudden drop occurs. It drops to a value of 100 ⍀/ᮀ are very similar implying that there is no further structural (␳ϭ10Ϫ3 ⍀ cm͒.
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