ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012) P 31
THE X-RAY ABSORPTION STUDIES OF THE Ti-Si-C FILMS STOICHIOMETRY IN FUNCTION
OF THE TECHNOLOGICAL PARAMETERS
K. Lawniczak-Jablonska1∗, M.T. Klepka1, A. Wolska1, and M.A. Borysiewicz2
1Institute of Physics Polish Academy of Sciences, Al. Lotnikow 32/46, PL–02668 Warsaw, Poland
2Institute of Electron Technology, Al. Lotnikow 32/46, PL–02668 Warsaw, Poland Keywords: High Electron Mobility Transistors, metallisations, EXAFS, MAX phases
∗e-mail : jablo@ifpan.edu.pl
During the recent years significant interest was devoted to materials which fulfil requirements of technology to produce high frequency and high power electronic devices. Among them there are new materials for metallisation in High Electron Mobility Transistors (HEMT) produced on the base of group III nitrides. Due to the wide band gap these transistors are suitable to work under high voltages. The high current transported by metal- lic contacts induces a significant internal heat lead- ing to a fast degradation of the conventional Ti/Al ohmic and Ni/Au Schottky contacts. Due to the unique combination of metallic electro-thermal con- duction and the ceramic resistance to oxidation, and thermal stability [1, 2], the Mn+1AXn phases are chosen as the material potentially applicable to met- allisation in these kind of devices. In the formula above M stands for transition metal, A for an ele- ment from group IIIA or IVA and X for carbon or nitrogen.
The MAX phases on one hand exhibit proper- ties of metals, showing good thermal and electri- cal conductivity, machinability, high hardness. On the other hand they show properties of ceramics with damage tolerance, oxidation resistance, and thermal stability even at temperatures as high as 1000◦C [3, 4]. These particular properties are re- lated to the nanolaminate structure of MAX phases [4, 5]. A monocrystalline MAX phase consists of M X monolayers intertwined with monoatomic A layers. Among the M3AX2 phases very promis- ing for applications in metallisations to III-N com- pounds is the Ti3SiC2phase. In the presented paper the attempts to grow thin and monocrystalline films of the Ti3SiC2phase by means of high-temperature magnetron sputtering from three independent cath- odes are reported and the problems with achieving the stoichiometric phase are discussed. In the first step the structural characterisation of the deposited films was carried out in a standard way, by means of x-ray diffraction (XRD). In many cases the XRD peaks were broad and asymmetric. We demonstrate that in such a case the constructive conclusions for technology can be provided by the x-ray absorp- tion (XAS) technique. The XAS as an atomic sensi- tive probe is the most suitable technique to examine the atomic order around Ti atoms as a function of
technological parameters. Due to the lack of long range crystalline order in the samples this informa- tion cannot be delivered by XRD. First the EXAFS studies were performed for one set of samples and suggestion for the change of technology were given.
According to them the second set of samples were produced with stoichiometry very close to Ti3SiC2 compound. The dependence of the numbers of Ti, C and Si atoms on the ratio of power provided at the Ti and Si cathodes is presented in Fig. 1.
Figure 1 : The number of C (triangles), Si (squares) and Ti (circles) atoms around central Ti atom in function of the ratio of powers at the Ti and Si cathode. The line indicates the values for stoichiometric Ti3SiC2phase (Ti-10.8, Si-1.2 and C-4).
Acknowledgments: Research in part financed by the European Union within the European Regional Devel- opment Fund-project InTechFun. The measurements performed at synchrotron have received funding from the European Community’s Seventh Framework Pro- gramme (FP7/2007 – 2013) under grant agreement n◦226716.
References
[1] M.E. Lin et al., Appl. Phys. Lett. 64 (1994) 1003.
[2] J.S. Kwak et al., Semicond. Sci. Technol. 15 (2000) 75.
[3] M.W. Barsoum Prog. Solid St. Chem. 28 (2000) 201.
[4] J. Emmerlich et al., Acta Mater. 55 (2007) 1479.
[5] W. Jeitschko et al., Monatsh. Chem. 94 (1963) 672.
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