Mass Spectrometric Thermal Evolution of Novel Indium Metalorganic Precursors for MOCVD
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MASS SPECTROMETRIC THERMAL EVOLUTION OF NOVEL INDIUM METALORGANIC PRECURSORS FOR MOCVD G. Bruno, P. Capezzuto, G. Cicala, M. Losurdo,
Centro Studio Chimica Plasmi CNR, via G. Amendola,173-70126 Bari (Italy) G. Rossetto, M. Porchia, P. Zanella, CNR-Istituto Chimica Tecnologia Materiali, Corso Stati Uniti, 35100 Padua (Italy)
ABSTRACT The thermal behaviour of dialkylindium-dialkylamides R2InNR'2 (R,R'=Me, Et) and dialkylindium-azolides R2InNR' (NR'=Pyrrole, Pyrazole) has been examined by a mass spectrometric thermal evolution technique, in the temperature range 30-400'C. Data on volatility, identity of gasified molecules, threshold temperature and products of the decomposition processes are reported and discussed.
INTRODUCTION Metalorganic Chemical Vapor Deposition (MOCVD) is, today, a well established technique to grow semiconductor epitaxial layers of indium phosphide (InP) for microwave and optoelectronic devices. Nevertheless, its further development on industrial scale production is limited by several drawbacks of the commonly used indium precursors, like Me3In, Et3In, Me2EtIn or their amine and phosphine adducts. Although good results have been obtained with these conventional sources, their high sensitivity to air and moisture, the low vapor pressure and the high tendency to react with impurities motivate the search for alternative indium sources. Among the novel indium precursors [1,2], we have focused our attention on dialkylindiumdialkylamides, R2InNR'2 (R, R'=Me, Et), and dialkylindium-azolides R2InNR' (NR'=Nheterocycle). The tendency to react with oxygen and moisture, and to give pre-reactions during the MOCVD growth can be reduced through a proper choice of R' groups. In addition, the knowledge of their thermal decomposition pattern is extremely important, since it will affect the MOCVD growth and material quality, such as the residual carbon impurities in the epilayers. In this paper, we report on the thermal behaviour of Et2InNMe2, Et21nPyrrole and Me21nPyrazole by mass spectrometric thermal evolution technique. Decompositon processes and products are discussed along with implications about the MOCVD growth of InP and, in particular, on the carbon and nitrogen content in the epilayers. Besides, vapor pressure data have been obtained for these In-precursors.
EXPERIMENTAL PROCEDURE All the measurements were performed on a VG-2000 quadrupole mass spectrometer evacuated by diffusive pumps to a base pressure better than 10-8 torr. The samples were directly introduced, under an inert atmosphere of argon, in the cross-beam ion source by a solid probe. The probe temperature was increased from 30'C to 350 0 C at the heating rate of l 0C/sec and then kept costant for 4 min. The mass spectra were recorded, at an electron impact ionization energy of 70 eV, in the mass range 1-500 amu, with a scan time of 1.0 sec and an interscan time of 0.1 sec. In these conditions only species desorbing from the sample, without external impurities, were revealed. Details on the preparation and characterization of indium deriv
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