SiO 2 Formation at the Aluminum Oxide/Si(100) Interface

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V6.4.1

SiO2 Formation at the Aluminum Oxide/Si(100) Interface A. Roy Chowdhuri,1 C. G. Takoudis,1 R. F. Klie,2 N. D. Browning2 1 Department of Chemical Engineering, University of Illinois at Chicago, 810 S. Clinton Street, Chicago, Illinois 60607-7000. USA. 2 Department of Physics, University of Illinois at Chicago, 845 W. Taylor Street, Chicago, Illinois 60607-7059. USA.

ABSTRACT Thin films of aluminum oxide were deposited on clean Si(100) substrates using trimethylaluminum and oxygen at 300°C. Infrared spectroscopic and x-ray photoelectron spectroscopic analyses of these films showed no aluminum silicate or SiO2 phase formation at the film/substrate interface. The O/Al ratio in the as deposited film was found to be higher than that in stoichiometric Al2O3. On annealing the as deposited samples in Ar at higher temperatures, a peak due to the transverse optical phonon for the Si-O-Si stretching mode appeared in the infrared spectra. A combination of Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope confirmed that the annealed samples developed a layer of silicon dioxide at the aluminum oxide-Si interface. Z-contrast images and electron energy loss spectra, obtained while heating the sample inside the scanning transmission electron microscope were used to follow the interfacial SiO2 formation.

INTRODUCTION Aluminum oxide has gathered considerable interest, primarily due to its potential to replace SiO2 as the dielectric layer in complementary metal oxide semiconductor (CMOS) device fabrication [1]. Among the desirable properties, perhaps the most notable one is the ability of stoichiometric Al2O3 to form a thermodynamically stable interface on Si [2]. However, the O/Al ratio of ultrathin (< 10 nm) alumina films, obtained by processes that are currently employed for deposition, may be higher than stoichiometric Al2O3, depending on the process [3-5]. As a result the interface between the deposited alumina film and the Si substrate may exhibit interfacial reactions. In this study the interface between ultrathin aluminum oxide films deposited at low temperature (300ºC) on Si substrates were subjected to annealing in inert atmosphere. Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), atomicresolution scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS) were used to investigate the as deposited films, and follow the structural and chemical changes resulting from annealing. Z-contrast images and EELS spectra from the bulk and interfaces were obtained while heating the sample inside the electron microscope, to monitor the annealing induced changes at the interface.

V6.4.2

EXPERIMENT The deposition process was carried out at 300°C and 0.5 Torr using trimethylaluminum and oxygen. Detailed description of the deposition process is given elsewhere [6]. Prior to the deposition, the substrates (double polished n-Si(100)) were thoroughly cleaned to remove organic contamination and native oxide

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