Growth of Dielectric Thin Films by Irradiation of Condensed Molecular Precursors with Synchrotron Radiation
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GROWTH OF DIELECTRIC THIN FILMS BY IRRADIATION OF CONDENSED MOLECULAR PRECURSORS WITH SYNCHROTRON RADIATION D.R. Strongin', J.F. Moore', M. W. Ruckman", and M. Strongin" *Department of Chemistry, State University of New York, Stony Brook, New York 11794 "*PhysicsDepartment, Brookhaven National Laboratory, Upton, New York 11973 ABSTRACT
Spectroscopic evidence is presented that shows that boron nitride and aluminum oxide can be synthesized by exposing a condensed layer of molecular precursors to synchrotron radiation. In the A120 3 circumstance a condensed layer of trimethylaluminum (TMA) and water at 78 K on a silver substrate produces pure layers of aluminum oxide. Using the same condensed layer technique boron nitride is produced by exposing a solid matrix of diborane and ammonia to synchrotron radiation. Near edge x-ray absorption fine structure and core level photoelectron spectroscopies are used to characterize the A120 3 and BN layers, which were typically 30A thick. During the formation of aluminum oxide the carbon component in the alkylaluminum precursor is completely removed during irradiation as a volatile methane product which was detected by mass spectrometry. In the absence of synchrotron radiation the molecular precursors in both the aluminum oxide and boron nitride systems show evidence of some interactions within the solid, but upon warming to near room temperature (260 K) the layers desorb from the substrate. INTRODUCTION
The synthesis of dielectric thin films from gaseous precursors by a photon assisted
technique has many potential applications in the microelectronics industry and in the area of insulating or hard coatings. We show in this paper that two such materials, aluminum
oxide (A120 3) and boron nitride (BN), can be synthesized from a condensed (78 K) layer of trimethylaluminum (TMA) - water and diborane - ammonia, respectively, in the 2
presence of synchrotron radiation.'' The use of synchrotron radiation to assist the growth of thin films is not new and has already been addressed by various researchers. 34' 5 We present, however, a novel technique that irradiates intimately mixed condensed molecular precursors with synchrotron radiation to synthesize thin films. Using a condensed layer as the reaction matrix offers several advantages over other
higher temperature deposition techniques. First, a layer of reactants can be condensed, typically 50 - 100 A, so that a high density of reactant molecules can be achieved, even in the ultra-high vacuum environment where the vapor pressure of the layer must be below
10` Torr. After exposure any unreacted material is removed by simply warming the sample to ambient temperatures. Second, the relative ratios of the reactants can be varied to achieve the desired thin film stoichiometry. Third, the film growth occurs on the substrate surface, opposed to gaseous reactants, so that epitaxial growth may be possible in some systems. Finally, since the deposition is performed in the ultra-high vacuum environment a variety of surface science techniques c
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