Low-temperature metalorganic chemical vapor deposition of Al 2 O 3 for advanced complementary metal-oxide semiconductor
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A low-temperature metalorganic chemical vapor deposition process was developed and optimized, using a design of experiments approach, for the growth of ultrathin aluminum oxide (Al2O3) as a potential gate dielectric in emerging semiconductor device applications. The process used the aluminum -diketonate metalorganic precursor [aluminum(III) 2,4-pentanedionate] and water as, respectively, the metal and oxygen source reactants to grow Al2O3 films over a temperature range from 250 to 450 °C. The resulting films were analyzed by x-ray photoelectron spectroscopy, x-ray diffraction measurements, Rutherford backscattering spectrometry, nuclear-reaction analysis for hydrogen profiling, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The as-deposited Al2O3 phase was amorphous and dense and exhibited carbon and hydrogen incorporation of, respectively, 1 and 10 at.%. Postannealing at 600 °C led to a reduction in hydrogen concentration to 1 at.%, while maintaining an amorphous Al2O3 matrix.
I. INTRODUCTION
With emerging sub-100 nm integrated circuitry (IC) technologies, one of the grand challenges facing the semiconductor industry is the extendibility of conventional silicon dioxide (SiO2) based gate dielectrics due to increased leakage current and deteriorating reliability as the allowable dielectric thickness is scaled down with shrinking device feature sizes. One approach to resolve this challenge is the implementation of high-dielectric constant (k) insulators, which are physically thicker than their corresponding SiO2 counterpart while providing the equivalent target capacitance.1 Accordingly, several such high-k dielectrics are currently being evaluated as potential replacements for SiO2, with emphasis on those materials that can be grown in amorphous form while displaying high thermal and chemical stability, adequate band-gap and breakdown voltage, and good compatibility with current IC integration protocols.2 Aluminum oxide (Al2O3) offers these requisite properties, while also exhibiting high thermal conductivity and very low permeability to alkali ions and other impurities.3–5 As a result, Al2O3 thin films have been widely studied as gate dielectrics for silicon (Si), gallium arsenide (GaAs), indium phosphide (InP), and GaInPAs metal-oxide semiconductor structures.6–10 1868
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J. Mater. Res., Vol. 18, No. 8, Aug 2003 Downloaded: 09 Jun 2014
In these studies, Al2O3 films were deposited using a variety of chemical vapor deposition (CVD) and physical vapor deposition techniques. Among these techniques, a low-temperature thermal CVD approach is especially attractive because of its reduced thermal budget, prospective ability to uniformly coat aggressive substrate topographies, and demonstrated compatibility with emerging microelectronics fabrication flows.11 In addition, the active role of the substrate surface in driving the CVD reaction mechanisms enables tight control of film texture and grain size, including the formation of metastable phases a
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