X-ray reflectometry and spectroscopic ellipsometry characterization of Al 2 O 3 atomic layer deposition on HF-last and N
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Al2O3 films are grown by atomic layer deposition (ALD) using trimethylaluminum and water as precursors on HF-last and NH3 plasma pretreatment Si substrates. The thickness, surface roughness, and density of Al2O3 films as well as the nature of their interlayers with Si substrates are characterized by x-ray reflectivity and spectroscopic ellipsometry techniques. The growth rates of Al2O3 films are 1.1 Å/cycle and 1.3 Å/cycle, respectively, on HF-last and NH3-plasma-nitrided surfaces. Al2O3 layer densities are rather independent of the number of growth cycles in all cases. The interfacial film thickness increases with the number of ALD cycles when deposited on an HF-last Si substrate. However, because SiOxNy inhibits oxygen diffusion, the interfacial film thickness is independent of the number of ALD cycles on the nitrided Si substrate.
I. INTRODUCTION
As the aggressive scaling of complementary-metaloxide semiconductor technology continues, the dielectric thickness in a metal-oxide semiconductor structure is reduced in response to drive device performance. However, one of the major limits to the scaling down of the gate dielectric is the exponential increase of tunnel current with decreasing silicon oxide (SiO2) thickness. Thus, high-dielectric constant (high-k) dielectric is required to replace the conventional SiO2, thereby preventing tunneling current while retaining the electrical properties of an ultrathin SiO2 film.1–4 Of the proposed alternative gate dielectrics for the metal-oxide-semiconductor field-effect transistor, aluminum oxide (Al2O3) is considered to be one of the promising candidates because of its relatively high dielectric constant and wide band gap.1,5,6 There have been many reports on the atomic layer deposition (ALD) of Al2O3 thin films on the Si substrate using trimethylaluminum (TMA) and water (H2O) precursors.7–9 The interface properties between Al2O3 and the Si substrate have also been extensively investigated. Some investigators have reported that as-grown Al2O3/Si film had an SiO2 layer or an Al silicate at the interface.6,10–13 Recently, Lee and Oh14 further investigated the depth profile of chemical
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0184 1214 J. Mater. Res., Vol. 22, No. 5, May 2007 http://journals.cambridge.org Downloaded: 22 Mar 2015
states of an Al2O3/Si interface using nondestructive photon energy-dependent high-resolution x-ray photoelectron spectroscopy (XPS). Their results show that there is no Al-silicate formation in the interface, which naturally leads us to identify the Al2O3/Si(100) interface as mainly consisting of Si2O3 and SiO2. The detailed interface properties obtained from our XPS and transmission electron microscopy (TEM) analyses show that the interface also mainly consists of silicon oxide when Al2O3 films are grown on an HF-cleaned silicon surface by ALD.15 As is well known, the interface layer will increase the final equivalent SiO2 thickness of the dielectric and degrades the electrical properties. T
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