A. Fissel

Low‐temperature growth of SiC thin films on Si and 6H–SiC by solid‐source molecular beam epitaxy

Epitaxial growth of stoichiometric SiC on Si(111) and 2°–5° off‐oriented 6H–SiC(0001) substrates was carried out at low temperatures (800–1000 °C) by means of solid‐source molecular beam epitaxy controlled by a quadrupole mass spectrometry based flux meter. The films were obtained on Si‐stabilized surfaces showing (3×3) and (2×2) superstructures in the case of SiC(0001). The reflection high‐energy diffraction (RHEED) patterns and damped RHEED‐oscillations during the growth on 6H–SiC(0001) at T≳900 °C indicate that two‐dimensional nucleation on terraces is the dominant growth process.

Impact of oxygen supply during growth on the electrical properties of crystalline Gd2O3 thin films on Si(001)

We investigated the influence of additional oxygen supply and temperature during the growth of thin Gd2O3 layers on Si(001) with molecular beam epitaxy. Additional oxygen supply during growth improves the dielectric properties significantly; however, too high oxygen partial pressures lead to an increase in the lower permittivity interfacial layer thickness. The growth temperature mainly influences the dielectric gate stack properties due to changes of the Gd2O3∕Si interface structure. Optimized conditions (600°C and pO2=5×10−7mbar) were found to achieve equivalent oxide thickness values below 1nm accompanied by leakage current densities below 1mA∕cm2 at 1V.

Interface formation during molecular beam epitaxial growth of neodymium oxide on silicon

The Si/dielectric interface properties influence device performance significantly. Often the interface is not stable and changes during and/or after the growth. For a better understanding of the interface and layer formation processes of Nd2O3 on Si(001), as an example for the lanthanide oxides, well-defined experimental studies by reflection high-energy diffraction and x-ray photoelectron spectroscopy were performed under ultraclean ultrahigh vacuum conditions of molecular beam epitaxy. Complementary investigations were performed by transmission electron microscopy. We found that Nd2O3 is a candidate for replacing silicon dioxide as gate dielectric in future Si devices with suitable band gap and offset with respect to silicon. However, under ultrahigh vacuum conditions, silicide formation occurs in the initial stage of growth, which can result in large silicide inclusions and hole formation during further growth. This effect can be completely prevented by modifying the oxygen partial pressure during the ...

Towards understanding epitaxial growth of alternative high-K dielectrics on Si(001): Application to praseodymium oxide

First investigations demonstrate that crystalline Pr2O3 on Si(001) is a promising candidate for highly scaled gate insulators, displaying a sufficiently high-K value of around 30, ultralow leakage current density, good reliability, and high electrical breakdown voltage. Here, we report on molecular beam epitaxial growth of crystalline praseodymium oxide (as Pr2O3 in the bixbyite or manganese oxide structure) on Si(001) substrates. The Pr2O3 was found to grow as (110)-single-crystalline domains, with two orthogonal in-plane orientations. Investigations of the initial growth phase indicate that the occurrence of these domains is due to the nucleation on neighboring terraces with Si dimer rows (2×1 reconstruction) perpendicular to each other. We postulate the formation of a layer consisting of very small Pr2O3 islands on top of the Si dimers in the initial stage of growth. This interface layer acts as a coincidence lattice on which further growth in the (110) orientation can occur. X-ray photoelectron spectr...

Influence of interface layer composition on the electrical properties of epitaxial Gd2O3 thin films for high-K application

The authors report on the impact of interface layer composition on electrical properties of epitaxial Gd2O3 thin films on Si(001) substrates. The electrical properties of epitaxial Gd2O3 thin films were improved significantly by controlled modification of interface layer composition. The minimum capacitance equivalent thickness estimated for Pt∕Gd2O3∕Si metal oxide semiconductor structures was as low as 0.76nm with leakage current density of 15mA∕cm2 at (Vg−VFB)=1V. The corresponding density of interface states was found to be 2.3×1012cm−2eV−1. The authors also find that a change in the interface layer composition significantly alters band alignment of Gd2O3 layer with respect to Si substrates.

Investigation of the electronic structure at interfaces of crystalline and amorphous Gd2O3 thin layers with silicon substrates of different orientations

Internal photoemission, photoconductivity, and spectroscopic ellipsometry experiments were carried out to characterize the electronic structure of interfaces of (001) and (111)-oriented Si with crystalline (epitaxially grown) and amorphous Gd2O3 insulators. The energy barriers for electrons and holes (3.2 and 3.9eV, respectively) appear to be sensitive neither to the orientation of the Si crystal surface nor to the oxide phase (crystalline or amorphous). This result indicates that despite the difference in Si–O bond density in going from (001) to (111)Si, the interface dipoles do not ensue any measurable effect on the electronic structure of the interface and the associated band offsets.

Crystalline ternary rare earth oxide with capacitance equivalent thickness below 1 nm for high-K application

Ternary neodymium-gadolinium oxide (NGO) thin films were grown epitaxially on Si(001) substrates using modified molecular beam epitaxy. The electrical properties of NGO thin films demonstrate that this ternary oxide could be one of the most promising candidates to replace the conventionally used SiO2 or SiOxNy in complementary metal oxide semiconductor devices. The films were characterized with various methods. The capacitance equivalent oxide thickness of 4.5nm thin films extracted from capacitance-voltage (C-V) characteristics was 0.9nm. For such films, leakage current density and the density of interface traps were 2.6×10−4A∕cm2 at ∣Vg−VFBV∣=1V and 1.4×1012∕cm2eV−1, respectively.

Impact of Si substrate orientations on electrical properties of crystalline Gd2O3 thin films for high-K application

The authors compare the properties of epitaxial Gd2O3 thin films grown on silicon substrates with three different orientations for high-K application. Pt∕Gd2O3∕Si(111) and Pt∕Gd2O3∕Si(110) metal oxide semiconductor heterostructures show promising electrical properties and hence, could be considered for future generation of complementary metal oxide semiconductor devices. Capacitance equivalent oxide thicknesses estimated from capacitance versus voltage characteristics are 0.97, 1.12, and 0.93nm for the films grown on Si(001), Si(111), and Si(110) substrates, respectively. The films exhibit good insulating property with leakage current densities of 0.4, 0.5, and 4.5mA∕cm2, respectively, at (Vg−VFBV)=−1V.

0.86-nm CET Gate Stacks With Epitaxial

In this letter, ultrathin gadolinium oxide (Gd2O3 ) high-k gate dielectrics with complementary-metal-oxide-semiconductor (CMOS)-compatible fully silicided nickel-silicide metal gate electrodes are reported for the first time. MOS capacitors with a Gd2O3 thickness of 3.1 nm yield a capacitance equivalent oxide thickness of CET=0.86 nm. The extracted dielectric constant is k=13-14. Leakage currents and equivalent oxide thicknesses of this novel gate stack meet the International Technology Roadmap for Semiconductors targets for the near term schedule and beyond

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We study the growth of insulator/Si/insulator nanostructures on Si(111) using molecular beam epitaxy. Based on different investigations, we develop an approach for the fabrication of a nanostructure with a continuous ultrathin single-crystalline silicon buried in a single-crystalline insulator matrix with sharp interfaces. This approach is based on an epitaxial encapsulated solid-phase epitaxy, in which the solid-phase epitaxy of silicon is accompanied by a vapor-phase epitaxy of the second insulator layer. We call this approach as cooperative solid-vapor-phase epitaxy. As an example we demonstrate the growth of buried epitaxial silicon in epitaxial Gd2O3.