Amorphous lanthanum lutetium oxide thin films as an alternative high-κ gate dielectric

Abstract

Lanthanum lutetium oxide thin films were grown on ͑100͒ Si by pulsed laser deposition. Rutherford backscattering spectrometry, atomic force microscopy, x-ray diffraction, and x-ray reflectometry were employed to investigate the samples. The results indicate the growth of stoichiometric and smooth LaLuO 3 films that remain amorphous up to 1000°C. Internal photoemission and photoconductivity measurements show a band gap width of 5.2± 0.1 eV and symmetrical conduction and valence band offsets of 2.1 eV. Capacitance and leakage current measurements reveal C-V curves with a small hysteresis, a dielectric constant of Ϸ32, and low leakage current density levels. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2393156͔The study of ultrathin gate dielectrics has recently gained great attention due to the technological need to replace SiO 2 films in metal-oxide-semiconductor field-effect transistors ͑MOSFETs͒. 1 The scaling has led to MOSFETs with ultrashort physical gate lengths ͑Ͻ50 nm͒ and insulating SiO 2 -based films with thickness less than 1 nm. At such a thickness, these films suffer from excessively high leakage of charge carriers and poor reliability with respect to dielectric breakdown. Therefore, to overcome these limitations new gate dielectric materials with a higher dielectric constant must be developed to replace the SiO 2 . According to the International Technology Roadmap for Semiconductors, 2 the implementation of high-gate dielectrics with a dielectric constant between 10 and 20 will be required by 2008, which will later be replaced by materials having a larger than 20, in order to meet both low leakage current density and performance requirements.Ternary rare earth oxides ͑e.g., DyScO 3 and GdScO 3 ͒ are emerging as promising candidates for high-applications. As shown by Schlom and Haeni, 3 single crystals of these oxides show values of 20-35 which were also observed for amorphous LaScO 3 , GdScO 3 , and DyScO 3 films deposited on silicon ͑ =22-23͒. 4,5 In addition, these materials fulfill the requirements for large optical band gaps ͑5.6 eV͒ and band offsets ͑2 -2.5 eV͒, 6 while their amorphous phase is stable up to 1000°C ͑for GdScO 3 and DyScO 3 ͒. 4,5 Lanthanum lutetium oxide ͑LaLuO 3 ͒, as a member of this class of ternary oxides, is predicted to have similar properties. 3,7 Experimental data related to high-gate applications of amorphous LaLuO 3 films are, however, still not available. In this letter, we present the results of a systematic study on the microstructural and electrical properties of amorphous LaLuO 3 thin films, deposited on silicon substrates by means of pulsed laser deposition ͑PLD͒.LaLuO 3 films were deposited by PLD using a stoichiometric ceramic target. The target was made by milling a stoichiometric mixture of Lu 2 O 3 ͑Alfa Aesar, 99.99%͒ and La 2 O 3 ͑Alfa Aesar, 99.999%͒ powders with a molar ratio of 1:1. The ground powder was dried and then fired at 1300°C in air for 12 h. After regrinding, the powder was pressed with a uniaxial press ͑3 tons͒. The pellets were the...

Engineered Si wafers: On the role of oxide heterostructures as buffers for the integration of alternative semiconductors

“…The formation of solid solutions between the isomorphic Pr 2 O 3 and Y 2 O 3 bixbyite structures over the whole compositional range was demonstrated in the past by powder studies [54,55]. Here, these oxides were chosen as buffer heterostructure materials because, with Pr 2 O 3 and Y 2 O 3 being 2.4 % bigger and smaller than twice the Si unit cell, a symmetrical lattice constant window can be set up for the integration of lattice matched as well as mismatched SiGe systems (it is noted for completeness that mixed double oxide systems were also studied in the past for advanced CMOS applications [19,[56][57][58] and as buffer layer for high quality high-T c superconductor growth [59]). Figure 6 shows the lattice window accessible by the ( Figure 6 Lattice window of (Pr…”

Current transport mechanisms in metal – high-k dielectric – silicon structures

“…LaLuO 3 is an attractive candidate as a gate dielectric material because of its low hygroscopicity, high thermal stability, high optical bandgap (~5.6 eV) and high kvalue close to 30 [30]. V I  characteristics measured on the Pt/LaLuO 3 /p-Si(100) MOS structures have revealed an apparent dependence of the leakage currents on temperature for all the range of reverse and low (|V g |<1 V) forward biases indicating the thermallyactivated charge transport mechanism.…”

Atomic Layer Deposition of Lanthanum-Based Ternary Oxides

“…3 Recent reports show that lanthanum-based ternary oxides, such as lanthanum scandate ͑LaScO 3 ͒ and lanthanum lutetium oxide ͑LaLuO 3 ͒, can meet all these requirements. These materials were grown by molecular beam deposition, 4 pulsed laser deposition, 5 or atomic layer deposition ͑ALD͒. 6 However, these lanthanide oxide films had nanometer-thick interfacial layers when deposited on Si substrates, which made it impossible to scale the effective oxide thickness ͑EOT͒ to the subnanometer range.…”