Spectroscopic studies of metal high‐k dielectrics: transition metal oxides and silicates, and complex rare earth/transition metal oxides

Abstract

PACS 78.70.DmThis paper uses X-ray absorption spectroscopy to the study of electronic structure of the transition metal oxides TiO 2 , ZrO 2 and HfO 2 , Zr and Hf silicate alloys, and the complex oxides, GdScO 3 , DyScO 3 and HfTiO 4 . Qualitative and quantitative differences are identified between dipole allowed intra-atomic transitions from core p-states to empty d*-and s*-states, and inter-atomic transitions from transition metal and oxide 1s states to O 2p* that are mixed with transition metal d*-and s*-states for transition metal oxides and silicate alloys. The complex oxide studies have focused on the O K 1 edge spectra. Differences between the spectral peak energies of the lowest d*-features in the respective O K 1 spectra are demonstrated to scale with optical band gap differences for TiO 2 , ZrO 2 and HfO 2 , as well as the complex oxides providing important information relevant to applications of TM oxides as high-k gate dielectrics in advanced Si devices. This is demonstrated through scaling relationships between (i) conduction band offset energies between Si and the respective dielectrics, and the optical band gaps, and (ii) the optical band gaps, the conduction band offset energies, and the electron tunneling masses as functions of the atomic d-state energies of the transition metal atoms.

Properties of rare-earth scandate single crystals (Re=Nd−Dy)

“…First, they are promising candidates for the replacement of SiO 2 in advanced Si-based MOSFETs. Their high dielectric constants between 18 and 35.5 [1][2][3], their large optical bandgaps 45.5 eV [1,[3][4][5][6], and their thermodynamic stability in contact with silicon [1,7] favor them for this application. Second, RE scandates with large RE ions ranging from La to Ho exhibit the perovskite structure.…”

An MOCVD Approach to High‐k Praseodymium‐Based Films

“…Beyond 450°C, a marked falloff in the rate points to precursor depletion due to reactions occurring either in the gas phase or on the reactor walls. The onset temperature of the deposition process (250°C) and the diffusion-controlled (375-450°C) interval are both significantly lower than found in homologous MOCVD processes to grow ZrO 2 and HfO 2 from Zr(mmp) 4 and Hf(mmp) 4 sources. [75,81] In summary, Pr(mmp) 3, the first ever alkoxide precursor used for deposition of praseodymium oxide phases, although volatile and liquid at room temperature (hence particularly suited for MOCVD) has shown some limitations in the deposition of pure Pr 2 O 3 phase.…”

“…In particular, MBE-deposited Pr 2 O 3 films have been shown to possess lower leakage current densities [27] than the observed values for HfO 2 and ZrO 2 films, [40,41] having an equivalent oxide thickness (EOT) of 1. 4 nm. An alternative, viable solution to epitaxial oxide films is the deposition of silicate or aluminate systems which remain amorphous up to 900°C.…”

“…Over the past few years, a wide variety of high-k dielectrics have been studied but, to date, no clear candidates have emerged to replace SiO 2 and, although understanding of high-k materials increases at a very rapid pace, several problems related to material deposition, stability, and also to electrical performances still remain unresolved. [4,5] Major requirements for gate insulators are: i) low O 2 diffusion coefficients to withstand high processing temperatures; ii) high-quality interfaces with Si to limit degradation of carrier mobility by interfacial defects or roughness; iii) potential barriers (over 1 V) for both electrons and holes to give low leakage currents by Schottky emission into the oxide conduction or valence band. These stringent requirements, imposed by CMOS device processing, have considerably shortened the list of possible candidates.…”

Electrical Characterization of High-K Dielectric Gates for Microelectronic Devices

“…Finally, meff is the electron effective mass at the dielectric and Heff is the insulator semiconductor energy barrier for majority carriers, that is, the dielectric to semiconductor conduction band offset. Figure 13 shows xon for some high-k dielectrics (electron effective mass and barrier height values have been obtained from References [3] and [37] respectively). One can see that xon is higher for dielectrics in which Heff and meff are low.…”