An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

This review article first presents a summary of current understanding of the magnetic properties and intrinsic ferromagnetism of transition-metal (TM)-doped ZnO films, which are typical diluted magnetic oxides used in spintronics. The local structure and magnetic behavior of TM-doped ZnO are strongly sensitive to the preparation parameters. In the second part, we discuss in detail the effects of doping elements and concentrations, oxygen partial pressure, substrate and its orientation and temperature, deposition rate, post-annealing temperature and co-doping on the local structure and subsequent ferromagnetic ordering of TM-doped ZnO. It is unambiguously demonstrated that room-temperature ferromagnetism is strongly correlated with structural defects, and the carriers involved in carrier-mediated exchange are by-products of defects created in ZnO. The third part focuses on recent progress in TM-doped ZnO-based spintronics, such as magnetic tunnel junctions and spin field-effect transistors, which provide a route for spin injection from TM-doped ZnO to ZnO. Thus, TM-doped ZnO materials are useful spin sources for spintronics.

Ferromagnetism and possible application in spintronics of transition-metal-doped ZnO films

Since the development of the first chemoresistive metal oxide based gas sensors, transducers with innovative properties have been prepared by a variety of wet- and dry-deposition methods. Among these, direct assembly of nanostructured films from the gas phase promises simple fabrication and control and with the appropriate synthesis and deposition methods nm to μm thick films, can be prepared. Dense structures are achieved by tuning chemical or vapor deposition methods whereas particulate films are obtained by deposition of airborne, mono- or polydisperse, aggregated or agglomerated nanoparticles. Innovative materials in non-equilibrium or sub-stoichiometric states are captured by rapid cooling during their synthesis. This Review presents some of the most common chemical and vapor-deposition methods for the synthesis of semiconductor metal oxide based detectors for chemical gas sensors. In addition, the synthesis of highly porous films by novel aerosol methods is discussed. A direct comparison of structural and chemical properties with sensing performance is given.

Semiconductor Gas Sensors: Dry Synthesis and Application

Silicides and ohmic contacts

The formation of TiSi2 thin films on silicon substrates has been investigated with several transmission electron microscope techniques. For films formed either by reacting titanium with a silicon substrate or by sintering a codeposited (Ti+Si) mixture, electron diffraction patterns show that a metastable phase—TiSi2 (C49 or ZrSi2 structure)—forms prior to the equilibrium phase—TiSi2 (C54 structure). High‐resolution images indicate that the metastable TiSi2‐silicon interface is atomically sharp, with no ‘‘glassy membrane’’ layer present. The annealing temperature required to transform the metastable TiSi2 to the low resistivity, equilibrium TiSi2 increases as the thin‐film impurity content increases. Previous studies of TiSi2 formation are discussed in light of these results.

Metastable phase formation in titanium‐silicon thin films

The oxygen behavior and its influence on Ti silicide formation is systematically studied in the TiO2/Si and Ti/TiO2/Si systems using Rutherford backscattering, nuclear reaction analysis, and x‐rays diffraction techniques. After annealing in vacuum ( p<5×10−7 Torr), no reaction was observed up to 900 °C in the TiO2/Si system, whereas in the Ti/TiO2/Si system, metallic titanium reacts with the TiO2 film above 400 °C and at 600 °C a uniform oxygen solid solution is formed. The silicide formation starts at 650 °C and up to 750 °C the only phase formed is Ti5Si3. We found that this phase is kinetically favored as long as the Ti is being supplied by the unreacted film. The growth rate kinetics was found to have parabolic behavior and was therefore controlled by Si volume diffusion. Above 750 °C, TiSi2 forms very rapidly, its growth being nucleation controlled. During the growth of the silicide layer, a diffusion of oxgen toward the surface region was observed. When the oxygen concentration in the surface layer exceeded the solubility limit, Ti oxide precipitated and the silicide growth nearly stopped, even if some silicon reached the surface. At a temperature higher than 850 °C, a marked oxygen loss takes place, most probably via SiO sublimation. The sublimation process is favored by the presence of Si in the surface region and prevents the formation of a stable SiO2 diffusion barrier at the TiSi2/TiOx interface.

Titanium silicide formation: Effect of oxygen distribution in the metal film

The precise C content of a series of Si1−yCy epilayer samples (0<y<0012) was determined by resonant backscattering experiments using a 4He+ ion beam at 572 MeV This beam energy is more suitable for the determination of the C content than the previously used 4265 MeV From the correlation of these investigations with x-ray diffraction experiments, a significant deviation of the lattice parameter variation in Si1−yCy from Vegard’s rule between Si and diamond or β-SiC was observed, which amounts up to 30% or 13%, respectively, for y<0012 This negative deviation is in agreement with recent theoretical predictions by Kelires

Lattice parameter in si1-ycy epilayers: deviation from vegard's rule

In this work the Si self-interstitial--carbon interaction has been experimentally investigated and modeled. The interactions between self-interstitials, produced by 20-keV silicon implantation, and substitutional carbon in silicon have been studied using a ${\mathrm{Si}}_{1\ensuremath{-}y}{\mathrm{C}}_{y}$ layer grown by molecular beam epitaxy (MBE) and interposed between the near-surface self-interstitial source and a deeper B spike used as a marker for the Si-interstitial concentration. The C atoms, all incorporated in substitutional sites and with a C-dose range of $7\ifmmode\times\else\texttimes\fi{}{10}^{12}--4\ifmmode\times\else\texttimes\fi{}{10}^{14}{\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}\mathrm{s}/\mathrm{c}\mathrm{m}}^{2},$ trap the self-interstitials in such a manner that the ${\mathrm{Si}}_{1\ensuremath{-}y}{\mathrm{C}}_{y}$ layer behaves as a filtering membrane for the interstitials flowing towards the bulk and, consequently, strongly reduces the boron-enhanced diffusion. This trapping ability is related to the total C dose in the ${\mathrm{Si}}_{1\ensuremath{-}y}{\mathrm{C}}_{y}$ membrane. Substitutional carbon atoms interacting with self-interstitials are shown to trap Si interstitials, to be removed from their substitutional sites, and to precipitate into the C-rich region. After precipitation, C atoms are not able to further trap injected self-interstitials, and the interstitials generated in the surface region can freely pass through the C-rich region and produce B-enhanced diffusion. The atomistic mechanism leading to Si-interstitial trapping has been investigated by developing a simulation code describing the migration of injected interstitials. The simulation takes into account the surface recombination, the interstitial diffusion in our MBE-grown material, and C traps. Since the model calculates the amount of interstitials that actually react with C atoms, by a comparison with the experimental data it is possible to derive quantitative indications of the trapping mechanism. It is shown that one Si interstitial is able to deactivate about two C traps by means of interstitial trapping and C clustering reactions. The reaction causing trapping and deactivation is tentatively described.

Interaction between self-interstitials and substitutional C in silicon: Interstitial trapping and C clustering mechanism

Transformation to amorphous state of metals by ion implantation: P in Ni.

The introduction of carbon into silicon-germanium--based heterostructures offers increased flexibility in tailoring their strain state and electronic properties. Still, however, fundamental physical properties such as the lattice parameter and the elastic properties of ${\mathrm{Si}}_{1\ensuremath{-}x\ensuremath{-}y}{\mathrm{Ge}}_{x}{\mathrm{C}}_{y}$ random alloys are not precisely known. In this paper, we present a quantitative study of the effect of carbon on the lattice parameter of ${\mathrm{Si}}_{1\ensuremath{-}x\ensuremath{-}y}{\mathrm{Ge}}_{x}{\mathrm{C}}_{y}$ alloys in the technologically relevant range of Ge and C compositions. A strong deviation from Vegard's rule is experimentally and theoretically derived. The influence of the correlation between Ge and C on the lattice parameter is discussed. The results allow us to establish the compensation ratio $\ensuremath{\nu}$ of Ge to C concentrations (where the ${\mathrm{Si}}_{1\ensuremath{-}x\ensuremath{-}y}{\mathrm{Ge}}_{x}{\mathrm{C}}_{y}$ epilayer is lattice matched to Si), for which we find a value of $\ensuremath{\nu}=12.$

Marina Berti

Papers

Titanium silicide formation: Effect of oxygen distribution in the metal film

Lattice parameter in si1-ycy epilayers: deviation from vegard's rule

Interaction between self-interstitials and substitutional C in silicon: Interstitial trapping and C clustering mechanism

Transformation to amorphous state of metals by ion implantation: P in Ni.

Lattice parameter of Si 1 − x − y Ge x C y alloys