High Pressure Reactive Sputtering Research Articles

Effect of interlayer trapping and detrapping on the determination of interface state densities on high-k dielectric stacks

The influence of the silicon nitride blocking layer thickness on the interface state densities (Dit) of HfO2/SiNx:H gate-stacks on n-type silicon have been analyzed. The blocking layer consisted of 3 to 7 nm thick silicon nitride films directly grown on the silicon substrates by electron-cyclotron-resonance assisted chemical-vapor-deposition. Afterwards, 12 nm thick hafnium oxide films were deposited by high-pressure reactive sputtering. Interface state densities were determined by deep-level transient spectroscopy (DLTS) and by the high and low frequency capacitance-voltage (HLCV) method. The HLCV measurements provide interface trap densities in the range of 1011 cm−2 eV−1 for all the samples. However, a significant increase in about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride barrier layers. In this work we probe that this increase is an artifact due to the effect of traps located at the internal interface existing between the HfO2 and SiNx:H films. Because charge trapping and discharging are tunneling assisted, these traps are more easily charged or discharged as lower the distance from this interface to the substrate, that is, as thinner the SiNx:H blocking layer. The trapping/detrapping mechanisms increase the amplitude of the capacitance transient and, in consequence, the DLTS signal that have contributions not only from the insulator/substrate interface states but also from the HfO2/SiNx:H interlayer traps.

Physical properties of high pressure reactively sputtered hafnium oxide

Hafnium oxide films were deposited on silicon by High Pressure Reactive Sputtering (HPRS) at pressures between 0.8 and 1.6 mbar. Growth, composition and morphology were investigated using Transmission Electron Microscopy (TEM), Heavy Ion Elastic Recoil Detection Analysis (HI-ERDA), Fourier Transform Infrared spectroscopy (FTIR) and X-Ray Diffraction (XRD). The growth rate was found to decrease exponentially with deposition pressure. The films showed a monoclinic polycrystalline structure, with higher grain size for intermediate pressures. All the films were slightly oxygen rich with respect to stoichiometric HfO 2, which is attributed to the oxygen plasma. Additionally, it was observed the formation of an interfacial silicon oxide layer, with a minimum thickness for deposition pressures around 1.2 mbar. These results are explained by the oxidation action of the oxygen plasma and the diffusion of oxygen through the grain boundaries of the HfO 2 film.

Electrical properties of high-pressure reactive sputtered thin hafnium oxide high-k gate dielectrics

Thin films of hafnium oxide have been deposited by the high-pressure reactive sputtering (HPRS) system. In this growth system the deposition pressure is around 1 mbar, three orders of magnitude higher than in the conventional ones, assuring that both reflected and sputtered particles reach the substrate with a low energy. The amorphous or polycrystalline structure is modified by adjusting the ratio of oxygen to argon of the sputtering gas. The electrical characteristics of both polycrystalline and amorphous films are compared. In all cases, the leakage current can be fitted to Poole–Frenkel emission. Amorphous films show the best characteristics in terms of capacitance–voltage behaviour, leakage current and interfacial state density, with conductance and flat-band voltage transients almost negligible.

Optical properties and structure of HfO2 thin films grown by high pressure reactive sputtering

Thin films of hafnium oxide (HfO2) have been grown by high pressure reactive sputtering on transparent quartz substrates (UV-grade silica) and silicon wafers. Deposition conditions were adjusted to obtain polycrystalline as well as amorphous films. Optical properties of the films deposited on the silica substrates were investigated by transmittance and reflectance spectroscopy in the ultraviolet, visible and near infrared range. A numerical analysis method that takes into account the different surface roughness of the polycrystalline and amorphous films was applied to calculate the optical constants (refractive index and absorption coefficient). Amorphous films were found to have a higher refractive index and a lower transparency than polycrystalline films. This is attributed to a higher density of the amorphous samples, which was confirmed by atomic density measurements performed by heavy-ion elastic recoil detection analysis. The absorption coefficient gave an excellent fit to the Tauc law (indirect gap), which allowed a band gap value of 5.54 eV to be obtained. The structure of the films (amorphous or polycrystalline) was found to have no significant influence on the nature of the band gap. The Tauc plots also give information about the structure of the films, because the slope of the plot (the Tauc parameter) is related to the degree of order in the bond network. The amorphous samples had a larger value of the Tauc parameter, i.e. more order than the polycrystalline samples. This is indicative of a uniform bond network with percolation of the bond chains, in contrast to the randomly oriented polycrystalline grains separated by grain boundaries.

High-pressure reactively sputtered HfO2: Composition, morphology, and optical properties

Hafnium oxide films were deposited by high pressure reactive sputtering using different deposition pressures and times. The composition, morphology, and optical properties of the films, together with the sputtering process growth kinetics were investigated using heavy ion elastic recoil detection analysis, Fourier transform infrared spectroscopy, ultraviolet-visible-near infrared spectroscopy, x-ray diffraction, and transmission electron microscopy. The films showed a monoclinic polycrystalline structure, with a grain size depending on the deposition pressure. All films were slightly oxygen rich with respect to stoichiometric HfO2 and presented a significant amount of hydrogen (up to 6at.%), which is attributed to the high affinity for moisture of the HfO2 films. The absorption coefficient was fitted to the Tauc law, obtaining a band gap value of 5.54eV. It was found that the growth rate of the HfO2 films depends on the deposition pressure (P) as P−1.75. This dependence is explained by a diffusion model of the thermalized atoms in high-pressure sputtering. Additionally, the formation of an interfacial silicon oxide layer when the films were grown on silicon was observed, with a minimum thickness for deposition pressures around 1.2mbars. This interfacial layer was formed mainly during the initial stages of the deposition process, with only a slight increase in thickness afterwards. These results are explained by the oxidizing action of the oxygen plasma and the diffusion of oxygen radicals and hydroxyl groups through the polycrystalline HfO2 film. Finally, the dielectric properties of the HfO2∕SiO2 stacks were studied by means of conductance and capacitance measurements on Al∕HfO2∕SiO2∕Si devices as a function of gate voltage and ac frequency signal.

Optimized dielectric properties of SrTiO3:Nb∕SrTiO3 (001) films for high field effect charge densities

The authors report the growth, structural and electrical characterizations of SrTiO3 films deposited on conductive SrTiO3:Nb (001) substrates by high pressure reactive rf magnetron sputtering. Optimized deposition parameters yield smooth epitaxial layers of high crystalline perfection with a room temperature dielectric constant ∼200 (for a thickness of 1150Å). The breakdown fields in SrTiO3:Nb∕SrTiO3∕Ag capacitors are consistent with induced charge densities >1×1014cm−2 for both holes and electrons, making these films ideal for high charge density field effect devices.

Hafnium oxide thin films deposited by high pressure reactive sputtering in atmosphere formed with different Ar/O 2 ratios

The physical and electrical properties of hafnium oxide (HfO 2) thin films deposited by high pressure reactive sputtering (HPRS) have been studied as a function of the Ar/O 2 ratio in the sputtering gas mixture. Transmission electron microscopy shows that the HfO 2 films are polycrystalline, except the films deposited in pure Ar, which are amorphous. According to heavy ion elastic recoil detection analysis, the films deposited without using O 2 are stoichiometric, which means that the composition of the HfO 2 target is conserved in the deposition films. The use of O 2 for reactive sputtering results in slightly oxygen-rich films. Metal-Oxide-Semiconductor (MOS) devices were fabricated to determine the deposited HfO 2 dielectric constant and the trap density at the HfO 2/Si interface ( D it) using the high–low frequency capacitance method. Poor capacitance–voltage ( CV) characteristics and high values of D it are observed in the polycrystalline HfO 2 films. However, a great improvement of the electrical properties was observed in the amorphous HfO 2 films, showing dielectric constant values close to 17 and a minimum D it of 2×10 11 eV −1 cm −2.

Compositional analysis of polycrystalline hafnium oxide thin films by heavy-ion elastic recoil detection analysis

The composition of polycrystalline hafnium oxide thin films has been measured by heavy-ion elastic recoil detection analysis (HI-ERDA). The films were deposited by high-pressure reactive sputtering (HPRS) on silicon wafers using an oxygen plasma at pressures between 0.8 and 1.6 mbar and during deposition times between 0.5 and 3.0 h. Hydrogen was found to be the main impurity and its concentration increased with deposition pressure. The composition was always slightly oxygen-rich, which is attributed to the oxygen plasma. Additionally, an interfacial silicon oxide thin layer was detected and taken into account. The thickness of the hafnium oxide film was found to increase linearly with deposition time and to decrease exponentially with deposition pressure, whereas the thickness of the silicon oxide interfacial layer has a minimum as a function of pressure at around 1.2 mbar and increases slightly as a function of time. The measurements confirmed that this interfacial layer is formed mainly during the early stages of the deposition process.

Physical properties of high pressure reactively sputtered TiO2

We present a study of the physical properties of TiO2 thin films deposited at 200°C on Si by high pressure reactive sputtering, a nonconventional deposition method. Just after deposition, the TiO2 films were in situ annealed in the deposition chamber at temperatures between 600 and 900°C in O2 atmosphere. Morphological, compositional, structural and electrical characterization of the samples was performed by means of several techniques, including transmission electron microscopy, heavy-ion elastic recoil detection analysis, infrared spectroscopy, x-ray and electron diffraction and capacitance-voltage measurements. Microscopy images show that the TiO2 films are polycrystalline, and that a SiO2 film spontaneously grows at the TiO2∕Si interface. The unannealed TiO2 films are oxygen rich, as shown by compositional measurements. By annealing this oxygen excess is released. For temperatures above 600°C the TiO2 films are stoichiometric. Infrared spectroscopy and diffraction measurements show that as-deposited films are a mixture of anatase and rutile grains. During annealing there is a phase transformation, and at 900°C the anatase phase disappears and only the rutile phase is found. The relative dielectric permittivity of the TiO2 film is calculated from capacitance-voltage measurements, and very high values in the 88–102 range are obtained.

A comparative study of the electrical properties of TiO2 films grown by high-pressure reactive sputtering and atomic layer deposition

Oxide–semiconductor interface quality of high-pressure reactive sputtered (HPRS) TiO2 films annealed in O2 at temperatures ranging from 600 to 900 °C, and atomic layer deposited (ALD) TiO2 films grown at 225 or 275 °C from TiCl4 or Ti(OC2H5)4, and annealed at 750 °C in O2, has been studied on silicon substrates. Our attention has been focused on the interfacial state and disordered-induced gap state densities. From our results, HPRS films annealed at 900 °C in oxygen atmosphere exhibit the best characteristics, with Dit density being the lowest value measured in this work (5–6 × 1011 cm−2 eV−1), and undetectable conductance transients within our experimental limits. This result can be due to two contributions: the increase of the SiO2 film thickness and the crystallinity, since in the films annealed at 900 °C rutile is the dominant crystalline phase, as revealed by transmission electron microscopy and infrared spectroscopy. In the case of annealing in the range of 600–800 °C, anatase and rutile phases coexist. Disorder-induced gap state (DIGS) density is greater for 700 °C annealed HPRS films than for 750 °C annealed ALD TiO2 films, whereas 800 °C annealing offers DIGS density values similar to ALD cases. For ALD films, the studies clearly reveal the dependence of trap densities on the chemical route used.

Influence of the sputtering gas on the preferred orientation of nanocrystalline titanium nitride thin films

Nanocrystalline titanium nitride thin films have been deposited by high pressure reactive magnetron sputtering from an elemental titanium target using a mixture of an inert gas and nitrogen. The mean crystallite or grain size in these films is in the range 8–12 nm as measured from X-ray line broadening. Interestingly, the type of inert gas used in the sputtering gas mixture significantly influences the microstructure and preferred orientation in these films. Thus, using a 70% He+30% N 2 gas mixture results in a strongly (002) oriented film whereas using a 70% Ar+30% N 2 gas mixture results in a strongly (111) oriented film with a similar grain size. In addition, films have also been deposited using pure nitrogen as the sputtering gas. These films exhibited a strong (002) orientation and had a significantly larger grain size as compared with those deposited using a mixture of an inert gas and nitrogen. Details of the microstructure in these films have been investigated by transmission electron microscopy. The ability to tailor the size and preferred orientation of grains in the TiN thin films (by proper choice of sputtering gas) is expected to have a significant impact on the properties of these films in a variety of technological applications.

Property Control for High-Quality Ba1-xKxBiO3 Epitaxial Thin Films Prepared by High-Pressure Reactive rf-Magnetron Sputtering

The electrical properties of Ba1-xKxBiO3(BKBO) epitaxial thin films on SrTiO3(110) substrates have been successfully controlled using high-pressure reactive rf-magnetron sputtering under an 80-Pa discharge gas. We investigated the relationship between the target composition and the electrical properties of BKBO films. The zero resistance temperature (Tce) and the temperature dependence of resistivity above the superconducting onset temperature (Tco) were found to be primarily influenced by the ratio of Ba/K and the Bi content of the target composition, respectively. Electrical measurements showed that the highest Tce of as-grown BKBO epitaxial film was 28 K.

Epitaxial Y-Ba-Cu-O thin films on MgO deposited by high-pressure reactive magnetron sputtering

Y-Ba-Cu-O thin films have been prepared on MgO(100) substrates by rf reactive magnetron sputtering from a single ceramic target. By adopting high total pressures, typically 280 mTorr, and relatively low substrate temperatures of approximately 650 °C, epitaxial films with the relations (001) YBa2Cu3Oy∥(001)MgO and [100]YBa2Cu3Oy∥[100]MgO can be reproducibly obtained. A high degree of epitaxy is confirmed by x-ray pole figure measurements and ion channeling. These films require a brief rapid thermal oxygen anneal at typically 850 °C, to exhibit sharp superconducting transitions with zero resistance around 75 K. Films deposited at higher temperatures above 700 °C show transitions as deposited with zero resistance near 80 K. The quality of the transition is correlated with expanded lattice constants with the best transitions occurring in films whose lattice constants approach that of the bulk. The films have high critical current densities of 1–5×106 A/cm2 at 4.2 K. They also show good uniformity and excellent surface morphology with a roughness less than 10 nm and can be readily patterned to micrometer and submicrometer dimensions.

YBa/sub 2/Cu/sub 3/O/sub 7/ thin films grown by high pressure reactive evaporation and high pressure reactive sputtering

A high-pressure reactive evaporation process and a high-pressure reactive sputtering process have been developed for the growth of high-quality thin films of YBa/sub 2/Cu/sub 3/O/sub 7/. Both techniques, when used with heated substrates, are effective in the formation of the 123 phase in situ during the film growth. With reactive evaporation only a cooldown anneal in a higher-pressure oxygen ambient is necessary to obtain good superconducting properties. For the reactive sputtering process, a brief, postgrowth, rapid thermal anneal step is required for best results. Fully epitaxial growth has been achieved with single-crystal MgO substrates. The resultant films, which can be quite smooth and uniform, have been patterned to micron and submicron dimensions, and the transport properties of these microstructures have been examined. >