Peter Nicholas Heys

Permittivity enhancement of hafnium dioxide high-κ films by cerium doping

The effect of cerium doping on the dielectric properties of hafnium dioxide is reported. Thin films of cerium-doped hafnium oxide Cex–Hf1−xO2 (x=0.10,0.17,0.34) have been grown by liquid injection atomic layer deposition. After annealing at 900 °C, all films were transformed from an amorphous state into a stabilized cubic or tetragonal phase. As-deposited films of Ce0.1–Hf0.9O2 showed low hysteresis voltages and negligible flat band voltage shifts. After annealing to form the crystalline cubic or tetragonal phase, the relative permittivity (κ) increased from 25 to 32 at 100 kHz with leakage current densities at ±1 MV cm−1 of ∼1.58×10−5 A cm−2.The effect of cerium doping on the dielectric properties of hafnium dioxide is reported. Thin films of cerium-doped hafnium oxide Cex–Hf1−xO2 (x=0.10,0.17,0.34) have been grown by liquid injection atomic layer deposition. After annealing at 900 °C, all films were transformed from an amorphous state into a stabilized cubic or tetragonal phase. As-deposited films of Ce0.1–Hf0.9O2 showed low hysteresis voltages and negligible flat band voltage shifts. After annealing to form the crystalline cubic or tetragonal phase, the relative permittivity (κ) increased from 25 to 32 at 100 kHz with leakage current densities at ±1 MV cm−1 of ∼1.58×10−5 A cm−2.

Deposition of lanthanum zirconium oxide high-κ films by liquid injection atomic layer deposition

Thin films of lanthanum zirconium oxide, LaxZr1−xO2−δ (x=0.22,0.35,0.63), have been grown by liquid injection atomic layer deposition using [(PriCp)3La] and [(MeCp)2ZrMe(OMe)] precursors. At lower La atomic fractions (x=0.22) films were stabilized in the cubic phase after annealing at 700°C in air. At higher La atomic fractions (x>0.35), the films remained amorphous after annealing. The films deposited showed good dielectric properties with low hysteresis voltages and negligible flatband voltage shifts. The relative permittivity (κ) ranged from 11 to 14 with leakage current densities at 1MVcm−1 in the range of 2.6×10−6–5.3×10−7Acm−2.

Advanced cyclopentadienyl precursors for atomic layer deposition of ZrO2 thin films

ZrO2 thin films were grown onto silicon (100) substrates by atomic layer deposition (ALD) using novel cyclopentadienyl-type precursors, namely (CpMe)2ZrMe2 and (CpMe)2Zr(OMe)Me (Cp = cyclopentadienyl, C5H5) together with ozone as the oxygen source. Growth characteristics were studied in the temperature range of 250 to 500 °C. An ALD-type self-limiting growth mode was verified for both processes at 350 °C where highly conformal films were deposited onto high aspect ratio trenches. Signs of thermal decomposition were not observed at or below 400 °C, a temperature considerably exceeding the thermal decomposition temperature of the Zr-alkylamides. Processing parameters were optimised at 350 °C, where deposition rates of 0.55 and 0.65 A cycle−1 were obtained for (CpMe)2ZrMe2/O3 and (CpMe)2Zr(OMe)Me/O3, respectively. The films grown from both precursors were stoichiometric and polycrystalline with an increasing contribution from the metastable cubic phase with decreasing film thickness. In the films grown from (CpMe)2ZrMe2, the breakdown field did not essentially depend on the film thickness, whereas in the films grown from (CpMe)2Zr(OMe)Me the structural homogeneity and breakdown field increased with decreasing film thickness. The films exhibited good capacitive properties that were characteristic of insulating oxides and did not essentially depend on the precursor chemistry.

Deposition of ZrO2 and HfO2 thin films by liquid injection MOCVD and ALD using ansa-metallocene zirconium and hafnium precursors

Thin films of ZrO2 and HfO2 have been deposited by liquid injection metalorganic chemical vapour deposition (MOCVD) and atomic layer deposition (ALD) using a range of ansa-metallocene precursors [(Cp2CMe2)ZrMe2] (1), [(Cp2CMe2)ZrMe(OMe)] (2) [(Cp2CMe2)HfMe2] (3), and [(Cp2CMe2)HfMe(OMe)] (4) with O2 (MOCVD) or ozone (ALD) as oxygen source. The crystal structures of the new complexes 2 and 3 have been determined and they are shown to be mononuclear and isostructural to complex 1, containing a chelating [Cp2CMe2] ligand leading to a pseudo-four-coordinate distorted tetrahedral geometry around the central Zr or Hf atom, in agreement with structures from Density Functional Theory (DFT). The ZrO2 and HfO2 films were deposited by MOCVD over the temperature range 400–650 °C and by ALD over the temperature range 175–350 °C. X-Ray diffraction analysis showed that the HfO2 films deposited by MOCVD were amorphous, whereas the ZrO2 films deposited by MOCVD were in the tetragonal phase. Auger electron spectroscopy showed that residual carbon was present in all the films and that the films grown by MOCVD contained more carbon (2.4–17.0 at.%) than the films grown by ALD (1.8–2.8 at.%). The dielectric properties of ZrO2 and HfO2 films deposited by ALD were evaluated using [Al/MO2/n-Si] metal oxide semiconductor capacitor (MOSC) structures which showed that the films had low current leakage densities of less than 6 × 10−7 A cm−2 at ±2 MV cm−1.

The optical properties of vertically aligned ZnO nanowires deposited using a dimethylzinc adduct

The optical properties of zinc oxide nanowires are critically influenced by the growth process. Herein, we describe a metal-organic chemical vapour deposition (MOCVD) process for the growth of ZnO nanowires with improved optical properties. A tetrahydrofuran adduct is used to control the reactivity of dimethylzinc to enable this. Vertically aligned zinc oxide nanowires have been grown on Si(111) substrates by liquid injection MOCVD, using a solution of [Me(2)Zn(tetrahydrofuran)] in the presence of oxygen. The ZnO morphology becomes nanowire-like in a narrow temperature range centred about 500 degrees C. Above and below this temperature range, the ZnO is deposited in the form of polycrystalline films. The ZnO nanowires grow from a polycrystalline nucleation layer, with the (0002) c-axis parallel to the Si[111] substrate orientation. High-resolution electron microscopy reveals a highly crystalline nanowire microstructure. Resonance enhanced ultraviolet Raman spectroscopy shows that the ratio of first- and second-order longitudinal optic modes is commensurate with electron-phonon coupling effects observed previously in ZnO nanostructures. Photoluminescence exhibits intense near band-edge emission with a full width at half-maximum of 110 meV at room temperature and shows negligible defect-related visible emission.